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27663_ftp 4. B. Sun, K. Hu, Y. Wei, D. Chen, S. Gao, and S. He, Double- pumped multiwavelength fiber optical parametric oscillator based on a Sagnac loop filter, Opt Lett 37 (2012), 106–108. 5. Y.G. Han, T.V.A. Tran, and A.B. Lee, Wavelength-spacing tunable multiwaveleng...
27663_ftp
4. B. Sun, K. Hu, Y. Wei, D. Chen, S. Gao, and S. He, Double- pumped multiwavelength fiber optical parametric oscillator based on a Sagnac loop filter, Opt Lett 37 (2012), 106–108. 5. Y.G. Han, T.V.A. Tran, and A.B. Lee, Wavelength-spacing tunable multiwavelength erbium-doped fiber laser based on four-wave mix- ing of dispersion-shifted fiber, Opt Lett 31 (2006), 697–699. 6. D.R. Chen, B. Sun, Y. Wei, S. Gao, and S. He, Some wavelength- spacing continuously tunable multi-wavelength fiber lasers based on four-wave-mixing effect, In Photonics in Switching, Monterey, USA, 2010, pp. JTuB37. 7. G.J. Cowle and D.Y. Stepanov, Multiple wavelength generation with Brillouin/erbium fiber lasers, IEEE Photon Technol Lett 8 (1996), 1465–1467. 8. L. Zhan, J.H. Ji, J. Xia, S.Y. Luo, and Y.X. Xia, 160-line multiwa- velength generation of linearcavity self-seeded Brillouin-erbium fiber laser, Opt Express 14 (2006), 10233–10238. 9. M.P. Fok and C. Shu, Spacing-adjustable multi-wavelength source from a stimulated Brillouin scattering assisted erbium-doped fiber laser, Opt Express 14 (2006), 2618–2624. 10. Y.G. Shee, M.H. Al-Mansoori, A. Ismail, S. Hitam, and M.A. Mahdi, Multiwavelength Brillouin-erbium fiber laser with double- Brillouin-frequency spacing, Opt Express 19 (2011), 1699–1706. 11. Y.J. Song, L. Zhan, S. Hu, Q.H. Ye, and Y.X. Xia, Tunable multi- wavelength Brillouin-erbium fiber laser with a polarization-main- taining fiber Sagnac loop filter, IEEE Photon Technol Lett 16 (2004), 2015–2017. 12. Z. Zhang, Li Zhan, and Y. Xia, Tunable self-seeded multiwave- length Brillouin-erbium fiber laser with enhanced power efficiency, Opt Express 15 (2007), 9731–9736. 13. M.H. Al-Mansoori and M.A. Mahdi, Multiwavelength L-band Bril- louin-erbium comb fiber laser utilizing nonlinear amplifying loop mirror, J Lightwave Technol 27 (2009), 5038–5044. 14. S. Qin and D. Chen, Ultra-broadband ASE source using combina- tion of bismuth- and silicon-based erbium-doped fibers, Acta Pho- tonica Sinica 36 (2007), 1480–1484. 15. A.M.R. Salem, M.H. Al-Mansoori, H. Hizam, S.B.M. Noor, and M.A. Mahdi, Broadly tunable multiwavelength fiber laser with bis- muth-oxide EDF using large effective area fiber, Laser Phys 21 (2011), 389–394. 16. A.M.R. Salem, M.H. Al-Mansoori, H. Hizam, S.B.M. Noor, M.H.A. Bakar, and M.A. Mahdi, Multiwavelength L-band fiber laser with bismuth-oxide EDF and photonic crystal fiber, Appl Phys B 103 (2011), 363–368. 17. M.H. Al-Mansoori and M.A. Mahdi, Tunable range enhancement of Brillouin-erbium fiber laser utilizing Brillouin pump pre-amplifi- cation technique, Opt Express 16 (2008), 7649–7654. VC 2013 Wiley Periodicals, Inc. A COMPACT UWB CPW BANDPASS FILTER WITH SHORT-ENDED H-SHAPED RESONATOR AND CONTROLLABLE NOTCHED BAND Kai Wang, Sai Wai Wong, and Qing-Xin Chu School of Electronic and Information Engineering, South China University of Technology, Guangzhou, Guangdong, People’s Republic of China Received 13 November 2012 ABSTRACT: An ultra-wideband (UWB) bandpass filter (BPF) using the hybrid microstrip and coplanar waveguide (CPW) structure is proposed in this article. The BPF composes of CPW feed lines and H-shaped microstrip resonator. By a CPW/microstrip back-to-back coupling structure, the UWB BPF was realized with the passband covering the entire UWB band (3.1–10.6 GHz). A narrow notched band achieved by etching slots on the lower impedance part of the H-shaped resonator to form an open circuit stub. At last, three U-slot DGSs are used to achieve a good upper-stopband rejection. The measured results are in good agreement with the simulated results. VC 