FIELD OF THE INVENTION

The invention relates to millimeter wave devices, and particularly to millimeter wave Wilkinson dividers and millimeter wave phased arrays. BACKGROUND OF THE INVENTION

The use of three-port power dividers is especially important for an tenna array systems that utilize a power-splitting network, such a corporate or par allel feed system. The corporate is simply a device that splits power between n output ports with a certain distribution while maintaining equal path lengths from input to output ports. It can be implemented with n-way power splitters where three-port power dividers are commonly used.

The Wilkinson power divider is a three-port network that is lossless when the output ports are matched; where only reflected power is dissipated. In put power can be split into two or more in-phase signals with the same amplitude. As illustrated in Fig. 1, the Wilkinson divider circuit may comprise two quarter wavelength (l/4) transmission lines TL1 and TL2 connected together directly at one end (port 1), and a resistor R _s connected between the other ends (ports 1 and 3) of the transmission lines. The resistor R _s isolates port 2 and port 3 and allows all three ports to be matched. Generally, for an equal amplitude combiner/divider in a Zo impedance system, the transmission lines TL1 and TL2 having a characteristic impedance of Z0V2 and a lumped isolation resistor of 2Zo with all three ports matched, high isolation between the output ports is obtained. Due to the symmetry, equal amplitude, in-phase combining/dividing is automatically ensured. A section of transmission line having an impedance of Zo may further be connected at each of the three ports. For the case of equal amplitude combiner/divider in a 50 W sys tem, a resistance of the resistor is 100 W, an the characteristic impedance of both transmission lines TL1 and TL2 is 50 V2 W (~70.7 W). The design of an equal-split (3 dB) Wilkinson is often made in stripline or microstrip form. The isolation resis tor Rs is generally implemented by means of a discrete resistor, e.g a surface mounted device (SMD) resistor which is a preferred technology for the resistors in modern printed circuits. SMD resistors are available in different sizes which im plies different dimensions of the pads required to attach (solder) the isolation re sistor.

Antenna arrays, or phased array antennas, are often used in modern tel- ecommunication and radar systems. As well known in the art, a phased array in cludes multiple radiating elements, such as 16, 64 or 256 elements. A power distri bution network or a feeding network is provided that splits a signal power from a single input (one transmitter) between multiple output ports (the multiple radiat- ing elements). In principle, each power division by two can be done passively, as with a Wilkinson power divider. Figure 2 illustrates a l-to-8 feeding network 2 in which the Tx signal is splitted by a first Wilkinson divider W1 to two parallel 1-to- 4 feeding networks W2, W3, W4 and W2', W3', W4', respectively which feed eight outputs or radiating elements AFl-AF8n total. A Wilkinson divider feeding net- work requires a lot of routing but, on the othe hand, ensures signal amplitude and phase uniformity among all front-ends. Nevertheless, as the size of the array grows, the amount of routing and the size of the feeding network increases rapidly.

Millimeter wave bands have conventionally been employed in radar systems. Recently, since the microwave bands applied in mobile cellular systems such as Global System for Mobile Communications (GSM) and Universal Mobile Tel ecommunications System (UMTS) cannot support high-data-rate traffic, millimeter wave bands have received more attention, for example, 60 GHz bands, which can provide a bandwidth of several GHz for these short-range communications. In ad dition, the communications in the 60 GHz band have some advantanges such as the possible miniaturization of the analog components and antennas.

Wilkinson divider configuration can be employed also for millimeter- wave antenna array feeding networks. In one approach, the feeding network for the antenna arrays comprises stripline Wilkinson dividers on a . However, the chal lenge in the PCB environment is the implementation of the isolation resistor of the Wilkinson divider. Discrete resistors, such SMD resistors at frequencies of 60 GHz and higher are expensive and for large arrays they might not be easily assembled. An alternative approach might be LTCC (low temperature co-fired ceramics) tech nology which has "built-in" resistors but the price of LTCC technology is higher than that of the basic PCB technology.

