We provide a conceptual and theoretical analysis of nonsinusoidal antennas with emphasis on how electromagnetics and communication theories can be integrated to propose ideas for near-field (NF) communications systems utilizing future antennas. It is shown through rigorous analysis that in nonsinusoidal antennas it is possible to derive and solve ordinary differential equations giving specialized time-domain excitation signals that lead to exact cancellation of the near field at specific radiation spheres. This opens the door to building NF communications systems with far-field-like communication receiver infrastructures utilized if the receive antenna is placed at the special sphere where the NF component is made to vanish. We deploy exact current Green's function analysis method and completely avoid the use of any frequency-domain method. Complete expressions of the electromagnetic near- and far-field contributions to all signals propagating from the source to the receiver are then derived and their physical content discussed. The distortion effects and signal-to-noise rations due to the near-field are also identified and derived theoretically. It is found that using this specialized pulse excitation method in nonsinusoidal antennas, distortion caused by near-field components can be eliminated at critical distances between the source and the receiver. Realization issues of this system are briefly discussed together with some potential applications.
This paper presents a hybrid sliding mode control of a multicell power converter. It takes into account the hybrid aspect of the conversion structure which includes the converter continuous and discrete states The idea is based on using a hybrid control and an observer-type sliding mode to generate residuals from the observation errors of the system by including diferent types of faults in the transition between modes. The case when a DC motor is coupled to the multicell converter is also considered. In this case, it is shown that under certain admissible assumptions, the voltages across the capacitors and the speed of the motor can be acceptably estimated. The simulation results are presented at the end to illustrate the performance of the proposed approach using stateflaw in sumulink (matlab). The developed method is illustrated in an example of the DC motor supply via a three cell converter which is a real example of an SDH characterized by continuous and discrete variables.
A new family of substrate integrated waveguide metamaterial bandpass filters is proposed which support the backward and forward wave propagations with two adjacent passbands under the cutoff frequency of the structure. Through varying the fractal slots sizes etched overthe SIW structures, different frequency transmission responses were realized. Extraction of the metamaterial parameters was achieved via scattering parameters. The equivalent circuit model was analyzed to provide comprehensionon the SIW-metamaterial unit cells. The equivalent electrical length of a fractal slot is larger than the conventional slot, making it suitable to design highly miniaturized filters. Three filters using the 3rd iteration H-shaped SIW-metamaterial unit cells were designed and testedusing subwavelength resonators. Filter designwas used to extract the coupling coefficient and external quality factor to obtain the filters' optimized physical dimensions. The out-of-band rejection can be enhanced by configuring the fractal slots or the SIW. A wide upper out-of-band rejection with attenuation >50 dB with the range 5.5 GHz to 9 GHz was realized. The proposed filters offer advantages through low insertion loss, easy fabrication, high selectivity, small size, and low cost. The measured scattering parameters S21 and S11 were in agreement with the simulated.
High Q-factor bandstop filter based on broadside-coupling between U-shaped coplanar waveguide (CPW) resonator and CPW through-line (CPWTL) is proposed in the present paper. The CPWTL is printed on the top layer of the dielectric substrate whereas the CPWR is printed on the bottom layer. Only over very narrow frequency band, around the resonant frequency of the CPW resonator (CPWR), the microwave power flowing in the CPWTL is coupled to (absorbed by) the CPWR leading to a bandstop filter of very high Q-factor. A CPWR with side ground strips of finite width is shown to have much higher Q-factor than that of infinitely extending side ground planes. Owing to the lower profile of the CPW with finite-width, the radiation loss is reduced, and the structure has narrower frequency band for coupling, which results in much higher Q-factor than other published works. The dimensions of the CPWTL are optimized for impedance matching whereas the dimensions of the U-shaped CPWR are optimized to obtain the highest possible Q-factor. The effect of the loss tangent of the dielectric substrate material on the Q-factor is investigated. A prototype of the proposed filter is fabricated and experimentally studied for more understanding of the underlying physical principles of operation and for experimental investigation of the filter performance. The experimental measurements show good agreement with the corresponding simulation results.
Automotive radars make use of angle information obtained from antenna arrays to distinguish objects that lie in the same range-Doppler cell (relative to the ego vehicle). This paper proposes novel ways of using presently known minimum redundancy arrays (MRAs) in single-input multiple-output (SIMO) and multiple-input multiple-output (MIMO) automotive radars. Firstly, an MRA-based sparse MIMO array is proposed as a novel modification to the nested MIMO array. The proposed sparse MIMO array uses MRAs as the transmitting and receiving modules, unlike the nested MIMO array, which uses two-level nested arrays (TLNAs) at the transmitting and receiving blocks. Upper bounds for the virtual array aperture and the overall attainable degrees of freedom (DOF) offered by the MIMO radar have been derived in terms of the number of sensors. Secondly, the suitability of large Low-Redundancy Linear Arrays (LRLAs) in SIMO automotive radars is also studied. A long-range automotive radar driving scenario was assumed for DOA estimation and simulations were carried out in MATLAB using the Co-array MUltiple SIgnal Classification (co-array MUSIC) algorithm. Simulation results confirm that the proposed MRA-based MIMO array provides better angular resolutions than the nested MIMO array for the same number of sensors and that LRLAs can serve as a handy replacement for ULAs in SIMO radars owing to their acceptable performance. As MIMO and SIMO radars designed from currently known MRAs were sufficient to satisfy the angular resolution requirements of modern automotive radars, a need to synthesize new MRAs did not arise.
