A simple-structure FMCW radar test system using PLL-Gunn oscillator and fundamental mixer in 79 GHz band

Transcription

1 A simple-srucure FMCW radar es sysem using PLL-Gunn oscillaor and fundamenal mixer in 79 GHz band Kohei Fujiwara and Hidehiko Yamaoka Tokyo Meropolian Indusrial Technology Research Insiue 2-4-, Aomi, Koo-ku, Tokyo , Japan Tasunori Onzuka and Shingo Ozaki NIHON DEMPA KOGYO CO., LTD , Sasazuka, Shibuya-ku, Tokyo , Japan Yoneo Akia and Yoshikazu Fujinaka Mebius Corporaion 2--27, Kiasaiwai, Nishi-ku, Yokohama-ciy, Kanagawa , Japan y akia@mebius.co.jp, y fujinaka@mebius.co.jp Absrac In his sudy, a simple frequency-modulaed coninuous wave (FMCW) radar es sysem for an ani-collision auomobile radar in he 79 GHz band has been developed. This sysem consiss of a down-converer based on a fundamenal mixer wih a phase-locked loop-gunn oscillaor and a mixed domain oscilloscope or a digial oscilloscope. This sysem can evaluae an FMCW signal in he ime domain, which includes he evaluaion of he chirp rae, chirp widh, chirp lengh, and lineariy. By employing he Gunn oscillaor, he down-converer aains a very simple configuraion. The down-converer has a conversion gain of 7.8 db a 79 GHz in ypical condiions and a bandwidh of 4 GHz. In his sudy, we explain he developmen of he radar es sysem and demonsrae he same using an FMCW chipse evaluaion board. Keywords E-band; FMCW radar; Gunn oscillaor I. INTRODUCTION Recenly, auomaically conrolled vehicles are being acively developed by many companies worldwide. To realize such vehicles, acive safey echnologies, such as pre-crash safey (PCS) sysems and adapive cruise conrol (ACC) sysems, are srongly required [1]. The PCS sysem can minimize he crash damage on deecing an imminen collision. The ACC sysem mainains a safe disance beween vehicles. There are many sensing equipmen for similar purposes. For example, laser, camera, and ulrasonic mehods have already been implemened in currenly selling vehicles. However, even hough such sensing sysems can be easily and inexpensively implemened in vehicles, he performance of hese mehods srongly depends on he weaher environmen. Alhough a radio wave is aenuaed in rain, he radar sysems are sill funcional. Therefore, i has become a rend o employ a frequency-modulaed coninuous wave (FMCW) radar in a millimeer-wave band for he PCS and ACC sysems. The FMCW radar ransmis a sweeping radio wave of several ens of mw o a moving objec and deecs he refleced wave o measure is posiion and velociy as well as is disance from anoher objec. Thus, an FMCW radar sysem has he advanage of having lower ransmiing power and cos han a radiional pulse radar sysem. The FMCW radar for an auomobile is allocaed boh 77 GHz and 79 GHz bands, and heir maximum allowed bandwidhs are 1 GHz and 4 GHz, respecively. Especially, in he 79 GHz band wih a usable bandwidh of 4 GHz, he radar can deec an objec of approximaely 4 cm size. I does ha using a high-speed frequency sweep; for example, he velociy resoluion is improved by 1.9 m/s in a 1 ms sweep ime. Thus, he radar can differeniae a pedesrian from a vehicle. To realize hese performances, i is imporan o mainain frequency lineariy and signal puriy in he radar sysem, because degradaions in hese parameers reduce he accuracy and resoluion of range and velociy of he radar sysem. Consequenly, he FMCW signal characerisics should be measured in he ime-domain. However, in general, i is difficul o measure he FMCW chirp rae, chirp lengh, chirp widh, and lineariy in he ime-domain using a convenional specrum analyzer. Therefore, i is necessary o prepare a imedomain FMCW es sysem, which is cos-effecive and easy o handle. In his sudy, we explain and verify he performance of he proposed 79 GHz band FMCW radar es sysem based on a down-converer implemened by a phase-locked loop (PLL)- Gunn oscillaor and a fundamenal mixer wih a ime-domain measuring insrumen. II. A. FMCW Signal Measuremen TEST SYSTEM Fig. 1(a) shows an ideal linear FMCW radar signal wih he up-chirp slope. A volage-conrolled oscillaor (VCO) or a PLL synhesizer is employed for a linear sweeper. The ransmied and received signals are described by he solid and doed lines, respecively. The frequency modulaed signal has a specific bandwidh of f sweep, chirp lengh of cl, and chirp rae. The bea frequency f B is measured by a frequency shif caused by he refleced signal from a arge. The bea frequency is proporional o he round-rip ime p. Boh he range and he radial velociy are obained by he measured frequency shif f B.

