Title :
Modelling helix antennas with NEC4
Author :
Trueman, C.W. ; Kubina, S.J. ; Slater, M.
Author_Institution :
EMC Lab., Concordia Univ., Montreal, Que., Canada
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;
Conference_Titel :
Antennas and Propagation Society International Symposium, 1997. IEEE., 1997 Digest
Conference_Location :
Montreal, Quebec, Canada
Print_ISBN :
0-7803-4178-3
DOI :
10.1109/APS.1997.631476
