High-Gain Yagi-Uda Antennas for Millimeter-Wave Switched-Beam Systems

3672 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 11, NOVEMBER 2009 [10] C. L. Tang, J. Y. Chiou, and K. L. Wong, A broadband probe fed patch antenna with a bent ground plane, in Proc. Microw. Conf., 2000, pp. 1356 1359. [11] C. L. Tang, J. Y. Chiou, and K. L. Wang, Beamwidth enhancement of a circularly polarized microstrip antenna mounted on a three-dimensional ground structure, Microw. Opt. Technol. Lett., vol. 32, no. 1, pp. 149 153, 2002. [12] C. W. Su, S. K. Huang, and C. H. Lee, CP microstrip antenna with wide beamwidth for GPS band application, Electron. Lett., vol. 43, no. 20, Sep. 27, 2007. [13] T. G. Jurgens, A. Taflove, K. R. Umashankar, and T. G. Moore, Finitedifference time-domain modeling of curved surfaces, IEEE Trans. Antennas Propag, vol. AP-40, pp. 357 366, Apr. 1992. [14] J. M. Tranquilla and S. R. Best, Phase center considerations for the monopole antenna, IEEE Trans. Antennas Propag, vol. AP-34, pp. 741 744, May 1986. Fig. 7. Amplitude and phase of the elevation patterns for the drooped annular antenna. The measured patterns are shown at the measured resonant frequency of 1.5703 GHz and the simulated patterns at 1.575 GHz. particularly by observing the effects of shape and orientation of the ground plane upon the amplitude and phase patterns. Results showed that the beam width has been slightly increased for the folded antenna without altering the bore-sight gain accompanied with improved phase center stability. A novel drooped antenna operating in the TM 30 mode has been presented using a square annular element. The drooped annular element permits significantly greater control over the radiation pattern as a result of the interference between the four radiating edges. Variations of the angle and position of the bend revealed a certain combination, giving complete upper hemispherical coverage with the pattern ripple reduced to 2 db. Notably, in general, there is a tradeoff in achieving coverage over the entire upper hemisphere and low cross polarization. If a broad beam width is of precedence, it may be necessary to operate the drooped antennas under less than optimal conditions in regard to cross polarization performance. REFERENCES [1] G. Lachapelle, M. Casey, R. M. Eaton, A. Kleusberg, J. Tranquilla, and D. Wells, GPS marine kinematic positioning accuracy and reliability, Canadian Surveyor, vol. 41, no. 2, pp. 143 172, Oct. 1987. [2] J. M. Tranquilla, The Experimental Study of Global Positioning Satellite Antenna Backplane Configurations NASA Jet Propulsion Lab., Radiating Systems Research Lab., Univ. New Brunswick, Fredericton, NB, Canada, Tech. Rep., 1988, Contract 957959. [3] J. M. Tranquilla and B. G. Colpitts, GPS antenna design characteristics for high precision applications, presented at the ASCE Conf. GPS-88 Eng. Applicat. of GPS Satellite Surveying Technol., Nashville, TN, May 11 14, 1988. [4] J. M. Tanquilla and B. G. Colpitts, Development of a class of antennas for space-based NAVSTAR GPS applications, in Proc. 6th Int. Conf. on Antennas and Propag. (ICAP 89), Coventry, U.K., Apr. 4 7, 1989, pp. 65 69. [5] J. M. Tranquilla and S. R. Best, A study of the quadrifilar helix antenna for global positioning systems (GPS) applications, IEEE Trans. Antennas Propag., vol. 38, pp. 1545 1550, Oct. 1990. [6] K. G. Clark, The Finite-difference time-domain technique applied to the drooped microstrip, Ph.D. dissertation, Dept. Elect. Eng., Univ. New Brunswick, Fredericton, NB, Canada, Jul. 1996. [7] W. Feller, Three Dimensional Microstrip Patch Antenna, U.S. Patent 5 200 756, Apr. 1993. [8] N. Fayyaz, N. Hojjat, and S. Safavi-Naeini, Rectangular microstrip antenna with a finite horn-shaped ground plane, in Proc. IEEE Antennas and Propag. Society Int. Symp., Jul. 13 18, 1997, vol. 2, pp. 916 919. [9] H. Nakano, S. Shimada, J. Yamauchi, and M. Miyata, A circularly polarized patch antenna enclosed by a folded conducting