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1、 外文翻译题目：紧凑的高阶谐波抑制Compact Multi-harmonic harmonic Compact Multi-harmonic suppression LTCC Bandpass Filter Using Parallel Short-Ended Coupled-Line Structure Xu-Guang Wang, Young Yun, and In-Ho Kang This paper presents a novel simple filter design method based on a parallel short-ended coupled-line str
2、ucture with capacitive loading for size reduction and ultra-broad rejection of spurious passbands. In addition, the introduction of a cross-coupling capacitor into the miniaturized coupled-line can create a transmission zero at the second harmonic frequency for better frequency selectivity and atten
3、uation level. The aperture compensation technique is also applied to achieve a strong coupling in the coupled-line section. The influence of using the connecting transmission line to cascade two identical one-stage filters is studied for the first time. Specifically, such a two-stage bandpass filter
4、 operating at 2.3 GHz with a fractional bandwidth of 10% was designed and realized with low-temperature co-fired ceramic technology for application in base stations that need high power handling capability. The measured and simulated results showed good agreement. Keywords: harmonic bandpass filter,
5、 LTCC. suppression, coupled-line, I. Introduction In recent years, compact, high-performance, and low-cost components for radio frequency (RF) applications have been the focus of a great deal of research and industrial pursuit with the explosive growth of modern wireless communication services. One
6、promising method for many miniaturizing and packaging technologies is to use low-temperature cofired ceramic (LTCC) on account of its multilayer structure and high unloaded quality factor. The bandpass filter is an essential component in the RF front-end of communication systems. It passes the desir
7、ed frequencies, rejects unwanted signals, and suppresses harmonics. However, as a result of the distributed characteristic of the transmission line, undesired spurious passbands or harmonics are a problem for conventional filters and can seriously degrade their performance, which may be critical in
8、certain applications. To find a way to suppress spurious responses, many studies have been carried out. Using the technique of photonic bandgap (PBG) and defected ground structure (DGS) is one of the most popular approaches. The PBG structure was initially proposed in the optical field, and essentia
9、lly comprises periodic etched defects on the back of a metallic ground plane which can provide effective and flexible control of the propagation of electromagnetic (EM) waves along a specific direction or in all directions. Since it was applied to microwave and millimeter frequency-band applications
10、, numerous novel PBG structures have been proposed for the design of both passive and active devices with the property of multi-harmonic suppressionHowever, Manuscript received July 6, 2008; revised Feb. 27, 2009; accepted Apr. 7, 2009. Xu-Guang Wang was with the Department of Radio Science & Engine
11、ering, Korea Maritime University, Busan, Rep. of Korea, and is now with the Department of Electronic Engineering, Sogang University, Seoul, Rep. of Korea. The DGS with periodic or nonperiodic arrays is another very practical approach because it can provide a rejection band in some frequency ranges.
12、Compared with the PBG structure, which needs many units to build a filter, the DGS is simpler because only a few units can be used to construct a filter, and this results in a smaller filter size. The rejection characteristic of the DGS is available to many microwave circuits, such as power-amplifie
13、r modules, planar antennas, power dividers and filters, and so on . However, due to the periodic structure of the PBG and DGS, these filters suffer from their large circuit areas and specific circuit configurations, which seriously hinder their application to wireless communication systems. In this
14、paper, we propose a compact multi-harmonic suppression LTCC bandpass filter based on the capacitive loading of the parallel short-ended coupled-line structure. This is a relatively simple way of reducing the coupled-line electrical length, which usually plays a decisive role in the filter size. On t
15、he other hand, the use of lumped elements can effectively suppress the spurious passbands. In addition, the cross-coupling capacitor and aperture compensation technique are employed for better performance. Such a compact twostage bandpass filter working at 2.3 GHz with high power handling capability
16、 was implemented in a multilayer LTCC substrate and examined carefully. Design Theory 1. Size Reduction Method Figure 1(a) shows the generalized bandpass filter structure to be miniaturized in this design. The admittance inverter, which is a quarter-wavelength transmission line with characteristic i
17、mpedance Z0 = 50 ?, can be replaced with a lumped circuit as shown in Fig. Improvement of the Filter Performance The attenuation level at the second harmonic frequency can be further improved by employing the cross-coupling capacitor CC in the miniaturized coupled-line section as shown in Fig. 3(a),
