Use of a simple ring-shaped defected ground structure is experimentally demonstrated to suppress considerable mutual coupling between two cylindrical dielectric resonators. About 5 dB suppression has been obtained near the operating frequency around 3.3 GHz. The radiation characteristics with and without defect in the ground plane are also reported.

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A HfSiO4 ceramic was prepared by a conventional solid state synthesis method by sintering at 1600 °C. The morphology of the sintered surface was characterized using scanning electron microscopy and atomic force microscopy and the average surface roughness was about 118 nm. The sintered HfSiO4 ceramic has εr = 7.0, Qu × f = 25 000 and τf = -44 ppm °C(-1) at 10 GHz. It exhibits promising thermal properties such as a low linear thermal expansivity (CTE) of -1.8 ppm °C(-1) (dilatometer) in the temperature range of 30-800 °C and a room temperature thermal conductivity of 11 W m(-1) K(-1).

The (Sr 1Àx A x ) 2 (Zn 1Àx B x )Si 2 O 7 ceramics (A 5 Ca, Ba and B 5 Co, Mg, Mn, Ni) were prepared by the conventional solidstate ceramic route and their structure and microwave dielectric properties were investigated. The majority of the compositions have an akermanite-type structure except for A/B 5 Ba/Zn and Sr/Ni. A structural change is observed from tetragonal to monoclinic with the increase in Ba 21 content at the Ca-site. When Zn 21 was completely replaced by Ni 21 , a mixture of SrSiO 3 and NiO phases resulted instead of the solid solution Sr 2 NiSi 2 O 7 . The variation of cell parameters and cell volumes of (Sr 1Àx A x ) 2 (Zn 1Àx B x )Si 2 O 7 was studied for various compositions (x) in the range 0-1. Excellent dielectric properties (e r 5 8.4, Q u  f 5 105 000 GHz (at 12.628 GHz) and s f 5 À51.5 ppm/1C) were obtained for the composition Sr 2 ZnSi 2 O 7 when sintered at 14751C/2 h. Addition of 2 wt% of SrTiO 3 to Sr 2 ZnSi 2 O 7 decreased the s f value to À13 ppm/1C with e r 5 8.8, Q u  f 5 60 000 GHz (at 12.585 GHz). Thus, a composite of Sr 2 ZnSi 2 O 7 and SrTiO 3 is a possible material for millimeterwave communication systems and as microwave substrates.