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1577–1581, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27663 Key words: coplanar waveguide; UWB bandpass filters; defected ground structure; notched band; microstrip-line 1. INTRODUCTION The U.S. Federal Communication Commission released the unli- censed use of the ultra-wideband (UWB) (3.1–10.6 GHz) for hand-held systems in 2002 [1]. Planar filters are an often-consid- ered candidate for the UWB technology and have been studied extensively in the past decade. As compared to microstrip struc- ture, there is little work on hybrid microstrip and coplanar- waveguide structure relatively. In [2], the authors present a UWB bandpass filter (BPF) with hybrid microstrip feed line and CPW resonator structure, and five modes allocated in the pass- band appropriately by using the back-to-back coupled structure. A broadside-coupled microstrip-coplanar waveguide (CPW) structure was proposed in [3] with tightened coupling degree uti- lized to design an alternative UWB filter with one, two, and three sections. An UWB BPF was constituted only by CPW structure [4] via cascading CPW lowpass and bandpass struc- tures, and it achieved good performance, for example, sharp skirt selectivity and good stopband rejection. A BPF with CPW feed line and microstrip resonator was presented in [5], this novel structure exhibits good in-band performance and a high out-of-band rejection level. On the other hand, to avoid unexpected signal interference between the UWB system and the local-area network Figure 1 (a) layout of CPW plane, (b) layout of microstrip plane, and (c) Equivalent J-inverter network DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 7, July 2013 1577 applications, a notched band UWB BPF is required within the defined UWB frequency spectrum as studied in [6–10]. In [6], a notched band is simply created by embedding an asymmetric shunt stub in the feed line, and the notched band can be change- able by adjusting the size of stub. Multinarrow-notched bands can be introduced by integrating slot lines on the bottom side of the CPW BPF, which is shown in [7], and its notched band can be control by changing the length of the slot lines. In [8], a dual notch band is formed by embedding two open circuited stubs in the form of defected microstrip structure. In this article, we present an UWB BPF with hybrid CPW feed line and microstrip resonator structure. The schematics are shown in Figure 1 with marked dimensions. The short-ended H- shaped microstrip resonator was studied in this article. A nar- row-notched band achieved by etching slots on the lower imped- ance part of the H-shaped resonator to form an open circuit stub. At last, three U-slot defected ground structures (DGS) are used to achieve a good stopband rejection. We found that the fil- ter exhibits good in-band and out-of-band performance, includ- ing a low insertion loss and a high out-of-band rejection level. Simulation design for the filter is carried out on the electromag- netic simulator ADS Momentum. 2. PROPOSED HYBRID BPF Figure 1(b) shows the coupling structure of the hybrid CPW and microstrip structure, and the equivalent J-inverter network is shown in Figure 1(c). This hybrid structure results in building up the UWB passband by virtue of the strong surface-to-surface coupling structure. Now, we look into the H-shaped resonator, it can be seen as a short-ended step impedance resonator, which is depicted in Figure 2(a). It consists of a low impedance line section in the middle section and four identical high impedance short-circuited line sections on the two sides, and the individual high imped- ance of one side can be described as two parallel short-ended stubs. A–A0 in Figure 2(a) is the symmetric plane and the char- acteristic of the high impedances of the resonator are defined as Z1, and the low impedances are defined as Z2, h1 and h2 is the corresponding electrical length. R ¼ Z2/Z1 is defined as the