An Orthogonal Mode Transformer (OMT) is a device that separates two differently polarized waves in a circular waveguide or square waveguide system for dual-linear polarization separation or synthesis. Together with the antenna, it can form a bilinear polarized antenna. Together with a circular polarizer and antenna, a dual circularly polarized antenna can be formed.

The OMT is a device with three ports, which are a through input port, a side wall coupling port and a common port. The common port of the circular waveguide OMT is a circular waveguide port, and the port directly connected to it is also a circular waveguide port. It is usually connected with a standard rectangular waveguide after adding a rectangular-circle transition waveguide. The output port in the direction perpendicular to the side wall is directly designed as a standard rectangular waveguide port, or the curved waveguide is output in parallel with the main waveguide. The polarization directions of the through-in ports and the sidewall-coupled ports are orthogonal.

There is also a T-shaped OMT structure, which is popular due to its small size and the symmetry of the dual-polarized coupling arms. The ports of the two polarizations of the OMT are perpendicular to the common port.

Common types are: circular waveguide orthogonal mode converter, square waveguide orthogonal mode converter, double-sided coupling circular waveguide orthogonal mode converter, broadband circular waveguide orthogonal mode converter, etc.

Due to its high efficiency and low cost, dual-polarized antennas are widely used in satellite communications, radio astronomy, electronic countermeasures and other fields. The dual-polarization technology first evolved from the frequency reuse technology in the communication system, and OMT is often used to solve the frequency reuse problem.

The two fundamental mode ports of the OMT are used as the receiving end and the transmitting end of the signal respectively, which can realize the function of a duplexer. On the same frequency, the OMT uses two channels with different polarization modes and isolated from each other, which increases the number of communication channels. and system capacity.