[HN Gopher] Homemade 6 GHz pulse compression radar
___________________________________________________________________
Homemade 6 GHz pulse compression radar
Author : henrikf
Score : 223 points
Date : 2024-04-04 13:32 UTC (9 hours ago)
(HTM) web link (hforsten.com)
(TXT) w3m dump (hforsten.com)
| throwup238 wrote:
| This is great.
|
| It's the last piece I needed for my suburban missile guidance
| system! This will be the last year the Joneses survive the annual
| block party.
|
| Can you do phased array radars next? I need the extra precision.
| There's a few neighbors who don't clean up after their dogs...
| gertrunde wrote:
| There is this:
|
| https://www.crowdsupply.com/krakenrf/krakensdr
|
| (Although they had to take the radar elements out of the
| firmware/software, most likely due to ITAR - ref link:
| https://forum.krakenrf.com/t/where-has-the-passive-radar-cod...
| )
| throwup238 wrote:
| Thank you for the link!
|
| I totally forgot about kraken. I cloned their repo in
| November 2022, probably in anticipation of the ITAR hiccup.
| Hopefully the radar code is there.
| CobaltFire wrote:
| I'd be interested in knowing if you've got that. I was
| going to buy one but the pull of the code put that on ice.
| I may pull the trigger if I can get the code!
| throwup238 wrote:
| No sadly it looks like I got the wrong repo or I cloned
| it too early. It includes a little Python code but no
| firmware from what I can tell.
| topynate wrote:
| A similar ITAR restriction on controlled reception pattern
| antennas means that GPS jamming is still much more of a
| problem than it needs to be. Three antenna elements are all
| you get, according to this: https://www.gpsworld.com/toughen-
| gps-to-resist-jamming-and-s...
| CamperBob2 wrote:
| Interesting article. I wonder if any progress on the ITAR
| issue has been made since 2022? If Brad Parkinson can't
| steer ITAR in the direction of common sense, nobody can.
| (For those who don't know, he was the principal architect
| of the original Navstar GPS system.)
| spitfire wrote:
| These should help.
|
| Tactical and Strategic Missile Guidance, Seventh Edition
| https://www.amazon.com/Tactical-Strategic-Missile-Guidance-S...
|
| Tactical missile warheads https://www.amazon.com/Tactical-
| Warheads-Progress-Astronauti...
| secondcoming wrote:
| Ha, I mentioned the first book the other day on here.
| Symmetry wrote:
| I'm sure the OP has already read his Skolnik given his
| comment but for those following along that's usually the best
| place to start.
|
| https://www.amazon.com/Radar-Handbook-Third-Merrill-
| Skolnik/...
| spitfire wrote:
| There's also Fundamentals of Astrodynamics
| https://www.amazon.com/Fundamentals-Astrodynamics-Second-
| Dov...
|
| Which builds up from first principles a ballistic missile
| defence system. Always useful to have.
| Modified3019 wrote:
| >phased array
|
| Jon Kraft apparently is doing a series on that:
| https://www.youtube.com/@jonkraft
| jcims wrote:
| If someone can figure out how to hack the starlink dish
| frontend we'll have a hell of a capability to tinker with.
| rlt wrote:
| FBI has entered the chat
| vlovich123 wrote:
| Could this be adapted into a voxel system? Seems like it could be
| cheaper than LIDAR which are a huge cost for why the HW for self-
| driving systems are so expensive & work in far more environments
| that LIDARs struggle with. I suspect getting multiple directions
| simultaneously is hard?
| itishappy wrote:
| Not without significantly complicating your antenna setup (and
| the data processing setup too). You guessed it, getting
| multiple directions simultaneously is hard. Note how the
| current system only detects distance and speed in 1 dimension.
|
| Here's an analysis from someone smarter than me:
|
| > To enable the new features, radar systems now use multiple
| input/multiple output (MIMO) antenna arrays for high-resolution
| mapping. Traditional radar systems usually contain two to three
| transmitting antennas and three to four receiving antennas,
| which lead to a beam providing limited short-range coverage and
| a narrow field of view unable to generate images. The limited
| angular resolution is insufficient to differentiate among
| vehicles, pedestrians, or objects that are close. The MIMO
| approach increases the underlying channels from only nine to
| anywhere between 128 and 2,000. Given radar's significantly
| lower costs -- even with all the enhanced technology -- it's
| easy to see how the two technologies will increasingly be on
| more equal footing.