Wilkinson power splitters can also be implemented with a Monolithic

Millimeter-wave Integrated Circuit (MMIC) technology, in which passive elements and interconnections are fabricated on the same semiconductor substrate as active devices. Example of this approach is disclosed in "60-GHz 64- and 256-Elements Wafer-Scale Phased-Array Transmitters Using Full-Reticle and Subreticle Stitching Techniques", Samet Zihir et al, IEEE Transactions On Microwave Theory And Tech niques, Vol. 64, No. 12, p. 4701-4719, December 2016. The same silicon wafer was used for the RF distribution network, power and SPI distribution, and phased-array channel Antennas were on a separate quartz wafer mounted on top of the silicon wafer The 1-64 distribution network divides the power equally to all phased-array channels, which being on the same wafer are very similar to each other.

However, a problem with of such on-chip power splitters is that they consume expensive MM1C area and additionally may lead to an extra power loss because of an additional wiring needed between the phased array cells.

BRIEF DESCRIPTION OF THE INVENTION

An aspect of the invention to provide a new Wilkinson divider design for millimeter wave frequencies which provides a cost effective and feasible imple mentation especially in large array feeding networks. The aspect of invention is characterized by what is stated in the independent claims. The preferred embodi ments of the invention are disclosed in the dependent claims.

An aspect of the invention is a hybrid millimeter-wave Wilkinson di- vider device, comprising

a carrier subtrate ,

an input port, a first output port, a second output port, and transmis sion lines connecting the input port to the first and second output ports imple mented by transmission lines in the carrier subtrate,

an isolation resistor connected between the first and second output ports, and the isolation resistor of the Wilkinson divider is integrated in a mono lithic microwave integrated circuit (MMIC) chip installed on the carrier subtrate, wherein the MMIC chip comprises a first input metal pad and a second input metal pad connected to first and second output ports, respectively, on the carrier sub- trate, and wherein the isolation resistors connected between the first input metal pad and the second input metal pad in the the MMIC chip, and the MMIC chip fur ther comprises a first parallel resonant circuit for compensating a paracitic capac itance of the first input metal pad and a second parallel resonant circuit for com pensating a paracitic capacitance of the second input metal pad.

A further aspect of the invention is a hybrid millimeter-wave device, comprising

a carrier subtrate ,

at least one monolithic microwave integrated circuit (MMIC) chip in stalled on the carrier subtrate,

a signal distribution network configured to feed one input signal to a plurality outputs, the signal distribution network including a plurality of Wil-kin- son dividers, each of the plurality of Wilkinson dividers furher comprising an input port, a first output port, a second output port, transmission lines connect-ing the input port to the first and second output ports, and an isolation resistor connected between the first and second output ports, and

wherein the transmission lines of each Wilkinson divider is imple mented in the carrier subtrate, and the isolation resistor of each Wilkinson divider integrated in the at least one MMIC chip, and

wherein the MMIC chip comprises a first input metal pad and a second input metal pad connected to first and second output ports, respectively, on the carrier subtrate, and wherein the isolation resistors connected between the first input metal pad and the second input metal pad in the the MMIC chip, and the MMIC chip further comprises a first parallel resonant circuit for compensating a paracitic capacitance of the first input metal pad and a second parallel resonant circuit for compensating a paracitic capacitance of the second input metal pad.

In an embodiment, the signal distribution network is a l-to-4, l-to-8, 1- to-16, l-to-64, l-to-256. or l-to-512 network, or any combination thereof.

In an embodiment, the first parallel resonant circuit comprises a first inductance connected from the first input metal pad to ground in the MMIC chip and thereby in parallel with the parasitic capacitance of the first input metal pad, and whereby the second parallel resonant circuit comprises a second inductance connected from the second input metal pad to ground in the MMIC chip and thereby in parallel with the parasitic capacitance of the second input metal pad.

