Probe feeding for pyramidal horn
The horn is a transition from a TE10 mode in a waveguide to free space. You should use a coax to waveguide transition to transform first the TEM wave on the coax to TE10 in the waveguide. The horn then transforms the varying waveguide impedance around 400 Ohms into 360 Ohms in free space.
Please explain in simple words. I'm a newbie. When i did wave guide excitation i achieved my expected results at frequency where T10 mode was dominant. Now for Coaxial my questions are
q1) In hfss how to know what cable should i use for my specific band 0.9ghz-1.6ghz
if i want to use Lmr 400 cable should i give that cable diameter and dielectric
for coaxial feeding or should i give any diameter with 50 ohms wave port and it will auto give me my results. Like in feko u just place probe at my feeding point and it give us results. And if I'm going to fabricate then which cable will suit me for 10 Meter length.
q2) i have followed the steps for probe feeding in hfss manual for MPA but in that manual probe touches the rad box. but in my case as aperture is large and therefor box is large and i cannot connect the probe to rad box so how should i do proper feeding. Just tell me steps after cutting a hole in horn and i will follow it. i know That my feeding point for coax is λg/4 and b/2
I think the best way to feed a horn from a coax is the standard, to use a short waveguide length and a coax to waveguide transition. I do not use models and do not believe a good transition can be modeled. Commercial transitions are based on empirical work and function well.
For frequency around 1 GHz you can use any good coax cable which has 50 Ohms specification. Cables are good for short lengths, 10 meters of any reasonable cable will be lossy. For low loss, waveguides are better but for 1 GHz a waveguide would be too bulky.
I have not seen a direct coax probe excitation in a horn, but you can try it. Probe position and length must be adjusted for a good match. You can use a VNA or a reflectometer for such experiment.
Professionals tend to use good commercial products like coax to waveguide transitions and cables with good connectors. For 1 GHz I would use SMA connectors and a semirigid coax cable but for 10 meters length I guess you will lose up to 10 dB of power. With N connectors and thicker cable the loss can be 6 dB at 1 GHz. For satellite IF, 0.95 - 2.2 GHz, F connectors and 75 Ohm cables are used, and in-line amplifiers are used to compensate cable loss.
Amateurs often get good results by experiments. So go and try, you may find a good solution.
ys i have lost 2 db gain and a little retun loss in feko using coax. what about defining diameters in hfss ?