Harmonic Radar

SciVIsion, Inc. has developed a substantially miniaturized prototype with enhanced capabilities at greatly reduced size, weight, and cost compared to the expensive legacy systems out there.

Harmonic radar is useful for detecting specific targets in high-clutter environments. A non-linear junction, such as a diode, will produce harmonics of RF energy incident on the diode, that can be detected with a radar receiver.

$1 harmonic radar planar tag developed by Michael Hirsch, with corrosion detecting element
$1 harmonic radar planar tag with corrosion detecting element

Modeled Harmonic Radar Performance

One of the first questions people have is what is the maximum range of the system. That depends on numerous factors, including transmit power of the radar, radar antennas, tag antennas, tag diode, and frequency band used. The typical radar equation is reconfigured into two-way Friis path loss, with a loss term for the harmonic radar tag. Conversion efficiency is typically less than 1%, so figure loss of at least 20dB for the tag.

In short, an unbiased diode tag will have maximum range of order 10 meters. You can push that up with more power or antenna gain. A biased tag may achieve 100-1000 meters range.

I have harmonic radar modeling code on Github. Please request what you’d like.

What frequency to use?

This depends on how large your tag can be. Work with insects has tended toward the 5/10GHz pairing or 10/20GHz. However the free space loss will be much lower at 917/1834MHz pairing, so if you can tolerate a larger antenna, and range is important to you, I would start thinking about 900MHz. Most of the world now has 900MHz license-free allocations with 1-4 Watts of transmit power allowed–just right for long range RFID and harmonic radar. See this page for further discussion.

Select Publications from the Author/Coauthor

Greg Charvat page on the 2005 era early harmonic radar system

Michigan State University Harmonic Radar Presentation

Michigan State University Harmonic Radar Paper

http://www.jpier.org/PIERM/pier.php?paper=15011605

has a list of worthwhile references.

Michigan State University Harmonic Radar

Historically, harmonic radar work at the Michigan State University has included tracking insects above and below ground. Harmonic radar tags and system were developed through a research partnership with the Dow Chemical Company. A patent was issued for the invention of a state-sensing harmonic radar tag to Michigan State University and Dow Chemical, U.S. Patent # 7,145,453.

The specific research work Michael has done in regards to harmonic radar technology include:

  1. Successful development of a miniature, low-cost harmonic radar tag that is half the size and costs 90% less to manufacture than the tag design patented above, while maintaining equal range of detection.
  2. Successful development of a more stable harmonic radar system than mentioned in the above patent. Specifically, the new design I developed provides for operation over a much wider temperature range, is unconditionally stable into any transmitter load, increased receive sensitivity and range, reduced transmitter harmonic leakage, increased RX/TX frequency stability through reference to one master TCXO, and increased mechanical robustness for transport.

Improving upon the original unmodulated CW Harmonic Radar

Because harmonic radar has many uses in the 10-100 meter range (radar to tag), a natural technology progression would be to implement an FMCW system. The planar patch antennas currently used have only several MHz of useful bandwidth, but a suitable FMCW system combined with a new more broadband harmonic radar tag is expected to allow even greater reliable detection range. Harmonic radar tags may be produced with bandpass elements that allow colocated tags to indicate more discrete states using additional sensing elements.

USRP B200
Rapid prototyping with SDR enabled advances in harmonic radar technology