A compact ultra-wideband (UWB) bandpass filter (BPF) with improved harmonic suppression using a modified coupling structure is presented in this paper. The modified coupling structure is constructed by taper-connecting two folded open stubs to the traditional parallel-coupled lines, which shows an improved characteristic in harmonic suppression. By integrating the proposed coupling and the stepped-impedance stub loaded resonator (SISLR), a UWB BPF is finally built and tested. The simulated and measured results are in good agreement with each other, exhibiting good wideband filtering characteristic and improved out-of-band performance.
Reflection of electromagnetic plane wave from a planar chiral nihility-chiral nihility interface is calculated as a special case of two different chiral media by assuming that permittivities and perme-abilities of the both media approach to zero. That is, εi→0, μi→0, and chiralities κi≠0, i=1, 2. These results are used to find the geometrical optics reflected fields of a cylindrical chiral nihility-chiral nihility interface, when it is excited by a plane wave. Using the Maslov's method, field expression which yields finite values around the focus of cylindrical interface is also determined.
This work demonstrates that the well-known box configuration comprising four inverter-coupled resonators is capable of realizing a dual-band filter characteristic. A dual-band filter is designed at 1 GHz and subsequently implemented as a Combline microstrip filter exhibiting measured frequency characteristics which closely matched the simulations.
We have derived simple analytical expressions for the frequency-dependent effective permittivity tensor of a one-dimensional metal-dielectric photonic crystal in the long wavelength limit. Our results describe the transition between the regime described by Rytov's formulas and that predicted by Xu et al , where the effective plasma frequency is independent of the metallic-layer parameters. The derived expressions can be useful for determining the frequency intervals where such an anisotropic system can exhibit metamaterial behavior.
An investigation on the possibility of obtaining a negative refractive index behavior in split ring resonators (SRRs) through magneto-electric coupling is presented. We have performed rigorous electromagnetic simulations using a full-wave 3D simulator, and the obtained results have been verified by our experimental realizations and measurements. The results confirm that the increase of magnetoelectric gyrotropic activity inside a bi-anistropic medium can lead to the establishment of backward-wave propagation.
A three sections circular waveguide aperture antenna with conical beam is presented. By using two waveguide steps, the aperture distribution of the antenna can be controlled to realize the requirements on the radiation pattern with conical beam including the flare angle, gain and the side lobe level. Through optimized design, the impedance bandwidth of 550MHz with -10 dB return loss, the gain of 8.1 dB and a flare angle of 50 degrees have been achieved at the central frequency 35 GHz. Good agreement has been observed between simulated results and measured ones. The proposed antenna is easy to be fabricated and suitable for many applications.
An open L-slot antenna with triple-band operation for WLAN and WiMAX applications has been designed and implemented with a slit and a strip, which can be used to generate two band-rejected characteristics. Both the strip and the slit play a very important role in suppressing the dispensable bands. By adjusting the dimensions of the slit and strip, the proposed antenna shows three separated operation frequencies with a bandwidth of 14% from 2.24 to 2.58 GHz, a bandwidth of 19% from 3.02 to 3.66 GHz, and a bandwidth of 10% from 5.62 to 6.21 GHz, respectively. Detailed designs and experimental results are reported in this paper.
This paper presents a numerical study of the thermal effects induced by a commercial RFID antenna in vials filled with blood plasma. The antenna is located under a conveyor belt which transports cardboard boxes bearing test tubes or pooling bottles. Part of the energy used to read the RFID tags penetrates into the vials and heats the plasma. Our aim is to assess if the RFID technology can alter the quality of the blood plasma by increasing excessively its temperature. To do so, we first compute the specific absorption rate inside the vials with the finite element method. Then, assuming that no heat dissipation process is present, we estimate the number of continuous reading cycles required to increase the plasma temperature 0.1°C in the worst-case scenario. Finally, we compare this number with the number of reading cycles required to obtain all the data from the tags under normal usage conditions.
An over-mode metal rectangular waveguide is widely used in the generation, propagation, coupling, and transition of microwaves. When applied as the beam-wave interaction circuit of some high power microwave devices, a rectangular waveguide is expected to operate at a single electromagnetic mode. To do that, unwanted modes resulted from spurious oscillations should be suppressed. In this paper, a method of selective suppression of electromagnetic modes in rectangular waveguides by loading distributed losses in some special position of waveguide inner wall is presented. By using the method, the unwanted modes can be attenuated much larger relative to the operating mode. The presented method can be used to improve the stability of rectangular waveguide beam-wave interaction circuit.
In this paper, we investigate the exploitation of the polarimetric diversity signal properties in a bistatic polarimetric MIMO radar to improve the performance of joint estimation of direction of arrival (DOA) and direction of departure (DOD) of targets using Combined ESPRIT-RootMUSIC technique. Numerical simulations are carried out to illustrate the performance of the proposed approach.
