I have question about the rectangular micro-strip antenna input impedance at edge. I find the following formula referenced to Balanis antenna theory and design (but I still have not found it in Balanis as written below),
Z = 90(εr²/(εr-1))(L/W)²
where W and L are the respective width and length of the patch.
My questions are
1 - is there someone who already used this formula?
2 - is there any other formula calculating directly the input impedance at edge? I used the steps in Balanis (antenna theory and design, page 821)
Zin = 1/Yin = 1/2G1 where G1 = (W/120λ)[1-1/24(k0h)²]
and found different results of the input impedance.
Hi, as I know feeding a rectangular patch antenna directly at the edge is not a good idea, because the impedance is extreme high.To understand this you have to look at a currant and a voltage distribution on your patch or as Giovanni Maria Sardi already told, use a cavity model. This model also explain you why a patch radiets.To reduce the impedance or better to say to adapt it to a certain value like 50 Ohm you transmishion line has to be insede of you patch (see attached File). How deep it is (y0), is very nice described in this book C.A. Balanis, Antenna Theoty, 2nd ED. Wiley, New York, 1997. Conserning a formula that you wrote above, I have to say it's not so easy. (Look in a book :) )
I hope it helps you.
Better way u refer this link;
http://www.antenna-theory.com/antennas/patches/patch3.php
the formula you indicated is in the following equation 14-13 page 822 because there is relation in resonance between lambda or resonnant frequency and L lenght and permittivity
Every formula is specific to a particular geometry with some assumptions.
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