диафрагмированные волноводные фильтры / 86a604b5-7bfc-426a-a312-ff8686edd094

4. CONCLUSION

A new dual-band microstrip resonator, here addressed as hole resonator, has been presented. A theoretical analysis has been provided and its performance verified by simulation and measurements. It has been shown that it has a behavior comparable to the stepped-impedance resonator when the coupling between internal lines is small. In addition, its main advantage is the constant section, which permits easier and less time-consuming optimization at the design stage. A filter based on the proposed hole resonator has been implemented for WLAN applications (2.45/ 5.75 GHz).

ACKNOWLEDGMENTS

This paper was supported by the Spanish Government Projects TEC2005-06297/MIC, TEC2007-65705/TCM, and TEC2008- 06758-C02-02/TEC, the Catalan Government Project 2006ITT-

´

10005, and the URV 2007ACCES-17 Specific Research Support Action.

REFERENCES

1.M. Mokhtaari, J. Bornemann, and S. Amari, New reduced-size stepimpedance dual-band filters with enhanced bandwidth and stopband performance, IEEE MTT-S Int Microwave Symp Dig, San Francisco, CA (2006), 1181–1184.

2.Y.P. Zhang and M. Sun, Dual-band microstrip bandpass filter using stepped-impedance resonators with new coupling schemes, IEEE Trans Microwave Theory Tech 54 (2006), 3779 –3785.

3.M. Sagawa, M. Makimoto, and S. Yamashita, Geometrical structures and fundamental characteristics of microwave stepped-impedance res-

onators, IEEE Trans Microwave Theory Tech 45 (1997), 1078 –1085.

4.C. Quendo, E. Rius, and C. Person, Narrow bandpass filters using dual-behavior resonators, IEEE Trans Microwave Theory Tech 51 (2003), 734 –743.

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6.C.-Y. Chen and C.-Y. Hsu, A simple and effective method for microstrip dual-band filters design, IEEE Microwave Wireless Compon Lett 16 (2006), 246 –248.

7.B. Kapilevich and R. Lukjanets, Modelling varactor tunable microstrip resonators for wireless applications, Appl Microwave Wireless 10 (1998), 32– 44.

© 2009 Wiley Periodicals, Inc.

LOW-PROFILE DIELECTRIC RESONATOR ANTENNA WITH HIGHPERMITTIVITY FOR APPLICATION IN WiMAX

Yih-Chien Chen and Kai-Hao Chen

Department of Electrical Engineering, Lunghwa University of Science and Technology, Gueishan Shiang, Taoyuan County, Taiwan; Corresponding author: ycchenncku@yahoo.com.tw

Received 12 October 2008

ABSTRACT: In this article, the measurement results of the dielectric resonator antenna with high-permittivity have been presented. With this technique, a 5.4% bandwidth (return loss 10 dB) of center frequency at about 3.5 GHz for application in WiMAX has successfully been achieved. The copolarization radiation is strongest at 5° from the broadside in the E-plane. The cross-polarized patterns are about 10 dB less than the copolarized patters in the broadside direction. The antenna has a 3 dB beam angle of about 80°. Peak antenna gain is

about 5.96 dBi, with gain variations less than 1.0 dBi for frequencies within in the 10 dB S11 bandwidth. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1652–1654, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 24437

Key words: dielectric resonator antenna; mictrostrip line; return loss; bandwidth

1. INTRODUCTION

There are many commercial applications, such as mobile radio and wireless communications that use microstrip antennas. Microstrip antennas, however, have limitations in size, bandwidth, and efficiency. On the other hand, the dielectric resonator (DR) antenna is attractive due to its small-size, high radiation efficient, and ease of excitation [1–3]. Two dielectric properties of materials must be considered for DR antenna used as follows: a high-dielectric constant and a high-quality factor. The size of the DR antenna decreases with increasing the permittivity of the dielectric resonator. The quality factor is representative of the antenna losses. Typically, there are radiations, conduction, dielectric, and surface wave losses. Therefore, the total quality factor is influenced by these losses. The DR antenna offers very-high radiation efficiency due to its low-dielectric loss and it has no metallic loss.

