диафрагмированные волноводные фильтры / 52775b66-7580-45f4-a333-31896d8898e4
.pdfPIERS ONLINE, VOL. 3, NO. 7, 2007 |
1053 |
A Compact Band-selective Filter and Antenna for UWB Application
Yohan Jang, Hoon Park, Sangwook Jung, and Jaehoon Choi
Department of Electrical and Computer Engineering, Hanyang University 17 Haengdang-Dong, Seongdong-Gu, Seoul 133-791, Republic of Korea
Abstract| A novel compact CPW ultra-wideband (UWB) antenna combined with a compact band-selective ¯lter is proposed. The proposed antenna without ¯lter satis¯es the return loss requirement of less than ¡10 dB over the frequency range of 3.0 GHz to 12.1 GHz. The optimized antenna has dimensions of 10£16 mm2 on a Te°on substrate ("r = 3:48) with good radiation characteristics and is easy to fabricate. The proposed antenna with ¯lter has the frequency band of 3 GHz to 11 GHz for VSWR less than 2.0 with a rejection band around 5.0 to 5.9 GHz.
DOI: 10.2529/PIERS061006225850
1. INTRODUCTION
Since the recent approval of UWB radio system, many researchers have extensively investigated on the modern indoor wireless communication system with high data transmission rate such as sensors, radar, and tracking applications. For the reliable use of these communication services, the design of UWB devices such as antennas, ¯lters, and LNAs is required. Various types of UWB antennas operating from 3.1 GHz to 10.6 GHz have been studied [1{3]. However, due to the coexistence of the UWB frequency band with Wireless LAN and Hiper LAN service band from 5.15 GHz to 5.825 GHz, UWB radio signal can be interfered with those services. Also, the e®ect of unwanted noise increases Noise Figure (NF) of the entire receiving system and can cause performance degradation.
In this letter, novel compact CPW ultra-wideband (UWB) antenna using notches and stubs combined with a compact band-selective ¯lter is proposed. To enhance impedance bandwidth, notches and stubs at the rectangular radiation patch were used. To realize pseudo-highpass ¯lter transmission response over UWB frequency band, the distributed highpass ¯lter scheme is used. The narrow bandstop function is achieved using coupled resonators. To miniaturize the total ¯lter size, the shape of resonators was modi¯ed to have small dimension. Three attenuation poles for the ¯lter can be tuned by controlling the length of resonators to have narrow rejection band around Wireless LAN and Hiper LAN service band.
2. COPLANAR WAVEGUIDE-FED UWB ANTENNA DESIGN AND ANALYSIS
In UWB application, the antenna operates from 3.1 GHz to 10.6 GHz. Figure 1 shows the proposed antenna for UWB application. The proposed antenna structure consists of a main rectangular radiation patch with notches and stubs at side corners of the patch. They are printed on an
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Figure 1: The proposed antenna.
PIERS ONLINE, VOL. 3, NO. 7, 2007 |
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RO4350b substrate with thickness of 0.762 mm and relative permittivity of 3.48. The thickness of copper coating on the top side of the substrate is approximately 0.0175 mm. A 50 - CPW feed line, having a metal strip width Wf = 4 mm and a gap distance G = 0:28 mm, is used to excite the proposed antenna.
The dimensions of rectangular patch are optimized to have resonant frequency at 3.7 GHz. By optimizing parameters of L2, W 2, and T 1 a®ecting the length and width of stub and notch attached to the rectangular radiation patch, improved impedance bandwidth performance can be achieved for the proposed antenna. That is largely due to the fact that the two stubs and two notches a®ect the reactive coupling between the rectangular patch and the ground plane and input impedance of main patch. The impedance bandwidth of the antenna covers from 3.0 GHz to 12.1 GHz for the return loss of less than ¡10 dB. The ¯nal design parameters are as follows: W1 = 10 mm, W2 = 1 mm, L1 = 16 mm, L2 = 8:5 mm, T1 = 2 mm, G = 0:32 mm, Wf = 4 mm , and S2 = 1 mm.
3. FILTER DESIGN AND ANALYSIS
Figure 2 shows the geometry and equivalent models of the proposed ¯lter. This ¯lter can be divided into a conventional highpass and a bandstop ¯lter. To realize band-selective characteristic within UWB frequency band, two ¯lters are integrated on both sides of the 50-ohm microstrip line and design parameters are adjusted to obtain superior frequency response throughout the operating frequency band. The ¯lter is printed on 30-mil Rogers RO4350 substrate with dielectric constant ("r) of 3.48.
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Figure 2: (a) Geometry of the proposed ¯lter, (b) Equivalent transmission line model of the highpass ¯lter.
