A Transceiver Module for FMCW Radar Sensors Using ... - IEEE Xplore

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IEEE SENSORS JOURNAL, VOL. 11, NO. 2, FEBRUARY 2011

A Transceiver Module for FMCW Radar Sensors Using 94-GHz Dot-Type Schottky Diode Mixer Tae-Jong Baek, Dong-Sik Ko, Sang-Jin Lee, Yong-Hyun Baek, Min Han, Seok-Gyu Choi, Jae-Hyun Choi, Wan-Joo Kim, and Jin-Koo Rhee, Fellow, IEEE

Abstract—In this study, we fabricated a 94-GHz transceiver module for a millimeter-wave (MMW) frequency modulation continuous wave (FMCW) radar sensor. The transceiver modules consist of a waveguide voltage-controlled oscillator (VCO) and Rx module using a single balanced mixer. We designed a mixer with a conversion loss of 6.4 dB, without using an amplifier. Also, the waveguide VCO consisted of an InP Gunn diode, a varactor diode, two bias posts with LPF, and a Magic Tee for the MMW radar transceiver. The fabricated VCO has a tuning range of 20 V, 1.69% linearity range 1280 MHz by a varactor bias of 0 of 680 MHz, and current consumption of 154 to 157 mA. The completed module has a good conversion loss of 10.6 dB with an LO power of 11.4 dBm at 94 GHz. With this RF and LO input power, the conversion loss was maintained between 10.2–11.5 dB in the RF frequency range of 93.67–94.95 GHz. Index Terms—Diode mixer, frequency-modulated continuous-wave (FMCW), InP Gunn diode, millimeter-wave (MMW), voltage-controlled oscillator (VCO).

I. INTRODUCTION REQUENCY-MODULATED continuous-wave (FMCW) radars can be widely applied not only to car collision protection systems but also to military systems. The FMCW radar is operated by measuring the difference between the transmitted and received signals. The distance information can be obtained from literature [1]. Gunn diodes are one of the most important solid-state millimeter-wave (MMW) sources. It exhibits low FM noise and a wide operating frequency range and is extensively used as a local oscillator. The Gunn (or transferred-electron) effect has been observed in a number of III-V materials and compounds. However, only gallium arsenide (GaAs) and indium phosphide (InP) seem to be of significant importance for practical devices. In the past, theoretical treatments have attempted to define an upper frequency limit for Gunn diodes [2], [3]. The MMW, especially 35–94 GHz, is useful for radar due to low loss in air and vapor. In general, the VCO in high frequencies like MMWs has high resolution by wide modulation fre-

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Manuscript received February 17, 2010; revised July 01, 2010; accepted July 01, 2010. Date of publication September 23, 2010; date of current version November 17, 2010. This work was supported in part by the Millimeter-wave Innovation Technology (MINT) Research Center at Dongguk University and Han-wha Corporation through the Agency of Defense Development. The associate editor coordinating the review of this manuscript and approving it for publication was Prof. E. H. Yang. T.-J. Baek, D.-S. Ko, S.-J. Lee, Y.-H. Baek, M. Han, S.-G. Choi, and J.-K. Rhee are with the Millimeter-Wave Innovation Technology Research Center, Dongguk University, Seoul 100-715, Korea (e-mail: [email protected]). J.-H. Choi and W.-J. Kim are with the Agency of Defense Development, Daejeon 305-152, Korea. Digital Object Identifier 10.1109/JSEN.2010.2057419