In an embodiment, the MMIC chip comprises a third metal pad and a fourth connected to the ground, and wherein the first inductance is connected be tween the first input metal pad and the third metal pad, and wherein the second inductance is connected between the second input metal pad and the fourth metal pad.

In an embodiment, the third and fourth metal pads are configured to be ground contacts between the MMIC chip and the carrier subtrate.

In an embodiment, the MMIC chip further comprises at least one further integrated component and/or electronic circuit. In an embodiment, the carrier sub strate is based on a printed circuit board (PCB) technology, Low-temperature co fired ceramic (LTCC) technology, integrated passive device (IPD) technology, or quarz substrate.A still further aspect of the invention is a millimeter wave phased array comprising at least one or a plurality of millimeter wave Wilkinson divider devices according embodiments of the invention.

A still further aspect of the invention is a monolithic microwave inte grated circuit (MMIC) chip, comprising

at least a first input metal pad and a second input metal pad for mount- ing the MMIC chip on a carrier substrate ,

at least one integrated isolation resistor configured, when the MMIC chip is mounted on the carrier subtrate, to be connected via the first and second input metal pads to transmission lines in the carrier subtrate to form a hybrid mil limeter-wave Wil-kinson divider with said carrier subtrate transmission lines, and wherein the MMIC chip comprises a first parallel resonant circuit and a second parallel resonant circuit on the MMIC chip configured to compensate a a paracitic capacitances of the first input metal pad and the second input metal pad, respectively, and wherein the first parallel resonant circuit preferably comprises a first inductance connected from the first input metal pad to ground and thereby in parallel with the parasitic capapacitace of the first input metal pad, and whereby the second parallel resonant circuit preferably comprises a second inductance con nected from the second input metal pad to ground and thereby in parallel with the parasitic capacitance of the second input metal pad.

In an embodiment, the MMIC chip comprises a third metal pad and a fourth connected to the ground, and wherein the first inductance is connected be tween the first input metal pad and the third metal pad, and wherein the second inductance is connected between the second input metal pad and the fourth metal pad, and wherein the third and fourth metal pads are preferably configured to be ground contacts between the MMIC chip and the carrier subtrate.

In an embodiment, the MMIC chip comprises a plurality of integrated isolation resistors with respective pairs of first and second input metal pads to be connected to a plurality of transmission lines in the carrier subtrate to form a plu rality of hybrid millimeter-wave Wilkinson dividers, and wherein the MMIC chip optionally comprises at least one further integrated component and/or electronic circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of exemplary embodiments with reference to the attached drawings, in which

Figure 1 illustrates a basic configuration of a Wilkinson power divider; Figure 2 is a schematic block diagram illustrating an exemplary l-to-8 power distribution network;

Figure 3 shows a top view of a hybrid Wilkinson power divider accord ing to an embodiment of the invention;

Figure 4 shows a partially cross-sectional perspective view of a multi layer PCB;

Figure 5 illustrates an exemplary desing of a hybrid Wilkinson power divider according to an embodiment of the invention;

Figure 6 illustrates an exemplary design of a MM1C chip resistor accord- ing to an embodiment of the invention;

Figure 7 illustrates an exemplary design of a l-to-4 feeding network in cluding three hybrid Wilkinson power dividers according to an embodiment of the invention;

Figure 8 illustrates schematically an exemplary MM1C chip containing a plurality of MM1C isolation resistors according to an embodiment of the invention as well as other circuitry; and

Figures 9, 10 and 11 show S-parameter graphs that illustrate a simu lated port matching, a simulated coupling, and a simulated isolation in function of the signal frequency (60-90 GHz), respectively, for the l-to-4 feeding network (Fig. 7) at which port 1 is "IN" and ports 2-5 denote "AF1-AF4", respectively.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

