Amplifier module

Abstract

An amplifier module comprises an output waveguide integrated into the amplifier module, a first MMIC amplifier (A1) having a first power output (22), a second MMIC amplifier (A2) having a second power output (24), an output microstrip line (34B) having a capacitive end line (38B), an output microstrip line to output waveguide transition, and a power combiner combining the first and second power outputs (22, 24) to the output microstrip line (34B). The power combiner comprises a first bonding wire (40) coupled between the first power output (22) of the first MMIC amplifier (A1) and the capacitive end line (38B), and a second bonding wire (42) coupled between the second power output (24) of the second MMIC amplifier (A2) and the capacitive end line (38B).

Description

[0001] AMPLIFIER MODULE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to power combining, and more particularly to MMIC to waveguide power combining.

[0004] BACKGROUND OF THE INVENTION

[0005] Microwave frequency range spans from about 300 MHz to about 30 GHz corresponding to a wavelength range of 1 m to 10 mm), respectively. Millimetre waves occupy the frequency range from about 30 GHz to about 300 GHz corresponding to a wavelength range of 10 mm - 1 mm, respectively. The millimetrewave spectrum has been receiving more and more attention, and many applications, such as 5G, are under development. Benefiting from the low loss and the high power capacity, the waveguide components are widely used in millimetre-wave systems. There are several waveguide bands that occupy these frequency ranges. Standard waveguides, with rectangular and circular cross-sections, operate in a certain range of frequencies as a function of their width or radius dimensions, respectively. In EIA WR Rectangular Waveguide standard, the standard waveguide sizes are designated by a WR number, wherein the number is the width of the waveguide opening in mils, divided by 10.

[0006] In millimeter-wave systems, it is often necessary to use a number of individual semiconductor amplifiers in parallel to amplify a microwave signal received from a waveguide and combine the amplified power outputs to a single output waveguide in order to achieve the desired power levels. The amplifiers are typically implemented with a Monolithic Millimeter-wave Integrated Circuit (MMIC) technology. The parallel amplifiers may be integrated into a single MMIC chip or separate MMIC chips. However, the waveguide components cannot be directly connected to the MMIC circuits. The microstrip line is an essential component for interconnecting with the MMIC. Thus, a microstrip-to-waveguide transition is required to integrate the waveguide with the MMIC. An example of a microstrip-to- waveguide transition for a single MMIC amplifier is disclosed in the article of Varo- nen et al., "LNA modules for the WR4 (170-260 GHz) frequency range," 2014 IEEE MTT-S International Microwave Symposium (IMS2014), Tampa, FL, USA, 2014, pp. 1-4, doi: 10.1109 / MWSYM.2014.6848291.

[0007] Power division of the input signal to the amplifiers and especially power combining of the amplifier output signals present various challenges. Power combining is typically done on-chip to 50 ohm environment in order to be compliant to a variety of waveguide and antenna systems. This approach is not optimum for achieving the best overall efficiency of the output section. On-chip power combining enables an accurate power combining but medium or high combining losses depending on the technology used. Moreover, single chip power amplifiers may end up with heat issues due to the combining power losses.

[0008] Examples of an on-chip power combining are disclosed in the articles

[0009] - P. Colantonio and R. Giofre, "A GaN-on-Si MMIC Power Amplifier with 10W Output Power and 35% Efficiency for Ka-Band Satellite Downlink," 2020 15th European Microwave Integrated Circuits Conference (EuMIC), Utrecht, Netherlands, 2021, pp. 29-32.

[0010] - D. Sandstrom, B. Martineau, M. Varonen, M. Karkkainen, A. Cathelin and K. A. I. Halonen, "94GHz power-combining power amplifier with +13dBm saturated output power in 65nm CMOS," 2011 IEEE Radio Frequency Integrated Circuits Symposium, Baltimore, MD, USA, 2011, pp. 1-4, doi: 10.1109 / RFIC.2011.5940691.

[0011] Another approach is to do the power combining off-chip. For example, power amplifier chips have separate output waveguide that are combined in a hybrid waveguide coupler or combiner into a single output waveguide. As another example, separate output microstrip lines from power amplifiers may be combined by a microstrip line combiner having transition to an output waveguide, or the separate output microstrip lines may each end at a transition or a probe in the output waveguide. Examples of off-chip power combining are disclosed in US US202330806A1, US6967543B2, US20110006858A1, CN114094299B and J. Schellenberg, A. Tran, Lani Bui, A. Cuevas and E. Watkins, "37 W, 75-100 GHz GaN power amplifier," 2016 IEEE MTT-S International Microwave Symposium (IMS), San Francisco, CA, USA, 2016, pp. 1-4, doi:10.1109 / MWSYM.2016.7540195.

