Suitability of Ni-Zn Ferrites Ceramics with Controlled Porosity As Granular Substrates for Mobile Handset Miniaturized Antennas
Résumé
Low-loss Ni-Zn porous ferrite ceramics have been obtained (porosity close to 40%) after appropriate heat treatment and shaping of nanosized powders. The key point in this process is a moderate reaction sintering that promotes desired value of porosity. Measured complex permeabilities and permittivities in the [10 7 Hz -10 10 Hz] frequency range are presented. The developed materials show almost constant refractive index value n close to 5 up to 900 MHz. The sum of the magnetic and dielectric losses shows moderate values up to a frequency value f, unusual for spinel ferrites: tanδ μ +tanδ ε <; 0.083 at f=600 MHz. Their efficiency for miniaturization and performances improvement of several new antennas for Digital Video Broadcasting Handheld (DVB-H) devices (frequency ranging: 470-862 MHz) are presented. High miniaturizations (about 40% to 60% when compared to not loaded antenna) are obtained. Low loss, wide bandwidth and good radiation efficiency are measured. Antennas performances are enhanced. A new antenna is also presented. Its dimensions are very small and it covers the entire DVB-H band. Suitability of Ni-Zn porous ferrites ceramics for antenna miniaturization for DVB-H applications is demonstrated.