The directional coupler is a directional power coupling
(distribution) element. It is a four-port component, usually
composed of two transmission lines called a straight line (main
line) and a coupled line (secondary line). A part (or all) of the
power of the through line is coupled to the coupled line through a
certain coupling mechanism (such as a gap, hole, coupling line
segment, etc.) between the through line and the coupled line, and
the power is required to be transmitted to only one of the coupled
lines. Output port, the other port has no power output. If the
propagation direction of the wave in the through line becomes
opposite to the original direction, the output port of the power in
the coupled line and the port without power output will also change
accordingly, that is, the coupling (distribution) of power is
directional , So called directional coupler (directional coupler).
As an important part of many microwave circuits, directional
couplers are widely used in modern electronic systems. It can be
used to provide sampling power for temperature compensation and
amplitude control circuits, and can complete power distribution and
synthesis in a wide frequency range; in a balanced amplifier, it
helps to obtain a good input and output voltage standing wave ratio
(VSWR) ; In balanced mixers and microwave equipment (for example,
network analyzers), it can be used to sample incident and reflected
signals; in mobile communications, use
The 90° bridge coupler can determine the phase error of the π/4
phase shift keying (QPSK) transmitter. The coupler is matched to
the characteristic impedance at all four ports, which makes it easy
to be embedded in other circuits or subsystems. By adopting
different coupling structures, coupling media and coupling
mechanisms, directional couplers suitable for different
requirements of various microwave systems can be designed.
