Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P3/00—Waveguides; Transmission lines of the waveguide type
  • H01P3/02—Waveguides; Transmission lines of the waveguide type with two longitudinal conductors
  • H01P3/08—Microstrips; Strip lines
  • H01P3/085—Triplate lines
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P3/00—Waveguides; Transmission lines of the waveguide type
  • H01P3/02—Waveguides; Transmission lines of the waveguide type with two longitudinal conductors
  • H01P3/08—Microstrips; Strip lines
  • H01P3/081—Microstriplines

Definitions

• This invention is directed to devices formed from high temperature superconductors. More particularly, it is directed to electronic devices formed from such super- conductors into devices having substantial power handling capability.
• HTS high-temperature superconductivity
• Microwave systems have been greatly advanced by the application of planar circuit technology which makes possible the photoetching of complex, compact circuits with many components on a single substrate. These are often referred to as “hybrid microwave integrated cir ⁇ cuits" if the solid-state devices are produced in the circuit processing. These techniques have made feasible many sophisticated systems that would not have been practical if it had been necessary to use older non-planar circuitry such as circuits using waveguide and coaxial lines which are relatively large and heavy. Examples of non-superconducting, lumped element planar arrangements are shown, for example, in Swanson U.S. Patent No. 4,881,050, issued November 14, 1989. Further, work has been done towards the goal of reducing propagation losses in normal metal coplanar waveguides.
• conventional planar microwave circuitry has a serious limitation in that it has high losses compared to, say, waveguide and most coaxial circuitry. This limits the use of conventional microwave integrated circuits to applications where considerable loss in the circuitry can be tolerated. For example, it is not feasible to realize narrow-band microwave filters in conventional integrated circuit form because high-Q (i.e., very low loss with Q's in excess of 400) resonators are required. Also, in many conventional microwave circuits the circuit components are made larger than they would otherwise need to be, in order to reduce the losses. If loss were not a consideration many microwave integrated circuits could be made to be even smaller and lighter.
• This invention relates to methods and apparatus for increasing the power handling capabilities of high temper ⁇ ature superconductor devices.
• a stripline structure a long, thin center conductor is surrounded by a dielec ⁇ tric except at the center conductor's thin edges.
• the thin edges are preferably exposed to a material having a lower dielectric constant than a surrounding dielectric, most preferably air or vacuum.
• the removed dielectric portions provide tunnels or gaps of air adjacent the center conduc ⁇ tor edges.
• Yet another stripline embodiment has air gaps extending substantially completely between the ground planes in regions laterally external to the center conduc- tor edges.
• the dielectric between the center conductor and one of the ground planes may be removed.
• the ground planes may be optionally formed on yet other support substrates.
• a microstrip arrangement consists of a center conductor having a generally long thin shape disposed on a dielectric substrate. Trenches are formed adjacent and laterally exterior to the exterior edges of the center conductor. A ground plane, optionally superconducting, is formed on the side of the dielectric opposite to that of the center conductor.
• the trenches or gaps may be formed preferably by milling, such as ion, mechanical or laser milling, or may be etched via isotropic or anisotropic etches.
• the trench or gap may be undercut beneath the super- conductor, such as through the use of an etch.
• FIG. 1 shows a perspective view of a stripline config ⁇ uration.
• Fig. 2 shows a perspective view of a modified stripline configuration.
• Fig. 3 shows a perspective view of a microstrip configuration.
• Fig. 4 shows in perspective a detail of dielectric undercut from a center conductor.
• Fig. 5 is a cross-section of a stripline transmission structure without use of the instant invention.
• Fig. 6 shows the current distribution on a center conductor of Fig. 5 as a function of lateral displacement from the center of the conductor.
• Fig. 7 shows a cross-section of electric field lines in a stripline configuration.
• Fig. 8a shows current distribution as a function of lateral position from the center of conductors in the structures of Fig. 2 and Fig. 5.
• Fig. 8b shows the current distribution in the vicinity of the right edge of the center conductor in the struc- tures of Figs. 2 and 5.
• Fig. 1 shows a perspective view of a stripline config ⁇ uration of this invention.
