D ular in Japan. Several types of subscriber antennas for

Transcription

1 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 44, NO. 4, NOVEMBER A Single-Layer Slotted Leaky Waveguide Array Antenna for Mobile Reception of Direct Broadcast from Satellite Jiro Hirokawa, Member, IEEE, Makoto Ando, Member, IEEE, Naohisa Goto, Fellow, IEEE, Nobuharu Takahashi, Takashi Ojima, and Masahiro Uematsu Abstrucf- This paper proposes a single-layer slotted leaky waveguide array antenna for mobile DBS reception. A singlelayer feed structure is proposed, where the feed waveguide is in the same layer as the radiating waveguides. This results in the simple fabrication of slotted waveguide arrays, suitable for mass production. Short radiating leaky waveguides are used to get a large beam-tilting angle of about 50" for the horizontal installation of the antenna and a beamwidth broad enough to dispense with mechanical steering in the elevation plane. A prototype antenna sized 30 cm by 21 cm has a maximum of 74% efficiency and more than 69% efficiency within the DBS band. It also has a broad 1-dB beamwidth of 7.5" in the elevation plane, which enables clear DBS reception by a picture tube display over about one-third the area of Japan without elevation tracking. I. INTRODUCTION IRECT broadcast from satellite (DBS) has become pop- D ular in Japan. Several types of subscriber antennas for use on the roof of cars or trains are now being intensively developed [ 11-[9]. They should have a large beam-tilting angle of about 50" from the normal and a low-profile structure for aerodynamics. Satellite tracking in the azimuthal plane is required to compensate for changes in vehicle direction. However, tracking in the elevation plane can be omitted if the beamwidth in the elevation plane is broad enough to compensate for the road gradients of up to 55". This enables the simplification of the control unit to one-axis mechanical steering. Antennas using microstrip patches [2], 141, [6] have difficulty achieving large beam tilting angle of more than 30" due to high sidelobes. They thus need to be installed on an incline of about 20, which results in a relatively large height of the receiving system. Other types of the antennas using helixes or patches fed by a waveguide via probe [51, [7]-[9] produce a large beam-tilting angle by controlling the rotation angle of the array elements. However, the manufacturing process is complicated and the antenna structure with the probe-fed elements is not strong and is not appropriate for mobile use. Manuscript received August 24, 1994; revised February 1, J. Hirokawa, M. Ando, and N. Goto are with the Department of Electrical and Electronic Engineering, Faculty of Engineering, Tokyo Institute of Technology, okayama, Meguro-ku, Tokyo 152, Japan. N. Talcahashi, T. Ojima, and M. Uematsu are with Broadcasting Satellite Systems, Information Devices Development Division, Electronics and Information Systems Divisions Group, Nippon Steel Corporation, Shinkawa, Chuo-ku, Tokyo 104, Japan. IEEE Log Number A slotted leaky waveguide array [l], [3] is advantageous for mobile DBS reception because the leaky waveguide [lo], [ll] has inherently a large beam-tilting angle of about 50' in the elevation plane. The horizontal installation of the antenna can be realized as a low-profile receiving system. A broad beamwidth in the elevation can be obtained easily by using short radiating waveguides. However, conventional slottedwaveguide arrays have a complicated feed structure consisting of multilayer waveguides, resulting in high manufacturing cost. A simple feed structure is highly desirable for costreduction purpose. To this end, the authors have proposed a novel concept of a single-layer slotted-waveguide array shown in Fig. 1 [12], [13]. The feed waveguide is placed on the same layer as the radiating waveguides. This feed structure is twodimensional and is uniform along the height and is suitable for mass production by pressing or die-casting. The antenna consists of two pieces and is fabricated easily by adhering an etched slot plate on the groove feed circuit. This paper proposes a single-layer slotted leaky waveguide array antenna for mobile DBS reception. Section I1 presents the antenna structure suitable for mass production and mobile reception. It also describes the designs of both the feed and the radiating waveguides. Section 111 shows the specification of the antenna for noiseless reception using a picture-tube display. It also presents the radiation characteristics of the prototype antenna. Section IV describes the experimental results of the C/N (carrier-to-noise) ratio of the prototype antenna measured at various places in Japan, which demonstrates the feasibility of the mobile DBS receiving system. II. STRUCTURE AND DESIGN A. DBS Receiving System Using the Single-Layer Waveguide Array Fig. 2 shows a novel low-profile mobile DBS receiving system using the single-layer slotted leaky waveguide array. The horizontal installation of the array realizes a very small height for this system. The total height including the radome is 9 cm and is about half the height of a conventional system using microstrip arrays. The size is 45 cm by 55 cm (about half) and the weight is 8 kg (about one-third), including the control unit. Only the azimuthal mechanical steering of the array together with a frequency downconverter is included /95$ IEEE

