Extend detection of HB100 doppler radar module with a horn antenna

[Fire91]

Hi guys,
I built a horn antenna to increase the gain transmission of the HB100. However, I don't understand why it doesn't work properly, my antenna is able to extend the range only for few meters, from 2-3 metres of HB100's range I've reached 8 metres, and at 7-8 metres the IF signal is very weak. I want to extend the signal for 20 meters.
What's wrong in my antenna design? (Photos attached). As you can see, my horn antenna is made of two waveguide, one for TX and one for RX. I want to create in the waveguide a single-mode propagation. I started with a larger waveguide to adapt the physical dimensions of the HB100, then I continued with a smaller waveguide to create the single-mode propagation.
I read this interesting topic of JBeale https://www.eevblog.com/forum/projects/playing-with-cheap-hb100-doppler-radar-module-for-car-speed/, but I can't reach the same range detection.

Thanks.

[coppercone2]

thats pretty bootleg. You don't appear to make connections along all the seams. Try that first.

Also, I don;t know how that launcher section works, their pretty specific.

[TheUnnamedNewbie]

Those patch antennas are not designed to be wave guide launchers. They are probably quite significantly detuned. I don't want to know what kind of horrible mess of modes you are exciting in that first cavity, but I doubt it is much like a nice waveguide mode you want.

Oh and depending on the mode you do happen to excite, you really want a very good connection between your walls. Otherwise your waveguide won't even act much like a waveguide.

[Fire91]

I'am a student of electronic engineering and I'am trying to do a horn antenna for the HB100. I studied theory of waveguides and antennas, it's part of my first graduate thesis and so I'am sorry for my low knowledge but I'am still learning from theory to pratice, and this transition is not always simple. You mean that the metalizations are too irregulars and may not produce the desidered modes? I built it from cardboard coated with alluminium, I know that is not the best way but I haven't currently better materials available. Could be a good idea to build waveguides with PCB? In my land I don't know stores to buy it. Sorry for my grammatical errors but I'am not english.

[xaxaxa]

your waveguide walls need to not have breaks in it; try using copper foil and soldering the seams.

[coppercone2]

they do have horns that have dielectric walls, and open walls, but I always figured they were more advanced designs

[Fire91]

Thanks for your advice, I'll try to build a horn antenna with copper foils. But, I want to ask you a question. My idea with copper foils is to make a horn antenna from cardboard, then cover it with copper foils. I guess the best solution is to cover internally the cardboard, but this way is a bit complicated. It's possible tu cover it externally or will be altered the propagation medium of the electromagnetic wave?

[Beamin]

I'am a student of electronic engineering and I'am trying to do a horn antenna for the HB100. I studied theory of waveguides and antennas, it's part of my first graduate thesis and so I'am sorry for my low knowledge but I'am still learning from theory to pratice, and this transition is not always simple. You mean that the metalizations are too irregulars and may not produce the desidered modes? I built it from cardboard coated with alluminium, I know that is not the best way but I haven't currently better materials available. Could be a good idea to build waveguides with PCB? In my land I don't know stores to buy it. Sorry for my grammatical errors but I'am not english.

Don't let this forum put you off its different then other technical forums where people are know it all assholes that just try to prove they are smarter then you. Also keep in mind you are a graduate student of RF ask yourself if you think all the people you ask on the internet know more then Wikipedia or what they learned to get their ham license. There are some really smart people on this forum that will know. If some one just says "that's wrong" but doesn't tell you why/how to fix it take with a grain of salt they are often less knowledgeable and could be just frustrated with the fact they don't know. I have made many prototypes that are built like that and the radio signal doesn't care what it looks like.

Given my low intellect, why couldn't you just tape the seams with aluminum tape? Even if there is a seam only the long length would be anywhere near the wave length. Soldering metal is not an easy thing to do while prototyping card board. It has to be 1cm tight not airtight. To make that out of sheet metal would take a few hours IF you had all the right tools (large vice, cut off wheels, metal stock etc) then you would braze it not solder it unless you had copper but large sheets are expensive and copper can be hard to machine/ work harden. Actually I would braze the copper with the oxy/act torch as heating with a blow torch would take too long come out un even.

