Attenuation Of Spurious Impulses From An Ultra-Wideband .
Attenuation of Spurious Impulses from an Ultra-WidebandRadar: A High-Speed Switch for the Synchronous ImpulseReconstruction (SIRE) Frontendby Gregory Mazzaro, Marc Ressler, Gregory Smith, and Francois KoenigARL-TR-5750Approved for public release; distribution unlimited.September 2011
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Army Research LaboratoryAdelphi, MD 20783-1197ARL-TR-5750September 2011Attenuation of Spurious Impulses from an Ultra-WidebandRadar: A High-Speed Switch for the Synchronous ImpulseReconstruction (SIRE) FrontendGregory Mazzaro, Marc Ressler, Gregory Smith, and Francois KoenigSensors and Electron Devices Directorate, ARLApproved for public release; distribution unlimited.
Form ApprovedOMB No. 0704-0188REPORT DOCUMENTATION PAGEPublic reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining thedata needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing theburden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302.Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currentlyvalid OMB control number.PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.1. REPORT DATE (DD-MM-YYYY)2. REPORT TYPE3. DATES COVERED (From - To)September 2011FinalJanuary 2010 to May 20114. TITLE AND SUBTITLE5a. CONTRACT NUMBERAttenuation of Spurious Impulses from an Ultra-wideband Radar: A Highspeed Switch for the Synchronous Impulse Reconstruction (SIRE) Frontend5b. GRANT NUMBER5c. PROGRAM ELEMENT NUMBER6. AUTHOR(S)5d. PROJECT NUMBERGregory Mazzaro, Marc Ressler, Gregory Smith, and Francois Koenig5e. TASK NUMBER5f. WORK UNIT NUMBER7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)8. PERFORMING ORGANIZATIONREPORT NUMBERU.S. Army Research LaboratoryATTN: RDRL-SER-U2800 Powder Mill RoadAdelphi, MD 20783-1197ARL-TR-57509. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)10. SPONSOR/MONITOR'S ACRONYM(S)11. SPONSOR/MONITOR'S REPORTNUMBER(S)12. DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited.13. SUPPLEMENTARY NOTES14. ABSTRACTThe performance of ultra-wideband (UWB) radar systems suffers from reflections between frontend components caused byimpedance mismatch. The Synchronous Impulse Reconstruction (SIRE) radar built by the U.S. Army Research Laboratory(ARL) is no exception. While most of the radio frequency (RF) energy in each impulse is transmitted by the radar as desired,a portion of the RF energy reflects within the radar frontend. Undesired impulse echoes arrive back at the transmit antennasand are emitted from the radar. These undesired transmissions reflect from the radar environment and produce echoes in theradar image. The proposed solution for eliminating these echoes is to dissipate impulse reflections in a matched load beforethey are emitted. A high-speed switch directs the desired impulse to the antenna and redirects the undesired reflection fromthe antenna to a matched load. This report reviews the current SIRE frontend design and describes the solution for eliminatingthe echoes. The consequences of inserting each portion of the new circuit into the radar frontend are explained.Measurements on the new frontend show an attenuation of the undesired impulse transmissions of more than 18 dB at theexpense of an attenuation in the desired impulse transmission of less than 3 dB.15. SUBJECT TERMSRadar, ultra-wideband, front-end, reflection, attenuation, high-speed switching, relay17. LIMITATIONOFABSTRACT16. SECURITY CLASSIFICATION OF:a. REPORTUnclassifiedb. ABSTRACTUnclassifiedc. THIS PAGEUnclassifiedUU18. NUMBEROFPAGES3619a. NAME OF RESPONSIBLE PERSONGregory J. Mazzaro19b. TELEPHONE NUMBER (Include area code)(301) 394-0840Standard Form 298 (Rev. 8/98)Prescribed by ANSI Std. Z39.18ii
ContentsList of Figuresiv1.Introduction12.Current ARL SIRE Frontend and Proposed Upgrade23.Signal-delay Cable64.5.3.1Frequency-domain, Small-signal.63.2Time-domain, Large-signal .7High-speed Switch84.1Power Handling: Peak versus Average .84.2Radar Pulse Transmission: Pass-through, Without ON/OFF Transition .94.3Reflection Attenuation .104.4Radar Pulse Transmission: Pass-through, With ON/OFF Transition.12Printed Circuit Board135.1Switch Control: Dual-output Comparator .135.2PCB Diagram and Performance .136.Conclusions167.References17Appendix. Single-Transmitter Operation using an RF Relay19A-1. Balancing the Two Transmit Paths .20A-2. Electromechanical Relay Steady-State and Transient Responses .21A-3. Relay Control and Required Timing .23A-4. Printed Circuit Board Layout: Solid-State Switch Electro-Mechanical Relay .24List of Symbols, Abbreviations, and Acronyms27Distribution List28iii
