High metall losses in mm wave circuits
Metal losses are very high at mm wave frequencies (30 GHz+). How are such losses compensated for in MMICs ? Do they use amplification by active elements to overcome the metal losses ? Please let me know. Thanks.
-svarun
We have quite a few customers doing radio astronomy in the TeraHertz region. Complex molocules in interstellar clouds radiate at those frequencies. They tend to use super conductors. CPW also helps keep losses down a bit. Use of dielectric waveguides can also be helpful.
Is there a frequency ( or range) above which microstrip becomes unsuitable due to losses (even though the cut off for higher order mode may be very high) ?
Microstrip has a problem when the substrate is more than about 0.1 wavelength thick. You start to get a loop antenna effect and radiation.
At mm wavelengths, substrate thickness might be too thin to manufacture. CPW just takes the microstrip ground and, instead of having the ground underneath the microstrip, CPW puts the ground beside the microstrip on the same level. Now you can get the ground very close to the signal conductor, and kill the radiation. CPW also has much less dispersion than microstrip.