Copper tape seems like an interesting idea that to me makes sense but I don't know why the signal would care, but honestly Al Oxide is very thin/hard and would probably have minimal dielectric effect unlike copper after it loses its color. Does conductivity matter? Photons are neutral but the fields they create are not.

You are in RF voodoo territory. My experience is this is 2% theory and 98% experimentation: your dual cavity with the gap multiplies the variables probably to the 3rd power. Looks like a fun idea all though seems like it would work better as a rocket engine I didn't thing you could do that with wave guides.

[PointyOintment]

Keep in mind while reading this that I don't really know what I'm talking about.

I agree with Beamin that your ~1 mm gap "should" be fine at 10.525 GHz. However, perhaps, because the two are not in good contact along the edges, they're interacting differently with the radio waves? I mean: if charge in one of the panels is excited by a radio wave, and this isn't coupled properly to the adjacent panel (only going by a roundabout route where they're making contact), maybe this could cause some sort of multipath effect. On the other hand, you often see radio reflectors (dishes, flat reflectors for arrays, etc.) made of a grid of wires that are not connected all the way along. But, with those, the impinging radio wave is coherent, so they don't need to be connected all the way along. The coherent radio wave excites them in sync, so there are equal image signals in them at the points where they are connected. In your horn, that "should" also be the case, so what I said about multipath shouldn't apply. But maybe the signal is incoherent for some reason (low-quality radar module?).

Also, about metal tape: I've never understood why or even whether it works for things like this. I'd expect it to not make contact with the metal it's adhered to, because the adhesive has nonzero thickness. Though I guess that only applies at DC. So maybe what I said above about multipath due to the panels not being in contact doesn't apply even with such an irregular gap, because they really are forming a closed circuit all the way along at 10.525 GHz.

An interesting finding I just read of (in searching for whether a Faraday cage needs DC continuity for RF exclusion) is that a Faraday cage made of mesh is significantly less effective than one made of sheet metal. But it seems we all (except Richard Feynman) knew that already, just didn't necessarily consciously realize it.

As I said, I don't know what I'm talking about here, so take this all with a whole shaker full of salt.

[coppercone2]

consider the impedance of the capacitance formed by the dielectric glue and the metalization layers, at microwave frequencies the impedance is fairly low. But it still is a weird discontinuity.

You can make a better horn by buying a copper sheet, learning how to cut copper nicely with good metal cutting scissors, glue it together with temporary super glued on brackets and then solder it together. It's actually going to be easier then making bicone antennas.

A trick would be to use heavier copper at the end launcher sections, but what I see done on old prototypes was that a piece of wave guide was modified. I think the geometry of the end launchers matters a bit more then the tapered part of the horn.


I think the main problem your going to run into with fabrication is the hole drilling, for things like attaching a coaxial connector. So get yourself a step drill (looks like a chirstmas tree), which will cut very nice holes into thin materials. You can also glue or clamp it to a sacrificial material like aluminum bars for drilling, but I really recommend a step drill

 The other problem with copper is that it work hardens. A trick for this is to throw the copper, if it gets damaged, into a BBQ or such until it gets dull red hot, then dunk it into cold water, it will get oxidized but come out extremely soft, but oxidized. You can take the grate off a common BBQ grill and lay copper sheet in there until it gets soft, useful if you want to reuse old copper thats been hammered etc (from a roof or something).

If your cut did not come out perfect, since there are no curves used in common horns that are not broadband, you can temporarily glue copper (say with contact spray adhesive) to something metal that is strait and carefully use a file to shape it to the correct dimensions and then free it with solvent. For precise marking, I would recommend you get a flat plane, like glass, glue the copper to it with spray adhesive, sandwich is t down under high pressure (some weights ontop of a another piece of glass with some wood on top), let it glue to the glass plate (which will be very flat), mark it out carefully using a caliper and scribe lines, then unglue it and cut it out. You can get pretty precise stuff this way.

