A Novel Bidirectional Antenna With Broadband Circularly Polarized Radiation in X-Band

A novel bidirectional antenna with a broadband circular polarization (CP) property in X-band is proposed. The CP characteristics are simply achieved by the asymmetrical Y-shaped feeding line. Both the impedance bandwidth and the axial-ratio (AR) bandwidth can be greatly improved by a through-via that is in series with an inductive strip and the polygon slot structure. The antenna is fabricated and measured for verifying the theory. A good agreement is achieved between the simulated and measured results. The 10-dB return-loss bandwidth is 31.4%, in which the AR is less than 2 dB. The measured radiation pattern shows a near-symmetry bidirectional radiation with the peak gain of 4.6 dBi. This antenna is a good candidate as a unit element in beamforming array applications.