Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
It really depends upon how your patch antenna looks. If it is low profile with regular substrates, the Zin will be very stable with the ground planes 3 substrate thickness bigger than the patch. Certainly, the pattern is affected much. For some high profile patch antennas such as aperture coupled antenna with a big air layer between the patch and the feed line, the size of the ground plane will have big impact, it is hard to give a general guide line on the size of the ground plane. It really depends upon reality. If your patch antnena involves slots as part of your design, you may pay serious attnetion to the ground plane size, the finite ground can be an integral part of your radiator. The size and shape are very critical.
If my patch size is 0.85 X 1.15 cm, let say substrate thickness is 0.1 cm. How large should my ground plane to consider? Is there any formula to calculate the minimum of ground plane for patch antenna?
If it is just a patch antenna with the height much smaller than the length and width, I think even make the ground plane about 3-5 thickness wider than the width is good enough. The impedance of such a finite ground antenna will be very close to the infinite one. However, the pattern can be quite different because there will be much back radiation in the finite ground case while there is no back radiation in the infinite ground plane case.
The size for the ground plane depends on many issues. For a simple patch antenna the size of gorund plane significantly affects the return loss at resonances. But for UWB it also improves S11 at lower frequency. In my opinion, an optimiztion for the choice for the size of ground plane should be taken into consideration for any given antenna design.
If the frequency of the antenna working on is not so high,considering the purpose of using patch antenna,we should make the dimensions small as soon as possible.From the experience,set the ground plane 0.2*lamda lager than the patch is enough.
I think it is not a question whether you can make it. The question is whether the performance is what you want. The ground plane is not very big than the patch while you have enough margin. The impedance performance will be close to the infinite ground plane model. Certainly, you can use finite ground model using EM tools. You may not get a big front to back ratio. It may not be bad if you want a pattern to be closer to omni-directional.
This is one of those questions that needs the application of judgment based on the way the antenna will be used. A clear formula for the minimum size is illusive (non-existant?).
Faced with this quandary, the approach I would take is to decrease the groundplane size and watch the parameters of interest and see how much you can compromise. We fortunately now have excellent simulators available and do not need to do all the testing with hardware. Decreasing the groundplane in patch designs rarely improves their performance. Just cut until things start going bad and ease up a little.
I note that there are a number of comments about HFSS vs. Designer as a simulator. For planar antennas (patches) Designer is a good choice because it is faster. To quote one of the Ansoft sales engineers, Designer is really good if you stay close to the roads. But if you want to go off-roading, HFSS is a better choice. Exploring truncation of the groundplane, particularly if there are complex feed features may not clearly be in Designer's court as the tool of choice.
It has been my experience that the antenna is always too big. What the world wants is a high gain omni antenna the size of a pinhead. It also has to have infinite bandwidth.
The advice above is all good but you have to decide how much degradation your antenna can tolerate.