If you want  to scribe a line nicely, get yourself a metal workers ruler, which has a flat edge on it at 90 degrees, preferably a thicker one, and a scribe tool that has a flat blade (not one of those round point tip ones that is carbide for general work). Line up the ruler on the marker points and align the scraper so that the flat side is flat against the ruler

If you have trouble imagining the correct scribe tool, imagine a rectangular prism made of tool steel, like the size of a pencil.

Grind it like this : /___________| from the side and kinda like a F117 nighthawk from the front, with a flat nose, so you can drag it on a 45 degree angle with it making firm contact with a significant part of the metal working guide ruler. You will get very consistent results

If your ruler has a good shape, you clamped things down nicely, use a caliper for marking and you work slow, you will get very nice scribe lines. Just remember to work slow and careful (to the point where you wonder if your an idiot). Work in good light. Practice drawing some lines out on scrap so you don't end up with a scratched up peice of copper. Make sure you scribe fairly deep.

The cutting is kind of the hard part here, you want to get the smallest kind of shears that work for your work, don't use bulky imprecise cheap shears for cutting thin copper. Here you will need to experiment (I have a big assortment of various shears).

Then you need a good iron, aggressive flux and careful construction of jigs to setup your thing to be soldered. Practice making minimum solder joints with minimal fillets.

You can make very nice looking things this way.. my main problem was that I was used to working with paper and I tried to rush things. If it makes you feel better, buying a horn like this will cost you several hundreds of dollars, so working carefully to make something is not that much of a hurt to your pride.

[TheUnnamedNewbie]

Depending on the mode you want to excite, you need a good conductive path for the currents to flow around. For the 'usual' TE10 mode, this would be between the 'top' and 'bottom' (ie, the side walls need to be very conductive). This is why when they are manufacturing big blocks, they (tend to) prefer cuts along these long walls instead of the side walls.

RE: detuning - Your antennas are patches meant to resonate, and are designed (ie, their size) to do so in free space. By adding this big chunk of waveguide on top, their resonance will shift. This could result in a much larger amount of energy being reflected back at the antenna port, and thus the entire system being much less efficient than you started out with.

You also mention that you want single mode propagation. In single mode propagation, you will have a E-field that goes from the top to the bottom or bottom to top. But consider how the fields will originate from your patch antennas - going by the radiation pattern the array has, they will all be in fase. For the first section, where you have two waveguides 'stacked', this could work (as the resonance on the patch is similar to that which you want for a fundamental TE10). But when you merge them, I don't think it can work anymore in terms of launching the fundamental mode, and it will be more along the lines of TE11. I think it would be better to size the horn and that second section of waveguide with that in mind.

You also don't care that much about single-mode propagation, since modal dispersion wouldn't be a massive issue for your application. (The frequency, with which signals arrive, is the only thing that matters). So instead of reflecting a bunch of non-desired modes (because the waveguide is too small for them to be above cutoff) just accept they are there.

[Fire91]

I will follow Beamin's suggestion to use aluminum tape, in fact it's the best way to create the metallizations inside the waveguide.
However, I would like to ask you another question about HB100's design. Below the antenna arrays of this sensor (in the other side of the PCB) there is the ground extension. Why the ground extension is also applied under the antennas, does not disturb transmission/reception? I know that if you want to implement a reflector, it must be placed at a quarter-wavelength distance so that the reflected wave is added (in phase) with the transmitted/received wave. So the reflector must be placed at 7 mm (wavelength is 28 mm) of distance from antenna. So I ask, why the ground extension is placed under the antennas?

[Beamin]

I will follow Beamin's suggestion to use aluminum tape, in fact it's the best way to create the metallizations inside the waveguide.
However, I would like to ask you another question about HB100's design. Below the antenna arrays of this sensor (in the other side of the PCB) there is the ground extension. Why the ground extension is also applied under the antennas, does not disturb transmission/reception? I know that if you want to implement a reflector, it must be placed at a quarter-wavelength distance so that the reflected wave is added (in phase) with the transmitted/received wave. So the reflector must be placed at 7 mm (wavelength is 28 mm) of distance from antenna. So I ask, why the ground extension is placed under the antennas?

