Microwave Frequency Detector Using a 4x4 Butler Matrix

The paper presents an analysis of a microwave interferometer with a multi-ports architecture with one input and four outputs. The tested system consisted of two main parts: a subsystem consisting of a power divider and two transmission lines of different electric length - responsible for developing two signals whose phase difference will depend on the frequency of the input signal. The second part of the tested system consisted of a six-port element a 4 x 4 Butler matrix, whose task was to develop four signals. The output amplitude depends on the phase difference of the signals fed to the inputs of this six-ports. Frequency detector tests were carried out by calculations in the MATLAB computer program in a very wide band f(g)/f(d)=4. The system response was analyzed for different combinations pair of an input ports of a six-port system and for different values of coupler coupling coefficients. During the analysis it was shown that the parameters of such an interferometer depend on which ports pair is excited as well as on the value of the coupling factor of the couplers. It is important to specify the system parameters in order to make the optimal selection of the interferometer system configuration in terms of the acceptable frequency detection error, operating bandwidth, or even the topological distribution of the ports.