In this paper, a new robust computational method that applies the geometrical theory of diffraction (GTD) in conjunction with the ray tracing (RT) technique is developed to evaluate the electromagnetic scattering pattern due to a plane wave incident on a rough surface of quite arbitrary statistical parameters. The Fresnel reflection model is applied under the assumption of arbitrary electrical and optical properties of the rough surface material to obtain the scattering patterns for both the power reflected to the upper half-space and the power transmitted into the medium covered by the rough surface. Also, the polarization of the plane wave primarily incident on the rough surface is taken into consideration. The algorithm developed in the present work accounts for multiple bounces of an incident ray and, hence, it can be considered arbitrary higher-order GTD-RT technique. The accuracy of the obtained results is verified through the comparison with the experimental measurements of the scattering pattern of a light beam incident on rough sheets with specific statistical properties. Also, some of the obtained results are compared to other published results using the geometrical optics (GO) and the second-order Kirchhoff's approximation. The numerical results of the present work are concerned with investigating the dependence of the scattering pattern on the surface roughness, refractive index, angle of incidence, and the resolution of the geometric model of the rough surface. Also, it is shown that, for limited resolution of the rough surface model, the accuracy of the calculated scattered field depends on the angle of incidence of the primary beam and the surface roughness.
Wireless communication and/or wireless power transmission are highly desired in some of the practical environments fully enclosed by conducting walls. In this paper, a semi-analytical modal analysis is conducted for the purpose of characterizing wireless channels in a fully-enclosed space. The modal analysis is based upon an integral equation method. The cavity Green's function in the spectral domain (that is, expressed in term of cavity modes) is employed in the integral equation. The analysis results indicate that, when a transmitter and a receiver are symmetric to each other with respect to a certain cavity mode, the load of the receiver could be coupled to the transmitter with little dispersion, leading to excellent wireless channels with the potential of accomplishing efficient wireless communication and/or wireless power transmission. A cubic cavity with a side length of 1 meter is analyzed as a specific example, and the modal analysis results are verified by experiments. Measurement data agree with the theoretical analysis very well. As predicted by the theoretical analysis, excellent wireless channels associated with the TM220 mode (with a bandwidth of 40 MHz), TM310 mode (with a bandwidth of 10 MHz), and TM311 mode (with a bandwidth of 20 MHz) are demonstrated inside a cubic box with side length of 1 meter.
We have simulated ionospheric disturbances generated by the buoyancy and electrodynamic effects in a two-dimensional configuration in the vertical plane in the ionospheric F region using a simple two-dimensional mathematical model for internal gravity waves propagating in the lower atmosphere, and we have investigated the characteristics (e.g. buyoancy frequency, wavenumber, wavelength, speed) of the ionospheric disturbances. We find that electrohydrodynamic effects are mainly responsible for small scale non-travelling ionospheric disturbances, while magnetohydrodynamic effects are responsible for travelling ionospheric disturbances, including small scale travelling ionospheric disturbances (SSTIDs), medium scale travelling ionospheric disturbances (MSTIDs) and large scale travelling ionospheric disturbances (LSTIDs). Our results are in agreement with the results obtained from observations.
The present paper studies the characteristics of electromagnetic scattering from vegetation models constructed as random wire structures for the purpose of PolSAR imaging and ground surface cover recognition and classification. Radar vegetation index (RVI) has been developed for the purpose of vegetation growth monitoring. Anew method is proposed to use the RVI as an accurate monitor for the natural grassland height taking into account the operational parameters such as the PolSAR look angle and the operating frequency. Also, the present paper addresses a problem that may lead to false indications of the RVI measured for grassland areas. It frequently occurs that some of the narrow long leaves of the grass cloud are quasi-parallel and of nearly equal lengths leading to the generation of internally resonant modes. The enhancement or diminishing of the backscattered field at such internal resonances may give false indication of the RVI and, hence, wrong information can be estimated such as the water content and the grass height. A new method is proposed to model the natural grasslands as clouds of electrically conductive random curly strips for the purpose of obtaining the backscatter coefficients and, hence, the corresponding RVI. The error in height estimation using the proposed method due to the existence of the internal resonances is numerically investigated.
The precise positioning of an autonomous robot in the wireless sensor network with a high refresh rate is important for well-ordered and efficient systems. An orthogonally transmitted simultaneous multi-beam system improves the geometric dilution of precision (GDOP) and expedites the refresh rate of the system. In this paper, the beam-pattern analysis of an electronically steerable multi-beam impulse radio ultra-wideband (IR-UWB) transmitter tag is presented and demonstrated. The multi-beam transmitter tag is optimized to improve the real-time positioning accuracy of an autonomous robot for an indoor positioning and tracking system. Two linear arrays of four elements with an inter-element spacing of 18 cm and 10.2 cm are proposed and optimized. The array with spacing 10.2 cm is intentionally configured to produce orthogonal beams, which eventually provides better geometric dilution of precision. The beam steering-angle analysis is performed to better utilize the steering delay range and scanning angle range. The radiation intensity in the direction of the transmitted beam is calculated. Consequently, an intensity table for the Gaussian-modulated multi-cycle IR-UWB beamforming array is proposed. The intensity table gives an easier way to calculate the peak intensity and the number of cycles of the radiated IR-UWB pulse in the transmitted beam direction. The proposed beamforming transmitter arrays are observed to achieve the scanning range from -60˚ (-90˚) to +60˚ (+90˚) with a scanning resolution of 5˚ and 8˚ in the measurements.
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