Some thing I didn't factor that some one mentioned; I didn't realize it was important for the wave guide to be electrically connected together, I thought a wave guide was like a mirror, not something that actively creates a field in it like an element on a yagi. If this is true then you will need to figure out a way to make the aluminum conduct to each other peice. The aluminum tape has a adhesive that may form a non conductive layer or it may actually have spots that help it conduct. I would make several strips of your wave guide material then held together with tape then wave guide then tape, then get an ohm meter and see what the resistance is at the ends and middle seeing how well the tape connects electrically.

I have never found a good way to connect al foil to wires. You can't solder to it and using flame to melt it together makes shitty electrical connections. Maybe best would be those metal heavy duty paper clips (metal  reusable ones that hold together 100+ sheets) to connect wires to it and then put some sort of conductive paste (will thermal compound or solder paste conduct whiles its wet? Or conductive grease) compound over the wire and foil and squish it with the clip. Alligator clips might work too.

[coppercone2]

just get copper foil, seriously look at the price of a standard gain horn and it becomes obvious you should not waste your time trying to deal with fucking aluminum foil.

i noticed with brazing/soldering or even welding aluminum, alloy is imporant too

everything I tried to do with aluminum foil ended up like a bunch of bullshit.

now, if you have something like aluminum mesh thats not paper thin, you can go for conductive silver epoxy to do a OK job. Something like MG chemical high or better extreme conductivity.. but given its shelf life and cost I recommend you line up a few projects with it before you buy it.. its kind of expensive for a consumable.

Now you might also be able to do low current TIG welding, but expect to pay like 4000$ for a tig thats good enough to do thin foil reliably. You need very low currents.

If for some reason you really need to do foil, I would recommend tig welding aluminum to aluminum with copper attached, because you don't wanna do a dissimilar metal bond on a foil IMO. You want like a short bit of aluminum wire thats brazed/soldered to some copper to act as a intermediate. You might also want to get a few progressively thicker Al foils before you get to the wire maybe. Joining something very thin to very thick is more difficult.



I think the problem with flame is oxidation and the problem with a braze is penetration/brittler intermetallic that forms.

Now, you might be able to do something like use a indium solder foil (but its export controlled and you need a co-signature for purchasing it, and a foil kit is ~500 minimum).

Since the foil is very thin, it oxidizes easily and the braze or solder might actually make it brittle.. a weld might actually be better here for aluminum. Maybe if you can vacuum braze it.

I can try using some aluminum solder on it but I seriously doubt it will work well.

[hagster]

It would seem simplest to use a parabolic reflector dish instead.

[Beamin]

just get copper foil, seriously look at the price of a standard gain horn and it becomes obvious you should not waste your time trying to deal with fucking aluminum foil.

i noticed with brazing/soldering or even welding aluminum, alloy is imporant too

everything I tried to do with aluminum foil ended up like a bunch of bullshit.

now, if you have something like aluminum mesh thats not paper thin, you can go for conductive silver epoxy to do a OK job. Something like MG chemical high or better extreme conductivity.. but given its shelf life and cost I recommend you line up a few projects with it before you buy it.. its kind of expensive for a consumable.

Now you might also be able to do low current TIG welding, but expect to pay like 4000$ for a tig thats good enough to do thin foil reliably. You need very low currents.

If for some reason you really need to do foil, I would recommend tig welding aluminum to aluminum with copper attached, because you don't wanna do a dissimilar metal bond on a foil IMO. You want like a short bit of aluminum wire thats brazed/soldered to some copper to act as a intermediate. You might also want to get a few progressively thicker Al foils before you get to the wire maybe. Joining something very thin to very thick is more difficult.



I think the problem with flame is oxidation and the problem with a braze is penetration/brittler intermetallic that forms.

Now, you might be able to do something like use a indium solder foil (but its export controlled and you need a co-signature for purchasing it, and a foil kit is ~500 minimum).

Since the foil is very thin, it oxidizes easily and the braze or solder might actually make it brittle.. a weld might actually be better here for aluminum. Maybe if you can vacuum braze it.