2 750 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 44, NO. 4, NOVEMBER 1995 Fig. 1. Slot Wwguide Single-layer slotted leaky waveguide array antenna. in phase. Each 7r-junction has an inductive post to suppress the reflection due to the window coupling. The traveling-wave excitation enhances the frequency bandwidth of the divided characteristics. The post also suppresses the guide-wavelength reduction due to the window coupling [13]. This means that the guide wavelength is almost constant irrespective of the divided power and the radiating waveguides can be arrayed with a constant spacing equal to one half of the wavelength in the feed waveguide. The design procedure for the uniform power dividing of the feed waveguide by using Galerkin s method of moments is described in detail in [ Fig. 2. DBS receiving system using the single-layer slotted leaky waveguide array. The rotation angle is determined by calculating the time derivative of the signal-to-noise ratio in an interfrequency band with supplementary usage of vehicle yaw rate. Quick oneaxis steering is achieved which takes less than 2 s to find a completely missed satellite. B. Feed Waveguide Fig. 1 shows the structure of a single-layer slotted leaky waveguide array antenna. The feed waveguide is placed on the same layer as the radiating waveguides. This two-dimensional feed structure greatly simplifies not only the EM analysis for the design but also the fabrication of slotted-waveguide array antenna to a level suitable for mass production. The feed waveguide is designed to distribute input power to all the radiating waveguide both in equal amplitude and phase. Input power is fed by a probe at the center of the feed waveguide and is divided in two directions. Each side of the feed waveguide is a cascade of several waveguide r-junctions with an inductive post [14] and is terminated by a short circuit. The n-junction couples to two radiating waveguides in phase through one coupling window. The amplitude of the divided power is controlled by the window width while the phase is controlled by the notch length. The broad-wall width of the feed waveguide is chosen so that the guide wavelength is twice the broad-wall width of the radiating waveguide including the wall thickness. Then all the radiating waveguides are excited C. Radiating Waveguide The radiating waveguide is designed to get uniform amplitude distribution and to minimize the axial ratio of each cross slot in the desired tilted beam direction. The radiating waveguide is an array of nonresonant cross slots in the leaky wave excitation [16]. The spacing between the slots is set to be as narrow as possible to suppress grating lobes in the backfire direction. The waveguides are terminated by short circuits; absorbers, which increase thermal noise, are not used at all. For application to mobile DBS reception, the short radiating waveguides resulting in a broad beamwidth are advantageous since they remove the requirement of the mechanical steering in the elevation plane. In that case, the number of cross slots on a radiating waveguide becomes small and the coupling of each slot has to be stronger. The lengths of the nonresonant cross slots are varied to give a uniform amplitude distribution along the array. A nonresonant array with strong slot coupling causes a serious change in the guide wavelength in the radiating waveguide [17], [18]. Also, the phase of the radiation from the slots depends upon the coupling strength. These effects must be evaluated to predict the beam-tilting angle precisely in the leaky wave excitation. Fig. 3 shows two slots i and j on a rectangular waveguide with a spacing s. The two slots are assumed to be excited in equal amplitudes. Pti (deg) and Pri (deg) are the phase jumps of the transmitting and radiating waves from slot i, respectively, while P,j (deg) is the radiation phase jump of slot j. These values of Pt and P, are obtained numerically by Galerkin s method of moments [19], [20]. The equal-phase condition between these adjacent two slots in the direction of the beam-tilting angle et is given by the following equation: where A0 is a free-space wavelength and A, is an unperturbedguide wavelength of the incident TElo mode given by the broad-wall width a,.