An aspect of the invention is a hybrid Wilkinsion power divider or split ter which uses a carrier substrate or board for transmission line routing and a Monolithic Millimeter-wave Integrated Circuit (MM1C) technology for a resistor implementation. Transmission lines may be implemented in various alternative structures, such as microstrip line, stripline, coplanar waveguide (CPW). In the ex ample embodiments, transmission lines are mostly implemented with microstrip lines, but embodiments of the invention are not restricted to the use of microstrip lines. The carrier substrate or board (which can also be referred to as an RF plat- form) suitable for embodiments of the invention can be manufactured using vari ous different types of technologies, such as printed circuit board (PCB), Low-tem perature cofired ceramic (LTCC), integrated passesive device (1PD), quartz wafer, etc. The exemplary embodiments herein will be described and illustrated using the PCB technology as an example without intention to restrict embodiments of the invention to this technology. The novel hybrid, e.g. PCB/MM1C or LTCC/MM1C, Wil kinson power divider design may lead to minimal signal loss due to the routing and to minimal MM1C area consumption. The use of PCB technology for the transmis sion line routing, and implementation of the isolation resistor with a very small MM1C area, result in very cost-efficient Wilkinson design in comparision with con ventional designs. The low manufacturing cost of the Wilkinson divider is espe cially advantageous in applications having large arrays, such as in 5 G telecommu nication applications where every lamp post may have phased array radio-front- end(s) with several hundred radiating elements.

An example of a hybrid Wilkinson power divider according to an em bodiment of the invention is illustrated in Fig. 3. The exemplary Wilkinsion divider 30 has a transmission lines and routing in form of microstrip lines 32 in one or more electrically conductive layers of a carrier substrate (e.g. aprinted circuit board PCB) 31, eg. metal layers. In an embodiment the carrier subtrate 31 may be a multilayer carrier substrate (e.g. PCB or LTCC), and at least part of the microstrip lines 32 implementing transmission line routing may be provided in an intermedi ate electrically conductive layer between dielectric layers 33, for example as illus trated in Fig. 4. However, any one or ones of the conductive layers, such as conduc tive top and bottom layers 34 and 35, and possible other layers, may be utilized transmission line routing. The the dielectric layers 33 of the carrier substrate 31 may be made of any suitable dielectric material. In Figure 3, a MM1C chip resistor 40 installed on the carrier subtrate 31 and connected between output ports 2 and 3. Contact bumbs or pads 41 and 42 may be provided for making the connection.

An exemplary model of a hybrid Wilkinson power divider according to an embodiment of the invention is illustrated in Fig. 5. Port 1 is connected by a transmission line TL5 (eg. a straight microstrip line with length 4 mm and width 1 mm) to a branching T microstrip line SL1 (eg. having width 1 mm at the input branch 3 and width 2 mm at the output branches 1 and 2). Series connection of a straight transmission line TL8 (e.g. a straight microstrip line with length 1/2 mm and width 2 mm), a corner microstrip line SL3 (eg. having width 2 mm), a straight transmission line TL6 (eg. a straight microstrip line with length 1 mm and width 2 mm), a corner microstrip line SL4 (eg. having width 2 mm), and a straight trans mission line TL8 (e.g. a straight microstrip line with length 1/2 mm and width 2 mm) is connected to one input branch (e.g. branch 2) of a branching T microstrip line SL61 (eg. having width 2 mm at the input branches 1 and 2 and 3 mm at the output branch 3). The output of the branching T microstrip line SL16 is connected via a series connection of a corner microstrip line SL18 (eg. having width 3 mm) and a straight transmission line TL10 (eg. a straight microstrip line with length 3 mm and width 3 mm) to a port 2 of the Wilkinson divider. Thus the upper portion of the Wilkinson divider shown in Figure 5 may represents the transmission line between the ports 1 and 2 in the Wilkinson divider shown in Fig. 3, or generally in Fig.l. Similarly, a series connection of a straight transmission line TL12 (e.g. a straight microstrip line with length 1/2 mm and width 2 mm), a corner microstrip line SL2 (eg. having width 2 mm), a straight transmission line TL7 (eg. a straight microstrip line with length 1 mm and width 2 mm), a corner microstrip line SL5 (eg. having width 2 mm), and a straight transmission line TL13 (e.g. a straight mi crostrip line with length 1/2 mm and width 2 mm) is connected to one input branch (e.g. branch 1) of a branching T microstrip line SL17 (eg. having width 2 mm at the input branches 1 and 2 and 3 mm at the output branch 3) . The output of the branch ing T microstrip line SL17 is connected via a series connection of a corner mi- crostrip line SL19 (eg. having width 3 mm) and a straight transmission line TL10 (eg. a straight microstrip line with length 3 mm and width 3 mm) to a port 3 of the Wilkinson divider. Thus the lower portion of the Wilkinson divider shown in Figure 5 may represents the transmission line between the ports 1 and 3 in the Wilkinson divider shown in Fig. 3, or generally in Fig.l. Further, the branch 1 of the branching T microstrip line SL16 is connected to an RF pad 42 on the carrier subtrate 31, and the branch 2 of the branching T microstrip line SL17 is connected to an RF pad 41 on the carrier subtrate 31. A MM1C chip resistor 40 that implements an isolation resistor Rs (eg. 80 ohm) is connected between the RF pads 41 and 42, and thereby between the ports 2 and 3 of the Wilkinsion divider.