TABLE I EPI-STRUCTURE OF DOT-TYPE SCHOTTKY DIODE

quency. The radar or radiometer system usually uses the waveguide system and the waveguide size is decided by frequency [4]. Signal frequencies at the -band are very attractive due to their high spatial resolution, the resulting compact chip size, and small antenna dimensions. Systems requiring MMWs with high power are mostly used in the waveguide oscillator. Several applications exist for MMW design, including wireless communications, anti-collision radar of vehicles, concealed object radar, and various industrial sensors [5]–[8]. In the FMCW radar, the phase noise and linearity are important factors to determine the resolution, and the output power (Tx) affects the detection of distance. The frequency sweep of the source becomes nonlinear due to changes of load impedance and of characteristics of nonlinear active components such as a Gunn diode and a varactor diode. The Magic Tee is an excellent structure to divide powers because it is good for isolating each port, and an InP-based Gunn VCO has low power consumption compared with a GaAs-based Gunn VCO. In this paper, we fabricated a 94-GHz transceiver module for MMW FMCW radar sensor using the InP-based VCO and dot-type Schottky diode mixer without an amplifier and waveguide VCO. II. DESIGN OF DOT-TYPE DIODE MIXER Most -band MMW monolithic integrated circuit (MIMIC) mixers have been fabricated using the Schottky diode components of high-electron mobility transistors (HEMTs), because they can be integrated into a single chip with other active circuit components such as amplifiers [9]. However, this approach may not be effective for mixer applications without an amplifier, because they have drawbacks in terms of their fabrication cost, process reliability, and diode characteristics. The dot-type Schottky diode was designed based on the simple and low-cost n/n+ epi-structure without the need for high-overhead E-beam lithography. The epi-structure of the GaAs Schottky diode is shown in Table I. Moreover, high-performance and reliable diode characteristics can be achieved with this structure. From the measurements, an ideality factor of 1.41 can be achieved at room temperature, with a total resistance and capacitance of 18.3 and 0.02 pF, respectively. The cutoff frequency of the dot-type Schottky diode is 435 GHz.

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BAEK et al.: TRANSCEIVER MODULE FOR FMCW RADAR SENSORS USING 94-GHz DOT-TYPE SCHOTTKY DIODE MIXER

Fig. 1. Circuit schematic and SEM photograph of the fabricated 94-GHz single balanced mixer (chip size: 1:9 1:3 mm ).

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Fig. 3. diodes.

I

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–V characteristics measured from GaAs Schottky and MHEMT

Fig. 2. SEM photograph of the fabricated dot-type Schottky diode (anode diameter: 5 m).

The circuit schematic and SEM photograph of the proposed dot-type Schottky diode of a single balanced mixer is shown in Figs. 1 and 2. A typical – V characteristic of the GaAs Schottky diode is also compared with the 0.1- m metamorphic HEMT diode in Fig. 3 [10]. A tandem coupler in the -band was used to achieve LO-RF isolation over a wide bandwidth. The quarter wavelength ( at LO) line was designed to have a 180 phase difference between the tandem coupler and diodes [11]. To prevent phase change in the bias circuit, we designed it using a short-stub of at 94 GHz) through the tandem couquarter-wavelength ( pler. Therefore, the LO-RF isolation is improved. A band reject filter as an open stub of a quarter-wavelength was added to the IF stage for suppressing the LO signal at the IF port [12]. The fabricated mixer measured conversion loss versus IF frequency and LO power and an excellent conversion loss of 6.5 dB were obtained at an RF signal of 93.5 GHz ( 20 dBm) and an IF of 500 MHz. Also, high LO-to-RF isolation greater than 30 dB was maintained over the entire RF frequency range of 91 97 GHz. This high and broadband isolation was due to the good phase balance of the tandem coupler with high directivity. The high P1-dB of 5 dBm were measured.

Fig. 4. Structure of the waveguide VCO. (a) Cross section of the waveguide VCO. (b) Top view of the lower cavity of the VCO.

III. TRANSCEIVER MODULE FOR FMCW RADAR SENSOR The waveguide VCO consisted of two-bias posts, InP Gunn diode, varactor diode, Magic Tee, and power tuning back-short in the end of a WR-10 cavity. Fig. 4 shows the structure of the waveguide VCO. The Magic Tee has been designed and realized at 94 GHz. A Magic Tee has intrinsic power split, isolation, and phase-reversal characteristic. Due to its intrinsic power split, isolation, and phase-reversal characteristics, the Magic Tee is a very attractive microwave circuit element for many applications such as an E-H tuner, frequency discriminator circuits, or

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Fig. 5. Schematic Magic Tee and a matching element.

Fig. 7. Current consumption measured from InP and GaAs VCOs.

