let's consider this two planar biconical dipoles of total length and width each one 10mm, at a distance D = 25.6mm.
They are excited with the discrete ports in the picture, which corresponds in this case to a voltage source with 150$\Omega$ of source impedance. The two voltage sources, as indicated by the ports arrows in figure, are with opposite polarities. In other words, there is a 180° phase shift.
In this condition, I'm expecting that the radiation pattern of this system (for instance in terms of directivity) falls at the wavelength equal to R = 25.6mm (11.72GHz), because there will be destructive interference between the waves emitted by each antenna. And, in fact, that's what I've got by a simulation in CST MWS:
This graph represents the Directivity on Theta = 90° plane (XY plane) averaged with respect to Phi. There is a directivity drop at 12GHz because of destructive interference.
Nice, it's well predictable.
Why have I thought it's a destructive interference? Because the single elements patterns are, at 12GHz, on XY plane ($\theta = 90°$):
So, each element irradiates with peaks of 1.99dBi along y-axis. But, if we look at the radiation pattern of the total system, we have an hole along y-axis.
Since this happens at the frequency whose wavelength is equal to the y-axis distance between the two elements, I'd say it's caused by a field cancellation.
Now let's consider a more complex case with more elements in a circular array:
In this case, the simulation has shown me that the destructive interference frequency is shifted from about 12GHz to 14GHz:
Question: Can you help me on understanding (also qualitatively) how can the presence of other elements shift this frequency (and why it has been increased)?