Dielectric properties of alumina lamellar ceramics

Ceramic materials constituted of stacking of dense and porous layers of alumina were prepared and characterised at low (103–105 Hz) and high (109–1010) frequencies. At low frequency, the permittivity was measured perpendicularly to the layers. It depends on the thickness of porous layers but not on frequency. Low values were obtained which gives to these materials a real interest as substrates. In the microwave range, a microstrip circular patch was deposited on one of the sample faces and the resonances of this structure are characterised and compared to the resonances of an identical patch on a dense alumina substrate. Resonance frequency are only slightly modified but the return losses are increased: the laminar substrate improves the coupling of the circular patch to the excitation circuit.