Research On Broad-Band Power Combining Technology At E-Band

Millimeter wave power source is an important component in many application systems.Due to the limitations of semiconductor characteristics and technology of solid-state devices,the output power of a single solid-state device in millimeter-wave band is relatively limited,and it is usually difficult to meet the requirements of some application systems where high output power is needed.Combining the output power of multiple solid-state devices is an effective way to enhance the output power.Aiming at realizing a wideband high-power solid-state power source at E-band,the power dividing/combining networks based on a waveguide cross-coupling slot and branch waveguide bridge are studied in depth.Four independent E-band power amplifier modules are designed and assembled with the two power dividing/combining networks to form two kinds of four-way power combining assembly.The main contents of this paper include:1.The equivalent circuit model of a six-port network with the isolated port being included is established.Based on this circuit model,the S-parameters of the waveguide cross-coupling slot coupler are analyzed and calculated by ADS(Advanced Design System)for quickly obtaining the preliminary simulation results.On this basis,the three-dimensional model of the cross-coupling slot coupler is established by using HFSS(High Frequency Structure Simulator),and the performance of the cross-shaped coupler is simulated and optimized accurately.In this way,the efficiency of analysis and design has been effectively improved.According to the technical requirements of the project,a comprehensive simulation analysis is carried out on the performances of return loss,insertion loss,isolation and so on.A waveguide cross-slot based power dividing/combining network with high power capacity in E band is developed.The measured results show that the typical back-to-back insertion loss of the cross coupler is 1.5d B in the frequency range of 71.5-77.5GHz,which exhibits a good power dividing/combining performance over a broadband of 6GHz.2.Aiming at the structural requirement of a multi-way high power combining network,a design scheme of E-band four-channel waveguide power dividing/combining network is proposed,in which H-plane branch waveguide bridges are combined with waveguide E-plane right corner.Firstly,an independent HFSS model of the waveguide branch bridge and the E-plane waveguide corner are established and simulated.Based on the phase relationship between the branches of the passive network,a complete model of the four-channel waveguide power dividing/combining network that is composed of three waveguide branch bridges and four E-plane corner is established.An integrated accurate full-wave analysis is carried out.The simulation results show that the return loss of the passive network is better than 20 d B in the frequency range of 72-77 GHz,and the amplitude imbalance between the branches is less than 0.35 d B.The problem of mechanical accurate processing has been solved and the prototypes of the passive network have been fabricated.The measured results show that the typical back-to-back insertion loss of passive power dividing/combining network is around 1.8d B in the frequency range of 72-77 GHz.3.Using commercially available MMIC chip of medium power amplifier,an E-band medium power amplifier module is designed.Firstly,HFSS is applied to optimize the waveguide-microstrip transition structure with broadband and low insertion loss for a given working frequency band.As a coupling unit of RF input and output,the HFSS simulation model including the cavity structure in the nearby area of the MMIC chip is established.The parasitic resonance characteristics of the passive circuit including the cavity structure are mainly investigated.The cavity shape and the structural parameters are optimized.The flat transmission characteristics in wide band are guaranteed by placing absorbing materials and other methods.Finally,four independent power amplifier modules at E-band are fabricated and tested.The measured results show that the saturated output power of the module is greater than 24 d Bm in the frequency range of 71-77 GHz.4.By assembling the above mentioned four independent power amplifier modules with the waveguide cross-coupling slot coupler and the branch waveguide bridge,respectively,two kinds of four-way E-band power combining modules are developed to study the power combining efficiency and the overall combined output power.The measured results show that in the frequency range of 71-77 GHz,the saturated output power of the two power combining assembly is above 29.5 d Bm and 29.4 d Bm with the peak power being 30.8 d Bm and 31.0 d Bm,respectively.The power combining efficiency is over 53% and 64%,and the maximum combining efficiency is 80% and 79%,respectively.