15 replies to this topic

[Kenn Sebesta]

I know there are some members out there who really enjoy making antennas. Any of them interested in trying out this design?

http://www2.hawaii.e...agi Antenna.pdf

The construction itself is relatively easy. The usage is also non-complicated, as you only need a p-i-n diode on each antenna. They give the exact specifications.

So for any direction, you get a +8 or +9dB gain. That's pretty nice for most purposes. Not as good as a directional yagi, but this is far more compact.

[juz]

I would love to see someone test this out. Wonder if Alex Greve has seen this?

[Maineiack]

sweet
im gonna read this more,
and see if i can find more info

[Kenn Sebesta]

Glad to see you on the case Maineiack, you seem like the guy here who'd make the best one of these. If it works out, let us know so we can give some tries with the PipX stock antennas.

Would this interface well with a circularly polarized antenna? I should think so.

[Maineiack]

Glad to see you on the case Maineiack, you seem like the guy here who'd make the best one of these. If it works out, let us know so we can give some tries with the PipX stock antennas.

Would this interface well with a circularly polarized antenna? I should think so.

LOL,
I need to find more info and get some help on the size conversion,
and read more on the switch and how it works,
I know Little of how this all works,
but im real good at doing the DIY's i find,
so if ANYBODY out there wants to help out in doing this let me know,
I need some "brains" to put with my Love of soldering and building,

[KillaX]

soldering is the easiest thing in the world for me...I will say, for a 1Ghz that antenna sure is small!!!

[D-Lite]

So for any direction, you get a +8 or +9dB gain.

Ehmmm.. but not at the same time. You have to select in which direction you want to focus the beam. The cool thing about this antenna is that this is possible but you need additional electronics (pin diodes) to steer the beam - and a logic that tells you in which direction you want the beam to be focused (home location would be good here :-). You could mount it on a plane and slect via software in which direction to focus, like a non-mechanical antenna tracker - but to be honest I would consider a setup like this to be "very experimental" :-)

Edit: additional problem: in the paper they use a ground plane of 0.9 lamda which would be about 33x33cm. Maybe it's possible to make it smaller but this reduces gain of course.

[Kenn Sebesta]

Right, you'd need some kind of electronics to switch between which antenna is receiving the best signal, but I imagine that simply using a diversity-style approach is the way to go, and that's relatively trivial. Anyway, since you know where the UAV is, you probably don't even need to do that. You just switch in electronics to the antenna likely to be the best, instead of steering a yagi with stepper motors.

The 33x33cm ground plane is at 1GHz, so for users at 2.4GHz or 5.8 you wind up with 13.75cm and 5.7cm, respectively. That's pretty nice. However, for the PipX at 433Mhz, you make a great point that a 76cm ground plane winds up being unwieldy. The easy answer is to put it on your car roof, but that obviously isn't portable. I wonder if you could have a foldable ground plane? Am old monopoly board coated with heavy-duty aluminum foil, for instance. I don't see why not, but then again I don't know much about how thick the ground plane has to be in order to be effective.

What I like best about this design is that it is vertically polarized, instead of horizontally. For UAVs, that's certainly the better of the two (not taking circular into account).

[Stigoe]

The 33x33cm ground plane is at 1GHz, so for users at 2.4GHz or 5.8 you wind up with 13.75cm and 5.7cm, respectively. That's pretty nice.

But the distance between the feed and the directors would be only about 2mm for 5.8GHz antenna and 1mm from the driver to director 1 and 5. That's not quite so nice from a manufacturing point of view...

[D-Lite]

Right, you'd need some kind of electronics to switch between which antenna is receiving the best signal, but I imagine that simply using a diversity-style approach is the way to go, and that's relatively trivial.

But that's not how this antenna works . It only has one active element (the one in the center). That's where you connect the receiver. The poles around the center are directors just like any yagi has. The difference is that you can select which one of the reflectors is active (connected to ground) or just passive. Diversity is a rather different concept though.

Anyway, since you know where the UAV is, you probably don't even need to do that. You just switch in electronics to the antenna likely to be the best, instead of steering a yagi with stepper motors.

Yes, that's possible. But to be honest I don't see a point in this for a relatively low gain antenna like this, especially not on the ground where a real antenna tracker + high gain antenna is probably the better solution (I though you were thinking about putting it on the plane, that why I was concerned about the ground plane). You still have the problem with polarization (which is a serious one) for which circular still seems to be the best solution.
The main advantage of this antenna design is the electronic steering which is very fast - e.g. for applications like direction finders etc. Would even make a pretty good bat tracker :-) (If the dimensions at this frequencies you use would'nt make this impossible to go on a plane)

The 33x33cm ground plane is at 1GHz, so for users at 2.4GHz or 5.8 you wind up with 13.75cm and 5.7cm, respectively.

The antenna elements themselves are very small at 433 already, I don't think you will get good results at higher frequencies like 2.4Ghz with this design.