3 ~ ~ HIROKAWA et al.: A SINGLE-LAYER SLOIITED LEAKY WAVEGUIDE ARRAY ANTENNA 151 Spacing 5 Fig. 3. 'ho slots on a rectangular waveguide. The beam-tilting angle et is obtained by using Pt and P,. with (1) as Fig. 4. Configuration of the cross slot. The first term is a well-known value in a conventional leaky wave theory, which is independent of the slot coupling [lo]. The second term corresponds to the additional beam shift due to slot coupling, which cannot be neglected in the strong coupling associated with the short radiating waveguide. The EM analysis [19], [20] is indispensable for evaluating this additional term. In a practical design, the broad-wall width a, must be determined by including this additional beam shift. Fig. 4 shows the configuration of the cross slots, 1 and 2 and cut on a rectangular waveguide, whose broad-wall width and narrow-wall width are a, and b, respectively. The lengths of slots 1 and 2 are and &, respectively, and the width of each slot is w. The slots intersect at their center with an angle of I$ to the z-axis. The cross slot is placed at the left side of the broad wall with an offset of d from the center of the broad wall, in the propagating direction of incident wave, and radiates right-handed circularly polarized wave. The lengths of slot 1 and 2 and the crossing angle of all the slots are optimized. The length of slot 1 is used to control the radiation power, while the length of slot 2 and the crossing angle are used to control the axial ratio of each cross slot. The offset d can be chosen to minimize the axial ratio in the desired direction. It is confirmed that the optimum offset is almost the same for all the slots with different length. Furthermore, an important advantage numerically revealed in [19], [21] is that the optimum offset for the minimization of the axial ratio always reduces the reflection from the cross slot and the traveling-wave operation is realized in the radiating waveguide. The initial design assuming travelingwave operation greatly simplifies the design procedure of the cross-slot array. The final design of a one-dimensional array is based on the EM analysis including all the strong mutual couplings of the cross slots on one radiating waveguide [19] EXPERIMENTAL "JLTS A. Spec$cations for the Reception by a Picture-Tube Display A prototype antenna was fabricated for DBS reception by using a picture-tube display. The minimum C/N (carrier-tonoise) ratio for noiseless reception is regarded to be 9.0 db in this design. The desired C/N ratio should include a margin to compensate for the reduction of the signal level due to rainfalls, a radome, and off-beam loss associated with the omission of elevation tracking when a vehicle runs on a slope. The total margin is set to be 3.0 db. The required antenna TABLE I PARAMETERS OF THE DBS BAND ANTENNA gain is calculated to be 26.5 dbi by adding the desired CJN ratio of 12.0 db plus a constant of The derivation of this constant is presented in the Appendix. The aperture size is determined to satisfy this gain requirement by assuming an antenna efficiency of 70%. The aspect ratio of the aperture is determined by considering that i) the 1-dB beamwidth in the elevation plane is wider than 6O, which covers about one-third of the area of Japan, ii) the dead space associated with the mechanical azimuthal rotation of the rectangular antenna is not too large, and iii) the diagonal length of the antenna which determines the diameter of the total system should be as small as possible. The aspect ratio of the aperture projecting in the tilted-beam direction is about one-third in the prototype antenna and the beamwidth in the elevation plane is predicted to be about three times of that in