Open boundary quad ridged horn
Image of the Open boundary quad ridged horn.

The open boundary quad ridged horn is popular in EMC compliance measurements, and is often used when measuring radiation patterns of test antennas in an anechoic chamber.

Total gain 3D patterns at (a) fmin, (b) 2 x fmin, (c) 3 x fmin, (d) 5 x fmin and (e) 9 x fmin.

Although the antenna may be seen as a variation of the Quad ridged pyramidal horn, the propagating mode supported by the quad-ridged structure changes from TE (with sidewalls) to quasi-TEM when the sidewalls are removed. The operation mechanism or the antenna is therefore better understood by considering two planar Vivaldi antennas placed orthogonally to each other with co-located feed points.

A major advantage of removing the sidewalls is that the on-axis gain dips prevalent in classic quad-ridged horns with sidewalls are eliminated - though the overall gain is generally reduced.

The designed antenna achieves a VSWR below 3:1 over a 9:1 bandwidth with a relatively stable on-axis gain, especially considering its compact nature. At the upper end of the band the pattern shape does degrade to some extent. The gain typically varies between approximately 8 and 14 dBi across the 9:1 band.

The antenna may be divided into two distinct sections — a coaxial-to-ridged-waveguide transition as well as a flared ridge section. The feed section aims at proving a good return loss for both vertical and horizontal polarization.

Typical VSWR behaviour versus frequency.