Pin-fed single choke horn antenna
Image of the Pin-fed single choke horn antenna.

The pin-fed single choke horn antenna is a slight variation on the pin-fed circular waveguide antenna (Cantenna) already released in Antenna Magus 2.1. A single quarter-wavelength choke is introduced at the open end of the waveguide which will not only increase the gain, but will also decrease the side- and backlobes. A backlobe level reduction of more than 15 dB has been seen through the addition of a single choke.

The circular waveguide is designed to operate between the fundamental TE11 and next TM01 propagating circular waveguide mode. The feed-pin excites the TE11 mode, forming a coaxial-to-circular-waveguide transition. The distance from the waveguide back wall is used to control the input impedance.

The addition of a single quarter-wavelength choke at the open end of the waveguide supresses the current distribution on the outside of the circular waveguide walls which reduces the front/back ratio, sidelobes and improves the axial symmetry of the radiation pattern.

The design below is for 50 Ohm. A comparison between this device and the Cantenna shows the significant reducing in front/back ratio by the addition of this basic choke.

Typical reflection coefficient versus frequency
Typical total gain radiation pattern at the centre frequency
Gain pattern comparison between the antenna designed here and the Cantenna