antenna-theory.com

[jagadishvakati]

Is there any specific formulas to calculate the height of the substrate, width of transmission line, gap between transmission line and the patch??

I am trying to simulate a microstrip antenna in CST suite. And from what i have seen there are only ballpark estimates like height should be way less than wavelength and such.

Is CST the best software for doing this simulation? If no, please recommend other software.

Thank you in advance guys

[bigSteve]

Look up the microstrip antenna page here:
http://www.antenna-theory.com/antennas/patches/antenna.php

Generally the height should be at least lambda/20. Lambda/10 is better, as generally increased height gives you larger bandwidth.

The length should be lambda/2, unless you have a dielectric substrate, in which it scales down by a factor of sqrt( epsilon ).

CST works and is a fine tool for the job. There is no "best" software, it depends on personal preference and exactly what you want to do. People like HFSS as well, and some people like FEKO.

[jagadishvakati]

Thanks for the reply Steve.
1. But how do we end up with an estimate that the height of substrate has to be in that particular range for better bandwidth?Are there any conclusive mathematical results you depend on(for height of the substrate)?

2.We are using a transmission line (insert) feeding for the patch. How can we ideally fix the width of the feed line? For insert feed does the gap between the feed line and surrounding patch matter? If so how do we calculate the dimensions of this gap?

3.And, sir, our project is the analysis of microstrip antennas with magnetic substrates ( not just dielectric. has significant values of both permittivity and permeability.). How, do you think, the analysis of the antenna will consequently change?

We are trying to simulate a patch with magnetic substrates on CST. Do you think we are on the right path in approaching this problem of analysing microstrip antennas with magnetic substrates?

We have been stuck in this simulation for long now, and we believe a proper guidance could help us out. Sorry for the trouble.

[bigSteve]

1. No, there aren't specific formulas because antennas depend on too many variables (substrate, size of ground plane, geometry of patch, what is around antenna, etc). If you take the height up to lambda/4, the radiation mode will not be a patch antenna any longer, and may be more of a horizontal monopole. If the height is less htan lambda/20, the patch may act more as a capacitor.

2. If you want a fixed feed width, then you can play with the height of the substrate to ensure the transmission line is 50 Ohms. Generally more height decreases the characteristic impedance of your tx line. For the insert feed, the gap should be sufficiently large such that there's not too much capacitance between the antenna and the feed line. For thin copper patch antenna, you probably want to do at least lambda/20 width.

3. Permeability in your substrate? I'm not sure. Since the speed of light will slow down, increased permeability will shrink your patch. Any conductivity associated with this permeability will decrease the bandwidth and antenna efficiency.

CST is as good as anything else for analyzing magnetic substrates - just throw in some material parameters and see what happens.

[jagadishvakati]

Thanks for the reply Steve.
Does the height of the substrate have to be comparable in any way to the Length and width of the patch?