A simple IQ-regeneration technique for six-port communication receivers

Abstract

Modern radio terminals for high data rate communication require wideband receivers. The well-known receiver architectures, such as zero-IF-receivers usually require very accurate component matching. In order to relax these requirements digital techniques are used on one side. On the other side alternative receiver architectures such as the six-port are investigated. The six-port 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 communication receivers have been built upon the six-port principle. In order to generate the required IQ-signal from the output signals of a six-port, knowledge of the six-port structure and/or of the signal statistics must be available. The first can be obtained by means of calibration procedures, while the latter can be used in blind techniques. Classical calibration procedures employ probes that are connected to the six-port. This is not applicable in communication receivers. Alternatively, a method is presented that uses the incoming signal as the calibration-driving probe and moreover uses the fact that the I-component and the Q-component of the signal are uncorrelated in most practical scenarios.