|
| https://www.oliverwyman.com/our-expertise/insights/2023/jul/...
| user_7832 wrote:
| So would this mean that with a few more transmitting and
| receiving antennas it could have comparable resolution to
| lidar?
| itishappy wrote:
| In theory, though it sounds like to compete with LIDAR it
| will need about 1000x more antennas, with a related
| increase in electronics.
| beeeeerp wrote:
| Cutting-edge AESA radar like on the F-35 is incredible.
| It actually looks like a black and white photograph. I
| think your guess on antennas is roughly correct based on
| what we know about modern AESA.
| KeplerBoy wrote:
| Isn't that Synthetic Aperture Radar though? You can get
| similar results (black and white aerial pictures) by
| strapping a pretty basic siso radar system on a drone.
| pbmonster wrote:
| Look at the forward looking automotive 4D (distance, speed,
| azimuth angle, elevation angle) radar systems. The new ones
| work at around 80GHz, and the entire thing comes in one
| integrated, tiny package, 16x16 phased array antenna already
| included with the MCs and FPGAs on the same board.
|
| To go from those 4D radar maps to a voxel system requires a
| whole lot of software, of course.
|
| The end goal seems to be to beat LIDAR on price and reliability
| (turns out moving mirrors don't like years of constant
| vibrations), while delivering enough resolution for self-
| driving.
| georgeburdell wrote:
| I just want to know how much this cost
| davekeck wrote:
| > Cost was 330 USD for PCB manufacturing and assembly of two
| PCBs and additional 225 EUR (240 USD) for components from
| Digikey that I soldered myself. This is including 24% VAT and
| shipping costs.
| georgeburdell wrote:
| Plus the test and validation equipment which are $$$
| henrikf wrote:
| I actually didn't use any expensive test equipment, only
| oscilloscope and multimeter. Even design and simulation
| software was all open source.
|
| Expensive signal analyzer or spectrum analyzer would have
| been useful, but they aren't absolutely necessary. It's
| possible to use the radar itself for many tests and
| debugging.
|
| I have tried to limit the projects I do on my own to only
| the equipment that I have home and open source software.
| rkagerer wrote:
| I came to ask about that 24% VAT - ouch!
| CamperBob2 wrote:
| Beautiful piece of work. Henrik has a long history of interesting
| radar and other RF data-acquisition projects of the sort that you
| don't see publicly documented much, at least not at this level of
| quality.
| nick__m wrote:
| Why the ground planes are on layer 2 and 6 instead of 1 and 6 ?
|
| Naively, as someone who doesn't have high frequency PCB design
| experience, I would have placed my grounds to form a shield and
| put my voltage plane on layer 3 or 4. I am sure that there is a
| good reason behind that choice but I don't see it.
| _Microft wrote:
| > _Above is the final DDR3 routing on all the PCB layers.
| Layers 2 and 6 are ground, 5 is supply voltage, and others are
| reserved for signals. Two grounds are needed for correct
| impedances on the top, middle, and bottom traces of the PCB.
| With only one ground plane, the distance from the signal to
| ground would be too large on either the top or bottom layer._
|
| Is the textual description in the article correct? To me the
| images make it look like signals are on 1 (red), 3 (orange) and
| 6 (blue), with ground on 2 (green) and 5 (pink) and supply
| voltage on 4 (teal). If you match some vias, you will find that
| 2 and 5 are definitely connected.
| nick__m wrote:
| thanks, layer 2 and 5 would fit the rest of the description
| and the reason would then be in the text :
| Two grounds are needed for correct impedances on the top,
| middle, and bottom traces of the PCB
| _Microft wrote:
| Here are some resources on PCB layer stack-up by the way.
| While I'm an amateur, they didn't sound unreasonable.
| Chapter 10[0] has a list of links to different layer stack-
| ups for boards with 4 to 10 layers.
|
| [0] https://web.archive.org/web/20200124214936/http://www.h
| ottco...
|
| Edit: removed wall of links
| henrikf wrote:
| That's a mistake in the text. You're correct that layers 2
| and 5 are ground planes.
