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Ultra-Wide Band (UWB) is a promising technology for many wireless applications due to its large bandwidth, good ratio of transmission data and low power cost. the main goal of this work is to design an UWB filter suitable for that purpose. In order to achieve that goal, one UWB filter configuration have been investigated, designed and characterized after analyzing the typical filter parameters, such as the return loss, insertion loss and attenuation characteristics over the full frequency band. Setting the dimensions of the proposed filter in a miniaturized size is a requirement as per user specification. The size of this filter has also been studied because of its important aspect on the frequency behavior.
International Journal of Scientific Research Engineering &Technology (IJSRET) Volume 1 Issue2 pp 004-010 May 2012 www. ijsret.org ISSN 2278 - 0882 A Compact UWB filter for Wireless communication Manidipa Nath AICTR, Department of ECE, New Delhi 700031 email@example.com ABSTRACT where fc is the central frequency and BW is the bandwidth. UWB can operate between 3.1 and 10.6 Ultra-Wide Band (UWB) is a promising technology GHz at limited transmission powers for indoor for many wireless applications due to its large communications, as defined in FCC. bandwidth, good ratio of transmission data and low In 2002, the Federal Communications Commission power cost. the main goal of this work is to design (FCC) of the United States released the frequency an UWB filter suitable for that purpose. In order to band 3.1-10.6 GHz for ultra-wideband (UWB) achieve that goal, one UWB filter configuration have commercial communications. So recently, more been investigated, designed and characterized after attention has been paid to applications of ultra- analyzing the typical filter parameters, such as the wideband (UWB) technology on wireless return loss, insertion loss and attenuation communication system. UWB technology is characteristics over the full frequency band. Setting promising and attractive for local area networks, the dimensions of the proposed filter in a position location and tracking, and radar systems, miniaturized size is a requirement as per user because UWB has thecharacteristics of low cost, high specification. The size of this filter has also been data transmission rate and very low power studied because of its important aspect on the consumption. Many UWB devices and circuits have frequency behavior. been proposed and investigated widely. It is important to reducetheir size and weight in order to Keywords- UWB filter, resonator, miniaturization, integrate them with other components as a compact matching, stub, shortin system. Compact and broadband bandpass filter (BPF) is a key passive component and highly I. INTRODUCTION demanded in a UWB system. A planar BPF, based on a microstrip structure, can provide the advantages of As defined by the Federal Communications easy design, low cost, compact size, and is widely Commission (FCC), UWB technology is to used in a variety of RF/microwave and millimeter- transmit and receive information over a large wave systems to transmit energy in passband and to bandwidth attenuate energy in one or morestopbands. So, These are the two conditions of UWB technology: compact UWB microstrip BPF can be used in a UWB communication system. UWB filters must have a BW > 500MHz fractional bandwidth of more than 70%, and it is very or difficult to achieve such a wide passband with a BW /fc >0:2 traditional parallel-coupled transmission line structure. Therefore, there is a requirement for UWB BPF with a strong coupling structure that can be easily fabricated. In this design, a dual-line coupling IJSRET @ 2012 International Journal of Scientific Research Engineering &Technology (IJSRET) Volume 1 Issue2 pp 004-010 May 2012 www. ijsret.org ISSN 2278 - 0882 structure has been used to implement a strong third resonant mode at the edges of the UWB coupling between the input/output port and the passband. The parallel-coupled lines are modified to resonator, which is more compact than the inter- obtain the ultra-wide passband. This could be done digital coupling structure. A compact UWB by adjusting the coupling length, Lc , for example. microstrip BPF and Notched BPF with low insertion The second type is a hybrid coplanar waveguide loss have been presented and analyzed. In addition, (CPW) and microstrip structure. This type of the UWB filters have extremely compact size of 25 structure consists of a CPW MMR on one side and a mm X 10 mm for BPF and 25 mm X 28 mm for microstrip input and output on the other side . The Notched BPF when the length of the feed lines is CPW MMR is responsible for generating the first and ignored. third resonant mode for the UWB passband, which is After the release of UWB, bandpass filters with a similar to