I would imagine that given really bad luck, multipath indoors could end up given you a pair of ambiguous sources but I am guessing that you will not really encounter that.

If you have only one transmitter for your testing, you shouldn't have a problem. If you are testing in an anechoic chamber, you will have even less trouble. There are many companies trying to sell this technology right now to healthcare and logistics companies. Surely there must be literature with enough information to give you an idea of what is working for them.

 

@Yaakov

When talking about antennas, in specific directional antennas. Then one can observe the radiation pattern given in the azimuth and elevation plane. How does these correlate to accuracy of the measured signal in term of beam-width. I have recently contacted one of the professors of our university, and he told us that given the radion pattern of the antenna [http://assets.lairdtech.com/home/brandworld/files/ANT-DS-MD24-12 1115.pdf], we will get accuracy no more than 10 degrees, given almost perfect circumstances. Would you agree to that?

Your professor is correct. Even with the best that money could buy at the time, single antenna directional accuracy that depend on EM signal levels was always limited. Electronically scanned multi antenna systems were far superior.
https://en.wikipedia.org/wiki/AN/FRD-10

Sites in the Classic Bullseye network were connected by communications links to facilitate "near instantaneous" triangulation of received signals if two or more sites received the same signal. Signals could also be recorded for later direction finding. The system was four times more accurate than the prior Navy AN/GRD-6 system with bearing accuracy better than 0.5 degrees.[2]

https://www.navy-radio.com/frd10.htm

I would get a SDR and a cheap directional antenna for testing out possible ideas for improving accuracy.

 

@nsaspook

Hey!

I checked out the links you sent, and it seems like they structurally are huge in comparison to what we have to work with.

Considering single antenna direction vs. multiple antennas. How does this translate into the mentioned robotarm. I am concerned about how big the antenna structure will be way too big for the arm.

Do you think we will be able to have multiple antennas on the robot arm, connected antennas? antenna patches/array?

Or will this essentially boil down to an AoA-approach?

 

I would imagine that given really bad luck, multipath indoors could end up given you a pair of ambiguous sources but I am guessing that you will not really encounter that.

If you have only one transmitter for your testing, you shouldn't have a problem. If you are testing in an anechoic chamber, you will have even less trouble. There are many companies trying to sell this technology right now to healthcare and logistics companies. Surely there must be literature with enough information to give you an idea of what is working for them.

@Yaakov @nsaspook

We are indeed going to characterize our antenna in an anechoic chamber at the antenna lab at out university. However, the system is meant to be used in a normal room, where we have to calculate all the noise and from other devices and the reflections from the walls and such.

We are planning on further develop our system to be detecting moving transmitters or multiple transmittors using the cross-levels from both, but we are going to focus on one tx and our rx on the robor arm in the first place.

I can further explain our project that we are using the nrf52 chip from Nordic Semiconductor, where we are implementing the BLE protocol stack and algorithms using C. On the hardware end were using 2 stepper motors and 3d-printing parts for the construction, eventually ending up in a robot arm with 2 degrees of freedom, and fairly small in size maybe 40-50cm in height. Therefore, we wish an antenna structure that is reasonably sized.

We do have the resources and eventual equipment needed to build such a system as this is a school project in partnership with Nordic Semiconductors. So we are just wondering about how we can get the best possible antenna for the given specs of the robot arm.

 

Because the wavelength is so short, it is possible that an Adcock array with a some modern I²C controlled switching could be very effective in your application. The length and spacing of an Adcock is frequency dependent. Since it is electronically steerable, you might be able to combine it with the robot arm motion for an advantage, I don't know.

But, I surmise that it is also the case that the target will never be behind you (or will it?). If that's the case you might be able to optimize it further. A space pair of Adcock antennas my do really well, but it also potentially obviates the need for the robot.

Is the robot an actual constraint, as I believe it is?