List of FiguresFigure 1. SIRE radar frontend: single transmit-receive path. .2Figure 2. SIRE UWB radar pulse sample from Avtech generator: (a) time domain and(b) frequency domain. .3Figure 3. Reflection and transmission coefficients for SIRE frontend components:(a) reflection from TEM horn input, (b) reflection from Avtech pulse generator output,(c) transmission through MiniCircuits 2-ft cable, and (d) sum of S11 , S22 , S21 , and S12 . .4Figure 4. Sample radar image displaying target echoes. The true image of the barrier appearsdue to the desired reflection of the radar pulse. Echoes of the barrier appear behind thetarget due to the undesired reflection of the radar pulse. .5Figure 5. New SIRE radar frontend, incorporating a high-speed switch and 15-ft cable. .5Figure 6. Losses incurred by placing a 15-ft cable between the pulse generator and antenna,measured using the Rohde & Schwarz ZVB-8 network analyzer. .6Figure 7. Time-domain traces for cable comparison using the radar waveform: recordedusing the Lecroy Wavemaster 8300A oscilloscope (with 40-dB front-panel attenuation). .7Figure 8. Time and frequency-domain traces for switch comparison using the radarwaveform. .9Figure 9. Measurement setup for comparing switches by attenuating antennaretransmissions. .10Figure 10. Signal loss and retransmission attenuation vs. switch turn-off timing:(a) HMC536 switch and (b) HMC484 switch.11Figure 11. Desired-pulse loss vs. switch turn-on timing. .11Figure 12. SIRE frontend redesign block diagram. .14Figure 13. PCB containing the parts shown in figure 12. .14Figure 14. Timing diagram for the new transmitter configuration, incorporating the HMC536switch. .15Figure 15. Comparison of the new SIRE frontend design (with switch and 15-ft cable)against the old design: radar pulse transmitted to antenna (above) and retransmission toantenna (below). .16Figure A-1. Transmit antenna configuration for SIRE radar: (a) full antenna array, as seenfrom the front of the radar and (b) right transmit antenna, as seen from behind the radar,with its Avtech source circled. .19Figure A-2. SIRE radar frontend: two transmit paths, two Avtech pulse generators. .19Figure A-3. Output from two Avtech pulse sources: (a) time domain, (b) frequency domain. .20Figure A-4. New SIRE radar frontend: two transmit paths, one Avtech generator and onerelay.21iv
Figure A-5. Insertion loss and isolation for the HF353S relay: (a) radar pulse input toAntenna 1 connection and (b) radar pulse input to Antenna 2 connection. .22Figure A-6. Measured HF353S transient response: (a) control signal (0 to 5 V) and RFsignal transitions, zoomed out, and (b) RF signal transitions, zoomed in. .23Figure A-7. Measured HF353S transient response: (a) control signal (5 to 0 V) and RFsignal transitions, zoomed out, and (b) RF signal transitions, zoomed in. .23Figure A-8. PCB layout for the complete switch-and-relay circuit: Hittite HMC536 switchand Maxim MAX963 comparator, Axicom HF353S relay and Texas InstrumentsULN2003A driver. .24Figure A-9. Timing diagram for the new transmitter configuration, incorporating both thesolid-state switch and the electro-mechanical relay: (a) HFS353S-control timing and(b) HMC536-control timing. .25v
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1. IntroductionPulse reflection between frontend components is a common problem for impulse radar systems.Such reflections arise because radio frequency (RF) components are rarely impedance-matchedover an ultra-wide bandwidth (UWB). Any mismatch between components causes a portion ofthe impulse to reflect within the radar frontend. If the reflection couples into the transmitantenna, the radar emits an unintended, delayed, and distorted replica of the intended radartransmission.The performance of the U.S. Army Research Laboratory’s (ARL) synchronous impulsereconstruction (SIRE) radar has suffered from this problem. Because the transmit antenna isonly reasonably well-matched to the system impedance, an attenuated, distorted replica of theimpulse is reflected toward the impulse generator, which is poorly matched to the