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IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 5, 2006
Stub-Loaded Folded Dipole Antenna for Digital Terrestrial TV Reception H. Iizuka, Member, IEEE, T. Watanabe, K. Sakakibara, Member, IEEE, and N. Kikuma, Senior Member, IEEE
Abstract—A stub-loaded folded dipole antenna is proposed for digital terrestrial TV reception. The antenna has a pair of lines as stubs inside a folded dipole. The prototype antenna printed on polyethylene terephthalate (PET) film has dimensions of 20 by 240 mm with a line width of 1 mm. The antenna exhibits a relatively flat gain characteristic from 0.6 to 1.9 dBi with a stable figure-of-eight radiation pattern in the frequency range from 470 to 710 MHz. The voltage standing wave ratio (VSWR) is less than 2.6 in the frequency range. Index Terms—Digital TV, dipole antennas, moment methods, UHF antennas.
I. INTRODUCTION
D
IGITAL terrestrial TV services were started in Japan in December 2003, following Europe and North America. Terrestrial Integrated Services Digital Broadcasting (ISDB-T) system has been adopted. Frequency bandwidth is assigned from 470 to 710 MHz and horizontal polarization is used. With regard to vehicle antennas, pole antennas have been in use for AM radio reception since the 1950s and covered for VHF and UHF bands [1], [2]. On-glass antennas, which are generally preferred, have been developed for installation on rear windows for AM/FM radio and analog television [3]–[5]. In order to enjoy digital terrestrial TV services, modified H-shaped antennas on the front and rear windows of sedans have been developed for coverage of 360 degrees in the horizontal plane [6]. The antenna had a width of 60 mm. The development of antennas for the services is still required for other types of vehicles. A thinner structure is suitable for narrower installation space near the edge of windows at the sides as well as the front and rear of vehicles. In this letter, a folded dipole antenna with stubs is proposed. The antenna has a thin structure with a width of 20 mm. The configuration and performance of the prototype antenna in free space are presented.
Fig. 1. Stub-loaded folded dipole antenna. (a) Configuration. (b) Prototype. (L = 240 mm, W = 20 mm, l = 9 mm, g = 40 mm, g = 2 mm, w = 1 mm).
Fig. 2. Measured VSWR of folded dipole antennas with and without stubs. Calculated results for the stub-loaded antenna are also presented. [ : stub : without stub (Mea.), : stub loaded (Cal.)]. loaded (Mea.),
01010
0000
00000
for the lower frequencies and for the higher frequencies. A prototype antenna with an RF circuit is shown in Fig. 1(b). The antenna was printed on polyethylene terephthalate (PET) film with a thickness of 0.125 mm. The RF circuit consists of a balun, a filter, and a low noise amplifier. It contributes to reducing the effect of cable loss between the antenna on the window and a receiver inside a vehicle.
II. CONFIGURATION This letter proposes a stub-loaded folded dipole antenna as shown in Fig. 1(a). The antenna has a pair of lines as stubs inside of 20 mm and a a folded dipole. The antenna has a width length of 240 mm. The width of the lines is set at 1 mm. The frequency bandwidth can be controlled mainly by the lengths Manuscript received December 16, 2005; revised February 10, 2006. H. Iizuka and T. Watanabe are with Toyota Central Research and Development Laboratories, Inc., Aichi 480 1192, Japan (e-mail:
[email protected]. co.jp). K. Sakakibara and N. Kikuma are with the Department of Computer Science and Engineering, Nagoya Institute of Technology, Nagoya 466 8555, Japan. Digital Object Identifier 10.1109/LAWP.2006.873955
III. PERFORMANCE This section presents the measurement results of the prototype antenna through the LC balun. The LC balun transforms to 50 . Fig. 2 shows the measured impedance from 200 voltage standing wave ratio (VSWR) of the stub-loaded folded dipole antenna as a solid line. The VSWR is less than 2.6 over the frequency band from 470 to 710 MHz. The measured results for a folded dipole antenna without stubs are represented as a dotted–dashed line for comparison. The comparison indicates that the stubs work in the higher frequency band. Numerical investigation was carried out by the commercial simulator “FEKO” [7] based on the method of moments. The calculation
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IIZUKA et al.: STUB-LOADED FOLDED DIPOLE ANTENNA
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Fig. 5.