 

@Yaakov

The robot arm should be able to move 360 degrees horizontally, and 180 degrees vertically, which should cover most of the space, and as i interpret your question, not a constraint in a system, such as for moveability. However, it is a constraint for the antenna construction, as we want it to be sized relatively small. In other words, we should be able to fit the robot arm in my backpack.

I have looked up antennas from a previous reply of yours, but i find the whole construction of the adcock antenna too big for the robot arm. We primarily want a smaller type of antenna, in which we can sweep the area using the robot arm, and evaluate the values given from the sweepings.

Is it possible to construct an adcock antenna on such a small scale that it we can mount on the robot arm?

 

My question is, are you required to use the robot?

As to the Adcock antenna, I am unaware of specific upper frequency limits and i do know of UHF Adcock antennas. A 1/4λ radiator at 2.4GHz will be less than 40mm, so it should be exceedingly small. It works by mixing antennas proportionally to get whatever radiation pattern you want and it can be very directional.

 

@Yaakov

Yes, the robot arm is a part of our project description. As the antenna is supposed to be mounted on the robot arm, we will be able to move and change the "direction of the antenna". The robot arm is supposed to aim both the antenna towards the location of the beacon, not only in the horizontal axis, but also vertical, if possible.

Interesting, we will look further into that. Also, i can see that you mention 1/4λ. Is it common to use that ratio? As the frequency is fairly high, the wavelength should be around 125mm, what are the benefits of using 1/4 of the wavelength in comparison to the whole wavelength?

 

The wavelength of an antenna determines its feed point, among other things. A ¼λ is end fed, that is, the feed point is aat the base of the antenna. But, it needs a ground plane to provide an image antenna for the monopole antenna to operate against. The Adcock uses a monopole (as opposed to a dipole) particularly.

An end fed 1/2λ antenna has the advantage of not needing a ground plane, and for some applications that's very useful. For example they are usually what you will find on a fiberglass hull boat which lacks metal to act as the ground plane, and, at the frequencies used for VHF marine radio (~160Mhz) an effective counterpoise or radials that would be needed for the quarter wave or various collinear composite antennas (e.g. ⅝λ and others, end to end) is too unwieldy and would be in the way.

Dipoles are center fed and they can be made of ¼V or ½λ elements. Some steerable arrays use a dipole of 1/4λ vertical elements.

In any case, once an antenna is resonant, the advantages of making it larger depend on application. It is possible to use, for example, ⅝λ antennas to achieve "gain". That gain is only over a ¼λ and it has to do with where the antenna radiates from. Like the "gain" in a directional antenna, it's the concentration of the radiation pattern that is called gain, and in this case it will radiate generally omnidirectionally but like a torus around the antenna.

It is also possible to control takeoff angle which can be a great benefit. For example, if you place an antenna up high, intending to provide service below it, the gain and takeoff angle need to be designed to concentrate the energy at a downward angle and locally.

On the other hand, an antenna intended for long distance HF communications, benefits from a takeoff angle that is facing up, to interact with the layers that allow for propagation of HF signals.

Antennas are very interesting, simple in some ways but ultimately very complicated. The are heavily affected by their environment so theoretical models are only useful for so much. We do have very good simulation software now, and amazingly sophisticated antennas, but it is a bit magical none the less.

 

@nsaspook

Hey!

I checked out the links you sent, and it seems like they structurally are huge in comparison to what we have to work with.

Considering single antenna direction vs. multiple antennas. How does this translate into the mentioned robotarm. I am concerned about how big the antenna structure will be way too big for the arm.

Do you think we will be able to have multiple antennas on the robot arm, connected antennas? antenna patches/array?

Or will this essentially boil down to an AoA-approach?

That system was for HF as a impractical demo of what's possible even at larger wavelengths if you need precise bearing accuracy from mainly signal strength. A useful antenna array for BLE should easily fit a robot arm.
https://www.bluetooth.com/wp-content/uploads/Files/developer/RDF_Technical_Overview.pdf
https://www.ti.com/lit/an/tida029/tida029.pdf
https://www.silabs.com/documents/public/application-notes/an1195-antenna-array-direction-finding.pdf