An antenna is the mechanism by which the electromagnetic signal is radiated and received. For radars (although not necessarily for antennas in other electromagnetic applications), it is essential that the antenna enhance performance. A radar antenna has three roles: to be a major contributor to the radar's detection performance, to provide the required surveillance, and to allow measurements of angle of sufficient accuracy and precision. A reasonable place to begin is with the two expressions used to derive the radar range equation: antenna gain and effective area. For a transmitting antenna, antenna gain is simply a measure of how much focusing of the transmitted waveform is being accomplished by the antenna. Focusing is the ability to add up energy preferentially. Energy arriving at the antenna from a given direction is integrated; that arriving from elsewhere is not. It is assumed that energy arriving at the antenna is in the form of plane waves, that is, the phase of the arriving energy is constant over any plane perpendicular to the direction of arrival.

Radar cross section (RCS) is a measure of the electromagnetic energy intercepted and reradiated at the same wavelength by any object. The dimensions are those of an area, usually square meters (m²) or decibels relative to a square meter (dBsm). The relationship between square meters and dBsm. The RCS of an object is a complex combination of multiple factors: size, shape, material, edges, wavelength, and polarization. Simple objects tend to have a single, or few, scattering sources. Complex objects (such as airplanes) tend to have multiple scattering sources (e.g., nose, fuselage, inlet, wing root, wing, and so forth). Thus, for complex objects, the RCS is the complex (amplitude and phase) combination of contributions from each scattering source.

The paper is about defining and discussing ECM and ECCM. Developing the basic relationships in mainlobe jamming. Expanding to the sidelobe jamming case. Sidelobe canceling, concepts of adaptivity. The low probability of intercept (LPI) radar and radar warning receivers (RWRs). Active ECM techniques and their counter-countermeasures. Passive ECM techniques and their counter-countermeasures.

Several other brief quantitative notions and a list of rules of thumb should be included in any set of radar fundamentals. Some are good for general day-today use; others are important to detailed radar design calculations. They are pulled together in this chapter without concern for their relevance to each other and only because they are valid radar lore.

Because radar engineers often deal in power, decibels relative to a watt or decibels relative to a milliwatt are used. Another common use of decibels is for RCS, decibels relative to a square meter. Some approximate decibel values usually memorized by radar people are shown in this appendix.

Working in the field of heat transfer in the early nineteenth century, Jean B. S. Fourier found that virtually all functions of time, particularly repetitive ones, could be described in a series of sine and cosine waves of various frequencies and amplitudes. His work has been described as one of the most elegant developments in modern mathematics. Whatever its stature for the world, the benefits for the radar engineer are epic.

This glossary provides assistance in understanding terms used in this book. There may be more general, more specific, or entirely different meanings for these terms when they are used elsewhere.