Quasi-Frequency-Independent Combined Antenna with Dual-Circularly Polarized Capability

A novel antenna composite with greatly extended bandwidth of a baseline 4-arm log-periodic (LP) antenna is introduced. The antenna combines LP, turnstile bowtie, and circular ring into a single configuration. Wide bandwidth and miniaturization factor > 2 are achieved by coupling the currents from the bow-tie (boom) of the LP to a ring, thereby providing an efficient well-matched radiator at frequencies below the cut-off frequency of the LP. A 160 mm diameter antenna is designed and fabricated to demonstrate the proposed concept. Measured VSWR and radiation patterns verify multi-octave dual CP operation and demonstrate a size reduction factor of 2.25.