[G. Eric Rogers] is a radar-systems engineer who just happens to live within sight of the aircraft approach path for the local airport. We wonder if that was one of the criteria when looking for a home? Naturally, he wanted his own home-based system for tracking the airplanes. He ended up repurposing a motorized telescope for this purpose.

The system does not actually use Radar for tracking. Instead, the camera strapped to the telescope is feeding a video experimenter shield. A tracking algorithm analyzes the video and extrapolates vector data. From there, the base unit can be controlled by the Arduino via an RS232 interface.

There are some bugs in the system right now. The Arduino has something of an ADHD problem, losing interesting and going to sleep in the middle of the tracking process. [Eric's] workaround uses the RS232 board to periodically reset the Arduino, but he hopes to squash this bug soon.

[Gustaf] has been playing around with machine vision for a while and sent in his latest project in on our tip line. It’s a video based car radar system that can detect cars in a camera’s field of vision while cruising down the highway.

Like [Gustaf]‘s previous experiments with machine vision where he got a computer to recognize and count yellow cylinders and green rectangles, the radar build uses ADABoost and the AForge AI/Machine Vision C# framework. [Gustef] used an evolutionary algorithm to detect the presence of a car in a video frame, first by selecting 150 images of cars from a pre-recorded video, and the another 1,850 images were selected by a computer and confirmed as a car by a human eye.

With 2000 images of cars in its database, [Gustaf]‘s machine vision algorithm is able to detect a car in real-time as he drove down a beautiful Swedish highway. In addition to overlaying a rectangle underneath each car in a video frame and an awesome  Terminator-style HUD in the upper right corner, [Gustaf] also a distance display above the hood of his car.

It’s an awesome build that makes us wonder if [Gustef] is building an autonomous car. Even if he’s not, it really makes us want to install a video HUD in our whip, just to see this in action.

Turns out you don’t need to be Superman to see through walls. Researchers at University College London have developed a way to passively use WiFi as a radar system. Unlike active radar systems (which themselves send out radio waves and listen for them to echo back), passive radar systems cannot be detected.

The system is small enough to fit in a briefcase, and has been tested through a one-foot-thick brick wall. It can detect position, speed, and direction of a person moving on the other side of that wall, but cannot detect stationary object. [Karl Woodbridge] and [Kevin Chetty], the engineers behind the prototype, think it can be refined to pick up motion as minuscule as a person’s rib cage moving with each breath. For some reason we get the picture in our mind of that body scanner from the original Total Recall.

[via Reddit]

[Image Credit]

[Gregory Charvat] decided to see what he could do with this old Police radar gun. It is an X-band device that broadcasts continuous waves and measures the Doppler shift as they echo back. He cracked it open to see if he could interface the output with a computer.

After a little poking around he’s able to get it connected to a 12V feed from his bench supply, and to monitor the output with an oscilloscope. He established that it draws about 0.5A in current he built a companion board which uses AA batteries for power, and provides an audio output which can be plugged into his laptop’s audio-in jack. This technique makes reading the device as easy as recording some audio. From there a bit of simple signal processing lets him graph the incoming measurement.

In the video after the break you’ll see his inspection of the hardware. After making his alterations he takes it into the field, measuring several cars, a few birds, and himself jogging.

[Gregory Charvat] continues to have a great time testing out radar systems. He and a friend have pointed the radar out the garage door and are using it to see who can reach a high running velocity.

The last time we looked in on [Greg's] work he had acquired an old police radar unit and wired it up to use with a laptop. The hardware he’s working with now is a lot more bulky and we don’t think it will be hitting the road with him anytime soon (although it is on wheels). The video after the break starts off which an overview of the test system which is mounted in a waist-high rack. He illustrates how Labview is monitoring the radar inputs and then moves on to show off the hardware which is actually harvesting the data. The box is quite versatile, able to run five different systems and includes a slew of different connector types.

A few profs from MIT’s Lincoln Lab are giving those poor MIT undergrads something to do over winter break: they’re teaching a three-week course on building a laptop-powered radar system capable of radar ranging, doppler, and synthetic aperture imaging. Interestingly, the radar system that teams will build for the class has a BOM totaling $360, and they’re also putting the entire class online if you’d like to follow along and build your own.

