Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – High frequency waveguides – resonators – electrical networks,...
Reexamination Certificate
1997-12-04
2001-02-13
Lee, Benny T. (Department: 2817)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
High frequency waveguides, resonators, electrical networks,...
C505S700000, C505S701000, C505S866000, C333S0990MP, C333S219000, C333S235000
Reexamination Certificate
active
06187717
ABSTRACT:
BACKGROUND
The present invention relates to tunable microwave dielectric monolithic integrated circuits. The invention also relates to a method for tuning the phase velocity of microwaves in a microwave monolithic integrated circuit. Tunable microwave devices as such are of considerable interest for example within microwave communication, radiosystems and cellular communications systems etc.
A number of tunable microwave devices have been suggested. U.S. Pat. No. 5,285,067 for example shows a superconducting resonator on a non-ferroelectric (linear) substrate wherein input and output respectively are formed by microstrips. Via optical illumination the properties of the superconducting films are changed (tuning) which results in a shift in resonant frequency. Apart from optical illumination also other means can be used to change or control the properties of the superconducting films and thus provide controllability. However, for optical tuning a high optical power is required and the tuning is not very effective.
U.S. Pat. No. 5,179,074 illustrates dielectric resonators in super-conducting cavities having a low loss at high microwave power levels. However, the designs are bulky and involve a complicated and expensive fabrication technology and they are not suitable for monolithic microwave integrated circuits.
From WO 94/13028 a number of tunable microwave devices based on high temperature superconductors and ferroelectric thin film microstrip waveguide designs are known. However, these devices suffer from unacceptable high microwave losses and low tunability due to the low inherent quality of the ferroelectric film. Moreover the microwave power handling capability is low among other reasons due to the low quality of the ferroelectric film and the high non-linear behaviour (over-tone generation) of narrow HTS-strips.
Furthermore, image waveguides comprising a dielectric arranged on top of a metallic ground plane have been used for millimeter and submillimeter wavelength integrated circuits, see for example P. Bhartia and I. J. Bahl in “Millimeter Wave Engineering and Applications”, J. Wiley, 1984 and for devices in the optical spectrum, c.f. M. J. Adams, “An Introduction to Optical Waveguides”, J. Wiley, 1981. However, the implementation of this Microwave Integrated circuit (MIC) technology at frequencies below 3 GHz has been limited by dielectrics having a low dielectric constant, and low losses, tan&dgr;>10
−4
, which imply large dimensions of the dielectric MIC.
Generally, dielectric materials used in microwave technology have had a dielectric constant of 0-100, which would only result in gigantic devices at the frequencies of about 1-2 GHz. In “High Temperature Superconducting Microwave Devices”, by Z-Y Shen, Artech House, 1994 dielectric resonators based on TM
01&dgr;
delta modes are disclosed. The dielectric resonator is clamped between thin high temperature superconducting films which are deposited on separate substrates arranged between the thin film and the dielectric. Even if the surface resistance and the associating microwave losses of the high temperature superconductor materials are extremely low at 1-2 GHz, typically 10
−4
Ohm, these devices suffer from not having the desirable properties in that the dimensions of the superconducting films and the dielectric substrates at these frequencies (e.g. 1-2 GHz) are large and the devices are expensive to fabricate. Moreover they can only be tuned mechanically and therefore the devices get bulky and introduce complex problems in connection with vibrations or microphonics.
SUMMARY
Therefore tunable microwave devices are needed through which microwave monolithic integrated circuits can easily and inexpensively be fabricated and through which the size can be further reduced. Particularly fully integrated devices as circuits are needed for e.g. compact devices. Particularly microwave monolithic integrated circuits are needed which can be fabricated in a single processing chain with standard integrated circuits technology and with precise sizes and dimensions. Moreover microwave integrated circuits are needed having a good performance. Particularly devices are needed which do not require complicated assembling processes at all. Still further microwave integrated circuits are needed which have a high electrical performance. Particularly microwave monolithic integrated circuits are needed for use in the frequency band of about 1-2 GHz. In the copending patent application “Tunable microwave devices” by the same applicant filed at the same day published as WO 961 42118 and which is incorporated herein by reference, tunable microwave devices are described.
Therefore a tunable microwave monolithic integrated circuit is provided which comprises a dielectric material and a superconducting arrangement which is so arranged in relation to the dielectric material that at least one interface is formed between the superconducting material and the dielectric material which is a low loss non-linear bulk material and wherein the dielectric and/or the superconducting material has/have a variable dielectric constant. Frequency tuning is obtained by controlling the propagation of surface plasma waves of the microwave signals along the interface or the interfaces. The superconducting arrangement particularly comprises a high temperature superconducting material such as e.g. YBCO; for example YBa
2
Cu
3
O
7
, TlBa
2
CaCu
2
O
7
, Ba(Bi,Pb)O
3
. Further examples on HTS materials are given by Z-Y Shen in “High Temperature Superconducting Microwave Devices”. The dielectric material may e.g. be SrTiO
3
or anything having similar properties. In an article by Krupka et al, IEEE Microwave Theory Techn., 1994, Vol 42, No 10, p. 1886, it was stated that dielectric materials with non-linear properties, such as e.g. SrTiO
3
, have an extremely high dielectric constant, &egr;=3000-25000, at temperatures of liquid nitrogen (77° K) and below that: Further examples are e.g. solid solutions of Strontium and Barium Titanates. Particularly the arrangement comprises a waveguide arrangement.
Generally it can be said that the strongly negative dielectric constant of the high temperature superconducting material is a precondition for the existence of surface plasma waves. The fact that high temperature superconducting materials have a strongly negative dielectric constant was first recognized in a publication by K. K. Mei and G. Liang in “Electromagnetics of superconductors” IEEE Trans. Microwave Theory Techn. 1991 Vol 39, No 9. Tuning means are provided for controlling the propagation of the surface plasma waves or the surface plasmons. In a particular embodiment the microwave integrated circuit/circuits comprises a dielectric ridge waveguide and particularly a superconducting film may be arranged on one side of the slab of dielectric material opposite the side on which a ridge is formed thus forming an image ridge waveguide. The superconducting film, particularly the high temperature superconducting film in the waveguide may act as a channel for electromagnetic waves having a frequency of approximately 1-2 GHz. Of course it may be appropriate for other frequencies. Generally, also other strip waveguides could be used such as raised strip and strip loaded waveguides.
In a particularly advantageous embodiment of the invention the dimensions of the waveguide are such that it only supports propagation of the fundamental transverse magnetic mode TM
o
of the electromagnetic wave whereas all transverse electric modes TE are prevented from propagation. By controlling the surfaces plasma waves, i.e. the supported modes, that propagate along the interface or the interfaces, the phase velocity of the waves can be tuned.
In another embodiment of the invention a first superconducting film is arranged on one side of the dielectric material which is provided with a ridge or a rib forming as stripguide and a second superconducting film is arranged on the dielectric ridge thus forming a parallel plate waveguide. The dimensions of the parallel plate waveguide
Gevorgian Spartek
Kollberg Erik
Vendik Orest
Wikborg Erland
Burns Doane Swecker & Mathis L.L.P.
Lee Benny T.
Telefonaktiebolaget LM Ericsson
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