Improving the pass-band return loss in liquid crystal dual-mode bandpass filters by microstrip patch reshaping
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In this paper, the design and experimental characterization of a tunable microstrip bandpass filter based on liquid crystal technology are presented. A reshaped microstrip dual-mode filter structure has been used in order to improve the device performance. Specifically, the aim is to increase the pass-band return loss of the filter by narrowing the filter bandwidth. Simulations confirm the improvement of using this new structure, achieving a pass-band return loss increase of 1.5 dB at least. Because of the anisotropic properties of LC molecules, a filter central frequency shift from 4.688 GHz to 5.045 GHz, which means a relative tuning range of 7.3%, is measured when an external AC voltage from 0 Vrms to 15 Vrms is applied to the device. © 2014 by the authors.
dual-mode filters; inverted-microstrip structure; liquid crystals; microwave frequencies; tunable devices; microstrip filters; anisotropic property; device performance; dual-mode bandpass filter; experimental characterization; liquid crystal technology; microstrip band-pass filter; tunable device; bandpass filters