Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-04-19
2001-06-26
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000
Reexamination Certificate
active
06252476
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to microstrip line filters which are used, for example, in miniature receivers and transmitters. More particularly, the present invention relates to microstrip preselectors.
BACKGROUND OF THE INVENTION
Bandpass filters are two-port networks that provide transmission at frequencies within the passband of the filter and attenuation of other frequencies outside of the band. Microstrip bandpass filters are small in size and easy to fabricate. Microstrip coupled line bandpass filters comprise a cascade of parallel half-wavelength-long printed resonators open-circuited at both ends. The resonators are positioned parallel to each other, in such a way that adjacent resonators are coupled along the length equal to the guided quarter-wavelength of the center frequency of the filter.
Disadvantages of conventional microstrip bandpass filters include the existence of a spurious mode which occurs at nearly twice the passband frequency. The spurious mode is caused by the different even-mode and odd-mode propagation velocities of the coupled microstrip resonators. Other disadvantages of these conventional microstrip filters are radiation from open ends, and difficulty obtaining a narrow passband. Also, as with many microelectronic circuit components, the required physical size of conventional microstrip bandpass filters is a limitation to circuit miniaturization.
SUMMARY OF THE INVENTION
Disclosed are microstrip bandpass filters. The bandpass filters of the present invention include an input, an output and multiple resonators coupled between the input and the output. A first resonator coupled in series between the input and the output includes a first line conductor having first and second ends and a second line conductor having first and second ends. The first and second line conductors are positioned relative to one another such that the second end of the first line conductor is connected to the second end of the second line conductor, forming a first angle of the first resonator between the first and second line conductors. The first angle of the first resonator is substantially less than 180 degrees so that a physical length of the resonator, taken in a direction from the input to the output, is less than an electrical length of the first resonator. The open ended line is connected to the remainder of the resonator at the point where the resonator is bent.
REFERENCES:
patent: 2606974 (1952-08-01), Wheeler
patent: 5021757 (1991-06-01), Kobayashi et al.
patent: 5900308 (1999-05-01), Koike et al.
patent: 5990765 (1999-11-01), Mansour et al.
patent: 1283877 (1985-09-01), None
Matthaei, G. L., Young, L., Jones, E. M. T., “Microwave Filters, Impedance-Matching Networks, and Coupling Structures”, 1964.
Eppele Kyle
Jensen Nathan O.
Jones Stephen E.
Lee Benny
O'Shaughnessy James P.
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