Research And Design For Integration Of Filtering Power Divider

In traditional RF microwave systems,filters and power dividers are usually designed independently and cascaded together for achieving filtering and power dividing.However,the insertion loss would be increased with a large area occupied of the whole circuit.Integrating filter and power divider into one device can effectively reduce circuit area,improve system performance and reduce production costs.In addition,the filtering power divider with wideband 90°phase shift output has broad application prospects.It can be used to feed network of circularly polarized antenna,Doherty amplifier circuits and sum-difference direction finding antenna array with ratio amplitude.Therefore,the research on filtering power divider with wideband 90°phase shift output has important application value in practical engineering design.Based on the design theory of filter and power divider,the structure of filtering power divider with bandpass response is designed in this paper.Combined with the study of broadband 90°phase shifting structure,the integration of filtering power divider and phase shifter is realized.The main works of this paper are as follows:Firstly,based on traditional Wilkinson power divider and open-load stub,a filtering power divider is cascaded directly with filter and power divider.The designed structure has a transmission zero on each side of the passband to achieve a good bandpass response.However,the out-of-band suppression and isolation performance of the power divider has yet to be obtained.Secondly,in order to expand the isolation bandwidth and improve the performance of rejection bandwidth,a filtering power divider is studied and designed by using open stub-loaded resonator and parallel coupling lines.Furthermore,two resistors are placed between two open-circuit stubs to improve the isolation performance.Meanwhile,by using the impedance conversion characteristics of stepped impedance resonator,the designed device has a wide operating bandwidth.The experimental results show that the filtering power divider is designed for a working frequency from 1.7 to 3.0 GHz with S₁₁under-20 dB.With the rejection level is higher than 20 dB,the upper stopband is extended to 3.74f₀.The isolation between the two output ports is better than 20 dB in the range of DC to 10 GHz,and the isolation is greater than 24 dB over the operating range.Finally,based on the improved structure of the traditional Schiffman phase shifter,a filtering power divider with wideband 90°phase shifting is designed.In the passband,S₁₁of the structure is less than-15 dB,but the output phase difference is 90°±6.1°.To further improve the passband performance and phase shifting accuracy,a new phase shifter structure is proposed,based on parallel coupled line and short stub-loaded resonator with the terminal is short circuit.It is cascaded directly with the filtering power divider,which has a wide stopband.Without changing the performance of filtering power divider,the return loss is better than 20 dB,and the output phase difference is 90°±3.7°.