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Radar related progress in RF technology over the past decade (A short trip down Memory Lane) PW van der Walt Reutech Radar Systems University of Stellenbosch.

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Presentation on theme: "Radar related progress in RF technology over the past decade (A short trip down Memory Lane) PW van der Walt Reutech Radar Systems University of Stellenbosch."— Presentation transcript:

1 Radar related progress in RF technology over the past decade (A short trip down Memory Lane) PW van der Walt Reutech Radar Systems University of Stellenbosch

2 Introduction We’re on the threshold of the last year of the decade – good time to look back! We’re on the threshold of the last year of the decade – good time to look back! The first decade of the 21 st century has witnessed the maturation of important high speed device technologies The first decade of the 21 st century has witnessed the maturation of important high speed device technologies Hetero-junction Bipolar Transistors and HBT ICs Hetero-junction Bipolar Transistors and HBT ICs HEMPT and pHEMPT devices and ICs HEMPT and pHEMPT devices and ICs LDMOS power devices LDMOS power devices Ever smaller and faster silicon CMOS devices Ever smaller and faster silicon CMOS devices During the past decade devices using these technologies have matured, driven mainly by cell phone and other communications systems During the past decade devices using these technologies have matured, driven mainly by cell phone and other communications systems In many cases radar applications benefit because the devices also meet radar requirements In many cases radar applications benefit because the devices also meet radar requirements Looking back, it has been an exciting 10 years! Looking back, it has been an exciting 10 years! In this paper a brief outline is given of some of the more spectacular advances in RF devices that have made them useful in the implementation of radar systems In this paper a brief outline is given of some of the more spectacular advances in RF devices that have made them useful in the implementation of radar systems

3 Contents Frequency synthesis Frequency synthesis DDS DDS PFD PFD Signal conditioning Signal conditioning Amplification Amplification Frequency translation Frequency translation Modulators, demodulators and mixers Modulators, demodulators and mixers Data conversion Data conversion RF Power RF Power Packaging microwave components Packaging microwave components PCB materials PCB materials PCB design PCB design

4 Frequency synthesis DDS DDS A DDS consists of a phase accumulator (= a wrap around counter), a sine look-up table and a digital to analog converter (DAC) A DDS consists of a phase accumulator (= a wrap around counter), a sine look-up table and a digital to analog converter (DAC) The direct digital synthesizer has become a key element in frequency synthesizers The direct digital synthesizer has become a key element in frequency synthesizers Radar requirements are strict in terms of bandwidth, phase noise and spurious signals. The bandwidth and spurious responses of earlier DDSs limited the application of early generation DDSs in radar systems. Radar requirements are strict in terms of bandwidth, phase noise and spurious signals. The bandwidth and spurious responses of earlier DDSs limited the application of early generation DDSs in radar systems. DDS spurious caused by DDS spurious caused by DAC harmonics that alias back to baseband DAC harmonics that alias back to baseband Mitigated by improved linearity Mitigated by improved linearity Phase truncation spurs when the frequency tuning word msb’s > DAC resolution Phase truncation spurs when the frequency tuning word msb’s > DAC resolution Situation improves with ADC resolution Situation improves with ADC resolution

5 DDS Application Because the DDS output is a sampled signal, aliasing of harmonics occurs Because the DDS output is a sampled signal, aliasing of harmonics occurs DDS wide band spurious can be quite high DDS wide band spurious can be quite high DDS narrow band spurious can be quite low DDS narrow band spurious can be quite low A PLL acts as a tracking narrow band filter and is the ideal companion for a DDS A PLL acts as a tracking narrow band filter and is the ideal companion for a DDS The following slide shows the preferred application of a DDS in a wide-band frequency synthesizer for radar The following slide shows the preferred application of a DDS in a wide-band frequency synthesizer for radar

