ANTENNA ARRAYS

Technical Field

[0001 ] The present disclosure relates to an antenna array and, more specifically, to detection of faults or obstructions for antenna elements or antenna element subarrays in an antenna array.

Background

[0002] Antenna arrays are used to increase the network capacity in Fourth Generation (4G) and Fifth Generation (5G) systems. An antenna array includes a large number of antenna elements, which may be grouped in a number of antenna element subarrays. In systems using beamforming, a fault in an antenna element or antenna element subarray will degrade beamforming performance. It is therefore important to have a mechanism to detect faulty antenna elements or faulty antenna element subarrays and properly adjust the beamforming to compensate for the fault. In addition, it is desirable to have the ability to detect an obstruction of the radiated antenna field by a foreign object close to an antenna element or antenna element subarray.

[0003] Existing solutions measure Voltage Standing Wave Ratio (VSWR) per transmitter branch with a switch sharing the same receiver to detect an antenna column failure. Note that, in traditional non-beamforming antennas, a column is a number of antenna elements combined together in the vertical direction. In contrast, in a beamforming antenna array, a column could have several sub- arrays in the vertical direction. Using this VSWR measurement method in an antenna array that includes many antenna elements or antenna element subarrays can be costly and time consuming.

[0004] International patent application WO 2017/081522 A1 published under the Patent Cooperation Treaty (PCT) teaches a radio unit and a method of operation of the radio unit to obtain simultaneous VSWR measurements for multiple antenna ports. However, the accuracy of the VSWR measurements obtained in WO 2017/081522 A1 is less than ideal and cannot be used to determine whether the fault is located / has occurred on the Radio Frequency (RF) Feeder system connected to the antenna, or is a fault with an antenna element or subarray in the antenna array.

[0005] As such, there is a need for systems and methods for determining antenna element or subarray faults in an antenna array that is not costly, complex, or time-consuming and that is able to determine whether any detected fault is due to a failure in an RF connection between the radio unit and the antenna array or a failure in the antenna element or subarray. Summary

[0006] Systems and methods for providing antenna fault detection in a transmitter system are disclosed. In some embodiments, a transmitter system that is configured to detect antenna faults comprises an antenna unit comprising a plurality of antenna elements or antenna element subarrays, a plurality of antenna input ports, and a plurality of directional couplers. The directional couplers comprise a plurality of directional coupler input ports coupled to the plurality of antenna input ports, respectively; a plurality of output ports coupled to the plurality of antenna elements or antenna element subarrays, respectively; a plurality of coupled ports, respectively; and a plurality of isolated ports, respectively. The transmitter system further comprises a radio unit comprising a plurality of radio unit output ports coupled to the plurality of antenna input ports, respectively; a plurality of transmitter branches coupled to the plurality of radio unit output ports, respectively; and one or more receiver branches. The one or more receiver branches are configured to receive: (a) a combined forward feedback signal and a combined reflected feedback signal, the combined forward feedback signal being a combination of a plurality of forward signals output at the plurality of coupled ports of the plurality of directional couplers and the combined reflected feedback signal being a combination of a plurality of reflected signals output at the plurality of isolated ports of the plurality of directional couplers, or (b) separate forward feedback signals obtained by switching the plurality of forward signals output at the plurality of coupled ports of the plurality of directional couplers and separate reflected feedback signals obtained by switching the plurality of reflected signals output at the plurality of isolated ports of the plurality of directional couplers. The transmitter system further comprises processing circuitry coupled to the one or more receiver branches.

[0007] In some embodiments, the transmitter system further comprises combining circuitry comprising a first plurality of inputs coupled to the plurality of coupled ports of the plurality of directional couplers, respectively, and a second plurality of inputs coupled to the plurality of isolated ports of the plurality of directional couplers, respectively. The one or more receiver branches are coupled to the combining circuitry and configured to receive the combined forward feedback signal and the combined reflected feedback signal from the combining circuitry.

[0008] In some embodiments, during transmission of a plurality of transmit signals from the plurality of transmitter branches, respectively, the combining circuitry is operable to combine the plurality of forward signals received at the first plurality of inputs coupled to the plurality of coupled ports of the plurality of directional couplers to provide the combined forward feedback signal and combine the plurality of reflected signals received at the second plurality of inputs coupled to the plurality of isolated ports of the plurality of directional couplers to provide the combined reflected feedback signal. The one or more receiver branches are operable to receive and sample the combined forward feedback signal and the combined reflected feedback signal to provide a combined digital baseband forward feedback signal and a combined digital baseband reflected feedback signal, respectively. The processing circuitry is operable to perform antenna fault detection based on the combined digital baseband forward feedback signal and the combined digital baseband reflected feedback signal.

[0009] In some embodiments, in order to perform antenna fault detection, the processing circuitry is further operable to, for each transmitter branch of at least one of the plurality of transmitter branches, determine a return-loss or a value that is a function of the return-loss for the transmitter branch based on the combined digital baseband forward feedback signal and the combined digital baseband reflected feedback signal and determine whether there is a fault in the antenna element or antenna element subarray coupled to the transmitter branch based on the return-loss or the value that is a function of the return-loss for the transmitter branch.

[0010] In some other embodiments, in order to perform antenna fault detection, the processing circuitry is operable to, for each transmitter branch of at least one of the plurality of transmitter branches: determine a forward power for the transmitter branch based on the combined digital baseband forward feedback signal; determine whether the forward power for the transmitter branch is greater than a predefined power threshold; and make a determination that there is a hardware fault for the transmitter branch if the forward power for the transmitter branch is not greater than the predefined power threshold. Further, in some embodiments, in order to determine the forward power for the transmitter branch, the processing circuitry is operable to determine the forward power for the transmitter branch based on a cross-correlation of the combined digital baseband forward feedback signal and one of the plurality of transmit signals transmitted by the transmitter branch.

