Camelot - The Google Group : Rec.Radio.Amateur.Antenna
http://groups-beta.google.com/group/...ateur.antenna/
Has many Antenna Experts that may have the Answers
to your Antenna Simulation Questions.

hope this helps ~ RHF

= On Jan 21, 10:45 pm, "camelot" wrote:
- Any suggestion?
-
- camelot ha scritto:
-
- Hello,
- I'm new in antenna simulation world and I would like to ask
- you some questions on some topics.
-
- I hope someone could help me.
-
- The first question is if it is true that Directivity, Gain and
- Efficency of an antenna are simply tied to the her topology
- and not to the goodness of the matching network or the
- source impedance, i.e, if I have to measure these values,
- should I necessary verify that the antenna is correctly matched
- with source?
-
- Second (and last!) question,
- I have to simulate a folded dipole with a ground connection in
- the center (necessary to the supplying chip as ground reference).
- The structure had hence 3 ports. My question is if a inductive
- or capacitive load connected to the middle virtual ground port
- (and the chip) can significantly affect the matching and other
- parameter (D,G) of the port.
- In few words, that third branch connected to a virtual ground,
- how influence the antenna behavior?
-
- Sorry for my trivial questions
- but I'm continuing studying in order to fill my gaps.
- Regards,
-
- Camelot
-
-
- -



On Jan 22, 3:50 am, "RHF" wrote:
Camelot - The Google Group : Rec.Radio.Amateur.Antennahttp://groups-beta.google.com/group/rec.radio.amateur.antenna/
Has many Antenna Experts that may have the Answers
to your Antenna Simulation Questions.

hope this helps ~ RHF

= On Jan 21, 10:45 pm, "camelot" wrote:
- Any suggestion?
-
- camelot ha scritto:
-
- Hello,
- I'm new in antenna simulation world and I would like to ask
- you some questions on some topics.
-
- I hope someone could help me.
-
- The first question is if it is true that Directivity, Gain and
- Efficency of an antenna are simply tied to the her topology
- and not to the goodness of the matching network or the
- source impedance, i.e, if I have to measure these values,
- should I necessary verify that the antenna is correctly matched
- with source?
-
- Second (and last!) question,
- I have to simulate a folded dipole with a ground connection in
- the center (necessary to the supplying chip as ground reference).
- The structure had hence 3 ports. My question is if a inductive
- or capacitive load connected to the middle virtual ground port
- (and the chip) can significantly affect the matching and other
- parameter (D,G) of the port.
- In few words, that third branch connected to a virtual ground,
- how influence the antenna behavior?
-
- Sorry for my trivial questions
- but I'm continuing studying in order to fill my gaps.
- Regards,
-
- Camelot
-
-
- -

Thank you very much! :-)

RHF ha escrito:
Camelot - The Google Group : Rec.Radio.Amateur.Antenna
http://groups-beta.google.com/group/...ateur.antenna/
Has many Antenna Experts that may have the Answers
to your Antenna Simulation Questions.

hope this helps ~ RHF

= On Jan 21, 10:45 pm, "camelot" wrote:
- Any suggestion?
-
- camelot ha scritto:
-
- Hello,
- I'm new in antenna simulation world and I would like to ask
- you some questions on some topics.
-
- I hope someone could help me.
-
- The first question is if it is true that Directivity, Gain and
- Efficency of an antenna are simply tied to the her topology
- and not to the goodness of the matching network or the
- source impedance, i.e, if I have to measure these values,
- should I necessary verify that the antenna is correctly matched
- with source?
-
- Second (and last!) question,
- I have to simulate a folded dipole with a ground connection in
- the center (necessary to the supplying chip as ground reference).
- The structure had hence 3 ports. My question is if a inductive
- or capacitive load connected to the middle virtual ground port
- (and the chip) can significantly affect the matching and other
- parameter (D,G) of the port.
- In few words, that third branch connected to a virtual ground,
- how influence the antenna behavior?
-
- Sorry for my trivial questions
- but I'm continuing studying in order to fill my gaps.
- Regards,
-
- Camelot
-
-
- -



On Jan 22, 3:50 am, "RHF" wrote:
Camelot - The Google Group : Rec.Radio.Amateur.Antennahttp://groups-beta.google.com/group/rec.radio.amateur.antenna/
Has many Antenna Experts that may have the Answers
to your Antenna Simulation Questions.

hope this helps ~ RHF

= On Jan 21, 10:45 pm, "camelot" wrote:
- Any suggestion?
-
- camelot ha scritto:
-
- Hello,
- I'm new in antenna simulation world and I would like to ask
- you some questions on some topics.
-
- I hope someone could help me.
-
- The first question is if it is true that Directivity, Gain and
- Efficency of an antenna are simply tied to the her topology
- and not to the goodness of the matching network or the
- source impedance, i.e, if I have to measure these values,
- should I necessary verify that the antenna is correctly matched
- with source?
-
- Second (and last!) question,
- I have to simulate a folded dipole with a ground connection in
- the center (necessary to the supplying chip as ground reference).
- The structure had hence 3 ports. My question is if a inductive
- or capacitive load connected to the middle virtual ground port
- (and the chip) can significantly affect the matching and other
- parameter (D,G) of the port.
- In few words, that third branch connected to a virtual ground,
- how influence the antenna behavior?
-
- Sorry for my trivial questions
- but I'm continuing studying in order to fill my gaps.
- Regards,
-
- Camelot
-
-
- -

Hello Camelot,

Directivity is determined solely by the antenna structure. I dipole
has a directivity of about 2.14 dB, no matter from what impedance you
will feed it. Be carefull that in many cases the feedline will carry
common mode current and will radiate too. If so, you must model at
least the screen of the feeder as part of the antenna too.

Directivity is strongly related to the radiation pattern of the
antenna.

If the match is perfect and there are not heat losses, directivity =
gain.

Efficiency is the ratio between total radiated power and real input
power (always less then 1). Efficiency is limited by heat losses in
conductors and dielectrics.

In general: gain = directivity - (mismatch loss) - efficiency.
All in dB.

So if you have an antenna with a maximum directivity of 6 dBi, a VSWR=2
and efficiency = 0.5, you gain in the direction of maximum directivity
is 6 - 0.5 - 3 = 2.5 dBi.

From the input impedance you cannot say something about directivity.
For example, look to a HW dipole, it has about 50..73 Ohms. A folded
dipole (with same radiation pattern and hence same directivity) has
about 200 to 300 Ohms input impedance.

About the effect of the middle ground port.
When the output of your RF chip has good symmetry, and your antenna
will have good symmetry too, the RF current into the middle port will
be negligible. A decoupling coil or capacitor may have a small effect
on resonant frequency of the antenna (because of small capacitive
coupling to the actual antenna). The change in input impedance will be
minimal/negligible also.

If you might expect asymmetry, using a capacitor to ground, will cause
(significant) current through the capacitor and hence will affect
radiation pattern, input impedance, etc.


Best Regard and good luck,

Wim
PA3DJS.

Thank you very much PA3DJS for your interest! ;-)

Camelot

On Jan 23, 12:40 pm, "Wimpie" wrote:
RHF ha escrito: