Design of Ultrawideband Circularly Polarized Phased Array Antenna With Low VSWR and Low Axial Ratio

A novel ultrawideband circularly polarized (CP) phased array antenna was developed by combining the low-profile design of a stripline-to-slotline balun with the wide scanning characteristics of a tightly coupled dipole array (TCDA). This antenna boasts a low voltage standing wave ratio (VSWR) and low axial ratio (AR). To address the common-mode resonance issue, a circular slotline cavity was implemented as a four-stage series fan-shaped cavity. This design effectively extends the length of the short-circuit stub, enhancing the short-circuit impedance value and expanding the scanning bandwidth from 3:1 to 6.4:1. Notably, a rotating wide-angle impedance matching layer was introduced for the CP TCDA, marking the first time this approach has been employed. This innovation not only increased the number of matching network stages for achieving a low VSWR but also enhanced the consistency of the main polarization, reducing the cross-polarization ratio to achieve a low AR. The resulting 8 x 8 CP phased array antenna demonstrated exceptional performance, operating over a remarkable 6:1 bandwidth (2-12 GHz). It satisfies the criteria of Active VSWR < 2.5 and AR < 2.7 dB within a +/- 60 degrees scanning range.