• a center conductor 12 is disposed substantially equidistant from a first ground plane 16 and a second ground plane 18.
• the center conduc ⁇ tor 12 generally is wider than it is thick and extends into the plane of the drawing as shown in cross-section.
• the center conductor 12 terminates in center conductor edges 14.
• the center conductor 12 is formed from high temperature superconductor materials. While any of the superconductive materials may be utilized, the YBCO and thallium superconductors are preferred for their relatively high critical temperature T c and power handling capabilities.
• the center conductor 12 is supported by dielectric 22.
• the dielectric 22 may be of any material compatible with the center conductor 12, such as lanthanum aluminate, sapphire, and magnesium oxide. In this embodiment, the dielectric 22 is disposed between the center conductor 12 and the first ground plane 16, as well as between the center conductor 12 and the second ground plane 18. Gaps 20 are formed in the dielectric 22 adjacent the center conductor edges 14. Preferably, the gap 20 is formed of a material having a dielectric constant which is lower than the dielectric constant of dielectric 22. Most preferably, the dielectric comprising the gap 20 is air or vacuum. The gap 20 runs parallel to the center conductor 12 adjacent the center conductor edges 14.
• the gap 20 is formed sufficiently large as to improve the power handling capability of the stripline structure 10 but not made so large as to imperil the structural integrity of the overall device. Generally, the larger the gap 20 is relative to the overall stripline structure 10, the better the power handling capabilities.
• the width and depth of the gap should be of the order of size of the width of the center conductor and the substrate thickness, respectively. In one embodiment, the gap depth and width is greater than 20 microns. Ideally, the gap depth would extend to the ground planes as in Fig. 2.
• the structure of Fig. 1 is preferably constructed by hybridizing two units together.
• a first unit comprising the upper portion of dielectric 22 has two substantially parallel faces, the first face bearing ground plane 16 and the second face bearing all or part of the gap 20.
• the lower module consists of substantially planar, parallel faces whereon the first face bears the center conductor 12 and all or part of the gap 20 and the second ground plane on the opposite side of the dielectric.
• the two units are then hybridized forming an interface 24 of the two mod ⁇ ules.
• the modules preferably are held together via pressure clamps.
• the gap 20 may be formed through any material removal process compatible with the other materials in the stripline structure 10.
• the gap 20 may be milled, such as by mechanical milling for relatively large structures (e.g., radio frequency devices) or by ion milling or laser milling for smaller structures (e.g., microwave and millimeter wave devices) .
• the gap 20 may be etched into the dielectric 22.
• Etching provides the opportunity to undercut the dielectric 22 from the center conductor 12.
• the gap 20 (shown in partial) has an undercut 26.
• the undercut 26 extends a distance u from the vertical line extending downward from the center conductor edge 14.
• FIG. 2 shows a modified stripline structure.
• a center conductor 30 is generally planar, having a thickness which is much less than its width and length.
• the center conductor 30 has center conductor edges 32 at the lateral edges of the center conductor 30.
• First ground plane 34 and second ground plane 36 are disposed generally parallel to the center conductor 30 and arranged with the center conductor 30 being parallel to and equidistant from each of the ground planes 34 and 36.
• a first dielectric 38 is disposed between the center conductor 30 and the first ground plane 34.
• a second dielectric, opti ⁇ mally having the same dielectric constant is disposed between the center conductor 30 and the second ground plane 36.
• Fig. 3 shows a perspective view of a microstrip configuration.
• the microstrip structure 50 includes a substrate 52 having generally planar, parallel disposed faces, a first face 54 and a second face 56.
• a center conductor 58 is formed on the first face 54 of substrate 52.
• the center conductor 58 has a thickness t which is substantially less than its width s.
• Trenches 62 are formed laterally adjacent to the center conductor edges 64.
• the trench 62 has a depth h and a width w.
• Ground plane 60 is disposed on the second face 56 of the substrate 52.
• Fig. 4 shows a gap 20 having an undercut portion 26 under the center conductor 1 .
• the undercut amount of distance u may be as desired, consistent with maintenance of structural integrity.
• the conductive materi ⁇ als namely the center conductor and the ground planes, be formed from superconducting materials.
