Polarization Reconfigurable Active Antenna

Active antennas (AAs) are a class of radiation system that integrates an antenna and backing active circuits which results in considerable reduction in complexity of the matching networks and filters [1]. This is done by carefully designing the radiating element to provide proper load for active elements. Hummer and Chang have investigated active antenna elements using a microstrip patch antenna and fieldeffect-transistors (FETs) [2]. Similarly, Ho, Fan and Chang have used FET devices using the simple transmission line method [3]. Reconfigurable patch antenna has also designed with frequency and radiation reconfigurability [4]. Polarization diversity is required for operations under different standards such as GSM, GPS, Wireless Local Area Network (WLAN) to reduce the multi-path fading and cochannel interference. The ability to operate both sense of circular polarization allows the system to reuse frequency and double the system capacity. Moreover, if the antenna can be switched between two senses of circular polarization as well as linear polarization, it will allow the user to roam virtually any existing network [5, 6]. This can be also very useful in RFID system. Polarization switchable active antenna can be used in spatial power combiner in the compact size. The reconfigurable antenna proposed in this paper operates at the three different polarizations (Linear, RHCP, and LHCP) with the frequency 2.2 GHz. It has been fabricated on low cost substrate. It can switch the polarization using the PIN diode.