Yes, waveguides are used for high frequencies. Although the relevant frequencies are are not very high in this case, something like 4-8 GHz.
First or all, alumina is not the same thing as aluminium in this context. Alumina is Al2O3, i.e. aluminium oxide; when grown as a single crystal this material is generally known as sapphire (which is milky white by the way, the sapphires used in jewellery get their colour from impurities).
Alumina is sometimes used instead of ordinary laminate to make PCBs for high frequency applications ("ordinary laminate" here means duroid or other low-loss materials). We want to use it because in additional to being a low-loss material it is also a good thermal conductor which is important in our application.
A coplanar waveguide consits of a thin strip of metal (a few hundred nanometers thick), a gap on each side, and then wide ground planes. I.e if if you look at the profile it will look something like.
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if you choose the dimensions correctly you get a 50 ohm waveguide suitable for transmission of high frequencies. In our application the waveguide is perhaps 10 mm long and the distance between the ground planes around 50-500 micrometer (the waveguide starts out being pretty wide but gets gradually narrower).
"Waveguides" is a general name for just about everything that can support a TEM,TE or TM wave. Some waveguides are very large and "3 dimensional", essentially pipework, where the diameter of the pipe is of the same order of magnitude as the wavelengt of the wave (i.e. it can be centimeters for e.g. radar).
As you might have guessed this is work-related....
My problem is that although this is standard technology I haven't been able to find a company which accepts small orders, we are doing research and only need a few samples; we don't want to order 1000 boards. We could make them ourself (it is pretty straigthforward, plain photolithography) but we haven't got access to a cleanroom at the
moment.
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