0:00:00.000,0:00:03.660
>> Okay. Now let's talk[br]about the antenna block.

0:00:03.660,0:00:05.880
The antenna right here is what's

0:00:05.880,0:00:08.085
used to receive the signal[br]in the first place.

0:00:08.085,0:00:11.520
The antenna is a 2.4 or 2.6

0:00:11.520,0:00:15.225
gigahertz antenna so they can receive[br]both of the possible frequencies.

0:00:15.225,0:00:19.385
They come into this antenna which[br]is a quarter of a wavelength long,

0:00:19.385,0:00:24.060
and underneath there's copper[br]underneath each of these strips.

0:00:24.060,0:00:28.080
So, that this thing right here is[br]a microstrip as a transmission line.

0:00:28.080,0:00:31.530
Now, the transmission lines are[br]normally modeled like this.

0:00:31.530,0:00:35.804
Their model is a combination of[br]resistors, inductors, capacitors,

0:00:35.804,0:00:39.335
and conductors G so that[br]each little distance

0:00:39.335,0:00:42.920
along this transmission line can[br]be assumed to be a resistive,

0:00:42.920,0:00:46.090
capacitive, inductive, conductive network.

0:00:46.090,0:00:47.645
So that's a transmission line.

0:00:47.645,0:00:51.950
Okay now, as the signal is[br]received by this antenna,

0:00:51.950,0:00:54.740
the antenna has[br]a particular input impedance.

0:00:54.740,0:00:58.520
On the other side, the amplifier has[br]a particular input impedance as well,

0:00:58.520,0:01:01.080
and these two impedances[br]need to be matched at

0:01:01.080,0:01:04.535
the stub and they wouldn't be and[br]so we have to manually match them.

0:01:04.535,0:01:08.930
This thing right here is an open-circuited[br]stub that's used to impedance match

0:01:08.930,0:01:11.630
the antenna to the transmission line and

0:01:11.630,0:01:14.705
then the amplifiers also matched[br]to this transmission line.

0:01:14.705,0:01:18.080
This particular transmission line[br]is a 50 Ohm transmission line.

0:01:18.080,0:01:21.245
So, we need this antenna[br]to be matched to 50 Ohm's.

0:01:21.245,0:01:22.610
The way we do it is we have

0:01:22.610,0:01:27.545
a particular distance here and a[br]particular length of the stub.

0:01:27.545,0:01:30.290
It's literally just a little stub[br]of copper that we

0:01:30.290,0:01:33.230
cut with scissors and stuck down,

0:01:33.230,0:01:35.090
this literally stuck it right down there

0:01:35.090,0:01:37.160
so it's touching this transmission line.

0:01:37.160,0:01:39.905
The length of the stub is[br]going to make it either

0:01:39.905,0:01:43.295
capacitive or inductive depending[br]on the length of the stub.

0:01:43.295,0:01:46.970
Remember that inductors and[br]capacitors create phase shifts.

0:01:46.970,0:01:48.950
A phase shift is just a time delay.

0:01:48.950,0:01:52.460
So as a little bit of signal goes[br]up this line and comes back,

0:01:52.460,0:01:55.130
that's the time delay[br]that it experiences and

0:01:55.130,0:01:58.105
consequently the phase[br]shift that it also obtains.

0:01:58.105,0:02:00.225
So, once we get past this point,

0:02:00.225,0:02:02.570
the antenna and this combination of

0:02:02.570,0:02:07.110
impedance matching network are[br]now matched to a 50 Ohm line.