The Components of a MMW Cavity Spectrometer for Quantitative Measurements

The MMW region of the electromagnetic spectrum is characterised by quasi-optical electronic components for generation, transmission and detection. MMW sources and detectors are typically semiconductor devices with transmission lines of open tube rectangular waveguide, or coaxial cable at frequencies below 30 GHz. The cables are rather lossy and waveguide is the favoured transmission line for any other than the shortest links or where dielectric loss is less critical than mechanical flexibility, e.g. connecting to a frequency counter. 

Commercial MMW components are precisely machined to tight specifications and can be bought on their specification with assured performance. Machining the cavities and interfacing the pumping and sampling systems does not require particularly sophisticated tools, and the mirrors can even be built around surface coated optical reflectors where suitable sizes are available. Experimentation is nonetheless an expensive business for the MMW components alone, particularly at higher frequencies. 

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