the azimuthal plane. The design parameters of the prototype antenna are listed in Table 1. Fig. 5 shows the variation in the slot lengths and the crossing angle of the cross slots on one radiating waveguide. The length of the cross slot increases as its location approaches the end of the radiating waveguide, which results in uniform amplitude distribution. The length of slot 2 is slightly longer than that of slot 1 to minimize the axial ratio. The crossing angle is almost constant at about 57O, except for the few cross slots with strong coupling which are located close to the end of the radiating waveguide. B. Radiation Characteristics Fig. 6 shows the aperture field distributions measured along the feed waveguide, which show the power-dividing characteristics of the feed waveguide. The uniform distributions both in amplitude and phase are obtained at the design frequency. It was confirmed that the amplitude distributions remain uniform in the DBS band in Japan (1 1.7 GHz-12.0 GHz), however,

4 152 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 44, NO. 4, NOVEMBER I) 0 0 'I 12- A A E Slot #2 g 00 II 5- \:/ jr * f x A 101, I,, 0 : :, I,, ::I lot #I,,, ' ' ' 1.2 I -I 2-1 I Frequency(GHz) I - -5 ~ % Slot Number (b) Fig. 5. Slot lengths and crossing angles of the cross slots. (a) Slot lengths. (b) Crossing angle. -IO! IO0 150 Position(mm) (a) m 11.85GHZ A 12.MH;Hz -904 I I Position(mm) Fig. 6. Aperture field distributions along the feed waveguide. (a) Amplitude. (b) Phase. the phase distribution becomes tapered as in Fig. 6(b). Fig. 7 shows the frequency characteristic of the phase gradient in the feed waveguide. The dotted line presents the value from the measured phase distribution in Fig. 6(b) while the solid line presents the value due to the long-line effects calculated for the wavelength variation in (2). These lines agree fairly well which confirms that the frequency characteristic of the phase distribution is mainly dominated by the long-line effect [13]. Fig. 8 shows the frequency characteristic of the overall reflection at the feed point. It is suppressed below -13 db in the DBS band. Fig. 9 shows the far-field radiation patterns of the righthanded circularly polarized component at the design frequency. In the elevation plane, the measured beam-tilting angle is 50.5". The additional beam shift due to the slot coupling is no less than 10.5" while the first term of the beam-tilting angle in (3) is calculated to be 40.0". The 1-dB beamwidth is 7.5", which is broad enough to satisfy the requirement. The axial ratio in the main-beam direction is 1.O db. The reflection from the shorted end of the radiating waveguides causes a -9-dB sidelobe with the left-handed circularly polarized component in the opposite direction (0 = -52") of the main beam. In Fig. 9(b), the radiation pattern in the azimuthal plane containing the main beam has good symmetry and suppressed sidelobes, reflecting the uniform power-dividing of the feed waveguide. The 1-dB beamwidth is 2.5". Fig. 10 shows the frequency characteristic of the gain and the efficiency. The measured peak gain is 26.7 dbi (74% efficiency) at GHz. The gain is more than 26.3 dbi (69% efficiency) within the DBS band, where the efficiency is calculated for the aperture projecting in the main-beam direction. The measured C/N ratio is about 12.0 db at Tokyo on sunny days. N. CARRIER-TO-NOISE RAno MEASUREMENT IN JAPAN In the mobile receiving system, the antenna is horizontally installed and automatic mechanical steering is adopted only in the azimuthal plane. In the elevation plane, the peak of the main beam is not always oriented in the direction of a broadcasting satellite, depending on the geographical position as well as the road gradient. It is important to estimate the coverage area of this receiving system. A tilted installation by f5' will also be prepared for an optional requirement to cover all parts of Japan. The C/N ratio of this model antenna

