3D Printed 2.25 Ghz Microwave RADAR horn antenna

[Tech2025]

So I printed this antenna with some conductive filament , however the microwaves seems to be going between the layers of the plastic. I surrounded it with Aluminum and still leaking, what can I do to fix it? Can conductive silver paint work?

 

[berkeman]

So I printed this antenna with some conductive filament , however the microwaves seems to be going between the layers of the plastic. I surrounded it with Aluminum and still leaking, what can I do to fix it? Can conductive silver paint work?

What does your RF feedline look like? What is the 2.25GHz source? What power level are you trying to run? What band is this for?

I'm not able to see how you form the edges of the horn, but all of the conducting material needs to make good electrical contact. Did you 3-D print the conductor too, or just the plastic horn piece? What kind of structure is that -- I'm not used to seeing a thick layer of plastic inside a horn antenna (but I'm not a microwave antenna expert)...

 

[Tech2025]

What does your RF feedline look like? What is the 2.25GHz source? What power level are you trying to run? What band is this for?

I'm not able to see how you form the edges of the horn, but all of the conducting material needs to make good electrical contact. Did you 3-D print the conductor too, or just the plastic horn piece? What kind of structure is that -- I'm not used to seeing a thick layer of plastic inside a horn antenna (but I'm not a microwave antenna expert)...

What does your RF feedline look like? What is the 2.25GHz source? What power level are you trying to run? What band is this for?

I'm not able to see how you form the edges of the horn, but all of the conducting material needs to make good electrical contact. Did you 3-D print the conductor too, or just the plastic horn piece? What kind of structure is that -- I'm not used to seeing a thick layer of plastic inside a horn antenna (but I'm not a microwave antenna expert)...

This is S-Band, less than 1.5 W. The thick walls were meant to try to prevent microwave from leaking , which as you can see did not work.

 

[berkeman]

Is this a copy of a known design? Can you provide a link? And how are you coupling your coax feedline to the horn?

 

[Tech2025]

Is this a copy of a known design? Can you provide a link? And how are you coupling your coax feedline to the horn?

There is no coax feedline as this is for an electronic transmitter using gunn diodes. I generated the horn measurements from a tool that used to be on this website : http://67.225.133.110/cgi-sys/defaultwebpage.cgi

 

[berkeman]

I generated the horn measurements from a tool that used to be on this website : http://67.225.133.110/cgi-sys/defaultwebpage.cgi

Yeah, as you imply, that page is no longer working.

I see a few issues:

• I don't understand how the horn would work with such a thick dielectric structure inside the horn. It seems like this would present a discontinuity to the propagation modes inside of the conducting horn, but as I say, I'm not a microwave expert
• It looks like there is some conducting tape on the outside of the dielectric horn -- I don't understand how that conducting layer was 3-D printed. The horn is resting on a roll of copper tape, so maybe you tried to make it work better by putting conductive copper tape on the outside of the horn? If so, all seams need to be soldered to ensure good conductivity at the seams. Just overlapping the tape (even with "conductive adhesive" copper tape) does not give good continuity.
• If only the dielectric horn is 3-D printed, and you are trying to use copper tape to make the conducting part of the horn, I'd recommend printing a much thinner dielectric horn shape, and cutting the tape into pieces that you can stick on the horn's outside so that the edges of the tape pieces touch. Then solder the edges with a continuous bead of solder run along those butting edges.
• An alternate construction that might work better is to use Shim Brass cut into the pieces to form the sides and back of the horn, and run solder beads along all of the edges to give nice smooth conduction.

 

[Tech2025]

Yeah, as you imply, that page is no longer working.

I see a few issues:

• I don't understand how the horn would work with such a thick dielectric structure inside the horn. It seems like this would present a discontinuity to the propagation modes inside of the conducting horn, but as I say, I'm not a microwave expert
• It looks like there is some conducting tape on the outside of the dielectric horn -- I don't understand how that conducting layer was 3-D printed. The horn is resting on a roll of copper tape, so maybe you tried to make it work better by putting conductive copper tape on the outside of the horn? If so, all seams need to be soldered to ensure good conductivity at the seams. Just overlapping the tape (even with "conductive adhesive" copper tape) does not give good continuity.
• If only the dielectric horn is 3-D printed, and you are trying to use copper tape to make the conducting part of the horn, I'd recommend printing a much thinner dielectric horn shape, and cutting the tape into pieces that you can stick on the horn's outside so that the edges of the tape pieces touch. Then solder the edges with a continuous bead of solder run along those butting edges.
• An alternate construction that might work better is to use Shim Brass cut into the pieces to form the sides and back of the horn, and run solder beads along all of the edges to give nice smooth conduction.

Yeah I put the tape after to try to fix it. I will try brass with solder and thinner walls and let you know how it goes. Thanks.

 

[berkeman]

This is S-Band, less than 1.5 W. The thick walls were meant to try to prevent microwave from leaking

Are you transmitting in the ISM band inside the S band? Even so, 1.5W is high for the ISM band. What are you using for measuring your link budget? Do you have a 2nd horn for receiving, and some attenuation in the way? Which sub-band of the S band are you looking at transmitting in, and do you have a license for it?

https://en.wikipedia.org/wiki/S_band

 

[Tech2025]

Are you transmitting in the ISM band inside the S band? Even so, 1.5W is high for the ISM band. What are you using for measuring your link budget? Do you have a 2nd horn for receiving, and some attenuation in the way? Which sub-band of the S band are you looking at transmitting in, and do you have a license for it?

https://en.wikipedia.org/wiki/S_band

I do not have a license but I am doing this in a controlled environment. I have not detected microwaves outside of the room I am testing in.,

 

[Paul Colby]

Your conductive filament may be quite lossy at 2GHz. I would recommend making the walls thin as possible and rely on the coper tape. Also the horn has a very shallow feed section. This section should look like 1/4 (guide) wavelength at the operating frequency. Also leakage may just be diffraction.

You may want to show some details inside the feed section.

 

[Tech2025]

Your conductive filament may be quite lossy at 2GHz. I would recommend making the walls thin as possible and rely on the coper tape. Also the horn has a very shallow feed section. This section should look like 1/4 (guide) wavelength at the operating frequency. Also leakage may just be diffraction.

You may want to show some details inside the feed section.

I lined the inside and outside of the horn with Microwave paint , seems to work well enough for my use,