Resonant-tunneling-diode terahertz oscillator integrated with a radial line slot antenna for circularly polarized wave radiation

Abstract

We proposed a resonant-tunneling-diode (RTD) terahertz (THz) oscillator for circularly polarized radiation, which is convenient for THz wireless communication. The oscillator is composed of an RTD, a cross-slot resonator, and a radial line slot antenna (RLSA). The output of the RTD in the cross-slot resonator laterally propagates in the substrate, and is radiated from the RLSA in the upward direction of the substrate as a circular wave. In theoretical calculations, the axial ratio of the circular polarization was 1.6 dB and the directivity of the radiation pattern was 23 dBi at the oscillation frequency of 500 GHz. In a preliminary experiment, we fabricated this oscillator, and obtained circularly polarized THz radiation with the axial ratio of 2.2 dB and the directivity of 15 dBi for the oscillation frequency of 507 GHz. The measured radiation pattern was wider than the theoretical calculation, probably because the radiation from the substrate edge is mixed into the output from the RLSA. Using the fabricated oscillator, we demonstrated 1 Gbps wireless data transmission. The observed bit error rate was almost independent of the rotation angle of the oscillator around the transmission direction, indicating an alignment-free transmission for the polarization axis.