Impedance Measurement by Means of a Broadband Circular-Polarization Coupler

This paper describes a waveguide component particularly useful as a broadband impedance-measurement instrument. The component consists of a length of circular waveguide at right angles to the broad wall of a rectangular waveguide, and coupled to it by three apertures. A probe rotated one turn in the circular waveguide will sample a field variation exactly equivalent to that in one guide wavelength of the rectangular waveguide. This condition may be maintained with high accuracy over approximately a 20-per cent bandwidth. The principle of operation of the device is discussed in the paper and design equations given. Several possible applications are described.