a microstrip MMR in . Its geometry can passband of the same frequency range (3.1 GHz - be varied. Fig. 2 shows the CPW MMR in . The 10.6 GHz, a fractional bandwidth of 110%) were third type of filter which is also able to have a challenges for conventional filter designs. Before mid fractional bandwidth of 110% is the broadside- 2003, the bandwidth of the passband for a bandpass coupled microstrip-CPW structure  shown in Fig. filters was extended from 40% to 70% . These 3. There is a broadside-coupled microstrip line filters are named broad bandpass filters. They were on one side of the substrate [see Fig. 3 (a)] and an not covering the whole UWB frequency range yet. In open-end CPW on the other side of the substrate [see , a bandpass filter covering the whole UWB Fig. 3 (b)]. The length of the coupled line equals to frequency range with a fractional bandwidth of 110% λg/2 in order to obtain a 110% bandwidth. The last was realized by fabrication signal lines on a lossy type of filters that has a bandwidth as high as around composite substrate. A successful transmission of the 100% is the combination of a highpass filter and a UWB pulse signal was demonstrated using the lowpass filter . In , a stepped-impedance proposed bandpass filter. This is one of the early lowpass filter is embedded into a highpass filter with reported filters that possess an ultra-wide passband. quarter-wavelength short-circuited stubs, achieving a However, it has a high insertion loss in the passband passband from 3 GHz to 10 GHz. New fabrication due to the lossy substrate. Not much research work technique, such as Low Temperature Co-fire Ceramic was reported in 2003 and 2004. In 2004, a ring (LTCC), is applied in UWB bandpass filter designs resonator with a stub was proposed which shows a . In , a LTCC bandpass filter shows a bandwidth of 86.6% . A bandpass filter covering bandwidth of 48.75%. This filter has a small physical the whole UWB frequency band was a challenge for size due to the multi-layer configuration. However, microwave filter designers and researchers in that the bandwidth of the passband is relatively small period of time. compared to other UWB bandpass filters and the insertion loss is as high as around 2.2 dB. In 2005, there are 11 conference papers in total published in International Microwave Symposium, In 2006, microstrip MMR based UWB bandpass International Conference on Ultra-Wideband, Asia- filters are further optimized with improvement in the Pacific Microwave Conference, or European rejection of the upper stopband. It can be done by Microwave Conference. In the same year, there are introducing interdigital microstrip coupled lines at four journal publications. There are mainly four types the two sides of the MMR in . A highpass filter of structures that are able to realize an ultra-wide consisting of a transmission line with two embedded passband. One is a microstrip structure shown in Fig. U-shaped slots is cascaded with a lowpass filter 1 . It consists of a microstrip multi-mode resonator which is a dumbbell-shaped defected ground (MMR) and a parallel-coupled line at each end of the structure array in the ground plane, to obtain a network. The MMR has two identical high- passband from 3 GHz to 10.9 GHz . With novel impedance sections with a length of quarter guided highpass and lowpass structures, the bandpass filter wavelength at two sides and a low-impedance section obtains a wider bandwidth than the filter taking a with a length of half guided wavelength in the similar approach in 2005 . With regards to the middle. The MMR in the filter generates first and UWB bandpass filter designs by cascading a highpass IJSRET @ 2012 International Journal of Scientific Research Engineering &Technology (IJSRET) Volume 1 Issue2 pp 004-010 May 2012 www. ijsret.org ISSN 2278 - 0882 and a lowpass filter, a systematic consistent and the application in hand-held devices. A system analytical method is proposed . There are a good integrating both filters and antennas in UWB number of new structures proposed that exhibit an frequency range is very attractive to wireless ultra-wide passband  – . In , 3λg/4 communications using signals in this frequency band. parallel-coupled line resonators shown in Fig. 4 are UWB was originally developed for military used to realize a passband from 3 GHz to 10 GHz. communications and radar. In the field of UWB With the introduction of lumped components to a technology different methods and structures [20- microstrip line, a miniaturized UWB BPF with a 24]has pushed development of new UWB filters . length of 0.18λg is realized at a fractional bandwidth Lumped-element filter design is generally unpopular of 127% at a center frequency of 6.5 GHz . The due to the difficulty of its use at microwave small physical size is attributed to the lumped frequencies along with the limitations of