[0012] Off-chip power combining normally results in lower combining losses and a heat handling may be easier when power amplifiers are on separate chips. As a disadvantage, a higher number of waveguide probes, waveguides and / and bond wires are needed. This may increase complexity, size, and cost of the amplifier module as a whole.

[0013] BRIEF DESCRIPTION OF THE INVENTION

[0014] An object of the present invention is to provide a power combining design that alleviates the above disadvantages. The objects of the invention are achieved by an amplifier module recited in the independent claim. The preferred embodiments of the invention are disclosed in the dependent claims.

[0015] An aspect of the invention is an amplifier module, comprising a output waveguide integrated into the amplifier module, a first MMIC amplifier having a first power output, a second MMIC amplifier having a second power output, an output microstrip line, an output microstrip line to output waveguide transition, power combinercombining the first and second power outputs to the output microstrip line, wherein the output microstrip line comprises a capacitive end line, and wherein the power combiner comprises a first bonding wire coupled between the first power output of the first MMIC amplifier and the capacitive end line, and a second bonding wire coupled between the second power output of the second MMIC amplifier and the capacitive end line.

[0016] In an embodiment, the amplifier module comprises an isolation resistor connected between the power outputs of the first and second amplifiers.

[0017] In an embodiment, the amplifier module comprises a output waveguide integrated into the amplifier module, an input microstrip line, an input waveguide to input microstrip line transition, and power divider dividing an input power to inputs of the first and second MMIC amplifiers.

[0018] In an embodiment, the amplifier module comprises the input microstrip line comprises a second capacitive end line, and the power combiner comprises a third bonding wire coupled between the input of the first MMIC amplifier and the second capacitive end line, and a fourth bonding wire coupled between the input of the second MMIC amplifier and the capacitive end line of the output microstrip line.

[0019] In an embodiment, the amplifier module comprises an isolation resistor connected between the inputs of the first and second MMIC amplifiers.

[0020] In an embodiment, the first and second MMIC amplifiers are on a single MMIC chip.

[0021] In an embodiment, the amplifier module comprises an isolation resistor connected between the power outputs of the first and second MMIC amplifiers.

[0022] In an embodiment, the amplifier module comprises an on-chip isolation resistor connected between the inputs of the first and second MMIC amplifiers. In an embodiment, the first and second MMIC amplifiers are on separate MMIC chips.

[0023] In an embodiment, the amplifier module is a millimetre wave amplifier module.

[0024] In an embodiment, the amplifier module is configured to operate at signal frequencies that are selected from a range from 30 GHz to 300 GHz.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the following the invention will be described in greater detail by means of exemplary embodiments with reference to the attached drawings, in which

[0027] Figure 1A is a schematic partial top view of an exemplary amplifier module having an upper part of metal housing removed;

[0028] Figure IB is a schematic cross-sectional side view of an exemplary amplifier module with the metal housing assembled;

[0029] Figure 2 illustrates examples of an on-chip power divider on the input side and an off-chip power combiner on the output side of the MMIC amplifiers according to an embodiment of the invention;

[0030] Figure 3 illustrates examples of an off-chip power divider on the input side and an off-chip power combiner on the output side of the MMIC amplifiers according to an embodiment of the invention;

[0031] Figure 4 illustrates examples of an off-chip power divider on the input side and an off-chip power combiner on the output side of the MMIC amplifiers having on-chip isolation resistors according to an embodiment of the invention;

[0032] Figure 5 illustrates examples of an off-chip power divider on the input side and an off-chip power combiner on the output side of the MMIC amplifiers separated to different MMIC chips according to an embodiment of the invention;

[0033] Figure 6A illustrates an example of dimensioning of an off-chip power combiner and an microstrip line to waveguide transition according to an embodiment of the invention for WR10 standard waveguide;

[0034] Figure 6B illustrates an example of a waveguide to microstrip line transition, when the input waveguide is a standard rectangular and the input power divider is an on-chip divider;

[0035] Figs. 7A, 7B, and 7C show exemplary S-parameter graphs obtained by simulations for classical on-chip Wilkinson power divider and power combiner using microstrip lines, classical on-chip Wilkinson power divider and power combiner using grounded coplanar waveguide (GCPW) technology, and an off-chip power divider and an off-chip power combiner according to embodiment of the invention, respectively;

