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Antennas inside


Read more about the Virginia Tech Configurable Computing Lab at their website.

Jacob Couch with an antenna used to detect emissions from the FPGA

Jacob Couch

“A lot of times, your advisor’s weird ideas really work,” says masters student Jacob Couch, who is working with ECE professor Peter Athanas on a new use for a field programmable gate array (FPGA): a transmitter using the routing resources of an FPGA.

The transmit-only mechanism uses an oscillator to communicate binary data to an external antenna via amplitude shift keying (ASK). ASK works by keeping frequency constant while varying the amplitude of the signal. In this case, as in most ASK applications, the signal is either “on” or “off,” denoting logic 1 or logic 0.

Couch explains that “we’re redoing the routing on an FPGA to take an existing design and attach a geometric shape to it. If this shape oscillates at a high frequency, we can pick up the radiation.”

Once the oscillator is in place, Couch looks for unused routing resources to build the antenna. One of the most successful antenna designs uses a fractal design, which allows for the maximum wire length and number of corners. “Everything on the FPGA is so small that we are trying to make it bigger,” explains Couch. Also, longer antennas allow him to use a lower frequency: the frequency range he’s looking at now is in the hundreds of MHz.

“This is all done from within the FPGA,” Couch stresses, “there are no external ports. This is a mechanism to release data from the FPGA.” He is testing the designs on a Xilinx FPGA, which is less than one inch by one inch.

For testing purposes, Couch has borrowed a wideband antenna from ECE professor Bill Davis with the Virginia Tech Antenna Group (VTAG). “It has relatively uniform gain from 50 MHz to 2 GHz, so it’s good for testing,” explains Couch.

What data can this design transmit? Anything. “We could expose any data on the FPGA,” according to Couch. The project is funded through the Defense Advanced Research Projects Agency (DARPA) Trusted Integrated Circuits (TRUST) project, and the CCM lab is a subcontractor of USC ISI, which has a branch in Arlington. The TRUST project is making sure that the technology going into U.S. weapons systems is reliable. “We’re funded to insert black hat things into an FPGA, such that another group on this project can detect what we have done to the FPGA. But we’re also looking to do white hat applications from the tools we have developed,” says Couch.

“In the FPGA community we’re constantly looking at slight improvements here and there, but very few big picture ideas. This is something kind of off-the-wall that no one has ever tried before.”

And it works.