Magic-tee (hybrid-T) used as a continuous-wave (CW) duplexer Ports 1 and 2 are the collinear arms, port 3 is the E-plane (difference) arm, and port 4 is the H-plane (sum) arm. How should port 1, port 2, port 3 (E arm), and port 4 (H arm) be connected for CW duplex operation?

Introduction / Context:
The magic-tee (hybrid-T) is a four-port waveguide junction formed by combining an H-plane tee (sum port) and an E-plane tee (difference port). It is often used as a simple continuous-wave (CW) duplexer so that a transmitter and a receiver can share a single antenna while maintaining isolation.

Given Data / Assumptions:

• Port 4 is the H-arm (sum); port 3 is the E-arm (difference).
• Ports 1 and 2 are the collinear arms.
• Ideal, matched magic-tee behavior with correct phasing.

Concept / Approach:
Key properties: (1) Exciting the H-arm splits power equally and in phase to the collinear arms and is isolated from the E-arm. (2) Exciting the E-arm splits power equally but 180 degrees out of phase to the collinear arms and is isolated from the H-arm. To duplex CW, place the transmitter at the H-arm to feed the antenna (via one collinear arm) while isolating the receiver at the E-arm; terminate the unused collinear arm in a matched load to preserve the match and absorb the split power.

Step-by-Step Solution:

Verification / Alternative check:
The ideal S-matrix has S34 = S43 = 0 (E–H isolation). With the transmitter at the H-arm, the receiver at the E-arm sees minimal leakage in the ideal case; practical systems still add limiters and isolators to protect the receiver.

Why Other Options Are Wrong:

• B/C/D misplace the transmitter/receiver or the matched termination, breaking isolation or match.

Common Pitfalls:
Expecting zero loss—one collinear arm must be terminated, giving a 3 dB split; ignoring receiver protection in real hardware.

Final Answer:
matched load, antenna, receiver and CW transmitter