Power of reflected waves of a multi-port antenna apparatus is measured by connecting a circulator between the respective output of the multi-output feeding network and the multi-port antenna. Each circulator has a plurality of ports where the output signal from the network is communicated to a first port of through the circulator and from the second port of the circulator to the respective port of the multi-port antenna and such that the reflected waves from the respective port of the multi-port antenna are communicated back to the second port of the circulator and through the circulator to a third port of the circulator and measuring the reflected waves from a selected one of the ports of the multi-port antenna by connecting the third port of the respective circulator to a vector network analyzer while connecting each of the third ports of the remaining circulators to a standard matching load.

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