From the lecture notes from the course, the radio system is made out of an off-the-shelf  LNA, oscillator, and  splitter. By connecting two coffee can ‘cantennas’, it’s possible to record a .WAV file from the signal coming from the radar and use MATLAB to turn that audio signal into a doppler radar.

It’s a very ambitious project that goes deep down the rabbit hole of RF and analog design. One of the lecturers made a YouTube demo of the radar in ranging mode; you can check that out after the break.

Blinking lights is a lot of fun, but if you’re getting an EE degree the cool stuff becomes a bit more involved. In this case, building your own radar is the thing to do. Here’s a coffee can radar setup being shown off by a group of UC Davis students. Regular readers will recognize the concept as one we looked at in December. The project was inspired by the MIT OpenCourseware project.

One of the cans is being used as a transmitter, the other as the collector. The neat thing about this rig is that the analysis is performed on a PC, with the sound card as the collection device. The video after the break shows off the hardware as well as the results it collected. About a minute and a half into the clip they show a real-time demonstration where a student walks in front of the apparatus while another takes a video of the plot results. As the subject moves away from the receiver the computer graph changes accordingly. The rest of the video covers some operational theory and pcb assembly.

[Thanks Gregory]

Picking just one image to show off all of the hacks done on this Jeep Wrangler is a tough order. We decided to go with this custom ceiling console as it features the most work done in a confined area.

Give the video walk-around a bit of time before you decide it’s not for you. [Eddie Zarick] spends the first moments touting his “Oakley” branding of the vehicle in decals, emblems, embroidered seats, zipper pulls, and more. But after that you’ll get a look at the pressurized water system we previously saw. Pull open the back gate and there’s a nice cargo cover he built that includes a cubby hole which stores the soft sides when he wants to take the top off. There are several other interesting touches, like the police radar spoofer that he uses to scare the crap out of speeders. Ha!

The ceiling console we mentioned earlier was completely custom-built. It includes a CB, scanner, HAM, and seven-inch Android tablet. There is also a set of push buttons which control the various bells and whistles; well, spotlights and inverter actually. Just add a commode and he’s ready to live out of his car.

CAN Bus hacking is all the rage right now. This particular project uses an early development version of an Arduino compatible CAN bus tool to integrate radar detector control into a Mazda dashboard. This image shows the output as the Whistler Pro-3600 radar detector boots up. The self test demonstrates what you would see on the dashboard display if your speed is checked using any of a handful of technologies. But it’s not just the dash display that’s working. The steering wheel controls are also capable of affecting the radar detector so that it can always be hidden from sight.

With auto manufacturers adding more numerous and larger displays to our vehicles it’s refreshing to see someone come up with a hack that makes pushing our own info to those screens possible. The CANBus Triple is an Arduino compatible board which patches into the data bus found in all modern vehicles. To integrate the Whistler for this hack [TheDukeZip] prototyped the interface on a regular Arduino board, then moved it over to the CANBus Triple once he had it working. Check out the video after the break to see the setup in action.

[Thanks Randy via Mazda Speed Forums]

We would be remiss if we didn’t mention that all of SparkFun’s open source hardware is now on Upverter.

Not wanting to tie up an iPad as a mini-gaming cabinet [Hartmut] hacked an Arcadi cabinet to use EUzebox instead.

Time travel happens in the bedroom as well. But only if you have your very own Tardis entrance.  [AlmostUseful] pulled this off with just a bit of word trim and a very nice paint job. [via Reddit]

[Pierre] tricks an iPhone fingerprint scanner by making a replica out of hot glue.

Some of the guys from our parent company were over in Shanghai on business. [Aleksandar Bradic] made time to visit the Shanghai hackerspace while in town and wrote about the experience over on their engineering blog.

[Gregory Charvat] is a busy guy. In fact we’ve got a juicy hack of his saved up that we still need to wrap our minds around before featuring. In the mean time check out the Intern-built coffee can radar that he took over and tested on a  multi-million dollar Spherical Near Field Range.

And finally, everyone loves coffee hacks, right? Here’s what [Manos] calls a Greek style instant coffee machine.