An exemplary model of a MM1C chip resistor 40 according to an embod iment of the invention is illustrated in Fig. 6. The exemplary MM1C chip resistor 40 may comprise a first radio frequency (RF) input metal pad XI connectable to the corresponding RF pad 42 on the carrier subtrate 31, and a second radio frequency (RF) input metal pad X3 connectable the corresponding RF pad 41 on the carrier subtrate 31. The exemplary MM1C chip 40 further comprises an isolation resistor Rs integrated on the chip. The isolation resistor Rs may be implemented in any form applicable in the MM1C technology. Examples of different types of MM1C resistors include poly- and diffusion resistors for CMOS, NiCr resistors for GaAS, etc. The ma terial may be tantalum or nitride, for example. The resistor Rs may be a thin film MM1C resistor. In the exemplary embodiment, the resistor Rs may be a tantalum thin film resistor of 80 ohm. The resistor Rs is connected between the RF input metal pads XI and X3 by suitable means, for example by means of metal lines L2 and L3.

The RF input metal pads XI and X3 may have parasitic capacitance to wards ground potential. In an embodiment, a compensation circuit for parasitic ca- pacitances caused by the RF input metal pads XI and X3 may be provided on the

MMIC chip 40 so that the on-chip resistor Rs appears as a pure resistance to the ports 2 and 3 of the Wilkinson divider on the carrier subtrate 31. In an embodi ment, the compensation circuit may be condigured to create a parallel resonance circuit with the respective RF input metal pad XI or X3 so that the effect of the parasitic capacitance will be resonated out. In an embodiment, a metal pad X2 con nected to a reference potential or ground may be provided on the chip adjacent to the RF input metal pad XI. Further, an inductor LI (e.g. a metal line) is connected between the metal pads XI and X2 parallel with the parasitic capacitor caused by the RF input metal pad XI. Thereby, a parallel resonant circuit is obtained which compensates the parasitic capacitance of the RF input metal pad XI. Similarly, a metal pad X4 connected to a reference potential or ground may be provided on the chip adjacent to the RF input metal pad X3. Further, an inductor L4 (e.g, a metal line) may be connected between the metal pads X3 and X4 parallel with the para sitic capacitor caused by the RF input metal pad X3. Thereby, a parallel resonant circuit is obtained which compensates the parasitic capacitance of the RF input metal pad X3.

