This application claims priority from Japanese Patent Application No. 2006-274323, filed on Oct. 5, 2006, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a reflection-type bandpass filter for use in ultra-wideband (UWB) wireless data communication.
2. Description of the Related Art
This invention relates to a reflection-type bandpass filter for use in ultra-wideband (hereafter “UWB”) wireless data communication. By using this UWB reflection-type bandpass filter, U.S. Federal Communications Commission requirements for spectrum masks can be satisfied.
As technology of the prior art related to this invention, for example, the technology disclosed in the following references 1 through 10 is known.
Reference 1: Specification of U.S. Patent No. 2411555
Reference 2: Japanese Unexamined Patent Application No.
Reference 3: Japanese Unexamined Patent Application No.
Reference 4: Japanese Unexamined Patent Application No.
Reference 5: Japanese Unexamined Patent Application No.
Reference 6: Japanese Unexamined Patent Application No.
Reference 7: Japanese Unexamined Patent Application No.
Reference 8: Japanese Unexamined Patent Application No.
Reference 9: Japanese Unexamined Patent Application No.
Reference 10: A. V. Oppenheim and R. W. Schafer, “Discrete-time signal processing,” pp. 465-478, Prentice Hall, 1998.
Reference 11: G-B. Xiao, K. Yashiro, N. Guan, and S. Ohokawa, “An effective method for designing nonuniformly coupled transmission-line filters,” IEEE Trans. Microwave Theory Tech., vol. 49, pp. 1027-1031, June 2001.
Reference 12: Y. Konishi, “Microwave integrated circuits”, pp. 19-21, Marcel Dekker, 1991
However, the bandpass filters proposed in the prior art may not satisfy the FCC specifications, due to manufacturing tolerances and other reasons.
Further, bandpass filters which use coplanar strips do not use wide ground strips, and so are not suitable for coupling with transmission lines such as slot lines. This invention was devised in light of the above circumstances, and has as an object the provision of a high-performance UWB reflection-type bandpass filter which has excellent coupling characteristics with transmission lines such as slot lines, and which satisfies FCC specifications.
This invention provides a reflection-type bandpass filter for ultra-wideband wireless data communication, in which are provided on the surface of a dielectric substrate a center conductor and side conductors provided on both sides of the center conductor securing a prescribed distance between conductors with non-conducting portions intervening, and in which the center conductor width or the distances between conductors, or both, are distributed non-uniformly in a length direction of the center conductor.
In a reflection-type bandpass filter of this invention, the center conductor width may be constant, and the distances between conductors may be distributed non-uniformly.
Alternately, the distances between conductors may be constant, and the center conductor width may be distributed non-uniformly.
In a reflection-type bandpass filter of this invention, a difference of 10 dB or higher may exist between a reflectance in a ranges of frequencies f for which f<3.1 GHz and f>10.6 GHz, and a reflectance in a range of frequencies 3.9 GHz≦f≦9.8 GHz, and in a range 3.9 GHz≦f≦9.8 GHz a group delay variation may be within ±0.1 ns.
In a reflection-type bandpass filter of this invention, alternately, a difference of 10 dB or higher may exist between a reflectance in a range of frequencies f for which f<3.1 GHz and f>10.6 GHz, and a reflectance in a range of frequencies 3.7 GHz≦f≦10.0 GHz, and in a range 3.7 GHz≦f≦10.0 GHz a group delay variation may be within ±0.1 ns.
In a reflection-type bandpass filter of this invention, alternately, a difference of 10 dB or higher may exist between a reflectance in a range of frequencies f for which f<3.1 GHz and f>10.6 GHz, and a reflectance in a range of frequencies 4.1 GHz≦f≦9.5 GHz, and in a range 4.1 GHz≦f≦9.5 GHz a group delay variation may be within ±0.1 ns.
In a reflection-type bandpass filter of this invention, a characteristic impedance Zc of an input terminal transmission line may be in the range 10Ω≦Zc≦300Ω.
In a reflection-type bandpass filter of this invention, a resistance having the same impedance as the above characteristic impedance value, or a non-reflecting terminator, may be provided on the terminating side.
In a reflection-type bandpass filter of this invention, the center conductor and the side conductors may comprise metal plates of thickness equal to or greater than a skin depth of the metal plates at f=1 GHz.
In a reflection-type bandpass filter of this invention, the dielectric substrate may have a thickness h in a range 0.1 mm≦h≦10 mm, a relative permittivity εr in a range 1≦εr≦500, a width W in a range 2 mm≦W≦100 mm, and a length L in a range 2 mm≦L≦500 mm.
In a reflection-type bandpass filter of this invention, length-direction distributions of the center conductor width and of the distances between conductors may satisfy a design method based on the inverse problem of deriving a potential from spectral data in the Zakharov-Shabat equation.
In a reflection-type bandpass filter of this invention, length-direction distributions of the center conductor width and of the distances between conductors may satisfy a window function method.
In a reflection-type bandpass filter of this invention, length-direction distributions of the center conductor width and of the distances between conductors may satisfy a Kaiser window function method.
In a reflection-type bandpass filter of this invention, by applying a window function technique to design a reflection-type bandpass filter comprising non-uniform coplanar strips, the pass band can be made extremely broad and variation in group delay within the pass band can be made extremely small compared with filters of the related art, even when manufacturing tolerances are large. As a result, a UWB bandpass filter can be provided which satisfies FCC specifications.
