Wideband Small Loop-monopole HF Transmitting Antenna with Implications for Maxwells Equations and the Chu Criterion
A small un-tuned wideband loop-monopole transmitting antenna has been discovered and developed.A typical example can be fully contained in a sphere of radius a=0.75m and has been measured to be efficient(>~90%),in terms of power lost as heat,between 1.7MHz and > 200 MHz.This antenna can be considered to be small below 64 MHz.The antenna SWR typically varies from 11:1 at the lowest frequency to~6:1 at twice this(3.4MHz)and < 6:1at higher frequencies.After matching at a given frequency,the operating bandwidth is thus > 16%.An equivalent antenna Q can be estimated as < 6:6.This practically measured performance contradicts the Chu small antenna Q criterion by four orders of magnitude(~11,000)at the lowest frequency of operation.To explain this discrepancy we introduce a simple explanation of radiation,reception and antenna Q in terms of currents,charges,and potentials as derived from the Coupled Transmission Line model of Electromagnetics 1.This theory of radiation and reception has been compared with,and calibrated by.available single mode small antenna Q value measurements.Thereafter good agreement between theory and practice is then(obviously)to be found.Part of the radiation and reception theory includes a value of κ= 1/2π for the asymptotic electromagnetic coupling factor 2.This value is confirmed by the measured small(loop)antenna Q values.Maxwells equations should therefore be modified accordingly 2.The Chu small antenna Q theory and criterion 3 is thus not validated either in theory or in practice,and should now,on the basis of the latest practical and theoretical evidence,be discarded and never used in the future for small antenna performance prediction.A new fundamental discovery arising from this new antenna is the strong coupling that can taken place between magnetic and electric modes in a small antenna.With the correct phase relationship enforced between the modes the radiation resistance is considerably enhanced and the effective antenna Q is considerably reduced.This process also accounts for the typical measured bandwidths of half-wave dipoles.The conclusion is that such an effective small antenna could never have been predicted,or believed to be credible,without modification of Maxwells Equations 2 to include electromagnetic coupling,and the creation of the new theory of radiation and reception.
Michael J.Underhill
Underhill Research Ltd,Lingfield,UK
国际会议
Progress in Electromagnetics Research Symposium 2013(2013年电磁学研究新进展学术研讨会)
台北
英文
764-768
2013-03-01（万方平台首次上网日期，不代表论文的发表时间）