IEEE Std 291-1969 IEEE Standards Report on Measuring Field Strength in Radio Wave Propagation.pdf

IEEE Std 291-1969 .? IEEE Standards Remrt on Measuring Field Stiength in Radio Wave Propagation Published by The Institute of Electrical and Electronics Engineers, Inc 345 East 47th Street, New York, NY 10017, USA SHO1800 May 1969 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 10:55:20 UTC from IEEE Xplore. Restrictions apply. ACKNOWLEDGMENT The Institute wishes to acknowledge its indebtedness to those who have so freely given of their time and knowledge, and have conducted experimental work on which many of theIEEE publica- tions are based. The follodng members of the Wave Propagation Committee of the IEEE Antennas and Propagation Group were the main contributors to this publication:. H. H. Beverage S. A. Bowhill 1. Fine Reaffirmed May 21, 1981 IEEE Standards Board Copyright 1969 by The Institute of Electrical and Electronics Engineers, Inc. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the pkblisher. Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 10:55:20 UTC from IEEE Xplore. Restrictions apply. . CONTENTS 1 . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Symbols and Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 . Methods of Measuring Field Strength . 4 2.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.1. Standard-Antenna hfethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.3. Simplifications and Precmitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Standard-Antenna SIethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1. The Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.2. Calibration Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. Standard-Field hlethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3.1. Induction-Field lethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3.2. Radiation-Field Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4.1. Loop-Antenna Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4.2. Dipole-Antenna Calibration. 14 2.5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.5.2. Standard-Antenna Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.5.3. Effective Area of Antennas 15 2.5.4. Antenna Power Gain Measurement 15 2.5.5. Standard-Field Formulas 16 2.6. Miscellaneous . 17 2.6.1. Accuracy of FieldStrength Measurement . 17 2.6.2. Presentation of the Data of Measurement . 17 2.6.3. Automatic Recording . 17 2.6.4. Mobile Recording 18 Methods of Measuring Power Radiated from an Antenna 3.1. General 18 2.1.2. Standard-Field hlethod . 4 2.4. Calibration of Commercial Field-Strength Meters . 13 2.5. Microwave Power Deusity and FieldStrength Measurements . 14 3 . 18 3.2. Equivalent Radiated Power for Simple Ground-Based Vertical Antenna 18 3.3. Ground-Wave-Radiated Power Measurements Above About 5 Megahertz 21 3.4. Equivalent Radiated Power for Ionospheric Wave Transmission . 22 4 . References , 23 1 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 10:55:20 UTC from IEEE Xplore. Restrictions apply. IEEE Standards Report on MEASURING FIELD STRENGTH IN RADIO WAVE PROPAGATION 1. INTRODUCTION R = Resistance, in ohms. 1.1. General. Most measurements with which radio wave propagation is concerned involve the measurement of field strength. Thus, the determination of power radiated from an antenna (Section 3) depends principally upon the measurement of field strength, especially in the low-frequency and medium-frequency bands. Standard methods for the measurement of this fundamental quan- tity are outlined. 1.2. Symbols and Units. The general symbols and units used are given in the following list. Where more specific or restrictive meanings are indicated by sub- scripts, etc., they are further defined after the equation in which used. In some cases a symbol definition is re- peated where used, merely for convenience. Symbols C = Capacitance, in farads. d = Distance from transmitter to receiver, in meters. D = Conductor diameter of dipole antenna, in meters. E = Root-mean-square electric field strength of a radio wave, in volts per meter. Power gain of an antenna (over that of an ideal isotropic antenna) considering only its directivity - f = Frequency, in hertz. g = s = v= a= x= E , = ( I = c= 2, = Mean area per turn of loop, in square meters. Root-mean-square voltage, in volts. Attenuator ratio (equal to, or greater than, unity). Wavelength, in meters. Relative dielectric constant of the ground, i.e., the ratio of permittivity (dielectric constant) of ground to that of vacuum. Ground conductivity, in mhos per meter. Velocity of propagation of an electromagnetic wave in a vacuum (2.997 925 f 0.000 003 X 10' meters per second). Impedance of free space (47rc x 10- = 376.7304 f 0.0004 ohms). Unless otherwise stated, quantities are assumed to be those of the International System. For convenience, several relationships and prefixes are tabulated. 