Research And Design Of Microstrip Miniaturized Tunable Filter And Power Divider

With the continuous development of wireless communication technology and applications,spectrum resources are increasingly scarce,and improving the utilization rate of spectrum resources has become a research hotspot.Tunable or reconfigurable radio frequency devices are widely used in multi-band communication systems by introducing tunable components into circuits to cope with communication signals in different frequency bands,realizing efficient utilization of spectrum resources and making communication equipment more portable and miniaturized.As one of the key components of the radio frequency system,the filter is used to select useful signals and suppress noise signals,which can improve the anti-interference ability of the system;the power divider realizes the synthesis or distribution of power and plays an important role in the phased array radio frequency circuit.Therefore,it is of great significance to study tunable filters and power dividers to improve the utilization of spectrum resources and reduce the size of radio frequency systems.In this thesis,the coupling coefficient and external Q value extraction method of the fixed frequency filter are analyzed and studied,and a band-pass filter with multiple transmission zeros is designed based on the microstrip line.The test results show that the center frequency of the filter is14.25 GHz,the passband range is 14 ～ 14.5GHz,the insertion loss in the passband is better than-4d B,and the return loss is better than-10 d B.The filter folds the half-wavelength open-circuit resonator into an open ring,which not only reduces the circuit size but also introduces cross-coupling.There are four transmission zeros on both sides of the passband,and it has good frequency selectivity.Secondly,the basic structure and principle of the step impedance resonator are analyzed,the structure of the hairpin step impedance low-pass filter is studied,and a second-order low-pass filter based on the hairpin step impedance resonator is designed.The filter has a-3d B cutoff frequency of6 GHz and low passband insertion loss.Then a tunable low-pass filter based on varactor diode is designed.The-3d B cutoff frequency is continuously adjustable in the range of 2.59 to 4.01 GHz.Two transmission zeros appear outside the band,which improves the stopband rejection capability and frequency selectivity of the filter.Finally,the function of the low-pass filter is extended,a filtering power divider with low-pass response is designed,and the influence of step impedance resonator impedance ratio and isolation resistance on the performance of the filter power divider is analyzed.The design of a tunable filter power divider is further proposed.The electromagnetic simulation results show that when the bias voltage of the varactor diode is adjusted,the center frequency of the filter power divider basically remains unchanged at 5.5GHz.The working bandwidth with input return loss less than-15 d B is continuously adjustable in the range of 2.22 ～ 3.61 GHz,which shows that the filter power divider has good adaptability.