Test Procedures for Antennas
|Publication Date:||1 January 1979|
This document is a major revision of IEEE Std 149-1965 which it supersedes. It represents the second revision of the standard since the original issuance in 1948 of 48IRE2S2, Standards on Antennas - Methods of Testing. Practically every topic contained in the previous standard has been expanded to reflect the great changes that have taken place, since 1965, in metrology and instrumentation technology as applied to antenna measurements.
This document contains sections on the design, evaluation, and operation of antenna ranges, electromagnetic radiation hazards, and environmental factors which did not appear in the preceding standard. The section on the determination of scattering cross-section, which appeared previously, has been omitted since it wiil appear as a separate standard at a later date.
This document comprises test procedures for the measurement of antenna properties. It is a comprehensive revision and extension of the previous test procedure ANSI/IEEE Std 149-1965 (Reaff 1971).
Throughout this standard it is assumed that the antenna to be measured can be treated as a passive, linear, and reciprocal device. Therefore its radiation properties can be measured in either the transmitting or the receiving mode. Many of the test procedures decribed can, however, be adapted for use in the measurement of antenna systems containing circuit elements that may be active, nonlinear, or nonreciprocal. For these cases there is no simple relationship between the antenna system's transmitting and receiving properties. Therefore measurements shall be performed for the mode or modes in which the antenna system has been designed to be used.
A fundamental property of any antenna is its radiation pattern. The measurement of radiation patterns on an antenna range is discussed in Section 3, with the emphasis placed on amplitude patterns. The design of antenna ranges, or antenna test facilities, is described in Section 4.
The instrumentation required for the antenna range, directions for the evaluation of an (existing) range, and the operation of ranges are discussed in Sections 5, 6, and 8, respectively. A variety of special measurement techniques are included in Section 7.
The working environment in which an antenna is installed may substantially modify the intrinsic pattern of an antenna. Consequently measurements in situ are frequently required. These are discussed in Section 9.
For each direction of space, the radiation pattern is characterized by amplitude, phase, and polarization. The latter characteristics are taken up in Sections 10 and 11, respectively.
The relative amplitude-pattern information may be converted into absolute intensities through information derived from the measurement of antenna gain. The determination of gain and closely related directivity is described in Section 12. Errors in conventional gain Calibration measurements are discussed particularly in 12.5. Losses in the antenna itself can be of importance in some types of antennas. These losses can be accounted for by the radiation efficiency. Procedures for their determination are treated in Section 13.
Section 14 deals with boresight measurements, which are concerned with the precise determination of the direction of the beam or tracking axis of an antenna system. The sensitive components of the antenna frequently require protection from harsh influences of the environment. The electrically transmissive shield or radome which provides this protection shall frequently be evaluated so that its effect on the radiation pattem is understood. This topic is treated in Section 15.
Power transfer from generator to antenna is controlled by the input impedance to the antenna. This important parameter frequently limits the useful bandwidth of the antenna. Measurement procedures and network descriptions appropriate from low to microwave frequencies are presented in Section 16.
An important class of antennas relies on ground to enhance the received signal. In this case the ground shall be considered as an integral part of the antenna. The modification of antenna concepts and additional data on the ground-wave propagation are presented in Section 17.
The antenna and its associated circuits rather than the capacity of the transmitter generator may limit the amount of power, either average power or peak power, that can be effectively radiated. It is desirable therefore to determine these limitations as well as the environmental factors that may modify them independently of the system context. Procedures for testing power-handling capacity are outlined in Section 18.
Another concern to the antenna engineer is that of radiation hazards. It is well known that radio-frequency (rf) fields of sufficient intensity can cause damage to biological tissue. Therefore it is usually necessary to determine the level of the radiation intensity in the vicinity of antennas radiating high radio-frequency power so that appropriate safety precautions can be taken before personnel enter the area. This important aspect of antenna measurements is discussed in Section 19.
Mechanical or structural properties along with environmental factors are described in Section 20. Because these properties are so varied and specialized in nature, no attempt has been made to include descriptions of actual measurements in this test procedure. The environmental impact of an antenna is also an important consideration for the antenna engineer. One aspect of environmental impact is that of aesthetics. Large antenna structures are necessady conspicuous, and their appearance is of concern to those who live in their vicinity. This is particularly true in an urban setting. Since the aesthetic quality of the antenna structure is highly subjective, it is beyond the scope of this document to suggest any evaluation procedure.
Throughout this test procedure an attempt has been made to discuss measurement techniques as thoroughly as is practicable. However, in general step-by-step procedural descnptions have been avoided. References are provided which are illustrative of measurement techniques and in which details may be found. Because measurement techniques undergo continuing refinement, the reader should be alert to references on the subject of antenna measurement that will have appeared after this test procedure was prepared.
Many commonly used terms used in this test procedure are defined in ANSI/IEEE Std 145- 1973, Definitions of Terms for Antennas. Commonly used terms that do not appear in that standard are italicized in this test procedure.