Semi-rigid vs flexible cable for antenna feed

I designed an antenna feed that is capable of monopulse tracking.What I wanted to ask was which cable is better to use for both monopulse and antenna feed cable.I would like to use flexible cable t-flex 405 for ease of use but I also think the phase stability is critical for tracking accuracy so it might be better to use something like rg-402 also I had some experience with rg-402 cables but I am not sure if they can be bent in the tight spaces around the feed.

It depends on the location of your antenna. If its an outdoor space, I can recommend using something like lmr-400. You can ask the manufacturer's the s-parameters of the cable or look attn/meter numbers from datasheet. Can you elaborate on your environmental conditions?

it is for a cassegrain reflector antennas.power dividers,couplers and lna will be all around the feed for a compact design. They all will be in a metal cylinder cover and the cover can't exceed the diameter of the feed horn aperture diameter so the space is kinda tight.Also it will be in x band so some of the cables such as rg-142 are unusable.

If phase stability is not at the military/space level, I can advise using PE-P141. Flexibility is actually quite important as you mentioned, semi-rigid cables may put on too much torque to the feed point if not properly fixated on a surface.

This is a usual quandary.

Rigid and semi-rigid cables generally perform better and are more stable. Flexible cables are usually much easier to use and fabricate. Smaller cables of each type are more flexible but guess wha they have more loss.

There are some high performance cables (silicon dioxide dielectric and exotic metals) that work extremely well but guess what they are very expensive.

Bigger cables have significantly less loss, provided they are not too big. Guess what, they are rigid and hard to use.

To add more fun, bends can screw up the works too, particularly if the cables move around during operation. For drill put a quality cable on a VNA and watch the s parameters change as you move it around.



You did not say if you are going for amplitude or phase monopulse. One or two axes?

Flexible cable has a higher leakage than a semi-ridged cable would. So if you are receiving low level RADAR returns, that leakage could become self-jamming