[0036] Figs. 8A, 8B, and 8C exemplary S-parameter graphs obtained by back- to-back simulations for classical on-chip Wilkinson power divider and power combiner using microstrip lines, classical on-chip Wilkinson power divider and power combiner using grounded coplanar waveguide (GCPW) technology, and an off-chip power divider and an off-chip power combiner according to embodiment of the invention, respectively;

[0037] Figs. 9A, 9B, and 9C show further exemplary graphs obtained by simulations and illustrating gain and output power Pout in function of input power Pin for a single-channel MMIC amplifier chip, and for two-channel MMIC amplifier chips according to embodiment of the invention without and with on-chip isolation resistors, respectively;

[0038] Figs. 10A, 10B, and 10C show exemplary graphs obtained by simulations and illustrating certain S-parameters in function of frequency for a singlechannel MMIC amplifier chip, and for two-channel MMIC amplifier chips according to embodiment of the invention without and with on-chip isolation resistors, respectively; and

[0039] Figs. 11A and 11B show exemplary graphs obtained by simulations and illustrating gain and output power Pout in function of input power Pin a two-chan- nel MMIC amplifier according to embodiment of the invention when the bonding wires are symmetric and asymmetric, respectively.

[0040] DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0041] Figures 1A and IB illustrate schematically an exemplary amplifier module 10 comprising an input waveguide WG1 and an output waveguide WG2 implemented as cavities within a metal case 14. The metal case may preferably comprise two halves, a top half 14A and a bottom half 14B. In an embodiment, the top half 14A and the bottom half 14B of the metal case 14 is each made of aluminium [Al] body coated gold (Ag), copper (Cu) or another metal of high electrical conductivity. The opposing surfaces of the top and bottom halves 14A and 14B of the case may be mirror images of each other with coincident recessed areas which form enclosed cavities when the case halves are joined. Fig. 1A shows a partial top view of the amplifier module 10 with the top half 4A of the case removed and the top surface of the lower half 14A exposed, and Fig. IB shows a cross-sectional side view along line A-A in Fig. 1A. The input waveguide WG1 and the output waveguide WG2 may each have a closed end and an end opening to one of the outer surfaces of the metal case 14. The open ends of the waveguides WG1 and WG2 form the input port and the output ports of the amplifier module 10.

[0042] Exemplary embodiments will be described using the standard rectangular WR10 waveguides as input and output waveguides WG1 and WG2 as examples, but the invention is not restricted to this waveguide size, but it is applicable to all sizes of rectangular input and output waveguides, particularly in the millimetre frequency range and at higher frequencies.

[0043] MMIC amplifier chip or chips, an input waveguide-to-MMIC transition, and an MMIC to output waveguide transition may be arranged in one or more further enclosed cavities 12 within the metal case 14. Two or more amplifiers may be implemented on one or more MMIC chips. In the exemplary embodiments illustrated herein, two amplifiers Al and A2 are implemented in one MMIC chip 20.

[0044] In embodiments, the waveguide-to-MMIC transition is based on a microstrip line to waveguide (MSL-to-WG) transition. The MSL transition to the output waveguide WG2 may comprise a microstrip line E-plane coupling probe 30B, impedance transformer 32B, and a microstrip line having a characteristic impedance Zo on a carrier substrate 18B. The implementation of the impedance transformer may vary according to the desired impedance level. The microstrip line coupling probe 30B in form the microstrip line on the carrier substrate 18B is introduced into the perpendicular output waveguide WG2 through an aperture in the waveguide broad wall, i.e., in the E-plane of a rectangular waveguide, so that TE 10 mode of the waveguide is coupled to the quasi-TEM mode of the microstrip line. The impedance transformer 32B is a microstrip line section that matches the impedance of the coupling probe 30B to the characteristic impedance Zo of the microstrip line (for example, 30 ohms or 50 ohms).

[0045] In embodiments, also in the input side an WG-to-MSL transition may be employed. The MSL transition to the input waveguide WG1 may comprise a microstrip line E-plane coupling probe 30A, impedance transformer 32 A, and a 50- ohm microstrip line 34A on a carrier substrate 18A. The dimensions of the input MSL transition and the output MSL transition may be same or different depending on the application.