[0011 ] In some other embodiments, in order to perform antenna fault detection, the processing circuitry is further operable to determine a forward power for the transmitter branch based on the combined digital baseband forward feedback signal, determine a reflected power for the transmitter branch based on the combined digital baseband reflected feedback signal, determine a return loss for the transmitter branch as a ratio of the forward power for the transmitter branch to the reflected power for the transmitter branch, determine whether a difference between a known return loss and the determined return loss for the transmitter branch is greater than a predefined threshold, and make a determination that there is a fault in the antenna element or antenna element subarray coupled to the transmitter branch if the difference is greater than the predefined threshold. Further, in some embodiments, in order to determine the forward power for the transmitter branch, the processing circuitry is operable to determine the forward power for the transmitter branch based on a cross- correlation of the combined digital baseband forward feedback signal and one of the plurality of transmit signals transmitted by the transmitter branch. Further, in some embodiments, in order to determine the reflected power for the transmitter branch, the processing circuitry is operable to determine the reflected power for the transmitter branch based on a cross-correlation of the combined digital baseband reflected feedback signal and one of the plurality of transmit signals transmitted by the transmitter branch.

[0012] In some other embodiments, in order to perform antenna fault detection, the processing circuitry is operable to, for each transmitter branch of at least one of the plurality of transmitter branches, calculate a Voltage Standing Wave Ratio (VSWR) for the transmitter branch based on the combined digital baseband forward feedback signal and the combined digital baseband reflected feedback signal and determine whether there is a fault for the antenna element or antenna element subarray coupled to the transmitter branch based on the VSWR for the transmitter branch. The VSWR is a function of frequency.

[0013] In some embodiments, in order to calculate the VSWR for the transmitter branch, the processing circuitry is further operable to compute a forward transfer function and a reverse transfer function for the transmitter branch based on measurements of the combined digital baseband forward feedback signal and the combined digital baseband reflected feedback signal where the forward transfer function and the reverse transfer function are a function of frequency, compute a reflection coefficient for the antenna element or antenna element subarray coupled to the transmitter branch as a ratio of the reverse transfer function to the forward transfer function for the transmitter branch, compute a return-loss for the transmitter branch as a function of the reflection coefficient, and compute the VSWR for the transmitter branch as a function of the return-loss for the transmitter branch.

[0014] In some embodiments, the combining circuitry is comprised in the antenna unit. In some other embodiments, the combining circuitry is comprised in the radio unit. In some other embodiments, the combining circuitry is external to both the radio unit and the antenna unit. [0015] In some embodiments, the antenna unit comprises an antenna support structure comprising the plurality of antenna input ports and one or more Printed Circuit Boards (PCBs) within the antenna support structure and on which the plurality of directional couplers are implemented.

[0016] Embodiments of a method of operation of a transmitter system are also disclosed. In some embodiments, a method of operation of a transmitter system to perform antenna fault detection comprises determining a forward power for a transmitter branch of a plurality of transmitter branches of the transmitter system based on a combined forward feedback signal. The combined forward feedback signal is a combination of a plurality of forward feedback signals obtained from a plurality of coupled ports of a plurality of directional couplers that connect the plurality transmitter branches of the transmitter system to a plurality of antenna elements or antenna element subarrays of the transmitter system, respectively, during transmission of a plurality of transmit signals from the plurality of transmitter branches, respectively. The method further comprises determining a reflected power for the transmitter branch based on a combined reflected feedback signal. The combined reflected feedback signal is a combination of a plurality of reflected feedback signals obtained from a plurality of isolated ports of the plurality of directional couplers. The method further comprises determining a relationship between the reflected power for the transmitter branch and the forward power for the transmitter branch, and determining whether there is a fault in the antenna element or antenna element subarray coupled to the transmitter branch based on the relationship between the reflected power for the transmitter branch and the forward power for the transmitter branch.

[0017] In some embodiments, determining the relationship between the reflected power for the transmitter branch and the forward power for the transmitter branch comprises determining a ratio of the reflected power for the transmitter branch to the forward power for the transmitter branch. Further, determining whether there is a fault in the antenna element or antenna element subarray coupled to the transmitter branch comprises comparing the ratio for the transmitter branch to a predefined ratio threshold and making a determination that there is a fault in the antenna element or antenna element subarray coupled to the transmitter branch based on a result of the comparison of the ratio for the transmitter branch and the predefined ratio threshold.

[0018] In some embodiments, determining the forward power for the transmitter branch comprises determining the forward power for the transmitter branch based on a cross-correlation of the combined forward feedback signal and one of the plurality of transmit signals transmitted by the transmitter branch.

[0019] In some embodiments, determining the reflected power for the transmitter branch comprises determining the reflected power for the transmitter branch based on a cross-correlation of the combined reflected feedback signal and one of the plurality of transmit signals transmitted by the transmitter branch.

[0020] In some embodiments, the plurality of directional couplers are comprised in an antenna unit that comprises both the plurality of directional couplers and the plurality of antenna elements or antenna element subarrays.

[0021] In some embodiments, the plurality of directional couplers are interconnected between a plurality of antenna input ports of the antenna unit and the plurality of antenna elements or antenna element subarrays. In some embodiments, the antenna unit comprises an antenna support structure comprising the plurality of antenna input ports and one or more PCBs within the antenna support structure and on which the plurality of directional couplers are implemented.

[0022] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the embodiments in association with the accompanying drawing figures.

