Research Tunable Technology Of Wideband Millimeter-wave Filter Based On Liquid-crystal

In recent years,the spectrum resources used by military and civilian electronic systems,such as communication,radar,telemetry and remote sensing,and electronic countermeasures were been expanding to the millimeter-wave frequency band.In order to meet the requirements of dynamic frequency allocation,multi-function and intelligent reconfiguration the millimeter-wave reconfigurable filter becomes the key device in the millimeter-wave system.The performance of millimeter-wave reconfigurable filter plays an important role in the whole system,which directly affects whether the system target is up to standard.The first part of this paper is to test and analyze the dielectric constant and loss tangent angle of liquid crystal with microstrip device during the millimeter-wave band.A modulation electric signal applied on the microstrip test circuit,take vector network analyzer to measurethe scattering parameters and group delay of microstrip transmission lines by while liquid crystal molecules were under different voltage modulation states.Then we can figure the transmission matrix of the device transition structure by TL calibration technology,according to the electromagnetic field theory,the dielectric constant and loss tangent of the corresponding liquid crystal material can be inferred.The second part of this article is to study the dielectric anisotropy of the liquid crystal during the millimeter-wave frequency range with vertical transition of metal vias to solve the broadband conversion structure and apply the bias voltage without affecting the signal transmission.The trapezoidal impedance gradient line is designed for broadband impedance matching.A millimeter-wave dual-mode resonant structure frequency reconfigurable filter was proposed.Compared to the filter with the same order,using dual-mode structure can reduce the number of resonators by half,thus enabling the miniaturization of the filter.The last part of this paper is about the design of slow wave periodic frequency reconfigurable filters.Two kind of millimeter wideband frequency reconfigurable filters were designed by using stepped impedance hairpin resonators and square spiral resonators,respectively.Compared with other parallel cross-coupled filter structures,the new slow-wave structure resonant element filter topology eliminates coupling gaps between resonators and significantly reduces the insertion loss introduced in parallel and cross-coupled band-pass structures.Compared to using metal vias to connect upper and lower circuits of the substrate in previous chapter.In this chapter,the same circuit on the upper and lower circuit substrates is complete overlaped and stitched in order to realize the transition form between feed port and inverted-microstrip line.It can effectively reduce the high insertion loss caused by high-frequency metal via transition.Based on the above simulation analysis,several millimeter-wave wideband frequency reconfigurable filters with wide bandwidth and good passband response are designed.