New Electronic Switching Arrangement for (sub)mm-Wave Radiometer Calibration

This paper describes a new quasi-optical switching method for more efficient calibration of millimetre and submillimetre wave Earth Observation (EO) radiometers. Passive remote sensing instruments must be calibrated regularly to ensure high measurement accuracy and current systems require switching between known hot and cold reference target loads using large and heavy power hungry motor driven mechanical systems. The proposed switching method is based on a reconfigurable Frequency Selective Surface (FSS) which is composed of a thin dielectric slab placed above a periodic array of polarisation independent slot elements. The spacing between the FSS and the high permittivity dielectric is adjusted to provide a good impedance match to free-space and hence high transmission for the 'ON' state, whereas for the 'OFF' state the separation distance is chosen to degrade the match and hence suppress the signal transmission by -30 dB mid band. Numerical predictions and experimental results in the frequency range 316 - 334 GHz are presented to demonstrate the operation of the FSS switch.