Grating lobes suppression in stepped-frequency pulse train

Abstract

I. GLADKOVA CCNY D. CHEBANOV CUNY Frequency stepping is one of the known techniques employed by modern radars to achieve high range resolution. The main advantage of this approach is that the actual instantaneous bandwidth of a radar is quite small compared with the total processing bandwidth. This allows the transmission of waveforms with extremely wide overall bandwidth (and, as a consequence, the attainment of high range resolution) without the usage of the expensive hardware needed to support wide instantaneous bandwidth. Unfortunately, the autocorrelation function of uniform frequency stepped pulse trains can have undesirable peaks, known as "grating lobes." We address this issue, using an approach which allows us to suppress grating lobes below a desired threshold level in the case of appropriately chosen stepped frequency waveforms. We discuss in detail how to choose relevant parameters in order to produce such waveforms with small grating lobes, and give examples of waveforms with small overlap ratio. We also discuss the issue of high sidelobes in the vicinity of the mainlobe, which are inevitable in a stepped frequency train of linear frequency modulated (LFM) waveforms with small overlap ratio, and show that it is possible to suppress these, as well as the grating lobes, by means of nonlinear frequency modulation (NLFM).

Low-rate sampling technique for range-windowed radar/sonar using nonlinear frequency modulation

“…However, since the DFT is more efficiently implemented by the fast Fourier transform (FFT), this cost can be reduced to O(M log M) in the case of stretch of processing. The development of an efficient means to compute (12), however, is beyond the scope of this paper and is not discussed further.…”

“…(12) to obtain the range profile P(τ ). 5) Identify from P(τ )the target range/delay τ k and the relative amplitude α k , ∀ k.…”

“…Such NLFM waveforms have been investigated in the open literature (e.g. [3,6,8,12,13,16,17]) for the case of conventional matched filtering.…”

Orthogonal frequency division multiplexing linear frequency modulation signal design with optimised pulse compression property of spatial synthesised signals

“…Similar to OFDM LFM in MIMO radar which is the frequency division in transmit antennas, stepped frequency LFM pulses [21] implement the frequency division in transmit pulses and also has the problem of high sidelobes. Methods such as destroying the periodicity [22, 23], using non‐linear modulation [24] or setting relationship between waveform parameters [25] to further lower the sidelobes were discussed. However, the stepped frequency LFM signal is one signal with different carrier frequencies in the pulses; hence, these methods cannot be adopted to OFDM LFM waveform design directly.…”

A Robust Range Grating Lobe Suppression Method Based on Image Contrast for Stepped-Frequency SAR

“…One of the methods suppresses the range grating lobes to the desired level by restricting the relationships between the frequency step, subpulse bandwidth and subpulse-duration, which is presented in [8,9,10]. Another method sets the subpulse center frequencies at unequal spaces to eliminate the periodicity of the waveform, which disperses the grating lobes and thereby reduces the amplitudes of the grating lobes [11,12,13].…”