Half-wavelength resonator type high frequency filter

Details Half-wavelength resonator type high frequency filter Half-wavelength resonator type high frequency filter

1999-05-24

2001-02-06

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S219000

Reexamination Certificate

active

06184760

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a half-wavelength resonator type high frequency filter, exemplified primarily by a dielectric filter used in wireless equipment such as a portable telephone.
2. Related Art of the Invention
In recent years, there has been an increasing demand for half-wavelength resonator type high frequency filters as compact and high performance filters that have superior selectively characteristics in order to achieve efficient utilization of frequencies in wireless communications. An example of a prior art half-wavelength resonator type high frequency filter will be described below with reference to drawing.
FIG. 6
shows the configuration of the prior art half-wavelength resonator type high frequency filter constructed using strip lines. In
FIG. 6
, reference numerals
41
and
42
are half-wavelength resonators. Reference numeral
43
is an input terminal, and
44
is an output terminal. Reference numeral
45
is an input matching circuit block Yt,
46
is an output matching circuit block Yt, and
47
is an interstage coupling capacitor Cg. The half-wavelength resonators
41
and
42
are each a strip line with both ends open, and the input matching circuit block
45
Yt and output matching circuit block
46
Yt are formed, for example, input and output coupling capacitors.
The operation of the thus constructed half-wavelength resonator type high frequency filter will be described below.
First, the resonators are excited at the midpoints of the respective strip lines, i.e., the dividing points between L
1
and L
2
and between L
3
and L
4
, via the input and output matching circuit blocks which are, for example, input and output coupling capacitors. The interstage coupling capacitor Cg is electrically connected to both of the resonators at their resonator facets
48
. The thus constructed filter exhibits a band pass characteristic with its pass band center frequency at the antiresonant frequency of the resonators and a transfer characteristic with attenuation poles formed at series-resonant frequencies of the L
1
and L
4
sections of the strip lines where they are equivalently grounded. In this case, if we consider only the fundamental mode, the number of attenuation poles is one per resonator.
In the above configuration, however, since each resonator resonates only at one specific frequency in the fundamental mode, the number of filter attenuation poles is limited to the number of resonators used. Further, the magnitude of attenuation is not sufficient. Another problem is that since there is a significant limitation on input/output matching, freedom in attenuation pole frequency control is limited.
SUMMARY OF THE INVENTION
In view of the above-outlined problems, it is an object of the present invention to provide a half-wavelength resonator type high frequency filter that permits the number of attenuation poles to be increased in relative terms, provides a sufficient degree of attenuation, and can freely control the filter's attenuation pole frequencies.
The 1st invention of the present invention is a half-wavelength resonator type high frequency filter comprising: N half-wavelength resonators (where N is an integer not smaller than 2); an input terminal; an output terminal; first matching means for matching the first of said resonators to said input terminal; second matching means for matching the N-th of said resonators to said output terminal; and (N−1) interstage coupling means for coupling said resonators with one another, and wherein excitation positions of said first of said resonators and said N-th of said resonators are displaced from the center positions of the respective resonators toward an end thereof, and at least one of said interstage coupling means is electrically connected to its associated resonators at positions other than both ends thereof.
The 2nd invention of the present invention is a half-wavelength resonator type high frequency filter comprising: two half-wavelength resonators; an input terminal; an output terminal; first matching means for matching the first of said resonators to said input terminal; and second matching means for matching the second of said resonators to said output terminal, and wherein said resonators are each shaped in the form of the letter L, and are disposed close together at positions substantially mirror-symmetric to each other so that bent portions of said resonators are electromagnetically coupled to each other.
The 3rd invention of the present invention is a half-wavelength resonator type high frequency filter comprising: N half-wavelength resonators with both ends open (where N is an integer not smaller than 2); an input terminal; an output terminal; first matching means for matching the first of said resonators to said input terminal; second matching means for matching the N-th of said resonators to said output terminal; and (N−1) interstage coupling means for coupling said resonators with one another, and wherein sections of each of said resonators, extending from said coupling point to the respective open ends thereof, series resonate, thereby generating two attenuation poles with each of said resonators.


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“Tapped-Line Interdigitial Bandpass Filters with Narrow Bandwidth Using Asymmetric Broadside Coupled Coplanar Waveguides”; XP 000643202; by Wada et al. pp. 487-492.
Kouji Wada, et al., “A New Concept of a Bandpass Filter with Transmission Zeros Based on Tap-Connected Half-Wavelength Resonators,” Asia-Pacific Microwave Conference (1998), pp. 89-92.

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