TABLE OF CONTENTS The hybrid splitter/combiner is a four-port fundamental building block of RF signal processing. In one popular application, hybrids are used in image-balanced mixers to obtain image rejection while down-converting signals in frequency. There are two basic types of hybrid splitter/combiner circuits: (1) quadrature, and (2) sum/difference or sigma/delta; each type has an extensive variety of microwave circuit, transformer circuit, and lumped-component circuit implementations. This section will review the ideal standard s-parameters for both hybrid types and then develop the analyses for hybrid circuit mixed-mode s-parameters.
Figure 5.19 displays the symbol of a sigma/delta hybrid and the associated s-parameters for standard and mixed-mode formats. The sigma/delta hybrid is composed of two splitter/combiner components, a 0 circuit and a 180 circuit. There are separate single-ended ports, 1 and 2, for the 0 circuit and 180 circuit. A common mixed-mode port is shared by each of the splitter/combiner circuits. The mixed-mode port is comprised of single-ended ports 3 and 4 and is defined as port 5 to differentiate it from the four single-ended ports 1 through 4. Single-ended ports 1, 2, and 3 produce the 0 response, while single-ended port, 4 gives the 180 response. Single-ended port 1 is the sum of the waves into single-ended ports 3 and 4, and single-ended port 2 gives the difference of the waves into single-ended ports 3 and 4. Ideally a differential wave applied to mixed-mode port 5 is entirely transformed to an output at single-ended port 2, and a...