lumped- components used. A broadside coupled line in element values  suspended substrate stripline  can also be used to realize an UWB bandpass filter. A filter with short- II. THEORY circuited stubs could giverise to a UWB bandpass filters with a bandwidth of 110% . The size is another important factor in this work, because the final application requires a small filter In 2007, there are 26 papers reporting new UWB with a diameter around 3.1 cm. This restriction is the bandpass filters which is much more than the hardest specification due to the relationship between previous two years (15 papers in 2005, 18 papers in the size and the frequency.For lower frequencies as 2006). UWB bandpass filters with a notch stopband required in the specifications, the size should be from 5 GHz to 6 GHz for filtering the wireless local- bigger.Thus, the design of a small filter becomes a area network (WLAN) is a new topic branched out in challenging issue. UWB was originally developed for this area  - . Additional components are military communications and radar. In the field of introduced providing the notch stopband at the UWB technology different methods and structures [2- desired frequency. In , an embedded open-circuit 6]has pushed development of new UWB filters . stub is proposed providing a sharp notch stopband. It Lumped-element filter design is generally unpopular is integrated into a UWB bandpass filter providing due to the difficulty of its use at microwave the stopband from 5 GHz to 6 GHz. A stub is frequencies along with the limitations of lumped- introduced in the broadside-coupled microstrip-CPW element values . Hence, conventional microstrip structure  to generate a notch stopband at WLAN filters are often used. The new proposed filter design frequency range. Other than adding stubs to the is based on quarter wavelength short-circuited stub. structure, in , a notch stopband is generated in the In order to reduce filter size, bending connecting line UWB passband by an asymmetric parallel-coupled and let five short-circuited stubs via the same hole is line at two sides of a microstrip MMR. designed .Consequently,half hexagon UWB filter was simulated and optimized for its best achievable There are three main existing approaches to realize a performance. UWB bandpass filter. One is a microstrip or CPW MMR with the assistance of coupling mechanisms, The paper focuses the on systematic design and such as microstrip coupled line or coupling at the realization of a ultra wideband filter in printed circuit transit between a microstrip line and a CPW. configuration.The UWB filter has as one input and Broadside-coupled microstrip line with a CPW at the one output port.The filter is of hexagonal shaped back is another important configuration. The third microstrip configuration.The length and width of one is a direct or indirect combination of a lowpass fingers of the connecting lines are taken as design and a highpass filter. In terms of miniaturization, the parameter for optimization. The MOM simulation employment of LTCC or lump components is an tools used to investigate the performance of the this effective means to significantly reduce the size of the filter and the combined responses for structure. For future development and research in this ultrawideband.It is designed as per FCC area, miniaturization of UWB filters is important for recommended band from 3.1-10.6 GHz. It was IJSRET @ 2012 International Journal of Scientific Research Engineering &Technology (IJSRET) Volume 1 Issue2 pp 004-010 May 2012 www. ijsret.org ISSN 2278 - 0882 observed that the design dimensions are critical in stubs and the characteristic impedances of the deciding the filter responses. The line dimension and connecting lines are choosen at 3.1 GHz. coupling gaps are optimized to meet the specification and final pcb design is generated. The UWB filter is III. DESIGN designed to provide an Insertion Loss ≤ 1 dB and average roll off of 30 dB/decade. Simulated results To meet the design criterion particularly the predicts performance of the filter as per FCC bandwidth and size a half hexagonal microstrip Standard. The filter hardware based on the optimized structure with shorting pin configuration has been design has been fabricated and tested.The choosen. The filter design has been implemented on a measurement results are quite encouraging. high frequency circuit board.Here the substrate used is 25 mil(dielectric constant 10, loss tangent 0.009).A The structure under consideration consist of a TEM detail analysis has been done to find the response of mode or quasi-TEM mode transmission line the structure under consideration(Fig 2) using resonator elements arranged in a half hexagonal moment method and FDTD solver. It has been seen pattern. Each resonator element has an electrical that the bandwidth criterion (3.1-10.6 GHz.) is length of 90 degree at