Hello.

I've read the paper dealing with plasma interferometry with using mm wave. The frequency used is about 35 GHz.

The paper shows use of the waveguide to transmit signal of such a frequency rather than full use of the coaxial cable.

I thought it is due to the frequency-limitation of the coaxial cable.

What is the maximum frequency under which coaxial cable is available?


Donggyu Jang

 

There is coaxial cable availale that can operate up to 65GHz or more but it will always have a higher loss per meter length than waveguide. So it can be used for shorter runs where the loss can be tolerated, but for longer runs, where the loss would be unacceptable, waveguide must be used.
So it depends upon the application as to whether you use waveguide or coax.

 

Large diameter eg. 1.25" hardline is used up to the GHz range. The connectors are expensive and the bend radius is measured in feet!
Maximum frequency is generally not specified, but rather Attenuation per 100 feet. It doesn't take may dB per hundred feet to make it essentially useless.

 

Semi-rigid coax goes into the hundreds of gigahertz.

 

you have to check the specs of the coax, larger coax will exhibit some waveguide effects that cause excessive loss. diameter of waveguide is mostly determined by power rating to pervent flashover. if the internal diameter of waveguide reaches near the wavelength of the signal, it wont work. there is another form of transmissionl line with low loss, it is called "G" line. after its inventer, whose name starts with G, but I have forgotten the spelling. it uses a single conductor with "launchers" on either end.

 

Goubau
http://www.google.com/patents/US2685068
It works the same as Ground wave propagation with low frequency RF. The RF moves on the center conductor as a surface Evanescent wave. If it's a direct open path the losses can be minimal.

http://www.corridor.biz/FullArticle.pdf