2 If he ransmied signal has non-lineariy, as shown in Fig. 1(b), which is caused by a change of ambien environmen in he VCO or PLL synhesizer, he bea frequency by a fas Fourier ransformaion (FFT) of a arge will no be consan. This effec decreases he range, resoluion, and radial velociy accuracy. Fig. 1(c) shows an effec of rippling, which causes he undesired side-lobes in he IF specrum. This effec oo decreases he above accuracy and resoluion. Thus, he lineariy of he linear frequency sweeper is he corner sone of he radar sysem. Consequenly, in FMCW signal measuremen, i is imporan o measure he chirp widh, chirp lengh, chirp rae, and lineariy. DUT Fig. 2. RF IN 77~81 GHz Down-converer IF OUT 0.7~4.7 GHz Mixed domain oscilloscope Tekronix MDO44C Digial oscilloscope Keysigh DSO90804A Configuraion of he 79 GHz band FMCW radar es sysem. Analysis sofware f() fsweep f() Ideal Frequency deviaion Rippling p f() p f() p fsweep fsweep cl cl cl f() f() he analog bandwidh of more han 6 GHz and a mixed domain oscilloscope. Furher, he IF frequency should be a few GHz for he signal. The swep frequency informaion in he ime-domain can be direcly displayed by he mixed domain oscilloscope [2]. Therefore, he chirp rae, chirp lengh, chirp widh, and lineariy parameers are evaluaed easily. FFT FFT FFT Ampliude Ampliude Ampliude f f f (a) (b) (c) Fig. 1. (a) Ideal linear FMCW radar signal, (b) frequency deviaion by non-lineariy, and (c) rippling. TABLE I. SYSTEM REQUIREMENTS OF THE 79 GHZ TEST SYSTEM. RF inpu frequency 77 GHz 81 GHz Local frequency 76.3 GHz IF frequency 0.7 GHz 4.7 GHz Typical conversion gain >6 db Inpu P1dB >0 dbm Noise figure <16 db LO Accuracy <0.5 C Adapive measuring insrumens Digial oscilloscope (BW>6 GHz) and mixed domain oscilloscope Measuremen addendums Chirp rae, chirp lengh, chirp widh, and lineariy B. Configuraion and Requiremens The FMCW radar es sysem consiss of a down-converer and a convenional digial oscilloscope or a mixed domain oscilloscope, as shown in Fig. 2. The down-converer frequencyconvers from a FMCW signal in 79 GHz band o ha in a microwave-band o observe he chirp widh, chirp rae, chirp lengh, and lineariy in he ime-domain wih hese measuring insrumens. Using he mixed domain oscilloscope, he imedomain characerisics can be direcly obained by a funcion of he real-ime specrum analyzer wih he maximum bandwidh of 6 GHz inside he oscilloscope [2]. Employing his advanageous funcion makes i possible o configure an affordable simple-srucure es sysem. However, he mixed domain oscilloscope has hree bands of a block down-converer [3]. Therefore, he IF frequency mus be injeced o he mixed domain oscilloscope wihin he bands while measuring he FMCW signal. Anoher mehod is o analyze he ime-domain daa from a digial oscilloscope by he quadraure-demodulaion mehod in he dedicaed sofware by Mebius Corporaion. The requiremens of he 79 GHz FMCW radar es sysem are summarized in Table I. An RF inpu frequency from he 77 GHz 81 GHz band and a local oscillaion (LO) frequency of 76.3 GHz are chosen. The required down-conversion gain is higher han 6 db a he cener frequency of 79 GHz. The inpu 1 db compression poin (P1dB) is more han 0 dbm. The overall noise figure is less han 16 db. The LO frequency accuracy is wihin 0.5 ppm. The adapive measuring insrumens are boh, a convenional digial oscilloscope wih III. 79 GHZ DOWN-CONVERTER The 79 GHz down-converer is an essenial componen required o down-conver from a millimeer-wave signal o a few GHz o analyze on an oscilloscope. We developed he converer by combining i wih a Gunn oscillaor and a fundamenal mixer. The PLL-Gunn oscillaor was designed and implemened by NIHON DEMPA KOGYO CO., LTD., Tokyo, Japan. The developed oscillaor conribues a simple circui configuraion and is easy o seup and operae. A. Down-Converer Configuraion The 79 GHz fundamenal mixer is designed based on he V- band fundamenal mixer for he IEEE802.11ad es sysem [4]. The block diagram of he 79 GHz band down-converer is shown in Fig. 3. A bias volage of 1.28 V is applied o his mixer o improve he efficiency of frequency-conversion. The 79 GHz mixer consiss of a single balanced mixer wih a ra-race-circui and a Schoky-barrier diode; a low pass filer (LPF) wih a DC block capacior; a DC cu circui; and a broadband waveguide-o-microsrip line ransducer [5]. The cuoff frequency of he LPF is designed o be 7 GHz. All pars are mouned on a polyerafluoroehylene prined circui board. The PLL-Gunn oscillaor is used for he LO oscillaor o be simple-srucured and cos-effecive. The down-convered signal is pre-amplified by a broadband amplifier of he ypical gain of 26 db o obain enough signal level.

