Circularly Polarized Antennas

Chapter 5

Circularly Polarized Arrays

5.1 Introduction

Previous chapters have already discussed the basics of CP antennas as well as various techniques for designing small CP antennas, broadband CP antennas and multi-band CP antennas. Array antennas are useful for applications where a high gain, low sidelobe beam reconfigurability are required, such as satellite communications, DBS, WLAN and space communications. CP arrays are important for applications that need a high gain to overcome the free-space loss due to the long distance between radio transmitter and receiver. This chapter will review different techniques for designing CP array antennas, including CP patch arrays, CP DRA arrays, CP printed slot arrays, CP waveguide slot arrays, CP reflectarrays, CP active integrated arrays and CP arrays with beam reconfigurability. Basic principles of designing CP arrays will be illustrated together with examples. Performance of some CP arrays is compared at the end of this chapter.

5.2 CP Patch Antenna Arrays

5.2.1 Sequential Rotation

Microstrip patch arrays are widely used in wireless communications due to their advantages of low profile, light weight, easy fabrication, low cost and conformability to curved structures [1]. CP arrays can be formed by using a number of CP or LP radiating elements. Each antenna element can be single-feed or dual-feed in phase quadrature. Better polarization purity can be achieved if four feeds are employed for each patch element as the undesired modes ...