I´m designing a PIFA antenna. I have been modifying the ground plane size, the frequency shifts when I increase and decrease the lenght of the ground plane. I have found the size where the frequency is 2.5 GHz the frequecy, what I want.
With a small antenna, the ground plane often radiates more than the part you think is the antenna, so the size of the ground is very important. You need to find the size and shape of ground that gives the match you want at the frequencies you want. Reflections from the edge of the ground look like impedances at the feed point. If you don't want the size of the ground to affect the antenna impedance, then you need a large ground (several wavelengths), or one with loss so the currents don't reach the edges, or possibly with metamaterial to keep the currents low. However, I think a PIFA needs a ground plane, so ground currents near the PIFA need to be allowed to be high.
Malcolm White Thanks for you answer. Today I was reading about image theory. The monopole antenna ( λ/4) needs a λ/4 ground plane to allow a good performance this ground plane acts like another monopole and we obtain an "imaginary" dipole antenna λ/2 so I looked this principle occurs with my antenna all the structure (patch and ground plane) measures about λ/2. I was simulating another antenna with different frequency and I had the same results: the structure measures about λ/2 . The frequency for this new antenna is 5 GHz.
Yusset Ibrahim Fernandez Good information on image theory that u have found. However the antenna impedance need to be considered by looking at the edge of the ground plane as well as the metamaterial used in your design.
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