the midband frequency and is fulfilled with this structure and the size is perfect to short circuited at one end. The resulting filter is put in a predefined package for testing and compact and the tolerance required in their measurement.The shorting pin is used to suppress the manufacture are relatively relaxed. The second pass unwanted mode that may lead to additional loss for band of this filter is centered at about 3 times the this filter configuration.Final design has been midband frequency of the desired first pass band optimized several times for getting best filter while there is no spurious response in between. response over the frequency band of operation”. Another advantage is that the filter can be fabricated in structural forms which are self supporting so that dielectric material is not required to be used. An exact analysis of the structure is very tedious. Hence a synthesis procedure is followed which involves a number of simplifying approximations that permit straightforward, easy to-use design calculations. However these approximate design equations are found to be sufficiently accurate for most practical applications. The new proposed filter design is based on quarter wavelength short-circuited stubs. Here five short- circuited stubs was designed for an optimum distributed band pass filter performance whose connecting lines are non-redundant . Thus, the Figure 1.Simulation result of UWB filter(before filter can exhibit a frequency selectivity equivalent to optimization) that of a conventional 9-pole Chebyshev filter. But an optimum distributed high-pass filter requires a greater area. In order to reduce the filter size , the connecting line had been reduced.Thus, let 9-pole decrease to 5-pole, even though frequency selectivity of 5-pole is not better than 9-pole. However, circuit dimension can be reduced very much. The characteristic impedances of these short-circuited IJSRET @ 2012 International Journal of Scientific Research Engineering &Technology (IJSRET) Volume 1 Issue2 pp 004-010 May 2012 www. ijsret.org ISSN 2278 - 0882 Figure 4. UWB filter configuration with package. Fig2. Simulated S-Parameters of UWB Filter V. MEASUREMENT The fabricated filter was measured for transmission and reflection performance with the help of Network Analyzer (E8363B).The measured attenuation and VSWR plot of the filter is shown in figure(3-4).The fractional bandwidth is 0.76 instead of the design value 0.868 & simulation value 0.78, which indicates a shrinkage of bandwidth of 12.6 % as a result of various approximation involved in the design equations and due to fabrication inaccuracies.The insertion loss is found to be 3.5dB (average) over the band. The fabrication process is required to be better to improve this loss figure. The other performance is seen to be satisfactory. Figure 3.Simulation Result of UWB Filter(after optimization) IV. CHARACTERIZATION The filter layout has been fabricated using CER-10 with best precession available.The Final circuit after integration and packaging undergone for testing.Inital measurement results shows good filter characteristic over the whole UWB band.The measured return loss over the band is 1.0 dB(average).This loss can be further reduced using low loss substrate and SMA connectors. Figure 5 Attenuation Measurement of UWB Filter IJSRET @ 2012 International Journal of Scientific Research Engineering &Technology (IJSRET) Volume 1 Issue2 pp 004-010 May 2012 www. ijsret.org ISSN 2278 - 0882 passband are equal to 3.9 GHz and 11.2 GHz against their counterpart frequencies of 3.935 GHz and 10.81 GHz in the simulation. Furthermore, the UWB filter has achieved the return loss of less than -10 dB from 4 to 10.5 GHz. VII. CONCLUSION Compact UWB microstrip BPF have been designed using the structure having half hexagon resonator with the five stubs. The compact UWB filters have beenfabricated, and tested. The fabricated UWB BPF has a 7.3 GHz passband, -10 dB return lossbandwidth of 6.5 GHz. These results have indicated a very Fi goodagreement between simulation and gure 6. VSWR Plot of UWB Filter measurements. VIII. REFERCES 1. Federal Communications Commission, "Revision of Part 15 of the Commission's Rules Regarding Ultra-wideband Transmission Systems", Tech. Rep.,ET-Docket 98-153, FCC02-48, April 2002. 2. J.-T. Kuo and E. Shih, "Wideband bandpass filter design with three-line microstrip structures", IEE Proc.-Microw. Antennas Propag., Vol. 149, No. 5/6, October/December 2002, pp.243-247. 3. A. Saito, H. Harada, and A. Nishikata, “Development of Band Pass Filter for Ultra Wideband (UWB) Communication Systems,” International Microwave Symposium, Philadelphia, Pennsylvania, USA, June 2003. 4. H. Ishida and K. Araki, “A Design of tunable UWB Filters,” International Microwave Symposium, Fort Worth, Texas, USA, June 2004. 5 L. 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