Harmonic Radar Principles and Applications
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.
Harmonic radar work at Michigan State University has included tracking insects above and below ground. Recent work has focused on L-band implementations since diode junction capacitance works to limit harmonic generation at higher frequencies with inexpensive diodes.
Harmonic radar tags and system have also been 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 I (Michael Volz) have done in regards to harmonic radar technology are:
- 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.
- 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.
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.
Long range (>1km) applications may find a high-power pulse type system appropriate. The current focus is on sub-kilometer systems.