Re: NEC-LIST: Mast Radiator Ground losses

Phil,

You should be able to integrate the Poynting's vector normal to ground
((z.E x H = Ex*Hy-Ey*Hx) over a plane passing between the antenna and
ground to get the total power absorbed by the ground. I have not
tried this, but it is done in some analytic analyses for antennas over
ground. A problem is that E and H may be changing very rapidly near
the antenna. Also, you have to decide how far out you need to
integrate to get all significant power into the ground. Then the
surface can be closed with an integral over the hemisphere at
infinity, using the NEC "Average Gain" evaluation. That would let you
evaluate the total input power and the fraction radiated.

The easier way is to get the total input power from the source voltage
and current, as NEC prints under Antenna Input Parameters. Then you
can get the radiated power from the average gain. If you integrate
theta from 0 to 90 and phi from 0 to 360, the antenna radiation
efficiency (power radiated to infinity/Power in) is (Average Gain)/2,
since NEC multiplies by (4 Pi)/(solid angle integrated). You cannot
do this with NEC-2 for a monopole that ends on real ground with GE1
(the "ground stake approximation") since the input impedance and power
will not be accurate. Of course, you cannot integrate between the
antenna and ground in this case also.

Jerry Burke
LLNL
Received on Wed Mar 15 2000 - 17:35:02 EST