16+16 Slotted Waveguide...

Dear reader,

For a while now I'm 'playing' with a slotted waveguide design for use as an Wifi (2.440 GHz) antenna.

I've calculated, checked and recalculated the design with a lot i could find on the internet. Lots of reading was done. There are a lot of designs readily available, however I find it a lot more interesting calculating the design myself.

Designs I found are fairly basic and most of the time have square slots equaly alternating from the centerline. I found out that the holes are dipols, so I figured perharps rounded slots are better. Also the use of a tapered centerline ofset for a the slots in a slotted waveguide is supposed to give better gain. Even to add wings on the side of the waveguide to get a more evenly distributed gain.

I have one 'problem' stil; The placement of the feed into the waveguide. in some designs it is located off center to give better 50 Ohm impedance, or so is said. Can anyone eleborate on this?

The antenna virtuale has taken shape as a 3D drawing in AutoCAD and recently I have HFSS at my disposal.

I allready successfully made a section of waveguide with one short end and one open end, no feed, just added waveport in HFSS. With freq of 2.440 GHz nice E-fields show up in the waveguide.

The next step is adding holes, perhaps use the AutoCAD 3D drawing I allready made, and a feed. **broken link removed** for the pdf destilled from the AutoCAD design. And **broken link removed** for the 3D view.

Perhaps somebody on this forum has an example file of a (slotted) waveguide so I can learn from it. Especially radiation via slots and the attachment of a coax feed into a waveguide.

My goal is to be able to experiment in HFSS with the waveguide I virtuale shaped as shown in the pdf.

Hope this forum can help getting my experiment on track!

Regards,

Frogger

Virtual waveguide in HFSS...

I've created a waveguide with this site as example.

3D Model:


Detail 1:

Coax HDF400 is used, direct into the waveguide. The feed is 30.7mm long.

Detail2:

Feed close-up

3D gain plot

The gain is what I would expect. Max 13,05 + 2,15 = 15,2 dBi

VSWR plot

VSWR seems to be a problem. This is probably my bad, but I don't have a clue what to change en HFSS. The antenna is a real life axample, but HFSS says the VSWR is bad.

# Can anyone help me by reviewing the model? .hfss file is attached.

# I also want to get an idea about the impedance and how to measure this in HFSS.

Regards,

Frogger

I'm having the same problem but I'm using CST. Did you managed to solve this?

Not yet been able to solve this problem... Also still not had the guts to just build the antenna and check.

Also I have no experience with 3D EM by CST, sorry

Regards

Hello there frogger, the return loss (vswr or s11) is definetly a problem. You'll want a return loss better than 20dB or less than a 1.2 VSWR. To get this I suggest you divided your model into two parts. The first part being the waveguide with the slots and the second part being the transition from the coax to the waveguide.

Add a wavegport at one end of the waveguide and a short at the other. Then you want to parameterized the size and offset of the slots in HFSS. You can set goals in the optimizer to achieve a good return loss and let HFSS do your work for you. Be sure to check the radiation pattern to make sure the profile looks good. The gain will be dependent upon the number of slots you decided to throw in there.

Next would be too model the transition without the slots. Model your coax then waveguide (make sure the waveguide is the same size as the one you optimized for the slots). Put a short at the end of the waveguide close to where the coax extends into the waveguide. At the other end add a waveport. Then you'll want to parameterize the length of the center conductor and its location within the waveguide. Once again set the optimizer to achieve a good return loss.

After you have achieved a good return loss over your bandwidth for boths designs, it'll be time to merged them together. There will still be some fine tuning to do, for example you can try to optimize the distance of the short circuit to the last slot or the distance from the other short circuit to the center conductor of the coax, etc. Don't forget to apply the appropriate radiation boundaries.

Good luck with your design.

Thanks YoungEng,

I'll certainly work with your comments and post accordingly!

I'll hope to get the slotted waveguide theory down and more importantly get a very good working waveguide...

Can you also comment on the AutoCAD drawings I made (and attached) in earlier posts?

Regards,

Frogger

Hi Frogger, unfortunately I don't know much about AutoCAD so I can't help you much there. Perhaps you already know this but I forgot to mention in my last post that the lengths of the slots should be about half a wavelength and the seperation between adjacent slots should be about half a guide wavelength. Equations for a the guide wavelength can be found in any microwave textbook.

Keep me updated with your progress, I'm interested to see how your project is going.

Later

im doing slotted waveguide..i have seen the post where u told that divide the design in to 2parts.im doing the same thing .1st is that waveport assigned at one end and short other end.but return loss os -1 to -2.
is there any condition applied .radiation boundary ..i applied it but there is no progress..im trying it in many ways,can u help me.