6 DDS Application

7 DDS then and now 2000: 2000: State of the art represented by AD9854 State of the art represented by AD MHz clock, 12 bit ADC, 48 bit FTW 300 MHz clock, 12 bit ADC, 48 bit FTW 80 dB narrow band SFDR at 100 MHz 80 dB narrow band SFDR at 100 MHz Falls short of many radar requirements Falls short of many radar requirements Digital Phase Frequency Detectors (PFD) fall short on phase noise Digital Phase Frequency Detectors (PFD) fall short on phase noise 2008: 2008: Single IC state of the art represented by AD9912 Single IC state of the art represented by AD MHz clock, 14 bit ADC, 48 bit FTW 1000 MHz clock, 14 bit ADC, 48 bit FTW 86 dB narrow band SFDR at 400 MHz 86 dB narrow band SFDR at 400 MHz Backed by a matching PFD Backed by a matching PFD The DDS qualifies excellently for radar applications The DDS qualifies excellently for radar applications Agile LO Synthesizers Agile LO Synthesizers Chirped pulse generators Chirped pulse generators FMCW sources with excellent chirp linearity FMCW sources with excellent chirp linearity

8 Frequency Synthesis PFD PFD The phase-frequency detector is at the heart of a PLL The phase-frequency detector is at the heart of a PLL The first decade of the 21 st century saw the introduction of a low noise phase-frequency detector by Hittite, bettering its predecessors by about 20 dB in one spectacular leap The first decade of the 21 st century saw the introduction of a low noise phase-frequency detector by Hittite, bettering its predecessors by about 20 dB in one spectacular leap The HMC439 has a noise floor of -140 dBc/Hz at 1.3 GHz The HMC439 has a noise floor of -140 dBc/Hz at 1.3 GHz This is comparable to the noise performance of well-designed analogue synthesizers for radar This is comparable to the noise performance of well-designed analogue synthesizers for radar The PFD made possible the use of simple PLL architectures for high performance radar frequency synthesizers The PFD made possible the use of simple PLL architectures for high performance radar frequency synthesizers And it happened in the past decade And it happened in the past decade As a case in point, RRS now builds a synthesizer optimised for its X-band pulsed MTD radars on two PC boards with phase noise performance better than that of analogue synthesizers costing R1 million a decade ago As a case in point, RRS now builds a synthesizer optimised for its X-band pulsed MTD radars on two PC boards with phase noise performance better than that of analogue synthesizers costing R1 million a decade ago

9 Amplification Progress with amplifiers was steady rather than spectacular Progress with amplifiers was steady rather than spectacular Gain block performance has improved with lower noise figures and higher third order intercept points (IP 3 ) Gain block performance has improved with lower noise figures and higher third order intercept points (IP 3 ) Gain stability has reached an impressive ±0.2 dB over -40º to 85º C temperature range Gain stability has reached an impressive ±0.2 dB over -40º to 85º C temperature range Bandwidths of 20 GHz Bandwidths of 20 GHz Modern HBT based amplifiers have extremely low phase noise at high drive levels, as exemplified by the measured phase noise at 1 GHz of a ×10=×2×5 frequency multiplier implemented with a new generation of amplifiers. Modern HBT based amplifiers have extremely low phase noise at high drive levels, as exemplified by the measured phase noise at 1 GHz of a ×10=×2×5 frequency multiplier implemented with a new generation of amplifiers.

10 1 GHz Multiplier phase noise

11 Frequency Translation Modulators can produce single sideband RF output signals up to about 4 GHz from baseband IQ inputs from a single integrated circuit which incorporates the wideband LO quadrature polyphase phase shift filter Modulators can produce single sideband RF output signals up to about 4 GHz from baseband IQ inputs from a single integrated circuit which incorporates the wideband LO quadrature polyphase phase shift filter

12 Modulators At the turn of the century, baseband bandwidths were limited to 250 MHz and noise floors were at a level of about -152 dBc/Hz At the turn of the century, baseband bandwidths were limited to 250 MHz and noise floors were at a level of about -152 dBc/Hz Today modulators with baseband bandwidths of 700 MHz and noise floors of -158 dBc/Hz Today modulators with baseband bandwidths of 700 MHz and noise floors of -158 dBc/Hz Carrier suppression without trimming can exceed -50 dBc and sideband rejection is better than 40 dB Carrier suppression without trimming can exceed -50 dBc and sideband rejection is better than 40 dB The translinear multiplier cells far outperform diode mixers regarding spurious performance The translinear multiplier cells far outperform diode mixers regarding spurious performance These devices have proved to be high performance and versatile elements in radar frequency synthesizers and transmitter exciters These devices have proved to be high performance and versatile elements in radar frequency synthesizers and transmitter exciters With demodulators to match With demodulators to match