im- pedance ratio of low and high impedance lines. Figure 2(b) shows the condition under the odd mode excita- tion, the symmetric plane is short-circuit. We can easily obtain the input admittance Yino Yino ¼ �j 2Y1 tan h2 þ Y2 tan h1 tan h1 tan h2 Y1 and Y2 are corresponding input admittances of Z1 and Z2. Figure 2(c) shows the condition under the even mode excita- tion, the symmetric plane is open circuit. Herein, the input ad- mittance Yine is given below. Yine ¼ �j 2Y1 cot h2 � Y2 tan h1 tan h1 cot h2 Figure 2 (a) H-shaped resonator structure, (b) odd mode, and (c) even mode Figure 3 (a) Normalized resonant frequencies, (b) layout of gradual changes in feed line. (c) Circuit block diagram. (d) Simulation of the proposed structure. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] 1578 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 7, July 2013 DOI 10.1002/mop Under the resonance condition, the input admittance Yino and Yine are equal to zero, so the resonance frequency depends on h1 and h2. If 2h1 ¼ h2 ¼ h, three resonance frequencies can be obtained. hðfs1Þ ¼ 2 arctan ffiffiffiffiffiffiffiffiffiffiffiffi R Rþ 1 r ; hðfs2Þ ¼ 2 arctan ffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4Rþ 1p ; hðfs3Þ¼ 2p� 2 arctan ffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4Rþ 1p ; hðfs4Þ ¼ 2p� 2 arctan ffiffiffiffiffiffiffiffiffiffiffiffiffiffi R Rþ 1 ; r hðfs5Þ ¼ 2p Obviously, only the first resonance frequency h(fs1) is in the desired passband as shown in Figure 3(a), and the other four res- onance frequencies are out of band at the value of R ¼ 0.35. In this novel coupling structure, two modes are achieved by the strong coupling [9, 10] between the CPW and the microstrip line. Whereas, the other two modes are achieved by the tapered feed line, which is shown in Figure 3(b). The sections from the short-ended microstrip line to tapered feed line are quarter- wavelength (at 6.85 GHz), these two sections can be modeled as K-inverter. As a result, the network in Figure 1(c) should be modified as Figure 3(c). Another four modes are achieved by two J-inverters and two K-inverters. The simulation of the pro- posed UWB BPF with tapered feed line is depicted in Figure 3(d). 3. A NOTCHED BAND AND THREE U-SLOT DGSS To generate notch band, an embedded open circuit stub is real- ized in the low impedance part of the H-shaped resonator, which is shown in Figure 4(a). The stub is kg/4 in length at corre- sponding center frequency to stop signal interference between UWB system and systems. The length of the open circuit stub is defined as L, and the gap which is shown in Figure 4(a) is defined as W. Figure 4(b) displays the insertion loss with the fixed W ¼ 0.2 mm and vari- able L, and the notched band position moves to the low fre- quency due to increase of L, so the notched band can be con- trolled by altering the length of the stub. Actually, the controlled frequency ranges from 5 to 7 GHz. In this article, we chose L ¼ 8.85 mm which made the center frequency of the notched band designed at 6 GHz. With fixed L ¼ 8.85 and vari- able W, increasing the gap (W) widens the bandwidth of the notched band and vice versa as demonstrated in Figure 4(c). It should be noted that the center frequency of the notched band slightly shifted to lower frequency when the gap was increased (W), this may be caused by increasing the loading effect of the quarter-wavelength of the open stub. Apparently, the out of band performance has unwanted pass- band, so slot-shaped DGSs on microstrip line [11] are used to provide a good stopband property. The layout and simulated S- parameters of the three cascading U-slot DGSs is showed in Fig- ures 5(a) and 5(b), respectively. Obviously, three transmission zeros are generated in the stopband that are created by the three slot lines, and the three transmission zeros allocated from left to right in Figure 5(b) correspond to the three slot lines which are shown in Figure 5(a) from left to right. The simulation of the proposed structure with three U-slot DGSs is shown in Figure 5(c) with fixed L ¼ 8.85 mm and W ¼ 0.2 mm. In comparison between Figures 3(d) and (c), three transmission zeros were gen- erated by three U-slot DGSs and a good upper-stopband-band rejection is achieved. 