Chapter 1
Introduction to Circularly Polarized Antennas
1.1 Introduction
Circularly polarized (CP) antennas are a type of antenna with circular polarization. Due to the features of circular polarization, CP antennas have several important advantages compared to antennas using linear polarizations, and are becoming a key technology for various wireless systems including satellite communications, mobile communications, global navigation satellite systems (GNSS), wireless sensors, radio frequency identification (RFID), wireless power transmission, wireless local area networks (WLAN), wireless personal area networks (WPAN), Worldwide Interoperability for Microwave Access (WiMAX) and Direct Broadcasting Service (DBS) television reception systems. Lots of progress in research and development has been made during recent years.
The CP antenna is very effective in combating multi-path interferences or fading [1, 2]. The reflected radio signal from the ground or other objects will result in a reversal of polarization, that is, right-hand circular polarization (RHCP) reflections show left-hand circular polarization (LHCP). A RHCP antenna will have a rejection of a reflected signal which is LHCP, thus reducing the multi-path interferences from the reflected signals.
The second advantage is that CP antenna is able to reduce the ‘Faraday rotation’ effect due to the ionosphere [3, 4]. The Faraday rotation effect causes a significant signal loss (about 3 dB or more) if linearly polarized signals ...
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