Summary
International Symposium on Antennas and Propagation
2012
Session Number:4A3
Session:
Number:4A3-3
A Circularly Polarized Multimode Patch Antenna with Full Hemispherical Null Steering for GPS Applications
Nathan Labadie,
pp.-
Publication Date:2012/10/29
Online ISSN:2188-5079
Summary:
Communication systems in a dynamic electromagnetic environment benefit from antenna element radiation pattern reconfiguration. This is particularly true for sensitive receivers such as those employed in GPS systems, which are often paired with null forming antennas to avoid jamming. We present a novel circularly polarized multimode patch antenna element with the ability to point a null at any location in the upper hemisphere. The antenna is composed of a central TM11 patch embedded in a shorted annular ring patch supporting the TM21 mode. Both elements are designed to operate simultaneously over the L1 GPS band ranging from 1565 MHz to 1585 MHz. Reflection coefficients less than -10 dB are maintained at each port and worst case mutual coupling is less than -20 dB. Analysis of the complex radiated fields for each mode is used to explain the properties of the null. Phase difference between modes determines the azimuthal location of the null while its elevation angle is determined by the ratio of mode amplitudes. This suggests a simple feed network architecture for beam reconfiguration. A null depth greater than 15 dB is achievable for any scan angle while maintaining axial ratio less than 3 dB in the main beam.