Compound box pyramidal horn antenna

Image of the Compound box pyramidal horn antenna.

The classical pyramidal horn antenna supports a single propagating mode (TE10) that generates a field distribution (magnitude) across the mouth or aperture of the horn similar to the profile shown in the figure below. The radiating aperture of the horn is therefore only partially exploited, resulting in aperture efficiency in the order of 65% relative to an ideal aperture excitation.

One way to improve the efficiency of the aperture excitation of a horn antenna is to use a structure that supports multiple modes. The compound box horn is one simple modification of the pyramidal horn antenna that includes a step and a short un-flared box section that couples some of the energy in the TE10 mode to the TE30 mode. The length of the box is designed such that the TE10 and TE30 propagating mode components reach the waveguide-to-flare transition of the horn 180° out-of-phase, resulting in a more even aperture distribution and an improvement in aperture efficiency (a typical box-horn has an aperture efficiency around 82% relative to an ideal aperture excitation).

Antenna Magus allows the compound box horn to be designed for gain or beamwidth at a specific operating frequency. The feed waveguide dimensions are chosen based on the operating frequency and can easily be tweaked to specific standard waveguide sizes after design with minimal effect on the radiation performance of the antenna.

The comparative radiation patterns of a pyramidal and compound box horn with the same gain (note the smaller physical aperture size of the compound box horn.)
The comparative field magnitude across the waveguide section at the start of the horn flare in a pyramidal and a compound box horn.