Multitone Harmonic Radar

Transcription

1 8//03 Multitone Harmonic Radar Gregory J. Mazzaro & Anthony F. Martone U.S. Army Research Laboratory Adelphi, MD SPIE DSS 03 pre-recorded Presentation Overview Introduction to Nonlinear Radar Nonlinearity & Its Physical Sources Theory (for Single-Tone and Two-Tone Excitations) Prior (Published) Work Harmonic Radar, Nonlinear Radar Current Research Experiments Multitone Harmonic Radar Results Summary f E V

2 8//03 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 Linearity vs. Nonlinearity For a linear system, x x y y ax ax a y a y 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 frequency does not necessarily equal frequency

3 8//03 Power-Series Model Let the device response be memoryless and approximated by N 3 n out in in 3 in... n in n V av a V a V a V with V V out in simple polynomial model, a a n are complex numbers (amplitude and phase), no hysteresis (memory) effects, otherwise use Volterra Series model [] :... n V t H V t H V t H V t H V t out in in 3 in in n H h,,..., V t V t... V t d d... d n n in in in n n t N 5 Sources of Nonlinearity Active elements & components by design; above system noise floor + diodes transistors amplifiers mixers _ + f f + f _ f Passive elements & components unintended; below system noise floor contacts [,] connectors [3] ferro-electrics [4] temperature -dependent [5] metal oxide metal metal V R 3

4 8//03 Sources of Nonlinearity I out voltage applied, current flows 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 : constant : sinusoidal nonlinear system time time time Nonlinear Radar Research Tx Rx The target is viewed as a collection of nonlinearities. 8 4

5 8//03 Harmonic Radar Theory Let the waveform be a sinusoid: E E cos t in 0 0 Let the nonlinearity be approximated by a power series [6] E a E a E a E 3 out in in 3 in... Then the device response () is 3 Eout a E 0 cos 0t a E0 cos 0t a 3 E0 cos 0t... 3 ae0 a3e0 Eout ae 0cos 0t cos 0t 3cos 0t cos 3 0t... 4 harmonics 9 Harmonic Radar Theory Let the be a single tone, at MHz with amplitude = V: V V cos t V in V 0 f0 MHz V 0tanh V 5 6 sech V out in in The is a sum of sinusoids at MHz, MHz, 3 MHz, etc: cos cos 3 4 3V0 cos 3 0t 4V0 cos 40t 5 6 V t V t V V t V t out cos 5 cos

6 8//03 Harmonic Radar Theory Let the be a single tone, at MHz with amplitude = V: V V cos t V in V 0 f0 MHz = { f } V 0tanh V 5 6 sech V out in in = { f, f, 3f, 4f, 5f, 6f, } The is a sum of sinusoids at MHz, MHz, 3 MHz, etc: cos cos 3 4 3V0 cos 3 0t 4V0 cos 40t 5 6 V t V t V V t V t out cos 5 cos Multitone Radar Theory Let the waveform be a two-tone continuous wave: cos E E cos t E t in Let the nonlinearity be approximated by a power series [6] E a E a E a E 3 out in in 3 in... Then the device response () is t t t E cos cos 0 Eout aein a cos cos t t 9Ein cos 3 t cos 3 t 3 E 0 a3 3cos t 3cos t cos 3cos t intermodulation (IMD) 6

7 8//03 Multitone Radar Theory Let the be two tones at 99 MHz and 0 MHz: 6 6 V V cos 99 0 t V cos 00 t in The contains many frequencies: f 98 MHz 3 f 97 MHz... f 0 MHz 3 f 303 MHz... V 0tanh V 5 6 sech V out in in f f MHz f f 4 MHz... f f 00 MHz f f 400 MHz... f f 97 MHz f f 03 MHz 3 f f 95 MHz 3 f f 05 MHz 4 f 3 f 93 MHz 4 f 3 f 07 MHz integer sums of f, f 3 Multitone Radar Theory f 99 MHz f 0 MHz f 99 MHz f 0 MHz intermodulation harmonics (integer sums of f, f ) difference / beat frequencies 4 7

8 8//03 Prior (Published) Work RADAR TAGS for INSECT TRACKING [8] [7] [9] AUTOMOTIVE RADAR for detecting VULNERABLE ROAD USERS MILITARY RADAR for detecting MANMADE METALLIC OBJECTS [0] simulations show detection possible > m at 80 GHz 5 Current Research Tx signal generation Rx signal capture & processing Questions to be answered: Which frequencies and waveforms are advantageous to transmit? What is the minimum transmit power required for detection? Which is the best antenna design (gain, polarization, etc.) for detection and ranging? How should the transmitter be designed to achieve high linearity? How should the receiver be designed to achieve high sensitivity? How should the signal processor be designed to recognize familiar targets? 8