Fig. 6. Measurement results of the fabricated Magic Tee.

directional couplers [13], [14]. The Magic Tee has excellent performance to divide output power from the VCO at the -band with low loss. The Magic Tee is designed by Ansoft HFSS. Fig. 5 shows a schematic of the Magic Tee and a matching element and the output power of VCO come in through port 1, and then the power is divided by the matching element to LO (port2) and Tx (port3). Port 4 is isolated. The four waveguide arm regions are standard WR-10 and their electromagnetic fields can be expanded into the summation of modal functions in a rectangular waveguide weighted with the known incident and unknown reflected coefficients. A hybrid mode-matching Method-of-Moment (MoM) technique is applied for modeling arbitrarily shaped 3-D waveguide structures. The designed Magic Tee has Low_R of 1.9 mm, Corn_h of 0.75 mm, Cyl_h of 1.6 mm, Up_R of 0.2 mm, and L of 5 mm. The characteristic of the Magic Tee is changed by the position of the cylinder as port 4, so we could determine the optimal position of the cylinder through experiment. The height and diameter of corn are important to divide output power of the VCO, and Fig. 6 shows the measurement results, such as 24 dB of S11, 22 dB of S22 (LO), 19 dB of S33 (Tx), and 3.59 dB of S21 and S31 at 94 GHz. A mobility management scheme in an InP-based VCO is proposed to reduce battery power consumption of the FMCW radar sensor. Fig. 7 shows the measurement results of power consumption of the InP VCO compared with a GaAs-based

Fig. 8. Measurement results of InP-based VCO.

VCO. The fabricated InP-based VCO has measurements of 154–157-mA current consumption, while GaAs-based VCO has over five times that. The bandwidth is measured by an E4407B spectrum analyzer with an Agilent extended harmonic mixer, and the power is measured by an Agilent E4419B EPM series power meter. The fabricated InP-based VCO exhibits 705-MHz bandwidth from 93.98 to 94.815 GHz and output power from 11.4 to 11.68 dBm. The linearity is calculated by (1) where is the bias value, is the frequency, is the reference value, and is the slope. The values of and can be obtained from linear fit. In this paper, the 1.68% linearity is 680 MHz from 0 to 9.5 V. The output power (Tx) is 11.4 dBm through the Magic Tee at 5 V of varactor voltage. Fig. 8 shows the linear-fit result of the measured bandwidth and output power of the InP-based VCO. The phase noise is measured in a 50-MHz span and resolution bandwidth (RBW) of 100 kHz from 1-MHz offset. The phase noise is measured by 10Log(RBW) plus the value of the 1-MHz offset from the peak of the oscillation signal.


Fig. 9. Phase noise at 10-MHz span.

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Fig. 11. Measured results of the fabricated back-to-back transition.

Fig. 12. Photograph of the fabricated Rx module.

Fig. 10. Flip-chip packaging configuration on Al O sapphire substrate.

Fig. 9 shows the measurement results of phase noise at 5 V of varactor voltage. In this paper, the phase noise is usually lower than 100 dBc. The microwave monolithic integrated circuit (MMIC) was fabricated by mounting the fabricated Al O sapphire substrate on the Rx module and using the flip-chip bonding between the Al O sapphire substrate to the MMIC. Fig. 10 shows a photograph of the flip-chip bonding assembled MMIC dot-type Schottky diode mixer on Al O sapphire substrate. The electromagnetic field transition of the CPW to the rectangular waveguide is designed for low loss by using a fin-line taper structure in the LO and RF input port [15]. The layout of a flip-chip bonding packaging configuration on Al O sapphire substrate is shown in Fig. 10. The measured result of the fabricated back-to-back transition is shown in Fig. 11. The insertion loss of the back-to-back tran-

Fig. 13. Block diagram of the transceiver module.

sition is 3.4 dB and the return loss is 27 dB at 94 GHz. Over the 85–97-GHz frequency, the insertion loss and return loss showed good results. A photograph of the fabricated Rx module is shown in Fig. 12. The single layer capacitors and feedthroughs were added at the bias circuits of the module to prevent potential oscillations. Fig. 13 shows the block diagram of the transceiver module for FMCW radar sensors. A photograph of the completed trans-

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Fig. 16. Conversion loss versus tuning voltage (varactor bias: 0

20 V).

Fig. 14. Photograph of the fabricated transceiver module.

