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Materials (Basel). 2014 Jun 13;7(6):4524-4535. doi: 10.3390/ma7064524.

Improving the Pass-Band Return Loss in Liquid Crystal Dual-Mode Bandpass Filters by Microstrip Patch Reshaping.

Author information

1
Departamento de Tecnología Electrónica, Universidad Carlos III de Madrid, C.\Butarque n° 15, Leganés 28911, Spain. jtorreci@ing.uc3m.es.
2
Departamento de Tecnología Electrónica, Universidad Carlos III de Madrid, C.\Butarque n° 15, Leganés 28911, Spain. vurruchi@ing.uc3m.es.
3
Departamento de Tecnología Electrónica, Universidad Carlos III de Madrid, C.\Butarque n° 15, Leganés 28911, Spain. jmpena@ing.uc3m.es.
4
Institute of Applied Physics, Military University of Technology, Kaliskiego 2, Warsaw 00-908, Poland. nbennis@wat.edu.pl.
5
Departamento de Teoría de la Señal y Comunicaciones, Universidad Carlos III de Madrid, C.\Butarque n° 15, Leganés 28911, Spain. alamperez@tsc.uc3m.es.
6
Departamento de Teoría de la Señal y Comunicaciones, Universidad Carlos III de Madrid, C.\Butarque n° 15, Leganés 28911, Spain. dani@tsc.uc3m.es.

Abstract

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.

KEYWORDS:

dual-mode filters; inverted-microstrip structure; liquid crystals; microwave frequencies; tunable devices

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