MILLIMETER WAVE
INSTRUMENTATION LAB
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Last Modified: Wednesday, 10-July-01 10:05 AM EDT
This material is based on work supported by the National Science Foundation under Grants AST-9532046 and AST-9725951.
Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of the National Science Foundation.
Feed Horns
- Square feed horns are used, each with a 25mm aperture. Each horn has one pair of corrugated walls (the other pair smooth), which creates patterns that are symmetric with low side-lobes. The aperture field is cos((x)cos((y).
- Each horn is in two pieces with a 0.1mm gap. The aperture end of the horn is at room temperature and the waveguide end is at 20K. The sections are aligned with thermal insulators that greatly reduce the conducted and radiated heat loads.
- The cold section is machined out of aluminum as a split block, while the warm section (also aluminum) is comprised of four parts with long grooved parts common to four horns.
Detail of grooves and complete horn assembly
- Beam spacing is 2x HPBW at midband.
- The transition to the square grooved waveguide is similar to that in circular guide, but the match is not as good.
- The horns are very short (70mm), and aperture phase corrected with a double cylindrical lens that also serves as a vacuum window/corrector lens. This lens rests on top of the horn aperture assemblage.
Beam contour maps at three frequencies (2 dB interval) and aperture end of horn assembly
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