Ekrem Demirel

Polarization and angle independent perfect metamaterial absorber based on discontinuous cross-wire-strips

This study presents design, fabrication, and measurement of a metamaterial absorber (MA) based on discontinuous cross-wire-strip (CWS) resonators. This suggested that MA has a simple geometry configuration and introduces perfect absorption approximately 99.79% at 3.42 GHz for simulation and 99.72% at 3.44 GHz for experiment. In addition, the designed model can be used to realize the broadband absorber for desired frequency ranges. Besides, numerical simulations validate that the MA could achieve very high absorptions at wide angles of incidence for both transverse electric and transverse magnetic waves. The experimental results are in good agreement with the numerical simulations. Moreover, this study presents a numerical analysis in order to explain physical interpretation of MA mechanisms in detail. The proposed model and its variations enable myriad potential applications such as stealth and radar technologies.

New-Generation Chiral Metamaterials Based on Rectangular Split Ring Resonators With Small and Constant Chirality Over a Certain Frequency Band

Chiral metamaterials (MTMs), a new class of MTMs, provide a simpler solution for obtaining negative refraction and dynamic electromagnetic response. Many research groups have been studying chiral MTMs asking for strong chiral behaviors such as optical activity and circular dichroism. These studies have generally focused on the properties of a large chirality and circular dichroism. However, small and constant chirality over a certain frequency band have not been queried so far in the literature. In fact, this area is mostly ignored by the researchers. This study numerically and experimentally focuses on small and constant chirality with a new-generation planar chiral MTM based on rectangular split ring resonators (SRRs), in details by using two different geometries. We have successfully obtained small chirality values by using the proposed designs, which can be easily integrated into many interesting applications such as transmission and antireflection filters or polarization control devices.

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.

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.

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.

New generation chiral metamaterials with small and flat chirality over a certain frequency band based on circular split ring resonators for microwave filter applications

There are many studies in literature on chiral metamaterials (MTMs) to obtain large chiralities with dynamic optical activities. With this regard, this new generation planar chiral MTM study focuses on a small, non-dispersive (constant/flat) chirality admittance over an indicated frequency band which has not been investigated so far in literature. This new generation planar chiral MTM provides a small and a constant/fixed chirality which is mostly ignored by the scientists. This study numerically and experimentally investigates and examines these new generation MTMs based on circular split ring resonators (SRRs) with an increased capacitance in details. Obtained results show that the suggested structure can provide a small and constant/flat chirality admittance over a certain frequency band and hence it can be used to design myriad novel electromagnetic (EM) devices such as transmission and antireflection filters, polarization rotators for any desired frequency regions.

New generation chiral metamaterials based on omega resonators with small and smooth chirality over a certain frequency band

In this paper, we have designed, simulated and analyzed a new generation chiral metamaterials (MTMs) with two geometries. There are various types of chiral MTM structures in the literature and almost all of them are indented to be designed for high level of chirality. In fact, small chirality and its application areas were mostly ignored by researchers. In this sense, our study is one of the pioneer works for this type of research. Each structure based on omega resonators (ORs) with small chirality value is investigated both numerically and experimentally. The results are in very good agreement which will lead us to conclude that our structures can be easily used as devices for controlling polarization, EM wave transmission filtering, antireflection and so on for a wide range of the EM spectrum.

New generation planar chiral metamaterials with small and constant chirality over a certain frequency band

Chiral metamaterial (MTM) researchers generally concentrate and aim to obtain large chirality with optical activity in certain frequencies. However, new generation planar chiral MTM which have small and constant/flat chirality over a certain frequency band have not queried by this time in literature. In fact, this area is mostly ignored by researchers. This study, first one according to best of our knowledge in the literature, is investigating the small and constant/fixed chirality and focuses on the new generation planar chiral MTM based on circular split ring resonators (SRRs), in details. It can be seen from the results that the proposed model can provide small and constant/flat chirality over a certain frequency band and thus it can be used to design myriad novel devices such as polarization rotators, and electromagnetic transmission and antireflection filters for several frequency regions.

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.