3 RF= 77~81 GHz Mixer (N=1) ConvLoss=16 db LPF R L I PLL Gunn fc=7 GHz LO=76.3 GHz Broadband Amp ZVA-213X-S+ PG=26 db IF= 0.7~4.7 GHz f=8.775 GHz Gunn Osc. f=76.3 GHz x 4 PFD CP LP Coupler N=2 0~ V Fig. 3. Block diagram of he 79 GHz band down-converer. Fig. 4. Block diagram of PLL-Gunn oscillaor. B. PLL-Gunn Oscillaor In general, a Gunn oscillaor is employed as a reliable, compac, and low-cos solid-sae millimeer-wave source. I exhibis various desirable characerisics, such as high power, low phase noise, and 1/f noise. However, using a general Gunn oscillaor is difficul o adjus an oscillaion frequency and o mainain frequency sabiliy because of he free-running oscillaion mechanism. Thus, i has an individual difference in frequency and oupu power. To employ he LO for he down-converer wih frequency sabiliy, a PLL-Gunn oscillaor has been developed. I is based on he free-running oscillaor wih a varacor diode for frequency uning. The free-running Gunn oscillaor is fabricaed on an aluminum niride subsrae using a flip-chip Gunn diode. This echnology can realize a low-cos mass producion owing o he use of unpackaged flip-chip Gunn diodes and flip-chip bonding echnology. I has a high oupu power of more han 20 mw in he W-band. The block diagram of he PLL-Gunn oscillaor is shown in Fig. 4 and he phoograph of he PLL-Gunn oscillaor is shown in Fig. 5. A reference signal of 35.1 GHz is generaed by muliplying he frequency four imes. The frequency sandard used is he GHz emperaure-conrolled crysal oscillaor (TCXO). The sandard signal is frequency-mixed in a second order harmonic mixer wih a signal of 76.3 GHz, which is generaed by a free-running Gunn oscillaor via a direcional coupler. Furher, he frequency-convered signal of 6.1 GHz is injeced ino a phase frequency deecor (PFD), a charge pump (CP), and a loop filer (LP) o change a frequency difference o a volage difference beween 0 V. The volage from he PFD is applied o a varacor diode o fine-une he desired oscillaion frequency. A signal is produced by he waveguide, which is prepared on he boom of he module. More han dbm oupu is obained a he bias volage of 3.7 V. The frequency accuracy is 0.13 ppm. Fig. 6 shows he phase noise characerisics of he packaged PLL-Gunn oscillaor by changing he frequency offse from 0 Hz o MHz using he Rohde & Schwarz FSW67 specrum and signal analyzer wih he FSZ-1 W-band down-converer and he phase noise measuremen opion FSW-K40. As a resul, he phase noise a he offse of 1 khz is 53.3 dbc/hz. C. Performance The down-conversion gain wih a sweep of he RF is shown in Fig. 7. The injeced LO signal level from he PLL-Gunn oscillaor is 11.7 dbm; moreover, he RF sweep range is 79.0 Fig. 5. Phoograph of PLL-Gunn oscillaor. Gunn Osc. ± 2.0 GHz. The performance is saisfacory owing o a ypical conversion gain of 6 db. The measured noise figure is 14.8 db a he cener frequency of 79 GHz. The P1dB is aken using a Keysigh SMS-AG millimeer-wave source module and he Rohde & Schwarz FSW67 specrum and signal analyzer. Fig. 8 shows he lineariy characerisics for he down-converer by sweeping he inpu power from 37.0 dbm 8.0 dbm a he frequency of 79 GHz. The lineariy is kep wih he inpu power beween 37.0 dbm 8.0 dbm. Fig. 8 shows he phoograph of he inernal srucure of he 79 GHz band down-converer. A ypical IF specrum response by he down-conversion is measured as shown in Fig. 9. The specrum is produced by dbc/hz Hz Fig. 6. Phase noise characerisics of he PLL-Gunn oscillaor by changing he frequency offse from 0 Hz o MHz.

