RADAR stands for Radio Detection And Ranging. It uses electromagnetic waves to: - Detect objects (presence) - Determine their distance (range)

By measuring the round-trip time of a transmitted signal: $$ R = \frac{c \Delta t}{2} $$ - $c$ = speed of light - $\Delta t$ = round-trip time

Because the signal travels to the target and back. - Total measured time is round-trip - Distance must be divided by 2 to get one-way range

The maximum distance before Earth curvature blocks the signal: $$ r_{\max,LOS} = \sqrt{2h_{\text{radar}}} + \sqrt{2h_{\text{target}}} $$

A measure of how much energy a target reflects. - Denoted $\sigma$ - Units: $\text{m}^2$ or dBsm - Larger RCS → easier detection

$$ S = \frac{P_T G_T}{4 \pi R^2} $$

$$ P_R = P_T G^2 \sigma \frac{\lambda^2}{(4\pi)^3 R^4} $$

$$ P_R \propto \frac{1}{R^4} $$ - Doubling distance → power decreases by 16 - Much steeper than Friis ($1/R^2$)

- Higher transmit power $P_T$ - Higher antenna gain $G$ - Larger wavelength $\lambda$ - Larger RCS $\sigma$ - More sensitive receiver (lower $P_{R,\min}$)

A receiver that detects incoming RADAR signals. - Acts like a communications receiver - Uses Friis equation - Alerts target before RADAR detection (ideally)