Circularly Polarized Antennas

Chapter 3

Broadband Circularly Polarized Antennas

3.1 Introduction

The increasing demands for more capacity and higher data rate in wireless systems have led to the development of broadband CP antennas. During recent decades, a variety of broadband CP antennas have been proposed for applications in mobile satellite communications, WLAN, DBS, RFID, GNSS, space communications and wireless power transmission systems.

This chapter reviews different techniques of designing broadband CP antennas, including broadband CP microstrip patch antennas, broadband CP helix antennas, broadband QHAs and PQHAs, planar spiral antennas, broadband CP slot antennas, broadband CP DRAs, broadband CP loop antennas, and so on. Many antenna design examples are explained and their performances are discussed. Advantages and disadvantages of each antenna design are illustrated. A table summarizing the performance of some typical broadband CP antennas is presented at the end.

3.2 Broadband CP Microstrip Patch Antennas

3.2.1 Broadband Single-Feed CP Patch Antennas

3.2.1.1 Thick Air Substrate

As discussed in Chapter 1, a CP patch antenna can be realized by using a single- or multi-feed technique, and single-feed CP patch antennas have the advantages of simple structure and compact size. It is well-known that the traditional CP patch antenna has a narrow bandwidth due to the high quality factor Q. The closed-form expressions for the axial-ratio bandwidth (ARBW) and return-loss bandwidth (RLBW) of a single-feed ...