In traditionally, the DR with relatively small permittivity around 10 is chosen for DR antenna to enhance the radiation capability [4 –9]. However, low-profile DR antenna with relatively low-resonant frequency can be achieved by using high permittivity. In our study, aperture-coupled circular DR antenna composed of DR with high-permittivity of 57 was designed and built. The resonant frequency of the DR antenna is around 3.5 GHz. The DR antenna can be application in the IEEE 802.16-2004 3.5 GHz licensed band of WiMAX (Worldwide Interoperability for Microwave Access). The characteristics of aperture-coupled circular DR antenna, such as return loss, input impedance, radiation pattern, and gain, have been measured and discussed.

2. SIMULATION AND MEASUREMENT

The resonant frequency of the circular disk DR antenna excited at the dominant TM110 mode is as follows [1]:

where X11 1.841 is the first zero of the equation J1 x 0, and c is the speed of light in a vacuum. The parameters of a, h, and ra is the radius, height, and permittivity of the DR, respectively. One advantage of the DR is ease of excitation. Among the various excitation methods for the DR antenna, the aperture coupling has been widely used as it allows the DR antenna to be integrated with the MMICs [9, 10].

The configuration of DR antenna composed of high-permittiv- ity DR is as shown in Figure 1. The rectangular RF4 substrate has dimensions of 50.0 50.0 mm2 and thickness of 1.6 mm. The DR antenna is fed with microstrip line. Impedance matching could be realized by adjusting the length of the microstrip feed line to DR antenna. Therefore, the bandwidth could be adjusted by modifying the length of the microstrip feed line. Dimensions of the microstrip feed line on FR4 substrate were calculated by close-form formulas given in Ref. 11, assuming infinite ground plane and finite dielectric thickness. The microstrip feed line dimensions were confirmed by AWR Microwave Office. The microstrip feed line dimensions were compatible with a subminiature version A (SMA) connector.

Figure 1 Configuration of DR antenna composed of high-permittivity DR

The diameter of dielectric core of conventional SMA connector was about 4.5 mm. The microstrip feed line has length Lf of 31.0 mm and width of Wf of 5 mm are stretched in a rectangular aperture with dimensions L W of 11.0 20.0 mm2. The DR is

Ca0.97Zn0.03La4Ti5O17 (CZLT) with 0.5 wt% CuO additives and sintered at 1450°C for 4 h. Following is a list of the microwave

parameters of the CZLT.

Permittivity, r 57.

Loss tangent, tan 0.0004.

Diameter of the dielectric resonator 8.8 mm.

Thickness of the dielectric resonator 4.4 mm.

Simulation has been carried out by using a commercial electromagnetic simulator. In simulation, the conducting grounds and the substrates were assumed to be finite in transverse plane. The microstrip feed line was fabricated by using wet etching process. A coaxial connector was soldered to the microstrip feed line to output signal from the DR antenna to the Port 1 of network analyzer. Reflection coefficient was measured on a PNA-L network analyzer (N5230A). Radiation pattern measurement was measured in a chamber. A standard double ridged horn antenna was used as a transmitting antenna. The DR antenna fed with microstrip line is mounted on a position which is controlled by a computer.

3. RESULTS

The measurement and simulation return loss of the DR antenna fed with microstrip line is as shown in Figure 2. The measurement and simulation frequency range is from 2.5 to 4.4 GHz. The measurement return loss of the DR antenna is 14 dB at 3.53 GHz. The measurement resonant frequency 3.53 GHz is very close to the resonant frequency of 3.5 GHz (0.86% error) predicted from Eq.