wall, in IEEE Topical Conf. on Wireless Commun. Technol., Oct. 15 17, 2003, pp. 134 135. High-Gain Yagi-Uda Antennas for Millimeter-Wave Switched-Beam Systems Ramadan A. Alhalabi and Gabriel M. Rebeiz Abstract A high-efficiency microstrip-fed Yagi-Uda antenna has been developed for millimeter-wave applications. The antenna is built on both sides of a Teflon substrate ( = 2 2) which results in an integrated Balun for the feed dipole. A 7-element design results in a measured gain of 9 11 db at 22 26 GHz with a cross-polarization level of 16 db. The antenna is matched to 50 (microstrip feed). A mutual coupling of 20 db is measured between two Yagi-Uda antennas with a center-to center spacing of 8.75 mm (0 7 at 24 GHz), and a two-element array results in a measured gain of 11.5 13 db at 22 25 GHz. The planar Yagi-Uda antenna results in high radiation efficiency ( 90%) and is suitable for mm-wave radars and high data-rate communication systems. Index Terms Automotive radars, endfire antennas, millimeter-wave antennas, millimeter-wave communication systems, planar antennas, Yagi-Uda antenna. I. INTRODUCTION Planar Yagi-Uda antennas are very attractive for many microwave and millimeter-wave applications due to their high gain, low cost, high radiation efficiency and ease of fabrication. The Yagi-Uda antenna is one of the most popular endfire antennas which can be designed to achieve a medium gain with relatively low cross-polarization levels. Previously, Kaneda et al. presented a microstrip-fed Quasi-Yagi antenna at X-band with a gain of 3 5 db and a cross-pol. level of < 0 15 db [1]. Grajek et al. showed a Yagi-Uda antenna with a directivity of 9.3 db at 24 GHz [2]. These antennas utilize planar microstrip-to-coplanar stripline (CPS) transition which is based on a Manuscript received July 28, 2008; revised March 12, 2009. First published July 07, 2009; current version published November 04, 2009. This work was supported in part by Intel Corporation and in part by the UC-Discovery Program. The authors are with the Electrical and Computer Engineering Department, University of California, San Diego, CA 92122 USA (e-mail: ralhalabi@gmail. com; rebeiz@ece.ucsd.edu). Color versions of one or more of the figures in this communication are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2009.2026666 0018-926X/$26.00 2009 IEEE

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 11, NOVEMBER 2009 3673 TABLE I SIMULATED CROSS-POL. LEVEL VERSUS SUBSTRATE THICKNESS Fig. 1. Microstrip-fed Yagi-Uda antenna geometry: L = 5:4; Ld = 4:1; L1 = 1:5; L2 = 2:6; Ls = 20; W=0:4; W1 = 0:4; W2 = 1:0; W3 = 1:2; d= 2:4; dr = 2:7 and ground plane width = 29 (all dimensions are in mm). half-wave delay line to achieve the 180 phase shift for the balanced dipole feed, and the frequency dependence of the balun limits the antenna performance versus frequency. A Yagi-Uda antenna with one director, a truncated ground plane acting as a reflector and with a simplified feeding structure was presented by Zheng [3] where the balun between the microstrip feed and the balanced dipole feed was built using the top and bottom-sides of the substrate. Lee and Chung presented a 38 GHz microstrip-fed Yagi-Uda antenna which uses 6 directors and the microstrip ground plane as a reflector to achieve a gain of 9.5 db [4]. DeJean and Tentzeris presented a high gain microstrip Yagi array with high front to back ratio [5]. Woo et al. presented a microstrip-fed Yagi-Uda antenna with a new microstrip-to-cps transition [6]. This new transition performs the required field and impedance match between the microstrip line and the CPS feed line using via holes. Using one director and one reflector, this antenna showed a gain of 5.2 5.8 db with a bandwidth of 29.1% from 30 to 40 GHz. H. K. Kan et al. showed a CPW-fed Quasi-Yagi antenna with a 44% 10 db impedance matching bandwidth at X-band [7]. Recently, Hsu et al. showed a 60 GHz CPW-fed on-chip Yagi-Uda antenna with a gain