Ask Hackaday: How Did They Shoot Down a Stealth Aircraft?

sketch of f117 fighter flying

It was supposed to be a routine mission for U.S. Air Force Lt. Col. Darrell P. Zelko, a veteran pilot of the 1991 Gulf War. The weather over the capital city of Serbia was stormy on the night of March 27th, 1999, and only a few NATO planes were in the sky to enforce Operation Allied Force. Zelco was to drop 2 laser guided munitions and get back to his base in Italy.

There was no way for him to know that at exactly 8:15pm local time, a young Colonel of the Army of Yugoslavia had done what was thought to be impossible. His men had seen Zelco’s unseeable F117 Stealth Fighter.

Seconds later, a barrage of Soviet 60’s era S-125 surface-to-air missiles were screaming toward him at three times the speed of sound. One hit. Colonel Zelco was forced to eject while his advanced stealth aircraft fell to the ground in a ball of fire. It was the first and only time an F117 had been shot down. He would be rescued a few hours later.

How did they do it? How could a relatively unsophisticated army using outdated soviet technology take down one of the most advanced war planes in the world? A plane that was supposed be invisible to enemy radar? As you can imagine, there are several theories. We’re going deep with the “what-ifs” on this one so join us after the break as we break down and explore them in detail.

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The First Arduino Radar Shield

The first Radar Arduino ShieldThe very first fully operational radar Arduino shield was recently demonstrated at Bay area Maker Faire. It was built by [Daniel] and [David], both undergrads at UC Davis.

Many have talked about doing this, some have even prototyped pieces of it, but these undergrad college students pulled it off. This is the result from Prof. ‘Leo’ Liu’s full-semester senior design course based on the MIT Coffee Can radar short course, which has been going on for 2 years now. Next year this course will have 30 students, showing the world the interest and market-for project based learning.

Check out the high res ranging demo, where a wider band chirp was used to amazing results. Video below.
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DIY Ultra Wideband Impulse Synthetic Aperture Radar And A MakerBot

state

What could possibly be better than printing out a few low-resolution voxels on a MakerBot? A whole lot of things, but how about getting those voxels with your own synthetic aperture radar? That’s what [Gregory Charvat] has been up to, and he’s documented the entire process for us.

The build began with an ultra wideband impulse radar we saw a while ago. The radar is built from scraps [Greg] picked up on eBay, and is able to image a scene in the time domain, creating nice linear sweeps on a MATLAB plot when [Greg] runs in front of the horns.

With an impulse radar under his belt, [Greg] moved up the technological ladder to something that can produce vaguely intelligible images with his setup. The synthetic aperture radar made from putting his radar horns on the carriage of a garage door opener. The horns slowly scan back and forth along the linear rail, taking single impulse readings and adding them together in an image. In the video below, [Greg] is able to image a few pieces of copper pipe only a few inches in diameter. The necessary equipment for this build only cost [Greg] a few hundred bucks at the Dayton Hamvention, and a similar setup could be put together for even less.

If building an X band impulse synthetic aperture radar isn’t impressive enough. [Greg] also 3D printed one of his radar images on a MakerBot. That’s just applying stlwrite to the 2D radar image and feeding it into MakerWare. Gotta have that blog cred, doe. It also makes for the best headline I’ve ever written.

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Radar Imaging in your Garage: Synthetic Aperture Radar

xband_uwb_fmcw_sar_callouts-no-border

Learn why you were pulled over, quantify the stealthiness of your favorite model aircraft, or see what various household items look like at 10 GHz. In this post we will describe the basics of Synthetic Aperture Radar (SAR) imaging, beginning with a historical perspective, showing the state of the art, and describing what can be done in your garage laboratory. Lets image with microwaves!

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Guest Post: Try Radar for Your Next Project

greg_sar_radar

(photo taken by Matt Metts)

Sensors. The low-end stuff that we can get our hands on usually suffers from poor range, lack of sensitivity, and no way to characterize what the target is. But today we can use the good stuff that, until recently, was only available to military: radar. In this post we will discuss how radar works, commercially available small radar devices, and where to learn more to help make it easy to add radar to your next project. Reach out and sense something!
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Homebuilt Ultra Wideband Impulse Radar

wideband impulse radar

[Dr. Gregory Charvat] tipped us off to a video demonstration of his ultra-wideband impulse radar he built using some of his existing radar gear and a few bits purchased off eBay. The homebuilt radar system worked well in his backyard but not much is covered about the build. [Greg] is promising a new book on practical approaches to developing and using small radar devices titled “Small and Short Range Radar Systems“. He told us that the draft is finished and covers radar systems like doppler, linear FM, synthetic aperture, phase array and also UWB impulse radar. It sounds like an interesting book, which can be pre-ordered on Amazon, and will include schematics and bill of materials so you too could build a UWB impulse radar or other small radar systems. Some of the advantages of a UWB impulse radar system are that it produces sub-nanosecond pulses good for tracking moving objects as well as imaging stationery objects. Such radar technology can even image buried objects like metallic and nonmetallic landmines.

Join us after the break for a little background on [Dr. Gregory Charvat] and to watch his demonstration video.

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Making a 9GHz doppler radar

[Kalle] is currently building an FMCW radar, but as he doesn’t have all the parts finished he decided to build a 9GHZ doppler radar in the mean time. The H-plane horn antennas were made from brass sheet and soldered together. [Kalle] checked the matching between the emitter and the antenna by inserting a directional coupler between the two and measuring the intensity of the reflected signal (approximated return loss). At 9Ghz, the Doppler shift for a 1 meter per second speed is about 30Hz so he connected the radar’s output signal to his soundcard.

A quick explanation of the Doppler effect that a radar uses: if you send an RF signal at a given frequency to a moving target, the reflected signal’s frequency will be shifted. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession. Hackaday featured plenty of projects using this effect: a small doppler motion sensor, gesture control using doppler shift, hacking an old radar gun

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