Balun for printed dipole
 

Hello, I am presently designing a 915MHz printed dipole that will be
directly connected to a transmitter chip (one arm is directly
connected to the RF pin and the other to the RF GND pin) all on the
same PCB. Since the dipole is not connected to a coaxial cable, do I
need a balun? Theoretically, I'm assuming I don't need one since the
input to the antenna and the input to the chip are both balanced. I
did some simulations with HFSS and I seem to be able to make my dipole
decently resonate at the frequency (S11 is about -7dB). So I assume I
don't need a balun, and I should be happy with the results. I'm just
not sure I should completely rely on the simulation results. I also
don't understand why S11 isn't lower at the resonant frequency.

Any feedback would be appreciated. I need to design this antenna by
Monday!

Thank you!

On 20 Mar 2004 18:05:44 -0800, (Marty)
wrote:
Any feedback would be appreciated. I need to design this antenna by
Monday!

Thank you!

Hi Marty,

Expecting miracles are we?

Just do it and live with the results. As for it being balanced, that
is arguable, but only as a philosophical reward. Even if it wasn't
you would still be radiating power. The S11 parameters are of
interest only to an academic - is this a practical problem? If so and
analysis has you in suspended animation, your customer already has one
foot out the door.

The ream of questions that lie behind this appeal are more compelling.

Do you have a power budget (does this have to be 100% efficient)?

Is there a directionality requirement?

..... I won't go into others, these two are enough to kill any
application.

73's
Richard Clark, KB7QHC

On 20 Mar 2004 18:05:44 -0800, (Marty)
wrote:

Hello, I am presently designing a 915MHz printed dipole that will be
directly connected to a transmitter chip (one arm is directly
connected to the RF pin and the other to the RF GND pin) all on the
same PCB. Since the dipole is not connected to a coaxial cable, do I
need a balun? Theoretically, I'm assuming I don't need one since the
input to the antenna and the input to the chip are both balanced. I
did some simulations with HFSS and I seem to be able to make my dipole
decently resonate at the frequency (S11 is about -7dB). So I assume I
don't need a balun, and I should be happy with the results. I'm just
not sure I should completely rely on the simulation results. I also
don't understand why S11 isn't lower at the resonant frequency.

Any feedback would be appreciated. I need to design this antenna by
Monday!


Transmitting from EARTH to MOON?
Or rather from Mummy's kitchen to Dummy's bedroom?

Your design will be ok, I guess, as you described it.

w.

"Marty" wrote in message
om...
Hello, I am presently designing a 915MHz printed dipole that will be
directly connected to a transmitter chip (one arm is directly
connected to the RF pin and the other to the RF GND pin) all on the
same PCB. Since the dipole is not connected to a coaxial cable, do I
need a balun? Theoretically, I'm assuming I don't need one since the
input to the antenna and the input to the chip are both balanced.

"input to the antenna ...*Input* to the chip" ??? This is
confusing. "balanced"...yet one side goes to "ground".


I
did some simulations with HFSS and I seem to be able to make my dipole
decently resonate at the frequency (S11 is about -7dB).

Is HFSS driving it with a balanced drive?

Nonetheless, if it works use it.

--
Steve N, K,9;d, c. i My email has no u's.

So I assume I
don't need a balun, and I should be happy with the results. I'm just
not sure I should completely rely on the simulation results. I also
don't understand why S11 isn't lower at the resonant frequency.

Any feedback would be appreciated. I need to design this antenna by
Monday!

Thank you!