Feature Analysis and Extraction for Specific Emitter Identification Based on the Signal Generation Mechanisms of Radar Transmitters

Abstract

In this study, a feature analysis and extraction method was proposed for specific emitter identification based on the signal generation mechanisms of radar transmitters. The generation of radar signals by radar transmitters was analyzed theoretically and experimentally. In the analysis, the main source of unintentional modulation in radar signals was identified, and the frequency stabilization of the solid-state frequency source, the nonlinear characteristics of the radio frequency amplifier chain, and the envelope of the pulse front edge were extracted as features for specific emitter identification. Subsequently, these characteristics were verified through simulation. The results revealed that the features extracted by this method exhibit "fingerprint characteristics" and can be used to identify specific radar emitters.

Keywords: feature analysis and extraction; radar transmitter; signal generation mechanisms; specific emitter identification.

Figure 1

Composition of the MOPA transmitter, where the low-power RF signal is generated by the solid-state frequency source and amplified by the RF amplifier chain.

Figure 2

Radar waveform under ideal circumstances.

Figure 3

Composition of the PLL frequency synthesizer, where the reference frequency is generated by the crystal oscillator, and the low-power carrier signal is generated by the VCO; the frequency of the low-power carrier signal is controlled by the phase discriminator.

Figure 4

(a) The value of standard deviation at five different carrier frequencies; (b) the value of frequency stabilization at five different carrier frequencies.

Figure 5

(a) Frequency stabilization of three emitters; (b) frequency stabilization of ten distinct emitters; the x-axis represents the number of pulses used to calculate the standard deviation of the frequency, and the y-axis represents the value of frequency stabilization.

Figure 6

Actual gain curve of the RF amplifier chain.

Figure 7

Frequency spectrum of two distinct emitters.

Figure 8

(a) $$k_1,k_2$$ of two distinct emitters at 30 dB SNR; (b) $$k_1,k_2$$ of two emitters at 20 dB SNR; (c) $$k_1,k_2$$ of two emitters at 10 dB SNR.

Figure 9

Gain curve of the RF amplifier chain of six distinct emitters.

Figure 10

(a) $$k_1,k_2$$ of six distinct emitters at 30 dB SNR; (b) $$k_1,k_2$$ of six distinct emitters at 20 dB SNR; (c) $$k_1,k_2$$ of six distinct emitters at 10 dB SNR.

Figure 11

(a) Mean value of $$k_1,k_2$$ of six distinct emitters at 10 dB SNR (10 pulses in each group); (b) mean value of $$k_1,k_2$$ of six distinct emitters at 10 dB SNR (20 pulses in each group).

Figure 12

Real waveform of the modulated signal.

Figure 13

Envelope of the radar signal.

Figure 14

Equivalent circuit of the pulse modulator at the time of the pulse front edge [26], where $$E_p$$ is the discharge voltage of energy storage element, $$Z_0$$ is the impedance of energy storage element, $$L_L$$ is the excitation inductance of pulse transformer, $$C_s$$ is the distributed capacitance of pulse transformer, and $$R_L$$ is the equivalent impedance of the pulse transformer.

Figure 15

Front edge of the simulation modulation signal.

Figure 16

Envelope of the pulse front edge.

Figure 17

Envelope of the pulse front edge after filtering by downsampling.

Figure 18

(a) Envelope of the pulse front edge at 30 dB SNR; (b) envelope of the pulse front edge at 20 dB SNR; (c) envelope of the pulse front edge at 10 dB SNR.

Figure 19

(a) Mean curves of the envelope at 30 dB SNR; (b) mean curves of the envelope at 20 dB SNR; (c) mean curves of the envelope at 10 dB SNR.

Figure 20

Experimental process.