of 010 db [8]. This communication presents a seven-element microstrip-fed Yagi-Uda antenna with high gain (>10 db), wide bandwidth (22 26 GHz) and low cross-polarization levels (018 db). The antenna utilizes five directors, and the truncated ground plane acts as a reflector to maximize the antenna gain. Two-element arrays with a center-to-center spacing of 8.75 mm (0:7 0 at 24 GHz) are also presented. Fig. 2. (a) Fabricated microstrip-fed Yagi-Uda antenna, ground plane width is 29 mm and microstip line length is 20 mm, (b) measured and simulated S. II. ANTENNA DESIGN AND MEASUREMENTS A. Antenna Design The microstrip-fed Yagi-Uda antenna was built on a Rogers RT/Duroid 5880 substrate (" r = 2:2) with a thickness of 15 mils (0.381 mm) and utilizes five directors (Fig. 1). The directors are printed on the top side of the substrate with a director-to-director spacing of d=2:4mm. The initial dimensions of the antenna were obtained from tables for maximum directivity in air [9] and then scaled to compensate for the duroid substrate (" e =1:41) [2]. The microstrip truncated ground plane is located at dr = 2:7 mm from the driving dipole and acts as a reflector. The antenna is designed to have an input impedance of 50 and is connected to a microstrip line with Ws = 1:2 mm (Zo = 50 ). The balun between the microstrip feed and the balanced dipole feed is built using the top and bottom-sides of the Teflon substrate. The driving dipole is fed by a parallel-plate transmission line of width W f =0:4mm and impedance Z f = 130, and this transmission line becomes a microstrip feed line of length

3674 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 11, NOVEMBER 2009 Fig. 3. Radiation patterns for the microstrip-fed Yagi-Uda antenna: measured Co-pol, - - - - - simulated Co-pol., -:-:-:- measured Cross-pol. Fig. 4. Measured and simulated gain of the microstrip-fed Yagi-Uda antenna. L 1 = 1:5 mm and impedance Z 1 = 93 followed by another microstrip section of length L 2 =2:6mm and impedance Z 2 =56to arrive to the 50 microstrip feed. The driver dipole is built on both sides of the substrate and allows a wideband balun feed from the single-ended microstrip line to the differential dipole. However, it also results in an increase in the cross-polarization level (Table I). The cross-polarization simulations were done using HFSS and the antenna dimensions were modified so that the driving dipole of the Yagi-Uda antenna resonates at the same frequency for each case. It is clear that a substrate thickness of 15 mils or less should be chosen for low cross-polarization levels. B. Impedance and Pattern Measurements The input impedance of the microstrip-fed Yagi-Uda antenna was measured using a microstrip to coaxial line transition [Fig. 2(a)], and shows a good agreement with HFSS simulations with measured S 11 < 09 db (simulated S 11 < 010 db) from 22.1 to 25.5 GHz [Fig. 2(b)]. The microstrip to coaxial transition was not included in the HFSS simulations. We believe that the slight difference between the measured and simulated S 11 is due to the effect of this transition. Fig. 5. Fabricated 2-element arrays of microstrip-fed Yagi-Uda antennas (top side), d=8:75 mm: (a) with Wilkinson coupler, (b) with matched T-junction. The radiation patterns were measured in the receive mode using a zero-bias Schottky diode detector (Krytar model 303B) and a lock-in amplifier (Stanford Research Systems, SR830 DSP Lock-in Amplifier). The diode detector was connected to the microstrip line using a high performance Southwest microwave 2.92 mm connector [Fig. 2(a)]. The RF signal is amplitude modulated with a 1 khz sine-wave signal and the rectified 1 khz is measured using the lock-in amplifier. The measured patterns agree well with HFSS simulations and show a front to back ratio of 20 db and cross-polarization level of 020 db at 24 GHz (Fig. 3). The patterns are quite symmetric at 24 GHz with an E and H-plane 3-dB beamwidths of 44 and 50, respectively.