[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

[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.

[Greg] has his PhD in Electrical Engineering from Michigan State University. As a technical staff member at MIT Lincoln laboratory he taught radar courses and developed the top ranking MIT professional education course in 2011 titled “Build a Small Radar Sensor” which is included under MIT OpenCourseWare (OCW), you might recall this as the coffee can radar. You can also catch [Greg] on the famous Amp Hour radio show recorded back on October 1, 2012.

(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!

Radar Basics

Radar uses a radio transmitter and receiver to measure the time of flight from a transmitted radio wave that scatters off a target back to the receiver.

Radar is simple, it consists of a radio transmitter and receiver. Radar is a World War Two acronym meaning Radio Direction and Ranging, in other words a radar consists of a radio transmitter and receiver where the range to an object is measured by clocking the time between the transmitter transmitting a known modulated waveform and the receiver receiving this waveform scattered from a target.

This block diagram represents a conventional radar that comes to mind when you think about radar, you might find this design used on a fishing boat or commercial aircraft.

One enabling technology for Radar was the cathode ray tube (CRT), which facilitated a method of measuring the time delay between transmitted and received waveforms. This led to the development of numerous radar sensors used in the second world war, which generally followed the Plan Position Indicator (PPI) architecture.

Toady, rather than using a CRT we can use high-speed digitizers. This offers the obvious advantage of applying signal processing to acquired data so that only moving targets are detected, tracking can be achieved, imaging, and a multitude of other modes.

But for hobbyist and consumer projects we do not need this much power, range, and can not afford the cost. We need the ability to sense like a long range radar (detecting only moving targets, imaging, Doppler, signatures, etc) but at short ranges and at low costs.

Very few off-shelf small radar options exist as of today. In this post we’ll review these, their basic architectures, and direct you on the next steps.

Continuous Wave (CW) Doppler Radar

How CW Doppler radar works.

If you are not interested in ranging or imaging but would like to measure velocities or radar signatures then consider CW Doppler radar. CW Doppler radar works by feeding the output of a CW oscillator to an antenna and radiates that carrier towards a moving target. This carrier scatters off the moving target back to the receive antenna where it is amplified and fed to a frequency mixer. The mixer mixes the oscillator and the scattered carrier resulting in a Doppler shift product. This product is the Doppler shift off of the carrier’s center frequency and is generally in the KHz range. Low enough to be easily digitized by the audio input port of a laptop computer or other low-cost digitizer.

A low-cost X-band CW Doppler Radar Module, readily available on Ebay.

Try a CW Doppler radar. You can hack an old police radar gun  by locating the video amplifier or mixer’s output and plugging that signal into the audio input port of your laptop and displaying this data using a ‘water fall’ Fourier transform.

If you find an old motion sensor or door opener. These typically use CW Doppler radar modules known as Gunnplexers. Hack into one just as you would with the Police radar.

Or, you can procure new off-shelf X-band CW Doppler radar devices from China for < $10 on Ebay. I’ve used these devices before, they do work but have limited range. This may not matter for your project.

Impulse Radar

The most basic impulse radar simply feeds the output of the impulse generator directly to the transmit antenna. Scattered impulses are amplified and digitized.

Short range radars sense at 150m or less. At these short ranges extremely short pulses (meaning short in time duration, nS or pS in duration) are required to provide sufficient resolution to be useful. Short pulse, or impulse radar systems, generally follow a simple architecture where the impulse generator is often tied directly to a transmit antenna and a low noise amplifier (LNA) is tied to a receive antenna. A high speed digitizer is triggered off the impulse generator and acquires data on the output of the LNA.

Novelda manufactures single-chip impulse radar devices.

You can incorporate impulse radar technology into your next project. Commercial versions of impulse radars are available to hobbyists and developers. Most notable are the ASIC based impulse radar manufactured by Novelda. These devices do require external antennas but contain on-board radar and high speed digitizers.

Additional impulse radar systems are being manufactured in quantity for automotive applications (blind spot detection, parking aids, etc), but details on these are not easy to find unless you directly engage the manufacturers. Manufacturers of automotive radar equipment include, Delphi, Continental, TRW, Bosch, Denso, and Autoliv.

