nec simulation - what is going on with this antenna?
 

All,

Can someone explain what is going on with this antenna? There are two resonant
points, one at about 4.5 MHz and one at about 6. The first one has a low
impedance and the second one has a high impedance. I actually saw this
phenomenon with a physical antenna being measured with an 8405a but had did not
recall ever hearing it discussed.

Thanks - Dan

CM Length X1 = 3
CM Length X2 = 2
CM Length Y = 2
CM X sections = 2
CM Y sections = 2
CM Rotate X, Y, Z = 0, 0, 0
CM Move X, Y, Z = 0, 0, 0
CE
GW 1 25 0.5 0 15 6.5 0 15 0.025
GW 2 25 -0.5 0 15 -6.5 0 15 0.025
GW 3 5 -0.5 0 15 0.5 0 15 0.025
GE 0
LD 0 2 13 13 1.e-3 3.e-5
LD 0 1 13 13 1.e-3 3.e-5
EX 0 3 3 0 1 0
GN 2 0 0 0 13 5.e-3
FR 0 1 0 0 4 0
EN

nec simulation - what is going on with this antenna?
 

Dan, your LD commands are incomplete. You have specified a series RLC in
the middle of each of the end tags. You show an R of 0.001 ohms, and an L
of 30uH. There is no corresponding series C. What you have is an end
inductivly loaded dipole., with floating end segments. This probably
accounts for your anti-resonance at about 6 MHz.

Your GE 0 card is ok -- indicating no ground plane -- but you have retained
a Sommerfeld/Norton ground description in the GN card. Not that it makes
any difference to the final result.

Frank


"dansawyeror" wrote in message
. ..
All,

Can someone explain what is going on with this antenna? There are two
resonant points, one at about 4.5 MHz and one at about 6. The first one
has a low impedance and the second one has a high impedance. I actually
saw this phenomenon with a physical antenna being measured with an 8405a
but had did not recall ever hearing it discussed.

Thanks - Dan

CM Length X1 = 3
CM Length X2 = 2
CM Length Y = 2
CM X sections = 2
CM Y sections = 2
CM Rotate X, Y, Z = 0, 0, 0
CM Move X, Y, Z = 0, 0, 0
CE
GW 1 25 0.5 0 15 6.5 0 15
0.025
GW 2 25 -0.5 0 15 -6.5 0 15
0.025
GW 3 5 -0.5 0 15 0.5 0 15
0.025
GE 0
LD 0 2 13 13 1.e-3 3.e-5
LD 0 1 13 13 1.e-3 3.e-5
EX 0 3 3 0 1 0
GN 2 0 0 0 13 5.e-3
FR 0 1 0 0 4 0
EN