An Efficient Adaptive and Steep-Convergent Sidelobes Simultaneous Reduction Algorithm for Massive Linear Arrays

Antenna arrays have become an essential part of most wireless communications systems. In this paper, the unwanted sidelobes in the symmetric linear array power pattern are reduced efficiently by utilizing a faster simultaneous sidelobes processing algorithm, which generates nulling sub-beams that are adapted to control and maintain steep convergence toward lower sidelobe levels. The proposed algorithm is performed using adaptive damping and heuristic factors which result in learning curve perturbations during the first few loops of the reduction process and is followed by a very steep convergence profile towards deep sidelobe levels. The numerical results show that, using the proposed adaptive sidelobes simultaneous reduction algorithm, a maximum sidelobe level of −50 dB can be achieved after only 10 iteration loops (especially for very large antenna arrays formed by 256 elements, wherein the processing time is reduced to approximately 25% of that required by the conventional fixed damping factor case). On the other hand, the generated array weights can be applied to practical linear antenna arrays under mutual coupling effects, which have shown very similar results to the radiation pattern of the isotropic antenna elements with very deep sidelobe levels and the same beamwidth.

Near-surface imaging from traffic-induced surface waves with dense linear arrays: an application in the urban area of Hangzhou, China

Accurate understanding of near-surface structures of the solid Earth is challenging, especially in urban areas where active source seismic surveys are constrained and difficult to perform. The analysis of anthropogenic seismic noise provides an alternative way to image the shallow subsurface in urban environments. We present an application of using traffic noise with seismic interferometry to investigate near-surface structures in Hangzhou City, eastern China. Noise data were recorded by dense linear arrays with approximately 5 m spacing deployed along two crossing roads. We analyze the characteristics of traffic-induced noise using 36 hr continuous recordings. Coherent Rayleigh surface waves between 2 and 20 Hz are retrieved based on crosscorrelations within 1 hr time windows. Robust phase-velocity dispersion curves are extracted from virtual shot gathers using multichannel analysis of surface waves and coincide with the results from active seismic data, noise beamforming analysis, and measurements with the spatial autocorrelation method (SPAC). Shear-wave velocity profiles are derived for the top 100 m of the subsurface at the array locations. The estimated shear-wave velocities from traffic noise correspond to the velocities estimated from logging data. The 2D shear-wave velocity maps reveal different soil deposits and bedrock structures in the estuarine sedimentary area. The results demonstrate the accuracy and efficiency of delineating near-surface structures from traffic-induced noise, which has great potential for monitoring subsurface changes in urban areas.

Untilted edge slot antennas excited by T-shaped wires

An effective method is proposed to excite the untilted edge slot antennas. In the proposed method, two T-shaped wires are placed at both sides of each untilted slot. Two legs of each T-shaped wire are connected to the waveguide walls, while the third leg is open. One of the T-shaped wires connects the upper broad wall of the waveguide to the narrow wall of the waveguide which contains the slots. Similarly, the other T-shaped wires connect the lower broad wall of the waveguide to the narrow wall of the waveguide that contains the slots. The phase reversal between the adjacent slots can be accomplished by changing the orientation of the T-shaped wires. It is shown that the arm lengths of the connected wires can be employed as a parameter to control the radiated power by the slots. Furthermore, the arm lengths of the open wires can be selected properly to control the dynamic range of the equivalent normalized susceptance associated with each untilted slot antenna. To validate the effectiveness of the proposed antennas, two linear arrays consisting of 11 slots have been designed, implemented, and tested. The simulation and the measurement results of the designed arrays show that for the proposed untilted edge slot antennas, the dynamic range of the equivalent normalized susceptance is improved significantly which leads to a straightforward design process with no requirement to resort to any time-consuming tuning process.

Parametric Analysis of Linear Periodic Arrays Generating Flat-Top Beams

Several synthesis techniques are available to optimize amplitude and phase excitations of periodic linear arrays to generate flat-top beams. Clearly, the optimal tapering depends on design parameters such as the array length, the number of array elements, the beam flatness, the beam width, the side lobe levels, and others. In this paper, in order to derive useful guidelines and rule of thumb for the synthesis of periodic array antennas, relations between these parameters are derived employing linear programming techniques, which guarantee optimality of the solutions. Such relations are then plotted and used in some design examples.