2.4 ghz point detection

[Braeden Hamson]

I know little about antennas, this is my first foray into RF. I'm trying to find a good antenna that works with 2.4 ghz (wifi, bluetooth and such) I'd like it to have a very very narrow "field of view." Basically I want to be able to take point measurements of 2.5 ghz intensity. I don't know if a 1 degree or less "FOV" is possible or not but that's what I'm hoping for. I don't need to receive any data on this antenna, I just want to know the intensity at that point. I also want minimal. interference from the area outside of its "FOV." I've looked at Yagi-Uda antennas and they seem valuable to me but I'm not sure.

 

[davenn]

I know little about antennas, this is my first foray into RF. I'm trying to find a good antenna that works with 2.4 ghz (wifi, bluetooth and such) I'd like it to have a very very narrow "field of view." Basically I want to be able to take point measurements of 2.5 ghz intensity. I don't know if a 1 degree or less "FOV" is possible or not but that's what I'm hoping for.

1 deg, no, 15 - 20 deg would be the minimum. 20 - 40 deg would be the norm

 

[Braeden Hamson]

Why is 15-20 deg the minimum? Also, I don't know much about antennas, but I have a decent understanding of light and optics. wifi and other 2.4 ghz signals are just photons. Let's consider visible light for right now. If I have a long tube with a photoresistor at the base and an opening at the opposite end. If I coated the inside with a material that totally absorbed light, lets say vantablack then the only light reaching the photoresistor would be light that is directly in front of the tube. Now I understand that visible light has a wavelength of ~400-600 nm and 2.4 ghz signals have a wavelength of 122 mm. That causes some issues. But if I made a ~130 mm diameter tube that didn't reflect signals off its sides so I don't get internal reflections thus narrowing the "FOV" (What's the proper name?) and have a receiver at the end. I see this not working because I can't get a reflectionless surface, but perhaps I could redirect them? I'm not sure, just spitballing here.

 

[davenn]

Why is 15-20 deg the minimum?

because of the limitations of narrow beamwidth vs frequency
Even at 10 GHz less than 5 deg would be quite difficult
24 Ghz and now a couple of degrees is possible.
and by the time you get to t he frequencies of visible then yes very narrow beamwidths are possible

 

[davenn]

but I have a decent understanding of light and optics. wifi and other 2.4 ghz signals are just photons.

no, not as good as understanding as you think ... it is an electromagnetic wave, just as light is
there is NOT a beam of photons shooting out from the source .... photons are not like little bullets

They are a quantum particle, the energy moderator of an EM wave.
photons don't even really exist till they are detected and then they are gone, absorbed by the detector

. But if I made a ~130 mm diameter tube that didn't reflect signals off its sides so I don't get internal reflections thus narrowing the "FOV" (What's the proper name?) and have a receiver at the end.

not going to happen ( beamwidth)

I see this not working because I can't get a reflectionless surface,

for that reason

but perhaps I could redirect them?

which would require reflecting them

 

[Braeden Hamson]

I've learned that I want an antenna with a very narrow aperture. I'm sure this has been the subject of many years of research and a few careers. You seem to have an understanding of EM waves that I haven't yet been taught. Its always bugged me that in school (Second year EE major here) they say light is a particle. Then they say its a wave. Its a marble, it's like water. I feel like it should be some third thing we don't have an analogy for.
I also wonder, is there such a thing as coherent radio waves? Are radio lasers a thing? I'm straying from my original question now. Can radio waves only be received in a cone shape?

My original idea was to mount this antenna on a gimbal mount and sweep it back and forth up and down in a raster scan. This would create data that had X Y position and intensity measured at those points. This could then be interpreted into an image. However, it seems that I would end up running into the same issues that microscopes have. The objects you're trying to see are smaller than the wavelength you're seeing them with. I thought maybe I could get around this issue by using point detection. But I also know that there are objects that block and deflect, and reflect 2.4 ghz signals. So there is something happening.

Lastly I wonder if I could get around the beamwidth problem if I overlapped my measurements. Perhaps I could interpolate data that way?

 

[kellys_eye]

2.4GHz is 'radar' frequency band stuff therefore slotted waveguides will provide a very narrow beam width. The only other practical way to get such a narrow beam would be to use a microwave dish antenna.

 

[davenn]

2.4GHz is 'radar' frequency band stuff therefore slotted waveguides will provide a very narrow beam width. The only other practical way to get such a narrow beam would be to use a microwave dish antenna.

what RADAR are you thinking of ? .... some weather radar still uses 2.4 area..... definitely not cop radar ....
2.4 is for toy remote control, WiFi, microwave ovens, amateur radio and a dozen other similar uses

still very much wider than what he wants, VERY MUCH

Are radio lasers a thing?

The RF equivalent to a laser is a maser -- Microwave Amplification by the Stimulated Emission of Radiation


Dave

 

[kellys_eye]

S-band and X-band radars are used in the marine field. Beam widths of <1 degree.

 

[Braeden Hamson]

So is it impossible to measure the intensity of EM waves at 2.4 GHz at a point in front of a detector? Will any antenna operating at this frequency at minimum pick up a signal 15-20 deg in front of it? Is this because them EM waves are behaveing like visible light passing through a slit, as per the double slit experiment?

 

[kellys_eye]

You can measure the EM waves 'anywhere' - your problem is resolution of measurement.

The principles used in yagi antennas will give you a 'directed beam' both for detection of and radiation of RF energy. Have you looked at 'cantennas'? These are where the radiative element (dipole) is placed at the - essentially - focal point of an enclosed, but open-ended, tube. It's a common technique to transmit wi-fi at distance and also used in portable speed detection equipment.

You could also look into strip-line antenna methods.

At the more esoteric end of the scale you could research phase-array antennas.

 

[davenn]

So is it impossible to measure the intensity of EM waves at 2.4 GHz at a point in front of a detector?

no it isn't, I never said that .... it's about the beamwidth of your wanted antenna that is the problem

Will any antenna operating at this frequency at minimum pick up a signal 15-20 deg in front of it?

of course

Is this because them EM waves are behaveing like visible light passing through a slit, as per the double slit experiment?

No, nothing to do with it. Why would you think that ?

 

[davenn]

S-band and X-band radars are used in the marine field. Beam widths of <1 degree.

I have already commented on those frequencies, and without specialist antennas, narrow beamwidth wont be achieved

eg ........

Achieving a beam width less than 1 degree is the "gold standard" by which any weather radar system is measured. Such a beam width speaks to the quality of the antenna and the overall accuracy of the system. A typical S-Band radar system operates in the 2.7 – 3.0 GHz frequency range using an 850kW Klystron transmitter. In order to attain a beam width less than 1 degree, you need a 28-ft (8.53m) antenna. Such a large antenna requires an even larger radome; 40-42-ft (12.2 – 12.8m). All of these large components come with large costs. Additionally, civil works must account for these massive, heavy parts.

Dave

 

[kellys_eye]

I didn't say such an S-band antenna wouldn't be impractical

Experimentally, a small yagi would be the only reasonable solution.