диафрагмированные волноводные фильтры / 13ca9c4e-cdd0-4779-bdda-3c6e216aa96c

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VC 2015 Wiley Periodicals, Inc.

DESIGN AND PERFORMANCE ANALYSIS OF METALLIC POSTS COUPLED SIWBASED MULTIBAND BANDPASS AND BANDSTOP FILTER

Amit Patel, Yogeshwar Prashad Kosta, Alpesh Vala, and Riddhi Goswami

Department of Electronics and Communication, Chandubhai S Patel Institute Technology, Charotar University of Science & Technology, Anand 388421, Gujarat, India; Corresponding author: amitvpatel.ec@ecchanga.com

Received 13 November 2014

ABSTRACT: This article consists of the design of single band bandpass filter, multiband bandpass filter, and multiband bandstop filter based on a substrate integrated waveguide technique. First, proposed structure of single band bandpass filter has been designed with the combination of inductive and capacitive metallic posts at 14.8 GHz center frequency of Ku band application. Moreover, the tuning scheme for frequency has been also demonstrated for the same band. Similar concept has been applied for the design of multiband bandpass filter keeping distance between posts as a function of guided wavelength. In addition to above, multiband bandstop filter has been proposed by providing E-plane dis-

continuities with the use of the metallic edge (by putting multiple cylinder posts). The effect of position of the metallic edge on the performance has been observed and analyzed. All the proposed structures have been simulated by Ansoft High frequency structural simulator and its equivalent models by Ansoft system designer (which compared and shows its performance parameters are equal and they are sensitive to parameter variations). VC 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1409–1417, 2015; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.29105

Key words: substrate integrated waveguide; bandpass filter; bandstop filter; high frequency software simulator

1. INTRODUCTION

The numbers of microwave and millimeter components have been designed such as filter, coupler, power divider, antenna, circulator, and so forth based on post wall waveguide proposed by F. Shigeki [1] in 1994 and microstrip-line techniques. Conventional methods such as a planar microstrip line and nonplanar waveguide for the designing of passive filter component have certain disadvantages. Microstrip line has low power handling capacity and due to the openness of the structure radiation loss occurs [2]. Conversely, nonplanar waveguide (Metallic hollow waveguide) is available with high cost, weight, and with large physical size. The substrate integrated waveguide (SIW) represents good candidate for the design of microwave and millimeter wave component due to high power handling capacity, light weight, and high density integration of active and passive components [1]. As per need of, wireless and satellite communication systems, a low cost low profile planar resonator (SIW) is used in place of microstrip line and rectangular waveguide resonator [1].

The requirement of microwave filters having multiple pass band and wide spurious free frequency ranges are increasing in the rapid development of wireless communication systems. Many techniques have been developed for the design of multiband bandpass and bandstop filter based on conventional microstrip and rectangular waveguide [3–6]. However, tuning of frequency in microstrip line is very difficult and it required individual frequency resonant structures [7]. In waveguide, it is possible using either electronically or mechanically tunning but the cost increased the weight of structure and due to high order mode excitation outer region of band degraded. SIW is one of the intermediate solutions of design multiband bandpass and

bandstop filter. However, improving stopband response in SIW, it is difficult to utilize E-plane discontinuities on a single layer substrate compare with rectangular waveguide [7]. In Ref. 8, by cascading circular and rectangular cavities, stopband has been achieved based on SIW. Numbers of structures have been proposed for the design of bandpass filter based on SIW [9,10]. A wideband bandpass filter with the use of defected ground structure and electromagnetic band gap structure based on SIW has been designed in [11].

A dual band bandpass filter has been designed using four double folded SIW resonators and it is fabricated using low temperature cofired ceramic technology. Tuning of frequency is also created for the one passband while maintain second one stable. To create transmission zero near the passband edges, source load coupling is also used [12]. Tunable filter using MEMS varactor diode, using ferroelectric material, using ferromagnetic material has been presented in this literature. Also an overview is also presented for the tunable radio frequency and microwave tunable circuit [13]. A bandpass filter design has been designed for the X-band of frequency range using SIW based on defected ground structure. Mineral type of defect has been used on the top of the structure for the reduction in size of the structure. Further, three cascades defected cell is used to achieve low insertion loss, good return loss, compact size as well as smooth group delay [14]. A bandpass filter has been designed for a center frequency of 25.5 GHz with the use of flexible liquid crystal polymer as a substrate material. With the use of this liquid crystal parameter as a substrate further reduce in the size of 75 percent in the area of the structure.

