Yasser Attia Albagory

EFFICIENT SIDELOBE REDUCTION TECHNIQUE FOR SMALL-SIZED CONCENTRIC CIRCULAR ARRAYS

Concentric circular antenna array (CCAA) has interesting features over other array configurations.A uniform arrangement of elements is assumed where the interelement spacing is kept almost half of the wavelength and the array parameters such as the steering matrix and gain are determined.The array performance such as beam power pattern, sidelobe level and beamwidth are discussed in two cases of central element feeding.The two cases are compared showing the reduction in the sidelobe level to more than 20 dB in the case of central element feeding without extra signal processing especially for small- sized arrays that have smaller number of elements and rings.

A novel tapered beamforming window for uniform concentric circular arrays

A new tapering window is proposed for the uniform concentric circular arrays (UCCA) in order to reduce the sidelobe level at lower cost of wider beams and more practical feasibility and stability. The window has decaying exponential variation with the number of rings depending on the exponent used. The optimum value of the exponent is found to be between 0.4 and 0.5 for noncentral element UCCA and between 0.2 and 0.3 for central element UCCA. The sidelobe level can be reduced to about 26 dB and this level occurs when the number of rings equals the number of elements of the innermost ring at the optimum values of the exponent.

OPTIMUM NORMALIZED-GAUSSIAN TAPERING WINDOW FOR SIDE LOBE REDUCTION IN UNIFORM CONCENTRIC CIRCULAR ARRAYS

In this paper, a new tapered beamforming function for side lobe reduction in the uniform concentric circular arrays (UCCA)is proposed. This technique is based on tapering the current amplitudes of the rings in the array, where all elements in an individual ring are weighted in amplitude by the same value and the weight values of different rings are determined by a function that has a normalized- gaussian probability density function variation. This novel tapering window is optimized in its parameters to have the lowest possible side lobe level that may reach 43 dB below the main lobe and these optimum weights are found to be function of the number of elements of the innermost ring and the number of rings in the array. The proposed tapering window can be modified to compensate the gain reduction due to tapering when compared with the uniform feeding case.

Geometrical Analysis of High Altitude Platforms Cellular Footprint

Cellular communications using high altitude platforms will predominate the existing conventional terrestrial or satellite systems. Radio coverage of HAPs is an important issue that affect the cellular system design, therefore a deep analysis of the HAP cell footprint will be presented in two coverage models and the cell parameters are also deduced for subsequent cellular design. In the design stage, a cell generating algorithm is introduced to define their locations more accurate. When deploying the cellular system with such algorithm, the cells have proper overlap and interspacing.

Design of High Altitude Platforms Cellular Communications

Cellular communications using high altitude platforms (HAPs) will predominate the existing conventional terrestrial or satellite systems but requires some optimization especially in the cellular radio coverage design. The design of HAPs cellular system suffers from increasing cell area when directing the same beam to cover lower elevation regions and therefore requires some modification in its location. In this paper either spot-beam antennas or antenna phased arrays are used in the radio coverage which are optimized in directing their beams to satisfy mostly uniform cellular layout with minimal coverage problems such as coverage gaps between cells or excessive cells overlap. The cells locations determination is done through proposed algorithm that takes into consideration the cell area increase at lower elevation angles and provides mostly uniform radio coverage especially at the cell edges.

An Approach for Dolph-chebyshev Uniform Concentric Circular Arrays

In this paper, a new design approach for sidelobe reduction in the uniform concentric circular arrays (UCCA) is proposed. This technique is based on tapering the current amplitudes of the rings in the array by the coefficients of an even predesigned Dolph-Chebyshev linear one-dimensional array which has a number of elements that equals twice the number of rings and a prewarped sidelobe level obtained from prewarping curves. These curves map the UCCA desired sidelobe level to a level used in the design of the corresponding one-dimensional array. The UCCA with this tapering scheme is analyzed to have the lowest possible sidelobe level that may reach 53 dB below the mainlobe and the tapering weights are found to be function of the number of elements of the innermost ring and the number of rings in the array.

CONCENTRIC CIRCULAR ANTENNA ARRAY SYNTHESIS USING COMPREHENSIVE LEARNING PARTICLE SWARM OPTIMIZER

Concentric circular antenna array (CCAA) is synthesized to generate pencil beam with minimum side lobe level (SLL). The comprehensive learning particle swarm optimizer (CLPSO) is used for synthesizing a ten-ring CCAA with central element. This Synthesis is done by flnding the optimum current excitation weights and interelement spacing of rings. The computational results show that sidelobe level is reduced to i40:5dB with narrow beamwith about

A novel cellular structure for stratospheric platform mobile communications

A novel cellular structure is proposed for the ambitious stratospheric platform mobile communications. The innovated structure adopts a multibeam scanning antenna array to create ring-shaped cells instead of the classical honey cells. This helps in avoiding the impact of positional instability especially the rotational motion of the platform around its vertical axis. Furthermore the transmitted power is reduced as well as the handover and location updating rates. The adaptation of the cell area for traffic balancing is easier than using the traditional hexagonal one. The geometry of the ring cell is analyzed in order to investigate the main parameters affecting the system performance such as the beam visiting time and the beam-scanning rate.

Chaotic Interleaving for Robust Image Transmission with LDPC Coded OFDM

This paper presents a new technique for progressive image transmission over low-density parity-check coded orthogonal frequency division multiplexing (LDPC-OFDM) system. This technique adopts chaotic Baker map to improve the performance and reduce the peak-to-average power ratio (PAPR) of the OFDM signal. It helps improving the error resilient ability and also enhancing the efficiency of progressive image transmission over frequency selective fading channels. The proposed technique can effectively resist the fading impact of the frequency selective channels using simple frequency domain equalization. The proposed technique also utilizes the set partitioning in hierarchical trees as a source coding algorithm for the transmitted images. The distinctive feature of the proposed technique is that the transmitted data sequence has less data correlation, which leads to minimizing the PAPR. Simulation results show that the proposed technique improves the visual quality of the received images and reduces the PAPR of the OFDM signal as well.

GEOMETRICAL CORRECTION FOR CELL DEPLOYMENT IN STRATOSPHERIC CELLULAR SYSTEMS

In this paper, cellular communications from Stratospheric platforms (SPs) is studied, and the coverage footprint analysis and design is demonstrated. In the analysis, two coverage schemes are introduced; ∞at-earth and real-earth models and cell footprint are determined in each case. The ∞at-earth provides simple footprint equations describing the cell dimensions especially for the cells of higher elevation angles while more accurate coverage equations, which well determine the geometry of the cells of lower elevation angles, can be obtained from the real-earth scheme. The design of a cellular system using the proposed coverage models is then introduced through a procedure that determines the cells locations and dimensions on the ground according to the teletra-c information. The procedure takes into considerations the cell broadening when going outwardly from the central cell to the outer lower elevation cells and constructs a cellular layout that has the most proper cells overlap and uniform coverage edges, which helps the linking between difierent SPs coverage areas.