Patch Antenna Inset Feed Past Exam Question

1. Jun 13, 2014

fred3142

I'm trying to work out what 3.d) is meant to be. I'm not entirely sure which part of the antenna it is referring to; I assume it's referring to width of the gap between the feed and the patch. If this is the case, I have no idea what width one would want to make it. I would've thought as small as possible to not perturb the antenna much.

As far as I can tell, the textbook we're using (Antenna Theory: Analysis And Design by Balanis) doesn't really talk about it, except for saying that it'll introduce some capacitance and perhaps shift the resonance by up to 1%.

Question The red numbers are the lecturer's answers. I'm not really sure how he got 13.36mm for 3.c). I believe the inset should be about 9mm based on:
$$R_{in} (y=y_0) = R_{in}(y=0) \cos^2\left(\frac{\pi}{L} y_0\right) \\ 75=150 \cos^2\left(\frac{\pi}{40.1\text{m}} y_0\right) \\ y_{0} \approx 9\,\text{mm}$$

I really have no idea about part 3.d) though.

Could someone please point me in the right direction?

Thanks.

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2. Jun 30, 2014

Greg Bernhardt

I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?

3. Jul 8, 2014

fred3142

I can confirm that the lecturers answer for the width is simple wrong and what I've done is correct.

As for the width the inset gap has to be, I still don't know. I think it is meant to have something to do with the phase of the wave (perhaps it should be made, say, half or quarter wavelength).