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 (S
11
) 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 λ
0
×0.805 λ
0
.