(1). The measurement resonant frequency is also very close to the simulation resonant frequency of 3.52 GHz as shown in Figure 2. As seen from the measurement results, the DR antenna has a 10 dB S11 bandwidth of 5.4%. Caused of DR antenna composed of high-permittivity DR was used in our study, the bandwidth is smaller than the typical value of 6 12% using conventional DR antennas with permittivity around 10 [3– 8]. However, the achieved bandwidth is enough for many practical applications. The corresponding Smith Chart representation of the S11 from 2.5 to 4.4 GHz is shown in Figure 3. To match an antenna, the impedance

Figure 2 The measurement and simulation return loss of the DR antenna fed with microstrip line. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]

locus should be shifted as near as possible to the center of the Smith Chart to obtain a low-return loss at resonant frequency. As seen from the measurement results, the input impedance values of the DR antenna is 38.09 j12.89 ohm at the resonant frequency of 3.53 GHz. A matching point is near the point of 3.5 GHz and the matching point is very close to the center of the Smith Chart.

The measured radiation pattern of the DR antenna in the E-plane at resonant frequency of 3.53 GHz is shown in Figure 4. The patterns are observed to be stable across the return loss 10 dB bands. As seen from Figure 4, the copolarization radiation is strongest at 5° from the broadside in the E-plane. The DR antenna has a 3 dB beam angle of about 80°. The cross-polarized patterns are also shown in the same figure for comparison. It is seen from the figure, the cross-polarized patterns are about 10 dB less than the copolarized patters in the broadside direction. The measured DR antenna gain in the broadside direction is shown in Figure 5. As observed from Figure 5, the peak is 3.53 GHz, close to the resonant frequency as expected. Peak DR antenna gain is

Figure 3 Input impedance of the DR antenna fed with microstrip line. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]

Figure 4 Radiation pattern of the DR antenna fed with microstrip line in the E-plane at resonant frequency. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]

about 5.96 dBi at 3.53 GHz. The gain variations are less than 1.0 dBi for frequencies within the 10 dB S11 bandwidth.

4. CONCLUSIONS

Successful design of DR antenna composed with high-permittivity for application in WiMAX has been presented. Characteristics of the DR antenna have been investigated in this article. The return loss is 14 dB at 3.53 GHz, which corresponds to a 10 dB S11 bandwidth of 5.4%. The copolarization radiation is strongest at5° from the broadside and a 3 dB beam angle of about 80° of the DR antenna in the E-plane. Peak DR antenna gain is about 5.96 dBi in the E-plane. The gain variations are less than 1.0 dBi for frequencies within the 10 dB S11 bandwidth. The diameter and thickness of the presented DR antenna with high-permittivity are 8.8 and 4.4 mm, respectively. A compact size of DR antenna with high-permittivity when compared with a conventional DR antenna has been successfully achieved.

Figure 5 Measured antenna gain of the DR antenna fed with microstrip line

ACKNOWLEDGMENTS

This work was supported by the Department for Education of the R. O. C. under Grant E-88-166.

REFERENCES

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©2009 Wiley Periodicals, Inc.

EXPERIMENTAL DEMONSTRATION OF A CLOCK RECOVERY SCHEME UTILIZING NONLINEAR RELAXATION OSCILLATION IN DIRECTLY MODULATED LASERS

Minhui Yan,1 Chih-Hung Chen,1 Qing-Yang Xu,2 and Wei-Ping Huang1

1 Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1; Corresponding author: yanm2@mcmaster.ca

2 Department of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4L7

Received 12 October 2008

ABSTRACT: An experimental demonstration was presented for a clock recovery scheme suitable for low-cost short-haul optical communications. This scheme utilizes the nonlinear relaxation oscillation in a directly modulated laser, which creates clock information in modulated nonreturn-to-zero optical signals. At the receiver, an injection locked oscillator is employed to extract and restore the clock. Eye diagrams of both received data signal and recovered clock demonstrate the capability of recovering clock from the data signal with an almost closed eye at

9 Gbps. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett