Technical Field

The invention relates to a test device and a test set up for locating a PIM source in a device under test. The invention further relates to a method for locating a PIM source in a device under test. Background

Passive intermodulation (PIM) is a major problem in radiofrequency equipment of mobile communication base stations. PIM leads to significant degradation of receiver sensitivity and overall signal quality. Thus, it is important to test any devices for PIM sources and to locate the PIM source with high accuracy in order to quickly eliminate them.

Summary

It is thus the object of the invention to provide a test device, a test setup and a method for locating a PIM source in a device under test that allows locating the PIM source with high accuracy at low costs. For this purpose, a test device for locating a PIM source (source of passive intermodulation) in a device under test (DUT), in particular in an antenna for a mobile communication base station is provided. The test device comprises a first test port for establishing a connection to a first side of the device under test, a second test port for establishing a connection to a second side of the device under test, a first signal generator, a second signal generator and a receiver. The first signal generator is designed for generating a first probing signal with a first frequency in a first frequency range, the second signal generator is designed for generating a second probing signal with a second frequency in a second frequency range, and the receiver is designed for measuring a response signal in a response frequency range. The first signal generator and the receiver are connected to the first test port and the second signal generator is connected to the second test port.

By feeding the two probing signals from different sides to the DUT, frequencies in the first and second frequency range combined are not present on the same test port of the test device. Instead, only frequencies in the first frequency range and the response frequency or only frequencies in the second frequency range are present. Thus, the requirements on the quality of the filters at the first test port can be reduced drastically without any loss in accuracy.

The response signal is, for example, a combination of the first probing signal and the second probing signal, in particular the response signal being a third order intermodulation product.

Within the disclosure of the invention, the two sides of a DUT, for example, correspond to an input and the respective output. In particular, the DUT may be a two gate device and each gate corresponds to one of the sides. In an aspect, the response frequency range lies below the first frequency range and the second frequency range, allowing the best coverage of a bandwidth of the DUT.

In order for an efficient measurement, the first frequency range and the second frequency range may overlap at least partly and/or the first frequency range may lie below the second frequency range at least party, in particular fully.

For example, the response frequency range is spaced apart from the first and/or second frequency range by at least one duplex distance of the duplex filter so that the bandwidth of the DUT may be used optimally without the need for specialized duplex filters.

In an embodiment, the test device comprises a second receiver connected to the second test port designed for measuring the response signal, further increasing the measurement accuracy.

To simplify the setup, the first signal generator and the receiver may be connected to the first test port via a duplex filter.

Also, the second signal generator and the second receiver may be connected to the second test port via a duplex filter.

In an embodiment, a circulator is provided between the first signal generator and the first test port and/or between the second signal generator and the second test port protecting the power amplifiers from the signals of the other signal generator while allowing an overlap of the first and second frequency range.

For example, the respective test port is connected to the port of the circulator directly after the port connected to the respective signal generator.

In another embodiment, one of the first test port and the second test port, in particular the second test port, is a probe antenna, particularly wherein the probe antenna is movable relative to the first test port and/or the device under test. Using an antenna as a test port allows for probing the second side of an antenna as a DUT.

The probe antenna may be movable in one, two or three dimensions.

For example, the other one of the test ports, in particular the first test port, is cable bound.

For the above mentioned purpose, further a test setup is provided for locating a PIM source. The test setup comprises a device under test, in particular an antenna for a mobile communication base station, and a test device as described above. The DUT comprises a first side and a second side, wherein the first side is coupled to the first test port of the test device and the second side is coupled to the second test port of the test device.

The features and advantages discussed with respect to the test device also apply to the test setup and vice versa.

For optimal measurement, the first frequency range, the second frequency range and the response frequency range may be within a bandwidth of the DUT at least partly, in particular fully.

In an embodiment, the first side of the DUT is a cable bound interface and the second side of the DUT is a wireless interface or a cable bound interface, enlarging the types of DUTs that may be probed with the test device.

In case of a wireless interface of the DUT as a second side, the connection between the second test port of the test device and the second side of the DUT is over-the-air (OTA).

The second side of the DUT may be an antenna, in particular an antenna array, allowing PIM source location in antennas. The antenna array may extend in one or two dimensions. For example, the probe antenna is movable in front of the antenna of the DUT, in particular in the same two dimensions that the antenna array is extending in, allowing to systematically target specific areas of the antenna array.

Further for the above mentioned purpose, a method is provided for locating a PIM source in a device under test, in particular using a test device as described above or a test setup as described above. The method comprises the following steps:

- applying a first probing signal with a first frequency in a first frequency range to a first side of the DUT,

- applying a second probing signal with a second frequency in a second frequency range to a second side of the DUT,

- measuring, in particular at the first side, a response signal received from the DUT in response to the first and second probing signals, and

- determining the location of the PIM source in the DUT based on the response signal measured.

The features and advantages discussed with respect to the test device and the test setup also apply to the method and vice versa. In particular, the components of the test device and/or test setup that perform a certain step in the method are designed to carry out this step.

In an aspect, the first frequency is swept through the first frequency range, wherein the second frequency is simultaneously swept through the second frequency range such that the response frequency of the response signal is kept constant. In doing so, twice as large frequency sweeps for a given bandwidth of the DUT are possible, drastically increasing the detection accuracy.

The response signal is in particular a third order intermodulation product. Further, in combination with feeding the first and second signal to different sides of the DUT, only the sweep of the second frequency contributes to the phase shift at the receiver. As this frequency sweep is twice as wide compared to existing devices, the accuracy of PIM source localization is doubled.

In an aspect, the lower end of the first frequency range is spaced apart from the response frequency of the response signal by one duplex distance of a duplex filter of the test device and/or wherein the lower end of the second frequency range is spaced apart from the response frequency of the response signal by two duplex distances of a duplex filter of the test device, allowing very large sweeps without the need for specialized filters.

In a different embodiment, the first frequency or the second frequency is kept constant and the other one of the first frequency and the second frequency is swept through the respective frequency band, simplifying the measurement.

In order to make full use of the bandwidth of the DUT, the response frequency of the response signal may be chosen to be the lower limit of a bandwidth of the DUT and/or the upper end of the second frequency range may be chosen to be the upper limit of the bandwidth of the DUT.

In an embodiment, the probe antenna is moved relatively to the DUT, in particular in parallel with the DUT, during the measurement, wherein the location of the probe antenna with respect to the DUT is taken into consideration when determining the location of the PIM source. This way, additional spatial information about the location of the DUT is generated, further increasing the detection accuracy.

In another aspect, after applying the first probing signal with the first frequency to the first side and the second probing signal with the second frequency to the second side, the second probing signal with the second frequency is applied to the first side and the first probing signal with the first frequency is applied to the second side. This way, the arbitrary phase of the PIM source can be separated from the phase due to the position of the PIM source, further increasing detection accuracy.

Brief Description of the Drawings

Further features and advantages will be apparent from the following description as well as the accompanying drawings, to which reference is made. In the drawings:

Figure 1: shows a schematic diagram of a test setup according to a first embodiment of the invention with a test device according to a first embodiment of the invention,

Figure 2: shows a schematic diagram of a second embodiment of a test setup according to the invention with a second embodiment of a test device according to the invention,

Figure 3: shows a diagram of the frequencies used during a first embodiment of a method according to the invention, and

Figures 4, 5: show the frequencies used during a second and third embodiment of a method according to the invention.

Detailed Description

Figure 1 shows a test setup 10 according to a first embodiment of the invention with a test device 12 according to a first embodiment of the invention and a device under test 14 (DUT).

In the DUT 14, a source of passive intermodulation - PIM source 16 in the following - is present deteriorating the signal that passes the DUT 14.

The DUT 14 has two sides, namely a first side 18 and a second side 20, corresponding to two gates or interfaces of the DUT 14. The gates may be an input and an output of the DUT 14. More generally, a signal that is inputted at one of the sides is transformed by the DUT 14 and outputted on the other side of the DUT 14.

In the shown first embodiment, the DUT 14 is a coaxial cable having a PIM source 16.

Thus, the first side 18 of the DUT 14 and the second side 20 of the DUT 14 are the ends of the cable.

The test device 12 comprises a first signal generator 22, a second signal generator 24, a receiver 26, a first test port 28 and a second test port 30.

The first signal generator 22 and the receiver 26 are connected to the first test port 28 via wiring.

To this end, the test device 12 further comprises a duplex filter 32, a receive filter 34 (RX-filter), a first transmit filter 36 (TX-filter), a first circulator 40, a first terminator 42 as well as a power amplifier 44 and a low noise amplifier 46.

The first signal generator 22 is connected to the power amplifier 44 which is, in turn, connected to one port of the first circulator 40.

The port of the first circulator 40 directly after this is connected to the first transmit filter 36, which is in turn connected to the duplex filter 32.

The third port of the first circulator 40 is connected to the first terminator 42.

The duplex filter 32 is connected directly to the first test port 28 for transmitting the signals generated by the first signal generator 22 to the first test port 28 and thus to the DUT 14.

For signals received by the first test port 28, the duplex filter 32 is connected to the receive filter 34, which is in turn connected to the low noise amplifier 46. The low noise amplifier 46 is then connected to the receiver 26. The second signal generator 24 is connected to the second test port 30 also by a wired connection.

To this end, the test device 12 further comprises a second transmit filter 48, a second circulator 50, a second terminator 52 and a second power amplifier 54.

In much the same way as explained with respect to the first signal generator 22, the second signal generator 24 is connected to the second power amplifier 54, which is in turn connected to a port of the second circulator 50.

The port directly after is connected to the second transmit filter 48 and the third port is connected to the second terminator 52.

The second transmit filter 48 is directly connected to the second test port 30.

It is also conceivable in an alternative embodiment that a second receiver 56 is present. In this case, the test device 12 also comprises a second duplex filter 58, a second receive filter 60 and a second low noise amplifier 62, set up correspondingly as the branch of the receiver 26. For example, the second duplex filter 58 is connected to the second test port 30 and the second transmit filter 48.

In Figure 1, the second receiver 56, the second duplex filter 58, the second receive filter 60 and the second low noise amplifier 62 are shown in dashed lines.

The first test port 28 is coupled to the first side 18 of the DUT 14, i.e. in the shown embodiment, the first test port 28 is connected to one end of the coaxial cable.

The second test port 30 of the test device 12 is coupled to the second side 20 of the DUT 14, i.e. in the shown embodiment, the second test port 30 is connected to the other end of the coaxial cable. Further, for calibration, a calibration element 64 may be connected between one of the test ports 28, 30 and the respective side 18, 20, in particular between the first test port 28 and the first side 18. In particular, the calibration element 64 is provided between the respective test port connected to the receiver 26 and the corresponding side 18, 20.

The calibration element 64 is a PIM source with known properties.

Figure 2 shows a second embodiment of the test set up 10 with a test device 12 according to the invention, which generally corresponds to the first embodiment shown in Figure 1. Thus, in the following, only the differences are discussed and the same and functionally the same components are labeled with the same reference signs.

In the second embodiment, the DUT 14 is an antenna 66, more particularly an antenna 66 for a mobile communication base station. Thus, the second side of the DUT 14 is a wireless interface.

The antenna 66 is an antenna array 68 extending in at least one dimension. In the shown embodiment, the antenna array 68 comprises two columns of radiators, thus extending into two dimensions, referred to as the X-direction and the Y-direction in the following.