I can try using some aluminum solder on it but I seriously doubt it will work well.

Cool video but I wonder how many tries that would take to not burn through, seems like NSA would do that for the amateur that's not easy.

Welding al is foil is out of the scope as 99% of people don't own a tig, let alone the skill. I know with a lot of practice you can weld al cans but the op might not have a tig or welded a day in the his life. Also I wouldn't want to tig weld more then one of those bow tie shapes that's lots of bead to run to just find out: sucks doesn't work. Copper tape and solder is probably the best idea you could reinforce it with copper flashing too and solder the whole thing for cheap more importantly quick and cut it to length...

But does it really matter that much if the seams are perfect for just proving it works? Could be wasting hours when the whole shape or concept is flawed. When prototyping you have to focus on what the real variables are and not get hung up on time wasters. I know I have built things spending hours making a component of it work just to realize the piece wasn't connected and the thing worked fine.

[coppercone2]

i dont care about him i just want to make a special machine

[JBeale]

I know this is an old topic but just FWIW I would not recommend the compound converging + diverging design shown here, even though I did try that as well.  That probably gives you a lot of local feedback (transmit directly back to receive before escaping the horn). I think the better performing option is a simple diverging horn like what I did here: https://www.eevblog.com/forum/projects/playing-with-cheap-hb100-doppler-radar-module-for-car-speed/msg1274864/#msg1274864
Self-stick copper foil, or blank copper PCB works fine with some overlap along tape seams. Assuming you've got a plain diverging horn (not a waveguide) I would not expect much benefit to soldering or welding the seams; most of the RF energy will still be reflected from the flat surfaces, rather than leaking through an unsoldered edge joint.  The horn will improve the range, but don't expect miracles.  Also make sure it is solid and does not vibrate or move at all! Any motion at all of the horn relative to the PCB will be a big local reflection and drown out the signal you are looking for.  So a strong rigid PCB construction, or a wood or metal frame is better than foil on cardboard.

[Melt-O-Tronic]

HB100 is a dielectric resonator.  It relies on the PCB material to form part of the resonant circuit.  You stick a piece of aluminum foil with a slit right next to that and then what happens?  My bet is that there is no more oscillation.  As others have said, the fundamental design of the HB100 is all about radiating into free space.  I'm not sure even Shahriar could pull this project off.

[Oldgreybeard]

Not sure if this is at all helpful or not, but I have been playing around with adding different horn antennas designs to these modules, using the excellent work posted here by @JBeale as a starting point.  I used 3D printed parts, covered with very thin self-adhesive copper foil, and gave some details back in the earlier thread that may be of interest: https://www.eevblog.com/forum/projects/playing-with-cheap-hb100-doppler-radar-module-for-car-speed/msg3668809/#msg3668809

[coppercone2]

I was interested in doing the same thing, I just got nickel conductive paint in the mail, I was going to try to electroform the end launcher section, but my experience with electrochemistry has been bad to say the least. Mg chemicals paint works well and I tried it on styrofoam, PVC, cardboard.. it appears to work well, I have yet to try a resin 3d printed part, but I suspect it should be OK. Its somewhat high resistance though.. not sure if its directly suitable for an antenna


how did you bond those corners though? big lap joint? It would also be a good project for someone with a laser wood cutter to make a wooden or acrylic one and coat it with tape, that would be very mechanically precise. I was thinking that since its interior only, very thin acrylic can be used, so long its self supporting, then it can be covered in fiberglass and polyester or epoxy resin to stiffen it, and it should retain its precise interior geometry, so long there is a way to coat the inside. I thought prior to gluing together you can do copper tape/laminations with a bit of clearance around the edges (say 1/4 inch), then later to mold copper tape around a stick cut to fit in the dimensions formed by the corner, so that it can be wrapped in copper tape, sticky side out, so it can be pressed into the corner and make a professional lap joint covering the entire seam, as soon as the stick is pressed into the corner, if you are precise, the outer sticky part should grip the sidewall and release from the stick, then it can be smoothed using a stiff thin powder spatula