5 HIROKAWA et al: A SINGLE-LAYER SLOTTED LEAKY WAVEGUIDE ARRAY ANTENNA 153 _ ",,,,,,,,,, YO AngMdeg ) (a) m -75 -HI -45-1o -is o is m 75 90!\llplcldc,g ) (b) Fig. 9. Spin-linear radiation pattems in Fresnel region (11.85 GHz). (a) Elevation plane. (b) Azimuthal plane pertaining to the main beam. Fig. 11. Measuring points and direction of the broadcasting satellite AngWdeg) Fig. 12. Measured C/N ratio as functlon of the zenlthal angle (channel 7, GHz). Fig. 10. Gain and efficiency. was measured at various points in Japan. Fig. 11 shows the measuring points covering Japan as well as the zenith angle of Japanese broadcasting satellite (BS-3) at the points. The zenith angle is defined as the angle from the zenith or the antenna boresight in the horizontally installation. Fig. 12 shows the measured C/N ratio of the test antenna with three kinds of installations (O", f5"), and a reference antenna (gain: 29.5 dbi) as functions of the zenith angle. In each measuring point, the reference antenna is always oriented to the satellite. The variation of C/N ratio in the reference antenna comes from the weather and the geographical distribution of the E.I.R.P. of the satellite. The difference between the test and the reference antenna comes not only from the difference in the peak gain and the noise figure of the frequency downconverter but also from the beam-pointing loss of the test antenna without elevation steering. The tilted installation of the antenna has a shifted coverage of the zenith angle by about 5". The optional requirement to cover most of Japan would be realized by switching between these three kinds of installations. Fig. 13 shows the C/N ratio difference between the test antennas with the horizontal installation and the reference antenna. The 1-dB width of the C/N ratio 0 B p: -6 z Awle(deg) Fig. 13. C/N ratio difference between the test antenna with the horizontal installation and the reference antenna (solid line--c/n ratio difference; dotted line-radiation pattem). difference for the horizontal installation is about 7O, which covers about one-third of the area of Japan. It is as wide as the 1-dB beamwidth of the test antenna in the elevation plane included in Fig. 8 for comparison. In this area, the typical C/N ratio is found to be more than 11 db. V. CONCLUSION This paper proposes a single-layer slotted leaky waveguide array antenna for mobile DBS reception. N o key technologies used in the design of a prototype antenna are i) to realize uniform power division in the single-layer-feed waveguide and

6 -- r_p_ WEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 44, NO. 4, NOVEMBER 1995 ii) to predict an additional beam-shift of about 12 due to the slot coupling in the radiating waveguides. The broad 1-dB beamwidth of 7.5 in the elevation plane enables clear DBS reception by a picture-tube display over about one-third the area of Japan without elevation tracking. The feasibility of a low-profile mobile DBS receiving system consisting of the single-layer slotted leaky waveguide array with the azimuthal mechanical steering is fully demonstrated. APPENDIX RELATION BETWEEN A GAIN AND A C/N RATIO OF A PLANAR RECEIVING ANTENNA A carrier power C and an average noise power N are given by the following equations (in decibels): C = P, - Lf + G (AI) N=K+T+B (A21 where P, is the E.I.R.P. of a satellite, Lf is the free-space propagation loss, K is Boltzmann s constant, and B is the bandwidth of the carrier. T is the system noise temperature and is