Fig. 3. Current distributions in the xy plane. (a) 470 MHz. (b) 590 MHz. (c) 710 MHz. The length of the arrows represents the strength of the currents in to 0 dB. the range from
020 dB
Measured gain versus frequency.
installed on a vertical window of a vehicle. Stable figure-ofeight radiation patterns were obtained from 470 to 710 MHz. The frequency characteristic of gain is shown in Fig. 5. The measured gain has a relatively flat characteristic from 0.6 dBi to 1.9 dBi in the frequency range from 470 to 710 MHz. Loss of 0.3 dB for the LC balun was included. IV. CONCLUSION
Fig. 4. Measured radiation patterns in the zx plane. ( 590 MHz, : 710 MHz).
00+00
00500: 470 MHz, 00200:
model was composed of wires with a radius of 0.25 mm. The lengths and were adjusted to 250 and 28 mm, respectively. Other parameters were the same as those of the prototype antenna. The calculated VSWR is represented by a dotted line when the antenna impedance is normalized by 200 . The calculated results agree with the measured results. The calculated current distributions at 470, 590, and 710 MHz are shown in Fig. 3. The intensity of currents is normalized by the maximum value at each frequency. The length of the arrows represents the intensity of the currents in the range from to 0 dB. It is observed that strong currents flow on the stubs in the higher frequency band, as expected from the VSWR characteristics. On the other hand, the antenna works as a folded dipole antenna in the lower and middle frequency bands. plane, Fig. 4 shows the measured radiation patterns in the which corresponds to the horizontal plane when the antenna is
A stub-loaded folded dipole antenna has been proposed. Numerical analysis showed the stubs worked to cover the higher frequency band. It was confirmed experimentally that the antenna obtained a figure-of-eight radiation pattern and a relatively flat gain characteristic from 470 to 710 MHz. The antenna, which has a thin structure of 20 by 240 mm, will be used for digital terrestrial TV reception on vehicles. REFERENCES [1] R. G. Vaughan, J. B. Andersen, and M. H. Langhorn, “Circular array of outward sloping monopoles for vehicular diversity antennas,” IEEE Trans. Antennas Propagat., vol. 36, no. 10, pp. 1365–1374, Oct. 1988. [2] S. Egashira, T. Tanaka, and A. Sakitani, “A design of AM/FM mobile telephone triband antenna,” IEEE Trans. Antennas Propagat., vol. 42, no. 4, pp. 538–540, Apr. 1994. [3] H. K. Lindenmeier, J. F. Hopf, and L. M. Reiter, “Antenna and diversity techniques for broadcast reception in vehicles,” in Proc. IEEE Int. Antennas Propagation Symp. Dig., Chicago, IL, Jul. 1992, pp. 1097–1100. [4] K. Fujimoto and J. R. James, Mobile Antenna Systems Handbook, 2nd ed. Norwood, MA: Artech House, 2001. [5] R. Abou-Jaoude and E. K. Walton, “Numerical modeling of on-glass conformal automobile antennas,” IEEE Trans. Antennas Propagat., vol. 46, no. 6, pp. 845–852, Jun. 1998. [6] H. Iizuka, T. Watanabe, K. Sato, and K. Nishikawa, “Modified H-shaped antenna for automotive digital terrestrial reception,” IEEE Trans. Anetnnas Propagat., vol. 53, no. 8, pp. 2542–2548, Aug. 2005. [7] FEKO User’s Manual, Suite 5.0, EM software and systems-S.A. (Pty) Ltd., Stellenbosch, South Africa, 2005.
