Differentially Proximity-coupled Circular Ring-shaped Array Antenna with Improved Radiation Characteristic

One of important parameters in array antenna is radiation characteristic which can be satisfied by implementing several design techniques. In this paper, by utilizing differentially proximity-coupled feeding technique, a circular ring-shaped array antenna is designed with improved radiation pattern characteristics. The proposed array antenna consists of 20 circular ring-shaped antenna elements arranged in 4 × 5 array. Differentially proximity-coupled feeding technique applied for each antenna element is aimed to have symmetrical radiation pattern. The array antenna which is designed to work at the frequency of 1.275 GHz for L-band frequency application is implemented using two layers of FR4 epoxy dielectric substrate with the total dimension of 199.3 mm × 189.5 mm. The characterization result shows that the proposed array antenna has good impedance matching with the reflection coefficient (S11) of -21.65 dB and -10 dB impedance bandwidth of 80 MHz (1.21 GHz to 1.29 GHz). Meanwhile, a symmetrical radiation pattern at E- plane is achieved with the half power beamwidth (HPBW) of 43°.