Phase mode analysis of directional elements in a circular array
A technique for analyzing the directional elements of a circular array is presented. The technique is based on phase mode decomposition of measured element patterns. It can be used to calibrate the array and may help identify sources of measurement errors. It is illustrated with patterns from a 108-element circular array.
Pattern synthesis of uniform circular arrays with directive elements
The article discusses the synthesis of radiation patterns using circular arrays of directive elements. This type of array is suitable for phased array applications and for multiple beam systems, and it could also be an excellent candidate to face up base-station demands for future wireless communication services. A Fourier series synthesis method is utilized to synthesize different radiation patterns using circular arrays of N elements with a cardioid pattern (ideal elements) and of N dipoles uniformly arranged in front of an infinite metallic cylinder.
The fragmentation of small asteroids in the atmosphere
The fragmentation of a small asteroid in the atmosphere greatly increases its cross-sections for aerodynamic braking and energy dissipation. The differential pressure across a meteoroid disperses its fragments at a velocity that increases with atmospheric density and impact velocity and decreases with meteoroid density. At a typical impact velocity of 22 km/s, the atmosphere absorbs more than half the kinetic energy of stony meteoroids with diameters, D M < 220 M AND IRON METEOROIDS WITH D M < 80 m. The corresponding diameter for comets with impact velocity 50 km/s is D M < 1600 m. Most of this energy dissipation occurs in a fraction of a scale height, which causes large meteoroids to appear to »explode« or »flare« at the end of their visible paths