Frequency (GHz)
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Return Loss (dB)
0
5
10
15
20
25
30
Measurement Simulation
Fig. 4.16. Simulated and measured return loss for the dual-band current driver with a ground plane of 50 mm × 100 mm. The other parameters are the same as given in TABLE VI.
In this section, the measurement results and the related discussion are presented.
Simulation and measurement results are compared in Fig. 4.16, which shows the simulated and measured return loss for dual-band current driver with a ground plane of size L × W = 50 mm × 100 mm. As seen in the figure, the simulated result basically agrees with the measured one. The measured center frequency in the low band is at 2.48 GHz with a 10-dB return-loss bandwidth of about 140 MHz, which covers the required band for IEEE 2.4 GHz WLAN operation. In the high band, the measured 10-dB bandwidth at the center frequency of 5.25 GHz satisfies the requirement for 5.2 GHz WLAN operation from 5.15 GHz to 5.35 GHz.
The measured 2D radiation patterns at 2.45 GHz in the three principal planes are illustrated in Fig. 4.17. The dual-band current driver comprising two current drivers lies in the xy plane. There are generally no nulls for the total-power radiation pattern Etotal
observed in the three principal planes, which is attractive to many applications. Also, it is noted that the measured patterns basically have the same shapes as the ones in the configuration of the single 2.4 GHz current driver shown before. This suggests that the
58
Fig. 4.17. Measured 2-D radiation patterns for the dual-band current driver at 2.45 GHz with a connected ground of 50 mm by 100 mm. (a) xy plane. (b) xz plane. (c) yz plane.
59
60
combination with the 5.2 GHz current driver will also not influence the radiation characteristics of the 2.4 GHz current driver. The corresponding values of the peak gains and average gains are given in TABLE VII. The measured average gain for the nearly omni-directional pattern in xz plane is about -0.4 dBi.
Fig. 4.18 shows the measured 2D radiation patterns in the three principal planes at 5.2 GHz. The shapes of the radiation patterns are similar to the ones shown in Fig. 4.16 at 2.45 GHz except in the yz plane. This is caused by the asymmetry position of the 5.2 GHz current driver on the ground edge. In this thesis, the dual-band current driver is placed in the center of the shorter ground edge. Thus, the 5.2 GHz current driver is shifted a distance from the center of the ground plane. This distance shift causes the asymmetry patterns at 5.2 GHz but has minor effect at 2.45 GHz. The corresponding values of the measured peak gains and average gains are given in TABLE VIII. The measured average gain for the nearly omini-directional patterns in xz plane is about -1 dBi. Additionally, the measured radiation efficiency for both bands is illustrated in Fig. 4.19. The efficiency in 2.4 GHz WLAN varies between 63 % and 70 %. Over the bandwidth for WLAN 5.2 GHz, value of the radiation efficiency is between 52 % and 60 %. The 10 % difference between the antenna efficiency comes from the high dielectric loss in the high band. Finally, the photograph of the fabricated dual-band current driver is shown in Fig. 4.20.
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Frequency (GHz)
2.35 2.40 2.45 2.50 2.55
Radiation Efficiency (%)
0 20 40 60 80 100
(a)
Frequency (GHz)
5.10 5.15 5.20 5.25 5.30 5.35 5.40
Radiation Efficiency
0 20 40 60 80 100
(b)
Fig. 4.19. Measured radiation efficiency for the dual-band current driver. (a) 2.4 GHz WLAN (b) 5.2 GHz WLAN
62 Dual-Band
Current Driver
2.4GHz Driver
5 GHz Driver
(a)
Dual-Band Current Driver
5 GHz Driver
2.4 GHz Driver Feed Line
Feed Line
(b)
Fig. 4.20. Photograph of the fabrication for the proposed current driver with a printed capacitor. (a) Top view. (b) Bottom view.
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Chapter 5 C ONCLUSION
In this thesis, a new microwave component called current driver is proposed to activate the ground edge current for radiation. The main point of the current-driver based antenna is that the main radiator is the ground plane as opposed to the current driver. Therefore, the driver can be designed very small while good radiation properties are maintained. The equivalent circuit model of the current driver viewed as a miniaturized planar balun helps to explain the edge-current inducing mechanism. Also, the results of the parameter study for the current driver are consistent with the characteristics of the miniaturized balun. In addition, the current driver is shown to be insensitive to the ground size. This suggests that the current driver can be easily applied to various applications. The influence of the shielding box for the proximity circuitry near the current driver is also thoroughly investigated, which indicates that the effect of the shielding box on the performance of the current driver is minor even when the box is placed very close to the current driver.
