The six-port as a communications receiver

Configurable radio terminals require receivers with wide-band capabilities in order to support as many services as possible at most different carrier frequencies. Conventional well-known receiver architectures employing active circuitry are limited in this respect. Therefore, alternative architectures are investigated, such as the six-port, which has been introduced as a very flexible and elegant means for microwave measurements in the 1960s and 1970s. Later on, it has been used in radar applications. It was not until recently that communications receivers have been built upon the six-port principle. However, in all publications, there is always a certain mystic about the six-port. It has even been described as a "black box". In order to help paving the way for a wider application of the six-port technology, this paper describes the basic six-port theory and sets it into relation with the conventional receiver architectures such as the homodyne and heterodyne receiver. Finally, the advantages and possible applications of receivers based on the six-port technology are discussed.