《4aHelix Antenna》.pdf

A-1 Appendix A Helical Antennas S = spacing between turns(center to center) D = diameter of helix C = circumference of helix = πD −1 S α= pitch angle =tan ( ) πD L = length of 1 turn N = number of turns A = axial length = NS d = diameter of helix conductor Normal C λ A-2 mode ： Axial C ≈ λ A-3 mode ： A-4 §1. Small Loop Antenna antennas in pagers −jk r ′ e 0 ∆Aφ I ∆l 4π r Ch. 4, p.4-5 ： ： ˆ D 2 Ie−jk 0r A −a jk 0 (π ) sinθ φ 4 4πr (A-1) E jωµ A o ˆ ˆ 2 D 2 Ie−jk 0r E a E a k φ φ φ η (π ) sinθ (A-2) 0 0 4 4πr 1 2 πD 2 Ie −jk 0r ˆ ˆ (A-3) H a E