What is a Magic Tee?

A Magic Tee or Hybrid Tee is a 4 port waveguide tee that is a combination of an E-Plane and H-Plane Waveguide Tee.

A magic tee has four ports:

• Port 1 - Co-linear
• Port 2 - Co-linear
• Port 3 - Difference Port
• Port 4 - Sum Port

Operation of a Magic Tee:

Case 1: When two signals of equal magnitude are fed from port 1 and 2, we get a zero at port 3 and the sum of the two signals at port 4.

Case 2: When a signal is fed through port 4, it gets divided equally between port 1 & 2 and both the outputs are in phase. No output comes from port 3.

Case 3: When a signal is fed through port 3, we get an output of equal magnitude but opposite phase at port 1 & 2 (the signals are 180 degrees out of phase). Output at port 4 is zero.

A magic tee is ideally lossless. But the biggest disadvantage of magic tee is that reflections arise within it due to impedance mismatches, which causes some level of power loss. These reflections can be minimized by optimizing matching.

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A magic-tee, or hybrid tee, is a 4-port waveguide structure that behaves as an electric field and magnetic field 3dB coupler, and is in fact, a combination of E-plane and H-plane tees. The magic-tee can be used as a power combiner or divider, depending on the needs of the application. The H-plane port and E-plane ports must be matched for a magic-tee to function properly, and hence are only effective over a select range of frequencies. If properly constructed, a signal injected into the H-plane port will be split equally into the two colinear ports and remain in phase. A signal injected into the E-plane port will also be equally split into the two colinear ports, but will be 180 degrees out of phase.

Interestingly, and possibly the justification for the “magic” in the name, the two colinear ports are also matched and isolated from each other. Though the quality of the matching networks in the E-plane and H-plane ports dictate the quality of the isolation and the frequency over which the colinear ports are isolated. The electric field of the dominant mode of each port is perpendicular to the long wall of the waveguide structure, enabling orthogonal polarization of the E-plane and H-plane ports.