Re: NEC-LIST: TL card

YH Lee <yhl100_at_york.ac.uk> wrote:
>...I am trying to feed two dipoles using two transmission lines
>connecting the two dipoles at the middle. As shown below:
>
>
> Dipole 1 Dipole 2
> | |
> | |
> | Transmission Transmission |
> | Line 1 Line 2 |
> | |
> |---------------|----------------|
> | Voltage |
> | source |
> | |
> | |
> | |
>
> As can be seen from the structure above, because I need to connect
> the two ends of the TL card, I have made a small segement in the
> middle to act as a source (where the exciation voltage and load
> impedance are applied to the segment and the two TL cards are also
> connected to that segment). The two ends of the transmission line
> are loaded such that they are perfectly matched.
>
> The TL card seems to have amplified my excitation voltage by quite a
> lot and therefore giving me unexpected results....

1. What do you mean by "the exciation voltage and load impedance are
applied to the segment and the two TL cards are also connected to that
segment"?

Do you mean that you inserted a lumped-impedance "load" in the same
segment as the voltage source? If so, why? I don't recall (It's been
a while since I read this part of the manual; you should read it.) but
in NEC a lumped-impedance load in the same segment as a source may
appear in series with the source. I do recall that without a load,
the transmission lines will be connected in parallel with a
voltage-source.

2. What do you mean by "The two ends of the transmission line are
loaded such that they are perfectly matched." Do you mean that you
inserted a lumped-impedance "load" into each dipole's center-feedpoint
segment? (I don't know why you'd do this.) You can't (correctly)
mean that each transmission line sees a matched load, because it's
highly unlikely or virtually impossible that the driving-point
impedance of each dipole equals the characteristic impedance of the
line.

3. The quickest way to get the answers you need may be to tell us what
you're trying to accomplish with this two-dipole array antenna. E.g.,
do you want a cardioid pattern? Then perhaps one of us can tell you
how to configure the dipoles, the transmission lines, etc.

73, Chuck W1HIS
Received on Fri Mar 12 1999 - 19:02:13 EST