Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – High frequency waveguides – resonators – electrical networks,...
Reexamination Certificate
2000-03-31
2002-12-31
Lee, Benny (Department: 2817)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
High frequency waveguides, resonators, electrical networks,...
C505S700000, C505S866000, C333S09900R, C333S219000
Reexamination Certificate
active
06501972
ABSTRACT:
BACKGROUND
The present invention relates to microwave devices comprising a number of parallel-plate resonators allowing selection of modes. The invention also relates to a method of suppressing undesired modes in a microwave device.
It is often desirable to be able to select the modes of microwave devices such as microwave resonators and filters. WO 98/32187 shows the use of aperiodic gratings for mode conversion/selection. However, the grating structures/surfaces are of complex shape and long. These devices furthermore suffer the drawback of being complicated and costly to fabricate and it is also difficult to obtain a mode selectivity which is as accurate as would be desired. Still further they can not be used for thin film resonators for which the thickness is less then &lgr;
g
/2, &lgr;
g
being the wavelengths of the microwave signal in the resonator. In several implementations it is however desirable to be able to use such resonators. Still further, the size of the resonators is changed when structures as in WO 98/32187 are used.
The Swedish patent application SE 9502137-4, which is the counterpart of allowed U.S. application Ser. No. 08/989,166, filed Dec. 11, 1997, discloses parallel-plate resonators, specially with superconducting plates for low-loss narrow-band filter applications. In “Lower Order Modes of YBCO/STO/YBCO Circular Disc Resonators”, IEEE Transactions on Microwave Theory and Technics, Vol. 44 (10), pp. 1738-1741, 1996, it is shown that in electrical thin resonators (the thickness being smaller than &lgr;
g
/2), the higher order TM modes, so called whispering gallery modes, have higher quality factors. It would thus be desirable to utilize these modes in low loss narrow band filter applications. It is however a drawback related to using higher order modes since due to the resonant frequencies of these modes being very close to each other, the rejection bands of for example filters have parasitic undesirable transmission poles, i.e. in other words they are not free of spurious components. SE 9701450-0 “Arrangement and method relating to microwave devices” suggests one way to overcome this problem through the use of special mode selective coupling loops. However, such a device is comparatively bulky and most suitable for input/output coupling of resonators in multiresonator filters. Furthermore, since the coupling loops are quite bulky for certain applications, the parasitic modes will not be sufficiently suppressed. Still further such coupling loops are not possible to use in the resonators away from the input/output ports of for example filters.
U.S. Pat. No. 5,710,105 shows high power, high temperature superconductor filters having TM
0i0
mode circular shaped high temperature superconductor planar resonators. To suppress interfering non TM
0i0
modes, radially directed slots are provided which are positioned parallel to the current of the desired operating mode and perpendicular to the current of an undesired mode. However, these slots are centered at the radius of the disk. They do not cut the maxima. Moreover such slots will affect the useful modes. Thus this device will not work as efficiently as needed. Moreover, this document merely contemplates the TM
0i0
-modes as attractive for selection.
SUMMARY
Therefore microwave devices, particularly microwave resonators and filters, are needed which are mode selective, particularly with a precise mode selectivity. Particularly, devices are needed wherein means enabling mode selectivity are provided which are suitable for use for input/output coupling as well as away from input/output ports of resonators of filters. Particularly a device is needed which is small and for example comprises thin resonators, particularly having a thickness smaller than &lgr;
g
/2, &lgr;
g
being the microwave wavelength in the resonator. Still further a device is needed through which it is possible to use higher order TM modes in low loss narrow band filter applications. Particularly a device is needed through which higher order modes having close resonant frequencies can be used and through which parasitic and undesirable transmission poles can be avoided. Particularly a device is needed through which any standard thin film fabrication technology can be used and through which mode selectivity is enabled without changing the size of the resonators. Still further a device is needed which generally is inexpensive and easy to fabricate and through which the use of higher order TM modes is enabled without problems being caused by the close resonant frequencies of such modes. A method of suppressing undesired modes in such devices is also needed. A device and a method respectively is also needed which is more efficient in suppressing undesired modes than hitherto known devices at the same time as the effect of the suppression of undesired modes on the desired modes is minimized. Further yet a device and a method respectively is needed through which any mode can be selected or suppressed.
Therefore a microwave device is provided which particularly comprises a number of parallel-plate resonators. Each parallel-plate resonator comprises at least one dielectric substrate with first and second conducting (superconducting) plates arranged on either side of said dielectric substrate. The field (the field produced by coupling arrangement or similar, e.g. discussed in the applications by the same applicant which are incorporated herein by reference above) generates currents in both of the plates of the parallel-plate resonator or resonators (the resonator is thin). At least one of the first and second plates of each of a number of the parallel-plate resonators is patterned or formed in such a way, or comprises current interrupting means, that the current lines of at least one undesired mode are interrupted at their maxima (where the current lines have a maximum) to suppress the undesired mode or modes, thus providing for selectivity. The current interrupting means may be provided in a number of different ways, as actual means or as a particular pattern in, or forming of, the resonators. According to one embodiment the current interrupting means are constituted of cuts in at least one resonator plate of one or more parallel-plate resonators. Particularly the resonator plates comprise metal and the current interrupting means consists of metal being removed except for along the current lines of the desired modes which, in other words, means that the parallel-plate resonator is patterned or formed in such a way.
In an alternative embodiment, the resonator plates comprising metal strips, are the current interrupting means formed by resistive strips arranged along the current lines of the undesired modes, thus replacing the metal strips. This is particularly convenient if the device comprises a number of electrically tunable resonators requiring whole resonator plates, i.e. resonator plates which should not contain any cuts or similar. Also in other implementations requiring “whole” resonator plates this implementation consisting of replacing metal strips through resistive strips, is appropriate.
For parallel-plate resonators, or devices built of or including parallel-plate resonators, the current interrupting means may either be provided on one only of the resonator plates of a respective parallel-plate resonator or current interrupting means may be provided on both plates. In a particular implementation the device comprises one or more circular parallel-plate resonators.
Particularly one or more modes are suppressed. In some embodiments the current interrupting means, i.e. the cuts, resistive films or removed metal parts, are arranged to interrupt the current lines of for example one or more of the TM
210
, TM
310
and TM
410
modes respectively. Then a number of current interrupting means are arranged which are directed substantially towards the center of the circular parallel-plate resonator. The current interrupting means are so formed that they have a larger width at the edge of the disc whereas the width is substantially zero, or zero, at t
Carlsson Erik
Gevorgian Spartak
Wikborg Erland
Burns Doane et al.
Lee Benny
Telefonaktiebolaget L M Ericsson (publ)
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