A Dual Circularly Polarized Patch Antenna Array for S-band

In this paper, a high gain dual circularly polarized patch antenna array containing 5 x 5 radiating elements and operating at S band is presented. Each radiating element contains a radiating patch and a parasitic patch placed above a metal reflector. All components of a beam forming network and micro strip conductors exciting patches are formed on a one surface of a dielectric substrate mounted on a back surface of a metal reflector. The radiating patch comprises four metal strips bent towards a metal reflector and directly connected to exciting micro strip lines through holes made in the metal reflector and a dielectric substrate. Each patch excited by 3-dB branch line coupler radiates right hand circular polarization and left hand circular polarization. The reflector has dimensions 4.3 lambda(0) x4.7 lambda(0), where lambda(0) is wave length in a free space. Calculated directivity of such antenna array is 22.3 dBi at central frequency f(0). Measured return loss is -20.1 dB and isolation is 20.5 dB within the required 11% frequency band. Measured axial ratio is less than 1.5 dB and cross polarization better than -25 dB. Measured insertion loss of a beam forming network is -1.3 dB therefore estimated gain of both circular polarization is 21 dB.