3. IMPLEMENTATION AND EXPERIMENTAL RESULTS According to the earlier analysis, the proposed UWB BPF is designed, simulated, and fabricated. The final dimensions of the UWB BPF is shown in Table 1, and the dimensions of the open circuit stub is shown in Figure 4(a), and fixed L ¼ 8.85 mm and W ¼ 0.2 mm, and the three U-slot DGSs dimensions are marked in Figure 5(a). The filter was fabricated on a substrate with a relative dielec- tric constant of 2.55 and thickness of 0.8 mm, and the photo- graph of fabricated UWB BPF is shown in Figures 6(a) and 6(b). Figure 6(c) provides a comparison of the simulated and measured characteristics of the filter, and a good agreement is observed over the passband. The measured insertion loss of the filter is better than 0.7 dB, and the return loss is greater than 15 Figure 4 (a) Layout of etch slots on H-shaped resonator. (b) Simula- tion results of rejection characteristics with fixed W ¼ 0.2 mm and vari- able L. (C) Simulation results of rejection characteristics with fixed L ¼ 8.85 and variable W. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 7, July 2013 1579 dB. The notch band is well located at 6 GHz with 17 dB attenu- ation in measurement. The upper stopband is beyond 15 dB from 11 to 16.5 GHz. The novel hybrid structure with H-shaped resonator is implemented for UWB BPF, and it is suitable to apply in UWB communication systems. 4. CONCLUSION A novel UWB BPF with hybrid CPW and microstrip structure is proposed and implemented. The H-shaped resonator has been discussed, a narrow notched band has been realized by embed- ding an open circuit stub, and three U-slot DGSs were used to achieve a good stopband rejection. The fabricated UWB BPF has a wide passband of 2.9–10.9 GHz, and insertion loss is bet- ter than 0.7 dB. The notch band is well located at 6 GHz with 17 dB attenuation in measurement. The upper stopband is beyond 15 dB from 11 to 16.5 GHz. ACKNOWLEDGMENT This work is supported by the National Natural Science Foundation of China (61101017) and the Fundamental Research Funds for the Central Universities (2012ZM0024). REFERENCES 1. Revision of Part 15 of the Commission’s Rules Regarding Ultra- Wide-band Transmission System, FCC ET-Docket 98–153, Washington, DC, Feb. 14, 2002. 2. H. Wang, L. Zhu, W. Menzal, and Z. N. Chen, Ultra-wideband (UWB) bandpass filters using hybrid microstrip/CPW structures, In: Microwave conference, 2006, pp. 1216–1219. 3. K. Li, D. Kurita, and T. Matsui, An ultra-wideband bandpass filter using broadside-coupled microstrip-coplanar waveguide structure, In: IEEE international conference on ultra-wideband, 2005, pp. 446–451. 4. N.-W. Chen and K.-Zi Fang, An ultra-broadband coplanar-wave- guide bandpass filter with sharp skirt selectivity, IEEE Microwave Wireless Compon Lett 17 (2007), 124–126. 5. H.L. Hu, X.D. Huang, and C.H. Cheng, Ultra-wideband bandpass filter using CPW-to-microstrip coupling structure, Electron Lett 42 (2006), 586–587. TABLE 1 Dimensions of Proposed UWB Filter Shown in Figure 1 (unit: mm) W1 W2 W3 W4 W5 W6 W7 0.2 5.4 0.7 3.48 6.2 2.1 0.7 L1 L2 L3 S1 R r 3.3 2.75 12 5.8 0.6 0.6 Figure 6 (a) CPW plane of fabricated filter, (b) microstrip plane of fabricated filter, and (c) results of measured and simulated. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] Figure 5 (a) Layout of H-shaped resonator with three U-slot DGSs. (b) Simulation of three cascading U-slot DGSs. (c) Simulation of the proposed structure with DGSs. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] 1580 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 7, July 2013 DOI 10.1002/mop 6. S.W. Wong and L. Zhu, Ultra-wide bandpass filters with sharpened roll-off skirts, extended upper-stopband, and controllable notch- band, Microwave Opt Technol Lett 50 (2008), 2958–2961. 