[time-nuts] Smaller, and smaller antennas

[Bill Slade]

My calculation was a bit hasty. Q_rad is around 123, not 7e6 (misplaced factor of 2pi).  Still pretty bad, tho'. So, we have 1/24 -1/123=1/Qloss or Qloss = 25; typical of what you'd find in a lumped LC circuit.
Cheers

________________________________
From: time-nuts <time-nuts-bounces at lists.febo.com> on behalf of Bill Slade <slade_bill at hotmail.com>
Sent: Wednesday, March 6, 2019 10:32 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Smaller, and smaller antennas

The Chu-Harrington limit for passive antennas (ones without active, non-Foster circuits) states that for small antennas Q_rad>lambda^3/(2pi a)^3.  at 2.4GHz, lambda = 12.5cm.  For an antenna of a=4mm dominant dimension, Q_rad>7e6!  If a VSWR BW of 100 MHz is measured at the feedpoint (Q_tot approx 24) and we remember that 1/Q_tot = 1/Q_rad + 1/Q_loss, we see that the Q factor is dominated by antenna losses and radiation efficiency is very poor.  My feeling is that the feed network on the PCB will radiate more than this antenna.

It would not be the first time that I have seen electrically small antennas that exhibit suspiciously substantial VSWR bandwidth that are like resistors than antennas.

Cheers,
Bill

________________________________
From: time-nuts <time-nuts-bounces at lists.febo.com> on behalf of Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Sent: Wednesday, March 6, 2019 8:11 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Smaller, and smaller antennas

2.4/0.1 = 24 not 240 !!!

Bruce
> On 06 March 2019 at 17:36 jimlux <jimlux at earthlink.net> wrote:
>
>
> On 3/5/19 3:05 PM, Charles Steinmetz wrote:
> > Ho, hum, yet another fantastical claim for magical gain from a
> > tiny-for-wavelength antenna.
> >
> > See the many discussions of same by Kurt N. Sterba over the last several
> > decades, among many, many others.
> >
> > The laws of physics are stubborn things....
>
>
> these don't violate the theoretical limits.. 100 MHz BW at 2.4 GHz is
> pretty high Q (240).
>
> What I'm interested in is the internal construction -  lambda at 2.4 GHz
> is 122 mm, and these things are 3x3x4mm.  If you tried to dielectrically
> load a half wavelength from 61 down to 3mm, that's a factor of 20, which
> implies an epsilon of 400.  Clearly, that's not what they're doing.
>
> I'm a bit suspicious about that long feedline in the test fixture.
>
>
> Johansen has lots of these in various frequencies and sizes
> https://www.johansontechnology.com/antennas
>
> Tons of WiFi (2.45 GHz) antennas in all sizes and shapes.
>
> GPS/GLONASS antennas too
> https://www.johansontechnology.com/datasheets/1575AT54A0010/1575AT54A0010.pdf
> 12x4mm
>
>
>
>
> >
> > Best regards,
> >
> > Charles
> >
> >
> > On 3/5/2019 1:48 PM, jimlux wrote:
> >> On 3/5/19 9:33 AM, Gregory Beat via time-nuts wrote:
> >>> No, this is not an “L-band”, GNSS antenna ... BUT it demonstrates the
> >>> shrinking size.
> >>>
> >>> NEW Molex 206513 Antenna for 2.4 GHz, 3x3x4 mm in size.
> >>> Less than $1.00 for quantity 1, both Mouser and Digi-Key now stocking.
> >>> https://www.digikey.com/en/product-highlight/m/molex/2-4-ghz-ceramic-antenna
> >>>
> >>>
> >>>
> >>> Molex’s 206513 series is a 2.4 GHz embedded ceramic antenna with high
> >>> efficiency over 55% on all frequency bands. This miniature SMT ceramic
> >>> component requires a very small (4 mm x 4 mm) keep-out area and is
> >>> designed to be mounted directly at the corner of the main device PCB.
> >>> It has a frequency range of 2.4 GHz - 2.5 GHz, return loss of <-6 dB,
> >>> and peak gain (max) 3.6 dBi. It features an omnidirectional radiation
> >>> pattern.
> >>>
> >>
> >> One needs to carefully look at the 55% claim with these kinds of things.
> >>   Are they including that in the gain, 50% efficiency is a gain hit of
> >> 3dB? Peak gain of 3.6dBi (is that circular or linear?) (is that
> >> directivity, or gain?). Does the efficiency count the 25% of the power
> >> reflected back from the 6dB return loss?
> >>
> >> https://www.molex.com/pdm_docs/ps/2065130001-PS.pdf is more about
> >> packaging
> >>
> >> https://www.molex.com/pdm_docs/as/2065130001-AS.pdf has the antenna
> >> patterns..
> >>
> >>
> >>
> >> Also, what's the axial ratio off boresight...
> >>
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> >
> >
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