Using Invar material in Septum Polarizer and Feed

[jesuschrist]

Hi. For a project i had to design a septum polarizer. But they wanted it to work from +55C to -30C. If i hit these limits my crosspol drops below 30 dB if i use Aluminium.So I found this Invar which is %64 iron and %36 Nickel and has a very low thermal expension coefficient.Here is the Link https://www.nickel-alloys.net/invar_nickel_iron_alloy.html. Aluminium has around 23*10^-6 expansion coefficient while invar has around 1*10^-6. I just wanted to ask if anyone used in their projects or is it usable in EM applications?

Thank you.

 

[FvM]

Invar has high resistivity similar to stainless steel and won't be used for waveguides without galvanic silver or gold plating. It's main application is for the design of metal-ceramic or metal-glass vacuum sealings.

Isn't it sufficient to make all waveguide and polarizer parts with matched thermal expansion coeffcient, e.g. from aluminium?

 

[jesuschrist]

When i ran simulations for both aluminium and invar for septum only, I saw only 0.1 dB loss at S31 and S32(3 is the common port, 1 and 2 are input ports) for changing material from aluminium to invar.For a good measure i'm going to plate it too with silver. The thing is Since im gonna use this septum for a wide bandwidth, at the start and end of the band i get bad crosspol values because of thermal expansion affects the polarizer step sizes.