Abstract
Since the advent of “pulse compression” radar, the “chirp” signal (Linear Frequency Modulation, LFM) has been one of the most widely used radar waveforms. It is well known that, by changing its modulation into a Non-Linear Frequency Modulation (NLFM), better performance in terms of Peak-to-Sidelobes Ratio (PSLR) can be achieved to mitigate the masking effect of nearby targets and to increase the useful dynamic range. Adding an appropriate amplitude modulation, as occurs in Hybrid-NLFM (HNLFM), the PSLR can reach very low values (e.g., PSLR < −60 dB), comparable to the two-way antenna sidelobes in azimuth. On the other hand, modern solid-state power amplifier technology, using low-power modules, requires them to be combined at the Radio Frequency (RF) stage in order to achieve the desired transmitted power. Noise Radar Technology (NRT) represents a valid alternative to deterministic waveforms. It makes use of pseudo-random waveforms—realizations of a noise process. The higher its time-bandwidth (or BT) product, the higher the (statistical) PSLR. With practical BT values, the achievable PSLR using pure random noise is generally not sufficient. Therefore, the generated pseudorandom waveforms can be “tailored” (TPW: Tailored Pseudorandom Waveforms) at will through suitable algorithms in order to achieve the desired sidelobe level, even only in a limited range interval, as shown in this work. Moreover, the needed high BT, i.e., the higher time duration T having fixed the bandwidth B, matches well with the low power solid-state amplifiers of Noise Radar. Focusing the interest on (civil) surveillance radar applications, such as ATC (Air Traffic Control) and marine radar, this paper proposes a general review of the two classes of waveforms, i.e., HNLFM and TPW.
Highlights
IntroductionThe waveforms design is a key element, in which conflicting requirements have to be satisfied, i.e., (to mention the main ones), range resolution and accuracy (defined as the degree of conformance between the estimated or measured position and the true position), dynamic range, Multiple-Input Multiple-Output (MIMO) or polarimetric channels orthogonality, Low Probability of Intercept (LPI) [1,2,3], low interference to other apparatuses [4], and best exploitation of the transmitter power with a low (or unitary) crest factor
For any new radar, the waveforms design is a key element, in which conflicting requirements have to be satisfied, i.e., range resolution and accuracy, dynamic range, Multiple-Input Multiple-Output (MIMO) or polarimetric channels orthogonality, Low Probability of Intercept (LPI) [1,2,3], low interference to other apparatuses [4], and best exploitation of the transmitter power with a low crest factor
Focusing the interest on surveillance radar applications, such as ATC (Air Traffic Control) and marine radar, this paper proposes a general review of the two classes of waveforms, i.e., HNLFM and TPW
Summary
The waveforms design is a key element, in which conflicting requirements have to be satisfied, i.e., (to mention the main ones), range resolution and accuracy (defined as the degree of conformance between the estimated or measured position and the true position), dynamic range, Multiple-Input Multiple-Output (MIMO) or polarimetric channels orthogonality, Low Probability of Intercept (LPI) [1,2,3], low interference to other apparatuses [4], and best exploitation of the transmitter power with a low (or unitary) crest factor. A new design method to cope with the sidelobe problem has been presented in [21,22], leading to a kind of Hybrid NLFM (HNLFM) whose amplitude, is not constant during the duration T of the signal Such a requirement creates implementation problems with the widely-used saturated (C-class) power amplifiers. The longer time duration allows to lower the transmitted peak power (with respect to an equivalent pulse compression radar) by about a figure of approximately 30 times, keeping unchanged the overall system requirements (e.g., maximum range, range resolution, bandwidth allocation) for the same application; the lower transmitted power calls for less solid-state modules to be combined, easing the radar transmitter architecture;. The paper is organized as follows: Section 2 describes the deterministic waveforms design and compares classical pulse compression waveforms with the novel ones; Section 3 shows a different approach to pulse compression based on random waveforms (noisy signals) making use of CW operation; Section 4 reports conclusions and future perspectives
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