HF Oblique Incident Sounding For Calibration Of An Over-The-Horizon Radar (OTHR) System

Over the horizon radar (OTHR) systems have recently garnered increased attention as cost-effective surveillance systems.  OTHR systems operate by transmitting a radar signal in the HF range (3 MHz - 30 MHz) which bounces off the ionosphere, encounters a target, reflects back to the ionosphere, bounces off the ionosphere again, and returns to the OTHR's receiver.  Due to the continuously changing state of the ionosphere, the exact frequency that can be reliably transmitted is continually changing.  To operate an OTHR reliably, calibration must take place at regular intervals during operation.  The proposed method for calibration is to use HF oblique incident sounding to find the exact frequencies that are reliably being transmitted and received at the time of broadcast.  HF oblique incident sounding will broadcast a step-function of narrowband signals throughout the HF range, and the frequency range that returns to the receiver with the greatest amplitude will be used by the OTHR as the broadcast and monitoring frequency.  The University of Oklahoma College of Electrical and Computer Engineering has experience building step-function based radar transmitter and receiver circuits which have had their operation confirmed through testing for delta-function presence in the frequency domain caused by near targets, matching the mathematical derivation of this effect.  The proposed method of calibration promises to quickly and accurately calibrate OTHR systems regardless of target presence in the target area.