Abstract:
It is well known that quad-ridged horn antennas in general have impedance and radiation
characteristics that are significantly worse than that of their double-ridged counterparts.
Normally a voltage standing wave ratio (VSWR) of 3 over the operational bandwidth is
used for the design specification of quad-ridged horn antennas. The bandwidth of operation
is severely restricted due to the excitation of higher order modes in the co-axial to
waveguide transition of the antenna. The higher order modes cause a break-up in the
radiation pattern of the antenna and large dips in the boresight gain.
The performance of the quad-ridged horn antenna with pyramidal sidewalls is improved by
separating the antenna into the transition and flared horn sections, and optimizing these
sections individually. It is shown that a transition section with a pyramidal cavity and
steps, and a flared horn section with an exponential profile with a circular segment for the
ridges deliver the best performance. These configurations for the transition and flared horn
sections are combined in the complete antenna. The optimized antenna has a 12.5:1
operational bandwidth with improved performance in terms of the VSWR, the coupling
between the ports and the boresight gain. A prototype of this antenna is manufactured.
Good agreement between the measured and simulated performance is achieved.
