Filter having resonant frequency adjusted with dielectric layer

Details Filter having resonant frequency adjusted with dielectric layer Filter having resonant frequency adjusted with dielectric layer

1999-07-08

2001-11-06

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Resonators

Dielectric type

C333S204000, C333S205000

Reexamination Certificate

active

06313722

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims benefit of priority of Japanese Patent Application No. Hei-11-046878 filed on Feb. 24, 1999, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filter having resonators, the resonant frequency of which is adjusted with a dielectric layer formed on the resonators, and to a method of adjusting the resonant frequency of such resonators.
2. Description of Related Art
A filter characteristic such as resonant frequency has to be adjusted after its manufacturing process is completed, because the characteristic usually deviates from its target due to various deviation factors such as dielectric constant of a substrate, thickness of layers, accuracy of a mask, manufacturing process conditions and the like. Such characteristic adjustment, or tuning is especially necessary for narrow band and low ripple filters.
Conventionally, a resonant frequency of a filter has been tuned by adjusting an effective dielectric constant of a resonator with a screw that carries a dielectric member at its tip, or by trimming a resonator pattern with a laser beam. In both methods, it is necessary to carry out the adjustment or tuning while the filter characteristic is being measured. Such adjustment under measurement is not easy, especially when a filter is constituted by a large number of resonators.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a filter, the resonant frequency of which is easily adjusted, and more particularly, to provide a filter having plural resonators, in which the resonant frequency of each resonator is easily adjusted independently from one another. Another object of the present invention is to provide an improved method of adjusting the resonant frequency of the resonators, which can be carried out without watching a measuring instrument.
A filter is composed of a dielectric substrate, plural resonators formed on one surface of the substrate and a ground plane formed on the other surface of the substrate. A dielectric layer is formed on each resonator to adjust or tune the resonant frequency of the resonator. The resonators and the ground plane may be made of a superconductive material, and each resonator is ring-shaped with one portion opened with a narrow gap. The resonant frequency of each resonator is equalized to a target resonant frequency by accumulating a proper amount of a dielectric material as a layer formed on the resonator.
The resonators are designed so that their resonant frequencies are a little higher than a target resonant frequency, because the resonant frequency is adjusted by the dielectric layer only in the direction to decrease the resonant frequency. After the plural resonators are formed on the substrate, the resonant frequency of each resonator is measured and compared with the target frequency, thereby determining frequency deviation of each resonator. The larger the deviation is, the higher amount of the dielectric material is accumulated on the resonator. Thus, the resonant frequencies of all the resonators are adjusted to the target frequency.
The dielectric layer may be formed in a photolithography process. Preferably, the dielectric layer having the same thickness is formed on each resonator, and the amount of the dielectric material is controlled by changing the areal size of the dielectric layer covering each resonator. The resonant frequency of each resonator is adjusted independently from one another by changing the covering area of the dielectric layer. It is preferable to pattern all the dielectric layers, each covering each resonator with a respective areal size, at the same time using a single mask in the photolithography process. Preferably, one resonator showing the highest frequency deviation is fully covered with the dielectric layer while other resonators are partially covered. Alternatively, the amount of the dielectric layer may be controlled by changing its thickness while keeping the covering area constant.
Since the resonant frequency deviation from the target frequency of each resonator is measured, and the amount of the dielectric material required to eliminate such deviation is determined before the adjustment process, it is not necessary to measure the resonant frequency during the adjustment process. Thus, the adjustment or tuning process is simplified, especially when a large number of resonators are used in a filter.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.


REFERENCES:
patent: 3938064 (1976-02-01), O'Bryan, Jr. et al.
patent: 3963982 (1976-06-01), Roberts
patent: 4142164 (1979-02-01), Nishikawa et al.
patent: 4623835 (1986-11-01), Mehdizadeh et al.
patent: 4629977 (1986-12-01), English
patent: 4735906 (1988-04-01), Bastiaans
patent: 5227730 (1993-07-01), King et al.
patent: 5334941 (1994-08-01), King
Gerhard Sollner et al., “High-Power YBCO Microwave Filters and Their Nonlinearities”, 5thInternational Superconductive Electronics Conference (ISEC '95), Sep. 18-21, 1995, Nagoya, Japan.
Co-pending Application No. 09/349,450.
Gerhard Sollner et al, “High-Power YBCO Microwave Filters and Their Nonlinearities”,5thInternational Superconductive Electronics Conference(ISEC '95), Sep. 18-21, 1995, Nagoya, Japan, pp. 517-520.

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