Frequency Modulated Continuous Wave (FMCW) Radar

FMCW radar was originally used in radar altimeters starting in the 1930′s. Today, FMCW radar is the leading short-range radar architecture because it offers short-pulse radar resolution while providing significantly greater sensitivity with the same peak transmit power. This is because FMCW radars transmit continuously and leverage the discrete Fourier transform (DFT) to increase SNR in proportion to the time over which the DFT is applied. But for a hobbyist the key take-away is that these radars use a simple architecture and radar signals can be acquired by low-bandwidth digitizers such as the audio input port on your laptop, ADC input ports on micro controllers, the lower cost National Instruments NIDAQ units, etc.

How FMCW radar works.

For an FMCW radar, a CW oscillator is frequency modulated with a linear ramp. In other words, the CW oscillator starts at one frequency and ramps-up to a second over a relatively long period of time (0.5-10 uS). This waveform is radiated out of the transmit antenna towards the target scene. Some of this waveform is fed to the receiver mixer. What is scattered off the target is amplified by the LNA and fed into the receive mixer where it is mixed with the transmit waveform. The mixing product results in a low frequency (KHz range) beat tone that is proportional to range. The higher the frequency of beat tone the further the target. If measuring a multitude of targets then expect to see a multitude of beat tones superimposed on each other. To measure the range to targets you digitize with a low bandwidth digitizer being careful to synchronize the digitizer’s trigger with the start of the up-ramp. With this digitized data for each up-ramp, apply the DFT. This results in a time domain representation of the round trip time from transmitter, to targets, and back to receiver.

Add an FMCW radar to your next project. FMCW radar devices are available for developers and hobbyists. Some of the lowest cost FMCW radar devices are manufactured by RF Beam Microwave GmbH, who offers 24 GHz FMCW radar modules for less than $10 in quantity, shown here is a K-LC1.

In addition to this, you can build your own ‘Coffee Can Radar’ from the MIT Opencourseware site.

Not interested in building your own coffee can radar from scratch? You can buy a ready-made coffee can radar kit form Quonset Microwave. This radar provides data via a USB or BlueTooth.

And coming soon will be the radar Arduino shield! Credit for this belongs to Tony Long, who developed this shield loosely based on the MIT Coffee Can radar.

Learn more

Add a radar sensor to your next project. It is not difficult to do with some basic understanding of architectures and signal processing. To learn more,

• teach yourself for free with the MIT OCW course,
• Pick up Gregory Charvat’s book: Small and Short-Range Radar Systems (use promo code EEE24 for discount),
• If you need help please visit the community forum which Greg set up.
• Want to learn fast and your employer is willing to pay for a short-course?  Sign up to the MIT Professional Education Short-Course ‘Build a Small Radar System,’ and learn about small radar systems by making your own in 5 days.  This was the top-ranked MIT Professional Ed course in 2011.

We can do this.

Soon small radar devices will be everywhere, let your project be one of the first!

Gregory L. Charvat, is author of Small and Short-Range Radar systems, co-founder of Butterfly Network Inc., visiting research scientist at the Camera Culture Group MIT Media Lab, and editor of the Gregory L. Charvat Series on Practical Approaches to Electrical Engineering. He was a technical staff member at MIT Lincoln Laboratory from September 2007 to November 2011, where his work on through-wall radar won best paper at the 2010 MSS Tri-Services Radar Symposium and is an MIT Office of the Provost 2011 research highlight. He has taught short radar courses at the Massachusetts Institute of Technology, where his Build a Small Radar Sensor course was the top-ranked MIT professional education course in 2011 and has become widely adopted by other universities, laboratories, and private organizations. He has developed numerous rail SAR imaging sensors, phased array radar systems, and impulse radar systems; holds several patents; and has developed many other radar sensors and radio and audio equipment. He earned a Ph.D in electrical engineering in 2007, MSEE in 2003, and BSEE in 2002 from Michigan State University, and is a senior member of the IEEE, where he served on the steering committee for the 2010 and 2013 IEEE International Symposium on Phased Array Systems and Technology and chaired the IEEE Antennas and Propagation Society Boston Chapter from 2010-2011.

