[MLB-WIRELESS] Antenna Orientation

[John Dalton]

In theory, yes you can squeeze more capacity by using orthogonal
antennas.  (In *theory*, a horizontally polarised antenna will
receive no signal, ie. infinite dB attenuation, from a vertically
polarised antenna and vice versa.)

In practise, simply rotating antennas may not work very well as
there are environmental effects which can change the angle of polarisation
as a radio signal propagates.

Some WLAN manufacturers are already working on exactly the system you
have proposed.  They use two orthoganal receiving and transmitting
antennas, with signal processing in the receiver to resolve the 'horizontal'
and 'vertical' components despite rotation during propagation.

Such 'orthogonal antenna' systems will probably get blown out of the water
by systems using a more general technique called 'space-time'coding
(of which orthogonal antennas is a special case).  It uses similar
ideas but allows more than two antennas to be used, with more than
a doubling in capacity.

Regards
John


A quick note on an error in terminology in some posts:
dBm is an absolute measure of power (ie. dB referred to a power of 1mW) = 10 * log10(power/1mW).
Ratios, such as attenuation, are measured in dB (no 'm' suffix) = 10 * log10(output power / input power). {usually with a sign reversal if talking about attenuation}
A small, but important, difference.

There are lots of other 'dB's as well, each with a different reference level.  For example:
dBW = power in dB relative to 1 watt
dBV = power in dB relative to 1 volt across a constant impedance
dBc = power in dB relative to the carrier
and so on, ...

To unsubscribe: send mail to majordomo at wireless.org.au
with "unsubscribe melbwireless" in the body of the message