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VK3ABK > WIFI 22.04.07 07:04l 51 Lines 2615 Bytes #999 (0) @ WW
BID : 55022_VK3HEG
Read: DG5YM GUEST DK5RAS OE3GMW DL1BAH
Subj: A patch antenna (GM7HUD, ZS6MI)
Path: DB0FHN<DB0MRW<DK0WUE<7M3TJZ<HS1LMV<CX2SA<ZS0MEE<VK4TRS<VK3HEG
Sent: 070422/0441Z @:VK3HEG.#WEV.VIC.AUS.OC #:55022 [Ballarat] $:55022_VK3HEG
From: VK3ABK@VK3HEG.#WEV.VIC.AUS.OC
To : WIFI@WW
Hello again.
In reply to Roy, ZS6MI, who wanted info on a 'flat plate antenna', GM7HUD
recommended a pcb based 'plate' antenna. This can get complicated due to
the need to know the dielectric properties of the pcb substrate, so that
calculations can be made to cut to the frequency required. I doubt that
ZS6MI wanted to go to this extreme just to see if his WIFI would work.
G8MNY has sent, several times, his design for a 'flat plate antenna' using
wire construction over a flat plate ground plane. This may be something ZS6MI
can consider later, and my previous suggestion of a stub fed dipole, also
over a flat plate ground plane, was intended to be a simple solution. I think
the helical antenna suggestion would be the quickest and easiest way to go.
But just to add to the general idea of 'flat plate'( what ever that is),
it occurred to me that what is known as a 'patch' antenna, with a simple
construction method, might be of interest. This antenna has been described
elsewhere; notably for me, in 'Amateur Radio' (WIA Journal) for February 2003
by VK3BLG, with details of theory and construction.
Basically, a patch antenna consists of two or more squares of sheet metal
cut to resonate at the desired frequency, and mounted close to a back or
ground plane with an unusually small spacing reminiscent of the DDR antenna.
Each patch is cut to approximately half wave squares, but spaced at only
one sixth wavelength from the back plane.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ ³ This represents a 'Patch' antenna.
³ ³ The centre support at + can be a
³ ³ metal thread to allow adjustment of
³ +--x-----³ the spacing to a back plane. As this
³ ³ point is virtually 'ground', a metal
³ ³ connection is ok. The coax braid is
³ ³ connected to + and the centre conductor
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ goes to point x, selected as Z=50 Ohm,
on a line perpendicular to a side.
Imagine this 'patch' in plan view, over a much larger metal plate, with the
coax connected via a small hole from behind. An array of these patches will
interact to increase gain, and can also provide Cw or ACW circular polarity
of reception or transmission. This antenna obviously has an unbalanced feed
point, so any problems of matching with a balun are eliminated.
For interest after Roy's original request. What do you think, Roy?
73. Dick. VK3ABK.
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