Design Of Tunable Filter Based On Substrate Integrated Waveguide

At present,the development of wireless communication technology has always been accompanied by huge opportunities and challenges,especially in the 5G era,and the performance of various aspects of microwave filters is facing more demanding challenges.Conventional rectangular waveguides have the disadvantage of being difficult to integrate with planar circuits,while substrate integrated waveguides are not,with significant advantages such as better high frequency transmission performance and higher Q values.As one of the most important components of wireless transceivers,tunable filters have always had a wide range of applications and high research fever.At present,most of the tunable filters are based on microstrip structures or cavity structures.The combination of substrate integrated waveguide technology and adjustable technology is less,and it has attracted many scholars'attention and attempts in recent years,and has also achieved some achievements and breakthroughs.This paper aims to investigate a variety of tunable techniques and methods for implementing various tunable characteristics of SIW filters in substrate integrated waveguide circuits.This paper mainly includes the following aspects:1.The structure and transmission theory of SIW has been introduced.Based on different resonant cavities of SIW,examples and analysis of various modes of SIW resonators with different shapes have been introduced.At the same time,several conversion structures of SIW to planar circuits have been described.Design of SIW-microstrip and SIW-coplanar waveguide converters has been simulated.A wide range of tunable methods for implementing filters has been extensively investigated to select and illustrate tunable techniques for SIW.2.Multi-cavity cascaded bandpass filters based on square-shaped cavities and triangular-shaped cavities of the fundamental mode(TE₁₀₁ mode)have been designed,including a second-order triangular-shaped cavity cascaded tunable bandpass filter and a third-order square-shaped cascaded bandpass filter.The feedings are carried out in the form of coplanar waveguides,and their tunable characteristics are verified by simulation analysis.3.The design of a dual-mode multi-function tunable bandpass filter based on SIW and a tunable third-order bandpass filter based on combining dual-mode square-shaped SIW resonator with triangular-shaped resonator.Firstly,according to the degenerate mode of the square-shaped SIW cavity and the principle structure of surface slit ring resonator,the first SIW bandpass filter not only achieves the center frequency tunable function,but also realizes bandwidth reconfiguration and transmission zeros adjustment.These functions can be implemented in a single cavity by only changing the capacitance value of the five tuning elements into different combinations with simultaneously compact size and low insertion loss.Then,the method that combines the resonators with different shapes and multiple modes into an organic whole while achieving multi-mode synchronous tuning has been proposed.A square dual-mode SIW resonator and an isosceles right-angled triangle-shaped SIW resonator are directly magnetically coupled to achieve simultaneous frequency tuning.Square-shaped cavity introduces two transmission zeros and the triangular-shaped cavity can suppress out-of-band spurious modes.The complementary advantages of the two together promote out-of-band rejection of the second tunable filter.The proposed third-order SIW tunable filter has good tunability in both simulation and measurement.4.The design of a novel dual-mode magnetically adjustable bandpass filter based on SIW.The method and principle of magnetic tunability have been introduced.The filter of this design can modify the magnetic permeability of four ferrite substrates embedded in the filter by changing the magnitude of external bias magnetic field to adjust working frequency of the filter,and has the advantages of miniaturization and low insertion loss.Simulation results show the feasibility of dual-mode magnetic tunability.