Novel High Performance Feed Horns for Large Format Arrays at Millimetre and Submillimetre Wavelengths.

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The ability to rapidly map large areas of the sky to a high sensitivity is of prime importance for many scientific goals at mm and sub-mm wavelengths. The next generation of telescopes will incorporate hundreds or thousands of horns feeding ultra-sensitive detectors into focal plane array receivers. Therefore, the ability to manufacture large numbers of high quality telescope feed horns rapidly, reliably and at a manageable cost is vitally important. Traditionally, focal plane arrays of radio and submillimeter telescope receivers have employed corrugated horns to couple power form the sky to the detectors. This is because they exhibit excellent beam patterns over bandwidths of up to 50%. To give the required high performance however, these horns must have many 1/4 wavelength deep azimuthal grooves (corrugations) along their interiors. This makes them extremely difficult and expensive at increasingly smaller wavelengths. For the next generation of large format focal-plane arrays, with many hundreds or thousands of such horns, the cost of the corrugated horns alone can be a significant fraction (~50%) of the entire cost of the complete receiver. Another disadvantage of corrugated horns is that the wall needs to be thick enough to accommodate relatively deep corrugations. This makes them too heavy for key applications such as space telescopes and communication systems at microwave frequencies where the weight of only a few horns could prove to be problematic. The Oxford Astrophysics group have developed smooth-walled horns which are much easier and cheaper to fabricate than corrugated horns, in collaboration with researchers at Mahidol University, Thailand. These horns only require one or more discontinuities in the flare angle near the throat of the horn to excite the right balance of higher-order waveguide modes. We optimise the positions of these discontinuities, using a software suite that we have developed for this purpose. Our fully optimized horns show excellent beam pattern over a significant (30%) operating bandwidth. The relatively simple geometry of our horn designs allows them to be manufactured using rapid, low-cost fabrication techniques. We have developed a technique which involves directly machining the horns by using an appropriately shaped tool to drill the horns into a block of aluminum. This technique will make it possible to quickly fabricate large format arrays of horns by simply drilling repeatedly into a single plate of aluminum. We have successfully fabricated and tested individual prototype 230 GHz horns using this technique and found that they give the expected beam patterns by theory. The commercial opportunity for the high performance Oxford smooth-walled feed horns is massive and at half the price, they are likely to replace the conventional corrugated horns in many applications. The target markets would include research groups building mm and sub-mm astronomical receivers, remote earth sensing, space based satellite communications and earth based telecommunications and radar applications. In this grant application we are requesting support to develop a completely new technology which is a spin-off of academic research supported by the STFC. As a result a relatively small amount of development fund is required to bring it to the stage of commercialisation. The products includes software licensing, design according to customer specifications and a product at less then half the cost of existing technology and much faster time of delivery. Our effort of commercialisation is supported by Isis Innovation Limited, the technology transfer subsidiary company of the University of Oxford.