18、 which can create a transmission zero such that a sharper falloff rate at the right passband edge is obtained. The presence of this transmission zero (as long as it is not too close to the passband) does not change the passband characteristics of the filter too much. Figure 3(b) shows the equivalent
19、 lumped circuit of the final miniaturized one-stage bandpass filter, from which we can see that it is the dotted resonator that creates the transmission zero in the upper stopband. Therefore, the location of this transmission zero may easily be adjusted by varying the capacitor value. Figure 4 shows
20、 the simulated filter responses for different values of the capacitor CC. With nearly the same passband performance, the attenuation poles are located at the frequencies of 3.3 GHz, 3.9 GHz, 4.6 GHz, and 5.5 GHz when the capacitor values are 1.5 pF, 0.8 pF, 0.5 pF, and 0.3 pF, respectively. However,
21、 it should be noted that the stopband attenuation levels differ in these different cases. By selecting the capacitor value properly, it can be designed to achieve a transmission zero to suppress the second harmonic with same passband response as the proposed filter in the previous subsection. 3. (a)
22、 Final structure of the miniaturized one-stage bandpass filter with a transmission zero and (b) its equivalent lumped circuit. also suppress the spurious response resulting from cascading as explained in detail in the next section. Note that the insertion of this cross-coupling capacitor will change
23、 the coupling situation of the coupled-line. In the proposed design, it is coupled both electromagnetically and electrically through CC, whereas the initial coupled-line is coupled only electromagnetically. Consequently, some modifications of the parameters of the coupled-line are necessary. This is
24、 not a troublesome problem since we can use Agilents Advanced Design System (ADS) to find the proper new parameters quickly, which will also be expounded in detail in the next section. In this case, the spacing between two strip conductors is usually smaller than that for a conventional parallel cou
25、pled-line, which means that the EM coupling is larger. However, the narrow spacing may only be reduced to a certain extent due to the limitation of fabricating tolerance. To relieve this limitation and realize a tightly coupled section, the aperture compensation technique is applied in this study. F
26、igure 5 shows a schematic layout of the coupled striplines in which a wide aperture with rectangular configuration is formed on both ground planes over and underneath the coupled striplines in the center. This aperture has an effect on the equivalent capacitances between the strip conductors and the
27、 ground as shown in Fig. 5. With this aperture, the even-mode characteristic of the coupled striplines increases as the effective 256 Xu-Guang Wang et al. 5. However, the odd-mode characteristic remains nearly the same because its value is mainly determined by C12 which is barely influenced by the a
28、perture. As a result, coupling coefficient K could be increased tremendously. Filter Implementation with LTCC Technology Table 1 gives the specifications of the desired compact twostage bandpass filter. The first step was to obtain the circuit parameters of the one-stage filter according to the desi
29、red specifications and fine tune each element value. Then, two identically tuned filters were cascaded through a short connecting transmission line 17. After converting the circuit parameters to physical filter structures, some necessary tuning and optimizations were carried out to accommodate the p
30、arasitic effects of each lumped element, mutual coupling effects between elements, and to finalize the layout design by employing a full-wave EM simulation tool. Finally, the designed bandpass filter was fabricated with multilayer LTCC technology and carefully examined. To design the filters in a ti
31、me-efficient way, we adopted both the circuit simulation software Agilent ADS and the full-wave 3-D EM simulation tool Ansoft HFSS to expedite the otherwise difficult work. Fig. 6. Simulated frequency responses of both the initial miniaturized bandpass filter and its modified version in ADS. 1. Circ
32、uit Simulation First, a one-stage bandpass filter was designed to have a center frequency of 2.3 GHz with a fractional bandwidth of 10%. The bandwidth of this proposed filter depends on the coupling coefficient K. When K increases, the bandwidth becomes broader, and vice versa 18. Therefore, the ban
33、dwidth of the filter can be controlled by varying the coupling coefficient when the quarter-wavelength transmission line is miniaturized. However, the broad bandwidth leads to a large coupling coefficient K, and accordingly, there is a great difference between Z0e and Z0o, which results in a large e