| henrikf wrote:
| Putting ground planes on top and bottom layers isn't usually
| done with high speed PCBs because components are there. There
| would need to be a cutout on the ground plane near every chip.
| High speed signals really need continuous ground plane and ICs,
| especially RF ICs, need short access to ground. Second layer is
| the best layer to minimize the distance from ICs to ground
| plane.
| kurthr wrote:
| Obviously not the designer, but my guess is to lower capacitive
| loading on the matched high frequency signals (those with
| squiggles on top and flood underneath) and make modeling and IC
| mounting easier without flood. Note there's not flood near
| those either. I'm not quite sure on the ordering in the picture
| but it looks like 123/654? (edit ahh looks like the text was
| wrong and it is 123/456 with 2&4 Gnd). I'll note it looks like
| the internal "low speed" digital signals are squeezed between
| the gnd/pwr (edit: between gnd/gnd) planes, which is probably
| good since they're usually the biggest source of "noise" if you
| keep it away from other PCBs. You'd definitely want power/gnd
| planes immediately next to each other since bypass caps don't
| work at anything close to this frequency.
| bangaladore wrote:
| It is common to route high-speed signals on the top and bottom
| layers to avoid vias that cause impedance mismatches even when
| back drilled ($$$).
|
| To maintain a specific characteristic impedance, you need a
| plane (GND) some distance from the traces which themselves have
| a specific width. Without a plane under/above the signals, you
| can't get a specific impedance value.
|
| You can additionally fill the top and bottom layers, which
| marginally affects the impedance.
| auspiv wrote:
| Incredible work. Crazy that this could be done by a single
| person. Stick it on a rotating pedestal and you've got a planar
| radar detector. Add some tilt and then it's not much different
| than aircraft/weather radar I suppose.
|
| The cost (in $LOCAL_CURRENCY, or $570 according to another
| comment) isn't great but I can only imagine how many hours this
| took.
|
| Given a proper budget, the sky is the limit.
|
| Anyone know how .mil aircraft would interpret being tracked by a
| 6 GHz radar build by a civilian(yes I am aware that his estimated
| max distance is 1200m, assume he increased that by a factor of 10
| with larger antennas or something)?
| throwway120385 wrote:
| Wouldn't the FAA or FCC in the US have some jurisdiction over
| such a setup?
| maestroia wrote:
| The "6 GHz" band is an unlicensed frequency for very-low
| power (VLP) devices in the US.
|
| Specific bands are: "U-NII-5 (5.925-6.425 MHz) and U-NII-7
| (6.525-6.875 MHz)".
|
| VLP is defined as those devices which "operate at up to -5
| dBm/MHz power spectral density (PSD) and 14 dBm EIRP".
|
| https://www.federalregister.gov/documents/2024/01/08/2023-28.
| ...
| gambiting wrote:
| In fact you can get WiFi routers that use 6Ghz as the third
| band after 2.4Ghz and 5Ghz.
| aidenn0 wrote:
| > Anyone know how .mil aircraft would interpret being tracked
| by a 6 GHz radar build by a civilian(yes I am aware that his
| estimated max distance is 1200m, assume he increased that by a
| factor of 10 with larger antennas or something)?
|
| Regulations for signal strength are ERP, so a more directional
| antenna could make it no longer legal to use the 6GHz band.
| AlwaysNewb23 wrote:
| This is really impressive. Do you plan to use it for anything or
| another project?
| henrikf wrote:
| I built it to see if I could. I didn't have any particular use
| case in mind.
| AnarchismIsCool wrote:
| Would this be useful for another SAR setup?
| amirhirsch wrote:
| Did you test this with arbitrary waveforms? Is it possible for
| you to accumulate complementary Golay Codes?
| jcims wrote:
| I remember this article from the same site a while back -
| https://hforsten.com/heartbeat-detection-with-radar.html
|
| I bought some cheap 10ghz and 24ghz dopper radar units off of
| amazon and started tinkering with them. You can absolutely pick
| up heartbeats and breathing just visually in the spectrogram.