In the second embodiment, the test device 12 differs from the test device 12 of the first embodiment in that the second test port 30 establishes a connection or coupling to the DUT 14 wirelessly, i.e. the connection or coupling between the second test port 30 and the second side 20 of the DUT 14 is over-the-air (OTA).

The second test port 30 of the test device 12 of the second embodiment is a probe antenna 70 designed to emit the signals generated by the second signal generator 24. The probe antenna 70 is movable in the X- and Y-direction along the antenna array 68 of the DUT 14. Thus, the probe antenna 70 is movable in the same dimensions or directions that the antenna array 68 is extending in. For example, the probe antenna 70 is moved in parallel in front of the antenna array 68 during a measurement.

Of course, the probe antenna 70 may also be movable in the third dimension not being one of the two dimensions of the antenna array 68.

The connection or coupling between the first test port 28 and the first side 18 is established via a cable, wherein the first test port 28 is connected to one of the ports of the antenna 66.

Further, the calibration element 64 may be attached between the first test port 28 and the first side 18, namely the port of the antenna 66. In particular, the calibration element 64 is located directly at the port of the antenna 66.

For determining the location of the PIM source 16 in the DUT 14, the following method is performed. The method may be performed, for example, with test setups 10 and test devices 12 of either one of the first or second embodiment.

Figure 3 shows a spectral diagram of the bandwidth BW of the DUT 14, showing a first frequency fi, a second frequency f2 and a response frequency fR.

The first signal generator 22 is designed to generate a first probing signal SI. The probing signal SI has the first frequency fi being in a first frequency range Afi.

Likewise, the second signal generator 24 is designed to generate a second probing signal S2 with a second frequency f2 in a second frequency range Af2. Further, a response signal R is generated by the PIM source 16 based on the first and second probing signals SI, S2. In particular, the response signal R is the third order intermodulation product of the probing signals SI and S2 having a response frequency fR equal to 2fi - f2.

In particular, the receiver 26 and the optional second receiver 56 are designed to receive the response signal R.

The receive filter 34, the first transmit filter 36, the second transmit filter 48, the duplex filter 32 as well as optionally the second duplex filter 58 and the second receive filter 60 are chosen such that the first probing signal S 1 is fed to the first test port 28, that the second probing signal S2 is fed to the second test port 30, that the response signal R received at the first test port 28 is fed to the receiver 26 and optionally that the response signal R received at the second test port 30 is fed to the second receiver 56.

For locating the PIM source 16, the first signal generator 22 generates the first probing signal SI which is then fed via the first test port 28 into the DUT 14 via its first side 18. Simultaneously, the second signal generator 24 generates the second probing signal S2 which is then fed via the second test port 30 in the DUT 14 via the second side 20.

At the PIM source 16, intermodulation between the first probing signal S 1 and the second probing signal S2 occurs and the response signal R is generated. The response signal R then travels to the first side 18 and to the second side 20.

The response signal R propagating through the first side 18 and the first test port 28 is measured by the receiver 26.

Optionally, the response signal R propagating through the second side 20 and the second test port 30 is measured by the second receiver 56. Thus, the response signal R is measured at the first side 18 and optionally also at the second side 20.

During the measurement and as indicated in Figure 3, the first frequency fi is changed by the first signal generator 22. More particularly, the first frequency fi of the first probing signal SI is swept through the entire first frequency range Afi.

Simultaneously, the second frequency f2 of the second probing signal S2 is swept through the second frequency range Af2.

The frequency f2 is changed at twice the speed of the frequency fi so that the response frequency fR remains constant throughout the measurement.

In particular, the lower end of the first frequency range Afi has a distance to the response frequency fR of the response signal R of one duplex distance A of the duplex filter 32 (and of the optional second duplex filter 58).

Further, the lower end of the second frequency range Af2 has a distance to the lower end of the first frequency range Afi of also one duplex distance A of the duplex filter 32, resulting in a distance between the response frequency fR of the response signal R and the lower end of the second frequency range Af2 of two duplex distances A of the duplex filter 32.