Fig. 17. Conversion loss versus IF output frequency.

Fig. 15. Conversion loss and IF output power versus RF input power.

ceiver module is shown in Fig. 14. The module includes the Rx module, waveguide VCO (Tx module), cable guide, and bias PCB. The thicknesses of the Rx module, waveguide VCO, and cable guide are 3, 9, and 7 mm, respectively. The total size of mm . the module is Fig. 15 shows the conversion loss and IF output power versus RF input powers obtained from the measurements conducted at an IF frequency of 500 MHz. Fig. 16 shows the conversion loss versus the tuning voltage obtained from the measurements conducted at an IF frequency of about 500 MHz. Fig. 17 shows the conversion losses versus IF frequency of the MMW module at an RF power of 20 dBm. We fabricated a mixer with a conversion loss of 6.4 dB. In the case of the completed module, a conversion loss of 10.2 11.5 dB and an excellent P1-dB were obtained. Fig. 18 shows an LO-RF isolation of 19.39 21.56 dB in the frequency range of 93.67–94.95 GHz (varactor bias: 0 20 V).

Fig. 18. LO-to-RF port isolation versus Tx output frequency.

IV. DISCUSSION In this paper, the transceiver module was fabricated using a Magic Tee, an InP-based VCO, and a Schottky diode mixer. The essential parts of the VCO module consist of an InP-based Gunn


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TABLE II COMPARISON OF REPORTED VCO CHARACTERISTICS

diode and a varactor diode. We fabricated that the VCO has an excellent linearity and a high output power at 94-GHz frequency. From the measurement results, the phase noise is lower than 100 dBc from 0 to 20 V, output power (Tx) 11.5 dBm, and linearity range is 680 MHz (1.69%). The InP-based VCO for mobile equipment can reduce battery power consumption of the FMCW radar sensor compared with a GaAs-based VCO, because of the fabricated InP-based VCO has a lower operating current. The phase noise, linearity, output power, and current consumption in this paper shows better performance than the recent achievements as listed in Table II. V. CONCLUSION We have designed and fabricated a 94-GHz transceiver module using a commercially available InP Gunn and a varactor diode. In addition, we have fabricated a Schottky diode without an amplifier in which a single balanced mixer was applied to the Rx-module. The completed transceiver module shows excellent characteristics of the linearity range, low current consumption, conversion loss, and LO power at the -band. In conclusion, the fabricated MMW radar sensor module described in this paper has a good conversion loss of 10.6 dB at an LO power of 11.4 dBm at 94 GHz. With this RF and LO input power, the conversion loss was maintained between 10.2–11.5 dB in the RF frequency range of 93.67–94.95 GHz. REFERENCES [1] M.-S. Jung and W.-J. Kim, “Design of a W-band radiometer simultaneously operating with a single-antenna configured FMCW radar,” Inst. Electron. Eng. Korea, vol. 43, no. 4, pp. 67–74, Apr. 2006, TC. [2] A. M. Mazzone and H. D. Rees, “Transferred-electron oscillators at very high frequencies,” Electron Lett., vol. 17, pp. 539–540, Jul. 1981. [3] P. A. Rolland, E. Constant, G. Salmer, and R. Fauquembergue, “Frequency limitation of GaAs transferred-electron devices: Influence of operating d.c. and r.f. field values,” Electron. Lett., vol. 15, pp. 373–374, Jun. 1979. [4] W. H. Haydl, M. Neumann, L. Venveyen, A. Bangert, S. Kudszus, M. Schlechtweg, A. Hulsmann, A. Tessmann, W. Reinert, and T. Krems, “Single-chip coplanar 94-GHz FMCW radar sensors,” IEEE Microw. Guided Wave Lett., vol. 9, no. 2, pp. 73–75, Feb. 1999.