|
| Here's a few samples from that era:
|
| 10ghz pointed at ceiling fan:
|
| https://www.youtube.com/watch?v=tIiFvByf1CQ
|
| 10ghz pointed straight up underneath a quarter that I flipped and
| allowed to land on the surface
|
| https://www.youtube.com/watch?v=8riretP8ylE
|
| 10ghz pointed at a quarter spin on the surface
|
| https://www.youtube.com/watch?v=5lnYvJoxRak
|
| The comb filtering of the signal from the spinning surface is
| really cool.
|
| 10ghz module on amazon - https://www.amazon.com/HiLetgo-
| Microwave-Detector-Wireless-1...
| spxneo wrote:
| interesting does/can it work behind structures? is it safe to
| point this at yourself?
| KeplerBoy wrote:
| yes, it's safe. It's not that different from regular WiFi or
| cellular signals.
|
| It's non ionizing (aka it doesn't have enough energy to
| instantly destroy cells unlike uv radiation) but it can heat
| up tissue, which is linked to cancer and worse (think
| microwave ovens).
| a_random_canuck wrote:
| There's no risk of cancer from heating up tissue.
| SheldonSteves wrote:
| There is but it's sun burn type risks, not nuclear
| reactor type.
|
| A few unlucky people have been literally cooked to death
| by military radar. It's as awful as it sounds.
| pythonguython wrote:
| Can someone explain why those differential pairs are routed with
| so many curves instead of straight paths? (E.g. see the photo
| under the "ADC and DAC rotting" section)
| cwillu wrote:
| Matching overall length with other traces, is my guess.
| _Microft wrote:
| _" The traces are length-matched with squiggly lines[...]. The
| trace matching requirement is +-10 ps according to the Zynq PCB
| design guide, which is approximately +-2mm in trace length.
| [...] There is also some delay difference inside the FPGA
| package which should be considered in the length matching."_
|
| This is a shortened excerpt from the article. It can be found
| below the image with six colorful images of PCB layers. I'm
| curious how the delays inside the FPGA package are known. Is
| there a table which pin adds how much delay to a signal or
| something like that?
| henrikf wrote:
| The FPGA manufacturer has characterized all their package pin
| delays. It's possible to export a csv file with internal
| delays of the package for each pin from the FPGA design tool.
| With Xilinx Vivado it's just File -> Export I/O Ports.
| _Microft wrote:
| Does KiCad allow to take these delays for each pin into
| account automatically or do you need to do all that
| manually?
|
| Edit: it's using the pad property of "pad-to-die-length" if
| doing it manually, right?
| henrikf wrote:
| No, it needs to be done manually. It wasn't as tedious as
| it sounds though. Most of the pins are very close in
| delay already and there were just few traces that I had
| to adjust a little.
| mhh__ wrote:
| How is kicad getting along with RF work in 2024, would
| you say?
|
| I did some prototyping but never got the stage if
| actually fumbling around with PCBs a few years ago,
| things seemed to progressing quite well.
| Brusco_RF wrote:
| One of the main benefits of using an FPGA is that you can
| compensate for trace length mismatch with timing constraints
| rcxdude wrote:
| Not usually with IO ports directly associated with hard IP
| blocks like the DDR controller in the Zynq though.
| amanda99 wrote:
| The Finns strike again. Just the depth and number of different
| areas of expertise is insane to me. It seems he planned it all
| out, had it printed in China, and then 1/2 of the boards actually
| worked. That's like building a whole backend+frontend app and
| hoping it works after a month of coding on startup.
| Brusco_RF wrote:
| That's pretty typical for hardware development. You software
| people have it too good!
| ein0p wrote:
| Badass work. Rarely do you see such technical depth being
| demonstrated across the entire stack from RF to hardware to
| firmware to software. The article just gets better and better as
| you read on.
| belzebalex wrote:
| This is incredible.
|
| I've wanted to thank the author for a while for his past articles
| [1][2] which have been a wonderful source of information when
| working on my sonar systems [3]. This article again explains
| really well a complicated topic. Please, keep up the great work!
|
| [1]: https://hforsten.com/radar-phase-measurements.html
|
| [2]: https://hforsten.com/6-ghz-frequency-modulated-radar.html
|
| [3]: https://twitter.com/alextoussss/status/1756371553460121766
| KeplerBoy wrote:
| Henrik Forsten is definitely the coolest radar guy on the
| internet I'm aware of.
|
| Hats off to you!
___________________________________________________________________
(page generated 2024-04-04 23:00 UTC)