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Silver Spring, MD, United States

Nunn C.,Technology Service Company | Moyer L.R.,Technology Service Company
IEEE Aerospace and Electronic Systems Magazine | Year: 2012

High-resolution radar operation requires the use of wideband waveforms. In microwave systems, the waveform bandwidth can exceed I GHz, while in UHF systems the waveform bandwidth might exceed 200 MHz. A maj or issue in the operation of such systems is that their emissions often overlap the spectrum used by other radars, and even the spectrum allocated fo r communications and navigation devices. The impact of the spectral overlap, which can include energy in the spectral sidebands of the radar, is two-fold. First the high-power radar can jam the other systems. To prevent this from occurring, the spectral managers from agencies including the Department of Defense (DoD), the Federal Aviation Association (FAA), the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) will each examine the in-band and out-of-band spectral content of the radar waveform, determine what systems in the operating locale could be adversely affected, and require spectral notches be incorporated into the radar waveform. Typical requirements are to suppress the radiated signal by 30 dB or more at frequencies allocated to the other systems. Additionally, hostile or illegal systems, whose signals could degrade the radar perfo rmance, might be operating within the radar 's band. As shown in an NTIA report I , "Radar receivers exp erience loss of desired targets when interference fr om high duty cycle (m ore than about 1-3%) communication-type signals is as low as -1 0 dB to -6 dB relative to radar receiver inherent noise levels. Conversely, radars perform robustly in the presence of low duty cy cle (less than 1-3%) signals such as those emitted by other radars. Ta rget losses at low levels are insidious because they do not cause overt indications such as strobes on displays. Therefo re op erators are usually unaware that they are losing targets due to low-level interference. In terference can cause the loss of targets at any range. Low interference thresholds fo r communication-type signals, insidious behavior of target losses, and potential loss of targets at any range all combine to make low-level interference to radar receivers a very serious problem. " Thus being able to null these signals on receive with the radar 's matched filter is also very important. An excellent chapter on the requirements fo r the management of the RF spectrum has been presented in a recent text2. The seriousness of the impact that radars can have on telecommunications and the need fo r out-of-band spectral notching, as well as in-band notching, is shown in a Clear Mobitel (UK.) press release3 that is available on the web. Thus providing the ability to notch the radar 's signal spectrum and to provide proper matched and mismatched filters is seen to be a very important problem of great concern to the radar and communications communities. © 2012 IEEE. Source

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