Figure 1: H-type T- junction with field line distribution and equivalent circuit diagram
When it is required to combine two or more signals(or split a signal into two or more parts) in waveguide system, different types of junctions may be used. The “T–Junction” is the most simple of the commonly used waveguide junctions. T–junctions are divided into two basic types, the E–TYPE and the H–TYPE.
An H-type T-junction is illustrated in the beside figure. It is called an H-type T-junction because all three arms lies in plane of Magnetic field, which divides among the arms. This is current or parallel junction. The E-field is fed into arm A and in-phase outputs are obtained from the B and C arms. The reverse is also true.
Figure 2: E-type T- junction with field line distribution and equivalent circuit diagram
This junction is called an E- type T junction because the junction arm extends from the main waveguide in the same direction as the E-field in the waveguide. The outputs will be 180° out of phase with each other.
A simplified version of the magic-T-hybrid junction is shown in the figure 4. The magic-T junction can be described as a dual electromagnetic plane type of T-junction. It is a combination of the H-type and E-type T-junction therefore. It has four arms. Arm B and arm C are referred as collinear arms or side arms. Arm D is also called “difference port”, and arm A is called “sum port”. The most common applications of this type of junction are for example as the mixer section for microwave radar receivers or as a part of a measurement system.
If a signal is fed into the E-plane arm (arm A) of the magic-T, it will divide into two out-of-phase components (arm B and C). The signal entering the E-arm will not enter the H-plane arm (arm D) because of the zero potential existing at the entrance of the H-plane arm. The potential must be zero at this point to satisfy the boundary conditions of the E-plane arm.
Normally a magic-T needs an impedance matching (shown in the figure as matching screws).
Figure 3: Magic-T Hybrid (Schematic)
The scattering matrix for a magic tee is: