On Transmitting, Receiving, and Scattering Radiation Pattern of Finite Arrays

9 ON TRANSMITTING, RECEIVING, AND SCATTERING RADIATION PATTERN OF FINITE ARRAYS 

In the last section we introduced the radiation pattern concept for finite arrays. We shall in this section consider in more detail what happens under transmitting versus receiving or scattering conditions. 

Consider a finite array being fed from a single pair of terminals via some kind of harness. If we transmit from those terminals it is a conceptually simple process to obtain a far field transmit pattern Paf based on the element currents under transmitting condition. 

If we instead receive an incident signal at the same pair of terminals as above and rotate the antenna around its center we will record the receiving pattern Paf. From the law of reciprocity we know that the transmit and receiving pattern will always be identical, i.e. 

However, as also stated in the law of reciprocity, this fact does by no means imply that the currents under transmit and receiving conditions are identical. In fact, while they in some cases may be similar, they will in general be different. 

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