The IHP researchers developed receiver and transmitter prototypes in SiGe technology that work in the frequency range between 238GHz and 252GHz. "This is a relative narrow frequency range", a researcher admitted, but "after all, this is just a demonstrator, better implementations will follow", he said.
The demonstrator utilizes an optical bench that carries the transmitter and the receiver module. The effective antenna gain is amplified through a lens. For the gas spectroscopic measurements, a gas absorption cell the size of 0.6m had been positioned between transmitter and receiver. The receiver IF signal has been recorded as a function of the transmitter frequency, using commercially available laboratory measurement technology. The researchers used an integrated local oscillator for transmitter and receiver likewise, whose frequency has been stabilized by an external PLL circuit. The two PLL units use two reference frequencies with constant offset to achieve a constant intermediate frequency for the receiver through a complete sweep. Thus, it is possible to detect even small amplitude changes as a result of gas absorption.
This article was originally published on EE Times' sister site, EE Times Europe.