Development of Circularly Polarized Ring-shaped Array Antenna for L-band Radar Application

This paper presents the development of circularly-polarized ring-shaped array antenna which is intended to work at the center frequency of 1.275 GHz for L-band radar application. The proposed array antenna which consists of 4×5 ring-shaped elements is differentially fed at the opposite side using proximity-coupling feeding in order to generate different phases among radiating elements producing circular polarization. The measured reflection coefficient (S11) has good agreement to the simulated result with –10 dB impedance bandwidth of 76 MHz in the frequency range of 1.217–1.293 GHz for both, while the measured 3 dB axial ratio bandwidth is 30 MHz. In addition, the dimension of array antenna fabricated on two layers of FR4 epoxy dielectric substrate is 0.847 λ0×0.805 λ0.