Tailored and anisotropic dielectric constants through porosity in ceramic components
ABSTRACT In this paper, different densities within a ceramic are used to provide a wide continuous range of dielectric constants for high-frequency applications. Cofiring different ceramic materials together to make a single unified structure to obtain different dielectric constant combinations is quite difficult due to phase stability issues and shrinkage mismatches. However, using various levels of porosity in order to alter the effective dielectric constant in the same material allows patterning different dielectric constants into a single unit. Since the structure is made from a single material, the varying porosity regions can be made compatible. Glassy-carbon-assisted and microcellular-structure-based porous titania allow for an extremely wide range of dielectric constants, ranging from 12 to 90, while maintaining a low loss tangent. Highly anisotropic materials are demonstrated herein to achieve a dielectric constant contrast of 90/9.6 using large-range aligned microcellular structure. Dielectric-resonator antennas are shown as an application of adjusting the bandwidth between 0.5% and 2.5% by tailoring the ceramic dielectric constant. A stratified-medium-loaded cavity resonator and a buried dielectric ring resonator internal to a microcellular substrate are used to demonstrate both the cofiring and variable dielectric constant capabilities of structured porosity.
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ABSTRACT: The Maxwell Garnett and Bruggeman effective medium theories are derived for the average dielectric permeability of heterogeneous materials from a unified theoretical approach. It starts by specifying two random unit cells which represent different microstructures. Requiring that these cells should not be detectable by electromagnetic radiation when embedded in an effective medium, we show from an extended optical theorem that the forward scattering amplitude must vanish. Setting the leading term in the expansion series of this quantity equal to zero yields the effective medium theories pertaining to the two microstructures. The remaining terms provide estimates of the accuracy of the approximations. This approach is then used in numerical computations for Co-AI(2)O(3) cermets.Applied Optics 01/1981; 20(1):26-30. · 1.69 Impact Factor
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ABSTRACT: This paper presents the state of the art of high-Q TE01 mode DR cavity filters for PCS wireless base station applications. In order to have TE01 mode filter to be competitive with other high-Q cavity technologies, employment of nonadjacent coupling to implement advanced filter features and easy filter machining and integration are essential. The quadruplet and trisections are regarded as basic blocks to implement symmetric and asymmetric transmission zeros in filter stop band. The relative alignment of the magnetic mode field across the coupled adjacent cavities is analyzed to identify the sign of nonadjacent coupling. A direct cascading of a wide band combine filter to a TE01 mode dielectric resonator (DR) filter is proposed to suppress the spurious response of the DR cavity filter. This approach simplifies the integration between the DR filter and the spurious suppression device and has been proved to be very cost effective. Experimental eight- and six-pole quasi-elliptic function filters show the typical performances. To take advantage of the special property of magnetic mode field alignment across the adjacent cavities, a five-pole canonical asymmetric filter with three transmission zeros in low side is implemented. We believe this filter is a new design for high-Q cavity filter, while a three-pole elliptic function filter is new for DR filter technologyIEEE Transactions on Microwave Theory and Techniques 01/1999; · 2.23 Impact Factor
Article: Design of microwave filters[show abstract] [hide abstract]
ABSTRACT: A survey of the major techniques used in the design of microwave filters is presented in this paper. It is shown that the basis for much fundamental microwave filter theory lies in the realm of lumped-element filters, which indeed are actually used directly for many applications at microwave frequencies as high as 18 GHz. Many types of microwave filters are discussed with the object of pointing out the most useful references, especially for a newcomer to the fieldIEEE Transactions on Microwave Theory and Techniques 04/2002; · 2.23 Impact Factor