Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-03-22
2001-12-04
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S204000, C333S134000
Reexamination Certificate
active
06326865
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to a dual-mode band-pass filter comprising a circular resonator having a circular periphery and a pair of input/output ports.
BACKGROUND OF THE INVENTION
Such a dual-mode filter typically includes a circular resonator, such as a ring resonator, having a circular periphery, which is formed on a substrate made of a dielectric material, and a pair of input/output ports connected to the circular resonator through a capacitance for external circuit coupling, which is formed on the substrate at a symmetrical position with respect to a symmetry plane passing through the center of the circular shape of the circular resonator. Perturbation stubs are formed on the substrate to extend radially along the symmetry plane of the circular resonator at the diametrically opposite sides of the circular resonator. The pair of input/output ports is disposed outwardly in diametral direction with respect to the circular resonator in a manner to define a right angle therebetween.
In the paper of Lei Zhu, et al, “A Joint Field/Circuit Design Model of Microstrip Ring Dual-Mode Filter: Theory and Experiments”, 1997 Asia Pacific Microwave Conference, pp. 865-868, several forms of such type of dual-mode filters are described.
As typically shown in
FIG. 2
of the aforementioned paper, in the conventionally proposed dual-mode filters, the length of the stub pole should be changed in order to optionally determine an attenuation pole frequency of the filter. However, when the length of the perturbation stub was changed, there causes a problem that a coupling condition of the filter would be swerved from a critical coupling condition so that a passbandwidth of the filter would be simultaneously changed. Thus, in such conventional dual-mode filters, it has been highly difficult to optionally set an attenuation pole frequency with maintaining a constant passbandwidth of the filter.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a structure of a dual-mode filter and a design method therefor, which is capable of optionally setting an attenuation pole frequency with maintaining a constant passbandwidth of the filter.
Another object of the present invention is to provide a duplexer which has a new configuration comprising two dual-mode filters formed on a single dielectric substrate and a design method therefor.
A dual-mode filter of the present invention includes a circular resonator, such as a ring resonator, a circular disc resonator and the like, having a circular periphery, which is formed on a dielectric substrate, and a pair of input/output ports connected with the circular resonator through a capacitance for external circuit coupling, which is formed on the substrate at a symmetrical position with respect to a symmetry plane passing through a center of the circular shape of the circular resonator, stub perturbations are being formed on the substrate radially extending along the symmetry plane of the circular resonator from opposite positions of the circular pole in the diametrical direction with each other, wherein the pair of input/output ports are formed with defining an angle different from a right angle therebetween.
According to the findings of the inventors of the present invention, when an angle between the pair of input/output ports is different from a right angle, an attenuation pole frequency causing a minimum pass value of the filter can be controlled by a combinations of input/output angle and the size of the stub perturbation. More specifically, when the angle between the pair of input/output ports is at a right angle, the I/O port has no contribution on mutual coupling between the dual-modes as well as in the change of the attenuation pole frequency wherein energy transmission of the filters shows a minimum value. In contrast, when the angle between the pair of input/output ports takes a value different from a right angle it contributes in mutual coupling between dual-modes of the circular resonator as well as in positioning of the attenuation pole frequency. Hence we can fabricate a bandpass filter by having mutual coupling effect from the stub perturbations as well as input/output angle simultaneously, when I/O angle is different from right angle. But here the contribution of input/output angle and stub perturbations on the control of attenuation pole frequency does not cancel each other. As a result we can make various combinations of these two parameters to obtain a constant coupling for design of a constant bandwidth filter with controlled attenuation pole frequencies. A unique but complicating (second order) effect of external circuit susceptance is also included to characterize the coupling constant. With this principle, the attenuation pole frequency of the filter can be controlled over a wide range and a transmission characteristic of the filter can also diversely be changed.
Thus, in one aspect, the present invention provides a dual-mode filter including a dielectric substrate, a circular resonator having a circular periphery, which is formed on the dielectric substrate, a pair of input/output ports coupled to the circular resonator through a capacitance for external circuit coupling, which is formed on the substrate at a symmetrical position with respect to a symmetry plane passing through the center of the circular shape of the circular resonator, and stub perturbations are formed on the substrate to extend radially along the symmetry plane at the diametrically opposite sides of the circular resonator. One of the features of the present invention is that the pair of input/output ports is disposed to define an angle different from a right angle therebetween with maintaining a particular passbandwidth by the size of the stub perturbations.
In another aspect, the present invention provides a method of designing the aforementioned type of dual-mode filter. This method includes steps of: setting a particular passbandwidth of the filter, finding the aforementioned capacitance required for external circuit coupling, determining an angle between the pair of input/output ports a value different from a right angle, and figuring out a size of the stub perturbations for achieving the particular passbandwidth.
The present invention further provides a method for a dual-mode filter to control an attenuation pole frequency over a wide range, with maintaining a passbandwidth substantially constant. This method includes steps of: setting a particular passbandwidth of the filter, finding the capacitance for external coupling, determining a particular value of the attenuation pole frequency with which the pass value of the filter shows a minimum value, and then figuring out a combination of an angle different from a right angle between the pair of input/output ports and a size of the stub perturbations, required for achieving the particular value of the attenuation pole frequency with which the pass value of the filter shows a minimum value, with maintaining the aforementioned particular passbandwidth.
In yet another aspect, the present invention provides a duplexer in which two dual-mode filters are formed on a single substrate. This duplexer comprises a dielectric substrate; a first dual mode filter including a first circular resonator having a circular periphery, which is formed on the substrate, a pair of input/output ports coupled to the first circular resonator respectively through capacitances for external coupling, which are formed on the substrate at symmetrical positions with respect to a symmetry plane passing through the center of the circular shape of the first circular resonator, first stub perturbations for internal coupling, formed on the substrate radially extending along the symmetry plane from opposite positions of the first circular resonator in the diametral direction each other; and a second dual-mode filter including a second circular resonator having a circular periphery, which is formed on the substrate laterally alongside of the circular resonator, a pair of input/output ports coupled to the secon
Awai Ikuo
Kundu Arun Chandra
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Nguyen Patricia T.
Pascal Robert
TDK Corporation
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