This article contains, multiple transmission and reflection zeros which generated by the position of multiple metallic posts (coupled the higher order modes) for improving the performance of bandpass and bandstop filters. By putting the posts at multiple of guided wavelength generates bandpass response which is shown in Section 3. Section 4 shows the multiband bandpass fil-

Figure 3 Simulated scattering parameter of SIW structure. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com]

ter having the same design concepts of single band bandpass filter but increasing distance between two post, structure resonant at higher order modes. Finally, bandstop filter has been designed based on putting metallic posts in angular manner with respect to traveling of waves in Section 5.

2. REALIZATION OF SIW

The basic structure of SIW is shown in Figure 1 in which top metal layer and ground layer within a substrate is connected by metallic vias. In this way, hollow metallic nonplanar waveguide can be created in the form of planar wave structure [2]. The propagation characteristics of a SIW structure such as field pattern and dispersion are similar to that nonplanar waveguide [1]

As shown in Figure 1, h is the height of the substrate, w is the width of the waveguide, p is the center to center distance between two metallic posts, and d is the diameter of the metallic vias. As we are aware that basically waveguide acts as a highpass filter and pass the energy depending on the cutoff frequency on which it has been designed. The cutoff frequency of the SIW is decided based on the height and width of the planar structure [15]. In SIW, the width between two posts can be calculated using equation

where aequ is the lateral center to center distance between two vias and can be calculated from the cutoff frequency equation [15]

where fc is the cutoff frequency, c is the velocity of light in free space (3 3 108 m/s), and er is the relative permittivity of the substrate material. Spacing between the posts (p) and the diameter (d) of post should be decided such that they should satisfy the condition shown in Eq. (3) otherwise it increases the dispersion loss[].

With the use of above equation, we have designed rectangular SIW for the specification given in Table 1.

With the use of above equations, we have designed X-band SIW for the cutoff frequency of 8 GHz (consider the fundamental mode is TE10). Figure 2 shows the electric field distribution within a SIW structure. For the feeding purpose and transition

from microstrip line to the waveguide, tapered microstrip line is inserted. We have selected Arlon (AD300A) as the substrate material having a permittivity of 3, height (h) of the substrate is equal to 0.507 mm, the diameter (d) of the post is 1.4 mm, center to center distance (p) between the two posts is 2 mm, and width (w) of the waveguide is equal to the 11.83 mm. Simulate scattering parameters (S11 and S21) of the structure is shown in Figure 3 provides cutoff frequency at 8 GHz and reflection coefficient has a value more than 15 dB. Equivalent LC model and its scattering parameter of the structure that we have implemented in ADS simulator are shown in Figure 4.

3. DESIGN OF SINGLE BAND BANDPASS FILTER FROM SIW STRUCTURE

Bandpass filter is an essential device in wireless and satellite communication for frequency selective application. Here, we

have designed bandpass filter for Ku band based on SIW technique (coupled metallic posts). As we know that metallic post can be used as an impedance changing device within a structure, because it generates the effect of inductance or capacitance depending on penetration of post (when metallic post penetrates inside SIW such that it connects the top and bottom plane of the structure then it reacts as an inductor, and if the metallic post placed partially felt into the structure, it reacts as a capacitor) [16].

Here, we have used eight metallic posts within structure which react as resonators. Geometry view for the placement of the post in the structure is shown in Figure 5. Two posts are placed on same vertical alignment and repeat the same structure four times periodically. The complete geometry of the structure that has been implemented in high frequency structural simulator (HFSS) is shown in Figure 6. As we are aware that when we

Figure 5 Views of placement of post in design for the bandpass filter. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com]

Figure 6 Complete geometries of the bandpass filter design implemented in HFSS. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com]

transform LPF element into bandpass element, at that time, inductor will replace by series LC element and capacitor is replaced by parallel LC element. Same technique is applied here and its equivalent model is implemented in ADS software which is shown in figure.

Simulated scattering parameters of the proposed structure are shown in Figure 7. Proposed structure provides pass band of 0.8 GHz starting 3 dB frequency from 14.30 to 15.10 GHz. The proposed filter provides good selectivity within a pass band region having the insertion loss of 0.2 dB and return loss more than 20 dB.

TABLE 2 Numerical Value for Tuning of Frequency by Changing the Distance Between the Two Posts

Tuning of frequency has been carried out using two techniques. First, changing the distance between two metal posts which ultimately change the value of inductance and capacitance. Figure 7 shows the characteristic of reflection coefficient for the different values of B (distance between metallic posts). A relative detail of the Figure 8 is numerically mentioned in Table 2. By changing distance between posts, this structure can transform passband at any frequency of Ku

TABLE 3 Numerical Value for Tuning of Frequency by Changing the Diameter of Post of Figure 8

band. Second, changing the diameter of the post, tuning of frequency has been carried out. Table 3 shows the detail of the passband frequency, insertion loss, and return loss by changing the diameter of post.

