| In military communications,frequency-hopping communication is often used to prevent enemy eavesdropping or interference.The receiving system of this code controlled carrier hopping communication relies on a filter with hopping function.Reconfigurable filters can realize fast and continuous channel switching within their tuning range,making them very suitable for replacing the original switching filter module,which not only significantly reduce the size,but also obviously cut the cost.The performance of reconfigurable filter directly affects the entire system,so it is necessary to research reconfigurable filter.Microstrip structure not only facilitate the loading of reconfigurable component,but also easy to integrate and suitable for mass production,which has inherent advantages in designing reconfigurable filters.This thesis focuses on the passband of the microstrip reconfigurable filter,and explores single-band reconfigurability,multi-band reconfigurability,and notch reconfigurability for suppressing interference within passband.The details are as follows:1.The goal of design the dual-port single-band reconfigurable filter is to achieve a wide range adjustable of center frequency,and the design method is mainly PIN switching.To achieve the goal of large-scale reconfiguration,a composite multi-mode fully reconfigurable filter is designed.This filter is based on a cross-shaped triple-mode resonator.Varactor diodes and switching diodes are added at the end of the resonator and at the external coupling feed.It combines the low frequency and the high frequency operating modes,greatly broadening the adjustment range of the center frequency.The center frequency is continuously changeable,and the bandwidth is also reconfigurable.When the absolute bandwidth of this composite fully reconfigurable filter is 180 MHz,the center frequency can be tuned from 0.78 GHz to 1.93 GHz,with a relative adjustment range of 84.9%.When the center frequency is 1.355 GHz,the bandwidth can be adjusted from 0.11 GHz to 0.95 GHz,with a relative bandwidth adjustment range of 8.1% to 70.1%.2.The goal of design the four-port single-band reconfigurable filter is to realize a high common-mode(CM)suppression reconfigurable filter.The design method is mainly by analyzing the electromagnetic field distribution of the resonators to find the optimal coupling position.A 5-order bandpass reconfigurable balanced filter with high CM suppression is proposed.The concept of local electric/magnetic walls is applied to the λ/2 resonator to realize the balance function.A pair of stable transmission zeros(TZs)introduced by the cross-shaped triple-mode resonator greatly improves the selectivity of the differential-mode(DM)channel.When the absolute bandwidth of the reconfigurable balanced filter is 120 MHz,the center frequency can be tuned from 1.1GHz to 2.1 GHz,the tuning range is 62.5%,and the in-band reflection is less than-20 dB.The insertion loss is between 7.6 dB ～ 3.3 dB and the in-band CM suppression is between 52.5dB ～44.3dB in the whole central frequency tuning range.The absolute bandwidth tuning range is 100 MHz to 320 MHz,the relative bandwidth tuning range is4.8% to 15.2%,and the in-band CM rejection is 51.8 dB.The stopband suppression range of more than 22 dB exceeds 20 GHz,and the CM suppression range of greater than 18 dB also exceeds 20 GHz.3.The goal of design the multi-band reconfigurable filter is to achieve a four-band reconfigurable filter and variable of channel number.The design method is the application of stepped impedance multi-mode resonators and PIN diodes.In this thesis,a multi-band bandpass filter is designed with stepped impedance dual-mode resonators,and then loaded with varactors to upgrade it to a multi-band reconfigurable filter.The first three bands can be independently adjustable,and the last one is a fixed band.The tunable range of the first channel is 1.7GHz～2.1GHz,the adjustable range of the second channel is 2.7GHz～3.1GHz,the changeable range of the third channel is3.7GHz～4.1GHz,and the center frequency of the fourth channel is 4.9GHz.Then a three channel bandpass filter with optional adjustable function is proposed.For the single band,the bandwidth is 150 MHz,and the adjustment range is 1.27 GHz ～ 1.85 GHz.In case of three channels,the bandwidth of the low frequency channel is 200 MHz,the adjustment range is 0.46 GHz ～ 0.82 GHz,the bandwidth of the intermediate frequency channel is 200 MHz,the adjustment range is 1.37 GHz ～ 1.71 GHz,and the bandwidth of the high frequency channel is 150 MHz,the adjustment range is 2.22 GHz～ 2.70 GHz.To solve the problem of whether each channel is independently adjustable in multi-band filters,this thesis presents a simple and rigorous judgment method,namely rank criterion,which is a necessary and sufficient condition for each channel to be independently adjustable.4.The goal of design the notch reconfigurable ultra wideband filter is to realize the dual-notch independent reconfigurable.The main design method is to load the reconfigurable notch element.First,a triple-loop ultra-wideband bandpass filter with wide stopband is etched on the superconducting film,and then a four-order dual-notch reconfigurable unit is cascaded.When the first notch is at 8.14 GHz,the tuning range of the second notch is 9.68 GHz ～ 10.2 GHz.When the two notch overlap,the notch depth can be increased,and the suppression can be increased from 10 dB ～ 11 dB of single notch to 12.6 dB ～ 16.9 dB of deep notch,which is obviously improved. |
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