That's pretty nice. However, for the PipX at 433Mhz, you make a great point that a 76cm ground plane winds up being unwieldy.

Ground plane dimensions are not as critical. Bigger is better but a smaller ground plane will work, you'd just lose a bit of gain.

I wonder if you could have a foldable ground plane? Am old monopoly board coated with heavy-duty aluminum foil, for instance. I don't see why not, but then again I don't know much about how thick the ground plane has to be in order to be effective.

Yes, that should work well (beside mechanical problems). The thickness doesn't matter at all.

[Kenn Sebesta]

Yes, that's possible. But to be honest I don't see a point in this for a relatively low gain antenna like this, especially not on the ground where a real antenna tracker + high gain antenna is probably the better solution (I though you were thinking about putting it on the plane, that why I was concerned about the ground plane). You still have the problem with polarization (which is a serious one) for which circular still seems to be the best solution.

A real antenna tracker is a scary thing. It's mechanized components are prone to failure, and as we saw in Portugal the software side can also be the source of failure. The nice thing about this design is that it's all passive, except for a little in the way of switching electronics. These are as robust as anything in the circuit.

My thinking with diversity was that active circuitry just chose which was the stronger signal. I gather from what you're saying this isn't how it works. So I'll retract that, as my approach here would be just to sample each channel in turn and use the one that has the best RSSI. Once you find where the plane is, you simply stay on that channel. Periodically, you can switch to see if there's a better channel, but if you have relative position data than even this isn't necessary except near edge cases.

The circular polarization is something that can be done on the airplane, as it's nice and compact. On the ground, this design appeals to me because you can whip it out, run it up a tall tripod or light stand, and it works. Because it's omni-directional, you don't have to concern yourself about which way it's pointed.

It doesn't get you the extreme range a yagi would, but I think most people are using either a dipole antenna or are forced to fly only in one downfield sector, like we were in Portugal. So if this works as the paper implies it does, it would be really nice in a lot of cases. It would mean you could fly far downfield, but then fly behind yourself or to the side without fear of loss of signal.

The main advantage of this antenna design is the electronic steering which is very fast - e.g. for applications like direction finders etc. Would even make a pretty good bat tracker :-) (If the dimensions at this frequencies you use would'nt make this impossible to go on a plane)

As above, I think the main advantage for UAVs is ease of setup, reliability, and omni-directionality. On the flip side, I thought about it for the bats, but the bats have horizontally polarized antenna. So alas, this doesn't work at all! Otherwise, I would have already made ten of them.

Well, that and at 150MHz the ground plane is 2m big.

But the distance between the feed and the directors would be only about 2mm for 5.8GHz antenna and 1mm from the driver to director 1 and 5. That's not quite so nice from a manufacturing point of view...

Completely by hand, I think you're right. But if you had a PCB with through-holes, it would make this very easy to assemble. You could just take a copper PCB from McMaster and drill some holes with a CNC machine. It'd be straightforward to get the dimensions necessary, and the CNC could route out the rest of the circuit, including the placement for diodes and feed connection.

[D-Lite]

A real antenna tracker is a scary thing. It's mechanized components are prone to failure, and as we saw in Portugal the software side can also be the source of failure.

Yes, that's true but that's nothing that cannot be solved. Of course you are right - it will always remain a potential source for problems.

My thinking with diversity was that active circuitry just chose which was the stronger signal. I gather from what you're saying this isn't how it works.

No, it works exactly like this - the point is, you don't have multiple signals at the same time on this antenna. Only a single signal but with a steerable direction.

So I'll retract that, as my approach here would be just to sample each channel in turn and use the one that has the best RSSI. Once you find where the plane is, you simply stay on that channel.

Yes, that would work. You can rotate the antenna beam until you find the strongest direction and then stay there. The cool thing is because you cann rotate the antenna beam as fast as you want (100Hz, no problem) you can scan from time to time in all directions without losing too much data.

The circular polarization is something that can be done on the airplane, as it's nice and compact. On the ground, this design appeals to me because you can whip it out, run it up a tall tripod or light stand, and it works. Because it's omni-directional, you don't have to concern yourself about which way it's pointed.

It doesn't get you the extreme range a yagi would,

Oh, I would use a high gain helical on the ground of course. But the higher the gain, the more important becomes tracker accuracy.
Speaking of high gain antennas, there's always the legal issue, but that's a different topic :-)

Completely by hand, I think you're right. But if you had a PCB with through-holes, it would make this very easy to assemble.

The problem is that you cannot just downscale the dimensions. At this size, the diameter of the wire plays a mature role, you would have to re-calculate the whole antenna. Some designs just don't work well at smal sizes and you'll most likely lose at lot of gain. 2.4Ghz may probably work but I doubt 5.8 would.

[Kenn Sebesta]

No, it works exactly like this - the point is, you don't have multiple signals at the same time on this antenna. Only a single signal but with a steerable direction.

