Control System Specifications and Radar Fundamentals Explained

Control System Specifications

1. Steady-State Value: The final value of the step response, or the steady-state error (the difference between the reference and output signal after the transient response).
2. Rise Time: The time elapsed up to the instant at which the step response reaches, for the first time, the value K*Y. The constant K varies from author to author, being usually either 0.9 (overdamped) or 1 (underdamped).
3. Overshoot, M: The maximum instantaneous amount by which the step response exceeds its final value. It is usually expressed as a percentage of Y.
4. Undershoot, M: The (absolute value of the) maximum instantaneous amount by which the step response falls below zero.
5. Settling Time, T: The time elapsed until the step response enters (without leaving it afterwards) a specified deviation band ±d around the final value. This deviation is usually defined as a percentage of Y.

Control System Architecture

1. Reference Input: Is the desired value of the output.
2. Plant: Is the system to be controlled (motor, plane, car, etc.).
3. Actuator: Is the device that produces the input to the plant (amplifier, elevator, etc.).
4. Sensor: Is the device that measures and converts the output variable into a type suitable for control (potentiometer, accelerometers, etc.).
5. Controller: Is the device that ensures that the output variable be equal to or follows the reference input using a control action or control algorithm.

Radar: Radio Detection and Ranging

Radar is an electronic system that uses electronic waves for detecting presence, position and velocity in any weather conditions. Radars can be classified as primaries (the same system emits signals and receives echoes) and secondaries.

Primary Radars

Inside the primaries group, we can find radars that work with continuous waves or pulses.

• Continuous Wave (CW): Classified as modulated or unmodulated.
• Pulse: Classified as MTI (Moving Target Indication) or Doppler.

Basic Radar Systems

In the basic radar systems, an antenna is mounted on a mobile platform. The platform is able to rotate with respect to magnetic north (azimuth angle) and to elevate the antenna with respect to the ground surface (elevation angle). To complete the position measurement using spherical coordinates, a distance (or range) from the plane (target) to the antenna is electronically measured.

Range Measurement

In basic range (distance) measuring, an electromagnetic (EM) wave is sent, and the time from sending it to receiving its echo is measured.

Continuous Wave (CW) Radar

A continuous wave radar measures speed of targets by means of the Doppler frequency shift of the echoes. It cannot measure range unless it uses some modulation of the signal (CW modulated, FM). Doppler frequency shift is based on the Doppler effect.

Applications of Radars

• Aircraft weather avoidance radars
• Aircraft Doppler radars
• Aircraft radio altimeters
• TCAS (Traffic Alert and Collision Avoidance System)
• ATC (Air Traffic Control) radars
• Space
• Military
• Sports
• Ships
• Traffic, etc.