Resonator of radio-frequency filter

#The invention relates to a dielectric double-mode resonator used in radio-frequency filters.

#High-frequency filters, such as radio-frequency filters, are used to implement high-frequency circuits in the base stations of mobile networks, mobile phones and other radio transceivers. Possible radio-frequency filter applications include the adapter circuits and filter circuits of transmitter and receiver amplifiers.

#In telecommunications applications in particular, good performance in a desired operating range, temperature stability and a small size are required of radio-frequency filters. These properties can be achieved using dielectric resonators, the frequency properties of which, such as the resonance frequency, can be influenced by the structure of the resonator, the physical dimensions of the resonator and the resonator material, for instance.

#The invention will now be described in more detail by means of preferred embodiments and with reference to the attached drawings, in which

#FIG. 1 shows a dielectric one-mode resonator,

#FIG. 2A is a perspective view of a block structure of a dielectric double-mode resonator,

#Let us first examine an annular dielectric resonator 100 having an opening according to the prior art as shown in FIG. 1, which resonator 100 comprises a main block 102 made of dielectric material and comprising side walls 120, 130, 140, 150 and end walls 160, 170. In addition, the resonator 100 comprises an opening 110 for adjusting the frequency properties of the resonator 100, the opening 110 being formed between the end walls 160, 170 and the boundary between the opening 110 and the main block 102 forming the walls 112 of the opening 110. A resonator ring is formed by the dielectric material around the opening 110. The opposing walls 120, 140 and 130, 150 of the side walls are usually parallel with each other, whereby the main block 102 forms a hollow rectangular structure. The angles between the side walls 120, 130, 140, 150 can also be rounded, whereby the walls 120, 130, 140, 150 form a cylindrical outer surface of the main block. The end walls 160, 170 are preferably parallel and the distance between them is typically less than half of the used wavelength of the electromagnetic field. The resonator 100 has one primary resonance mode that is generated when a radio-frequency electromagnetic field is directed to the resonator 100.

#Let us next examine the preferred embodiments of a double-mode resonator used in a radio-frequency filter by means of examples and figures.

#FIGS. 2A, 2C and 2D show an example of the block structure 200 of a double-mode resonator, which is formed by setting a first block 204 and second block 206 similar to those in FIG. 2B against each other. FIGS. 2A, 2C and 2D show the block structure 200 of a dielectric double-mode resonator comprising two resonator structures 220, 222 which as separate and unconnected resonators resemble in structure the resonator 100 shown in FIG. 1, but which in a double-mode resonator possibly comprise common structural parts. The resonator structures 220, 222 are structures of the double-mode resonator, whose frequency response generated in the double-mode resonator corresponds to the frequency response which would be obtained by connecting the resonance modes of fully separate resonator structures 220, 222 with an equal coupling. Even though the resonator structures 220, 222 comprise common structural parts of the dielectric double-mode resonator and the impact of the separate resonator structures 220, 222 on the properties of the double-mode resonator cannot entirely be distinguished from each other, the resonator structures 220, 222 are examined as separate entities for the sake of simplicity.