Brief Description of the Drawings

[0023] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure. [0024] Figures 1 A through 1 C illustrate example embodiments of a transmitter system incorporating embodiments of the present disclosure;

[0025] Figures 2A through 2E illustrate an antenna unit in more detail according to some example embodiments of the present disclosure;

[0026] Figure 3 is a flow chart that illustrates the operation of processing circuitry to perform antenna fault detection based on a combined forward feedback signal and a combined reflected feedback signal received during transmission of known transmit signals via transmitter branches of the transmitter system in accordance with some embodiments of the present disclosure;

[0027] Figure 4 is a flow chart that illustrates the operation of processing circuitry to perform antenna fault detection based on a combined forward feedback signal and a combined reflected feedback signal received during transmission of known transmit signals via transmitter branches of the transmitter system in accordance with some embodiments of the present disclosure;

[0028] Figure 5 illustrates numerical calculations that show return loss change versus coupler directivity, and specifically shows that a 3 decibel (dB) change in return loss may result in 2.4dB - 4dB range of measured values;

[0029] Figure 6 is a flow chart that illustrates the operation of processing circuitry to perform antenna fault detection based on a combined forward feedback signal and a combined reflected feedback signal received during transmission of known transmit signals via transmitter branches of the transmitter system in accordance with some embodiments of the present disclosure;

[0030] Figure 7 is an exemplary block diagram of an p ^th branch of the transmitter system that is referenced to describe one example of a Voltage Standing Wave Ratio (VSWR) and return-loss measurement calculation process;

[0031 ] Figure 8 is an equivalent block diagram to Figure 7 referenced to describe the one example of the VSWR and return-loss measurement calculation process;

[0032] Figure 9 illustrates the transmitter system in accordance with some other embodiments of the present disclosure; and [0033] Figure 10 illustrates one example of an alternative embodiment of the transmitter system.

Detailed Description

[0034] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0035] Systems and methods are disclosed herein that provide antenna fault detection for antenna elements or antenna element subarrays in an antenna array. As used herein, an antenna fault can be a hardware fault in an antenna element or antenna element subarray, a hardware fault in a component (e.g., a cable or connector) prior to an antenna element or antenna element subarray in a branch of a transmitter system, or an obstruction in the environment that is negatively impacting the performance of an antenna element or antenna element subarray. In general, a transmitter system includes a radio unit(s) and an antenna unit. The antenna unit includes an antenna array that consists of multiple antenna elements or antenna element subarrays. For each antenna element or antenna element subarray, a respective directional (i.e., dual or bidirectional) coupler is connected between a respective antenna port of the antenna unit and the antenna element or antenna element subarray. Forward coupled ports of all of the directional couplers are connected to a first combining network. The output of the first combining network is a combined forward feedback signal. Similarly, isolated ports of all of the directional couplers are connected to a second combining network. The output of the second combining network is a combined reflected feedback signal. The combined forward feedback signal and the combined reflected feedback signal are received by one or more receiver branches and processed by processing circuitry to perform antenna fault detection.

[0036] During transmission of a known transmit signal, the combined forward feedback signal and the combined reflected feedback signal are received, sampled, and processed to obtain individual power contributions at the forward coupled port and isolated port of the directional coupler for each antenna element or antenna element subarray. Using these power measurements, an estimate of the power reaching the antenna element as well as the reflected power from the elements can be determined. Specifically, in some

embodiments, the combined forward feedback signal is processed to obtain, for each antenna element or antenna element subarray, a measurement of forward power for that antenna element or antenna element subarray. Likewise, the combined reflected signal is processed to obtain, for each antenna element or antenna element subarray, a measurement of reflected power for that antenna element or antenna element subarray. The forward and reflected power measurements are used to compute a return-loss, or a value that is a function of the return-loss, for the antenna element or antenna element subarray. The return-loss, or the value that is a function of the return-loss, is used to determine whether there is an antenna fault for that antenna element or antenna element subarray.

[0037] Embodiments of the present disclosure provide a number of advantages over conventional systems. As an example, using embodiments of the present disclosure, the fault location can be isolated, i.e., whether the fault is before the antenna element or the antenna element itself. As another example, the directional couplers are in the antenna unit and therefore close to the antenna elements or antenna element subarrays, which in turn allows more accurate fault detection as well as foreign object obstruction in front of the antenna elements or subarrays. In some embodiments, the combining networks are implemented within the antenna unit. This provides a cost efficient solution that does not need an active switched network for switching to separately obtain forward and reflected signals from every antenna element. As yet another example, embodiments of the present disclosure can potentially be used for Passive Intermodulation (PIM) detection at the antenna elements. As yet another example, some embodiments of the present disclosure do not perform full scale Voltage Standing Wave Ratio (VSWR) measurement and therefore have no need for full coupler calibration. As yet another embodiment, the present disclosure can potentially be used to determine the mutual coupling for the antenna elements or subarrays for system performance improvements and optimization in the beamforming and receive diversity combining.

[0038] Figures 1 A through 1 C illustrate example embodiments of a transmitter system 10 incorporating embodiments of the present disclosure. As illustrated, the transmitter system 10 includes a radio unit 12 and an antenna unit 14. The radio unit 12 includes a number (P) of transmitter branches 16-1 through 16-P having inputs coupled to radio unit input ports 18-1 through 18-P, respectively, and outputs coupled to radio unit output ports 20-1 through 20-P, respectively. As will be appreciated by one of ordinary skill in the art, the transmitter branches 16-1 through 16-P include various components such as, e.g., Power Amplifiers (PAs) 22-1 through 22-P and filters 24-1 through 24-P, respectively. The transmitter branches 16-1 through 16-P are generally referred to herein collectively as transmitter branches 16 and individually as transmitter branch 16. Likewise, the radio unit input ports 18-1 through 18-P are generally referred to herein collectively as radio unit input ports 18 and individually as radio unit input port 18; the radio unit output ports 20-1 through 20-P are generally referred to herein collectively as radio unit output ports 20 and individually as radio unit output ports 20; the PAs 22-1 through 22-P are generally referred to herein collectively as PAs 22 and individually as PA 22; and the filters 24-1 through 24- P are generally referred to herein collectively as filters 24 and individually as filters 24.

