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Hi, my name is Gara Kodndebe. Hi, and my name is Emre Aydın.
We are senior level undergraduate students at faculty of Electrical and Electronics.
We do our expriences at the RF Electronics Laboratory.
Firstly, we will tell you about radar principles, radar types and how our Cookie Can Radar works.
Ok, lets examine human sensing radar. The term Radar stands for Radio Detection and Ranging.
We can understand that the radar is a device
that can detect range, altitude, direction or speed by manipulating radio waves.
Ok. How does radar work?
It basically transmits radio wave modulated by a particular type of waveform.
The signal is then reflected back from target object. And the radar's receiver extracts the necessary data.
But Gara, I do not know what radio wave is.
Radio wave is the sum of packets that carries energy in any medium.
Radars are classified according to their waveform as continuous wave radars and pulse wave radars.
Ok, Emre what is a continuous wave radar?
Well, initially continuous wave is a radio wave that carries energy continuously at all time.
The continuous wave radar is a radar using this type of signal.
And it cannot measure the range. The continuous wave radar principle depends on the doppler effect.
The doppler effect is the change between the
transmitted signal frequency and received signal frequency.
The Doppler frequency helps getting velocity information about an object at distance as we can see formula.
So, what is the pulse wave radar?
A Pulse Radar is radar that is used to determine the range of distant objects.
The range is calculated by measuring the time difference between the emission and reflection reception from the antennas.
Finally, look our Cookie Can Radar design.
For a basic demonstration of remote sensing, we prepared a Cookie Can Radar.
Our radar works by measuring reflected signals power.
In normal condition, power at the receiver is very low. When a person passes across,
signal power on receiver antenna rises by reflecting from human.
So we can understand if a human is passing.
How it works?
The signal generator generates continuous waves at specific frequency and power.
Transmitter antenna emits electromagnetic signal to target.
Reflected signal from the target is received by receiver antenna.
Basically, antenna is a passive device that converts electrical signal to electromagnetic
wave energy and vice-versa. Antenna is used for transmitting generated
signal and receiving reflected signal. We preferred cookie cans because it is the
easiest way to have a directional antenna. After eating the cookies, we cleaned them,
calculate the best radiation frequency according to their size, then we mounted SMA feeder.
RF to DC converter. With this device,as we can see from the table,
we get a spesific DC voltage at the output according to the RF signal at the input.
And finally the comparator.
Now, we have DC voltage from RF to DC converter.
when there is no target, converter output voltage is lower than threshold.
When there is a human, converter output voltage is higher than threshold.
So, we need to know whether the voltage increases or not.
If the voltage rises, the led blinks. At the end, we can understand if there is
a human by observing the led. Now we have a demonstration for you.
Following is how we build the cookies can antenna system.
The power supply is for RF-DC converter and comparator.
There is a coupler and then rf-dc converter comes.
The coupler samples the received signal to observe it on the spectrum analyzer.
And the comparator is decision unit of the system for detection.
Spectrum analyzer shows us the power level of received signal.
Signal generator generates the signal with
2.15 Ghz frequency and 5 dBm power.
And finally there are our receiver antenna on the left and transmitter antenna on the right.
Until a target passes, received power level is around -43 dBm. So, we get 1.2 V DC voltage at RF-DC output.
When the target enters range, transmitted
signal reflects from him. Therefore received signal power increases. Proportional to increasing,
RF-DC output voltage becomes higher than 1.2 V.
Detector senses this change,so led turns on. We hope you understand what a radar is and
how continuous wave radar works.