wideband integrated feeding system for spiral antenna

[sara67]

Hi guys

I'm working in a integrated feeding system for a type of spiral antenna

my antenna work very well , I have a return loss better than -10dB in 2-12 GHz
my Balun work very well too
but when I connect them together
my results are so bad and I dont have a wide band

Can anyone help me ?

 

[jiripolivka]

You should measure the impedance of your antenna, then design a matched feed from a 50 Ohm line. You have certainly done that if you measured RL. Apparently your balun is not matched over the wide band. BTW, the correct name of a "spiral" antenna is HELICAL.
What is the balun for? Helicals are matched to coaxial lines, no balancing needed.

 

[sara67]

Hi
thank you
my balun's impedance is 50 to 200 ohm ,and it have return loss better than 10dB in 200 ohm (my structure is Microstrip to CPS)
input impedance of antenna is 200 ohm and it work really good in 2-10GHz (my antenna is sinuous antenna with 2 arms
it is very amazing that when I connect them toghether ,results are so bad
may there are another problem ? because I dont have mismatch
how I can use of Z smith chart , do you know ?
both work very well in same impedance but when they connect, all things are owful
I think may I use of z smith chart , is it good ?