Design And Analysis Of Miniaturized Broadband Bandpass Filter

With the development of modern communication systems,the requirements for system portability are becoming more and more stringent,and the miniaturization of wideband bandpass filters has become a challenging issue.The improvement of the manufacturing process of lumped elements provides a new idea for circuit miniaturization.The subject can be carried out through the idea of reducing the circuit size by using the transmission line as lumped elements.This paper is based on the design of broadband bandpass filters.The main research contents and achievements are as follows:（1）According to the idea of miniaturization and equivalent,the equivalent lumped element network of transmission line is discussed and analyzed.Based on the two-port network theory,the basic performance of low-pass network and bridged T-type network is analyzed,and the equivalent formulas of low-passπ-type network,low-pass T-type network,electromagnetic hybrid coupled T-type network and non-magnetically coupled all-pass network are deduced respectively.The S-parameter comparison between the equivalent results of each network and the performance of the ideal transmission line shows that the result of bridged T-type non-magnetic coupled network is optimal.And choose octagonal plane spiral inductor and ACCU-P?0201 series film capacitor for electromagnetic simulation.At the same time,bridged T-type networks are cascaded to form a flat delay network,and a parallel resonant circuit is added.In the frequency range from 0.6 GHz to 1.85GHz,the return loss S₁₁ is all less than-10 d B,the insertion loss S₂₁ is all within-0.5 d B,and the delay flatness is 12%,which can effectively provide filtering function and delay flatness performance.（2）The multi-mode resonator is calculated and designed based on the odd-even mode parameter method.By adjusting the impedance and electrical length of each section of the transmission line,three resonance points at 0.65 GHz,0.795 GHz and 1.05 GHz are realized in the band.And form two additional transmission zeros at 1.6 GHz and 2.12 GHz out-of-band to improve the upper stopband rejection of the wideband bandpass filter.Increase the coupling to achieve broadband filtering performance,and analyze the effect of coupling capacitors on filtering performance.According to the equivalent analysis results,the circuit is divided into 5 units.The bridged T-type non-magnetic coupling network is selected for transmission line equivalence,and the optimal unit circuit layout is realized.After combining the equivalent elements to optimize the circuit,the bandwidth limitation of the bridged T-type non-magnetic coupling network is effectively neutralized.The transmission zeros of the HFSS simulation circuit appear at 1.5 GHz and 2.3 GHz,and the return in the range of 0.55 GHz to 1.21 GHz is achieved.The wave loss S₁₁ is less than-20d B,and the insertion loss S₂₁ is controlled within-1 d B with good broadband filtering performance.