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!

The H2S radom (antenna covering, above) and antenna (below).

The History of SAR

Ground mapping (or imaging the ground terrain) using microwave radar was done routinely in the Second World War by the Royal Air Force for the purpose of navigation and bomb laying using the H2S radar system. The H2S used a large aperture rotating antenna in the belly of a bomber aircraft. This antenna would rotate in circles with its beam directed toward the ground. Range to target was plotted in a plan position indicator (PPI, or a radar screen as most would recognize it) showing what was below and around the aircraft.

The angular resolution of this radar set depends on the antenna aperture size (e.g. antenna size). The bigger the aperture the finer the angular resolution, just like the reflector on a flashlight provides a tighter light beam the larger it is (this is why spotlights shine tight beams well into the sky). A typical example of an H2S radar image is shown below recorded during s bombing raid over Berlin. In this image the river is clearly visible as well as other blob-like targets which are landmarks that a trained operator would recognize.

Radar ground image of Cologne during a bombing raid in the Second World War.

Earlier versions of the H2S were at S-band (3 GHz) and later higher resolution sets were at 10 and 24 GHz (for an interesting read on this technology, Echos of War: The Story of H2S Radar).

Synthetic Aperture Radar (SAR) is a modern ground mapping technique where high resolution is achieved by a very large aperture that is synthesized over the flight path of an aircraft. This is done by recording reflected radar pulses at known locations along the flight path. The radar must accurately know the aircraft’s position and back-out perturbations in flight path so that all scattered pulses are aligned in time and phase. After this a SAR imaging algorithm is applied to the data to process an image.

An aircraft (or other moving vehicle) synthesizes an extremely large aperture by recording scattered radar pulses over the flight path and processing these pulses in a SAR imaging algorithm, thereby synthesizing a very large aperture which provides high angular resolution.

Developments in SAR Technology

This technique was first developed in 1957 using photographic film to record the radar data and an image processor made from lenses. Today digitizers and other data acquisition equipment can store data for offline processing or even process imagery in real-time.

State of art airborne SARs include the MIT Lincoln Laboratory LIMIT system (PDF), which operates at X-band (10 GHz) and is mounted on an old 707 aircraft for testing advanced SAR imaging concepts.

Another is the Sandia National Laboratory’s Ka Band SAR imaging system (to see an amazing portfolio of airborne SAR imagery visit here PDF), an example airborne SAR image from this system is shown below.

SAR imagery from the Sandia National Laboratory’s Ka band airborne SAR imaging system.

SAR imagery appears to be nearly photographic but it is not a photograph, it is a 2D hologram. Unlike a satellite image the radar is not measuring the target scene from above it is measuring from the side at a fairly significant distance. The resulting image is a birds-eye view with many shadows where each pixel is mapped directly to the aircraft’s flight path in range and cross-range.

Most recently, small and light weight airborne SAR imaging systems weighing only a few lbs have been developed for micro-UAVs, for example the NanoSAR imaging system manufactured by IMSAR.

Create your own SAR imaging system.

To SAR image in your garage, try making a rail SAR imaging system, where a UWB radar sensor moves down well controlled path on a linear rail.

Airborne SAR imaging is beyond the means of most hackers and hobbyists. The good news is that you can do it yourself with better resolution if you limit the scope of the problem and reduce maximum range, power, and the complexity of your radar sensor. To achieve this consider the rail SAR imaging system. In this, an ultrawideband (UWB) radar device is mounted on a long linear stage (typically 6′ to 8′ in length). The radar pulses once, moves, pulses again, each echo is recorded. This process repeats itself along the rail until a complete data set is acquired.

For the UWB radar sensor you can use one of the sensors described in my previous post that is either an impulse or an FMCW radar or create your own. For the linear rail stage you can use anything from a Genie garage door opener assembly (which contains a lead screw inside of a long aluminum extrusion with a car that rides on the threads) to one stage on a full-size CNC router table.