[5] A. G. Stove, “Linear FMCW radar techniques,” Proc. Inst Elect. Eng., vol. 139, no. 5, pt. F, pp. 343–350, Oct. 1992. [6] J. Otto, “Radar applications in level measurement, distance measurement and non-destructive material testing,” in Proc. 27th Eur. Microw. Conf., Sep. 1997, vol. 2, pp. 1113–1121. [7] M. E. Russell, A. Crain, A. Curran, R. A. Campbell, C. A. Drubin, and W. F. Miccioli, “Millimeter-wave radar sensor for automotiveintelligent cruise control (ICC),” IEEE Trans. Microw. Theory Tech., vol. 42, no. 12, pp. 2444–2453, Dec. 1997. [8] D. S. Goshi, Y. Liu, K. Mai, L. Bui, and Y. Shih, “Recent advances in 94 GHz FMCW imaging radar development,” in IEEE MTT-S Int. Microw. Symp. Dig., 2009, pp. 77–80. [9] A. Orzati, F. Robin, H. Meier, H. Benedikter, and W. Bächtold, “A V -band up-converting InP HEMT active mixer with low LO-power requirements,” IEEE Microw. Wireless Compon. Lett., vol. 13, no. 6, pp. 202–204, Jun. 2003. [10] J.-H. Oh, S.-W. Moon, D.-S. Kang, and S.-D. Kim, “High-performance 94-GHz single-balanced diode mixer using disk-shaped GaAs Schottky diodes,” IEEE Electron Device Lett., vol. 30, no. , pp. 206–208, Mar. 2009. [11] S.-W. Moon, M. Han, J.-H. Oh, J.-K. Rhee, and S.-D. Kim, “V -band CPW 3-dB tandem coupler using air-bridge structure,” IEEE Microw. Wireless Compon. Lett., vol. 16, no. 4, pp. 149–151, Apr. 2006. [12] M.-K. Lee, B.-O. Lim, S.-J. Lee, D.-S. Ko, S.-W. Moon, D. An, Y.-H. Kim, S.-D. Kim, H.-C. Park, and J.-K. Rhee, “A novel 94-GHz MHMET-based diode mixer using a 3-dB tandem coupler,” IEEE Microw. Wireless Compon. Lett., vol. 18, no. 9, pp. 626–628, Sep. 2008. [13] D. S. Ko, S. W. Moon, M. K. Lee, S. J. Lee, D. H. Ko, S. H. Bang, Y. H. Baek, M. Han, S. G. Choi, T. J. Baek, S. D. Kim, and J. K. Rhee, “94 GHz waveguide VCO with Magic_T for FMCW radar,” in Proc. 38th Eur. Microw. Conf., 2008, pp. 1234–1237. [14] D. S. Ko, M. K. Lee, S. J. Lee, S. W. Moon, D. H. Ko, S. H. Bang, Y. H. Baek, M. Han, S. G. Choi, T. J. Baek, D. C. Park, S. D. Kim, and J. K. Rhee, “94 GHz waveguide VCO for FMCW radar,” in Proc. Global Symp. Millimeter Waves, 2008, pp. 44–47. [15] S.-W. Moon, M.-K. Lee, J.-H. Oh, D.-S. Ko, I.-S. Hwang, J.-K. Rhee, and S.-D. Kim, “Sapphire based 94 GHz coplanar waveguide-to-rectangular waveguide transition using a unilateral fin-line taper,” Inst. Electron. Eng. Korea, vol. 45, pp. 65–70, Oct. 2008, Issue TC. [16] K. W. Chang, G. S. Dow, H. Wang, T. H. Chen, K. Tan, B. Allen, and J. Berenz, “A W-band single-chip transceiver for FMCW radar,” in IEEE Microw. Millimeter-Wave Monolithic Circuits Symp. Dig. Papers, 1993, pp. 41–44. [17] A. Tessmann, S. Kudszus, T. Feltgen, M. Riessle, C. Sklarczyk, and W. H. Haydl, “Compact single-chip W -band FMCW radar modules for commercial high resolution sensor applications,” IEEE Trans. Microw. Theory Tech., vol. 50, no. 12, pp. 2995–3001, Dec. 2002. [18] W. H. Haydl, M. Neumann, L. Verweyen, A. Bangert, S. Kudszus, M. Schlechtweg, A. Hülsmann, A. Tessmann, W. Reinert, and T. Krems, “Single-chip coplanar 94-GHz FMCW radar sensors,” IEEE Microw. Guided Wave Lett., vol. 9, no. 2, pp. 73–75, Feb. 1999.

