2 FSK WLAN antenna

>> Okay. Now let's talk
about the antenna block.

The antenna right here is what's

used to receive the signal
in the first place.

The antenna is a 2.4 or 2.6

gigahertz antenna so they can receive
both of the possible frequencies.

They come into this antenna which
is a quarter of a wavelength long,

and underneath there's copper
underneath each of these strips.

So, that this thing right here is
a microstrip as a transmission line.

Now, the transmission lines are
normally modeled like this.

Their model is a combination of
resistors, inductors, capacitors,

and conductors G so that
each little distance

along this transmission line can
be assumed to be a resistive,

capacitive, inductive, conductive network.

So that's a transmission line.

Okay now, as the signal is
received by this antenna,

the antenna has
a particular input impedance.

On the other side, the amplifier has
a particular input impedance as well,

and these two impedances
need to be matched at

the stub and they wouldn't be and
so we have to manually match them.

This thing right here is an open-circuited
stub that's used to impedance match

the antenna to the transmission line and

then the amplifiers also matched
to this transmission line.

This particular transmission line
is a 50 Ohm transmission line.

So, we need this antenna
to be matched to 50 Ohm's.

The way we do it is we have

a particular distance here and a
particular length of the stub.

It's literally just a little stub
of copper that we

cut with scissors and stuck down,

this literally stuck it right down there

so it's touching this transmission line.

The length of the stub is
going to make it either

capacitive or inductive depending
on the length of the stub.

Remember that inductors and
capacitors create phase shifts.

A phase shift is just a time delay.

So as a little bit of signal goes
up this line and comes back,

that's the time delay
that it experiences and

consequently the phase
shift that it also obtains.

So, once we get past this point,

the antenna and this combination of

impedance matching network are
now matched to a 50 Ohm line.