Jozef Modelski

Surface resistance measurements of HTS films by means of sapphire dielectric resonators

A sapphire dielectric resonator with a copper cylindrical shield and two endplates replaced by high-temperature superconducting (HTS) layers was used for very accurate surface resistance measurements on laser-ablated YBCO films. A system using the TE/sub 011/ mode has a resonant frequency of about 18.1 GHz and parasitic-loss Q factor of about 120000. It allows 10 mm*10 mm samples to be measured with sensitivity of +or-30 mu Omega . Individual samples can be measured with somewhat lower accuracy. Using larger HTS samples, one can reduce parasitic losses of the system to an unsignificant level. The exact formulas presented for the resonant system allow for avoiding calibration procedures during the evaluation of the surface resistance.<<ETX>>

Rigorous analysis and investigations of the scan antennas on a ferroelectric substrate

In this paper, the radiation characteristics of a new microstrip electrically controllable scan antenna are investigated theoretically and experimentally. Both longitudinal and transverse currents are taken into account. The substrate of this antenna consists of a ceramic-polymer composite with modified ferroelectric powder Ba0,65 Sr0,35TiO3 and an appropriate polymer. The permittivity of the substrate can be varied by an applied electric control dc-bias field. It allows to change electrically phase constant of the propagation wave and, in turn, changes the main beam direction. It is shown that the main beam position changes over 30deg when dc-bias field is applied up to 200 V. The comparison with experimental results has fully confirmed the usefulness of the scan-antenna concept and method of analysis. Presented results of the electrical scanned antenna investigation are promising for various fixed-frequency applications where frequency scanning is impossible

Voltage-controlled ferroelectric microstrip antenna for phased arrays

A new concept of microstrip antenna for phased arrays is proposed using a voltage-controlled ferroelectric thin tape in the multilayered structure. This paper presents the ferroelectric thin tape, its theoretical analysis and design. The results indicate that this concept has many advantages, is very practical and promising. It gives possibilities of several applications, e.g. in phased arrays and smart antennas.

Development and Investigation of an Antenna System With Reconfigurable Aperture

The concept and results of investigation of a waveguide slot antenna with reconfigurable aperture is presented. Solutions are based on the utilized semiconductor material, which allows one to design the electronically reconfigurable antennas. The key element of the reconfigurable antenna is a surface PIN (SPIN) diode whose conductivity changes proportionally to the plasma density. SPIN structures can be activated selectively and cause, in turn, the generation of the desired shapes of radiation pattern. It allows one to extend the function possibilities of waveguide slot antennas compared with the conventional one.

Attenuation of multipath components using directional antennas and circular polarization for indoor wireless positioning systems

This paper presents results of investigation concerning method for decreasing errors of TOA based indoor wireless positioning systems caused by multipath components. Presented method is based on directional antennas with small side lobes level. Additionally, for attenuation some of multipath components arriving from LOS direction circular polarization antennas are analyzed. The paper describes typical channel profiles for indoor environment and its influence to positioning error. Next, results of simulations are presented. Paper concludes with evaluation of antenna beamwidth and polarization into positioning accuracy based on simulation results.

The leaky-wave antenna with ferroelectric substrate

The leaky-wave antenna is investigated using the 3D FDTD method. The structure analyzed is a ferroelectric dielectric waveguide on the ground plate. The top of the ferroelectric material is covered with a conducting sheet with slots. It is shown that this antenna may have further advantages of smaller thickness, simpler beam-steering control and lower cost.

Rigorous analysis and investigations of the scan antenna on ferroelectric substrate

In this paper the radiation characteristics of new microstrip electrically controllable scan antenna are investigated, theoretically and experimentally. Both longitudinal and transverse current are taken into account. The substrate of this antenna consists of ceramic-polymer composite with modified ferroelectric powder Ba/sub 0.65/Sr/sub 0.35/TiO/sub 3/ and appropriate polymer. It shows that the beam angle changes are over 30/spl deg/ when DC bias field is applied up to 200 V.

Null pattern synthesis of ferroelectric smart antennas

In this paper, new method of null pattern synthesis of antenna arrays without phase shifters and attenuators has been presented. This concept is based on utilizing a voltage-controlled ferroelectric array, where the variable pattern of each antenna element is used to synthesize the array pattern with desired nulls.

Experimental results of testing interferences in 2.4 GHz ISM band

In the paper some experimental results of interference measurements between Bluetooth and IEEE 802.11 devices are presented. For the measurements special hardware test environment was designed. Both systems utilize the unlicensed 2.4 GHz ISM band, so the potential problem of interferences is very important. In the paper negative effects of the interferences for the system performance are presented. Methods for improving coexistence and for avoiding interferences are also discussed.

Extending Functionalities of Waveguide Slot Antennas by Means of Reconfigurable Aperture

The concept and results of investigation of some waveguide slot antenna with reconfigurable aperture have been presented in this paper. Discussed solutions have been based on the utilized semiconductor material. It allows to design the electronically reconfigurable antennas. The key element of the reconfigurable antenna is a surface PIN (SPIN) diode whose conductivity changes proportionally to the plasma density. SPIN structures can be activated selectively and cause, in turn, a generation of the desired shapes of radiation pattern. It allows to extend function possibilities of waveguide slot antennas compared with conventional one.