Research Of Microwave Absorptive Filters Based On Suspended Coplanar Waveguide

The performance of a microwave passive device is inseparable from the structure of the microwave transmission line it uses.As an important microwave integrated transmission line,coplanar waveguide has gradually attracted attention due to its low dispersion,good high-frequency performance,flexible design,easy processing,convenient installation of lumped components in series or parallel,and effective improvement of circuit density.The self-packaged suspended structure has the advantages of good shielding characteristics,low loss,high Q value,small size,low cost,easy to mass production,and easy to connect with other microwave devices.Combining it with the coplanar waveguide structure can achieve a new type of suspended coplanar waveguide transmission line structure with both advantages.This paper has realized this work through modeling and a large number of optimization simulations,and has processed and tested it.Compared with the traditional planar structure,it has been confirmed that the structure improves the performance of transmission line.Microwave filters are important components of communication systems.At present,most of them are reflectionless filters.To avoid interference with sensitive components in the communication system,an attenuator is often used before and after the filter to suppress the reflected wave of the stopband,which increases the noise coefficient of the system and is not conducive to the miniaturization of the system.In recent years,the absorptive filter can absorb the reflected wave of the stopband in the filter,and at the same time solve the above problems,which has attracted more and more researchers'attention.For reflective filters,since the 1930s,there have been filter theories such as Butterworth,Chebyshev,and elliptic functions to support their design,and later they have been extended to the design of digital filters and microwave filters.However,there is no mature and universal design theory for absorption filters.This paper will solve this problem for the first time.First,two types of lowpass prototypes of absorption filters are proposed.Then,based on the definition of non-reflection and referring to scattering parameter S₂₁ standard of the same order Butterworth(Chebyshev),the popular symbiotic biological search algorithm solves the normalized parameters of the circuit and the common order of normalized value table is made of.The design formula of lumped parameter absorptive filter and microwave absorptive filter is further deduced.First designed a third-order absorptive bandpass and a third-order absorptive bandstop filter,and the return loss in the full frequency band is above 20dB,the non-reflection effect is good,which verifies the correctness of the proposed theory.Combined with the new suspended coplanar waveguide structure,a third-order microwave absorptive bandstop filter is designed,in which the J converter is implemented using a quarter wavelength line,and the size of the open branch is calculated by the lumped resonance circuit and the microwave resonance line equivalence principle.The return loss of the filter circuit in the whole frequency band is more than 10dB,the center frequency is more than 35dB,and the non-reflection effect is good.The theory of absorption filter is further verified and perfected.Finally,from the perspective of simplifying the structure and design,and based on the proposed new suspended coplanar waveguide structure,a absorptive bandstop filter of defected ground structure is designed.This structure has two levels of L-shaped defected ground structure unit.The first level is used as the absorption stage.The branches formed after etching defects are connected to the patch resistor,and the other end of the resistor is short-circuited to ground.And the second stage is not processed.The impedance matching problem at the center frequency and within a certain bandwidth range on both sides is solved.The return loss in a large frequency range exceeds 15dB,achieving non-reflection effect.