Linearizing an Intermodulation Radar Transmitter by Filtering Switched Tones

Transcription

1 12-Apr-2017 Linearizing an Intermodulation Radar Transmitter by Filtering Switched Tones Gregory J. Mazzaro The Citadel, The Military College of South Carolina Charleston, SC Andrew J. Sherbondy, Kenneth I. Ranney, Kelly D. Sherbondy, Anthony F. Martone U.S. Army Research Laboratory, Sensors & Electron Devices Directorate Adelphi, MD THE CITADEL, THE MILITARY COLLEGE OF SOUTH CAROLINA 171 Moultrie Street, Charleston, SC 29409

2 Presentation Overview (Brief) Review of Nonlinear Radar UWB Nonlinear Radar Investigations & Lessons Learned Harmonic Radar: Continuous-Wave vs. Pulsed Step-Frequency Harmonic Radar Intermodulation Radar Summary Linearization by Time-Multiplexed Spectrum (LITMUS) U.S. Army Research Laboratory Synchronous Impulse Reconstruction Radar 2

3 Nonlinear Radar Concept Tx electronic target Rx Target presence/location is indicated by receiving frequencies that were not transmitted. Applications: locate personal electronics during emergencies detect electronically-triggered devices Advantages: It is easier to separate targets from clutter because most clutter is linear. Disadvantages: Targets require high incident power to drive them into non-linear behavior. Received responses are usually very weak compared to the transmitted probe signals. 3

4 Nonlinear Radar Research Tx Rx one possible signal path: E in E refl... LNA BPF We view each target as a collection of RF nonlinearities. 4

5 Nonlinear Radar Research Tx Rx Which frequencies and waveforms are best to transmit? What is the minimum transmit power required for detection? How should the transmitter be designed to achieve high linearity? How should the receiver be designed to achieve high sensitivity? Can traditional (linear) radar techniques be used to perform ranging & imaging? How should the signal processor be designed to recognize familiar targets? 5

6 Presentation Overview (Brief) Review of Nonlinear Radar UWB Nonlinear Radar Investigations & Lessons Learned Harmonic Radar: Continuous-Wave vs. Pulsed Step-Frequency Harmonic Radar Intermodulation Radar Summary Linearization by Time-Multiplexed Spectrum (LITMUS) U.S. Army Research Laboratory Synchronous Impulse Reconstruction Radar 6

7 Harmonic Radar: Theory Let the input waveform be a sinusoid: E E cos t in 0 0 [1] Let the nonlinearity be approximated by a power series [2] E a E a E a E 2 3 out 1 in 2 in 3 in... input output Then the device response (output) is cos Eout a1 E 0 cos 0t a2 E0 0t a 3 E0 cos 0t... cos Eout a1e 0 0t 2 a2e0 2 cos 20t 3 a3e0 0t 4 cos harmonics 2 input = { f } output = { f, 2f, 3f, 4f, 5f, 6f, } 7

8 Harmonic Radar, CW: Experiment [3] Many commercially-available RF devices respond harmonically to incident continuous waves. 8

9 Harmonic Radar, Pulsed: Experiment Transmitted waveform: f 0 f 0 D c P peak = P trans P refl P trans = 400 mw (fixed) [4] target For a fixed transmit power, it is best to maximize peak-to-average ratio to generate a stronger response from the target. 9

10 Received Processed Transmitted Stepped-Frequency Harmonic Radar: Theory [5] amplitude phase A 1 f 1 A 2 f 2 A 3 f 3 A 4 f 4 A 5 f 5 frequency 2f 0 2f 0 + 2Df 2f 0 + 4Df 2f 0 + 6Df 2f 0 + 8Df R c 2 IDFT t After constructing H() of the environment, an inverse DFT provides range (distance-to-target). 10

11 SF Harmonic Radar: Experiments Received Power (dbsm, normalized) [6] harmonic radar MTI has been demonstrated on nonlinear targets using stepped frequencies. linear radar 11 Linear and nonlinear modes may be operated using a common Tx/Rx backbone.