4 injecing an RF signal of 77 GHz coninuous wave. The second order harmonic of 53.6 dbc is obained a he frequency of 1.4 GHz. Conversion Gain (db) db Fig GHz, dbm 1.4 GHz, dbm GHz IF spurious response by down-conversion. RBW=0 khz VBW=1 MHz ATT=0 db RF Frequency (GHz) Fig. 7. Down-conversion gain by sweeping he RF frequency from 77 GHz 81 GHz a 76.3 GHz LO frequency wih a power of 11.7 dbm from he PLL-Gunn oscillaor. Pre-amplifier IF Oupu Power (dbm) Phoograph of he inernal srucure of he 79 GHz band down- Fig.. converer. Fundamenal Mixer PLL-Gunn Osc RF Inpu Power (dbm) Fig. 8. Measured oupu IF power and inpu RF power by sweeping RF power from 37.0 dbm 8 dbm a inpu frequency of 79 GHz. IV. SYSTEM EVALUATION The performance evaluaion of he es sysem is conduced using an evaluaion board of a millimeer-wave sensing device in an anechoic chamber. The emied FMCW signal is received and down-convered by he down-converer using a horn anenna wih he ypical gain of 25 dbi. The down-convered signal is ransmied from inpu ino he real-ime specrum analyzer on he MDO44C mixed domain oscilloscope or he Keysigh DSO90804A digial oscilloscope o obain he chirp rae, chirp lengh, chirp widh, and lineariy. The DSO90804A has an analog bandwidh of 8 GHz. These figures are obained using a signal analysis sofware developed by Mebius Corporaion and a Keysigh vecor signal analyzer (VSA), v20.0, wih he 89601B/BN-BHP FMCW opion [6]. The evaluaion board is used as a ransmier, which is he AWR1443BOOST evaluaion module from Texas Insrumens Incorporaed [4]. This sensing device has he abiliy of producing an oupu power of dbm and a maximum anenna gain of 12 dbi using prined anennas. The measured equivalen isoopic radiaed power (EIRP) is 18.9 dbm-eirp a he frequency of 80.5 GHz. The evaluaion board generaes a saw-ooh waveform wih ime delay. According o he consrain of he inpu frequency range over he real-ime specrum analyzer on he mixed domain oscilloscope [3], a ransmiing signal is configured by he chirp widh of 00 MHz a he cener frequency of 80.5 GHz, he chirp lengh of 200 µs, he chirp rae of 5 MHz/µs, and he ime delay of µs. As per his configuraion, he IF frequency is beween 3.7 GHz and 4.7 GHz. The disance and he heigh of boh he ransmier and he down-converer are 1.65 m and 1.54 m, respecively. Thus, he esimaed ransmission loss by Friis s equaion is 74.9 db a 80.5 GHz, and he esimaed receiving power is 56 dbm. Fig. 11 shows he experimenal seup in an anechoic chamber. V. EVALUATION RESULTS The down-convered signal is analyzed using a digial oscilloscope wih wo ypes of signal analysis sofware, which are Keysigh VSA v20.0 and he sofware by Mebius Corporaion, or he real-ime specrum analyzer on a mixed domain oscilloscope. The performance comparison of each measuremen mehod is summarized in Table II. The chirp