13 Frequency translation Another welcome component is the balanced diode mixer whith incorporated LO amplifier, reducing external LO drive requirements to less than 0 dBm, while internally driving the mixer at a level of 20 dBm Another welcome component is the balanced diode mixer whith incorporated LO amplifier, reducing external LO drive requirements to less than 0 dBm, while internally driving the mixer at a level of 20 dBm This comes as a blessing to everyone who has had the pleasure of suppressing leakage from high level LO signals This comes as a blessing to everyone who has had the pleasure of suppressing leakage from high level LO signals At the same time offering mixer/demodulator with very large dynamic range At the same time offering mixer/demodulator with very large dynamic range

14 Data Conversion The performance of ADCs has improved by leaps and bounds during the past 10 years The performance of ADCs has improved by leaps and bounds during the past 10 years 2000: 2000: 80 MS/s, 10 bits, 300 MHz bandwidth (AD) 80 MS/s, 10 bits, 300 MHz bandwidth (AD) 50 Ms/s, 12 bits, 300 MHz bandwidth 50 Ms/s, 12 bits, 300 MHz bandwidth 2009: 2009: 1 GS/s, 12 bits, 2.1 GHz bandwidth (TI) 1 GS/s, 12 bits, 2.1 GHz bandwidth (TI) Rate of increase in speed: Rate of increase in speed: 1 decade/decade! 1 decade/decade!

15 Bad and Good News The Bad News for RF engineers The Bad News for RF engineers The digital domain is encroaching on their analogue world The digital domain is encroaching on their analogue world One of these days we will be left with nothing but antennas and LNAs! One of these days we will be left with nothing but antennas and LNAs! The Good News for RF engineers The Good News for RF engineers Mixed circuit technology has become an RF problem Mixed circuit technology has become an RF problem PCB design is now done by a multi-disciplinary team PCB design is now done by a multi-disciplinary team

16 Power Transistors Prior to about 2000, bipolar transistors were the only devices on offer for L-band radar transmitters Prior to about 2000, bipolar transistors were the only devices on offer for L-band radar transmitters Up to 200 W peak power per device Up to 200 W peak power per device 7 dB power gain 7 dB power gain LDMOS transistors are now the devices of choice LDMOS transistors are now the devices of choice Up 500 W of peak power per device (IFF) Up 500 W of peak power per device (IFF) 12 dB power gain 12 dB power gain 50 V supply 50 V supply These devices dramatically impact on the complexity of radar transmitters, reducing the number of stages and the number of devices per stage These devices dramatically impact on the complexity of radar transmitters, reducing the number of stages and the number of devices per stage

17 Power transistors The next decade promises to be equally exciting The next decade promises to be equally exciting GaN device technology is maturing GaN device technology is maturing The first devices have reached production status The first devices have reached production status Output power of 100 W per device at X band frequency have been reported by laboratories Output power of 100 W per device at X band frequency have been reported by laboratories Currently 25 W from MESFET devices Currently 25 W from MESFET devices The devices hold the promise that powerful solid-state transmitters will become reality at frequencies up to X-band in the next decade The devices hold the promise that powerful solid-state transmitters will become reality at frequencies up to X-band in the next decade

18 PCB Materials Rogers introduced its 4000 series of laminates in the early 90’s. Rogers introduced its 4000 series of laminates in the early 90’s. This substrate material is compatible with fiber-glass FR4 PCB and can be stacked up with fiber-glass to make multilayer PCB’s handling signals up to mm wave frequencies This substrate material is compatible with fiber-glass FR4 PCB and can be stacked up with fiber-glass to make multilayer PCB’s handling signals up to mm wave frequencies This material is steadily impacting the way professional microwave systems are built This material is steadily impacting the way professional microwave systems are built Slowly but surely extending RF construction techniques to microwave and millimetre wave frequencies Slowly but surely extending RF construction techniques to microwave and millimetre wave frequencies