12 Presentation Overview (Brief) Review of Nonlinear Radar UWB Nonlinear Radar Investigations & Lessons Learned Harmonic Radar: Continuous-Wave vs. Pulsed Step-Frequency Harmonic Radar Intermodulation Radar Summary Linearization by Time-Multiplexed Spectrum (LITMUS) U.S. Army Research Laboratory Synchronous Impulse Reconstruction Radar 12

13 Intermodulation Radar: Theory f f MHz 101 MHz input output f f MHz 101 MHz intermodulation harmonics In the frequency domain, nonlinearity manifests itself as spurious spectral content (e.g. harmonics, intermodulation). difference / beat frequencies 13

14 Intermodulation Radar: Measurements [7,8] Detection and ranging may be performed using intermodulation only (Rx in the same band as Tx frequencies). 14

15 Linearization by Time-Multiplexed Spectrum LITMUS: (1) lower the Tx waveform peak-to-average ratio (2) amplify the Tx waveform (3) restore the original peak-to-average ratio [9] Self-generated intermodulation masks weak target responses. Linearize the transmitter. Improve detection for over-the-air tests (higher self-generated products, weaker targets). 15

16 Linearization by Time-Multiplexed Spectrum f 0 = 910 MHz Df = 700 khz f s = 35 MHz P awg MiniCircuits ZHL-42W MiniCircuits ZVBP-909-S+ Tx coupled P trans Tektronix AWG7052 Rx coupled The fast-switch-tomultitone conversion was successful. 2-tone signal slow switching fast switching 16

17 Linearization by Time-Multiplexed Spectrum f 0 = 910 MHz Df = 700 khz f s = 35 MHz P awg MiniCircuits ZHL-42W MiniCircuits ZVBP-909-S+ Tx coupled P trans Tektronix AWG7052 Rx coupled The fast-switch-tomultitone conversion was successful. fast-switched signal bandpass filtering multi-tone signal 17

18 Intermodulation Radar: Experiment MiniCircuits ZHL-42W or Amplifier Research 4W1000 P awg MiniCircuits ZVBP-909-S+ Tx coupled HG824-11LP P trans GA mixer Tektronix AWG7052 or Keysight N5193A Rohde & Schwarz FSP-40 Rx coupled HP 778D-12 P rec 50-W terminations 2 meters target These experiments were conducted using laboratory-grade RF instruments only. Tektronix AWG7052 GWInstek GPS-2303 Rohde & Schwarz FSP-40 Lecroy WaveMaster 8300A amplifier-filter cascade laptop, Matlab Keysight N5193A 18

19 Intermodulation Radar: Experiment MiniCircuits ZVBP-909-S+ MiniCircuits ZHL-42W Hewlett-Packard 778D-12 L-Com HG824-11LP GA These experiments were conducted using laboratory-grade RF instruments only. 19

20 Intermodulation Radar: Measurements without LITMUS Implementing LITMUS improved detectability by up to 21 db. with LITMUS DIM3U for f s = 75 MHz DIM3U f 0 k = 0 only k = 1,0,+1 improve 906 MHz 1.2 db 12.1 db 10.9 db 907 MHz 1.5 db 13.3 db 11.8 db 908 MHz 1.7 db 12.3 db 10.6 db 909 MHz 0.5 db 17.1 db 16.6 db 910 MHz 0.5 db 22.0 db 21.5 db 911 MHz 2.0 db 15.9 db 13.9 db 912 MHz 2.3 db 15.6 db 13.3 db 913 MHz 2.5 db 19.5 db 17.0 db 914 MHz 3.4 db 23.9 db 20.5 db 20

