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Friday, 27 September 2019

Microwave Radar Transmitters and Receivers

Microwave Radar Transmitters:

The radar transmitter is generally a RF power source. It includes exciter and driver amplifiers that provide amplification for the signal to be transmitted. If the transmitter generates a pulse waveform, then the modulator used is a pulse modulator. There must be a DC power supply for generating necessary voltages and currents to operate the device. The transmitter conversion efficiency is defined as the ratio of RF power output available from the device to the dc power input. Normally the RF conversion efficiency is between 10 to 60%. The transmitter system efficiency is the ratio of RF power available from the transmitter to the total power required to operate the transmitter. The total power includes the power required to generate electron beams from the cathode, the power required to generate electromagnetic fields, the power required for cooling the device etc.

Types of Radar Transmitters:

1. Klystron

It has high gain and efficiency.
It has high average and peak powers.

2. Travelling Wave Tube

It has less power, less gain and less efficiency than Klystron
• It has wider Band Width

3. Hybrid Klystron

• They are similar to Klystron but single cavity is replaced by multiple cavities.

4. Solid State Transistor Amplifier

• They are wider Band Width devices which operate with low voltages.
• They are easy to maintain and have long life.

5. Magnetron

• They are smaller in size and utilizes low voltages for operation.

The klystron, travelling wave tube and magnetron are called slow wave devices in which the phase velocity of electromagnetic wave is slow compared to velocity of electrons. The Gyrotron is a fast wave device in which the phase velocity of the Electro Magnetic wave is higher than velocity of electron.

Microwave Radar Receivers:

The function of the receiver is to extract the weak eco signals and amplify them. It employs a matched filter to maximize the signal to noise ratio and eliminate unwanted signals. The radar receiver is always super heterodyne in nature. The superheterodyne receiver converts the RF input signal to an IF signal to achieve desired Band Width, gain and stability. The first stage or front end of a super heterodyne receiver is a low noise amplifier.

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