Summary
International Symposium on Antennas and Propagation
2010
Session Number:4FB4
Session:
Number:4FB4-4
Design of Frequency-Agile Microstrip Antennas with Conical-Beam Radiation
Jia-Fu Tsai, Jeen-Sheen Row,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
Microstrip antennas are attractive to wireless communication systems because they have the features of low profile and easy integration with microwave circuits. To provide more communication channels, wideband operation has become a basic requirement of the microstrip antennas. From the system point of view, the wideband microstrip antenna represents a resonant structure with a low quality factor (Q), and consequently numerous unwanted signals can enter receiver circuits along with the desired signal, leading to a worse signal-to-noise ratio. Frequency reconfigurable antenna is a possible candidate to improve the problem. In addition, the frequency reconfigurable antenna has other advantages over the wideband antenna, such as smaller size and more stable radiation pattern. Therefore, a great number of designs related to the reconfigurable microstrip antenna have been proposed in recent years [1]-[5]. For these designs, the frequency agility is achieved by introducing perturbation segments on the radiating patch to alter the resonant current path or by adding a loading into the feed structure to vary antenna input impedance. On the other hand, the radiation pattern of the reconfigurable microstrip antennas is related to the operating mode. Planar inverted-F mode [1], fundamental half-wavelength mode [2, 3], and monopolar patch mode [5] have been employed in the past designs, in which only the design described in [5] can generate uniform conical radiation that is required to the wireless mobile communication. However, the antenna in [5] operates at a monopolar patch mode and therefore it needs a sufficient substrate thickness; besides, a complex dc bias network is also required to separately control the state of each diode. In this paper, a design method to frequency reconfigurable microstrip antenna is proposed. The frequency agility is realized by placing a tunable capacitor at the feed structure of the microstrip antenna operating at the TM01 mode. With the increasing of capacitance, the resonant frequency is decreased, and successive operating frequencies can be obtained. Details of the design concept are described and the obtained experimental results are also presented.