Multiport power amplifiers for mobile-radio systems using microstrip Butler matrices

A multiport power amplifier (MPA) is an amplifying system consisting of two networks, a power divider and a combiner, connected by an array of identical amplifiers. In this case both the divider and the combiner are Butler matrices (designed to operate over the 1.7-1.9 GHz band). A signal entering one port of the input matrix is divided in equal parts, phased, and amplified by all the amplifiers and then recombined by the combining matrix at the output port corresponding to that particular input port. In this way the failure of one of the amplifiers no longer causes the total loss of a beam or carrier. Furthermore, for coping with traffic variations it´s possible to properly apportion the available RF power among the various beams simply making small adjustments of the low level input signals. Finally, being a signal divided into equal parts by the input matrix, lower power amplifiers operating in linear region are required and intermodulation products can be kept very low. The paper describes the design and implementation of various order Butler matrices and MPAs with thick film microstrip technology for cellular DCS 1800 base stations.<>