A Corrugated horn for 30 GHz An asymmetric lens for shaped beam
The lens was shaped to achieve the required two different beamwidths. It was machined from a low cost polymer billet. (You'll see that white plastic is not very photogenic !) You could try this with a reflector antenna too, but would probably struggle to illuminate it with a well behaved primary feed which would need to sit in front of the reflector aperture. With the lens the reverse applies and so the feed does not get in the way. On these topics I contributed a chapter to this text book published in 2013:
optimizer window CAD modelTaking this starting point, I experimented with different horn lengths, widths, and ridge flare parameters until the specification could be met while still mounting the antenna in its intended host vehicle. The final design was quite novel and only slightly resembled the example shown. Sometimes, lack of familiarity with established principles allows one to approach a problem with an open mind, and so arrive at an unusual solution.
Quad ridged horn, typical radiation patternFeed region.The feed region is also very critical. Here, a coaxial cable spans opposite ridges. The ridge chamfer, cable dimensions and location along the z-axis, and the proximity of the back short (waveguide end) all have an influence, which of course changes with frequency. Everything interacts with everything else. The two polarisations each have a dedicated cable feed, but these of course cannot be exactly co-located.
coaxial probes in feed region
Following this electrical design exercise, I was asked to produce mechanical models which would allow the client to manufacture a prototype according to a set of drawings. Later, measurements of both input match and radiation patterns confirmed the validity of the design.Simulated VSWR
The fabricated quad ridged horn.
The above horn was developed for a UHF airborne radar. I can adapt the design to most other radio frequencies and bandwidths. Here's a link to simulation results for another horn for 5-18 GHz (it's from my old site).