A 100-300-GHz Free-Space Scalar Network Analyzer Using Compact Tx and Rx Modules

This paper presents a 100-300-GHz quasi-optical network analyzer using compact transmitter and receiver modules. The transmitter includes a wideband double bow-tie slot antenna and employs a Schottky diode as a frequency harmonic multiplier. The receiver includes a similar antenna, a Schottky diode used as a subharmonic mixer, and an LO/IF diplexer. The 100-300-GHz RF signals are the 5th-11th harmonics generated by the frequency multiplier when an 18-27-GHz LO signal is applied. The measured transmitter conversion gain with P in = 18 dBm is from -35 to -59 dB for the 5th-11th harmonic, respectively, and results in a transmitter EIRP from +3 to -20 dBm up to 300 GHz. The measured mixer conversion gain is from -30 to -47 dB at the 5th-11th harmonic, respectively. The system has a dynamic range > 60 dB at 200 GHz in a 100-Hz bandwidth for a transmit and receive system based on 12-mm lenses and spaced 60 cm from each other. Frequency-selective surfaces at 150 and 200 GHz are tested by the proposed design and their measured results agree with simulations. Application areas are low-cost scalar network analyzers for wideband quasi-optical 100 GHz-1 THz measurements.