Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1993-12-06
1995-11-28
Lee, Benny T.
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
3332191, 343909, H01P 120, H01P 710
Patent
active
054711800
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
Resonant cavities form an essential part of many microwave components including filters, waveguides, couplers and power combiners. A typical dielectric resonator for a microwave integrated circuit comprises a metallic box enclosing a disk of dielectric material deposited on a substrate& with a much smaller dielectric constant. Dielectric materials are favored for most microwave applications because the high-dielectric constants available through some materials make compact circuit components possible.
These compact micowave components, however, are realized at the cost of power dissapation. Practical microwave integrated circuits are lossy compared to metallic resonant cavities, suffering power losses through the following two principle mechanisms. Since practical dielectrics are far from lossless, power is dissipated through the induced polarization of the dielectric material in a time-harmonic electric field. Also, practical dielectrics do not completely confine electromagnetic radiation, so a conductive metallic shielding surrounds the resonator to reduce radiation losses. The shield has a non-zero resistivity which results in ohmic power dissipation.
SUMMARY OF THE INVENTION
It is known that a three-dimensional periodic dielectric structure having the proper symmetry can perfectly reflect incident electromagnetic radiation, incident from any orientation, within a frequency band producing a photonic band gap. Thus, electromagnetic energy at frequencies within the band gap is prohibited from propagating through the structure. In accordance with the present invention, a dielectric resonator comprises a resonant defect structure positioned in a lattice structure formed of a plurality of multi-dimensional periodically related dielectric elements which are disposed in a dielectric background material. The resonant structure confines electromagnetic energy within a frequency band in the photonic band gap. The photonic band gap is preferably within a frequency range of 1-3000 GHZ. More specifically, electromagnetic energy having frequencies near the resonant frequency of the defect structure is stored within the resonant structure. Significantly, a dielectric resonator that employs this unique structure provides a reduced power dissipation over conventional devices, leading to more effecient performance.
The dielectric resonator lattice structure has a preferred diamond crystal symmetry, although any face-centered cubic lattice arrangement may be used. The periodically related dielectric elements may comprise overlapping spheres or disks of a high-dielectric material. Since the elements overlap, the background material may comprise air or an equivalent low-dielectric material. Alternatively, the dielectric elements may be spherical or disk-shaped regions of air or an equivalent low-dielectric material positioned in a high-dielectric background material.
In either case, the resonant defect structure is positioned in the lattice structure creating a resonant defect within the resonator. The resonant defect structure may comprise air or a dielectric material. Further, a coupling means may be coupled to the resonant cavity. The coupling means may comprise a first waveguide for coupling electromagnetic energy to the resonant structure and a second waveguide for coupling electromagnetic energy out of the resonant structure.
By positioning the defect structure in the dielectric resonator, electromagnetic energy in a narrow frequency band within the photon band gap propagating through the resonator is coupled into the defect structure. Once inside the defect structure, this energy remains trapped. Since the resonant frequency of the defect structure corresponds to the center frequency of the frequency band of the stored energy, the frequency band may be tuned during construction of the resonator. Course tuning may be accomplished by choosing a diamond lattice constant which centers the photonic band gap on the desired resonant frequency. Fine tuning may be accomplished by changing the size of the defect
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Brommer Karl
Joannopoulos John
Meade Robert
Mullaney Henry
Rappe Andrew
Lee Benny T.
Lockheed Sanders, Inc.
Massachusetts Institute of Technology
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