Source: have worked with some of the (admittedly last-gen) automotive RADAR chips, NXP in particular.

The issue is the number of false positives, stationary objects need to be filtered out. Something like a drainage grill on the street generates extremely strong returns. RADAR isn't high enough resolution to differentiate the size of something, you only have ~10 degree resolution, and after that you need to go by strength of the returned signal. So there's no way to differentiate a bridge girder or a railing or a handful of loose change on the road from a stationary vehicle. On the other hand, if you have a moving object, RADAR is really good at identifying it and doing adaptive cruise control etc.

Edit: it looks like some of the latest Bosch systems have much better performance in terms of resolution and separability: https://www.bosch-mobility-solutions.com/media/global/produc...

Hi, thanks. Thought it might be so. Still...

RADAR can have high(er) angular resolution with (e.g.) phased arrays (linear or not) and digital beamforming. I guess it's the way the industry works and it wants small cheap composable parts, but using the full width of the car for a sensor array you could get amazing angular accuracy, even with cheap simple antennas. MIMO is also supposed to give somewhat better angular accuracy, since you can perform actual monopulse angular measurement (as if you had several independent antennas). There's even recent work on instant angular speed measurement through interferometry if you have the original signals from your array.

And with the wavelengths used in car RADARs you could get far down on range resolution, especially with the recent progress on ADCs and antenna tech.

I'm not saying you're wrong, you're describing what's available today (thanks for that).

Wondering when all this (not so new) tech might trickle down to the automotive industry... And whether there's interest (looking at big fancy manufacturers forgoing radar isn't encouraging there).

In theory a big phased array of cheap antennas is cheap, in practise not because you need to have equal impedance routing to all of the antennas, which means you need them all to be roughly equidistant to the amplifier. You could probably get away with blowing it up to the size of a large dinner plate, but then you also need a super stiff substrate to avoid flexing, and you need to convince manufacturers that they should make space for this in their design language without any metallic paint or chromed elements in front.

Which car brand do you think would take up these restrictions, and which customer is then going to buy the car with the big ugly patch on the front?

Thanks for the thoughtful reply.

Modern phased arrays can have independent transmitters (synchronized digitally or with digital signal distribution) or you can have one 'cheap and stupid' transmitter and many receivers, doing rx beamforming, and as for complexity you mostly 'just' need to synchronize them (precisely). The receivers can then be made on the very cheap and you need some signal distribution for a central signal processor.

Non-linear or sparse arrays are also now doable (if a bit tricky to calibrate) and remove the need for complete array or rigid substrate or structure.

If you imagine the car as a multistatic many-small-antennas system there's lots that could be done. Exploding the RADAR 'box' into its parts might make it all far more interesting.

I'll admit I'm way over my head on the industrial aspects, so thanks for the reality check. Just enthusiastic, the underlying radar tech has really matured but it's not easy to use if you still think of the radar as one box.

I know even for the small patch antennas we were looking at, the design of the waveguides was insanely complicated. I can't imagine blowing it up to something larger with many more elements.

If you wanted separated components to group together many antennas I suspect the difficulty would be accurate clock synchronization what with automotive standards for wiring. I'm still not sure I understand how they can get away without having rigid structures for the antennas, but this would be a critical requirement because automotive frames flex during normal operation.

Cars are also quite noisy RF environments due to spark plugs.

I guess what you're speaking of will be the next 10-20 years of progress for RADAR systems as the engineering problems get chipped away at one at a time.

Ah I'm probably oversimplifying and working in an industry with a far higher price per sold unit, so have a very distorted view of 'easy' or 'recent'.

Thanks for humouring me. RADAR is a very fun and interesting topic.

There's also a legitimate harm to consumers with such a large radar array in the front bumper. Because even a minor fender bender could total a $50k car.

So the car would be very difficult to sell since few people are willing to pay much higher insurance premiums just for that.

Ah thanks, didn't take that into account.

I've heard people on the internet claim that, in automotive radar the first thing they do when processing the signal is discard any stationary objects. Apparently this is because the vast majority of the time it's a sign or overhead gantry or guard rail - any of which could plausibly be very close to the lane of travel thousands of times per journey - and radar doesn't provide enough angular resolution to tell the difference.

Personally I've never seen these claims come from the mouth of an automotive radar expert, and many cars do use radar in their adaptive cruise control, so I present it as a rumour, not a fact :)

Indeed, my VW which uses a forward looking radar has signaled several times for stationary objects. In fact, the one time it literally stopped an accident was for a highway that suddenly turned into a parking lot. People keep repeating BS said by tesla and tesla apologists for why their cars run into stopped things and others seem to have less of a problem with it.

> I find very strange the claim that a moving doppler (pulsed doppler?) radar 'generally doesn't help to detect stationary objects'. I mean if the car is moving, it generates a doppler shift on all objects moving at a different speed, right?

I’m in the same boat as to not understanding why, but from what I have read the problem indeed isn’t that it doesn’t detect them, it’s that there are too many of them, and nobody has figured out how to filter out the 99+% of signals you have to ignore from the ones that may pose a risk, if it’s doable at all.

I think that at last part of the reason is that spatial resolution of radar isn’t great, making it hard to discriminate between stationary objects in your path and those close to it (parked cars, traffic signs, etc). Also, some small objects in your path that should be ignored such as soda cans with just the ‘right’ orientation can have large radar reflections.

Especially when most car radars are FMCW radars. They not only do know the speed, they also know the distance.

Some of the newest car radars can do some beam formimg, but not all.

Most models have multiple radars pointing in multiple directions as that's cheaper than AESA.

Only just recently have "affordable" beamformer's come to the market. And those target 5G basestations.

So the spec in most K/Ka-band models starts at 24.250GHz, where the 5G band starts. While the licence free 24GHz band that the radars use is 24.000-24.250GHz.

If this was not bad enough there has been consistent push from regulators to get the car radars on the less congested 77GHz band. And there's even less afforable beamformers for that band.

Might be time for some state sponsorship to have the beamforming asics, fpga designs for these bands. Although I might be missing something: once you're back down in your demodulated sampling frequency, your old beamformer should suffice? Or are we talking 'adc+demodulator+filter+beamforming' asic?