In recent years, metamaterials have been the subject of research interest for many investigators worldwide. However, most of reported metamaterial microstructures are obtained based on human intuition, experience or large numbers of simulation experiments which were time-consuming, ineffective or expensive. In this paper, we propose a novel negative index metamaterial microstructure design methodology that uses a FDTD solver optimized by genetic algorithm (GA) technique in order to achieve a simultaneously negative permeability and permittivity. Firstly, an novel genetic algorithm optimization model for wide frequency band of negative refraction was proposed. Then the effectiveness of the new technique was demonstrated by a microstructure design example that was optimized by GA. By using numerical simulations techniques and S-parameter retrieval method, we found that the GA-designed optimal solution can exhibit a wide LH frequency band with simultaneously negative values of effective permittivity and permeability. Therefore, the design methodology presented in this paper is a very convenient and efficient way to pursue a novel metamaterial microstructure of left-handed materials with desired electromagnetic characteristics.
The dispersion relation of piecewise linear recursive convolution finite difference time domain (PLRC-FDTD) method for space-varying plasma is analyzed using a novel equivalent method. The equivalent dispersion and dissipation errors have been taken into account. The efficiency of the novel equivalent method is substantiated by computing the test and reference transmitted electric field. The comparison of the test and reference solutions validates that the equivalent method is an efficient method to analyze the dispersion relation of PLRC-FDTD method used for space-varying plasma.
In present work, a microstrip Sierpinski modified and fractalized antenna using multilayer structure to achieve dual band behavior for WLAN applications has been proposed. Due to the space-filling properties of fractal geometry, the proposed antenna is smaller in size than the conventional Euclidean-type. An equilateral triangular patch antenna with Sierpinski Gasket fractal shape has been designed and studied. An electromagnetic coupled stacked structure of two different patches operating at two frequencies (2.4 GHz Bluetooth and 5.8 GHz Wireless LAN) has been designed for dual band WLAN applications.
An improved composite right/left-handed (CRLH) unit cell optimized for a leaky-wave (LW) antenna is presented. This CRLH cell consists of a series of one transmission line, an interdigital capacitor, another transmission line and a shunt shorted stub. Introducing the transmission lines, the parasitic self-resonances of the capacitor are shifted outside the operational band, the radiation range is extended and the transition frequency at which the balanced cell condition is achieved can be chosen in the design process from a broader range of frequencies. The characteristics and performances of the proposed cell are verified by simulation and by measuring two artificial transmission lines.
The frequency shift of the transfer function of single layer composite materials has been analyzed and tested. The effects are studied by means of planar pseudo-elliptical filters in Ka waveguide. The filters, consisting of a frequency selective surface placed perpendicularly to the waveguide axis, have been realized by a high resolution photolithographic technique. Deviations of the experimental transfer functions from the simulation are analyzed with particular emphasis to the effect of metal thickness. The finite thickness of the metal constituting the frequency selective surface causes a shift of the transfer function towards high frequencies (blueshift), attributed to dipole-dipole interaction in the metal layer. Such an effect is only partially predicted by full wave analysis based on finite element method. The increase of the thickness determines a reduction of the attenuation for thickness values between 10 and 100 skin depths.
In this paper, a novel compact microstrip-fed ultra-wideband (UWB) step-slot antenna with a rotated patch is demonstrated and experimentally studied. With an effective combination of the step-slot and rotated patch and proper dimensions, bandwidth enhancement for UWB operation is obtained. From the simulated and measured results, the enhanced impedance bandwidth is brought up to about 117.5% from 2.88 to 11.08 GHz defined by 10 dB return loss. Details of the proposed antenna are described, and experimental results are presented and discussed.
We experimentally characterize the pulse propagation in two-dimensional composite right- and left-handed transmission lines periodically loaded with Schottky varactors. A properly designed line structure should produce that nonlinearity rendered by the varactors creating a self-focused pulse on the line and finally collapses, which allows it to be engineered for pulse processing systems. We built a test breadboard line and observed self-focused pulses.
In this paper, a novel narrowband frequency selective surface (FSS) with a stable performance based on substrate integrated waveguide technology is presented. The unit cell of the FSS consists of a double-sided metalized substrate with a circular hole and a SIW circular cavity. In this way, incident EM waves enter the circular cavity and excite a TM110 cavity resonance, leading to a narrow pass-band. The high-Q property of the TM110 cavity resonance provides a very good wide-angle and polarization-independent stability. Both the simulation and experimental results show that such narrowband FSS owes its advantages to high selectivity, low profile stable performance with various incident angles and different polarizations, which is suitable for impulse detections, narrow-band communications, electronic countermeasures, etc.
Excitation and propagation of a pulse electromagnetic wave in an open circular dielectric waveguide is considered. Partition of the pulse field into radiated wave, surface wave, and guided wave has been revealed and the corresponding physical effects are interpreted directly in the time domain. Namely it was shown that there is a precursor at the rod axis that propagates with speed of light in free space, it originates from the pulse surface wave that propagates along the rod surface and radiates into the rod in a Cherenkov like manner.
A novel self-similar antenna for band-notched ultra-wideband (UWB) applications is proposed. The UWB performance is obtained by introducing a quasi-trapezoidal radiating patch and a self-similar ground plane. By etching two similar slots on the radiating patch, band-notched characteristic can be obtained. The measured results show that the antenna covers the band of UWB from 2.6 to 12.8 GHz excluding the rejected bands from 3.3 to 3.6 GHz and from 4.8 to 6.0 GHz. In addition, the antenna exhibits nearly omni-directional radiation patterns and stable gains over the operating bands.