Transmitter-in-the-loop optimization of physical radar emissions

Abstract

Ongoing work is exploring the optimization of physical radar emissions based on the continuous phase modulation (CPM) implementation of polyphase codes. Here a modification to the code search strategy known as Marginal Fisher's Information (MFI) is presented that enables this greedy approach to further improve upon the performance of the resulting CPM-implemented continuous waveform in terms of range sidelobes. The optimization process is also expanded to include the effects of the transmitter (from both modeled and physical hardware perspectives) to facilitate the optimization of physical emissions that are specifically tuned to the transmitter. This approach is particularly useful for high-power transmitters in which the actual physical emission is a spectrally modified and non-linearly distorted version of the intended radar waveform.

Physical emission of spatially‐modulated radar

“…Defining an aggregated bandwidth as that established by the 3 dB collective bandwidths demarcated by the outermost element emissions, it is found in Fig. 11 that the normalised aggregated bandwidth for the null-to-null linear spatial modulation of Case 2 is 202, a 1% increase over standard beamforming which agrees with (27). Likewise, the (Case 3) double null-to-null linear spatial modulation result in Fig.…”

“…Likewise, the (Case 3) double null-to-null linear spatial modulation result in Fig. 12 realises a normalised aggregated bandwidth of 204, a 2% increase as predicted by (27). For the half-cycle sinusoidal Case 4 we must use the more general (28).…”

Calculation of the radar ambiguity function from time-domain measurement data for real-time, amplifier-in-the-loop waveform optimization

“…This is commonly known as an "amplifier-in-the-loop" problem. Jakabosky et al also demonstrate a setup that measures the zero-Doppler range portion the ambiguity function and further uses this capability to optimize a nonlinear frequency-modulation (FM) chirp [3]. Our present paper demonstrates calculation of the entire ambiguity function from the measured output waveform from a radar amplifier to be calculated in real-time, enabling the cognitive radar to reconfigure its waveform to meet detection requirements and spectral constraints.…”

“…Amplifier distortion due to nonlinearity is capable of altering the ambiguity function of the waveform input to the transmitter, so a measurement at the transmitter's output is a way to ascertain the actual detection capabilities of the radar. This problem is explored extensively by Jakabosky et al, who demonstrate that radar transmitter amplifier distortion results in increased range sidelobes [3]. This is commonly known as an "amplifier-in-the-loop" problem.…”

Hardware-in-the-loop radar waveform optimization using radiated emissions

“…The advantages of this approach to optimize physical radar emissions has been shown [6], [7]. In addition, physical radar emissions based on this CPM implementation have been optimized with some of the hardware in the loop (the entire transmit chain), but not the antenna, using the peak sidelobe level as the sole metric for designing the waveform [8]. The chosen method of optimization in [8] was the marginal Fisher's information (MFI) algorithm [9], which uses an essentially greedy search structure that enables rapid convergence to a sufficient quality solution.…”