The directional coupler can be considered as a four-port network, whose characteristics can be expressed by scattering matrix "s", i.e. The values of the reflection coefficients sii (I=1, 2, 3, 4) of each port are very small (the ideal value is 0), which indicates the matching situation of each port, and the attenuation coefficient s13=s31=s24=s42 value is very small (ideal value is 0), which indicates isolation; S14=S41=S23=S32 is the coupling coefficient,
The value is designed to suit your needs. The main technical indexes of directional coupling are coupling degree C (db), directional D (DB) and working frequency band, among which c=-20lg|s14|
The scattering matrix of the ideal directional coupler is
Two output signals have a phase difference of 90°. The working frequency bands of the single directional coupler coupled by the two-hole or double branch are narrow. Multi-section directional coupler (Multiple-node cascade) with porous or multiple-branch feeder coupling structure can broaden the working frequency by means of comprehensive design method.