Microstrip lines at variable temperatures

Hi everybody,

I'm trying to design a microstrip line that needs to work at different temperatures, i.e. between room temperature and liquid helium temperature (4.2 K). The way I understand microstrip lines, their impedance depends on the dielectric constant of the substrate, the substrate height and the trace width. When the temperature changes the substrates change their dielectric constant, do I have to take that into account? Is it possible to design microstrip lines that will work at any temperature? Does anybody have experience with this?
Thanks a lot,

Hans

Not an expert on liquid helium temps, but I did have a batch of micrstrip boards accidentally exposed to liquid nitrogen temps once. A lot of them popped off of their metal housings due to thermal expansion coeff. mismatch. It will, obviously, be even harder.

I would guess you want something like quartz substrate on stainless steel housing, or something with an even better coeff. matchup.

Google around for cryo experiments and see what other guys have used.

Your question sounds like cyrogenic electronics have been invented just a few days before.:D As there would be no communication
satellites or earthbound cryo-cooled microwave circuits. You can check e.g. Rogers product information for cryo application data.
As far as I remember, most RF dielectrica, e.g. teflon or aluminia have a small er t.c., even down to liqiud helium temperatures.

Hi hmalissa,
Have you tried with air dielectric?

I do not know about satellites or earthbound cryo-cooled microwave circuits.