Gap Waveguides

Chris Bartram G4DGU

I don't believe gap WGs will have much application in amateur microwaves unless low-cost micromachining becomes available.

What is attractive and not currently used in any amateur designs AFAIK is 'Substrate Integrated Waveguide'. I played with this for my own nefarious purposes just before I left GW, and it isn't difficult to make work.

Essentially, it's relatively easy to design TM-mode dielectric loaded waveguide structures which can fit within double sided PCBs. These can be transmission-lines,  filters, couplers, and resonators and basically anything which you can do with conventional microstrip or waveguide. The losses are dependent on the conducting materials and the substrate. Calculation of the size of structures, unlike microstrip, isn't complicated by the consequence of the differing simultaneous propagation characteristics air and the substrate which you get with microstrip.

There is even a variant of the SIW technique called 'empty SIW' where the substrate within the structures is removed completely, and the dielectric losses are completely eliminated. That even makes it possible to make low-loss structures using FR4 as a substrate ...

Once my current unpaid employment as a house builder is completed, and I've got myself back on the air, I'll try to sit down and write something for 'Scatterpoint'.


Chris G4DGU

Ethan Waldo

Thanks for responding.  As I said copper electrodeposition seems feasible for amateurs and gets from 4um to 400um accuracy in lieu of micromachining, but is a lot slower.  I'm curious if air is the effective dielectric, do you use a dielectric constant of 1 in calculations or some very small number?

Chris Bartram G4DGU

Hello Ethan

The problem (for me) with components involving metasurfaces, such as in a a gap waveguide is that they need a different sort of approach to conventional TEM/TM/TE waveguides. Although I'm more-or-less comfortable with conventional waveguide structures, I don't feel competent to give an answer, as my involvement with metasurfaces has been rather cursory.

There is quite a literature on the subject, and it is probably worth starting a search on-line away from the amateur literature. If you can find back issues of the IEEE Microwave Theory and Techniques Society Magazine, you may well be able to find an introductory paper. I think I remember reading rapidly through one a couple of years ago. There are also a several books on metasurfaces - but be prepared for some difficult (at least for me!) maths.

Iin another life, I did have some experience of electroforming. Trom what I remember, copper requires a lot of care, and the careful selection of plating currents to get to a suitably small 'grain' size in the deposited metal. Particularly am mmWave frequencies, this will be very important in getting the lowest losses in an electroformed structure.

I hope these are useful comments.

73 Chris  G4DGU