Cavity backed Spiral antenna in the range of 1-18GHZ

I am working on cavity backed Spiral antenna in the range of 1-18 GHZ . I have designed linearly tapered balun in order to feed the structure. But there is squint in the radiation pattern. i tried to optimize the balun design, but am not able to avoid the squint. kindly advice me the steps that can avoid squinting .

hi Vaigamenon
please explain more. what is the application of this antenna? high power or low power? connector type? vswr?
what kind of balun did you use?
what is your maximum acceptable squint?
do you have good radiation patterns with your design in high frequencies?
attach a file if you can

I would be inclined to deep six the linear tapered balun and use an exponential taper instead. I recall squint as being an issue with conical spirals but not to any great extent in a planar antenna. I assume that you are loading the cavity.

There is a chapter in the Antenna Handbook (the Johnson edition as I recall). There are four editions and I periodically find them all useful. Look at Jim Scherer's chapter. The squint might also be a function of the termination of the arms ( using a two arm spiral? ) .

Hopefully you are intending to make the cavity around 6 to 9 inches in diameter so it will actually work at 1 GHz.

Dear Sir
Thanks A lot for your reply.
It is for defense applications.
and the squint is appearing in the higher frequencies. i have designed the spiral and squint is appearing at 12 GHz. Acceptable squint level is 6 degrees.

for spiral antenna termination of arms will effect the pattern.
i think feeding has no role in squint of its pattern.