Patch Antenna Inset Feed Past Exam Question

[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.

 

[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?

 

[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).