Design Of Filter Magic T Circuit Based On Circular Patch Resonator

With the rapid development of modern wireless communication systems,research on multi-function integrated circuits with small size,low cost and high performance has become a trend.The filter and magic-T play important roles in the front end of the radio frequency circuit.The integration of two devices into a circuit greatly reduces the overall size of the communication system while improving the performance of the circuit.The microstrip patch resonator has the advantages of simple structure,high quality factor,easy processing,etc.,and has attracted extensive attention in modern wireless communication systems.However,the design of filtering magic-T circuits based on patch resonators still lacks corresponding research.In view of this,this paper designs a series of filtering magic-T circuits with different performances by exploring the resonant modes of circular patch resonator.In summary,the main research work of this thesis is as follows:1.A single-band filtering magic-T circuit is designed based on the circular patch resonator:The electric field distributions of the TM₁₁ degenerate modes of the circular patch resonator is explored in detail.By elaborately arranging the input/output ports and using coupling extent between the two designed patch resonators in the back-to-back form,the desired single-band filtering response can be obtained.The finally designed single-band filtering magic-T circuit has the advantages of compact size,good filtering power division response and amplitude-phase balance.The circuit is modeled and simulated and optimized,and the circuit is processed and measured.The measured results are basically consistent with the simulated results,which verifies the validity of the design.2.A dual-band filtering magic-T circuit is designed based on the slotted circular patch resonator:Creatively proposed a slotted circular patch resonator with two pairs of arc-slots and four radial-oriented slots.The influence of arc-slots and radial-oriented slots on the resonant frequency of the resonator was explored through simulation.The electric field distributions vector diagrams of TM₁₁-like degenerate modes and TM₁₂-like degenerate modes are given.Using these two pairs of degenerate modes,a dual-band filtering magic-T circuit is designed,which greatly reduces the size and energy loss of the circuit.It has excellent performances of filtering power division responses,amplitude and phase balance,and compact size.A transmission zero is introduced between the two passbands,which creates a high degree of isolation between the two close passbands.Finally,a physical processing measurement is carried out.The simulated and measured results are in good agreement,which fully proves the effectiveness of the design method.3.A balanced-unbalanced filtering magic-T circuit is designed based on the circular patch resonator:Using the inherent resonant characteristics of TM₁₁degenerate modes of the circular patch resonator,the characteristics of differential-mode transmission and common-mode suppression required by the balanced circuit are realized.By etching the quarter-wavelength microstrip open stub in the input/output feed line,two transmission zeros are generated at the upper stopband and the lower stopband,thereby improving frequency selectivity.Measured and simulated results show that the designed balanced-unbalanced filtering magic-T circuit has excellent performances of filtering power division responses,amplitude and phase balance,good differential-mode bandpass response and common-mode suppression,which further verifies the effectiveness of the design.