Investigations On Broadband And Miniaturization Technology Of Omnidirectional Pole Antennas

Broadband omnidirectional antennas have been widely applied in mobile communications,electronic countermeasures,and satellite mapping.Nowadays,with the development of integrated and portable communication system,the demand of miniaturized broadband antenna is becoming more and more urgent.Thus,the research on broadband and miniaturization of omnidirectional antennas have become a research hotspot.Among the antenna broadband and miniaturization techniques,antenna structure optimation,passive loading and non-Foster matched antenna are popular.This paper applies these techniques on pole antennas for broadband and miniaturization.The main research contents are as follows:1.The basic theory of dipole is introduced and the common broadband forms of dipole are summarized.The circular monopole is chosen to be optimized for wider bandwidth and smaller size.The influence of parameters of the ground on the antenna performance is studied and the unimportant part is removed.A broadband U-shaped monopole is designed to further reduce the antenna size whose ground has more contribution on antenna radiation.2.The theory of real frequency technique and network synthesis are introduced and applied on antenna broadband matching.Dividing point impedance function and admittance function are used respectively to optimize the transducer power gain of two monopoles.The optimized dividing point functions are synthesized into matching networks which are simulated by ADS then.The applicability and reliability of real frequency technique in antenna wideband design are verified.3.In order to break through the gain bandwidth limitation and improve antenna miniaturization,non-Foster circuit is studied.Different forms of non-Foster circuits are compared and the method of stability determination are analyzed.The Rollet condition for circuit stability determination on non-Foster circuits is proved to be unreliable and the feasible method is proposed.The influence of the circuit connectors and layout are analyzed and the EM models of transmission lines are added into citcuit simulation to improve accuracy and reliability of the simulation.4.A printed dipole with its resonant frequency of 450 MHz is matched by negative capacitor generated by Linvill type non-Foser circuit.The reflection coefficient of the matched dipole is less than-10 dB within 30?580 MHz.Although the measured results indicate that the non-Foster circuit introduces 18 dB loss to the antenna,the gain of the dipole is still increased by 10 dB in electrically small case,which verifies the effectiveness of the non-Foster loaded antenna.