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Microwave meets milling

Submitter: Johan Pragt
Description: In early 2011, the mechanical prototype group of ASTRON received a request from Chalmers University (Sweden) to produce two special waveguide filters. These consist of a sort of small aluminum box with a specific configuration of long square pins inside. The pins are 1 mm square (paperclip size) and 25 mm long.

Stringent tolerances on the position accuracy of the long pins made it a challenge to manufacture, and to keep the pins straight in the process. We used 90000 rpm (dentist type) milling equipment with diamond tooling. The main body of the filter, with its pins, is made out of a massive block of aluminum. We succeeded, and the pins were very nicely positioned within 10 micron. We had to check this by optical means: a mechanical measurement could deform the product.

To see a short film about the High speed milling of a Gap Waveguide at ASTRON: http://www.youtube.com/watch?v=twVL2L1j6cE.

Chalmers then measured the performance of the filters, and this corresponded nicely with simulations. An IEEE paper will be published called “Narrow-Band Microwave Filter Using High Q Groove Gap Waveguide Resonators without Sidewalls”, authors Ashraf Uz Zaman, Per-Simon Kildal and Ahmed Kishk. This paper has the following abstract:

"The paper presents a new type of narrow-band filter with good electrical performance and manufacturing flexibility, based on the newly introduced groove-gap waveguide technology. The designed 3rd order and 5th order filters operate at Ku band with 1% fractional bandwidth. These filter structures are manufactured with an allowable gap between two metal blocks, in such a way that there is neither a requirement for electrical contact nor for alignment between the blocks. This is a major manufacturing advantage compared to normal rectangular waveguide filters. The measured results of the manufactured filters show reasonably good agreement with the full-wave simulated results, without any tuning or adjustments."
Copyright: Chalmers (Gothenburg, SWEDEN), ASTRON (Dwingeloo, Netherlands)
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