IEICE Electronics Express, Vol.5, No.8, 291–295
Two-layered ultra-wideband (UWB) bandpass filter Daisuke Kuritaa) and Keren Lib) National Institute of Information and Communications Technology, YRP–1, 3–4, Hikari-no-oka Yokosuka-shi, 239–0847, Japan a)
[email protected] b)
[email protected]
Abstract: In this paper, a two-layered ultra-wideband (UWB) bandpass filter has been proposed and developed. The filter consists of two-layered dielectric substrate and one metal layer, modified from our original UWB bandpass filter using a single-layer microstrip-CPW (coplanar waveguide) structure. To miniaturize the filter length, a folded CPW, short-circuited at the right end, was introduced to reduce the length of the CPW. In this two-layered structure, we discovered from our simulation and experiments that some configuration of the filter can produce transmission zeros at the low and high sides of the passband which improve the skirt performance of the filter. The transmission zero was considered due to the direct coupling between the input and output ports. Measured results demonstrated the excellent filter performance: its frequency bandwidth form 3.1 GHz to 10.1 GHz, good insertion loss of 0.5 dB at the center frequency of passband, respectively. Parameter study of length dependence of the filter has been carried out based on EM simulator. The ratio of the filter length to the guided wavelength of the second higher transmission zero frequency keeps almost constant as 0.48. Keywords: bandpass filters, broadside, coupling structure, UWB, multi-layered Classification: Microwave and millimeter wave devices, circuits, and systems References
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[1] Federal Communications Commission, Revision of Part 15 of the Commission’s Rules Regarding Ultra-Wideband Transmission Systems, “First Report and Order,” FCC 02. V48, April, 2002. [2] Keren Li, Daisuke Kurita, and Toshiaki Matsui, “An Ultra-Wideband Bandpass Filter Using Broadside-Coupled Microstrip-Coplanar Waveguide Structure,” 2005 Int. Microwave Symp. (IMS2005), WE2F-1, Long Beach, California, USA, June 11–17, 2005. [3] Keren Li, Daisuke Kurita, and Toshiaki Matsui, “A Novel UWB Bandpass Filter and Its Application to UWB Pulse Generation,” IEEE Int. Conference on Ultra-Wideband (ICU2005), S17-4, Zurich, Switzerland, Sept. 5–8, 2005.
DOI: 10.1587/elex.5.291 Received February 17, 2008 Accepted March 07, 2008 Published April 25, 2008
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[4] J. S. Hong and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, New York: Wiley, 2001. [5] N. Thomson, and J. S. Hong, “Compact Ultra-Wideband Microstrip/Coplanar Waveguide Bandpass Filter,” IEEE Microw. Wireless Compon. Lett., vol. 17, no. 3, March 2007.
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Introduction
Since Federal Communications Commission (FCC) of the USA released the microwave frequencies from 3.1 GHz to 10.6 GHz for commercial radio systems in Feb. 2002, the ultra-wideband (UWB) radio system has been paid attention as one of future high speed wireless communication system [1]. A UWB bandpass filter is one of the key components for the UWB system to control the spectrum of the UWB signals. To implement the UWB bandpass filter, however, has been a challenging work since the ultra wideband over 100 percent of the fractional bandwidth. Despite of the difficulty, we have successfully developed a novel UWB bandpass filter using microstrip-CPW broadside structure in our previous works [2, 3]. To miniaturize the UWB bandpass filter, we introduce two-layered structures into our single-layered UWB filter in this paper. Multi-layered structure is widely used for reducing the size of modern microwave components. In this paper, we achieved two-layered ultra-wideband (UWB) bandpass filter and investigated the characteristics. The simulation and experiments of the twolayered filters are carried out, where some interesting phenomena was found: some configuration introduced the transmission zeros which can improve the filter performance significantly and can then reduce the size of the filter.
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Two-layered UWB Bandpass Filter
Structure of two-layered ultra-wideband (UWB) bandpass filter is shown in figure in Table I. It was constructed with next three steps. First, additional layer is inserted to the single-layered UWB bandpass filter. Thus the two microstrip lines and CPW share the ground conductor on the middle metal layer. Second, we rearranged the output port reversed, considering the size reduction of the output port and ease for implementing further multi-layered structure. Finally. In order to reduce the length of CPW part by folding the right half side to the left side, making a short-circuited point at the center of the CPW, as shown in the figure. The folded CPW can still work as a coupled section. This technique is well-known, and first developed for interdigital filter back to fifty years ago [4], and used in recent UWB bandpass filter [5].
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DOI: 10.1587/elex.5.291 Received February 17, 2008 Accepted March 07, 2008 Published April 25, 2008
Simulated and Measured Results
Simulated result of the filter is shown in Fig. 1. We found an interesting phenomena that this rearrangement of output port introduced two transmission
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Table I. Structure and parameters of dielectric substrate and geometrical dimensions of the two-layered ultra-wideband (UWB) bandpass filter.
Fig. 1. Measured filter performance of two-layered ultrawideband (UWB) bandpass filter.
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DOI: 10.1587/elex.5.291 Received February 17, 2008 Accepted March 07, 2008 Published April 25, 2008
zeros at the low and high sides of the passband. The reason why the transmission zeros occur in this configuration is under investigation. We consider
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Fig. 2. Simulated results of the bandpass characteristics with different lengths of the filter. they are due to the direct coupling between input and output. These zeros are useful and effective to improve the skirt performance, even without implementing a multi-stage filter. Parameters of the two-layered UWB bandpass filter are listed in Table I. As listed in the table, the length of the filter is about 10 mm which is almost half size of the single-layered filter. Fabrication is carried out by using a wet etching system, and the filter is formed on a dielectric substrate (DICLAD 880, ARLON) with εr = 2.17 and thickness of 0.254 mm in this work. Measured results are shown in Fig. 1 as well. As shown in this figure, simulated and measured results show almost the same and demonstrate the excellent filter performance: its frequency bandwidth form 3.1 GHz to 10.1 GHz, good insertion loss of 0.5 dB at the center frequency of passband, respectively. Therefore using two-layered structure with shorted CPW, we can miniaturize the filter with good filter performance which almost meets FCC’s indoor spectrum mask. Parameter study of the developed UWB bandpass filter is carried out by using EM simulator (IE3D). Figure 2 shows simulated results of the bandpass characteristics with different lengths of the filter. As one can see, the three resonant frequencies at lower and two higher frequencies shifted when by changing the length of the filter. The ratio of the filter length to the guided wavelength of the second higher transmission zero frequency keeps almost constant as 0.48.
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DOI: 10.1587/elex.5.291 Received February 17, 2008 Accepted March 07, 2008 Published April 25, 2008
Conclusions
In this paper, two-layered ultra-wideband (UWB) bandpass filters have been proposed and developed. In this two-layered structure, we discovered from our simulation and experiments that some configuration of the filter can produce transmission zeros at the low and high sides of the passband which improve the skirt performance of the filter. The transmission zero was considered due to the direct coupling between the input and output ports. Measured
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results demonstrated the excellent filter performance: its frequency bandwidth form 3.1 GHz to 10.1 GHz, good insertion loss of 0.5 dB at the center frequency of passband, respectively. Parameter study of length dependence of the filter has been carried out based on EM simulator and experiments. The ratio of the filter length to the guided wavelength of the second higher transmission zero frequency keeps almost constant as 0.48.
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IEICE 2008
DOI: 10.1587/elex.5.291 Received February 17, 2008 Accepted March 07, 2008 Published April 25, 2008
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