• normal metals such as gold, high purity copper, or other materi ⁇ als compatible with transmission of high frequency elec ⁇ tromagnetic radiation.
• HTS microwave circuits do have limitations in the amount of power they can carry. If the power level in a circuit gets too high the current density in some regions of the circuit will exceed a "critical" level J c , which depends on the temperature, frequency and microstructure, and the HTS in those regions will no longer operate as a superconductor.
• this critical current density J c is typically of the order of 3 x 10 6 amps/cm 2 in high quality thin films at 77K.
• the HTS transmission lines may be able to carry as much as hundreds of watts (or possibly more depending on the line cross-sectional dimensions) without appreciable effects due to the critical current density being exceeded.
• the cur ⁇ rents within the resonators of the filter may be as much as 100 times or more as large as the currents in the lines which connect to the ports of the filter. This is a result of the resonance conditions that exist in the resonators plus the loose couplings between the resona ⁇ tors. Since power varies as the square of the current, this means that the power rating of the transmission lines used in the resonators may need to be 10,000 times or more greater than is required for the transmission lines leading into or out of the filter. Other parts of an integrated circuit which may have relatively high currents due to high standing wave ratios may also need to have high power ratings. For these reasons apparatus and techniques for increasing the power handling ability of HTS transmission lines is quite important for some micro ⁇ wave integrated circuit applications which must handle relatively high power.
• Fig. 5 shows an HTS strip transmis- sion line which consists of a center conductor 60 sur ⁇ rounded by dielectric 62 with a relative dielectric constant e r with ground planes 64 at the top and bottom.
• the center conductor extends into and out of the paper.
• the current density on the center conductor is distributed as shown in Fig. 6, where there are high peaks of current density at the outer edges of the center conductor. High peaks of current density exist near the center-conductor edges, and it is in these edge regions where current saturation will first occur as the power level is being raised on a transmission line.
• Fig. 7 shows the same structure as in Fig. 5 but with electric flux lines D sketched in.
• the flux lines shown begin on positive surface charge on the center conductor 60 and end on negative surface charge on the ground planes, and the surface charge density at any point on the surface is equal to the electric flux density D associated with that point.
• the propagat ⁇ ing charge distributions comprise surface currents on the conductors flowing into or out of the paper. Flux lines from a sharp edge with positive charge will emanate out radially, as shown in Fig.
• Consis- tent with this invention in order to reduce the high current density along the edges of the center conductor this invention reduces the fringing flux along the edges of the strip.
• the presence of the dielectric discontinuity greatly reduces the intensity of the current singularity at the edges of the center conductor.
• the structure in Fig. 2 carries considerably more power than that in Fig. 5 without having part of the current density exceed the critical value J c and cause intermodulation and excess loss.
• the peaks of the current distribution would be rounded off some even before current saturation is included.
• the divergence towards extremely high values in the current density is somewhat reduced or cut-off by an effective penetration depth which depends on the wavelength and film thickness t.
• the apparatus and methods of this invention are useful in connection with electronic circuits carrying power through waveguide type structures having relatively thin, wide conductors in which fringing affects would otherwise occur.
• these techniques serve to improve the linearity of device operation, particularly the linearity of the surface resistance as a function of current, the structures are particularly useful in connection with any signal process- ing electronics, such as receivers, transmitters and filters. By reducing the non-linearities, interference is reduced substantially.

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• Superconductor Devices And Manufacturing Methods Thereof (AREA)
• Waveguides (AREA)

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• 1996
  • 1996-02-07 EP EP96911193A patent/EP0811257A4/de not_active Withdrawn
  • 1996-02-07 WO PCT/US1996/001780 patent/WO1996026555A1/en not_active Ceased
  • 1996-02-07 CA CA002211406A patent/CA2211406A1/en not_active Abandoned
  • 1996-02-07 JP JP8525721A patent/JPH11500879A/ja active Pending

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