Fatih Ustuner

Stacked Conical Ring Dielectric Resonator Antenna Excited by a Monopole for Improved Ultrawide Bandwidth

Stacked conical ring dielectric resonator antennas (DRA) excited by an axi-symmetric coaxial monopole are investigated numerically and experimentally for improved bandwidth. The bandwidth improvement is due to an extra resonance which occurs near the frequency where the monopole height is about a full wavelength. We consider two cases of the hybrid antenna: one case in which the tips of both cones face up and a second case in which the top cone is inverted to form a “sand-glass” shaped DRA. Measured data were obtained to validate the results of simulations. The proposed hybrid antennas can easily offer a fractional impedance bandwidth up to 138% along with monopole type radiation pattern. The antennas have a relatively low peak gain around the extra resonance.

Antenna radiation pattern measurement using an unmanned aerial vehicle (UAV)

The in-situ radiation pattern measurement of low frequency antennas on complex platforms is a challenging job due to the large antenna sizes and large distances for far field requirements. In order to propose a solution for this problem, an attempt is made by using an unmanned aerial vehicle for the radiation pattern measurement. A radio controlled (R/C) model aircraft equipped with an autopilot system is used for the concept demonstration. A log-periodic antenna is used as the antenna under test and the azimuthal radiation pattern of the antenna is measured. The quite good agreement of the measured pattern with that of the simulated pattern promises that the UAV may be used for antenna radiation pattern measurement.

Effects of sensor positions on military radiated susceptibility tests

The MIL-STD 461F RS103 test is one of the essential radiated immunity tests for military equipment. Unlike the pre-calibration method of commercial radiated immunity tests such as EN61000-4-3, the RS103 test requires the placement of an electrical field sensor close to the application point of the EUT (Equipment Under Test) and also requires active-leveling of the field based on the feedback from the sensor without use of a pre-calibrated field. In most cases, the position of the sensor is not certain in the standard and every laboratory uses their own selections for probe positions which are close to the application region. In this research, we showed that the chosen sensor position directly affects the value of power injected into the antenna, consequently affects the test results significantly for a constant electrical field value owing to the reflections coming from the EUT itself.

Experimental Validation of a 3D FSS Designed by Periodic Conductive Fibers Part-1: Band-Pass Filter Characteristic

In this study, an X-band band-stop frequency selective surface (FSS) consisting of aligned finite length periodic conductive cylindrical fibers embedded in a dielectric host material is designed, manufactured, and electrically tested in the frequency range of 2 to 18 GHz. Furthermore, an equivalent circuit model is developed to estimate the electrical characterization of the band-stop FSS. Finally, the transmission results obtained from simulations are experimentally validated using a free-space setup. Moreover, a quasi-isotropic multilayer band-stop FSS is recommended to design a polarization-independent FSS.

An EMC experimental kit for demonstrating the effect of printed circuit board layout on the radiated emissions

An EMC experimental kit is developed to illustrate the fundamental mechanisms of radiated emissions from printed circuit boards. The kit is then expanded to cover and demonstrate some of the EMC design techniques such as shielding and filtering that are useful for reducing radiated emissions. In this paper, the experimental kit and the experiment configurations are described. Representative results are given in order to show the PCB layout effect on the differential and common mode radiated emissions. Moreover, the need for integral application of shielding and filtering is emphasized as the outcome of the experiments.

Assessment of PED interference to ILS and VOR receivers in a small cargo plane

The use of personal electronic devices (PED) inside an aircraft still causes serious concerns due to the interference risk to the safety critical avionics. Recently, uncontrolled PED use constitutes a clear threat to the operation of some cargo aircrafts used by Turkish Air Force. In order to evaluate the degree of this risk, it is carried out an assessment of PED interference to ILS and VOR receivers. The interference path loss (IPL) is calculated. It is compared with the measurements on a scaled mockup. Finally interference margin is found for worst cases taking account all parameters.

Loop antenna pattern measurements

In this study, we installed a loop antenna pattern measurement system and investigated the radiation patterns of loop antennas, which has not been adequately investigated so far in literature. The loop antenna pattern measurements were realized in two modes, receiving and transmitting modes. During pattern measurement, the loop antenna under measurement was rotated from 0° to 360° for azimuth plane and from 0° to 180° for elevation plane by suitable steps and consequently, two-dimensional and three-dimensional patterns of the antenna were drawn. 3-dB beamwidths of the loop antenna were calculated by using the pattern data and the importance of beamwidth was emphasized in terms of EMC tests and measurements in azimuth and elevation plane. In addition, directivity values of the antenna were calculated with the assumption of far field by analyzing all the pattern data obtained from the measurements.

Interaction of a MW AM broadcast transmitter with a large crane and the analysis of the workers' safety

During the construction phase of a wind power plant in Turkey, an electromagnetic interaction was observed with a large crane and an AM broadcast transmitter. The interaction resulted in large current levels which poses health hazards to the workers. Initial grounding measures were not sufficient. In order to quantify the current levels, to assess the degree of the hazard and to find a practical remedy to the problem, the phenomenon is modeled and different cases with different worker configurations are analyzed. The analysis results emphasize the importance of the insulation and local grounding.

Design and realization of a planar near field antenna measurement system

Determination of the radiation pattern is one of the major issues in antenna characterization. Radiation pattern is a far field parameter and it must be measured at a point where wave trains are propagating in same phase. Although this range can be obtained inside a laboratory for isotropic antennas, in case of high gain directive antennas it can well extend to several tens of meters. Radiation pattern measurement using near field approach is possible for the latter case, even inside a small-scale laboratory. Nevertheless, since the design and the realization of near field antenna measurement systems require detailed engineering activities compared to that of far field systems, their costs are fairly high. In order to obtain a low-cost, maintainable and native near field antenna measurement system, an engineering study was conducted in TUBITAK BILGEM UEKAE EMC Laboratory and a near field measurement system was developed. In this article, antenna patterns measured by the developed system are presented.

Meeting the NSA Requirement for CISPR 16-1-4 in a MIL-STD-461E Type Semi Anechoic Room

The radiated emissions measurements require different types of anechoic chambers for civil and military EMC standards. An anechoic chamber constructed according to the requirements of MIL-STD-46IE may not meet the requirements in CISPR 16-1-4. Instead of constructing a new semi anechoic room (SAR), an investigation on the possible use of a SAR originally constructed for MIL-STD-461E tests to perform the commercial standard tests was carried out. To achieve the goal, the theoretical normalized site attenuation (NSA) formulation of an open area test site (OATS) is revisited in terms of RX antenna height scan range. The variations in the NSA depending upon the height scan range is analyzed both from a theoretical and measurement point of views. Then the chamber is evaluated according to a modified CISPR 16-1-4 approach. The comparative measurement results are presented.