9 8//03 Nonlinear Radar Experiments Tektronix AWG705 arbitrary waveform generator Amplifier Research 50-W -GHz RF amplifier -db step attenuator GTEM cell P trans target 5 m antenna. m P rec Rohde & Schwarz FSP 40-GHz spectrum analyzer 7 GTEM = Gigahertz Transverse Electromagnetic Nonlinear Radar Experiments Gigahertz Transverse Electromagnetic cell GTEM cell V Tx GTEM cell, outside, front 8 GTEM cell, outside, back 9

10 Power Received at nd Harmonic (dbm) 8//03 Nonlinear Radar Experiments Gigahertz Transverse Electromagnetic cell GTEM cell antenna, absorber V Tx target placement GTEM cell, inside V Tx 9 pictures from [] Single-Tone Experiments GTEM cell P D = 6 mw/cm 0 - W 0-5 W Transmitted Frequency (MHz) 0 0

11 8//03 Nonlinear Radar Experiments Tektronix AWG705 arbitrary waveform generator wireless Amplifier Research 0-W -GHz RF amplifier step atten uator P trans 3 m target P rec ETS Lindgren dual-polarized horn antenna Rohde & Schwarz FSP 40-GHz spectrum analyzer Multi-Tone Experiments wireless Two-tone harmonic response recorded from two DUTs at f 0 = 756 MHz, corresponding to the first row of the table below. The differences in P f0+df responses suggest a signature that may be used for device discrimination. f 0 P rec at f 0, T4500 (dbm) P rec at f 0, FV00 (dbm) DP rec at f 0 (db) P rec at f 0 ± Df, T4500 (dbc) P rec at f 0 ± Df, FV00 (dbc) DP rec at f 0 ± Df (db) P rec at f 0 ± Df, T4500 (dbc) P rec at f 0 ± Df, FV00 (dbc) DP rec at f 0 ± Df (db) 756 MHz MHz MHz Two-tone harmonic radar data: DUTs = Motorola T4500 and Motorola FV00, Df = 40 khz, P trans = 3 dbm per tone. P rec at f 0 ± Df is approximately 6 dbc for both DUTs, which is predicted by (3) in the paper. P rec at f 0 ± Df differs between the DUTs, by as much as.5 db depending upon the transmitted frequency.

12 8//03 Summary / Results Nonlinearity is present in all RF electronics. When viewed as a collection of nonlinearities, an RF electronic circuit is a nonlinear radar target. The primary advantage of nonlinear radar is to easily separate targets from clutter. The primary disadvantage is that targets require high linear power to produce a detectable response (> 00 W and < 0 dbc typical for practical standoff range). Nonlinear radar theory predicts that single-tone excitations will generate harmonics of the single tone from the target, and multi-tone excitations will generate integer sums of all transmitted frequencies from the target. Prior (unclassified) work has focused on designing and detecting nonlinear tags. Present work is focused on detecting electronics that are not designed to respond to radar. The harmonic responses of two DUTs, illuminated by the same frequency, at the same position, in the same orientation, at the same power, can vary by more than an order of magnitude. For a multi-tone excitation, the difference between P rec for tones away from the integer harmonics and P rec at the integer harmonics is dependent upon the device parameters (i.e. power series coefficients). Therefore, the power received at these off-center tones suggests a signature that may be used for device discrimination. 3 References [] 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. 005, pp [] H. Huan and F. Wen-Bin, On passive intermodulation at microwave frequencies, in Proceedings of the Asia-Pacific Electromagnetic Conference, Nov. 003, 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., Jan [4] G. C. Bailey and A. C. Ehrlich, A study of RF nonlinearities in nickel, Journal of Applied Physics, Vol. 50, No., Jan. 979, 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., Dec [6] J. C. Pedro and N. B. Carvalho, Intermodulation Distortion in Microwave and Wireless Circuits. Boston, MA: Artech House, 003. [7] N. Tahir and G. Brooker, Recent developments and recommendations for improving harmonic radar tracking systems, in Proceedings of the 5th European Conference on Antennas and Propagation, Apr. 0, pp [8] D. Psychoudakis, W. Moulder, C. C. Chen, H. Zhu, and J. L. Volakis, A portable low-power harmonic radar system and conformal tag for insect tracking, IEEE Antennas and Wireless Propagation Letters, Vol. 7, 008, pp [9] J. Saebboe, V. Viikari, T. Varpula, and H. Seppa, Harmonic automotive radar for VRU classification, in Proceedings of the International Radar Conference: Surveillance for a Safer World, Oct. 009, pp. 5. [0] C. L. Opitz, Radar object detector using non-linearities, U. S. Patent 4,053,89, Oct., 977. [] G. J. Mazzaro and A. F. Martone, Harmonic and multitone radar: Theory and experimental apparatus, U.S. Army Research Laboratory Technical Report, No. 635, Oct. 0. 4