[0039] In some embodiments, the radio unit 12 also includes conditioning circuitry 26. Note that the conditioning circuitry 26 is optional, as indicated by the dashed lines. As discussed below, the conditioning circuitry 26 may be used to condition the input signals of the transmitter branches 16 received via the radio unit input ports 18 in order to, e.g., de-correlate the input signals of the

transmitter branches 16, as discussed below.

[0040] The radio unit 12 also includes one or more receiver branches 28 and processing circuitry 30. As will be understood by one of ordinary skill in the art, the receiver branch(es) 28 include components such as, e.g., the filters 24, downconversion circuitry, Analog-to-Digital Converters (ADCs), and the like. The processing circuitry 30 may include any type of processing circuitry such as, e.g., one or more Application Specific Integrated Circuits (ASICs), one or more Field Programming Gate Arrays (FPGAs), one or more Digital Signal Processors (DSPs), one or more Central Processing Units (CPUs), or the like, or any combination thereof. Note that while the processing circuitry 30 is illustrated as being part of the radio unit 12 in the examples of Figures 1 A through 1 C, the present disclosure is not limited thereto. For example, the processing circuitry 30 may alternatively be implemented in a baseband processing unit or some other node external to but connected (e.g., via a physical connection such as, e.g., a fiber optic cable or via a logical connection such as, e.g., an Internet Protocol (IP) connection via a network interface).

[0041 ] The antenna unit 14 includes an antenna array that includes multiple antenna elements or antenna element subarrays 32-1 through 32-P, which are generally referred to herein as antenna elements or antenna element subarrays 32 or individually as antenna element or antenna element subarray 32. Note that the number (P) of antenna elements or antenna element subarrays 32 is generally equal to the number (P) of transmitter branches 16, but is not limited thereto (e.g., the output of a transmitter branch 16 may alternatively be split and provided to more than one antenna element or subarray 32). In Figures 1 A through 1 C, reference number 32-x, where x=1 , or P, refers to a single antenna element or a single antenna element subarray, depending on the particular embodiment. The antenna unit 14 also includes multiple directional couplers 34-1 through 34-P having coupler input ports 36-1 through 36-P, output ports 38-1 through 38-P, forward coupled ports 40-1 through 40-P, and isolated ports 42-1 through 42-P, respectively, as will be appreciated by one of ordinary skill in the art. The coupler input ports 36-1 through 36-P are coupled to antenna ports 44-1 through 44-P of the antenna unit 14, respectively. The antenna ports 44-1 through 44-P are coupled to the radio unit output ports 20-1 through 20-P, respectively, via, e.g., cables and/or connectors. The output ports 38-1 through 38-P are coupled to the antenna elements or antenna element subarrays 32-1 through 32-P, respectively. All of the forward coupled ports 40-1 through 40-P are coupled to first combining circuitry 46, and all of the isolated ports 42-1 through 42-P are coupled to second combining circuitry 48. The directional couplers 34-1 through 34-P are generally referred to herein collectively as directional couplers 34 and individually as directional coupler 34. Likewise, the coupler input ports 36-1 through 36-P are generally referred to herein collectively as coupler input ports 36 and individually as coupler input port 36; the output ports 38-1 through 38-P are generally referred to herein collectively as output ports 38 and individually as output port 38; the forward coupled ports 40-1 through 40-P are generally referred to herein collectively as forward coupled ports 40 and individually as forward coupled port 40; the isolated ports 42-1 through 42-P are generally referred to herein collectively as isolated ports 42 and individually as isolated port 42; and the antenna ports 44-1 through 44-P are generally referred to herein collectively as antenna ports 44 and individually as antenna port 44.

[0042] By locating the directional couplers 34-1 through 34-P in the antenna unit 14, the directional couplers 34-1 through 34-P enable direct monitoring of the antenna elements or antenna element subarrays 32-1 through 32-P. This enables computation of accurate measurements of the return-loss or values that are a function of the return-loss (e.g., VSWR) for each antenna element or antenna element subarray 32.

[0043] In the example of Figure 1 A, the first combining circuitry 46 and the second combining circuitry 48 are implemented in the antenna unit 14, and the outputs of the first and second combining circuitries 46 and 48 are coupled to output ports 50 and 52 of the antenna unit 14, respectively. The output ports 50 and 52 are coupled to feedback ports 54 and 56 of the radio unit 12, respectively, via, e.g., cables and/or connectors.

[0044] In the example of Figure 1 B, the first combining circuitry 46 and the second combining circuitry 48 are implemented separately from the radio unit 12 and the antenna unit 14, where the forward coupled ports 40-1 through 40-P of the directional couplers 34-1 through 34-P are coupled to the first combining circuitry 46 via first output ports 58-1 through 58-P of the antenna unit 14, and the isolated ports 42-1 through 42-P of the directional couplers 34-1 through 34-P are coupled to the second combining circuitry 48 via second output ports 60-1 through 60-P of the antenna unit 14. The outputs of the first and second combining circuitries 46 and 48 are coupled to the feedback ports 54 and 56 of the radio unit 12, respectively, via, e.g., cables and/or connectors.

