Radio-fRequency (Rf) engineeRs often cite designing RF emitters, such as RF/microwave antennas, as major technical challenges. This issue seems to stem from a lack of clear understanding of RF transmitting antennas. To alleviate this problem, Instruments For Industry (IFI) has released "Application Note 105: RF Antennas and Related Formulas." This note explains some of the more standard antenna terms. It also delves into the basic math that is required to calculate the RF field level with a given RF input-power signal.

The five-page document opens with a glossary of standard antenna terms. For example, free space is a location at which an antenna can operate without any external physical effects that would alter its performance. A signal's wavelength is the physical length of that signal in free space. Wavelength is measured as a unit of distanceusually in meters at lower frequencies and millimeters at microwave frequencies. The other terms defined in the application note include: radiator, radiation, near- and far-field radiation, polarization, bandwidth, gain, radiation pattern, and phase center.

The application note emphasizes that antenna gain is probably the least-understood and yet most important antenna characteristic. Gain is a relative term that can be related linearly or logarithmically. Either way, it is referenced to an isotropic radiator. That radiator is an infinitely small, theoretical point source of radiation. The electromagnetic (EM) radiation from that point source expands outward in a uniform, spherical manner to infinity. If the radiation pattern is altered in any way from its spherical shape, the energy will be concentratedthereby producing apparent gain.

The document goes on to provide three related field-strength formulas: field strength, field measurement units, and antenna-gain conversion. It then provides field-strength examples at both 1 and 3 meters. By covering these various sections, this application note provides a solid foundation for RF engineers who are unfamiliar with antenna fundamentals.

Instruments For Industry; 903 South Second St., Ronkonkoma, NY 11779; (631) 467-8400; internet: www.ifi.com.