Radar fundamentals and ARPA basics

Bowditch Ch. 13 §1303

Radar Navigation ARPA (Automatic Radar Plotting Aid) computes target tracks automatically and displays predicted CPA and TCPA. ARPA does not replace bridge watchkeeping; it supplements visual look-out.

NEETS Module 18 — Function Installation Vehicle ¶3

Q44. Which beam of missile-guidance radar is very wide? 1.6.4 Carrier-Controlled Approach (CCA) and Ground-Controlled Approach (GCA Radar) CARRIER-CONTROLLED APPROACH and GROUND-CONTROLLED APPROACH radar systems are essentially shipboard and land-based versions of the same type of radar. Shipboard CCA radar systems are usually much more sophisticated systems than GCA systems. This is because of the movements of the ship and the more complicated landing problems. Both systems, however, guide aircraft to safe landing under conditions approaching zero visibility. By means of radar, aircraft are detected and observed during the final approach and landing sequence. Guidance information is supplied to the pilot in the form of verbal radio instructions, or to the automatic pilot (autopilot) in th…

NEETS Module 18 — Glossary ¶3

A-9 NOISE FIGURE—The ratio of output noise to input noise in a receiver. NUTATING—Moving an antenna feed point in a conical pattern so that the polarization of the beam does not change. OMNIDIRECTIONAL ANTENNA—An antenna that radiates equally in all directions (nondirectional). ORANGE-PEEL PARABOLOID—A section of a complete circular paraboloid that is narrow in the horizontal plane and wide in the vertical plane. PARABOLIC REFLECTOR—An antenna reflector in the shape of a parabola. It converts spherical wavefronts from the radiating element into plane wavefronts. PARALLEL-CONNECTED DUPLEXER—Configuration in which the tr spark gap is connected across the two legs of the transmission line one-quarter wavelength from the T junction. PARASITIC ARRAY—An antenna array containing one or more eleme…

NEETS Module 18 — Learning Objectives ¶1

After you finish this chapter, you should be able to do the following: 1. Define range, bearing, and altitude as they relate to a radar system. 2. Discuss how pulse width, peak power, and beam width affect radar performance. 3. Describe the factors that contribute to or detract from radar accuracy. 4. Using a block diagram, describe the basic function, principles of operation, and interrelationships of the basic units of a radar system. 5. Explain the various ways in which radar systems are classified, including the standard Army/Navy classification system. 6. Explain the basic operation of cw, pulse, and Doppler radar systems. 1.1 INTRODUCTION TO RADAR FUNDAMENTALS The term RADAR is common in today’s everyday language. You probably use it yourself when referring to a method of recording t…

NEETS Module 18 — Learning Objectives ¶3

Q3. What is the speed of electromagnetic energy traveling through air? Q4. How much time is required for electromagnetic energy to travel 1 nautical mile and return to the source? Q5. In addition to recovery time, what determines the minimum range of a radar set? PULSE-REPETITION FREQUENCY AND POWER CALCULATIONS.—The energy content of a continuous-wave radar transmission may be easily figured because the transmitter operates continuously. However, pulsed radar transmitters are switched on and off to provide range timing information with each pulse. The resulting waveform for a transmitter was shown in figure 1-3. The amount of energy in this waveform is important because maximum range is directly related to transmitter output power. The more energy the radar system transmits, the greater t…

NEETS Module 18 — Learning Objectives ¶5

A sloping leading edge also affects minimum range as well as range accuracy since it provides no definite point from which to measure elapsed time on the indicator time base. Using a starting point at the lower edge of the pulse’s leading edge would increase minimum range. Using a starting point high up on the slope would reduce the accuracy of range measurements at short ranges which are so vital for accurate solution of the firecontrol problem. Maximum range is influenced by pulse width and pulse repetition frequency (prf). Since a target can reflect only a very small part of the transmitted power, the greater the transmitted power, the greater the strength of the echo that could be received. Thus, a transmitted pulse should quickly rise to its maximum amplitude, remain at this amplitude…