1 inch = 0.0254 meter. 1 mile = 1609.344 meters. 1 meter 1 square inch 1 square meter = 1550.0031 square inches. = 0.000 621 371 2 mile. = 0.000 645 16 square meter. but not its losses. isotropic antenna) considering both its di- rectivity and its losses. amperes per meter. g, = Power gain of an antenna (over that of an ideal piCO = lo-'* nano = lo-' micro = H = Root-mean-square magnetic field strength, in = centi = IO-' h = Height above ground of antenna center of radia- = lo-' I= K= 1, = L, = 1, = 1, = L, = N= P= Q= tion, in meters. Root-mean-square antenna current, in amperes. Calibration factor of a commercial field-strength meter. Effective length of dipole antenna, in meters. Physical length of a linear dipole antenna, in meters. Effective length of loop antenna, in meters. Effective length of grounded vertical antenna, in meters. Physical length of grounded vertical antenna, in meters. Number of turns. Power, in watts. 27r times the ratio of energy stored to energy dissipated per cycle (Q is normally expressed as the ratio of inductive reactance to resistance at resonance). Name of Quantity SI Unit length area frequency voltage electric field strength current power resj s tance conductivity inductance capacitance magnetic field strength meter square meter hertz volt volt per meter ampere watt ohm mho per meter henry farad deka = 10 hecto = loz mega = 10' giga = 10' tera = 10'' kilo = io3 ampere per meter Number of CGX Electromagnetic Units in 1 SI Unit 100 10 000 1 lo8 ioe 1/10 io7 io8 lo-“ ioQ 10-0 47r x 3 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 10:55:20 UTC from IEEE Xplore. Restrictions apply. 2 . METHODS OF MEASURING FIELD STRENGTH Alternatively, the attenuator may be included in the standard voltage source. The calibrating voltage is then, 2.1. General. Two general methods are applicable to itself, variable over a wide range and the voltmeter is the measurement of field strength 1-4. One consists of calibrated at sensitivities corresponding to the voltages measuring the voltage developed in a standard antenna being measured. In either case, the measurement resolves by the field to be measured and computing the field itself into the comparison of two voltages, the known strength from the measured voltage and the dimensions voltage and the voltage produced by the field, generally and form of the standard antenna. The other consists of introduced at different points in the measuring circuit. comparing voltages produced in an antenna by the field The method used in determining the voltage-transfer to be measured and by a standard field, the magnitude of ratio is generally dependent upon the particular form of which is computed from the dimensions of the transmitting antenna and the circuit arrangement employed. antenna, its current distribution, the distance of separa- The field strength is computed on the basis of the tion, and effect of the ground. The measuring sets for the effective length of the antenna, the voltage-transfer ratio, two methods are of the same general form. For the the voltage from the standard voltage source, and the standard-antenna method there are special requirements attenuator ratio. In some instances it may be difficult for the receiving antenna and the voltage-measuring to calculate accurately the effective length of the antenna equipment. Field-strength measurements or surveys are being used. In such cases, the product of the effective often made using commercially available meters that have length and the voltage-transfer ratio can be determined been previously calibrated* in a known field determined directly from a single measurement of the terminal voltage by either of these methods. of the antenna when placed in a standard field. The re- ciprocal of this product is sometimes called the antenna 2 . 1 . 1 . Standard-Antenna Method. In the standard- coefficient. This is the procedure usually followed in the antenna method, the receiving antenna is of some stan- calibration of commercial field-strength meters. In this dard form such that the voltage induced in it by a wave case, the value of the “antenna coefficient” determined of given field strength and polarization may be computed usually includes the gain factor of the receiver. readily l-5, 77. The ratio of this voltage to the com- ponent of the field producing it is called the effective 2 . 