given by the following equation for perfect matching of the receiving antenna: T = Ta + (F - 1)To where Ta and TO are the antenna noise temperature and room temperature, respectively, and F is the noise figure of the frequency downconverter. The relation between the gain and the C/N ratio is finally derived by substituting typical values of Japanese broadcasting satellite (BS-3) and planar receiving antennas into (AlHA3): P, = 57.4 dbw (at Tokyo), Lf = db (at 12 GHz), K = 1.38 x W/HzK, B = 27 MHz, Ta = 40 K, TO = 290 K, and F = 1.0 db G = C/N ACKNOWLEDGMENT 644) The authors wish to thank K. Sakurai and K. Sakakibara of Tokyo Institute of Technology for their help. [SI R. Yonezawa, K. Hariu, and M. Matsunaga, Low profile phased array antenna using inclined helical element antenna, in IEICE Nut. Conv. Rec., vol. B-49, Mar [9] T. Watanabe, K. Nishikawa, M. Ogawa, and E. Teramoto, Helical array antenna fed by waveguide, in IEICE Nut. Conv. Rec., vol. B-50, Mar [lo] L. 0. Goldstone and A. A. Oliner, Leaky-waveguide antennas-part I: Rectangular waveguides, IRE Tram. Antennas Propagat., vol. AP-7, pp , Oct [l I] R. F. Hyneman, Closely-spaced transverse slots in rectangular waveguide, IRE Trans. Antennas Propagat., vol. AP-7, pp , Oct [12] N. Goto, A planar waveguide slot antenna of single layer structure, IEICE Tech. Rep., vol , July [13] J. Hirokawa, M. Ando, and N. Goto, A single-layer multiple-way power divider for a planar slotted waveguide array, IEICE Trans. Commun., vol. 75, no. 8, pp , Aug [14] J. Hirokawa, M. Ando, and N. Goto, Waveguide.rr-junction with an inductive post, IEICE Trans. Electron., vol. 75, no. 3, pp , Mar [15] J. Hirokawa, K. Sakurai, M. Ando, and N. Goto, An analysis of a waveguide T junction with an inductive post, ZEEE Trans. Microwave Theory Tech., vol. 39, no. 3, pp , Mar [16] W. J. Getsinger, Elliptically polarized leaky-wave array, IRE Trans. Antennas Propagat., vol. 10, pp , [17] R. W. Lyon and A. J. Sangster, Efficient moment method analysis of radiating slots in a thick-walled rectangular waveguide, Proc. Inst. Elec. Eng., vol. 128, pt. H, no. 4, pp Aug [18] M. Takahashi, J. Takada, M. Ando, and N. Goto, A slot design for uniform aperture distribution in single-layered radial line slot antennas, IEEE Trans. Antennas Propagat., vol. 39, no. 7, pp , July [19] J. Hirokawa, A study of slotted waveguide array antennas, Doctoral Dissertation, Tokyo Institute of Technology, Mar [20] J. Hirokawa, M. Ando, and N. Goto, Analysis of slot coupling in a radial line slot antenna for DBS reception, Proc. Inst. Elec. Eng., vol. 137, pt. H, no. 5, pp , Oct [21] J. Hirokawa, A. Kiyohara, M. Ando, N. Goto, T. Ojima, and M. Uematsu, Design of a crossed slot array antenna on a leaky waveguide, IEICE Tech. Rep., vol. AP93-25, May Jim Hirokawa (S 89-M 90) was born in Tokyo, Japan, on May 8, He received the B.S., M.S., and D.E. degrees in electrical and electronic engineering from Tokyo Institute of Technology, Tokyo, in 1988, 1990, and 1994, respectively. Since 1990, he has been a Research Associate at Tokyo Institute of Technology. From 1994 to 1995, he was with the antenna group of Chalmers University of Technology, Gothenburg, Sweden, as a Postdoctoral Researcher, on leave from Tokyo Institute of Technology. His main interest has been analysis of slot coupling in slotted-waveguide array antennas. REFERENCES Y. Furukawa, N. Goto, and K. Maehara, A beam-tilt planar waveguide slot antenna of single layer structure for satellite TV, IEICE Tech. Rep., vol. AP88-40, July K. Omaru, A mobile satellite broadcasting receiver, Broadcast. Eng., vol. 43, no. 9, pp , Sept A. Kuramoto, N. Endo, A. Kawaguchi, R. Shimizu, Y. Furukawa, S. Oyaizu, K. Maehara, and Y. Suzuki, Mobile DBS