A Transmit–Receive Separation Scheme of Monopulse Antenna Applied in the Terahertz Band

In this letter, a transmit–receive separation scheme of monopulse antenna applied in the terahertz (THz) band is proposed. This scheme does not require the circulator to achieve the separation between the transmitting and receiving channels, which reduces the loss and complexity of the monopulse antenna system, and greatly improves the integration of the antenna. Although still adopting five units to realize the function of monopulse, the presented scheme is distinct from the traditional five-unit scheme. In the proposed scheme, one antenna is placed at the center of the array to generate the transmitting sum (T-Σ) signal, and the other four antennas are placed at the top, bottom, left, and right of the central antenna, to generate the receiving sum (R-Σ) and receiving difference (R-Δ) signals at the azimuth (AZ) and elevation (EL) planes. A 220 GHz Cassegrain antenna, fed by the horn antenna array designed in the transmit–receive separation scheme, is fabricated and measured. The measured impedance bandwidth of all ports exceeds 10.9% (from 208 GHz to 232 GHz). The isolation between the T-Σ and R-Σ ports is lower than −24 dB. The measured peak gains of the T-Σ and R-Σ beams are 38.4 and 37.7 dBi, respectively. The measured null depths of the R-Δ-AZ and R-Δ-EL beams are −23.1 dB and −25.6 dB, respectively. The experimental results are consistent with the expectation and indicate the feasibility and superiority of the presented scheme in the THz band.