19 Microwave systems Traditionally, microwave components such as mixers and amplifiers are individually packaged in connectorised enclosures Traditionally, microwave components such as mixers and amplifiers are individually packaged in connectorised enclosures These modules are expensive, with the enclosure contributing most of the cost These modules are expensive, with the enclosure contributing most of the cost At the same time they provide a very good shielding solution to contain radiation from microwave components At the same time they provide a very good shielding solution to contain radiation from microwave components With materials such as Rogers R4003, the PCB can become a microwave enclosure at a much reduced cost With materials such as Rogers R4003, the PCB can become a microwave enclosure at a much reduced cost

20 A PCB-housed 6-8 GHz doubler

21 Construction Top layer: Rogers R4003 Top layer: Rogers R4003 The cover is bent from thin sheet metal and soldered into place as a shield The cover is bent from thin sheet metal and soldered into place as a shield Bottom shielding is provided by ground plane layers inside and on the surfaces of the PCB Bottom shielding is provided by ground plane layers inside and on the surfaces of the PCB DC and BIT circuitry is housed outside the RF shield DC and BIT circuitry is housed outside the RF shield All connections into the RF volume is made through LC feed-through components via an internal layer All connections into the RF volume is made through LC feed-through components via an internal layer The key to a successful design is to know something of antennas… The key to a successful design is to know something of antennas…

22 Antennas 101

23 Take care! Example of how not to launch (ca 2000) Example of how not to launch (ca 2000) Gap! Poor Earthing Oops! Slot Antenna

24 Launchers There is obviously a serious leakage problem at the connector transitions There is obviously a serious leakage problem at the connector transitions Totally unacceptable for use in a complex system Launchers should be chosen with care Totally unacceptable for use in a complex system Launchers should be chosen with care The transition must be modeled and simulated The transition must be modeled and simulated Not only for S 11 and S 21 Not only for S 11 and S 21 Also for leakage! Also for leakage!

25 PCB Design The PCB electromagnetic problem is a 3D problem The PCB electromagnetic problem is a 3D problem Transitions must be carefully designed to prevent radiation (or susceptibility to outside radiation) Transitions must be carefully designed to prevent radiation (or susceptibility to outside radiation) The board layout must be carefully planned from a functional and also from an EMC view The board layout must be carefully planned from a functional and also from an EMC view Look at the board from all sides! Look at the board from all sides! Following is an example of a recent low-leakage (but not leakage free) edge launcher design on an evaluation board Following is an example of a recent low-leakage (but not leakage free) edge launcher design on an evaluation board

26 Low Leakage Launcher

27 PCB design PCB enclosures potentially offer big cost savings in microwave circuitry PCB enclosures potentially offer big cost savings in microwave circuitry The PCB design problem is far from trivial. The PCB design problem is far from trivial. Too complex and time-consuming to simulate EM fields fully, forcing us to make judicious use of EM analysis tools Too complex and time-consuming to simulate EM fields fully, forcing us to make judicious use of EM analysis tools Knowledge of where current flows and good insight into the behaviour of electromagnetic fields is essential for creating good PCB designs Knowledge of where current flows and good insight into the behaviour of electromagnetic fields is essential for creating good PCB designs PCB enclosure design is challenging! PCB enclosure design is challenging! A source of interesting research questions for the academics! A source of interesting research questions for the academics!

28 Finally The technological advances that had the greatest impact on RF progress? The technological advances that had the greatest impact on RF progress? Undoubtedly the maturation of 3D EM analysis packages Undoubtedly the maturation of 3D EM analysis packages Passive components such as filters and antennas often need only one design iteration Passive components such as filters and antennas often need only one design iteration Without these tools, the sophistication reached with RF active and passive components would be unthinkable! Without these tools, the sophistication reached with RF active and passive components would be unthinkable!


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