An equivalent LC circuit of the proposed structure and its simulate scattering parameter that we have implemented in ADS are shown in Figure 9.

A multiband bandpass filter has been designed with the use of inductive resonator post. The geometry view of the proposed

Figure 10 Placing of post for the multiband bandpass filter. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary. com]

structure is shown in Figure 10 which is based on the structure that we have implemented in hollow rectangular waveguide in [16]. The same technique has been adopted in the SIW structure with corresponding in the reduction of the size as compared with hollow rectangular waveguide.

In first structure, we have placed four posts with the lateral distance between the two posts equal to the one guided wavelength (21.65 mm) and in the second structure, lateral distance between two posts is 1.75 times the guided wavelength (32.75 mm) and the wider distance between the two posts is 6 mm. Placing the resonator at one guide wavelength intervals results in strong interaction among the fringing field in the vicinity of the coupled posts [16–19].

Simulate scattering parameter of the structure when the distance between two posts is one guided wavelength is shown in Figure 11. It provides multiple pass bands in Ku band of frequency range with the passband frequency equal to 250 MHz. Simulate scattering parameter of the structure when the distance between two posts is 1.75 times the guided wavelength is shown in Figure 12. With the use of this proposed structure, it is possible to create multiple pass bands in the Ku band of application (Tables 4 and 5).

Many techniques have been developed for the utilization of bandstop filter, for the hollow rectangular waveguide like iris, cavity coupled, and so forth, but the minor work done has been carried out in implementation of bandstop filter [3–6]. These techniques were utilized to provide discontinuities in either electric or magnetic field. However, it is difficult to realize this technique in the single layer substrate such as SIW [7]. In Ref. 17, a metallic edge with arbitrary length and inclination angle is embedded in the coplanar hollow rectangular waveguide for

transforming performance from highpass filter to bandstop filter. We have adopted and implemented similar technique to realize the bandstop filter performance into SIW.

A metallic edge (five connected posts) having a finite length and inclination angle h (angle of metallic edge with respect to the second row of posts, keeping less than 90 ) has been placed with respect to the second row of post as shown in Figure 13. Subtract height, diameter, and spacing of metallic post are kept same as above structure.

Figure 13 Wire-line structure of the proposed bandstop filter

Figure 14 Electric field distribution of bandstop filter in HFSS. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com]

The height of the metallic edge cylinder is equal to 0.407 mm and it is placed 0.1 mm above the ground (generate capacitive effects). Diameter of metallic edge cylinder is 0.8 mm. Here, we have observed that as the value h tends to increase toward the 90 , electric field within a structure attenuates more (As it generates parallel and series resonant of LC structure), means as h increase toward the 90 , the reflection coefficient value S11 goes toward the 0 dB. Similarly, as value of h increase toward the 0 , value of S11 increase toward the higher value. The complete view of the structure along with its electric field distribution that we have implemented in HFSS is shown in Figure 14.

Simulated S12 (transmission coefficient) and S11 (reflection coefficient) for the different value of inclination angle h are shown in Figure 15. From the figure, as the value of inclination angle decreases, reflection coefficient S11 tends to increase toward the higher value.

Simulated S11 and S12 parameters for the angle h 520 is shown in Figure 16. It provides two stop band. Its frequency range starts from 15.15 to 15.47 GHz and from 16.37 to 16.65 GHz. Insertion loss within a stopband is 230 dB for first band and 222 dB for the second band which gives quite good isolation between passband and stopband.

Its equivalent model is implemented in ADS and results are verified by HFSS which is shown in Figures 17(a) and 17(b). Both the results have matched with each other proved performance is equal in both the platform.

5. COMPARISON AND DISCUSSION

We have compared the proposed bandstop filter with traditional models like waveguide filter loaded with artificial SNG or DNG

particles and waveguide filter using split ring resonator in terms of band, 23-dB bandwidth, power handling capacity, passband and stopband loss as shown in table. From the table, it is clear that SIW-based bandstop filter is superior in characteristics compared with waveguide. However, narrow bandwidth is one of the drawback of this type of model.

