%0 Journal Article
%T Fully Distributed Tunable Bandpass Filter Based on Thin-Film Slow-Wave Structure
%A S¨¦bastien L. Delprat
%A JaeHo Oh
%A Feng Xu
%A Lin Li
%A Erick E. Djoumessi
%A Marwa Ismail
%A Mohamed Chaker
%A Ke Wu
%J International Journal of Microwave Science and Technology
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/468074
%X This paper presents simulation and measurement results of fully distributed tunable coplanar bandpass filters (BPFs) with center frequencies around 6£¿GHz that make use of ferroelectric Barium Strontium Titanate (BaxSr1£¿xTiO3 or BST-x) thin film as tunable material. The two experimental bandpass filters tested are based on a novel frequency-agile structure composed of cascaded half wavelength slow-wave resonators (2 poles) and three coupled interdigital capacitors (IDCs) optimized for bias voltage application. Devices with gap dimensions of 10 and 3£¿¦Ìm are designed and fabricated with a two-step process on polycrystalline Ba0.5Sr0.5TiO3 thin films deposited on alumina substrate. A frequency tunability of 9% is obtained for the 10£¿¦Ìm gap structure at ¡À30£¿V with 7£¿dB insertion loss (the BST dielectric tunability being 26% with 0.04 loss tangent for this gap size). When the structure gap is reduced to 3£¿¦Ìm the center frequency shifts with a constant 9£¿dB insertion loss from 6.95£¿GHz at 0£¿V to 9.05£¿GHz at ¡À30£¿V, thus yielding a filter tunability of 30% (the BST dielectric tunability being 60% with 0.04 loss tangent for this gap size), a performance comparable to some extent to localized or lumped element BPFs operating at microwave frequency (>2£¿GHz). 1. Introduction The next generation of wireless networks such as reconfigurable and cognitive radio systems will require low-cost and highly integrated tunable microwave components that must handle room-temperature operations for multibands with wide tuning range, low power consumption, and small size. In particular, there is an increasing need for frequency-agile bandpass filters (BPFs) to replace large and costly filter banks used in the design of multiband microwave receivers [1]. In this context, significant efforts have been made since the last decade on the development of frequency-agile structures operating at microwave frequencies (above 2£¿GHz). Compared to semiconductor diodes [2] and RF microelectromechanical systems (MEMS) [3], ferroelectric-based devices present many advantages such as high power handling, continuous tuning, nanosecond switching speeds [4], and operation in a large frequency range with ease of fabrication and operation. Generally, the tuning is obtained by applying a bias voltage on the ferroelectric material and ferroelectric devices can be fully coplanar, very compact, and do not require hermetic packaging [5, 6]. Ferroelectric materials, in particular BaxSr1£¿xTiO3 (BST-x with x~0.5), present almost continuous dielectric constant tuning in the presence of an electric field and can
%U http://www.hindawi.com/journals/ijmst/2011/468074/