All simulations are carried out by using Ansoft High Frequency Structure Simulator (HFSS) [4]. To design highpass ¯lter for wideband application up to 10.6 GHz, the mixed lumped/distributed (L/D) highpass ¯lter scheme is chosen [5]. The ¯lter consists of a cascade of three shunt shortcircuited stubs of electrical length of µc at the cuto® frequency fc, separated by connecting lines of electrical length of 2µc. The transfer function and ¯ltering function can be described by the following equations [6].
jS21(µ)j2 = |
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where " is the passband ripple constant, µ is the electrical length, and Tn(x) is the Chebyshev function of the ¯rst kind of degree n. The associated characteristic line impedance for the given terminating impedance Z0 are determined by
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The calculated characteristic impedances for line elements are Z1 |
= Z3 = 82:7 ohms, Z2 = |
58:5 ohms, and Z1;2 = 49:1 ohms. To realize the extremely wide passband, the line width is modi¯ed using full-wave EM simulation and determined to have much better performance throughout UWB frequency band. The initially calculated electrical length (µc) of each ¯lter is 40.68±.
PIERS ONLINE, VOL. 3, NO. 7, 2007 |
1055 |
A three-pole Chebyshev lowpass prototype with a passband ripple of 0.1 dB is selected to design narrowband bandstop ¯lter as introduced in [5]. For simplicity, the line width of the meandered resonators is ¯xed at 0.5 mm because the impedance of the resonators does not signi¯cantly a®ect the stop-band characteristic. The separation between the resonators is a quarter-guide wavelength (¸g/4) at the center frequency of 5.49 GHz and resonator length is approximately a half-guide wavelength (¸g/2). The designed ¯lter has the maximum attenuation of 49.2 dB at 5.65 GHz with three resonators and the 3-dB rejection bandwidth from 5.29 GHz to 5.85 GHz. Design parameters of the ¯nal ¯lter are summarized in Table 1.
Table 1: Parameters of the designed band-selective ¯lter [Unit: mm].
Parameters |
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Parameters |
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WH1 |
0.2 |
LR1 |
5.26 |
WH2 |
0.4 |
LR2 |
5.46 |
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0.2 |
LR3 |
5.36 |
LH1 |
7.5 |
LRV |
1 |
LH2 |
7 |
LRP |
5.76 |
LH3 |
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G |
0.1 |
WR |
0.5 |
WF |
1.7 |
4. RESULTS
Figure 3 shows the proposed antenna combined with a compact band-selective ¯lter for UWB application.
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Figure 3: The proposed antenna combined with a compact band-selective ¯lter.
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Figure 4: Measured return loss of the antenna with and without ¯lter.
PIERS ONLINE, VOL. 3, NO. 7, 2007 |
1056 |
The measured return loss characteristic of proposed antenna is shown in Figure 4. The impedance bandwidth of the proposed antenna reaches 9.1 GHz (3.0»12.1 GHz) for the return loss of less than ¡10 dB, which is enough to cover the entire UWB system. By using the ¯lter, the frequency stop band is created while maintaining the wide bandwidth performance.
Figures 5(a) to 5(c) show measured radiation patterns, including E-and H-planes and co-and cross{polariza tions at 3.5, 5, and 9 GHz. Good omni-directional performance at lower frequency band with a cross-polarization level of less than ¡15 dB are assumed.
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Figure 5: Measured radiation patterns of E- and H-planes and co-and cross-polarizations at (a) 3.5 GHz, (b) 5 GHz, and (c) 9 GHz. (- - ± - -: co-pol, | * |: x-pol)
Figure 6 illustrates the measured antenna gains of the designed antenna. From the results illustrated above, one can conclude that the suggested antenna system can be readily utilized for UWB application.
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Frequency, GHz
Figure 6: Measured antenna gain.
5. CONCLUSION
A novel and compact CPW-fed UWB antenna with a microstrip band-selective ¯lter is proposed. To obtain the wideband characteristic for UWB frequency band, notches and stubs are utilized. Combining an UWB antenna with a ¯lter having notch-function, the antenna with ultra-wideband performance over UWB band and band-rejection characteristic over WLAN band are obtained.
ACKNOWLEDGMENT
This work was supported by HY-SDR Research Center at Han-yang University, Seoul, Korea, under the ITRC Program of IITA, Korea.
REFERENCES
1.Ammann, M. J. and Z. N. Chen, \A wide-band shorted planar monopole with bevel," IEEE Trans. on Antennas and Propagation, Vol. 51, No. 4, 901{903, April 2003.
2.Chung, K., T. Yun, and J. Choi, \Wideband CPW-fed monopole antenna with parasitic elements and slots," Electronic Letters, Vol. 40, No. 17, August 2004.
3.Suh, S. Y., W. L. Stutzman, and W. A. Davis, \A new ultrawideband printed monopole antenna: the Planar Inverted Cone Antenna (PICA)," IEEE Trans. on Antennas and Propagation, Vol. 52, No. 5, May 2004.
4.Ansoft High Frequency Structure Simulator (HFSS), Ver. 9.2, Ansoft Corporation.
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1057 |
5.Levy, R., \A new class of distributed prototype ¯lters with applications to mixed lumped/distributed component design," IEEE Trans., Vol. MTT-18, 1064{1071, December 1970.
6.Hong, J. S. and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, Wiley, New York, 2001.