Dr. Gabriel BANCIU

This paper presents a comparison between dielectric resonator antennas with different dielectric constant parameter of the resonator. The antenna is fed with microstrip line. The dielectric resonators have cylindrical geometry. In HFSS software program, the simulations are up to compare the antennas' behavior as a function of different parameters, such as: center frequency, gain, frequency bandwidth etc.

In this paper, the design of aperture-couplet rectangular dielectric resonator antennas arrays is illustrated. The effect of slot feed on the dielectric resonator antenna (DRA) and the effect of the spacing between array elements is observed. This paperwork can be useful for WLAN applications with the operating frequency 5.8 GHz.

Ferroelectric (FE) thin film varactors can be a convenient technology for tuning miniature antennas. In this paper we present the design of a compact, agile, wire patch antenna integrating barium strontium titanate (Ba(1-x)SrxTiO3, BST) thin film interdigitated capacitors (IDC). The IDCs values were measured at different temperatures and bias voltages ranging from 0 to 120 V showing a capacitance variation of more than 40% between 11-13 GHz and up to 28% in the 2-3 GHz frequency interval. Their integration within a compact antenna design allows tuning its operating frequency on the whole WiFi band, with efficiencies higher than 70%.

The paper presents a CDRA (Cylindrical Dielectric Resonator Antenna) designed for wireless military and commercial applications. The antenna has been designed to radiate at 6.7 GHz, with a 160 MHz bandwidth at -10 dB. The antenna is made from a dielectric material with high quality factor. The dielectric resonator is Ba1-xPbxNd2Ti5O14 (BNT) and its relative permittivity has a value of 55.2. The feed technique used is direct coupling to micro strip-line.

In this paper we report electro-optic (EO) sampling of THz pulses using ferroelectric crystal in the non-collinear Cherenkov phase-matching scheme, where an effective velocity matching is achieved in an EO crystal with a large refractive index in the THz frequency region. We demonstrate efficient THz EO sampling using LiNbO3 and BaTiO3 crystals in the Cherenkov-phase-matching scheme. It is shown that the efficiency of EO sampling with BaTiO3 is smaller than that with LiNbO3, even though the EO coefficient (r(33)) of BaTiO3 is three times higher than that of LiNbO3. The reason of the poor performance of BaTiO3 is attributed to the strong absorption in the THz frequency region.

The microwaves are used for both civilian and military applications for communication and detection. Due to the emerging applications and the need for more bandwidth as well as for high speed there is a strong competition for ultra high frequencies devices. As it is know the size of different kind of microwave components is in a certain relation with the wavelength divided by root square of the dielectric permittivity. So the size of microwave component can be decreased by increasing the dielectric permittivity. Dielectric materials based on TiO2 are recommended for applications in electromagnetism and optics due to their nonlinear properties, to high value of the dielectric permittivity and their temperature behavior. The paper describes very shortly the technology applied to manufacture high dielectric permittivity materials based on TiO2 and microwave devices designed with this. In addition, the experimental data measured for a dielectric antenna are presented.

The paper refers to the study of patch antennas with a high permittivity dielectric substrate ((Zr-0.8 Sn-0.2)TiO4) obtained at National Institute of Materials Physics Bucharest. Because of the high value of the permittivity of the substrate material it was necessary to perform a comparative investigation of different prototypes and arrays. It was considered two substrate thickness h(1)=1mm and h(2)=2mm and two frequencies f(1)=2.4 GHz and f(2)=1.8 GHz. For each case we presented the radiation pattern in the two principal planes (E and H) and input impedance. Also, some radiation pattern for rectangular array with n=4, 16, 36 patches are presented. In the Conclusion section a discussion on the suitability of patch antennas with high permittivity substrate is done.