H.A. Sharshar

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.

Microstrip Antenna with Defected Ground Plane Structure as a Sensor for Landmines Detection

A proposed sensor for landmines detection consists of two parallel microstrip antennas placed on the same ground plane and with defected ground structure between them has been investigated. The microstrip patch array with defected ground structure has the advantage of a low mutual coupling compared with the classic one. The Finite-Difference Time-Domain (FDTD) is used to simulate the sensor for landmines detection.

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.

Microstrip antenna with corrugated ground plane surface as a sensor for landmines detection

A proposed sensor for landmines detection consists of two parallel microstrip antennas placed on the same ground plane and with corrugated ground surface between the arrays has been investigated. The microstrip patch array with corrugated ground surface has the advantage of a low mutual coupling compared with the classic arrays. The finite-difference time-domain (FDTD) is used to simulate the sensor for landmines detection.

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.

Optimization of Beams Directions for High Altitude Platforms Cellular Communications Design

Cellular communications using high altitude platforms will predominate the existing conventional terrestrial or satellite cellular systems but requires some optimization especially in the, radio coverage cellular design. In this paper either spot-beam antennas or antenna phased arrays are used in the radio coverage which is 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 Relation Between Lumped-Element Circuit Models for Cylindrical Dielectric Resonator and Antenna Parameters Using Mbpe

Finite-Difference Time Domain (FDTD) is used to calculate the input impedance of the cylindrical dielectric resonator (DRA) antenna with different dimensions. A lumpedelement circuit model for the input impedance calculation is proposed. The genetic algorithm is used to calculate the elements of the equivalent circuit. The Model-Based Parameter Estimation (MBPE) technique is used to find the variation of each element in the equivalent circuit with varying the physical dimensions of the antenna. The use of this method reduces the time required for calculating the input impedance of the cylindrical DRA in each variation of the antenna dimension.