Cavity-Backed Circularly Polarized Dual-Loop Antenna With Wide Tunable Range

A wide-band cavity-backed dual-loop antenna for circularly polarized (CP) applications is proposed in this paper. It is differentially fed by a parallel strip line, via a transition from a microstrip line. The operating frequency band of the antenna can be tuned from 2.07 to 2.98 GHz by changing a capacitor's value in a simple matching circuit, and the bandwidth of each operating band for |S11| les -10 dB is in a range of 2.6%-4.9%. Measurements and simulations reveal that the proposed antenna features total dimensions of 1.03lambda
₀
in diameter and 0.26lambda
₀
in height (lambda
₀
is the free-space wavelength at the center frequency of the tunable range), AR les 3 dB and stable radiation patterns with small cross polarizations over the whole tunable frequency range.