1 . 2 . Standard-Field Method. In the standard-fiold length (or the efTective height), i.e., method the standard field may be set up by a local trans- mitter. The field at the receiving antenna may be com- puted from the dimensions of the transmitting antenna, its current and current distribution, the distance, and the effect of the ground, Or it may be determined by direct measurement with a standard antenna 1-4. The measur- ing equipment associated with the receiving antenna generally consists Of a sensitive vacuum-tube Voltmeter employing double detection and having an indicator in the output of the second detector. While it is possible to adjust the strength of the its magnitude is dependent upon the point of introduction of the calibrating voltage into the measur- ing circuit. Separate determination of this ratio may be required in some instances. A standard voltage source is provided, usually as part of the field-strength measuring apparatus, for calibrating the voltmeter. The term voltmeter is used here to mean the rdio-receiving portion of the equipment. The Cali- brati .,Itage may be fixed or it may be adjustable over a wide range. It may be inserted in series with the stan- dard antenna, or at some point in the coupling circuit, - - or it may be -applied to the input terminals of the volt- meter in place of the coupling circuit. When a fixed calibrating voltage is employed, the voltmeter is cali- brated at a fixed sensitivity level, and a calibrated ab tenuator is employed in conjunction with the voltmeter, in order to measure voltages over the wide range required. A public calibration service is maintained by the National Bureau of Standards, Boulder, Colo., for field-strength meters in the frequency range of 10 kilohertz-300 megahertz. For information write: Director, National Bureau of Standards, Washington 25, D.C. 2 . 1 . 3 . Simplifications and Precautions. The problem of field-strength measurement is generally complicated by the varying nature of the field resulting from variability of the transmission medium 6-9, by the complex nature of the emission lo, ll, and by the influence of the ground and of disturbing structures 11-15. Simplifying ap- proximations are introduced into measurement methods to keep the measuring apparatus from becoming unduly complex or unduly difficult to use or to facilitate analysis of the data. - 4 Authorized licensed use limited to: Tsinghua University Library. Downloaded on December 25,2010 at 10:55:20 UTC from IEEE Xplore. Restrictions apply. In the case of ionospheric or tropospheric wave fields, a really complete measurement would involve determina- tion of: (a) the field strength of the vertical, longitudinal and lateral electric- and magnetic-field components in each wave arriving at the receiving point; (b) the phase angles between the different components; (c) the direction of arrival of each wave component. Fortunately, considerable practical information may be obtained by measuring only the vector components of the field 16 which are used for communication. Simple forms of receiving antennas thus become useful, the type of antenna used being dependent upon the component of the field to be measured. A simplification in the measurement of complex emis- sions may be achieved by removing the modulation so that a single-frequency field (the carrier) is measured. In emissions without a carrier wave, such as a single- sideband wave, it is sometimes desirable to restrict the modulation to a single frequency, so that a single-fre- quency field is again measured. Occasions arise, however, when it is necessary to retain the normal modulation, for example, when considering the interfering effect of the cross-modulation products of an ampli tude-modulated wave or the interfering effect of single-sideband emission. When measuring the harmonic content of a given field, special precautions should be taken to avoid errors due to harmonics that may be produced within the measuring equipment. The typical measuring system is a frequency-selective voltmeter arranged to indicate the average, peak, or quasi-peak value, over a suitable short time interval, of the root-mean-square voltage of the signal that has passed through the frequency-selective circuits. For single- frequency fields the root-mean-square value is measured, usually, by use of an average-indicating circuit calibrated by a single-frequency signal of known roo t-mean-square voltage. For pulse-modulated signals, the root-mean- square value during the peak of the pulse is usually mea- sured by means of a p