A Tunable Dual-Circularly Polarized Antenna With Broadband Triple-Branched Feed Structure

Abstract

A novel reconfigurable circularly polarized (CP) patch antenna with tunable operation band and switchable polarization states is proposed. Four varactors are placed symmetrically across the cross-shaped slot on the upper square patch so that the operation band of the proposed antenna can be continuously controlled through the specially designed bias. Meanwhile, a triple-branched broadband switchable feed structure loaded with p-i-n diodes is specially designed to achieve polarization reconfigurability (LHCP, RHCP). The structure novelly integrated a 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> broadband phase shifter with a 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> one by a shared reference branch. Simulation results of the feed structure exhibit stable phase-shift in a wide bandwidth of 58.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 5^{\circ }$</tex-math></inline-formula> phase imbalance. A prototype of the antenna is fabricated while both measured and simulated results agree well. The antenna achieves good impedance matching from 2 to 2.7 GHz and the axial ratios at both polarization states are smaller than 3 dB. The frequency and polarization reconfigurability make the antenna potentially suitable for satellite applications, such as multifrequency satellite data link transceiver.