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CHAPTER 3
RADAR INDICATORS AND ANTENNAS
LEARNING OBJECTIVES
Upon completion of this chapter, the student will be able to:
1. Describe the purpose of the A scope, the range-height indicator (rhi), and the plan position
indicator (ppi).
2. State the relationship between range and sweep speed and length on a radar indicator.
3. Explain the purpose of timing triggers, video, and antenna position inputs to a radar indicator.
4. List the major units of a ppi and describe their functions.
5. Describe the basic operation of sweep deflection and sweep rotation in a ppi.
6. List and describe the operation of the three range measurement circuits.
7. Describe antenna directivity and power gain characteristics.
8. Describe the focusing action of a basic parabolic antenna.
9. Describe the basic radiation patterns of the most common parabolic reflectors.
10. Describe the basic characteristics of horn radiators.
INTRODUCTION
Radar systems require an antenna to both transmit and receive radar energy and an indicator system
to display the video information generated. This chapter will briefly describe some commonly used
indicators and antenna systems. Antenna systems are described in more detail in NEETS, Module 10,
Introduction to Wave Generation, Transmission Lines, and Antennas, and Module 11, Microwave
Principles.
RADAR INDICATORS
The information available from a radar receiver may contain as many as several million separate data
bits per second. From these and other data, such as the orientation of the antenna, the indicator should
present to the observer a continuous, easily understandable, graphic picture of the relative position of
radar targets. It should provide size, shape, and insofar as possible, indications of the type of targets. A
cathode-ray tube (crt) fulfills these requirements to an astonishing degree. The cathode-ray tube's
principal shortcoming is that it cannot present a true three-dimensional picture.
The fundamental geometrical quantities involved in radar displays are the RANGE, AZIMUTH
ANGLE (or BEARING), and ELEVATION ANGLE. These displays relate the position of a radar target
