Magic-T Applications - E-H Tuner , Microwave Mixer

The combination of E-plane tee and H-plane tee is referred as magic-T or hybrid tee.The magic-T has following features when all the four ports are terminated with matched load.

•  Two equal amplitude waves fed at port 1 and port 2, produce zero at port 3(E-arm) and sum of port 1 and port 2 at port 4(H-arm).

•  A wave input at port-3 divides equally at port 1 and port-2,but opposite in phase with no coupling at port-4(H-arm)

•  A wave input at port-4 divides equally at port-1 and port-2 in phase with no coupling to port-3(E-arm)

•  A wave fed into one port-1 or port-2 will not appear in the other port-2 or port-1. Hence these two collinear ports 1 and 2 are isolated to each other.

magic T

The magic-T has many applications such as E-H tuner for impedance matching and balanced mixer in microwave receiver to balance out LO noise at the input of IF amplifier. Magic-T is also used in power combiner and duplexer circuit.

In a E-H tuner,both of the E and H arms are terminated by movable shorts which act as stubs. E-arm shorts are referred as E-plane stub and H-arm shorts are referred as H-plane stub. The position of these shorts can be adjusted to match broad range of load impedance to reduce VSWR of the waveguide system.

In a balanced mixer configuration, an incoming signal is fed to E-arm and LO signal is fed to H-arm. These two signals enter the collinear arms and beat with crystal diodes placed here to produce IF signal.


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