I observe strange behaviour. For 4 element array I have gain around 12dB, and S11 is around -20dB. It is extended version of my single patch and 2-patch array, where gain is also good and predictable. Series array is terminated with half wavelength open stub, and electric field and phase and radiation pattern is good. Extending array to five and more elements leads to gain loss and S11 of -5dB. Patches are optimized for inset fed. Patch spacing is a little less than half wavelength in free space! It works great for 4 elements. Reason for tight spacing is high dielectric constant. I expected that adding more patches in series will increase gain and produce narrower pattern. I did not do any patch radiation weighting, but inset and series phasing all matched, so I expected to see non-symmetrical pattern for 8 element array, as most power is radiated by first patches (not center of array).But for 8 element array all patches starting from 4th patch are poorly excited on EM field, but phase looks ideal. Only three first patches excited well, the rest 5 patches almost do not radiate. What could it be? I thought that maybe I optimized single patch element too good, so all power radiated through first three patches. But in this case should not I observe good S11 vvalu for whole array?
Pictures or drawings? Pattern plots?
My only guess from the info given is maybe you are getting destructive interferrence from some of the elements. Also, an open stub will reflect all the power back into your elements, so maybe this is why you are loosing S11 performance and your EM fields.
Are these observations theoretical or actual?
A poor designed array antenna can get worse performance than a single well designed antenna.
There are two main things that have to care when designing array antennas. Isolation between antenna elements, and proper phasing between them.
Observations are theoretical. I will provide drawings if problem remain. Yesterday I found out that larger array performance improves a little if patch height is reduced. So maybe patches loaded with neighbour patches and effective length increased. But bandwidth is very poor, may be it is common for series fed patches. Thank for your reply