34、lectrical length of the coupled-line. Therefore, a necessary design trade-off between broad bandwidth and small circuit size should be considered. Then, the cross-coupling capacitor CC was inserted to realize a transmission zero at 4.6 GHz for better upper skirt characteristic and second harmonic su
35、ppression. As previously mentioned, the insertion of CC leads to tight coupling; thus, we have to decrease the odd-mode impedance Z0o of the coupled-line and keep the even-mode impedance the same. The resulting circuit can be optimized with ADS to achieve the desired filter responses. This optimizat
36、ion process is very time-efficient because it is a lumped element circuit simulation. Here, the cross-coupling capacitor CC of 0.5 pF and the odd-mode impedance Z0o of 36.6 ? are the optimum values in this design. The ADS simulated results of the initial miniaturized filter and its modified version
37、are plotted and compared in Fig. 6. Obviously, without affecting the fundamental frequency response, the modified filter performance achieved significant improvement as we expected by trading off the attenuation level at the far end of the upper stopband and no spurious response appeared. The final
38、two-stage bandpass filter can be achieved by simply connecting two identical obtained circuits using a short transmission line. However, this connecting line will generate an extra spurious response unless its electrical length is 0, which is impossible in the practical situation. Figures 7(a) and (
39、b) show the spurious response in both cases of cascading the initial miniaturized one-stage bandpass filter and cascading its modified version with a transmission zero. Specific studies on the connecting transmission line have ETRI Journal, Volume 31, Number 3, June 2009 Xu-Guang Wang et al. Spuriou
40、s response resulting from the connecting transmission line: (a) cascading the initial miniaturized one-stage bandpass filter and (b) cascading its modified version with a transmission zero. Fig. 8. Simulated frequency responses in ADS according to (a) the electrical length of the connecting line and
41、 (b) the impedance of the connecting line. 2. Full-Wave EM Simulation and Optimization Once the bandpass filter equivalent circuit model was developed, physical filter structures such as resonators and coupled-line sections could be designed. However, it is important to note that the synthesized fil
42、ter model could not be transformed into physical structures at one time due to parasitic components (both internally and externally). As a result, either an optimization of the physical filter dimensions or a tuning of the filter responses is necessary. Usually, this is carried out using Ansoft HFSS
43、 until the EM simulation shows a performance close to the target one. As in the simulation procedure in ADS, a one-stage bandpass filter was first implemented in a seven-layer LTCC substrate, which has a dielectric constant of 5.6 and a metal thickness of 15 m. The distances between the metal layers
44、 are 585, 650, 20, 20, 650, and 200 m consecutively from the top. Figure 9(a) displays the 3-D physical architecture. The parallel coupledline is realized at layer 4 using stripline form because the dispersion and radiation of the stripline are negligible, and the upper and lower ground planes provi
45、de effective shielding. The been done with ADS. It has been found that the location of this spurious band is closely related to the electrical length and the impedance of the connecting line; thus, we can shift the peak of the spurious band to the transmission zero frequency to suppress it. Figure 8
46、(a), which gives the simulated results for various electrical lengths of the connecting line with the same impedance of 50 , indicates that a longer electrical length causes the spurious band peak to shift to a lower frequency. Figure 8(b) shows the frequency response in response to various impedanc
47、es of the connecting line with the same electrical length of 6.15. It can be seen that as the impedance of the connecting transmission line gets higher, the peak of the spurious band moves to a lower frequency. Therefore, based on the simulation results, a connecting transmission line with an electr
48、ical length of 6.15 and an impedance of 50 , which can move the peak of the spurious band to the second harmonic frequency, is adopted to make the undesired spurious band disappear in this design. 258 Xu-Guang Wang et al. ETRI Journal, Volume 31, Number 3, June 2009 Via-holes Ground CC Feed line (CP
49、W) Insulator CL Coupled-line Ground Fig. 10. 3-D view of the PCB environment. (a) LTCC layout of the designed one-stage bandpass filter and (b) the detailed capacitor configuration. capacitors are implemented on layers 3, 4, and 5 using the simple metal-insulator-metal structure. The detailed capacitor configuration schematic is shown in Fig. 9(b). Layers 2 and 6 are the stripline ground with rectangular configuration apertures over and underneath the coupled striplines. The minimum spacing between the coupled stripline conductors with