6. CONCLUSION

We have presented the concept for the designing of bandpass filter and bandstop filter based on post coupled SIW technique. The first proposed model consists of single band bandpass filter design for the Ku band application. Any passband with a specific center frequency can be possible by changing the relative distance between metallic posts and varying diameter of posts, with lower insertion loss, return loss, compact size, and less complexity achieved. A multiband bandpass filter has been achieved with the use of four metallic posts for the frequency range of 9–18 GHz. Depending on the requirement of number of passband, at a particular, center frequency can be designed by placing the post at a particular distance as a function of the guided wavelength. Another proposed structure consist of bandstop filter, it is designed with the use of the metallic edge placed at a certain angle (less than 90 ) with respect to the second row of the metallic post. It gives narrow bandwidth bandstop filter with higher quality factor which is used in rejecting spurious harmonics in Ku band. A proposed structure provides relatively less complex structure and easy to design as compared with [7,8]. Furthermore, it may be possible wideband bandstop filter can be designed with such metallic edge using less lossy substrate material such as a Duroid compared with Arlon.

REFERENCES

1.M. Bozzi, F. Xu, D. Deslandes, and K. Wu, Modeling and design considerations for substrate integrated waveguide circuits and component, In: IEEE-8th International Conference on Telecommunication in Modern Satellite, Cable and Broadcasting Services, Serbia, 2007, pp. 7–13.

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3.A. Shelkonikov, N. Suntheralingam, and D. Budimir, Novel SRR loaded waveguide bandstop filters, In: Antennas and Propagation Society International Symposium, Albuquerque, NM, 2006, pp. 4523–4526.

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VC 2015 Wiley Periodicals, Inc.

1. INTRODUCTION

Bandpass filters (BPFs) have become the key component in the RF front ends of both the receiver and transmitter circuits [1–4]. Many efforts and methods focusing on BPFs with compact size, high selectivity, sharp rejection, and wide bandwidth have been proposed. Resonators, as the main part of filters, usually determine their performance. Recently, using multimode resonators to construct BPF has gained more and more attention. In [5], a dual-mode open-loop resonator was proposed that results from different locations of the transmission zero (TZ). However, the problem is that only one TZ results in poor selectivity and limited bandwidth, which constrains its application. To improve the performance of dual-mode resonator (DMR), triple-mode resonators (TMRs) were proposed in [6–8]. However, the enhancement of the bandwidth and selectivity were not sufficient and the emergence of via led to a complicated fabrication process. Recently, quad-mode resonators (QMRs) were reported. In [9–11], stub-loaded QMRs were constructed to achieve a dualmode dual-band BPF, a via was added to the stub for the purpose of splitting the four modes into two dual-modes. In [12], the QMR was applied for the quad-band application by fully using each modes generated from the QMR. Therefore, a conclusion can be obtained based on [9–12]—none of them result in a wide bandwidth and relatively high selectivity. Although these BPFs in [9–12] achieved a compact size due to the reason of only one QMR involved in the design, the properties of wide bandwidth and high selectivity of QMR were neglected because of the split of four modes. It was the main reason that BPFs in [9–12] were not good at bandwidth and cut-off response. Furthermore, the introduction of via led to a difficult fabrication process.

In this article, a highly selective dual-wideband BPF using two QMRs is proposed. The proposed QMR is composed of two

HIGHLY SELECTIVE DUAL-WIDEBAND BANDPASS FILTER USING QUAD-MODE RESONATORS FOR WLAN AND WIMAX APPLICATIONS

T. Qiang, C. Wang, and N. Y. Kim

RFIC Center, Kwangwoon University, 447-1 Wolgye-dong, Nowonku, Seoul 139-701, Korea; Corresponding author: nykim@kw.ac.kr

Received 13 November 2014

ABSTRACT: A highly selective dual-wideband bandpass filter (BPF) using quad-mode resonators (QMRs) is presented. The proposed QMR loaded with two folded open-ended stubs and a T-shaped stub exhibits not only four transmission poles but also two transmission zeros, which results in a wider bandwidth and sharper cut-off responses. The dualband performance is realized with two QMRs sharing a common input and output. Four transmission zeros are found located at 2.09, 2.67, 3.18, and 4.14 GHz, with an attenuation level that is less than 220 dB. The measured center frequencies of the two operation passbands are 2.4 (WLAN) and 3.5 GHz (WiMAX), and the minimum insertion loss of the two passbands are 0.87 and 1.4 dB, with 3 dB fractional bandwidths of 17.5% and 16%, respectively. The stopband suppression is greater than 20 dB from 4.2 to 6.5 GHz. Good agreement between the simulated and measured results demonstrates the validity of the proposed BPF. VC 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1417–1423, 2015; View this article online at wileyonlinelibrary.com. DOI 10.1002/ mop.29100

Key words: highly selective; dual-wideband; bandpass filter; quadmode resonator; stopband suppression

Figure 1 (a) Schematic diagram of the proposed QMR and (b) equivalent circuits under even-odd-mode analysis