Two antenna applications based on current driver is presented, one is for WLAN 2.4 GHz applications and the other is for WLAN 2.4/5.2 dual-band applications. For WLAN 2.4 GHz applications, the current driver can be implemented by a lumped capacitor or printed capacitor with the size of about 4 mm × 4 mm, which is only about 0.03 λ0 × 0.03 λ0 (λ0 is the free-space wavelength at 2.45 GHz). The good radiation properties are achieved at 2.45 GHz with the measured radiation efficiency of above 60 % and the nearly omni-directional radiation patterns with the average gain of about 0 dBi. For WLAN 2.4/5/2 GHz applications, two drivers are combined together to achieve dual-band operation. The overall size is about 8.5 mm × 4 mm, which is still compact as compared to others miniaturized dual-band antenna. Basically, the radiation performance for the combined current drivers at 2.4 GHz is the same as the performance for the single 2.4 GHz current driver, which has the radiation efficiency over 60%. At 5.2 GHz, the measured radiation efficiency for the combined current drivers varies between 50% and 60 %, which is lower than the efficiency obtained at 2.45 GHz due to the highly lossy FR4 substrate in the high band. The nearly omni-directional patterns are observed at both 2.4 and 5.2 GHz. The current driver has advantages of compact size and ease of fabrication, so it is suitable for commercial applications.
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R EFERENCES
[1] H. Mosallaei and K. Sarabandi, “Magneto-dielectrics in electromagnetic: Concept and applications,” IEEE Trans. Antennas Propagat., vol. 52, no. 6, pp. 1558-1567, Jun. 2004.
[2] K. Buell, H. Mosallaei, and K. Sarabandi, “A substrate for small patch antennas providing tunable in miniaturization factors,” IEEE Trans. Microw. Theory Tech., vol. 54 pp. 135-146, Jan. 2006.
[3] H. Mosallaei and K. Sarabandi, “Design and modeling of patch antenna printed on magneto-dielectric embedded-circuit metasubstrate,” IEEE Trans. Antennas
Propag., vol. 55, pp. 45-52, Jan. 2007.
[4] A. Erentok and R. W. Ziolkowski, “Metamaterial-inspired efficient electrically small antennas,” IEEE Trans. Antennas Propag., pp. 691-707, Mar. 2008
[5] P. Jin and R. W. Ziolkowski, “Low-Q, Electrically Small, Efficient Near-Field Resonant Parasitic Antennas,” IEEE Trans. Antennas Propag., pp. 2548-2563, Sep. 2009
[6] Y.-S. Wang, M.-C. Lee, and S.-J. Chung, “Two PIFA-related miniaturized dual-band antennas, “ IEEE Trans. Antennas Propagat., vol. 55, no.3, pp. 805-811, Mar. 2007.
[7] C.-J. Lee, K. M. K. H. Leong, and T. Itoh, “Composite right/left-handed transmission line based compact resonant antennas for RF module integration,”
IEEE Trans. Antennas Propagat., vol. 54, no. 8, pp. 2283-2291, Aug. 2006.
[8] J.-G. Leee and J.-H. Lee, “Zeroth order resonance loop antenna,” IEEE Trans.
Antennas Propag., vol. 55, nol 3, pp. 994-997, Mar. 2007
[9] Y.-S. Wang, M.-F. Hsu, and S.-J. Chung, “A Compact Slot Antenna Utilizing a Right/Left-Handed Transmission Line Feed,” IEEE Trans. Antennas Propagat., vol. 56, no. 3, pp. 675-683, Mar. 2008.
[10] S. Pyo, S.-M. Han, J.-W. Baik, and Y.-S. Kim, “A Slot-Loaded Composite Right/Left-Handed Transmission Line for a Zeroth-Order Resonant Antenna With Improved Efficiency,” IEEE Trans. Microw. Theory Tech., vol. 57, no. 11, pp.
2775-2782, Nov. 2009.
