|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 center frequency|
|Gain pattern comparison between the antenna designed here and the Cantenna|