Compact circularly polarized short backfire antenna with improved bandwidth and less radiations blockage

A compact short backfire antenna (SBA) with H-shaped self-phased cross dipole excitation structure is presented in this paper. The self-phased cross dipole is used to achieve circular polarization with single feed by introducing +/- 45 degrees lead/lag angle on the long and short dipoles because of input impedance variation. The SBA excited with this self-phased cross dipole structure gives improved impedance bandwidth and reduced blockage of radiations reflected from primary reflector, that is, higher gain when compared with conventional cross aperture patch excited SBA. The operating frequency of the SBA can be changed and optimized for circular polarization by using adjustable cross dipole arms. This excitation structure gives 28.36% higher impedance bandwidth and an average increase in gain of 2 dB over conventional cross aperture patch excited SBA. The antenna has been made more compact by using an elliptical shaped primary reflector that reduces one dimension by 26.7%. A variant based on this excitation structure consisting of two cross dipoles parallel to each other is developed to achieve dual band operation. The simulation results are verified by experimental results.