Directional coupler is a four port component with directional transmission characteristics. It consists of two pairs of transmission systems which are connected by a coupling device. Firstly, the performance index of directional coupler is introduced. Then the double waveguide directional coupler, double branch directional coupler and parallel coupled microstrip directional coupler.

1). Performance index of directional coupler

The directional coupler is four port network port "for input port" the "direct output port" and "coupling output port", the "end of the isolation, and the scattering matrix for [S]. The performance index of the directional coupler is as follows: the coupling degree, the isolation, the orientation, the input Bobbi and the working bandwidth. The following are introduced.

2). Isolation degree

The output power of the P4 input "input power P1 and isolation" 4 "end is defined as the ratio of isolation, denoted as I.

3. Orientation degree

The output power of P4 coupling end "the" output power of P3 and isolation "the end" is defined as the degree of orientation, denoted as D.

4. Input VSWR

In the definition of "port Bobbi the second and the third and fourth" are connected to the input port matching the load when the "input in Bobbi, denoted by P.

The. Operating bandwidth

The working bandwidth is the frequency range that the C, I, D, directional coupler parameter P. can satisfy the requirements of the.