WR-1150 or WR-1000 wg to coax adapter?

[biff44]

Anyone out there have approximate dimensions for a WR-1150 or WR-1000 waveguide to coax adapter? My empirical attempts have been coming out with pretty poor VSWRs!

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[Higgler]

wr1150 is 0.64-0.96 ghz,
11.5"x5.75" inside dimensions tolerance 0.015"
11.75"x6" outside dimensions tolerance 0.015"
0.125" wall thickness.

wr975 or wr1500 are my other two items around the wr1150.

 

[biff44]

Sorry for being unclear. I mean for those various rectangular waveguides, for a wg to coax transition, what are the:
1) Backshort position
2) Efield proble length
3) Efield probe diameter
4) any tuning screw locations

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[biff44]

I am hoping someone has these various wg to coax transitions, and will just take out a vernier and tell me the measured dimensions.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[Higgler]

I've never seen one at that freq.

I expect you may have done this already, so at the risk of seeming obvious, I'd expect you could take a standard waveguide to coax transition like this one

http://www.pasternack.com/Pdf/PE9825.pdf

which gives the distance from the coax to the back wall and frequency scale it.
Then make the probe flare outward at various angles and add tuning screws or two at the bottom? If you've tried to use a straight probe, I'd guess a flared probe would be better. You could make the flare an X shaped brass shim stock soldered to the type N probe center conductor.

I have a feeling you've tried that. So maybe I'm asking what you've tried already out of curiousity.

kch

 

[biff44]

Hey thanks. I did not see that drawing yet. that certainly gives me the backshort position for wr430. I assume just linearly scaling that for 1/f for the 915 MHz would give me the lower frequency back short position. yes/no?

One thing that I noticed in the wg-coax transitions I have lying around the lab is that they use a larger diameter slug at the end of the efield probe. I would assume that is to better match the vswr. Does the diameter of that slug increase with linear to the waveguide width dimension?

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[Higgler]

One way to fine tune your result is to make a movable back short position for tuning. I thought 1/4 wave electrical distance is standard, but it's probably slightly off this.

I'm not used to seeing a large diam. stub, usually 3 tuning screws on the bottom, although some have none.

If I were making this, I'd get the waveguide, make a tunable short in the back, buy a type N-f to N-f bulkhead adapter. Stick it in the waveguide with a probe pin attached to the inside N-f, and add a copper or silver metal tape triangle to the probe and shape that. For a more permanent pin, you could use either a thin copper clad circuit card (FR4) or shim stock and solder it onto the probe. It might be better to have a real probe machined though.

Seal the probe in the N-f. Then maybe add tuning screws for fine tune on the bottom under the probe to tweak the final assy. You could add a large tuning screw to that formerly movable back wall too for a little extra control.

This all depends on power requirements of course.

If you're going to make alot of these, hire a consultant to fine tune your design and avoid tuning screws.

We use Jim Reed at optimal designs in Austin Texas to fine tune your design on CST and skip all the tuning screws and movable walls. Probably cost $5K ish. We use Jim alot, good Engineer and I wish he'd start paying me for recommending him.

kch