[0045] In the example of Figure 1 C, the first combining circuitry 46 and the second combining circuitry 48 are implemented in the radio unit 12, where the forward coupled ports 40-1 through 40-P of the directional couplers 34-1 through 34-P are coupled to the first output ports 58-1 through 58-P of the antenna unit 14 and the isolated ports 42-1 through 42-P of the directional couplers 34-1 through 34-P are coupled to the second output ports 60-1 through 60-P of the antenna unit 14. The first output ports 58-1 through 58-P of the antenna unit 14 are coupled to first feedback ports 62-1 through 62-P of the radio unit 12, which are themselves coupled to the first combining circuitry 46. The second output ports 60-1 through 60-P of the antenna unit 14 are coupled to second feedback ports 63-1 through 63-P of the radio unit 12, which are themselves coupled to the second combining circuitry 48. The first output ports 58-1 through 58-P are generally referred to herein collectively as first output ports 58 and individually as first output port 58; the second output ports 60-1 through 60-P are generally referred to herein collectively as second output ports 60 and individually as second output port 60; the first feedback ports 62-1 through 62-P are generally referred to herein collectively as first feedback ports 62 and individually as first feedback port 62; and the second feedback ports 63-1 through 63-P are generally referred to herein collectively as second feedback ports 63 and individually as second feedback port 63.

[0046] In some embodiments, the radio unit 12 is implemented on a Printed Circuit Board(s) (PCB(s)), where the radio unit input ports 18, the radio unit output ports 20, and the feedback ports 54 and 56 (Figures 1 A and 1 B) or feedback ports 62 -1 through 62-P and 63-1 through 63-P (Figure 1 C) are ports of the PCB(s). Likewise, in some embodiments, the antenna unit 14 is

implemented as a PCB(s), where the antenna ports 44 and the output ports 50 and 52 (Figure 1 A) or output ports 58-1 through 58-P and 60-1 through 60-P are ports of the PCB(s).

[0047] Note that the embodiments of Figures 1 A through 1 C are only examples. As one additional example, the transmitter system 10 may include multiple radio units 12 connected to the same antenna unit 14, where the feedback signal is provided to the multiple radio units 12 and forward and reflected signal processing is performed in the multiple radio units 12. Note that, in some embodiments, the radio unit(s) 12 can handle multi-band operation.

[0048] Figures 2A through 2E illustrate the antenna unit 14 in more detail according to some example embodiments of the present disclosure. These examples specifically refer to the example embodiment of Figure 1 A, but can be easily modified for either the embodiment of Figure 1 B or the embodiment of

Figure 1 C, as will be appreciated by one of ordinary skill in the art. As illustrated in Figure 2A, the antenna unit 14 includes an antenna support structure 64. The antenna support structure 64 includes the antenna ports 44 and the output ports 50 and 52. Only two antenna ports 44-i and 44-j are illustrated for clarity and ease of discussion. However, there may be more than two antenna ports 44. The directional couplers 34 and the combining circuitry 46 and 48 are

implemented within the antenna support structure 64, typically on the PCB 66. The antenna ports 44 are coupled to the coupler input ports 36 of the directional couplers 34 via respective connections 68 (e.g., connectors and/or cables). The output ports 50 and 52 of the antenna unit 14 are coupled to the outputs of the combining circuitries 46 and 48, respectively, via respective connections 70 (e.g., connectors and/or cables). The output ports 38 of the directional couplers 34 are coupled to, in this example, the respective antenna element subarrays 32 via respective connections 72 (e.g., connectors and/or cables). As illustrated, each antenna element subarray 32 includes an antenna element subarray splitter 74 and multiple antenna elements 76. The forward coupled ports 40 of the directional couplers 34 and the isolated ports 42 of the directional couplers 34 are connected to the appropriate inputs of the combining circuitry 46 and 48 via, e.g., traces on the PCB 66. The antenna unit 14 is enclosed by a radome 78.

[0049] The example of Figure 2B is substantially the same as that of Figure 2A but where the antenna element subarray splitters 74 are implemented together with the directional couplers 34 and the combiner circuitry 46 and 48, e.g., on the same PCB 66.

[0050] The example of Figure 2C is substantially the same as that of Figure 2A but where the antenna unit 14 further includes a remote electrical tilt component 80 connected between the directional couplers 34 and combining circuitry 46 and 48, which are typically implemented on the PCB 66, and the antenna element subarray splitters 74, which are typically implemented on one or more additional PCBs 66.

[0051] The example of Figure 2D is substantially the same as that of Figure 2B but where the antenna unit 14 further includes the remote electrical tilt component 80 implemented together with the antenna element subarray splitters 74, the directional couplers 34, and the combiner circuitry 46 and 48, e.g., on the same PCB 66.

[0052] The example of Figure 2E is substantially the same as that of Figure 2C but where the remote electrical tilt component 80 is coupled between the ports 44, 50, and 52 and, e.g., the PCB 66 on which the directional couplers 34 and the combiner circuitry 46 and 48 are implemented. Note that Figures 2A through 2E are only example embodiments of the antenna unit 14. Other variations will be appreciated by one of ordinary skill in the art.

[0053] As discussed below in detail, the transmitter system 10 operates to perform antenna fault detection. In general, during transmission of known transmit signals via the transmitter branches 16-1 through 16-P, the first combining circuitry 46 combines individual feedback signals output from the forward coupled ports 40-1 through 40-P of the directional couplers 34-1 through 34-P to provide a combined forward feedback signal and the second combining circuitry 46 combines individual feedback signals output from the isolated ports 42-1 through 42-P of the directional couplers 34-1 through 34-P to provide a combined reflected feedback signal. The combined forward feedback signal and the combined reflected feedback signal are received (e.g., downconverted and filtered) by the receiver branch(es) 28, sampled, and processed by the processing circuitry 30 to perform fault detection for each of the antenna element or antenna element subarrays 32-1 through 32-P.