7. B.Y. Yao, Y.G. Zhou, and Q.S. Cao, A UWB bandpass filter with multi notched bands using microstrip/coplanar waveguide, In: 8th international symposium on antenna, propagation and EM theory, 2008, pp. 637–640. 8. H. Shaman and J.-S. Hong, Ultra-wideband (UWB) microstrip bandpass filter with narrow notched band, In: 38th European microwave conference, Amsterdam, Holland, 2008, pp. 857–860. 9. J. Gao, L. Zhu, M. Menzel, and F. B€ogelsack, Short-circuited CPW multiple-mode resonator for Ultra-wideband (UWB) band- pass filter, IEEE Microwave Wireless Compon Lett 16 (2006), 124–126. 10. H. Wang and L. Zhu, Ultra-wideband bandpass filter using back- to-back microstrip-to-CPW transition structure, Electron Lett 41 (2005), 1337–1338. 11. D.-J. Woo, T.-K. Lee, J.-W. Lee, and W.-K. Choi, Novel U-slot and V-slot DGSs for bandstop filter with improved Q factor, IEEE Trans Microwave Theory Technol 54 (2006), 2840–2846. VC 2013 Wiley Periodicals, Inc. A LOW-POWER TECHNIQUE TO BOOST THE OUTPUT AMPLITUDE OF MULTI GIGAHERTZ PUSH-PUSH LC VCOS Reza Molavi,1,2 Shahriar Mirabbasi,1 and Hormoz Djahanshahi2 1 Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada; Corresponding author: reza@ece.ubc.ca 2 PMC Sierra, Burnaby, BC, Canada Received 23 November 2012 ABSTRACT: A design technique to increase the output amplitude and hence the output power of push-push LC-based voltage-controlled oscillators (LC VCOs) is presented that relies on LC resonance boosting of the second harmonic. Measurement results are in good agreement with the results predicted from the analysis. Using the proposed technique, a low-power push-push LC VCO is designed and implemented in 90-nm CMOS. Based on the measurement results, the VCO has a frequency tuning range of 23%, from 20.1 to 24.8 GHz. It exhibits up to 8 dB improvement in its output power at the middle of the frequency band compared to a traditional push-push VCO. VC 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1581–1584, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/ mop.27599 Key words: high-frequency oscillator; LC oscillator; push-push voltage- controlled oscillator; accumulation-mode MOS varactor 1. INTRODUCTION Push-push voltage-controlled oscillator (VCO) is a well-known cir- cuit architecture that offers higher oscillation frequencies than con- ventional fundamental-mode oscillators. In this architecture, the concept of harmonic amplification is used to constructively add the even-order harmonics of the oscillator’s fundamental frequency. Typically, the second-harmonic component is weak, hence a con- siderable amount of power is required to amplify it to an accepta- ble level. A recent work combines the outputs of two quadrature- coupled push-push LC VCOs to generate differential outputs with a two-fold increase in amplitude at the expense of doubling the power consumption as compared to a fundamental-mode VCO [1]. Different techniques have been used to extract the second harmonic from a fundamental-mode VCO [1–3]. These techni- ques are largely based on taking the second harmonic from a common-mode node of the VCO, for example, drain of the tail current source or a tap to the power supply path, and then use power-hungry amplifiers to bring this weak second-harmonic signal to a satisfactory level. In this work, relying on an inherent characteristic of an LC VCO, we create an extra resonance at the second harmonic to increase the desired output amplitude, while reducing the total power consumption of the push-push VCO. 2. ANALYSIS Consider the LC tank of a differential VCO with a center-tapped inductor, as shown in Figure 1. In this differential structure, the fundamental oscillation frequency of the tank (f0) appears as two voltage components in opposite phases at nodes A and B. On
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