Make your own from junk parts

One example of a hacked-together rail SAR is the ‘backyard SAR’ imaging system, where an X-band UWB FMCW radar front end was mounted to an 8′ long linear stage built from a Genie garage door opener, a cordless drill transmission, and a stepper motor following the block diagram shown. X-band microwave components were acquired at hamfests.

Block diagram of the ‘backyard SAR’ imaging system.

The ‘backyard SAR’ imaging system, deployed in my backyard.

To process data from a rail SAR like this follow the procedure outlined in the Range Migration Algorithm chapter from Spotlight Synthetic Aperture Radar: Signal Processing Algorithms, which follows these steps:

1. Cross range discrete Fourier transform (DFT).
2. Apply matched filter.
3. Perform Stolt interpolation.
4. 2D IDFT into image domain.

When implemented correctly this will result in the imagery shown below, achieving approximately 1×1” resolution at X-band with approximately 5 GHz of chirp bandwidth.

Build the coffee can radar kit

The MIT coffee can radar kit is capable of producing coarse SAR imagery.

To make SAR imaging accessible the MIT ‘coffee can’ radar course was developed, where you can SAR image with the coffee can radar. The goal of the SAR imaging experiment was to show students it is possible to differentiate in both rang and cross range when imaging some very large targets.

The coffee can radar does not produce the best imagery but it shows a concept to students. To acquire an image, it is placed on a linear track with a tape measurer for a position reference. This could be a length of 2×6” or a straight rail somewhere. The radar is manually moved in 2” increments where a toggle switch on the side mutes the synchronization signal output, showing the computer that the radar has moved.

Resulting in imagery comparable to that shown below.

Give it a try, but be sure to image a large target scene. The algorithm is already written and the procedure is straight forward (scroll down to ‘Experiment 3: SAR imaging’).

Many more examples of rail garage-made SAR imaging systems are shown here.

Learning Curve

It is not trivial to design, build, and write a an imaging algorithm for your backyard rail SAR. Caveats to implementation and processing include having to scale to your wavelength range, the need for calibration to a point target (a large pole or similar), use of coherent background subtraction, and other processing techniques. But we can philosophize about these all day, the best way to learn is to try it yourself:

1. Learn by doing, build the MIT Coffee Can Radar and try the SAR imaging experiment.
2. For a quick-read technical background read Chapter 4 and for details on numerous practical examples Chapter 5 in the book Small and Short-Range Radar Systems (use promo code EEE24 for discount).
3. Process a SAR image right now. Download data sets for X and S-band and their associated processing algorithms written in MATLAB. With this you will learn how to apply calibration and coherent background subtraction.
4. Need help? Post your questions to the Tin Can Radar Forum.

With these resources, patience, perseverance, and coffee anyone can create a SAR imaging system in their garage.

Gregory L. Charvat, is author of Small and Short-Range Radar systems, co-founder of Butterfly Network Inc., visiting research scientist at the Camera Culture Group MIT Media Lab, and editor of the Gregory L. Charvat Series on Practical Approaches to Electrical Engineering. He was a technical staff member at MIT Lincoln Laboratory from September 2007 to November 2011, where his work on through-wall radar won best paper at the 2010 MSS Tri-Services Radar Symposium and is an MIT Office of the Provost 2011 research highlight. He has taught short radar courses at the Massachusetts Institute of Technology, where his Build a Small Radar Sensor course was the top-ranked MIT professional education course in 2011 and has become widely adopted by other universities, laboratories, and private organizations. He has developed numerous rail SAR imaging sensors, phased array radar systems, and impulse radar systems; holds several patents; and has developed many other radar sensors and radio and audio equipment. He earned a Ph.D in electrical engineering in 2007, MSEE in 2003, and BSEE in 2002 from Michigan State University, and is a senior member of the IEEE, where he served on the steering committee for the 2010 and 2013 IEEE International Symposium on Phased Array Systems and Technology and chaired the IEEE Antennas and Propagation Society Boston Chapter from 2010-2011.

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.

The 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.

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.

Theory 1 – Lucky Shot

The Serbian Army was monitoring US and NATO UHF and VHF communications, which were oddly enough unencrypted. This combined with the fact that the stealth fighters were using the same entry and egress routes means they could have worked out the general area of where they were going to be and when they were going to be there.

