Re: NEC-LIST: Low angle radiation?

Hi Ed,

It's amazing how many different ideas that various people that work
with antennas on a daily basis can have. Do any of us really know why
and how an antenna radiates? In spite of this I will try to take a
stab at answering this question.

A dipole is connected to a transmission line which feeds it with a
travelling EM field. Let's assume that the t-line is a balanced
ladder line, to simplify things a bit by removing the need for a balun
and so forth. The antenna provides the proper impedance to prevent
the reflection of the travelling EM field back onto the balanced line.
The magnetic fields of each line conductor are oposite in polarity and
are split in opposite directions by the two wire segments of the
dipole. The magnetic waves continue up the legs of the dipole and are
reflected at the ends to create a standing magnetic wave. At the same
time, the electric field potential emanating from the center of the
dipole is accelerating charges along the antenna element's conductors
which further support this previously mentioned magnetic fields. So
now, our dipole antenna has a standing EM wave on it. As energy is
continually being introduced into this standing wave, it exits the
antenna in the form of a radiated EM field. If the energy of the EM
field exciteing this antenna were of a nonresonant frequency, the
standing wave would not be set up on the dipole elements. Since the
dipole elements are located in space, it's fields in space begin to
propagate since the unbound energy can't remain around the elements: a
time varying magnetic field will generate a time varying electric
field and visa versa. The entire length of the dipole is used to
create the propagating EM fields.

I don't know if anyone agrees with my views, but welcome any
constructive criticism.

I agree with Chuck Counselman about the fact that you can bend the
ends of a dipole and and still have it radiate effectively.

Good evening,

Roland Mueller
Received on Sat Feb 19 2000 - 11:58:44 EST