香港城市大学 天线设计 陆贵文教授课件Part 2.pdfVIP

DIPOLE ANTENNA + Two wire open line − Not an efficient radiator ～ + − The two vertical wires ∆l 2 constitute a dipole antenna. If ∆l λ , ～ results of infinitesimal element can be applied: (1) Not very directive (2) Not very efficient 1 DIRECTIVITY AND EFFICIENCY are improved if LENGTH is comparable to wavelength. λ2 λ Half-wave Full-wave dipole dipole 2 CURRENT DISTRIBUTION OF AN OPEN- CIRCUITED TWO WIRE LINE If b a, L µ ln b 4π a b πε C ln b a a See p.520 of Sadiku “Element of Electromagnetics” 3 ∆y y EQUIVAVENT CIRCUIT FOR A SECTION ∆y LONG ～ I L∆y ∂I I + ∆y V C∆y ∂y ∂V