Further, ground strips can be made wide, so that easy coupling with transmission lines such as slot lines is achieved. Here, “ground strips” refers to the conductors on both sides, which are connected together on the input end.
Below, exemplary aspects of the invention are explained referring to the drawings.
In the reflection-type bandpass filter 1 of this aspect, the center conductor 3 and side conductors 5a, 5b provided on either side of the center conductor 3, maintaining a prescribed distance between conductors and with non-conducting portions 4a, 4b intervening, are formed on the surface of the dielectric substrate 2; the non-uniform coplanar strips are such that the center conductor width or the distances between conductors, or both, are distributed non-uniformly in the length direction of the center conductor 3.
As shown in
A reflection-type bandpass filter of this aspect of the invention adopts a configuration in which stop band rejection (the difference between the reflectance in the pass band, and the reflectance in the stop band) is increased, by using a window function method (see Reference 10) employed in digital filter design. By this means, instead of expansion of the transition frequency region (the region between the pass band boundary and the stop band boundary), the stop band rejection can be increased. As a result, manufacturing tolerances can be increased. Also, variation in the group delay within the pass band is decreased.
The transmission line of a reflection-type bandpass filter 1 of this aspect of the invention can be represented by a non-uniformly distributed constant circuit such as in
From
Here L(z) and C(z) are the inductance and capacitance respectively per unit length in the transmission line. Here, the function of equation (2) is introduced.
Here Z(z)=√{L(z)/C(z)} is the local characteristic impedance, and φ1, φ2 are the power wave amplitudes propagating in the +z and −z directions respectively.
Substitution into equation (1) yields equation (3).
Here c(z)=1/√{L(z)/C(z)}. If the time factor is set to exp(jωt), and a variable transformation is performed as in equation (4) below, then the Zakharov-Shabat equation of equation (5) is obtained.
Here q(x) is as given by equation (6) below.
The Zakharov-Shabat inverse problem involves synthesizing the potential q(x) from spectral data which is a solution satisfying the above equations (see Reference 11). If the potential q(x) is found, the local characteristic impedance Z(x) is determined as in equation (7) below.
Here, normally in a process to determine the potential q(x), the reflectance coefficient r(x) in x space is calculated from the spectra data reflectance coefficient R(ω) using the following equation (8), and q(x) are obtained from r(x).
In this invention, in place of obtaining r(x) from the R(o) for ideal spectral data, a window function is applied as in equation (9) to determine r′(x).
r′(x)=w(x)r(x). (equation 9)
Here ω(x) is the window function. If the window function is selected appropriately, the stop band rejection level can be appropriately controlled. Here, a Kaiser window is used as an example. The Kaiser window is defined as in equation (10) below (see Reference 10).
Here α=M/s, and β is determined empirically as in equation (11) below.
Here A=−20 log10δ. where δ is the peak approximation error in the pass band and in the stop band.
In this way q(x) is determined, and from equation (7) the local characteristic impedance Z(x) is determined.
Here, when either the width w of the center conductor 6 (hereafter the “center conductor width w”) or the distance between conductors s, or both, of the coplanar strips are varied, the characteristic impedance can be changed (see Reference 12).
In this invention, the center conductor width w or distance between conductors s was calculated based on the local characteristic impedance obtained from equation (7), and a bandpass filter 1 was manufactured so as to satisfy the calculated center conductor width w or distance between conductors s. By this means, reflection-type bandpass filters 1 having the desired pass band were obtained.
Below, the invention is explained in further detail referring to embodiments. Each of the embodiments described below is merely an illustration of the invention, and the invention is in no way limited to these embodiment descriptions.
A Kaiser window was used for which the reflectance is 0.9 at frequencies f in the range 3.4 GHz≦f≦10.3 GHz, and is 0 elsewhere, and for which A=30. Design was performed using one wavelength of signals at a frequency f=1 GHz propagating in the coplanar strip as the waveguide length, and setting the system characteristic impedance to 75Ω. Here, the characteristic impedance is set so as to match the impedance of the system being used. In general, in a circuit which handles high-frequency signals, a system impedance of 50Ω, 75Ω, 300Ω, or similar is used. It is desirable that the characteristic impedance Zc be in the range 10Ω≦Zc≦300Ω. If the characteristic impedance is smaller than 10Ω, then losses due to the conductor and dielectric become comparatively large. If the characteristic impedance is higher than 300Ω, matching with the system impedance is not possible.
A Kaiser window was used for which the reflectance is 0.8 at frequencies f in the range 3.4 GHz≦f≦10.3 GHz, and is 0 elsewhere, and for which A=30. Design was performed using one wavelength of signals at a frequency f=1 GHz propagating in the coplanar strip as the waveguide length, and setting the system characteristic impedance to 75Ω.
A Kaiser window was used for which the reflectance is 1 at frequencies f in the range 3.7 GHz≦f≦10.0 GHz, and is 0 elsewhere, and for which A=30. Design was performed using 0.3 wavelength of signals at frequency f=1 GHz propagating in the coplanar strip as the waveguide length, and setting the system characteristic impedance to 50Ω.
In the above, exemplary embodiments of the invention have been explained; but the invention is not limited to these embodiments. Various additions, omissions, substitutions, and other modifications to the configuration can be made, without deviating from the scope of the invention. The invention is not limited by the above explanation, but is limited only by the scope of the attached claims.
Number | Date | Country | Kind |
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2006-274323 | Oct 2006 | JP | national |