In an embodiment, the grounded metal pads X2 and X4 are configured to be ground contacts between the MMIC chip and the carrier subtrate 31, i..e. to contact respective ground pads on the carrier subtrate 31. Thereby, the metal pads X2 and X4 are connected or grounded both to the local ground of the MMIC chip and the ground of the carrier subtrate 31, i.e. the MMIC chip and the carrier sub trate 31 share the same ground. As a result, a well-defined return path can be ob tained for a return current of the resonance circuit, i.e. the common ground.

A hybrid Wilkison divider according to embodiments of the invention can be employed as a building element to construct larger feeding networks, such as the l-to-8 feeding network 2 illustrated in Fig. 2. Figure 7 illustrates an exem plary model of a l-to-4 feeding network 70 including three hybrid Wilkinson power dividers according to embodiments of the invention. The feeding network 70 may implement, for example, each of the two parallel l-to-4 feeding networks W2, W3, W4 and W2', W3', W4', respectively which feed eight outputs or radiating elements FA1-FA8. In Figures 3-7, same reference symbols present same or similar structures or functions. Similarly, larger feeding or power divider networks can be provided to provide feeds for 16, 64, 256, or 512 elements, for example.

In an embodiment, an MM1C chip contains an integrated isolation resis tor for one hybrid Wilkinson divider having striplines for transmission line routing on a carrier subtrate on which the MM1C chip is to be mounted.

In an embodiment, an MM1C chip contains an integrated isolation resis tor for a plurality of hybrid Wilkinson dividers, i.e. two or more dividers, having striplines for transmission line routing on a carrier subtrate on which the MM1C chip is to be mounted.

In an embodiment, an MM1C chip contains, in addition to one or a plu rality of integrated isolation resistor, further MM1C components and/or electronic circuits, such as any one or more of passive components, active components, analog circuits, digital circuits, control circuits, etc. The MM1C area saved by using hybrid Wilkinson divider according to embodiments of the invention, may allow more ad- ditional circuitry on the same chip area, or allow same circuitry with less MM1C chip area.

Figure 8 illustrates schematically an exemplary MM1C chip containing a plurality of MM1C isolation resistors 40 according to embodiments of the invention. The MM1C isolation resistors 40 are shown with a diagonal line fill. The MM1C iso- lation resistors 40 may be positioned on the MM1C chip 80 layout so that they read ily connectable to the transmission line routing of the respective Wilkinsion divider on the underlying carrier subtrate when the MM1C chip is mounted. Positioning of each MM1C isolation resistors 40 and the associated contact pads XI and X3, as well as the optional ground pads X2 and X4 on the MM1C chip 80 layout can be such that the area MM1C chip used effectively with minimum routing on the chip. Contact pads XI and X3 of the MM1C isolation resistors 40, as well as the ground contact pads X2 and X3 may be on the edges of the MM1C chip 80, for example, as illustrated in Figure 8 . Contact pads XI and X3 f the MM1C isolation resistors, as well as the ground contact pads X2 and X3, can be also in close proximity to the MM1C isolation resistors 40 on the MM1C chip 80, apart from the edges of the MM1C chip 80, as also illustrated in Figure 80. The MM1C chip 80 shown in Fig. 8 might be suitable for the l-to-8 feeding network 2 shown in Fig. 2, for example. The MM1C chip 80 may also contain further MM1C components and/or electronic circuits, as illustrated by bro ken line elements 81. Such elements may be include any one or more of passive components, active components, analog circuits, digital circuits, control circuits, etc. Figures 9, 10 and 11 are S-parameter graphs that illustrate a simulated port matching, a simulated coupling, and a simulated isolation in function of the signal frequency (60-90 GHz), respectively, for the l-to-4 feeding network (Fig. 7) at which port 1 is "IN" and ports 2-5 denote "AF1-AF4", respectively. The simula- tions show the excellent performance of a hybrid Wilkinson divider according to embodiments of the invention. Embodiments of the invention are not intended to be limited to these exemplary frequencies but are applicable for all microwave and millimeter-wave signals, and especially frequencies higher than 20 GHz.

It will be obvious to a person skilled in the art that the invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.