[0046] In embodiments, the carrier substrate 18A or 18B may be made a suitable dielectric or isolator material, such as a metal oxide or quartz. In an embodiment, the carrier substrates 18A and 18B are made of alumina, i.e., aluminium oxide (AI2O3) . The carrier substrates 18A and 18B may be arranged to the cavities 12 in the metal case 14 connected to the inner surface of the bottom half 14B of the case 14 by a suitable method, such as with adhesive.

[0047] In embodiments, on the output side, the opposite end of the 50-ohm microstrip line section 34B may comprise an impedance transformer 36B and a capacitive transverse microstrip line 38B. The impedance transformer 36B and the capacitive microstrip line 38B are configured to match the characteristic impedance Zo microstrip line section 34B to output impedances of two or more MMIC amplifiers. In accordance with principles of the present invention, one end portion of the capacitive transverse microstrip line 38B is coupled with a first bonding wire 40 to the output 22 of the first amplifier Al, and the opposite end portion of the capacitive transverse microstrip line 38B is coupled with a second bonding wire 42 to the output 24 of the second amplifier A2 in the exemplary embodiments illustrated in Figs. 1A, IB, and 2-8. The coupling with the bonding wires 40 and 42 is configured form a power combiner that combines the power from the outputs 22 and 24 of the two amplifiers Al and A2 to the output microstrip line 34B. The combined power is further transferred to the coupling probe 3 OB and radiated into the output waveguide WG2.

[0048] The arrangement results in a low-loss MMIC to waveguide power combiner that solves challenges in power combining especially for power amplifier waveguide modules. It enables off-chip power combining and at the same time optimum MMIC matching outside of the traditional 50 Ohm system in order to maximize efficient power transfer. By means of off-chip combining the power losses of the on-chip combining are avoided, and the heat issues may be mitigated, at least with large power DC power levels. The invention enables more efficient power transition to the radiating element from the MMIC transistor output, thereby reducing system level power consumption. The arrangement is very simple and requires less space and extra components in comparison with off-chip microstrip line combiner or hybrid waveguide combiner. Invention is also possibly applicable for better heat handling in power amplifier waveguide modules.

[0049] In embodiments, the transition on the input side may be implemented by a WG-to-MSL transition. The microstrip line 34A have a characteristic impedance Zo (for example, 50 ohm or 30 ohms). Thus, in embodiments, the opposite end of the Zo microstrip line section 34A on the input side may comprise an impedance transformer 36A and a capacitive transverse microstrip line 38A. In embodiments, a power divider for dividing the input power to inputs of the MMIC amplifiers Al and A2 may be implemented by an on-chip power divider, such as the microstrip line divider 26, m e.g., as illustrated in Figs. 1A, IB and 2. Thus, in embodiments, the capacitive transverse microstrip line 38A is coupled with a bonding wire 42 to the input port of the 22 of the microstrip power divider 26, one output port of the microstrip power divider is connected to the input of the first amplifier Al, and the other output port is connected to the input. Again, the impedance transformer 36A and the capacitive microstrip line 38A are configured to match the characteristic impedance Zo of the microstrip line section 34A to the input impedance of the on-chip power divider 26.

[0050] In embodiments, the on-chip power divider is avoided, and a lower power loss and better matching outside of the traditional 50 Ohm system can be achieved by using an off-chip power divider based on bonding wires on the input side of the amplifiers too, for example as illustrated in Fig. 3. The impedance transformer 36A and the capacitive microstrip line 38A are configured to match the characteristic impedance Zo of the microstrip line section 34A to input impedances of two or more MMIC amplifiers. In accordance with principles of the present invention, one end portion of the capacitive transverse microstrip line 38A may be coupled with a bonding wire 46 to the input 28 of the first amplifier Al (e.g. an on- chip input microstrip line), and the opposite end portion of the capacitive transverse microstrip line 38A is coupled with a second bonding wire 48 to the input 29 of the second amplifier A2 ((e.g. an on-chip input microstrip line). The coupling with the bonding wires 46 and 48 is configured form an off-chip power divider that splits the input power from the microstrip line 34A to the inputs 28 and 29 of the two amplifiers Al.

[0051] In embodiments, an on-chip isolation resistor Rs may be connected between the outputs 22 and 24 of the amplifiers Al and A2, i.e. input ports of the power combiner, e.g., as illustrated in Fig. 4. The resistor Rs isolates the input ports and allows all three ports the to be matched. With all three ports matched, high isolation between the output ports is obtained. Due to the symmetry, equal amplitude, in-phase combining is automatically ensured. For more details on the implementation and dimensioning of an on-chip isolation resistor, reference is made to US 2011 / 0006858 Al.