receiving antenna system, in IEZCE Nut. Conv. Rec., vol. B-59, Mar K. Nishikawa, Mobile DBS receiving antenna system, Toyota Central Lab., R & D Rev., vol. 27, no. 1, p. 65, Mar H. Nakano, H. Yoshida, Y. Kitamura, H. Mimaki, and J. Yamauchi, A curl array antenna (III)-consideration of a tilted beam, in IEICE Nut. Conv. Rec.. vol. B-45. Mar [6] K. Takano, T. Murata, M. Fujita, and D. Kato, Compact mobile receiver for direct satellite broadcasting, in IEICE Nut. Conv. Rec., vol. 3-46, Mar [7] 0. Shibata, S. Saito, and M. Haneishi, Radiation properties of radial lie microstrip array antenna having large tilt-angle, in ZEZCE Nat. Conv. Rec., vol. B-54, Mar Makoto Ando (M83) was bom in Hokkaido, Japan, on February 16, He received the B.S., M.S., and D.E. degrees in electrical engineering from Tokyo Institute of Technology, Tokyo, Japan, in 1974, 1976, and 1979, respectively. From 1979 to 1983, he worked at Yokosuka Electrical Communication Laboratory, IT, and was engaged in development of antennas for satellite communication. He was a Research Associate at Tokyo Institute of Technology from 1983 to 1985, and is currently a Professor. His main interests have been high-frequency diffraction theory. His research also covers the design of reflector antennas and planar arrays for DBS and VSAT. Dr. Ando received the young Engineers Award of IEICE Japan in 1981, the Achievement Award and the Paper Award from IEICE Japan in He also received the 5th Telecom Systems Award in 1990 and the 8th Inoue prize for Science in 1992.

7 ~ HIROKAWA et al.: A SINGLE-LAYER SL0TlT.D LEAKY WAVEGUIDE ARRAY ANTENNA 155 Naohisa Got0 (M68-M78-SM89-F91) was bom in Utsunomiya, Japan, on June 8, He received the B.S., M.S., and D.E. degrees from Tokyo Institute of Technology, Tokyo, Japan, all in electrical engineering, in 1959, 1961, and 1964, respectively. From 1966 to 1968 he was an Associate Professor at the Training Institute for Engineering Teachers, Tokyo Institute of Technology. From 1%8 to 1975 he was an Associate Professor at Chiba University, Chiba, Japan. From 1975 to 1980 he was an Associate Professor, and since 1980 he has been a Professor at Tokyo Institute of Technology. He has been engaged in research and development of array antennas. He has developed a planar slottedwaveguide may called radial line slot antenna, and a ring patch antenna for dual-frequency use called self-diplexing antenna. Dr. Goto received the achievement awards in 1983 and 1993, and the Paper Award in 1993, both from IEICE Japan. Takashi Ojima was bom in Tokyo, Japan, on March 18, He received the B.S. degree in electronic engineering from Sophia University, Tokyo, Japan, in From 1982 to 1991, he worked at Victor Company of Japan, and was engaged in the development and design of high-frequency circuits in televisions. Since 1991, he has been with Electronics & Information Systems Division of Nippon Steel Corporation, Tokyo, Japan, where he has been engaged in the planning and design of mobile DBS systems. Nobuharu Takahashi was bom in Kanagawa, Japan, on April 2, He received the B.S. degree from Kokugakuin University, Tokyo, Japan, in Since 1989 he has been with Electronics & Information System Divisions Group in Nippon Steel Corporation, Tokyo, Japan, where he has been engaged in the development of antenna and mechanical designs for mobile DBS receiving systems. Masahim Uematsu was bom in Osaka, Japan, on October 30, He is currently a Senior Manager and Chief Engineer at the Broadcasting Satellite Systems Group, Electronics & Information Systems Division of Nippon Steel Corporation, Tokyo, Japan. He has been engaged in the development of mobile DBS receiving systems.

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