Modelling helix antennas with NEC4

Author

Trueman, C.W. ; Kubina, S.J. ; Slater, M.

Author_Institution

EMC Lab., Concordia Univ., Montreal, Que., Canada

Volume

3

fYear

1997

fDate

13-18 July 1997

Firstpage

1584

Abstract

The performance of helix antennas as a function of the length, diameter and pitch have been studied extensively by measurement. However, if a helix is modelled with a piecewise-linear approximation using straight wire "segments" in free space, the computed directivity and centre frequency differ from the measured data. This paper shows that the styrofoam cylinder or "former" on which a helix is wound for measurement has a marked effect on the electrical parameters of adjacent turns of the helix viewed as a transmission line. By modelling the additional capacitance between the turns due to the former, the computed centre frequency is brought into alignment with measured data. NEC4 offers an economical means of accounting for the capacitive effect using a dielectric sheath on the segments modelling the helix.

Keywords

antenna theory; capacitance; dielectric-loaded antennas; directive antennas; helical antennas; piecewise-linear techniques; wire antennas; 950 MHz; NEC4; adjacent turns; capacitance; centre frequency; diameter; dielectric sheath; directivity; electrical parameters; former; helix antennas; length; piecewise-linear approximation; pitch; straight wire segments; styrofoam cylinder; transmission line; Antenna measurements; Capacitance; Electric variables measurement; Frequency measurement; Helical antennas; Length measurement; Piecewise linear techniques; Transmission line measurements; Wire; Wounds;

fLanguage

English

Publisher

ieee

Conference_Titel

Antennas and Propagation Society International Symposium, 1997. IEEE., 1997 Digest

Conference_Location

Montreal, Quebec, Canada

Print_ISBN

0-7803-4178-3

Type

conf

DOI

10.1109/APS.1997.631476

Filename

631476