Design Of Several Novel Balanced Microstrip Couplers

In order to adapt to the rapid development of microwave communication systems,passive devices tend to be miniaturized and work in multiple frequency bands.At the same time,the application of multiple communication standards makes the spectrum resources crowded and noise interference restricts the minimum level that can be identified in the signal processing process.In this environment,RF microwave circuits are required to have higher reliability and anti-jamming capability.As an important component in microwave communication systems,couplers have been widely used in the design of integrated circuits such as balanced mixers,phase shifters and switches,and antenna feed networks.In this situation,balanced couplers have developed rapidly.Compared with the traditional single-port coupler,the balanced coupler suppresses the common-mode signal effectively,makes the system immune to ambient noise,and has a more compact structure that can reduce the insertion loss of the signal transmission.According to the above background,this thesis first introduces the development of single-port couplers and balanced microwave passive devices in recent years.Based on this,this paper focuses on the study of balanced microstrip couplers,and two single-band balanced microstrip directional couplers have been designed.Simultaneously a dual-band balanced microstrip directional coupler was further proposed.Finally,a balanced 0dB coupler(bridge)was designed.The main contributions of the thesis are as follows.1.Two single-band balanced microstrip directional couplers were proposed.Based on the traditional 3dB microstrip directional coupler,a 3dB balanced microstrip directional coupler was designed by using balanced port network theory and odd-even mode analysis.This coupler operating at 1.98 GHz and in the operating frequency band,differential mode signals are effectively transmitted and common mode signals are suppressed,and no significant conversion between differential mode and common mode signals.On this basis,a balanced microstrip coupler working at 2.15 GHz with a power distribution ratio of 1.5 was designed.The double T branch was used to replace the transmission line equivalently,and the differential return loss of the designed coupler in the operating band was better than 15 dB,the output port transmission coefficient difference is 3.52 dB,and achieved good differential mode signal transmission,common mode signal suppression.Finally, according to the simulation results,the coupler is processed and measured.Simulated and measured results show good agreement and meet the design requirements.2.A dual-band balanced microstrip directional coupler was proposed.On the basis of single-band balanced coupler,using E-type dual-band impedance transformer equivalent to replace the traditional quarter wavelength transmission line,this thesis proposed a novel dual-band balanced microstrip directional coupler.The operating frequency of the coupler is 0.92 GHz and 2.04 GHz,and its differential mode return loss is greater than 15 d B at the center frequency,the minimum insertion loss is 0.4dB and 1.35 dB respectively,and the common mode rejection is higher than 20 dB.The performance is good.Finally,the physical processing was carried out.The agreement of measured and simulation results verified the correctness of the theoretical analysis.3.Two 0dB balanced microstrip couplers(bridges)were designed.Firstly,a single-band 0dB balanced coupler operating at 2.25 GHz was proposed and it adopts a dual-section branch line structure.Based on the balanced port theory,the impedance of each transmission line was calculated.Then simulated and designed,and the results showed that the coupler differential mode signal cross transmission,the signals of the other ports are isolated with each other,common mode signals are suppressed,and the physical objects are processed and measured.The measured results are basically agreement with the simulation results.On this basis,a ?-type dual-band impedance transformer was used to replace the quarter-wavelength transmission line.A novel dual-band 0dB balanced coupler was proposed.After calculation and analysis,the frequency ratio that can be achieved in engineering isN?(7)0.43,0.66(8)(7)1.51,2.31(8).Finally,a dual-band balanced 0dB coupler operated at 0.5GHz and 0.8GHz with a frequency ratio of 1.6 is designed,and realized differential mode signals cross transmission and the common mode signals rejection in dual-band.