21 Intermodulation Radar: Measurements Target: DMB-400A X port ZEM-2B R port DIM3U for DIM3U for DIM3U for DIM3U for f 0 P trans = 40 mw P trans = 80 mw P trans = 40 mw P trans = 80 mw 907 MHz 13.3 db 20.5 db 8.2 db 7.2 db 908 MHz 15.1 db 11.9 db 12.4 db 9.6 db 909 MHz 15.3 db 16.3 db 13.1 db 10.5 db 910 MHz 14.3 db 13.4 db 14.9 db 8.7 db 911 MHz 9.7 db 12.2 db 14.0 db 7.2 db Having implemented LITMUS, 4 targets were successfully detected. ZEM-4300 R port DIM3U for DIM3U for P trans = 40 mw P trans = 80 mw 9.7 db 10.1 db 12.1 db 11.6 db 12.5 db 10.1 db 13.2 db 10.0 db 12.5 db 8.9 db ZAM-42 R port DIM3U for DIM3U for P trans = 40 mw P trans = 80 mw 6.9 db 5.7 db 9.8 db 7.6 db 10.8 db 9.5 db 10.5 db 9.1 db 8.5 db 7.2 db (LITMUS implemented, 2 transmit powers) 21

22 UWB Nonlinear Radar Research: To Date Doppler speed [m/s] Tx 1 Nonlinear Moving Target Rx Range [ft] -40 We have (a) shown that RF electronics react harmonically to incident RF waves, which enables detection of these targets (b) demonstrated that transmitting high peak-to-average ratio is best for receiving stronger responses from these targets (c) developed an experimental prototype of a stepped-frequency harmonic radar, which is able to detect & locate commercially-available RF electronic devices, and (d) applied LITMUS to linearize an intermodulation radar transmitter. We intend to (e) package the radar onto a mobile platform (vehicle), and (f) develop signal-processing techniques to identify particular targets. 22

23 References [1] G. J. Mazzaro, A. F. Martone, and D. M. McNamara, Detection of RF electronics by multitone harmonic radar, IEEE Transactions on Aerospace and Electronic Systems, Vol. 50, No. 1, Jan [2] J. C. Pedro and N. B. Carvalho, Intermodulation Distortion in Microwave and Wireless Circuits. Boston, MA: Artech House, [3] G. J. Mazzaro and A. F. Martone, Harmonic and multitone radar: Theory and experimental apparatus, U.S. Army Research Laboratory Technical Report, No. 6235, Oct [4] G. J. Mazzaro, A. F. Martone, K. A. Gallagher, R. M. Narayayan, and K. D. Sherbondy, Maximizing harmonic-radar target response: Duty cycle vs. peak power, IEEE SoutheastCon 2016, Norfolk, VA, Mar [5] G. J. Mazzaro, K. A. Gallagher, A. F. Martone, and R. M. Narayanan, Stepped-frequency nonlinear radar simulation, Proceedings of the SPIE, Vol. 9077, pp U(1-10), May [6] K. A. Gallagher, R. M. Narayanan, G. J. Mazzaro, K. I. Ranney, A. F. Martone, and K. D. Sherbondy, Moving target indication with non-linear radar, Proceedings of the IEEE Radar Conference, pp , May [7] K. I. Ranney, K. A. Gallagher, K. D. Sherbondy, A. F. Martone, G. J. Mazzaro, and R. M. Narayanan, Instantaneous, stepped-frequency, nonlinear radar, Proceedings of the SPIE, Vol. 9461, pp (1-8), Apr [8] K. I. Ranney, G. J. Mazzaro, K. A. Gallagher, A. F. Martone, and R. M. Narayanan, Instantaneous, steppedfrequency, nonlinear radar part 2: Experimental confirmation, SPIE DCS 2016, Baltimore, MD, Apr [9] G. J. Mazzaro, K. G. Gard and M. B. Steer, "Linear amplification by time-multiplexed spectrum," IET Circuits, Devices, and Systems, vol. 4, no. 5, pp , Sept [10] G. J. Mazzaro, K. G. Gard and M. B. Steer, "Low distortion amplification of multisine signals using a time-frequency technique," in IEEE MTTS International Microwave Symposium Digest, pp , June