[0052] In embodiments, an on-chip isolation resistor Rs may be connected between the inputs 28 and 29 of the amplifiers Al and A2, i.e. output ports of the power divider, e.g., as illustrated in Fig. 4. Again, the resistor Rs isolates the output ports and allows all three ports the to be matched, resulting in same benefits as explained with respect to the power combiner above.

[0053] In embodiments, two or more parallel amplifiers Al and A2 may be provided on different MMIC chips 20A and 20B, e.g., as illustrated in Fig. 5. It may be easier to handle the heat generated in the chips, if the power amplifies are separated to two or more chips.

[0054] Figure 6A illustrates an example of dimensioning of an off-chip power combiner and an microstrip line to waveguide transition, when the output waveguide is a standard rectangular WR10 waveguide having a frequency range 75 to 110 GHz, width 0.1 inches (2.54 mm), and height 0.05 inches (1.27 mm). The carrier substrate 18B is made of alumina and its thickness is 75 pm. The substrate of the MMIC chip 20 is made of gallium arsenide (GaAs) and its thickness is 50 pm. In the example, the impedance seen from the outputs of microstrip lines 22 and 24 from the amplifiers Al and A2 is 30 ohms at a frequency of 90GHzThe transmission microstrip line 34B has a characteristic impedance Zo of 30 ohm. The length of the bonding wires 40 and 42 is 190 pm. A further impedance transformer 33B is provided between the impedance transformer 32B and the microstrip line 34B. Dimensioning on the input side of the amplifier module may be, for example, similar to that of the output side, when an off-chip power divider according to embodiments of the invention is used, for example as illustrated in Figs 3 and 4.

[0055] Figure 6B illustrates an example of a waveguide to microstrip line transition, when the output waveguide is a standard rectangular and the input power divider is an on-chip divider, for example as in Figs. 1A, IB and 3. The characteristic impedance Zo of the input microstrip line 34A is 50 ohms in this example. A further impedance transformer 33A is provided between the impedance transformer 32A and the microstrip line 34A. The dimensioning of the sections in Fig. 6B can be similar to conventional input side dimensioning for a MMIC amplifier module, and thereby readily implemented by a person skilled in the art. Fig. 7A shows exemplary S-parameter graphs obtained by simulations for WG to 50-ohm microstrip line transitions and on-chip Wilkinson power divider and power combiner using microstrip lines. Fig. 7B shows exemplary S-parameter graphs obtained by simulations for WG to 50-ohm microstrip line transitions and on-chip Wilkinson power divider and power combiner using grounded coplanar waveguide (GCPW) technology. Fig. 7C shows exemplary S-parameter graphs obtained by simulations for WG to 50-ohm microstrip line transitions and an off-chip power divider and an off-chip power combiner according to embodiment of the invention. The invention enables more efficient power transition to the radiating element from the MMIC transistor output, thereby reducing system level power consumption. The simulated improvement in power loss is 0.2-0.3 dB compared to classical on-chip Wilkinson power combiners.

[0056] Fig. 8A shows exemplary S-parameter graphs obtained by back-to-back simulations for WG to 50-ohm microstrip line transitions and on-chip Wilkinson power divider and power combiner using microstrip lines. Back-to-back simulation is a simulation wherein two power combiners (or two power dividers) is coupled one after another so that a two-port simulation is obtained. Fig. 8B shows exemplary S-parameter graphs obtained by back-to-back simulations for WG to 50- ohm microstrip line transitions and on-chip Wilkinson power divider and power combiner using grounded coplanar waveguide (GCPW) technology. Fig. 8C shows exemplary S-parameter graphs obtained by back-to-back simulations for WG to 50- ohm microstrip line transitions and an off-chip power divider and an off-chip power combiner according to embodiment of the invention. The simulated improvement in power loss is 0.5 dB compared to classical on-chip Wilkinson power combiners.

[0057] Figs. 9A, 9B, and 9C show exemplary graphs obtained by simulations and illustrating gain and output power Pout in function of input power Pin in the frequency range from ml9 to m20 for a single-channel MMIC amplifier chip, a two- channel MMIC amplifier with off-chip power divider and combiner according to embodiment of the invention, and a two-channel MMIC amplifier with off-chip power divider and combiner having on-chip isolation resistors according to embodiment of the invention, respectively. In Fig. 9A there is a transition from the input waveguide WG1 to a 50-ohm MMIC input, and from a 40-ohm MMIC output to the output waveguide WG2. In Figs. 9B and 9C there is a transition from the input waveguide WG1 to 50-ohm MMIC inputs, and from a 30-ohm MMIC output to the output waveguide WG2.

