High-gain polarization-reconfigurable monopole antenna for GNSS applications

The design of a circular polarization (CP) reconfigurable monopole antenna with enhanced boresight gain for the Global Navigation Satellite System (GNSS) is presented. The antenna is composed of two meandered monopoles perpendicular to each other, a switchable feeding network and a metallic reflector. The switchable feeding network consists of a Wilkinson power divider, a 90 degrees-phase shifter, a double-pole double-throw (DPDT) switch, and a defected ground structure (DGS). The power divider divides the input signal into two signals with equal amplitude and 90 degrees-phase difference. The two signals arrived at the two monopoles have a phase difference of 90 degrees or -90 degrees, determined by two DC voltage inputs to the DPDT switch hence to generate a right- or left-handed CP signal. Compared with the previous work, the antenna requires only two control DC voltages and so is much simpler. Measured results show that the metallic reflector placed at the back of the antenna increases the boresight gain by 5 dBi. The measured impedance bandwidth (S11< -10 dB) and axial-ratio bandwidth (AR< 3 dB) are from 1.28 to 1.97 GHz and 1.44 to 1.85 GHz, respectively. Simulated and measured results on S11, AR, radiation pattern, and gain show good agreements. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:791-798, 2016