Patch antenna feedpoint

Hi to all,

We are currently working on patch antennas and tried to simulate the patch antenna with XFDTD software. The antenna is given in a paper (Analytical Eqs. or Compact Microstrip Arrow Shaped Antenna by S. Kundukulam, M. Paulson, Aanandan and Mohanan in Wiley Periodical in 2002.)

The shape is given in the attached file. But, the problem is; the feedpoint (shown s (x0, y0) in the file.). The exact position of the feedpoint isn't given in the paper and , as we change the feedpoint, the resonance frequency of the antenna changes rapidly.

Could anyone give information about the feedpoint? Is there a standard on the feedpoint, so the position is not given in paper?

Regards,
Thanks

Patch feeding point location should not significantly affect the resonant frequency.
The feeding point position gives the desired input impedance.

The impedance of a patch feedpoint is roughly 300 Ohms at the edge and decreases to 0 ohms at the center. Adjusting the feedpoint position changes the impedance. The relation is approximately along a cosine curve.

One occasionally sees a patch with a bolt (centered) supporting the patch. For quite some time I wondered how this might work. Actually, not too badly.

I am surprised to hear that you are seeing big frequency shifts.

Thanks folks for replies.

After reading the replies, I am suspicious about something: I am trying to find the resonance frequency of the antenna by plotting the S11 against frequency and I take the frequency at which S11 is a global minimum as the resonance frequency. Is this wrong?

Kindest regards.

When there are no antenna matching lumped components (as in patch antenna) you can trust S11 to be the antenna?s resonant frequency.

Have to know, the best feeding transmission line for patch antennas is to use coax cables, but if is not possible microstrip or CPW would be fine.

Thanks for the reply.

Another problem is that the resonant frequencies of TM10 and TM01 modes. How can I chose the polarization in the simulation using XFDTD, I think the voltage source direction sets the polarization. Am I right?

Regards.