A Frequency Agile Miniaturized Antenna Utilizing Ferroelectric Barium-Strontium-Titanate Capacitors
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A Frequency Agile Miniaturized Antenna Utilizing Ferroelectric Barium-Strontium-Titanate Capacitors S. Alzahrani, T.S Kalkur and H. Song Department of Electrical and Computer Engineering, University of Colorado, Colorado Springs, CO 80918 Abstract A miniaturized frequency agile multi-band antenna based on BST varactors is presented. The radiation patterns and frequency responses of this antenna are characterized. The measured tunability was 2.1%, 9.1%, and 6.6% for the first, second, and third band respectively. The lowest resonant frequency corresponds to an antenna size of . The size reduction of the antenna was achieved by employing the novel antenna structure and the thin film BST varactors. The measured -3 dB bandwidth was between 3.1% and 7.4% for all bands. Introduction The development of contemporary communication systems hardware have transformed into devices with more functionalities, enhanced performances, reduced size, less weight, and cost effectiveness. Nowadays, the necessity for multi-mode and multifunctional devices is becoming more demanding than ever. Tunable microwave front-end electronics such as tunable filter, antennas, and phase shifters are considered more powerful because they adapt to changing user demands and correct the slight deviations resulting from the manufacturing variations. Ferroelectric thin film Barium-Strontium-Titanate capacitors (BST) are considered good candidates to be integrated with these front-end microwave circuits for tunability purposes [1]. The tunability of ferroelectric varactors is based on the fact that the permittivity of BST thin films can be controlled by an externally applied DC electric field. The antenna is considered a key device for any wireless systems. Tunable antennas have become more attractive to fulfill the demands of multi-function requirements in wireless and satellite communications systems. These tunable antennas can be adapted to attain selectivity in frequency, bandwidth, and gain [2]. Some wireless communication systems may have several frequency bandwidths to be used concurrently [3]. In this paper, a tunable compact multi-band microstrip antenna using metal-insulatormetal (MIM) ferroelectric BST thin film varactors is introduced. Three tunable operational frequency bands were achieved with changing the applied bias from 0 to 5 V. The tunable multi-band microstrip antenna design The proposed tunable antenna consists of a meander line with two radial stubs and open transmission lines between each meander line turn as shown in figure 1. The dimensions of the antenna are given in table 1. The meander line structure is used for a size reduction purpose. The lower resonant frequency of the antenna before loading any varactors is 1.82 GHz as shown in figure 2, which corresponds to an antenna size of . Compared to a conventional patch antenna, it is considered much smaller due to the novel
structure. It can be seen that the proposed antenna can operate at multiple frequency bands, which is considered an advantage to be employed as a multi-functi
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