MIT Lincoln Laboratory researchers introduce students to radar engineering
During MIT's Independent Activity Period (IAP) between the fall 2010 and spring 2011 semesters, twenty-six students responded "yes" to this question posed in the course description for an activity led by MIT Lincoln Laboratory engineers: "Are you interested in building and testing your own imaging radar system?"
In just three weeks, the students worked in teams to design, fabricate, and test a laptop-based radar sensor that was capable of measuring Doppler and range, and of forming synthetic aperture radar (SAR) images. The teams received class instruction on the fundamentals of radar and SAR imaging, and kits from which to develop their systems. To their surprise, the kits contained coffee cans, which Dr. Gregory Charvat, one of the course instructors, explains were to be used as transmit and receive antennas:
"In developing the course, we were unable to find a kit that offered a suitable level of sophistication. All the commercial kits we could find were simple Doppler speed guns. So I designed a kit that is a coherent frequency-modulated continuous-wave radar capable of measuring Doppler versus time and range versus time, as well as performing SAR imaging. The kit supplies coffee cans as antennas to reduce cost." The kits also contained mini-circuit parts and a solderless breadboard that would allow quick fabrication and easy modification. The systems built from the kits run on AA batteries and use a laptop audio input for digitization. Data were recorded as .wav files and then processed in MATLAB computational software.
"One of the things I really grew to appreciate through the radar building process was how accurate a hand-built coffee-can radar could be," says Paresh Malalur, an MIT graduate student who took the course. "The system was much more responsive than I was expecting. For instance, one of the experiments we did was to measure the Doppler shift on a free-falling object (a book wrapped in foil). I was shocked to see the frequency ramp up in a perfectly linear manner over time. I was expecting a coffee cantenna system to have much higher noise and much less sensitivity."
During the three weeks, students performed in-class experiments with the radar systems they built. They also conducted field experiments (in Cambridge) such as measuring the speed of a passing car or plotting the range of a moving target. The culminating activity of the course was a contest to form the most detailed and creative SAR image. The winning image, created by Tony Hyun Kim, Nevada Sanchez, and Paresh Malahur, is of the outdoor steel sculpture La Grande Voile (Great Sail), designed by Alexander Calder and installed outside the List Visual Arts Center at MIT.
The winning SAR image. To the right is the actual sculpture that is depicted in the image.
Alexander Calder, La Grande Voile, 1968. Photo courtesy of MIT List Visual Arts Center.
"This is one of the most beautiful SAR images I have seen, and it was made by a radar built of coffee cans and that plugs into a laptop audio input," says Charvat.
The objective of the course was to generate student interest in applied electromagnetics, signal processing, and RF systems. The field experiments and the imaging contest were the incentives for students to configure their radars to work properly and to delve into the subjects more deeply. "The more radar experiments they attempted, the deeper their questions became," says Charvat.
The course, the full tile of which is "Build a Small Radar System Capable of Sensing Range, Doppler, and Synthetic Aperture Radar Imaging," was enthusiastically received by the students, who dedicated outside-the-classroom hours to conducting field trials.
"A few of the students were actively blogging as they were taking the course so we were able to watch their enthusiasm for the class grow as their radar started to come together," says Jonathan Williams, another instructor for the course. "We could also tell the enthusiasm students had for the class by how much work they did beyond the scope of the class. Not only did they build and test the radar from a kit of parts, some of them made significant improvements to the radar." Among those improvements were the development of a real-time data viewer that allowed a student to record live videos of data as they were being taken and the discovery of a simple algorithm that cleaned up "messy," real-world data.
In addition to Charvat and Williams, Drs. Alan Fenn, Stephen Kogon, and Jeffrey Herd served as instructors or co-developers of the activity. Kim, another MIT graduate student, was impressed by the curriculum these engineers developed. "The teaching staff emphasized the historical context that surrounded the development of radar technology. As our team implemented and tested our rudimentary radar system, we could appreciate the implications of our design choices not only by their technical performance, but also in terms of their broader societal and historical impact."
On the final class day, Dr. Eric Evans, Director of Lincoln Laboratory, Dr. Marc Bernstein, Associate Director, and Dr. Robert Shin, Head of the ISR and Tactical Systems Division, judged the SAR imaging contest. The trophy, featuring a coffee can antenna, was presented by Evans.
All nine teams of students were able to achieve Doppler/time and range/time measurements with their radar systems, and seven teams achieved SAR imaging.
|The graph on the left shows the Doppler vs. time measurements for a pendulum. The graph on the right shows range vs. time measurements of a student running in the basement MIT Building 5.
Posted April 2011
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