| Millimeter-wave communication has the advantages of broadband,narrow beam width,all-weather working,small element size,and so on.It has been widely applied in military,medical,satellite communication and other related areas.As the core component in most microwave communication systems,the performance of power amplifier often determines the structure and performance of transmitters.With the popularization of millimeter-wave system,there is a demand for the output power of transmitter from milliwatt to several hundred watt or even higher.The solid-state power-combining technology can accumulate the output power of multiple power amplifier chips to obtain higher output power and effectively solve the problem that the output power of a single chip is insufficient to meet the output power of the system.1?The low loss circuit units of millimeter wave power-combining are simulated and designed.First of all,we design the single-probe and dual-probe structure for waveguide-microstrip transition and a 90-degree twist waveguide for orthogonal waveguide transition.Then,the theoretical analysis and design for common waveguide power-combining units are carried out.Including waveguide T-junction,waveguide branch line bridge and waveguide magic T.And their advantages and disadvantages are analyzed by simulation and testing,All these will lay a foundation for the design and selection of combining networks.2?Two kinds of binary power-combining network are designed.Including four-way power-combining networks based on waveguide magic T and waveguide T-junction.And two kinds of non-binary power-combining network are also designed.One is based on unequal waveguide branch line bridge and waveguide-microstrip single-probe transition structure,the other is based on 4.8dB waveguide branch line bridge and waveguide-microstrip dual-probe transition structure.Their performances and application scope are analyzed and discussed by simulation.3?A millimeter-wave power-combining amplifier has been developed.According to the design target of the project,we complete the selection of chips at first.And a four-way power-combining scheme is designed for the ka-band 20 W power amplifier.The whole power amplifier module consists of a front-stage driving amplifier and a final stage power-combining amplifier.And the gain of the amplifier is compensated by temperature-compensated attenuators as the ambient temperature changes.Then,considering the simulation results,the feasibility of fabrication and the size requirements,we decided to use the four-way power-combining network based on waveguide T-junction to realize the power amplifier module.The back-to-back structure of the four-way power-combining network based on waveguide T-junction and waveguide-microstrip single-probe transition is fabricated and tested.The return loss of the wave port is better than-14 dB,and the average insertion loss is about 4.5 dB in the frequency range of 29.4 GHz to 31 GHz.Finally,the micro-assembly of the chip is completed and the performance of the power amplifier module is tested.The saturated output power is not less than 44 dBm within the frequency band below 30.6 GHz,the maximum saturated output power is 44.6 dBm at 30.2 GHz,and the minimum saturated output power is 43.7 dBm at 31 GHz.The combining efficiency of the power-combining amplifier is obtained after processing and testing the single-way power amplifier.The highest combining efficiency is 88.7% at the lower end of the test frequency,and the combining efficiency is over 75% at the higher end of the test frequency.In the frequency range of 29.4GHz~30.6GHz,the gain of the power amplifier is 51 dB,which decreases at the higher end of frequency,but also exceeds 49 dB under the condition of 10 dB back-off from saturation output power. |
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