[0054] Figure 3 is a flow chart that illustrates the operation of the processing circuitry 30 to perform antenna fault detection based on the combined forward feedback signal and the combined reflected feedback signal received during transmission of known transmit signals via the transmitter branches 16-1 through 16-P in accordance with some embodiments of the present disclosure. Dashed lines are used to illustrate optional steps. As illustrated, the processing circuitry 30 samples the combined forward feedback signal and the combined reflected feedback signal received via the receiver branch(es) 28 (step 100). A branch index p is set to 1 (step 102). If the branch index p is not greater than or equal to P (i.e., the total number of transmitter branches 16 and thus the total number of antenna elements or antenna element subarrays 32) (step 104, NO), the processing circuitry 30 determines, or computes, a return-loss for branch p or a value that is a function of the return-loss for branch p based on the samples of the combined forward feedback signal and the combined reflected feedback signal (step 106). As discussed below, in some embodiments, this value is a ratio of a reflected power measurement to a forward power measurement for branch p determined from the combined reflected feedback signal and the combined forward feedback signal, respectively. In some other embodiments, the value that is a function of the return-loss of branch p is a VSWR estimate. The processing circuitry 30 then determines whether there is an antenna fault for the antenna element or antenna element subarray 32-p based on the return-loss or the value that is a function of the return-loss for branch p determined in step 106 (step 108). As discussed in more detail below, in one example embodiment, the processing circuitry 30 computes the ratio of the reflected power

measurement to the forward power measurement and compares the computed ratio to a predefined threshold to determine whether there is a fault for the antenna element or antenna element subarray 32-p for branch p. As also discussed below, in another example embodiment, the processing circuitry 30 computes a VSWR estimate for branch p based on the forward power

measurement and the reflected power measurement for branch p, and compares the VSWR estimate to a predefined VSWR threshold to determine whether there is a fault for the antenna element or antenna element subarray 32-p for branch p.

[0055] The processing circuitry 30 then increments the branch index p (step 1 10), and the process then returns to step 104 and is repeated for the next branch p. Once all branches have been processed (i.e., once the branch index p is greater than or equal to P) (step 104, YES), the process ends.

[0056] Note that, in some embodiments, the process of Figure 3 is repeatedly performed (e.g., continuously or periodically) to monitor and record the forward and reflected power during the radio operation and to determine whether there is an antenna fault based on those measurements. In some embodiments, an alarm will be raised when a fault is detected.

[0057] Figure 4 is a flow chart that illustrates the operation of the processing circuitry 30 to perform antenna fault detection based on the combined forward feedback signal and the combined reflected feedback signal received during transmission of known transmit signals via the transmitter branches 16-1 through 16-P in accordance with some embodiments of the present disclosure. Dashed lines are used to illustrate optional steps. The process of Figure 4 is similar to that of Figure 3, but in Figure 4 the processing circuitry 30 determines whether there is fault for branch p based on a computed ratio of the reflected power measurement to the forward power measurement for branch p. [0058] As illustrated, the processing circuitry 30 samples the combined forward feedback signal and the combined reflected feedback signal received via the receiver branch(es) 28 (step 200). A branch index p is set to 1 (step 202). If the branch index p is not greater than or equal to P (i.e., the total number of transmitter branches 16 and thus the total number of antenna elements or antenna element subarrays 32) (step 204, NO), the processing circuitry 30 determines a forward power measurement for transmitter branch 16-p (i.e., branch p) (step 206). This forward power measurement is a measurement of the forward power transmitted via the antenna element or antenna element subarray 32-p and, as such, is also referred to herein as a forward power measurement for the antenna element or antenna element subarray 32-p. In some embodiments, the processing circuitry 30 determines the forward power measurement by performing a cross-correlation between the samples of the combined forward feedback signal and the known transmit signal transmitted via transmit branch 16-p, where the peak of the results of the cross-correlation is used as the forward power measurement for branch p. As one example alternative, the processing circuitry 30 determines the forward power measurement by estimating the transfer function between the reference transmit and forward signals.

[0059] Optionally, the processing circuitry 30 determines whether the forward power measurement for branch p is greater than a threshold (step 208). This threshold is a threshold that is known, e.g., from manufacturing or simulation, to be suitable for a sufficiently high signal to noise ratio. If the forward power measurement for branch p is not greater than the threshold (step 208, NO), the processing circuitry 30 makes a determination that there a problem or failure of the hardware in branch p, which may include a failure of the connection between the radio unit output port 20-p and the antenna port 44-p of the antenna unit 14 (step 210).

[0060] Returning to step 208, if the forward power is greater than the threshold (step 208, YES), the processing circuitry 30 determines a reflected power measurement for the transmitter branch 16-p (i.e., branch p) (step 212). This reflected power measurement is a measurement of the reflected power from the antenna element or antenna element subarray 32-p and, as such, is also referred to herein as a reflected power measurement for the antenna element or antenna element subarray 32-p. In some embodiments, the processing circuitry 30 determines the reflected power measurement by performing a cross- correlation between the samples of the combined reflected feedback signal and the known transmit signal transmitted via the transmit branch 16-p, where the peak of the results of the cross-correlation is used as the reflected power measurement for branch p. As one example alternative, the processing circuitry 30 determines the reflected power measurement by estimating the transfer function between the reference transmit and reflected signals.

[0061 ] Once the forward power measurement and the reflected power measurement for branch p have been determined, in order to determine whether there is a fault for branch p, the processing circuitry 30 calculates RL as a ratio of the forward power measurement to the reflected power measurement for branch p (step 214). The processing circuitry 30 determines whether a difference (Δ) between a known (or expected) RL and the determined RL for branch p is greater than a predefined threshold 7 ^~ (step 216). The predefined threshold 7 ^~ is determined during manufacturing and is known to be a value below which performance of branch p is acceptable (i.e., there is no fault). The predefined threshold may alternatively be determined via, e.g., simulation. In some embodiments, the known RL is zero, in which case the difference (Δ) is simply the determined RL. In some other embodiments, the known RL is a non-zero value. If the difference (Δ) is greater than the predefined threshold 7 ^~ (step 216, YES), the processing circuitry 30 determines that there is a fault for the antenna element or antenna element subarray 32-p for branch p (step 218) and the process then proceeds to step 220. The fault may be that, e.g., the antenna element or antenna element subarray 32-p is damaged or there is an obstruction that is negatively impacting the performance of the antenna element or antenna element subarray 32-p. If the difference (Δ) is not greater than the predefined threshold 7 ^~ (step 216, NO), the processing circuitry 30 then increments the branch index p (step 220), and the process then returns to step 204 and is repeated for the next branch p. Once all branches have been processed (i.e., once the branch index p is greater than or equal to P) (step 204, YES), the process ends.