Ah, I see what you're saying. I think we got confused somewhere down the line. There is only one feed point, but multiple reflectors. If you will, each reflector combination makes a "new" antenna so you'd be testing all your antennas to see which is best. The fact that there's only one feed point is an architectural consideration for how you wire up your "multiple" antennas. So we were basically saying the same thing all along. Cool.

The problem is that you cannot just downscale the dimensions. At this size, the diameter of the wire plays a mature role, you would have to re-calculate the whole antenna. Some designs just don't work well at small sizes and you'll most likely lose at lot of gain. 2.4Ghz may probably work but I doubt 5.8 would.

Interesting. That's not at all what I gathered from the guys at MIT's ham radio club. I was quite astounded that their approach toward yagis was largely "If you want to do better, do this, but it'll work fine without that". I guess this is one of those things where you have to either calculate everything out ahead of time, or build it and tinker until you like how it is.

I suspect that there are a wide variety of frequencies where this design would work without much modification, as the idea is primarily that of a yagi.

Based on simulation results, the presence of the other directors open to ground results has minimal impact on the array performance, as if the other director elements do not exist at all.

[D-Lite]

The fact that there's only one feed point is an architectural consideration for how you wire up your "multiple" antennas. So we were basically saying the same thing all along. Cool.

Ehhmm.. I'm not convienced that we mean the same thing, yet. You don't "wire up multiple antenna", only a single one. Then you apply DC voltage to one of the PIN diodes to activate the connected reflector. So you need e.g. 8 I/O pins (or 3 + binary decoder) to select the sending/receiving direction of the antenna.

Interesting. That's not at all what I gathered from the guys at MIT's ham radio club. I was quite astounded that their approach toward yagis was largely "If you want to do better, do this, but it'll work fine without that". I guess this is one of those things where you have to either calculate everything out ahead of time, or build it and tinker until you like how it is.

Concerning the diameter of the wires, it all depends on the scale. If the diameter is small compared to the distances of the antenna elements, it doesn't matter that much if it's 1mm or 2mm wire or 5. The influence on the design is neglible. But if we are talking about distances between antenna elements of just a few millimeter, the wire diameter has to be taken into account, otherwise teh design will just not work at all.

I suspect that there are a wide variety of frequencies where this design would work without much modification, as the idea is primarily that of a yagi.

Basically yes. Lower frequencies are easy but with higher frequencies, everything gets more and more critical and needs calculations and/or simulations.

[Kenn Sebesta]

Ehhmm.. I'm not convienced that we mean the same thing, yet. You don't "wire up multiple antenna", only a single one. Then you apply DC voltage to one of the PIN diodes to activate the connected reflector. So you need e.g. 8 I/O pins (or 3 + binary decoder) to select the sending/receiving direction of the antenna.

The way you wire up multiple antennas, for direction finding for instance, is to use switches on the feeder of each antenna. Then your switching strategy is to commutate between antennas and look at how the signal is deformed. You can do this in a ring to make an adcock antenna, or you could just to it between two dipoles to get a phase difference between the antennas and thus get an bearing to target.

Here, we effectively trigger a different antenna with each switch, but the effect is the same. It's as if we were turning on one antenna and off another.

Concerning the diameter of the wires, it all depends on the scale. If the diameter is small compared to the distances of the antenna elements, it doesn't matter that much if it's 1mm or 2mm wire or 5. The influence on the design is neglible. But if we are talking about distances between antenna elements of just a few millimeter, the wire diameter has to be taken into account, otherwise teh design will just not work at all.

So what would your guess be at 2.4GHz? I'm under the impression that generally these things scale pretty well for reasonable changes in frequency. In this case where at 5.8GHz the wire is practically touching I can see where you would for sure detune. I would naively guess that moving to .25mm radius copper would still work at 2.4GHz, not counting the fact that 24 gauge wire tends to be pretty fragile so you'd want to be sure not to smash it by accident!

In any case, for PipX at 433MHz we want to go the other direction, which of course has its own problems when you start scaling too large.

[D-Lite]

Here, we effectively trigger a different antenna with each switch, but the effect is the same.

Yes, that's true but the electronics required to do this is a very different one (actually much simpler with this antenna design than it would be with independant antennas)

So what would your guess be at 2.4GHz? I'm under the impression that generally these things scale pretty well for reasonable changes in frequency. In this case where at 5.8GHz the wire is practically touching I can see where you would for sure detune.

The problem is that these things are very sensitive. At this scale, 1 mm is a lot. And if the antenna is detuned by 10% or so, it's practically useless. A simple test would be to make only the dipol and one director with the director directly connected to the ground - very easy to build, no pin diodes and additional electronics required and you can test the behavior of the basic design.

In any case, for PipX at 433MHz we want to go the other direction, which of course has its own problems when you start scaling too large.

Yes, but this is much more likely to work than scaling it down.