65
[11] R. C. Hansen, “Fundamental limitations in antennas,” Proc. IEEE, vol. 69, pp.
170–182, Feb. 1981.
[12] R. F. Harrington, “Effect of antenna size on gain, bandwidth, and efficiency,” J.
Res. Nat. Bureau Stand., vol. 64D, pp. 1–12, Jan. 1960.
[13] J. S. McLean, “A re-examination of the fundamental limits on the radiation Q of electrically small antennas,” IEEE Trans. Antennas Propag., vol. 44, no. 5, pp.
672–676, May 1996.
[14] P. Vainikainen, J. Ollikainen, O. Kivekäs, and I. Kelander, “Resonator-based analysis of the combination of mobile handset antenna and chassis,” IEEE Trans.
Antennas Propagat., vol. 50, no. pp. 1433-1444, Oct. 2002.
[15] R. Hossa, A. Byndas, and M. E. Bialkowski, “Improvement of compact terminal antenna performance by incorporating open-end slots in ground plane,” Microw.
Opt. Technol. Lett., vol. 14, no. 6, pp. 283–285, Jun. 2004.
[16] P. Lindberg and E. Öjefors, “A bandwidth enhancement technique for mobile handset antennas using wavetraps,” IEEE Trans. Antennas Propagat., vol. 54, no.
8, pp. 2226-2233, Aug. 2006.
[17] Y.-S. Wang, J.-C. Lu, and S.-J. Chung, “A Miniaturized Ground Edge Current Choke—Design, Measurement, and Applications,” IEEE Trans. Antennas
Propagat,, vol. 57, no. 5, pp. 1360-1366, May 2009.
[18] J. Villanen, J. Ollikainen, O. Kivekäs, and P. Vainikainen, “Coupling element based mobile terminal antenna structures,” IEEE Trans. Antennas Propagat., vol.
54, no. 7, pp. 2142-2153, Jul. 2006.
[19] L. Huang and P. Russer, “Electrically Tunable Antenna Design Procedure for Mobile Applications,” IEEE Trans. Microw. Theory Tech., vol. 56, no. 12 Part 1, pp. 2789-2797, Dec. 2008.
[20] M. Cabedo-Fabres, E. Antonino-Daviu, A. Valero-Nogueira, and M. Ferrando-Bataller, “Wideband radiating ground plane with notches,” in Proc. IEEE Ant.
And Propag. Soc. Int. Symp. Dig., Washington, DC, USA, July 2005, pp. 560-563.
[21] P. Lindberg, E. Öjefors, and A. Rydberg, “Wideband slot antenna for low-profile hand-held terminal applications, “ in Proc. 36th European Microw. Conf. 2006, Manchester, UK, Sept. 2006, pp. 1698-1701.
66
[22] C.-L. Li, J.-P. Chang, and L.-J. Wong, “Miniature planar notch antenna of J shape,” Electron. Lett., vol. 42, no. 20, pp. 1134-1135, Sept. 2006.
[23] J. Holopainen, J. Villianen, R. Valkonen, J. Poutanen, O. Kivekäs, C. Icheln, and P. Vainikainen, “Mobile terminal antennas implemented using optimized direct feed,” in IEEE Int. Workshop on Antenna Tech, iWAT 2009, Santa Monica, CA, USA, March 2-4, 2009.
[24] K. S. Ang, Y. C. Leong, and C. H. Lee, “Analysis and design of miniaturized lumped-distributed impedance-transforming baluns,” IEEE Trans. Microw.
Theory Tech., vol. 51, no. 3, pp. 1009-1017, Mar. 2003.
[25] N. Marchand, “Transmission line conversion transformers,” Electron. Lett., vol.
17, pp. 142-145, Dec. 1944.
[26] M. C. Tsai, “A new compact wideband balun,” in IEEE Microwave
Millimeter-Wave Monolithic Circuits Symp. Dig., 1993, pp. 123–125.
[27] S. A. Maas and K. C. Chen, “A broad-band, planar, doubly balanced monolithic
Ka-band diode mixer,” IEEE Trans. Microw. Theory Tech., vol. 41, pp. 2330–
2335, Dec. 1993.
[28] High Frequency Structure Simulator (HFSS). Ansoft Corporation, Pittsburgh, PA, 2001.