Theory 2 – Radar Hack

It has been theorized that they modified the antiquated soviet radars to operate at longer wavelengths. So when the bomb bay doors opened, they could see the aircraft. But using a longer wavelength would have required modification to the radar antenna. Such modifications are not easy to pull off, and would require advanced test equipment and knowledge. Is it possible to do this in the field with no testing or equipment?

 Theory 3 – The Invisible Man in the Rain

Imagine Harry Potter had donned his invisibility cloak and was making his way out of the castle, when it started raining. Though other wizards and witches might not be able to see Harry directly, they would be able to see a disturbance in the rain. Want to see something invisible? Provide a medium and look for the disturbance within it.

It has been speculated that Colonel Dani tapped into the country’s cell phone network then looked for, found and targeted such a disturbance. But how would they pull this off? Would a stealth fighter, or any plane cause a visible disturbance in the RF field? If so, how do you detect it?

Theory 4 – Your Turn

How would you detect a stealth aircraft?

Public transit can be a wonderful thing. It can also be annoying if the trains are running behind schedule. These days, many public transit systems are connected to the Internet. This means you can check if your train will be on time at any moment using a computer or smart phone. [Christoph] wanted to take this concept one step further for the Devlol hackerspace is Linz, Austria, so he built himself an electronic tracking system (Google translate).

[Christoph] started with a printed paper map of the train system. This was placed inside what began as an ordinary picture frame. Then, [Christoph] strung together a series of BulletPixel2 LEDs in parallel. The BulletPixel2 LEDs are 8mm tri-color LEDs that also contain a small controller chip. This allows them to be controlled serially using just one wire. It’s similar to having an RGB LED strip, minus the actual strip. [Christoph] used 50 LEDs when all was said and done. The LEDs were mounted into the photo frame along the three main train lines; red, green, and blue. The color of the LED obviously corresponds to the color of the train line.

The train location data is pulled from the Internet using a Raspberry Pi. The information must be pulled constantly in order to keep the map accurate and up to date. The Raspberry Pi then communicates with an Arduino Uno, which is used to actually control the string of LEDs. The electronics can all be hidden behind the photo frame, out of sight. The final product is a slick “radar” for the local train system.

There aren’t many Hackaday Prize entries playing around in RF, save for the handful of projects using off the shelf radio modules. That’s a little surprising to us, considering radio is one of the domains where garage-based tinkerers have always been very active. [Luke] is bucking the trend with a FM continuous wave radar, to be used in experiments with autonomous aircraft, altitude finding, and synthetic aperture radar imaging.

[Luke]‘s radar operates around 5.8-6 GHz, and is supposed to be an introduction to microwave electronics. It’s an extremely modular system built around a few VCOs, mixers, and amplifiers from Hittite, all connected with coax.

So far, [Luke] has all his modules put together, a great pair of cans for the antennas, everything confirmed as working on his scope, and a lot of commits to his git repo.

You can check out [Luke]‘s demo video is available below.

The project featured in this post is a quarterfinalist in The Hackaday Prize.

A lot of hackers take the “learn by doing” approach: take something apart, figure out how it works, and re-purpose all of the parts. [Henrik], however, has taken the opposite approach. After “some” RF design courses, he decided that he had learned enough to build his own frequency-modulated continuous wave radar system. From the level of detail on this project, we’d say that he’s learned an incredible amount.

[Henrik] was looking to keep costs down and chose to run his radar in the 6 GHz neighborhood. This puts it right in a frequency spectrum (at least in his area) where radar and WiFi overlap each other. This means cheap and readily available parts (antennas etc) and a legal spectrum in which to operate them. His design also includes frequency modulation, which means that it will be able to determine an object’s distance as well as its speed.

There are many other design considerations for a radar system that don’t enter into a normal project. For example, the PCB must have precisely controlled trace widths so that the impedance will exactly match the design. In a DC or low-frequency AC system this isn’t as important as it is in a high-frequency system like this. There is a fascinating amount of information about this impressive project on [Henrik]’s project page if you’re looking to learn a little more about radio or radar.

Too daunting for you? Check out this post on how to take on your first radar project.