Contents I. Introduction
With the rapid development of the wireless communication systems, there is a huge demand for reconfigurable antenna. The reconfigurable antenna provides the ability to adjust various antenna parameters such as frequency, radiation pattern bandwidth, gain and so on. In last decades, there were plenty of successful works have been carried out to achieve antenna reconfiguration. Comparing to normal antennas, the frequency reconfigurable antennas offer many advantages such as compact size, similar radiation pattern, and proper gain for all desired frequency bands. The reconfigurable antenna can be mainly divided into frequency reconfigurable, radiation pattern reconfigurable, polarization reconfigurable and mixed reconfigurable [1]. By employing reactance components such as PIN diodes, MEMS switches, or varactors, frequency reconfigurablility can be realized [2]. In [3], there is proposed a compact frequency reconfigurable narrowband microstrip slot antenna using PIN diodes to achieve reconfiguration. Many methods are changing the effective length of the antenna to achieve frequency reconfiguration by using RF varactor diodes have been reported in [4]–[5].