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Tae-Jong Baek received the B.E. degree in information and communication engineering from Joongbu University, Daejeon, Korea, in 2003, and the M.E. degree in electronic engineering from the Dongguk University, Seoul, Korea, in 2005, where he is currently working toward the Ph.D. degree. Since 2003, he has been with the Millimeter-wave INnovation Technology Research Center (MINT), Seoul, Korea. His research interests include GaAs-based RF MEMS devices, compound semiconductor devices, and MMIC technology for millimeter-wave applications.

Dong-Sik Ko received the B.E. degree in electrical engineering from Dongguk University, Seoul, Korea, in 2007, where he is currently working toward the M.E. degree. Since 2007, he has been with the Millimeter-wave INnovation Technology Research Center (MINT), Seoul, Korea. His major field of study is the MMIC -band waveguide voltage-controlled design, oscillator and system.

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Sang-Jin Lee received the B.E. degree in information and communication engineering from Joongbu University, Daejon, Korea, in 2003, and the M.E. degree in electronics engineering from Dongguk University, Seoul, Korea, in 2005, where he is currently working toward the Ph.D. degree. Since 2003, he has been with the Millimeter-wave Innovation Technology Research Center (MINT), Dongguk University. His major field of study is the MMIC design and the millimeter-wave band packaging.

Yong-Hyun Baek received the B.E. degree and M.E. degree in electronics from Dongguk University, Seoul, Korea, in 2003 and 2005, respectively, where he is currently working toward the Ph.D. degree. His research interests include millimeter-wave devices, circuits, and system design.

Min Han received the B.E. degree and M.E. degree in electronic engineering from Dongguk University, Seoul, Korea, in 2003 and 2005, respectively, where he is currently working toward the Ph.D. degree. His research interests include MMIC and RF system design.

Seok-Gyu Choi received the B.S. degree from National Hankyung University, Anseong, Korea, in 2004, and the M.S. degree in electronics engineering from and Dongguk University, Seoul, Korea, in 2006, where he is currently working toward the Ph.D. degree. His research interests include III-V semiconductors, devices, and -band MMIC and module.

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Jae-Hyun Choi received the B.S. degree and M.A. degree in electronics engineering from Chungnam National University, Daejeon, Korea, in 1995 and 1997, respectively. Since 1998, he has been with the Agency for Defense Development (ADD), Daejeon, Korea. His research interests include millimeter-wave radar/radiometer and components for millimeter-wave applications.

Wan-Joo Kim received the B.S. degree in electrical engineering from Seoul National University, Seoul, Korea, in 1984, and the M.S. and Ph.D. degrees from the Korea Advanced Institute of Science and Technology (KAIST), Seoul, Korea, in 1987 and 1994, respectively. In 1987, he joined the Agency for Defense Development (ADD), Daejeon, Korea, where he is responsible for the development of fuze systems. His main research area is the development of millimeter-wave passive/active sensors for various fuze systems.

Jin-Koo Rhee (M’80–SM’05–F’09) received the B.E. degree from Hankuk Aviation University, Goyang, Korea, in 1969, the M.E. degree from Seoul National University, Seoul, Korea, in 1975, and the Ph.D. degree in electronics engineering from Oregon State University, Corvallis, in 1982. He was a Research Scientist with the Cray Research and Microwave Semiconductor Corporation and was with Department of Electrical Engineering and Computer Science, The University of Michigan at Ann Arbor, as a Visiting Research Scientist. He was president of The Institute of Electronics Engineers of Korea (IEEK) in 2005. He is currently a Professor with Department of Electronics Engineering, Dongguk University, Seoul, Korea, and a Director of the Millimeter-wave Innovation Technology Research Center (MINT), Dongguk University.