systemimpedance after making an impulse. Thus, most of this distorted signal is reflected from thetransmitter and radiated by the antenna. Upon reflection of the undesired impulses by theenvironment and reception of these signals by the receiver circuit, echoes from the radarenvironment appear in the radar image. Since an undesired reflection is recorded after eachdesired reflection, a weak target echo appears behind every actual target. These echoes generatefalse alarms during target detection and mask weak targets in their vicinity.The proposed solution for eliminating the echoes is to dissipate impulse reflections from theantenna in a matched load. The solution requires placing a high-speed solid-state switchbetween the impulse generator and antenna. The switch initially connects the antenna to thegenerator, and immediately after the UWB pulse is transmitted, connects the antenna to a 50- termination. In this way, the undesired reflection is dissipated before it can be transmitted.Section 2 presents the current SIRE frontend design, the origin of the undesired impulses, andthe solution for eliminating these impulses: a high-speed switch, a 15-ft cable, and a 50- load.Section 3 shows the effects of adding a 15-ft cable to the signal path. Section 4 compares theperformance of four solid-state switches for transmitting desired impulses while dissipatingundesired impulses. Section 5 provides the printed circuit board (PCB) layout for the switch andits control circuit, as well as the timing signals necessary to transmit the desired radar impulseswith minimal attenuation and dissipate the undesired impulses with maximum attenuation.Section 6 summarizes the performance improvement.1
2. Current ARL SIRE Frontend and Proposed UpgradeThe frontend of the SIRE radar consists of the following components: the Timing & Controlboard, a pair of Avtech AVB-1-3 pulse generators, a pair of transverse electromagnetic (TEM)horn antennas, an array of 16 Vivaldi-notch antennas, and a receiver circuit for each antenna.The Timing & Control board triggers the Avtech generators for each UWB pulse. Each Avtechgenerator sends large-amplitude short-duration pulses to its transmit antenna. The TEM hornstransmit the wideband pulses into free-space. The Vivaldi-notch antennas receive pulsereflections from the radar environment and the receiver circuit reconstructs received signals intoa time waveform. A two-dimensional (2-D) radar image is generated from the collection of the16 antenna signals. A block diagram of the SIRE radar frontend, for a single transmit-receivepath, is shown in figure 1. A sample pulse, as generated by the Avtech source and applied to theTEM horn, is shown in figure 2.Figure 1. SIRE radar frontend: single transmit-receive path.2
Figure 2. SIRE UWB radar pulse sample from Avtech generator: (a) time domainand (b) frequency domain.As illustrated in figure 1, part of the pulse is transmitted into free-space and part of the pulse isreflected back towards the Avtech generator because the TEM horn is not matched to the systemimpedance (50 ) over the entire bandwidth of the pulse. The antenna’s impedance mismatch,displayed as its reflection coefficient, is shown in figure 3a.The reflection coefficient of the TEM horn generally ranges from –35 to –10 dB over theoperating range of the radar. At the frequencies where S11 reaches its peaks, approximately10% of the radar pulse power is reflected from the antenna. The signal reflected from the hornantenna returns to the output of the Avtech generator, where it encounters an output circuit thathas changed state to a “quasi-open” circuit as a result of outputting the impulse. This impedancemismatch (higher reflection coefficient), after the radar trigger has fired, is shown in figure 3(b).The output reflection coefficient of the Avtech source generally ranges from –10 to –2 dB. Overthe operating range of the radar, the source re-reflects 10% to 60% (frequency-dependent, seefigure 3b) of the power that arrives back at its output.The forward and reverse transmission coefficients for th
Attenuation of Spurious Impulses from an Ultra-Wideband Radar: A High-Speed Switch for the Synchronous Impulse Reconstruction (SIRE) Frontend . by Gregory Mazzaro, Marc Ressler, Gregory Smith, and Francois Koenig . ARL-TR-5750 September 20
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