[Oldgreybeard]

I have some electroplating stuff on order, as that's something I'd like to try.  I found an article on using conductive copper paint to coat 3D printed horns and that seemed to word OK, as long as the 3D print was sanded smooth:  https://antennatestlab.com/3dprinting

The high conductivity paint is mighty expensive stuff, though, and I had some of the very thin copper foil around, left over from something else, so just tried it to see if it would work.  I have just tried to measure how thick it is, and it seems to be around 0.025mm, so well under 1 thou, although how good my digital calipers are down at that range I don't know.  It overlaps very smoothly, the secret is to use a very smooth small spatula to burnish it flat.  With a bit of care it's possible to get lap joints that are almost undetectable, and smooth enough to not cause a problem at this frequency, I think.

I have also been thinking of using the same technique to make a broadband vivaldi for another project, just because it seems easy enough to do.  One advantage of sticking thin copper foil on a substrate is that you get to just the dielectric constant, rather than take pot luck with whatever the PCB material happens to be.

I've also found some other cheap Doppler modules that use a single patch antenna, and operate on 5.8 GHz.  The single patch has the big advantage that a proper waveguide fed horn could be used, as it's easy enough to use a patch as a launcher.  Using just a single antenna like this should mean that the horn design can be more conventional, and so, hopefully, be a bit more predictable. with less trial and error.  The main snag is that the horn will be a fair bit bigger to get the required directivity, but if it has a better pattern then that may be a compromise worth making.

[coppercone2]

oh right yeah I was gonna do copper electroplating, the nickel was by chance for a substrate, I see the point you have with the skin depth.. that is something to consider switching substrate paints to, but yeah I would naturally try to go to thick structures

if you study the end launchers carefully, some of their designs are very difficult to burnish.. but maybe it can be made direct 2 waveguide fit so I can launch it from commercially made waveguide pieces, so long the junction at the base is good

[Oldgreybeard]

I'm not sure how much surface finish matters, but have been just sort of winging it, hoping that I can find out by trial and error what may or may not be OK.  This is the surface finish on the horn antenna I've been testing, compared with the finish that was tested in that antenna test lab article:





One slight advantage of 3D printing horns is that there's no real need to stick with the pyramidal design, with its small step impedance change at the start of the flare.  I'm tempted to try and design a true exponential horn, as that's no harder to 3D print than a standard pyramidal type.  Not sure that there will be any detectable benefit in doing this, but it has to be worth a try.  The surface finish I've been getting, printing with a 0.15mm layer height and a pretty has print speed seems to be a fair bit better than they were getting in the antenna test labs article, although I'd found that there is still a bit of light sanding to do to get a smooth surface.

I may have a go with trying to copper electroplate one, just to see how it compares.  It looks easy enough to do, just use some (relatively) affordable graphite paint to make the surface conductive and then copper plate in the normal way, with a copper electrode and some copper sulphate solution.  My guess is that I may get best results by putting the copper anode inside the horn, with the whole lot in the solution.  Intuitively it seems that may work more effectively, but it's not something I've ever played with before.

The more I think about it, the more options 3D printing seems to offer when it comes to making small and relatively precise antenna designs.  Just need to find an easy and reliable way to get a nice and smooth conductive coating where it's needed.

[cj]

What's wrong in my antenna design?

Your antenna (horn aperture) is too small to get you from 3meters to 20meters.
Have a look at basic radar theory specifically the basic radar formula.
Path losses are a 4th power which means to double the distance you’ll need 16 times the power or antenna gain.
If you want to increase distance from about 3meters to 20meter the antenna gain has to be increased (20/3)^4=1975 times. Increasing the antenna to that size you will most likely (I don’t know Italian law) violate the maximum allowed EIRP (Equivalent Isotopically Radiate Power = power*antenna gain) under which the HB100 is allowed to be operated.
   
With the antenna you have now the increase from 3meters to 8meter is about right.

The 4th power in the radar formula also explains why long distance radars have an insane amount of peak (pulse) power and large antennas.

CJ