Radar Fundamentals

Pulse Length

Can affect how many contacts you see and the fidelity of radar picture for decision making and collision avoidance Longer pulse length could have two contacts looking like one, lower resolution, higher range Shorter pulse length shows correct number of contacts, higher resolution, lower range

RAdio Detection And Ranging

Energy is transmitted from an antenna and returned from a reflecting contact in the form of an echo Radar beam is like a fan sweeping the surface of the ocean. It sends out very fast pulses of energy and listens for the energy to bounce off objects

Pulse Width

Greater pulse width = greater energy = b Shorter

RADAR Wave

One cycle = one wavelength Frequency = cycles per second expressed as hertz (Hz) W = velocity/frequency Speed of light (velocity) = 162,000 NM per second

Antenna Size

One half of wavelength The size of the radar array is affected by the frequency of the energy being emitted

PRR

Pulse Repetition Rate = one pulse per second (PPS) Maximum Theoretical Range (MTR) reduces as PRR increases because ample time must be allowed between pulses for an echo to return from any contact Echoes returning from more distant contacts will be blocked by succeeding pulses if the PRR is too high There is a trade off, enough pulses must hit the contact to get a sufficient return without sending out too many pulses When PRR increases, range decreases, pulse length decreases

Search RADAR

SPS-55 SPS-73 SPS-67

Commercial Marine RADARs

The S-band and X-band radars are used in maritime applications due to performance characteristics that offer better information to the user depending on environment and intended usage 10 cm (S-band) is better for long range and bad weather and 3 cm (X-band) is better for navigation

Pulse Shape

The size and shape of the pulse affects what you see and how it displays on screen The horizontal width is tight for accuracy and vertical width is wide to take into account side to side and up and down motion of a ship at sea

Bearing Resolution

Wide beam (10 cm S-band radar): looks like 1 contact Narrow beam (3 cm X-band radar): distinguishes both contacts Narrow beam is better for pilotage waters to distinguish between contacts that will be in closer proximity to each other (like buoys and small craft)