What allows a Radar system to detect the presence of a target?
Electromagnetic wave reflection
RADAR stands for RAdio Detection And Ranging. Its operation is based entirely on the reflection of electromagnetic waves, which is why that is the correct answer.
The basic sequence of operation is:
- A transmitter generates a short, high-power pulse of electromagnetic energy — usually in the microwave/radio band — which is radiated into space by a directional antenna.
- When the pulse strikes an object such as an aircraft, ship, or vehicle, part of the energy is scattered and reflected back toward the radar. This returned energy is called the echo.
- The same (or a nearby) antenna captures the weak echo and passes it to a sensitive receiver.
- Signal processing extracts the target information: the round-trip time delay gives the range (distance = c × t / 2, where c is the speed of light), the Doppler frequency shift of the echo gives the target's radial velocity, and the antenna pointing angle gives its direction.
Because radar depends on electromagnetic reflection, it works even in darkness, fog, or cloud, where optical sensing would fail.
Acoustic resonance is incorrect — sound-based detection is used in SONAR, which works underwater where sound propagates well but radio waves are heavily attenuated. Atmospheric refraction does bend radar waves slightly and can extend or distort coverage, but it is a propagation side-effect, not the mechanism that reveals a target's presence. Chemical ionization has nothing to do with detecting a reflecting object; it relates to processes such as gas-discharge and mass spectrometry.
Important Questions from Electromagnetic Wave Propagation
Arrange the formulas of $\beta$ in the order where plane wave is travelling in lossy dielectric, free space, good conductor, loss-less dielectric respectively.
A. $\beta = \omega \sqrt{\frac{\mu \epsilon}{2} [\sqrt{1 + (\frac{\sigma}{\omega \epsilon})^2} +1]}$
B. $\beta = \frac{\omega}{C}$
C. $\beta = \omega \sqrt{\mu \epsilon}$
D. $\beta = \sqrt{\frac{\omega \mu \sigma}{2}}$
Choose the correct answer from the options given below:
- A digital cellular system transmitter is sending signals at $f_c$ = 900 MHZ to a mobile user whose velocity is 70 km/hr. If the mobile is moving in a direction perpendicular to the direction of arrival of the transmitted signal, the received carrier frequency would be :
A plane wave is propagating in a uniform medium with propagation constant \((0.6\pi + j\,0.4\pi)\) its wavelength is
Assertion (A) : The ionosphere is that region of the earth’s atmosphere in which the constituent gases are ionised by radiations from outer space.
Reason (R) : Throughout the ionosphere, there are several layers in which ionization density either reaches maximum or remains almost constant. It depend on the intensity of sun. It also depends upon the atmospheric pressure.
Ultra High Frequency (UHF) spectrum is defined as :