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 11, NOVEMBER 2009 3675 Fig. 6. (a) Top layer of the fabricated two microstrip-fed Yagi-Uda antennas with center to center spacing of d = 8:75 mm (0:7 at 24 GHz), (b) measured and simulated mutual coupling (S ). Fig. 7. (a) Measured radiation patterns of the 2-element arrays: ------------ with Wilkinson, - - - - - with T-junction, -:-:-:- simulation, (b) measured S referenced to plane 1. C. Gain Measurements The absolute gain of the microstrip-fed Yagi-Uda antenna was measured using a standard gain horn antenna. A 2.92 mm Southwest microwave connector is used to minimize the reflection at the connector. The received power is measured using a calibrated Agilent Power Meter (E4417), and the same power meter is used to measure the transmit power. The Yagi-Uda antenna gain is then obtained using the Friis transmission formula. The loss of the microstrip line between the antenna and the Southwest connector is 0.44 db and is taken out from the gain measurements. The measurements show a gain of >10 db from 22 25 GHz and 10.4 db 60:5 db at 24 GHz (Fig. 4). HFSS reported a gain of 10.9 db with directivity of 11.2 db at 24 GHz and the difference is mostly due to the impedance mismatch loss. This results in a measured radiation efficiency of 90% within the 60:5 db measurement error. The Yagi-Uda antenna gain drops to 1 db at 26 GHz due to non-optimal phasing of the director elements. This design is therefore optimal for 21 25 GHz applications with a gain >8 db, and results in a bandwidth of 17.5%. D. Two-Element Array of Microstrip-Fed Yagi-Uda Antennas Two-element arrays of Yagi-Uda antennas with a center to center spacing of 8.75 mm (0:7 0 at 24 GHz) were also built and measured. The first design utilizes a Wilkinson power combiner to combine the signals [Fig. 5(a)], while the second design uses a matched T-junction [Fig. 5(b)]. The mutual coupling between two Yagi-Uda antennas, with a center to center spacing of 8.75 mm (0:7 0 at 24 GHz), was measured using the layout shown in Fig. 6(a). The measurement agrees Fig. 8. Measured and simulated gain of the two element array of the microstrip-fed Yagi-Uda antennas (with Wilkinson coupler) at ref. plane 2. with HFSS simulations and shows a mutual coupling of < 0 16 db from 20 to 26 GHz [Fig. 6(b)]. The measured radiation patterns of the two-element arrays show good agreement with simulations as shown in Fig. 7(a). The measured 24 GHz E-plane patterns has a 3-dB beamwidth of 30, while the measured H-plane pattern is similar to the single element pattern and has a 3-dB beamwidth of 46. The two-element array has nearly the same E-plane pattern as a Yagi-Uda antenna with 10 directors. The patterns were also measured at 22 25 GHz (not shown) and are very similar to the 24 GHz patterns. The measured S 11 of the two-element arrays is < 0 8 db from 22.0 to 26.0 GHz as shown in Fig. 7(b). The two-element array gain at ref. plane 2 in Fig. 5 was measured at 20, 22, 24 and 25 GHz, where the loss between ref. planes 1 and 2 was estimated to be 0.4 db. The measured gain is >10 db from 20 to 25 GHz with a peak value of 12.5 db and agrees well with simulations (Fig. 8).

3676 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 11, NOVEMBER 2009 III. CONCLUSION This communication presented a microstrip-fed millimeter-wave Yagi-Uda antenna with applications as single element radiator or for switched-beam systems with medium gain (9 13 db). The planar Yagi-Uda antenna can be arrayed for additional gain (+3 db) and with low mutual coupling between the elements. The antenna results in relatively wideband operation (22 26 GHz), low cross-polarization levels, and high radiation efficiency. This antenna can be scaled to 60, 77, or 94 GHz for automotive radars and high data-rate communication systems. REFERENCES [1] N. Kaneda, W. R. Deal, Y. Qian, R. Waterhouse, and T. Itoh, A broadband planar Quasi-Yagi antenna, IEEE Trans. Antennas Propag., vol. 50, no. 8, pp. 1158 1160, Aug. 2002. [2] P. R. Grajek, B. Schoenlinner, and G. M. Rebeiz, A 24-GHz high-gain Yagi-Uda antenna array, IEEE Trans. Antennas Propag., vol. 52, pp. 1257 1261, May 2004. [3] G. Zheng, A. A. Kishk, A. B. Yakovlev, and A. W. Glisson, Simplified feed for a modified printed Yagi antenna, Electron. Lett., vol. 40, no. 8, pp. 464 465, Apr. 15, 2004. [4] Y. Lee and S. Chung, Design of a 38-GHz printed Yagi antenna with multiple directors, in Proc. IEEE Antennas Propag. Symp., Jul. 2001, vol. 3, pp. 606 609. [5] G. R. DeJean and M. M. Tentzeris, A new