[0062] Note that, in some embodiments, the process of Figure 4 is repeatedly performed (e.g., continuously or periodically) to monitor and record the forward and reflected power during the radio operation and to determine whether there is an antenna fault based on those measurements. In some embodiments, an alarm will be raised when a fault is detected.

[0063] Figure 4 is one example of a process in which the forward power measurement for branch p is used to detect faults before the directional coupler 34-p, and the reflected power measurement for branch p is used to detect antenna element degradation or obstruction in front of the antenna element or antenna element subarray 32-p. Using the forward power measurements and the reflected power measurements, faults are detected by relative comparison to known power thresholds. The forward power level at the coupler isolated port as a function of the coupler directivity is shown in Table 1 . The reflected power as a function of the antenna return-loss for 22 Decibels (dB) coupling factor is shown in Table 2.

Table 2: Reflect power vs. actual antenna return-loss (power levels in dBm)

[0064] When the return-loss of the antenna element is degraded or a foreign obstacle is in front of the antenna, the total reflected signal power will increase.

[0065] A return loss can then be estimated as a ratio of the forward power, i.e., the power of the signal at coupling port 40, to the reflected power, i.e., the power of the signal at isolated port 42.

[0066] Since the directional coupler 34 is not ideal, there is always a leakage of the forward signal from the input port 36 to the isolated port 42, and of the reflected signal from the output port 38 to the coupled port 36. The coupler directivity determines the amount of leakage. The higher the directivity, the lower the leakage, and, as a result, the return loss estimation accuracy is higher.

[0067] In prior systems, high directivity is achieved by directional coupler calibration. The calibration uses loads with known return loss to estimate coupler's parameters, and to adjust the estimated return loss during

measurement.

[0068] In the disclosed system, the calibration is not possible, since integrated antenna units usually do not have access to individual antenna elements or subarrays.

[0069] Instead of estimating or measuring the return loss itself, a change between known and measured return loss values is measured and compared to a threshold. The known return loss of every antenna element or subarray is measured during the antenna unit manufacturing, integration, installation, commissioning, etc. The measured value is then recorded in a database to compare with during the radio operation.

[0070] Due to finite coupler directivity, the return loss change can only be measured within uncertainty range depending upon whether the leaking signals are added up in phase, in opposite phase, or incoherently. For example, numerical calculations show that 3dB change in return loss from 15dB to 12dB may result in 2.4dB - 4dB range of measured values if a directional coupler with 25dB directivity is used, see Figure 5.

[0071 ] Setting a threshold to ~4dB (the upper bound) will guarantee that if the measured change in return loss exceeds the threshold, the actual return loss had changed at least 3dB or more.

[0072] Figure 6 is a flow chart that illustrates the operation of the processing circuitry 30 to perform antenna fault detection based on the combined forward feedback signal and the combined reflected feedback signal received during transmission of known transmit signals via the transmitter branches 16-1 through 16-P in accordance with some embodiments of the present disclosure. The process of Figure 6 is similar to that of Figures 3 and 4, but in Figure 6 the processing circuitry 30 determines whether there is fault for branch p based on a VSWR estimate for branch p that is computed based on the reflected power measurement and the forward power measurement for branch p.

[0073] As illustrated, the processing circuitry 30 samples the combined forward feedback signal and the combined reflected feedback signal received via the receiver branch(es) 28 (step 300). A branch index p is set to 1 (step 302). If the branch index p is not greater than or equal to P (i.e., the total number of transmitter branches 16 and thus the total number of antenna elements or antenna element subarrays 32) (step 304, NO), the processing circuitry 30 calculates a VSWR estimate for branch p based on the samples of the combined forward feedback signal and the combined reflected feedback signal (step 306). A detailed example of how the VSWR estimate can be determined is provided below. The VSWR estimate is one example of a value that is a function of the return-loss for branch p. Further, the VSWR estimate varies over frequency (i.e., is a function of frequency). The processing circuitry 30 compares the VSWR estimate to a predefined VSWR threshold T (step 308). The predefined VSWR threshold 7 ^~ is determined during manufacturing and is known to be a value below which performance of branch p is acceptable (i.e., there is no fault). The predefined VSWR threshold may alternatively be determined via, e.g., simulation. If the VSWR estimate for branch p is greater than the predefined VSWR threshold 7 ^~ (step 308, YES), the processing circuitry 30 determine that there is a fault for the antenna element or antenna element subarray 32-p for branch p (step 31 0) and the process then proceeds to step 316. The fault may be that, e.g., the antenna element or antenna element subarray 32-p is damaged or there is an obstruction that is negatively impacting the performance of the antenna element or antenna element subarray 32-p. If the VSWR estimate is not greater than the predefined threshold 7 ^~ (step 308, NO), the processing circuitry 30 then increments the branch index p (step 312), and the process then returns to step 304 and is repeated for the next branch p. Once all branches have been processed (i.e., once the branch index p is greater than or equal to P) (step 304, NO), the process ends.

[0074] Now, a discussion of one example process for calculating the VSWR estimate in step 306 will be provided.

