It was a busy time. Papers galore.
In electrical engineering ( ) and telecommunications ( ) the *Chu¨CHarrington limit* or *Chu limit* sets a lower limit on the Q factor ( ) for a small radio antenna ( ). [1] ( ) The theorem was developed in several papers between 1948 and 1960 by Lan Jen Chu ( ) , [2] ( ) Harold Wheeler ( ) , [3] ( ) and later by Roger F. Harrington ( ). [4] ( ) The definition of a small antenna is one that can fit inside a sphere whose diameter is
(radius
) ¨C a little smaller than 1 ? 3 wavelength ( ) in its widest dimension. For a small antenna the Q is proportional to the reciprocal of the volume of a sphere ( ) that encloses it. In practice this means that there is a limit to the bandwidth of data that can be sent to and received from small antennas such as are used in mobile phones ( ).
More specifically, Chu established the limit on Q for a lossless antenna as
for a linear polarized ( ) antenna, where
is the radius of the smallest sphere containing the antenna and its current distribution and
is the wavenumber ( ). A circular polarized antenna can be half the size [5] ( ) (an extension of the theory of Chu by Harrington). [6] ( )
toggle quoted message
Show quoted text
On Mar 4, 2024, at 8:26?PM, Jim Lux <jimlux@...> wrote:
? Harrington & Chu, but yes.
On Mar 4, 2024, at 7:52?PM, AG6CX <edwmccann@...> wrote:
?Didn¡¯t Chu - Wheeler nail this one?
Ed McCann
AG6CX
MSEE MIT
On Mar 4, 2024, at 7:47?PM, W0LEV <davearea51a@...> wrote:
?One of the exercises we had in grad school was to prove that a radiating
structure could be down-sized to 10% of its full and ideal size without
losing efficiency, all other parameters being equal. ?The devil is in the
details, "all other parameters being equal".
Dave - W?LEV
On Tue, Mar 5, 2024 at 2:46?AM Jim Lux <jimlux@...> wrote:
How you define efficiency? ?If there¡¯s no loss, then an infinitely small
antenna (a hertzian dipole, for instance) just has 1.5 dB gain over an
isotropic antenna. Small antennas have low radiation resistance, but that
only affects efficiency if there¡¯s loss.
For the run of the mill, nearly full sized, dipole, whether or not it¡¯s
resonant doesn¡¯t change the radiation resistance much, neither does it
change the loss resistance, so the efficiency doesn¡¯t change much.
What might change is the loss in the matching network or feedline.
The compact loop is notorious for having high loss because it has low
radiation resistance compared to loss resistance. ?As is a mobile whip on
40 meters and down - they¡¯re a tiny fraction of a wavelength, so the
radiation resistance is low.
On Mar 4, 2024, at 1:01?PM, W0LEV <davearea51a@...> wrote:
?QUOTE (Jim Lux): ?.....short antennas have a different pattern than full
size antenna, but their "efficiency" isn't intrinsically different).
Jim, if we address small tuned loops on transmit, the efficiency over a
dipole radiator is considerably less, in round numbers, -20 dB.
In the limit of a point radiator (if it could radiate) - a true isotropic
source, the efficiency is zip, zero.
Dave - W?LEV
On Mon, Mar 4, 2024 at 7:28?PM Jim Lux <jimlux@...> wrote:
This is using resonance as a choke, not resonance of the entire antenna.
You want your choke to be high Z, so that currents don't flow on the
outside of the coax.
As far as the antenna goes, if you can drive it or couple power to/from
it, whether it's resonant or not makes no difference on the performance.
(aside from any other length related issues - short antennas have a
different pattern than full size antenna, but their "efficiency" isn't
intrinsically different).
-----Original Message-----
From: <[email protected]>
Sent: Mar 4, 2024 9:54 AM
To: <[email protected]>
Subject: Re: [nanovna-users] where is the end fed natural resonance
But then ARRL Antenna book says resonance has no affect on antenna
performance. Hams like to operate antennas at or near resonance as
that’s where drive point impedance is at its lowest value so
it’s easier to match,
Ray
--
*Dave - W?LEV*
--
Dave - W?LEV
--
*Dave - W?LEV*
--
Dave - W?LEV