high-gain microstrip Yagi array antenna with a high front-to-back (F/B) ratio for WLAN and millimeter-wave applications, IEEE Trans. Antennas Propag., vol. 55, pp. 298 304, Feb. 2007. [6] D. Woo, Y. Kim, K. Kim, and Y. Cho, A simplified design of Quasi- Yagi antennas using the new microstrip-to-cps transitions, in Proc. IEEE Antennas Propag. Symp., June 2007, pp. 781 784. [7] H. K. Kan, R. B. Waterhouse, A. M. Abbosh, and M. E. Bialkowski, Simple broadband planar CPW-fed Quasi-Yagi antenna, IEEE Antennas Wireless Propag. Lett., vol. 6, pp. 18 20, 2007. [8] S. Hsu, K. Wei, C. Hsu, and R. Chuang, A 60-GHz millimeter-wave CPW-Fed Yagi antenna fabricated by using 0.18-m CMOS technology, IEEE Electron. Device Lett., vol. 29, pp. 625 627, Jun. 2008. [9] W. L. Stutzman and G. A. Thiele, Antenna Theory and Design, 2nd ed. New York: Wiley, 1998. On the Transmission and Propagation of Low Attenuation Rate Electromagnetic Pulses in Debye Media Reza Safian, Costas D. Sarris, and Mohammad Mojahedi Abstract In a dispersive medium, the appearance of the steady-state part of the signal is preceded by oscillations known as precursors. These early oscillations are the product of the interrelated effects of phase dispersion and frequency dependent attenuation. Inside water, the attenuation rate of the Brillouin precursor is sub-exponential, following the inverse square-root of the distance traveled. Based on that, a near-optimal pulse that could achieve this attenuation rate, and, hence, would lend itself to underwater detection and communication applications, was recently proposed. The optimality of this pulse is shown to be related to the temporal support of the pulse and its spectral characteristics, rather than its shape. A family of alternative pulses is found to have the low attenuation feature of the optimal pulse, as they eventually evolve into the Brillouin precursor itself shortly after they enter water. In addition, this work considers the practical case when such a pulse would be generated in air, would impinge onto an air-water interface and then propagate inside water. It is shown how the presence of the interface affects the attenuation rate of the pulse inside water and a simple way to recover its low attenuation rate is suggested. The finite-difference time-domain technique is employed in all the simulations. Index Terms Dispersive media, finite-difference time-domain (FDTD) methods, wave propagation. I. INTRODUCTION The propagation of wideband electromagnetic pulses in a causal, temporally dispersive dielectric has been studied extensively [1], [2]. Significant contributions in this area have been recently made by Oughstun et al., through the investigation of pulse propagation in several temporally dispersive media [3]. In such media, the phase dispersion and frequency-dependent attenuation of a wideband pulse excitation can lead to the evolution of precursor fields, which precede the main part of the pulse. For a Debye-type dielectric, the electric field excited by a modulated pulse with a temporal support T where, T 1=f c (f c is the modulation frequency) evolves into the so-called Brillouin precursor, as the pulse propagates inside the medium [3]. Moreover, the peak amplitude of the Brillouin precursor decays as the inverse square root of the propagation distance, as opposed to the exponential decay of the main part of the pulse. This property of the Brillouin precursor was harnessed to design a pulse excitation with low attenuation rate in an infinite Debye medium [4]. Such an excitation consists of two mutually delayed and opposite in sign Brillouin precursors. The theoretical investigation of [4], limited to the case of an infinite Debye medium though, suggested that this double Brillouin pulse could indeed achieve an attenuation rate as the inverse square of the propagation distance for medium parameters that corresponded to those of the triply distilled water. This result renders the double Brillouin pulse a good candidate for applications ranging from communications to detection in lossy dispersive media that can be described by the Debye model. 0018-926X/$26.00 2009 IEEE Manuscript received July 09, 2007; revised November 18, 2008. First published July 28, 2009; current version published November 04, 2009. The authors are with the Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON M5S 3G4 Canada (e-mail: rsafian@waves. utoronto.ca). Color versions of one or more of the figures in this communication are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2009.2028678