How to match waveguide impedance with free space impedance Zo
Can somebody tell me in which ways can i match waveguide impedance to free space impedance Zo. Is there an equation or tutorial that could help me? I am constructing a double ridged Horn antenna. I want to match somehow 50Ω with 377Ω (free space).
Thank you.
Atsou
i think u can use λ/4 transformer which the has characcteristic impedance equal
√(z1*z1)
wish this help
khouly
Well...you start off at the flange of your double ridged waveguide. For those dimensions you need to compute the guide impedance.
At the other end that is open to the air, the wave impedance is 377 ohm. You need to taper the impedance between the calculated guide impedance and 377 ohms. Your taper can be:
1 single step where you start at the guide impedance, the step to a λ/4 section that is √((377)*(guide impedance)), like stated above.
a linear taper that starts at the guide impedance and ends up with an impedance at the open end of approx 377
an exponential taper that does the same
a custom taper
Check out this paper starting on page 20. If you have enough length, you can do almost any taper and have a good match. If you have a short length, you have to grind thru the math to get the optimum bandwidth and return loss.
http://cc.ee.ntu.edu.tw/~thc/course_mckt/note/note4.pdf
Antennas do this matching. Your horn will do it. All you have to worry about is the impedance seen by the waveguide at the throat of the horn.