Voltage-Controlled Polarization at 0.1 THz Based on Phase-Tuned Coupled Oscillation via a Magic Tee

Abstract

We propose a technique to implement voltage-controlled polarization at 0.1 THz using a pair of phase-tuned Gunn diode oscillators coupled through a WR10 magic tee hybrid coupler. By finely tuning the free-running oscillation frequency with bias voltage, we can control the phase difference between the two coupled oscillators. Since the two output ports of the hybrid coupler correspond to the sum and difference of the signals from the two coupled oscillators, the power ratio between the two output ports can be adjusted arbitrarily by tuning their phase difference. Thus, by connecting a pair of orthogonal horn antennas to the output ports, an arbitrary polarization ratio can be obtained. The maximum polarization ratio observed in this study is 31.8 dB. To fully switch the polarization between the vertical and horizontal directions, a frequency shift of 26.6 MHz (0.03%) at around 94.3 GHz is involved when changing the bias voltage of one of the two oscillators. This frequency shift could be compensated by carefully controlling the bias voltages of the two oscillators simultaneously. The proposed approach enables fully electrical control of the polarization of subterahertz waves using a waveguide platform, which will be of importance for a variety of applications in sensing and communication.