Thus, the first frequency range Afi and the second frequency range Af2 do overlap but the first frequency range Afi lies partly below the second frequency range Af2.

Further, both frequency ranges Afi and Af2 lie above the response frequency fR.

The response frequency fR of the response signal R is chosen to be the lower limit of the bandwidth BW of the DUT 14 and the upper end of the second frequency range Af2 is chosen to coincide with the upper end of the bandwidth BW of the DUT 14.

By sweeping the frequencies fi, f2 of the probing signals S 1, S2 and measuring the resulting response signal R throughout the sweep, the location of the PIM source 16 in the DUT 14 can be determined based on the response signal R measured.

The determination of the location of the PIM source 16 based on the measured response signal R may be performed in a maimer known in the art.

To this end, the position of the PIM source 16 may be determined based on the measured phase difference of the signal received by the receiver 16. The measured phase difference is set in relation to the phase difference of the calibration measurement and the obtained position is the position of the PIM source 16 relative to the calibration element 64.

In case that the second embodiment of the test setup 10 is used, during the measurement, the probe antenna 70 is moved relatively to the antenna array 68 of the DUT 14 and the location of the probe antenna 70 with respect to the DUT 14 is recorded.

For example, one full frequency sweep through the first and second frequency ranges Afi, Af2 may be performed at each location that the probe antenna 70 obtains.

When determining the location of the PIM source 16 in the DUT 14, the location of the probe antenna 70 with respect to the antenna array 68 may be taken into consideration. For example, when the amplitude of the response signal R reaches a maximum for a given location of the probe antenna 70, the location of the PIM source 16 will be related to the area in front of the probe antenna 70 at that location, for example the radiator of the antenna array 68 at that location. Thus, the detection accuracy may be increased by a moving probe antenna 70.

Before determining the location of the PIM source 16, firstly the test setup 10 is calibrated by inserting the calibration element 64 in the test setup 10 and performing the described method.

Thus, the test setup can be calibrated with the known location of the PIM source 16 within the calibration element 64.

Figures 4 and 5 show two further embodiments of the method explained with respect to Figure 3. The methods correspond to one another so that only the differences are explained in the following.

In the second embodiment of the method shown in Figure 4, the first frequency fi is swept through the first frequency range Afi, however, the second frequency f2 is kept constant. Thus, the response frequency fR of the response signal R changes within a response frequency range AfR. The response frequency range AfR of the response signal R lies below the first frequency range Afi, and the upper end of the response frequency range AfR is spaced apart by a duplex distance A from the lower end of the first frequency range Afi.

In the third embodiment according to Figure 5, the first frequency fi of the first probing signal S 1 is kept constant and the second frequency f2 is swept through the second frequency range Af2.

In this case, the upper end of the frequency range AfR of the response signal R is also spaced apart one duplex distance A from the constant frequency fi and the lower end of the second frequency range Af2 is spaced apart from the first frequency fi also by a duplex distance A.

The second frequency range Af2 lies fully above the first frequency fi. In any of the above methods, the response frequency fR or its frequency range Af _R always lies fully below the first frequency range Afi and the second frequency range Af2.

Further, all frequency ranges Afi, Af2 and AfR lie always fully within the bandwidth BW of the DUT 14.

In order to increase the detection accuracy further, after performing the frequency sweeps as explained with respect to any of the above embodiments, the measurement and thus the frequency sweeps may be repeated but with reversed frequencies. This means that for the second measurement, the first signal generator 22 generates the second probing signal S2 with the second frequency f2 and swept through the second frequency range Af2, which is then fed to the first side 18 of the DUT 14. The second signal generator 24 generates the first probing signal SI with the first frequency fi and swept through the first frequency range Afi, which is then fed to the second side 20 of the DUT 14. This way, phase shifts at the PIM source 16 cancel out which drastically increases the detection accuracy.