How Passive Radar Works

It’s reminiscent of what are known as “unbranded pharmaceutical websites,” which focus on educating patients about conditions and symptoms without promoting a specific brand-name drug, which means the regulatory bar is far lower and you don’t need to include any safety info etc.

An example would be a website creating awareness around a disease for which there is (or was at the time) only one or two treatments for, like ED, crohns, a specific type of cancer, etc. in fine print at the bottom will say “Pfizer” or “j&j” but no drugs are mentioned, just a call to “ask your doctor about possible treatments.”

(Not so) funny enough - I just did the same thing for https://gunsight.com complete with Claude generated interactive simulations for ballistics. We are actually building radars, and are likely going to use the domain in the future, but with zero effort I transformed an otherwise parked domain into something with a minimal amount of utility. So I do recognize the pattern.

Half-broken visualizations look suspiciously like ones I get from LLMs, so who knows, maybe it's some LLM setting up their first blog?

Multistatic radars (of which bistatic are just the case with N=2) are like the nuclear fusion of radar systems: everybody agrees it would be neat to have them, but they're always 20-30 years in the future. In practice it is extremely difficult to maintain the precise timing synchronization required for radar systems. Especially when used in moving vehicles or in sparsely populated areas the expected error goes WAY up to the point of unusability.

The survivability gains are also overhyped since 1. the enemy can just blow up the transmitters leaving you with a bunch of useless receivers and 2. most air defense doctrines already treat radars as something that should be distributed widely, so you can lose a few without the whole system collapsing.

The article goes into this only briefly, but modern radar systems don't just send out any random pulse but they very specifically tailor the waveform going out in order to do cool signal processing tricks like pulse compression. There is also the matter of frequency. The lower the frequency, the bigger the antenna you would need to get a proper direction reading out of it. Fire control radars typically operate in the X-band, around 10 GHz. Most civilian radio transmitters are around 100 MHz, so you'd need impractically large antennas and even then the bandwidth limitations would severely limit spatial resolution. One saving grace here is that stealth airplanes are typically most highly optimized against X-band radars from the direction they're going to bomb (forward), so you might have a better chance with a normal system, but then you still might not have a precise enough target to actually shoot at.

So while the multistatic system does offer some advantages, in practice it's just cheaper and (importantly for military use) requires less fiddly bits in the field to just use normal monostatic radars. Civilian use also doesn't benefit greatly from being multistatic. It's a bit like Tesla turbines or hyperloops: cool idea and it even "works" in a way, but the normal way of doing things is just way better when budgets and engineering realities come into play.

Source: I was a radar engineering officer in the Dutch navy about a decade back.

One reason is Low Probability of Intercept radars (and transmitters / datalinks) do exist, and are very difficult (but not impossible) to identify and locate.

We've already got a really extreme version of this.

https://en.wikipedia.org/wiki/GNSS_reflectometry

Probably more complicated to setup in a hostile environment because you'd need multiple transmitters, which also need to remain stationary, or at least you need to accurately know when they move.

Much more covert, and civilian infrastructure also less likely to be blown up.

The image screams Australia, the image title confirms ...

https://www.silentiumdefence.com.au/our-solutions/space-doma...

but whether they have any connection or are just getting image jacked ... couldn't say.

This is a very good point to start: https://www.rtl-sdr.com/tag/passive-radar/

If you have more than one receiver, the main issue is time sincronisation between the receivers.

Using the two transmitters will complicate things a lot

You can start with the radar receiver data from this 7 part DIY radar course [1] from a guy who works at a company who sell the needed chips.

Halfway in the video he mentions the MIT (or Stanford) course of a professor who recently died. That course is online and has a lot of documentation (much better than this course.

Build Your Own Drone Tracking Radar: Part 1 https://www.youtube.com/watch?v=igrN_wd_g74&t=292s

You can contact me if you want more guidance. For passive radar you can just start with recorded data. I have access to huge amount of recordings on the Ukraine battlefield. Buying or building cheap antennas and radios is not needed for passive radar software development.

Radar was developed during the last two years of WOII, mainly in Boston at MIT and hundreds of companies each building a radar, most were deployed months later to win the war. Development after the war shifted to Silicon Valley, founding Silicon valley and the later chip and software startups decades later.

Would suggest to take a look at Jackson’s book on classical electrodynamics to get some intuition.

Lots of clever tricks, all ITAR controlled.

I did some searching and seems like an active area of research: https://ieeexplore.ieee.org/document/8768105/ and https://ieeexplore.ieee.org/document/9905046/

With their movement you might get some strange SAR like effects. Computationally complex but could add another dimension over a static tower.

Such radar would be a game changer.