A Generalized Array Factor for Time-Modulated Hexagonal Based Antenna Array Geometry With Novel Trapezoidal Switching

The concept of the time-modulated array has been emerging as an alternative to the complex phase shifters,which lowers the cost of the array feeding network due to the utilization of radio frequency(RF)switches.The various forms of hexagonal antenna array geometries can be used for applications like surveillance tracking in phased array radar and wireless communication systems.This work proposes the generalized array factor(AF)for the hexagonal antenna array geometry based on time modulation.The time modulation in generalized hexagonal geometry can maintain the fixed static amplitude excitation,giving more flexibility over time.Furthermore,a novel trapezoidal switching function is also proposed and applied to the generalized array factor to enable future researchers to use this array factor in the field of advancement to observe how switching schemes like trapezoidal and rectangular affect the array pattern's side lobe level(SLL).The generalized equation can be utilized for the analysis and synthesis of radiation characteristics of the time-modulated hexagonal array(TMHA),time-modulated concentric hexagonal array(TMCHA),time-modulated hexagonal cylindrical array(TMHCA),and time-modulated hexagonal concentric cylindrical array(TMHCCA).The numerical result illustrates the generation of AF of time-modulated hexagonal structures and also shows that the trapezoidal switching sequence outperforms the rectangular switch using the cat swarm optimization(CSO)approach.

Field emission of carbon nanotube array with normal-gate cold cathode

A hexagon pitch carbon nanotube （CNT） array vertical to the normal gate of cold cathode field emission displayer （FED） is simulated by solving the Laplace equation. The calculated results show that the normal gate causes the electric field around the CNT tops to be concentrated and the emission electron beam becomes a column. The field enhancement factor and the emission current intensity step up greatly compared with those of the diode structure. Emission current density increases rapidly with the decrease of normal-gate aperture. The gate voltage exerts a critical influence on the emission current.

An Evolutionary Approach to Improve the Beam Steering Performance over Conventional Approach in CHAA

In this work,evolutionary algorithms are applied for the first time to achieve better radiation characteristics over the conventional beamforming algorithm in the concentric hexagonal antenna array(CHAA),which improves the performance of wireless communication.Multiple signal classification(MUSIC)algorithm is employed for direction of arrival(DoA)estimation.The conventional adaptive beam steering algorithm,least mean-square(LMS)algorithm,is used to steer the beam.Further,the proposed approach is employed by novel particle swarm optimization(NPSO)to reduce sidelobe level(SLL)even further.A six-ring CHAA with 126 elements for DoA estimation and beam steering is simulated.The simulation results of the MUSIC,LMS,NPSO,and particle swarm optimization(PSO)algorithms are provided for various DoAs.