I m trying to design a two-element microstrip patch antenna array at 2.95 GHz fed by a coaxial probe and a 3-port divider as I show in the attached files. The antennas impedence at the feed point is 100Ω as is the microstrip line that connects them. The impedence of the coaxial probe is 50Ω. In order to get the desired radiation pattern, the probe feed is offset to create the required phase difference, but this move interferes greatly with the impedence matching. Why is this happening and what can be done to fix the impedence back to 50Ω?
You are showing the real part of the impedance. What is the imaginary part? If it is not zero then the real and imaginary parts will vary along the line.
Can you show the impedance on the smith chart?
You probably know that you already have 180 degrees phase difference between you patches, because they are mirror images. Maybe it is the change in the phase of the near-field coupling when the feed-point is changed that changes the impedance?
Thank you for your answer. I ve attached the imaginary part and the impedence on the smith chart.
Yes, the phase difference is deliberate so that I acquire the desired radiation pattern.
I'm sorry that I can't make sense of this either. It looks like it should work. Maybe the centre-pin is not touching in the offset feed. Sometimes these things happen with models.
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