[0058] Figs. 10A, 10B, and 10C show exemplary graphs obtained by simulations and illustrating certain S-parameters in function of frequency for a singlechannel MMIC amplifier chip, a two-channel MMIC amplifier with off-chip power divider and combiner according to embodiment of the invention, and a two-chan- nel MMIC amplifier with off-chip power divider and combiner having on-chip isolation resistors according to embodiment of the invention, respectively. In Fig. 10A there is a transition from the input waveguide WG1 to a 50-ohm MMIC input, and from a 40-ohm MMIC output to the output waveguide WG2. In Figs. 10B and 10C there is a transition from the input waveguide WG1 to 50-ohm MMIC inputs, and from a 30-ohm MMIC output to the output waveguide WG2.

[0059] Figs. 11A and 11B show exemplary graphs obtained by simulations and illustrating gain and output power Pout in function of input power Pin in the fre- quency range from ml9 to m20 for a two-channel MMIC amplifier with off-chip power divider and combiner according to embodiment of the invention and with symmetric bond wires 40 and 42 (having the same length), and with asymmetric bond wires 40 and 42 (having different lengths), respectively, a two-channel MMIC amplifier with off-chip power divider and combiner having on-chip isolation resis- tors according to embodiment of the invention, respectively. The lengths of the bonding wires were 190 pm and 200 pm. It can be seen that the power combiner is quite insensitive to assembly variations.

[0060] The description and the related drawings are only intended to illustrate the principles of the present invention by means of examples. Various alternative embodiments, variations and changes are obvious to a person skilled in the art on the basis of this description. The present invention is not intended to be limited to the examples described herein but the invention may vary within the scope and spirit of the appended claims.

Claims

CLAIMS1. An amplifier module, comprising an output waveguide integrated into the amplifier module, a first MMIC amplifier having a first power output, a second MMIC amplifier having a second power output, an output microstrip line, an output microstrip line to output waveguide transition, power combiner combining the first and second power outputs to the output microstrip line, wherein the output microstrip line comprises a capacitive end line, and wherein the power combiner comprises a first bonding wire coupled between the first power output of the first MMIC amplifier and the capacitive end line, and a second bonding wire coupled between the second power output of the second MMIC amplifier and the capacitive end line.

2. The amplifier module as claimed in claim 1, comprising an isolation resistor connected between the power outputs of the first and second MMIC amplifiers.

3. The amplifier module as claimed in claim 1 or 2, comprising an output waveguide integrated into the amplifier module, an input microstrip line, an input waveguide to input microstrip line transition, and power divider dividing an input power to inputs of the first and second MMIC amplifiers.

4. The amplifier module as claimed in any one of the preceding claims, wherein the input microstrip line comprises a second capacitive end line, and wherein the power combiner comprises a third bonding wire coupled between the input of the first MMIC amplifier and the second capacitive end line, and a fourth bonding wire coupled between the input of the second MMIC amplifier and the capacitive end line of the output microstrip line.

5. The amplifier module as claimed in claim 4, comprising an isolation resistor connected between the inputs of the first and second MMIC amplifiers.

6. The amplifier module as claimed in any one of the preceding claims, wherein the first and second MMIC amplifiers are on a single MMIC chip.

7. The amplifier module as claimed in claim 6, comprising an isolation resistor connected between the power outputs of the first and second MMIC amplifiers.

8. The amplifier module as claimed in claim 6 or 7 , comprising an on- chip isolation resistor connected between the inputs of the first and second MMIC amplifiers.

9. The amplifier module as claimed in any one of claims 1-5, wherein the first and second MMIC amplifiers are on separate MMIC chips.

10. The amplifier module as claimed in any one of the preceding claims, wherein the amplifier module is a millimetre wave amplifier module.

11. The amplifier module as claimed in any one of the preceding claims, wherein the amplifier module is configured to operate at signal frequencies that are selected from a range from 30 GHz to 300 GHz.

12. The amplifier module as claimed in any one of the preceding claims, wherein the input waveguide and / or the output waveguide is a standard rectangular waveguide.

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