On the Sensitivity of Wideband Radiometric Detection for Low Probability of Intercept and Probability of Detection (LPI/LPD) in Frequency Hopped Systems

Using radiometric detection, the detection threshold for a wideband radiometer (WR) to detect bursty signals e.g., transmission with duty cycle in frequency hopped systems is discussed in the paper. For this detector, the detection threshold is characterized by the probabilities of false alarm and detection, hopping bandwidth, duration of transmission, and duty cycle. First, the detection threshold for constant noise power spectral density assumption over a large hopping bandwidth is developed. Next, a new detection threshold is derived for the case in which the constant noise density assumption is relaxed e.g., fluctuating but bounded noise density. The case where the noise density is constant, but unknown, and due to measurement errors, an incorrect value only is available to the interceptor, is also investigated. In all cases, the detection thresholds are inversely proportional to the duty cycle. For fluctuating noise density, the detection threshold is proportional to the square root of the peak-to-peak noise density variation. Finally, the sensitivity of the detection threshold due to noise density variations and interceptor´s G/T on the Circular Equivalent Vulnerability Radius (CEVR) is quantified. CEVR is the radius of a circular region whose area is equal to the detection region projected onto the surface of the earth. This paper provides a more accurate prediction of expected CEVR performance.