Co-located pair of Phased Array Antennas

[Swamp Thing]

I have been debating with a friend about a thought experiment that evolved out of an entirely unrelated discussion, but which has now become a subject of argument.

Consider a "dual" phased array antenna that has every odd-numbered radiating element driven from input port 1 and every even-numbered element driven from input port 2. Essentially, we have two phased array antennas that are 'co-located' or interleaved, so that their radiation patterns coincide, or at least their main radiation lobes coincide. The excitation is such that the main radiation pattern (normal to the array plane) is approximately Gaussian, for example.

Is it possible to achieve the following:

1. Isolation between port 1 and port two of the order of 20 dB or better. That is, sending power down port 1 with port 2 terminated will result in less than a hundredth of the power reaching the termination. The reflected power in a port (return loss) is also 20 dB down.

2. The radiation patterns of the two antennas are nearly identical to the extent that the amplitudes in any direction differ by less than 0.5 dB and the phases match within 5 degrees (these are just to give a sense of the orders of magnitude).

We are concerned mainly with fundamental constraints like reciprocity and conservation of energy. Would the above specs violate these principles?

 

[tech99]

A broadside array of co-phased elements spaced half a wavelength provides zero radiation in the edge-on direction. In this direction it can be considered as an endfire array with zero gain, but the zero radiation only arises at great distances. This is because for the end fire condition, the path loss from every element must be nearly equal and so the relative distances must be nearly equal.
If you measure the radiation close to the edge of the array, it is not zero, and inside the line of the array it is very high.
In a limiting case, if the arrays have one element each, when you introduce your second array there will be very small loss between the two.
This loss can never be less than 3dB but will in addition have a small path loss of a decibel or so.
So in my estimation the two arrays will have coupling of just a few decibels and not 20dB as desired.

 

[Swamp Thing]

Thank you. About the broadside radiation decreasing to zero at infinity, would it be correct to see it as a sort of evanescent mode?

Edit: As per wikipedia, that seems to be correct.

Thanks again.

 

[Swamp Thing]

Is there any open source software that I can use to simulate a small number of phased radiating elements?

 

[tech99]

Thank you. About the broadside radiation decreasing to zero at infinity, would it be correct to see it as a sort of evanescent mode?

Edit: As per wikipedia, that seems to be correct.

Thanks again.

Not evanescent, it is ordinary radiated energy. Intensity can fall off at different rates near an array due to geometrical/phase relations, and the pattern near an array differs from that far away.