5 TABLE II. SYSTEM REQUIREMENTS OF THE 79 GHZ TEST SYSTEM. Configured value VSA v20.0+dso90804a Mebius+DSO90804A MDO44C Chirp widh 00 MHz MHz MHz MHz Chrip lengh 200 µs µs µs µs Chirp rae 5 MHz/µs 4.97 MHz/µs 4.97 MHz/µs 5.00 MHz/µs Lineariy N/A 115 khz/µs 127 khz/µs 799 khz/µs Transmier AWR1443BOOST Fig m 79 GHz band down-converer Experimenal seup in an anechoic chamber. rae resuls are comparable o each oher. The measured chirp widh is obained as MHz by he Rohde & Schwarz FSW67 specrum analyzer wih he FSZ-1 W-band downconverer. The chirp widh and lengh analyzed by he VSA v20.0 is smaller han he oher resuls. I migh be caused by he difference of he analyzing algorihm in he VSA sofware. The lineariy obained by he MDO4140C mixed domain oscilloscope is approximaely six imes larger han he oher resuls. This migh also be he reason of why here is a difference in he analyzing algorihm in he MDO4140C mixed domain oscilloscope. Fig. 12 shows he measured and quadraure-demodulaed FMCW radar signal from he downconverer using he DSO90804A oscilloscope wih he sofware by Mebius Corporaion. VI. CONCLUSION In his sudy, we succeeded in developing a simple and affordable 79 GHz FMCW radar evaluaion sysem based on he PLL-Gunn oscillaor and fundamenal mixer. The PLL- Gunn oscillaor has a frequency accuracy of 0.13 ppm, a phase noise of 53.3 dbc/hz a he 1 khz offse, and an oupu power of 11.7 dbm. The down-converer has a ypical conversion-gain of 7.8 db and a noise figure of 14.8 db. The down-converer lineariy is kep up o he inpu power of 3 dbm a he cener frequency of 79 GHz. The sysem is easy o handle and can evaluae he chirp widh, chirp lengh, chirp rae, and lineariy. These evaluaions are configured in Table II a he receiving power of 56 dbm-eirp, using a real-ime specrum analyzer in a mixed domain oscilloscope or a convenional digial oscilloscope wih a signal analysis sofware. By employing he evaluaion sysem, he esimaed iniial cos of he implemenaion is approximaely one-hird ha of a curren es sysem. Furhermore, o improve performance, we are preparing a down-converer module combined wih he PLL-Gunn oscillaor and he fundamenal mixer o make i more compac and cos effecive, as shown in Fig. 13. The size will be mm. RF IN IF Ou DC +12 V Modulaion Delay Fig. 13. Developing he 79 GHz down-converer module. Deviaion (MHz) Time (µs) Fig. 12. Measured FMCW radar signal in he ime-domain. ACKNOWLEDGMENT The auhors would like o hank Dr. Asushi Kanno a Naional Insiue of Informaion and Communicaions Technology for he producive discussions. REFERENCES [1] K. Honda, K. Yoneda, and K. Yamane, Developmen of 76GHz millimeer-wave radar for rear shor range, Fujisu Ten Tech. J. No.30(2008). [2] Tekronix MDO4000C series oscillioscope daashee, available a hps:// daashee/mdo4000c-series-oscilloscope-daashee-48w pdf&nid=74936.

6 [3] RF riggering on a mixed domain oscilloscope, available a hps://www. ek.com/blog/rf-riggering-mixed-domain-oscilloscope. [4] K. Fujiwara, H. Yamaoka, T. Kobayashi, T. Onzuka, S. Ozaki, A. Nakagawa, Y. Akia, and Y. Fujinaka, A low cos and simple srucure IEEE802.11ad wireless nework appliance es sysem using Gunn oscillaor and fundamenal mixer, 2017 IEEE Asia Pacific Microwave Conference (APMC), Kuala Lumpur, Malaysia, November [5] K. Fujiwara and T. Kobayashi, Low ransmission loss, simple, and broadband waveguide-o-microsrip line ransducer in V-, E- and W- band, IEICE Elecronics Express 14 (2017) (DOI: hps: //doi.org/.1587/elex ). [6] Keysigh Technologies: 89601B/BN-BHP FMCW radar analysis VSA sofware, available a hps://lieraure.cdn.keysigh.com/liweb/pdf/ EN.pdf?id=