Jeff Liebermann wrote:
> On Tue, 21 Nov 2006 22:04:15 GMT, decaturtxcowboy
> <nope_none_@nowayspam.com> wrote:
>
> >miso@sushi.com wrote:
> >> All the biquad designs I've seen use bent wire. Has anyone tried an
> >> etched biquad antenna built on PCB?
> >>
> >> Is the issue that a PCB trace is too thin to use an an antenna?
> >
> >Commercial patch antennas use PCB materials often. Perhaps it easier
> >for DIYSers to bend and solder wire and etching a circuit board.
>
> Yep. Etched PCB antennas work. However:
>
> The dielectric constant of the PCB material will shrink the antenna by
> the square root of the dielectric constant. For example, G10/FR4 has
> a dielectric constant of about 5. One wavelength at 2.4GHz is about
> 12.5cm in free space and about:
> 12.5 / sqrt(5) = 5.6 cm
> The gain of the antenna is reduced very roughly by the same ratio. A
> common biquad with an air dielectric has a gain of about 10dBi. The
> PCB version on G10 will be about 2.5dB less.
>
> Lots of other complications when you get away from wire antennas and
> go to a PCB dielectric version. Tolerance issues, reduced bandwidth
> on the smaller antennas, non-symmetrical cross sections make calcs a
> bit complex, problems with PCB feeds, coax to PCB interface issues,
> surface conductivity (oxidized copper sucks), ad nausium.
>
> In my never humble opinion, if you're going to be building your own
> without adequate test equipment (i.e. network analyzer, antenna range,
> reference antennas, vswr bridge, etc), then do the wire antennas.
> They're much easier. However, if you have some control over
> tolerances, a good computer modeling program (4NEC2, EZNEC, etc), and
> a pile of test equipment, methinks you could try PCB antennas.
>
> As for the original question: Has anyone tried a PCB biquad? I
> dunno. I haven't. PCB material is commonly used as the reflector,
> but not the driven elements as in:
> http://martybugs.net/wireless/biquad/
>
> Well, I lied. Here's a commercial antenna that's close.
> http://802.11junk.com/jeffl/antennas...dBi/index.html
> It's a 9dBi Maxrad 2.4GHz antenna. It's NOT a biquad but rather a
> mono-quad or just one loop. There's a 12dBi version that has two
> loops and I guess would be considered a biquad. The PCB material is
> polysulfone with a dielectric constant of 3.1 and quite low loss at
> 2.4Ghz. Note the weird looking lumps on the trace connecting the loop
> with the coax connection. All that is impedance matching which will
> need to be done on your do it thyself PCB antenna. This can't be done
> without a VSWR bridge or network analyzer.
>
>
>
>
> --
> # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
> # 831-336-2558 jeffl@comix.santa-cruz.ca.us
> # http://802.11junk.com jeffl@cruzio.com
> # http://www.LearnByDestroying.com AE6KS
I'm trying to visualize how the pcb material interacts with the copper
track. It's not like you are doing stripline, i.e. metal traces with
the fr4 between the traces. The signal hits the copper from free air.
But a reflector would have the dielectric of the pcb in the path.