[0075] For the purpose of explaining how the combined forward feedback signal and the combined reflected feedback signal are used for RL and VSWR estimation, reference will be made to Figures 6 and 7. Figure 7 is an exemplary block diagram of a p ^th branch (where p=1 , P) of the transmitter system 10 that includes the p ^th transmitter branch, the directional coupler 34-p, and the antenna element or antenna element subarray 32-p that will be referenced to describe the VSWR/return-loss measurement calculation process. The equivalent block diagram of p ^th branch is illustrated in Figure 8. In particular, for clarity purposes, only a p ^th branch, p = 1 ... P, of a multi-antenna radio unit 12 is considered with, i.e., antenna feeder cable and antenna, connected at the radio unit output port are reference, forward and reversed

signals respectively in frequency domain, obtained, e.g., by applying Fast Fourier Transform (FFT) to the corresponding signals captured in time. The reference signals are captured from the digital circuit. The forward and reversed signals are those at the outputs of the directional coupler 34-p. Let H be the transfer function from the reference point where V is captured to the

directional coupler 34-p, and be the transfer function from the

directional coupler 34-P to the antenna element or antenna element subarray 32- P. Then, the measured reflection coefficient of the p ^th antenna element

or antenna element subarray 32-p (i.e., the p ^th Radio Frequency (RF) load) is given by:

where

[0076] Using transfer functions, the processing circuitry 30 performs simultaneous estimation of H and for the transmitter system 10

including the antenna unit 14 having multiple antenna elements or antenna element subarrays 32. For example, these formulas may be applied to the embodiments of Figures 1 A through 1 C with two combined feedback signals and∑ is the combined forward feedback signal

output by the first combining circuitry 46 and is the combined reflected

feedback signal output by the second combining circuitry 48. One may model and as:

where and are input noises of the receiver branch(es) 28 (i.e., the

observation receiver(s)). [0077] There are a number of methods to estimate and H by observing and given e.g., maximum likelihood, adaptive

filtering, Viterbi algorithm, etc. In a Minimum Mean Square Error (MMSE) method, and are estimated by and such

that

where operator £ denotes mathematical expectation. Through mathematical manipulations the matrix solution for every frequency w is

where the vectors and matrices are defined as

x is the matrix multiplication operator, and superscripts τ and ^* denote vector transpose and complex conjugate respectively.

[0078] It is assumed that V are de-correlated, i.e., the inverse of exists. If V are not inherently de-correlated, there are

various well known de-correlation methods, e.g., additive pseudo-noise, phase dithering, etc. If de-correlation is needed or desired, a de-correlation method may be implemented by the conditioning circuitry 26. [0079] In practice the mathematical expectation can be replaced by averaging the data collected in M measurements, i.e. , and can be

estimated as

where index m = l...M denotes the measurement sample.

[0080] In field operation during transmission of data traffic, VSWR/return-loss may be measured simultaneously on multiple antenna branches through the following steps:

1 . Collect M samples of ∑ and for

each branch p for in frequency domain, e.g., by applying FFT to

time domain signals.

2. Calculate and \ using Eq. 3.

3. Calculate and using Eq. 2.

4. Calculate the measured reflection coefficient for each branch p

(i.e., for each antenna element or antenna element subarray 32-p) for p using Eq. 1 .

5. Calculate the return-loss vs. frequency for each branch p (i.e., for each antenna element or antenna element subarray 32-p) for as:

Calculate the return-loss over the occupied band for each branch p as: where w - 1...W is the frequency index within the occupied band

6. Calculate any function of RL, e.g., the VSWR estimate vs. frequency for each branch p (i.e., for each antenna element or antenna element subarray 32-p) for as:

Calculate the VSWR over the occupied band for each branch p

In this manner, a return-loss and VSWR estimate is obtained for each antenna element or antenna element subarray 32 using the combined forward feedback signal and the combined reflected feedback signal, which allows for simultaneous measurement of multiple antenna paths/branches.

[0081 ] Note that, in some embodiments, the process of Figure 6 is repeatedly performed (e.g., continuously or periodically) to monitor and record the forward and reflected power during the radio operation and to determine whether there is an antenna fault based on those measurements. In some embodiments, an alarm will be raised when a fault is detected.

[0082] Figure 9 illustrates the transmitter system 10 in accordance with some other embodiments of the present disclosure. As illustrated, the transmitter system 1 0 includes one or more modules 82 that operate to provide at least some of the functionality of the transmitter system 10 as described herein. For instance, in some embodiments, the modules 82 include one or more modules that operate to provide the functionality of the processing circuitry 30 as described above with respect to Figure 3, 4, or 5. Specifically, the modules 82 may include a sampling module operable to perform the function of step 100, 200, or 300 and a fault detection module operable to perform the functions of steps 1 02-1 10 (Figure 3), steps 202-220 (Figure 4), or steps 302-312 (Figure 6). [0083] Note that while combined forward and reflected feedback signals are used in the embodiments described above, the present disclosure is not limited thereto. For instance, switching circuitry may alternatively be used to provide separate forward feedback signals for each antenna branch and separate reflected feedback signals for each antenna branch. In this regard, Figure 10 illustrates one example alternative embodiment of the transmitter system 10 that is similar to that of Figure 1 A but where the combiner circuitry 46 and 48 is replaced with switching circuitry 84 and 86. Similar variations may be made to the architecture of Figures 1 B and 1 C. The switching circuitry 84 operates to provide a separate forward feedback signal for each of the antenna branches where, for example, these separate forward feedback signals are multiplexed in time. Likewise, the switching circuitry 86 operates to provide a separate reflected feedback signal for each of the antenna branches where, for example, these separate reflected feedback signals are multiplexed in time. These separate feedback signals are received by the receiver(s) 28 and processed by the processing circuitry 30 as described above.

[0084] The following acronyms are used throughout this disclosure.

• RF Radio Frequency

• SIR Signal to Interference Ratio

• VSWR Voltage Standing Wave Radio

[0085] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.