A Magic Tee junction is formed by attaching two simple waveguides one parallel and the other series, to a rectangular waveguide which already has two ports. This is also called an E-H Plane Tee junction or Hybrid or 3dB coupler.
The arms of rectangular waveguides make two ports called collinear ports i.e., Port 1 and Port 2, while the Port 3 is called as H-Arm or Sum port or Parallel port. Port 4 is called as E-Arm or Difference port or Series port.
The connections are made by the side arms to the bi-directional waveguide to form both the parallel and serial ports. These connections can be indicated like this.
A null detector is connected to E-Arm port while the Microwave source is connected to H-Arm port. The collinear ports together with these ports make a bridge and the impedance measurement is done by balancing the bridge.
The duplexer is a circuit which works as both the transmitter and the receiver, using a single antenna for both the purposes.
Port 1 and 2 are used as receiver and transmitter where they are isolated and hence will not interfere. An antenna is connected to E-Arm port. A matched load is connected to H-Arm port, which provides no reflections. Now there exists transmission or reception without any problem.
E-Arm port is connected to the antenna and the H-Arm port is connected to the local oscillator. Port 2 has matched load which has no reflections and port 1 has the mixer circuit, which gets half of the signal power and half of the oscillator power to produce IF frequency.