Stepped-Frequency Nonlinear Radar Simulation

Transcription

1 Stepped-Frequency Nonlinear Radar Simulation Gregory J. Mazzaro The Citadel, The Military College of South Carolina Charleston, SC, Anthony F. Martone U.S. Army Research Laboratory Adelphi, MD, Kyle A. Gallagher, Ram M. Narayanan Pennsylvania State University University Park, PA, THE CITADEL, THE MILITARY COLLEGE OF SOUTH CAROLINA 171 Moultrie Street, Charleston, SC 29409

2 Presentation Overview Nonlinear Radar Concept, Motivations Nonlinearity, Sources, Harmonics Harmonic Radar Measurements Nonlinear Stepped-Frequency Radar Stepped-Frequency + Harmonic Radar Concept Nonlinear SFR Measurements U.S. Army Research Laboratory Synchronous Impulse Reconstruction (SIRE) Radar Summary & Future Work 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 Linearity vs. Nonlinearity For a linear system, input x x y 1 1 output y 2 2 a1x 1 a2x2 a1 y1 a2 y2 cos A cos t A H t For a non-linear system,? a x a x a y a y A cos t A H A, cos A, t A, transfer function depends on amplitude, and output frequency does not necessarily equal input frequency 4

5 Sources of Nonlinearity Active elements & components by design; above system noise floor + diodes transistors amplifiers mixers _ + f 1 f 1 + f 2 _ f 2 Passive elements & components unintended; below system noise floor contacts [1,2] connectors [3] ferro-electrics [4] temperature -dependent [5] metal 1 oxide metal 2 metal V R 5

6 Temperature-Dependent Resistance I out voltage applied, current flows 1 R T R T T 0 0 V in R resistor heats up resistance increases current decreases current increases resistance decreases resistor cools down V in R I out input: constant output: sinusoidal nonlinear system time time 6 time

7 Nonlinear Radar Research Tx Rx one possible signal path: E in E refl... LNA BPF The target is viewed as a collection of nonlinearities. 7

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

9 Recent 1-Tone Experiment Tektronix AWG7052 arbitrary waveform generator Amplifier Research 50-W 1-GHz RF amplifier 1-dB step attenuator GTEM cell P trans target 5 m antenna 1.1 m P rec Rohde & Schwarz FSP 40-GHz spectrum analyzer GTEM = Gigahertz Transverse Electromagnetic 9

10 Power Received at 2 nd Harmonic (dbm) Recent 1-Tone Measurements GTEM cell P D = 16 mw/cm 2 Nonlinear (harmonic) device response is experimentally verified, but ranging/imaging is not possible when receiving a single continuous frequency W W Transmitted Frequency (MHz) 10

11 Processed Received Transmitted Stepped-Frequency Radar amplitude phase A 1 f 1 A 2 f 2 A 3 f 3 A 4 f 4 A 5 f 5 frequency f 0 f 0 + Df f 0 + 2Df f 0 + 3Df f 0 + 4Df IDFT R c t 2 11

12 Processed Received Transmitted Nonlinear Stepped-Frequency Radar 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 IDFT R c t 2 12

13 Hardware Simulation Experiment Tektronix AWG7052 Transmitter NLP Amplifier Research AR4W1000 NLP Lecroy 8300A channel 2 in HP 778D V trans Tx coupled out Rx coupled Simulated Radar Environment CBL-25FT x4 d = 100 ft target V rec PSA-545+ VHF PSA VHF PSA Lecroy 8300A channel 3 VHF Receiver VHF

14 Hardware Simulation Measurements blue = transmitted to target, 880 MHz to 920 MHz, T env = 1 ms, N = 40 red = received from target, 1760 to 1840 MHz 14

15 Hardware Simulation Results As long as (a) the phase response of the target is linear and (b) the amplitude response is nearly flat over the band of interest Range-to-target is found from an inverse DFT of the nonlinear SFR response, as with linear SFR. h NL t tgt sin B t 2 t M 1 j ftgt t E E e M 0 d = 102 ft nonlinear impulse response, constructed from an IDFT of the data in red 1 c ft d t 0.34 t 2 ns r 15

16 Summary & Near-Term Future Nonlinear stepped-frequency radar was demonstrated by hardware simulation of a nonlinear target in a linear radar environment. Tektronix AWG7052 Transmitter NLP Amplifier Research AR4W1000 NLP Lecroy 8300A channel 2 in HP 778D V trans Tx coupled out Rx coupled Simulated Radar Environment CBL-25FT x4 target V rec PSA-545+ VHF PSA VHF PSA Lecroy 8300A channel 3 VHF Receiver VHF

17 Summary & Near-Term Future Nonlinear stepped-frequency radar was demonstrated by hardware simulation of a nonlinear target in a linear radar environment. step atten uator P trans 3 m target P rec Next step(s): Wireless experiments & verification of the NL SFR concept with multiple electronic targets. 17

18 References [1] C. Vicente and H. L. Hartnagel, Passive-intermodulation analysis between rough rectangular waveguide flanges, IEEE Transactions on Microwave Theory and Techniques, Vol. 53, No. 8, Aug. 2005, pp [2] H. Huan and F. Wen-Bin, On passive intermodulation at microwave frequencies, in Proceedings of the Asia-Pacific Electromagnetic Conference, Nov. 2003, pp [3] J. Henrie, A. Christianson, and W. J. Chappell, Prediction of passive intermodulation from coaxial connectors in microwave networks, IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 1, Jan [4] G. C. Bailey and A. C. Ehrlich, A study of RF nonlinearities in nickel, Journal of Applied Physics, Vol. 50, No. 1, Jan. 1979, pp [5] J. R. Wilkerson, K. G. Gard, A. G. Schuchinsky, and M. B. Steer, Electro-thermal theory of intermodulation distortion in lossy microwave components, IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 12, Dec [6] J. C. Pedro and N. B. Carvalho, Intermodulation Distortion in Microwave and Wireless Circuits. Boston, MA: Artech House, [7] 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