1、F- e EIA TEP171 72 = 3234600 0008488 Fe b. 1972 Recommended Practice for Measurement here the radiation leakage problem is really one of equipment design. Hicrowave energy leaking from a small aperture h a microwave enclosure radiates in accordance withMaxwells equations. equations governkg such lea
2、kage, it can be shorn that the energy is stored b the media in the vichity of the leak in two forms; (a) a radiative term whose field intensity varies inversely as the first power of range from the leakage source, and (b) reactive terms whose htensities decrease more rapidly with distance from the s
3、ource. As the size of the leakage aperture increases and becomes significant- relative to the microwave wavelength, the manner of variation of field Intensity of the radiative tern must also include the effect of the relative phase of excitation from discrete elements within the aperture and the eff
4、ect of wavefront curvature. case, the radiative field will not vary inversely with range from the aperture until the range exceeds Since microwave tubes are most frequently operated with planar triodes, From a study of the Thus, for the large aperture where: D = major dimension of the aperture 2.0 3
5、 mo EIA TEP171 72 = 3234600 0008492 T 1.3 Inatrments used my materially influeace the indicated magnitude of the fi Id, If the aperture D of the instrument ia large enough so that R - ions+ delivers more Chan 1/4 watts of average pawer through its normal rf output connection, it is recornended that
6、- all the caution mechanisms shown below be used: rl_ EIA TEP171 72 m 323LlbOO 0008496 7 m -6- 8.1 Label - A tag or decal should be attached to each tube shipped, Recommended design is shown in Figure 1. 8,2 Applications Notes, Bulletins, and Tube Specification Sheet (TSS) Applications Notes, Bullet
7、ins and TSSs should include the following recommended paragraph: tlPERS(“EL SHCIITU NCV BE EXPOSED TO THE MICROWAVE ENERGY WiiICR HAP FADIATE FRCM THIS I)EVICE IF fMIpROI?wLY OSED OR CWECTED. AND TPUi RF CCNNEClIONS, WAVEGUIDES FIANGES, AM GASKETS HST BE A MICROWAm FNEZGY ABSORBDIG LO ATTACHED. WAVE
8、GUIDE. an AMIIENNA WHILE THE DWICF; IS FNERGZED. ALL INPUT RF LEAK PROOF AND mZ0PERL;Y EXAGED. NEVER OPBUTE THIS DEVICE WXTH(BPT NEVER MO9c INTO AN OPW 9.0 REFERENCES 9,l Proceedings of the IRE, Vol. 49, No. 2, pp 427447, February 1961, Vorne Technical Aapects of Microwave Radiation Hazards W W. Mum
9、ford. 9.2 USAS C95.1-1966 “Safety Level of Electromagnetic Radiation (10 MHz to 100 GHz) with Respect to Personnel. 9.8 USAS C95.2-1!366 !Radio-Frequency Radiation Hazard Warning Symbolll. . 9.4 Proceedings of the DEE, Bol. 57, No. 2, pp 171-178, February 1969. Heat Stress Due to RF Radiationtt - W.
10、 W. MWop3. I “ EIA TEP171 72 m 3234b00 0008497 9 m 6i1D 1 I RED BACKQROUND r , 7 I I -. EkERY WHICH MAY RADIATE FROM THIS DEVICE IF IMPROPERLY USED OR CONNECTED. ALL INPUT AND OUTPUT RF CONNECTIONS, WAVEQUIDE FLANGES AND GASKETS MUST BE LEAKPROOF. NEVER OPERATE THIS DEVICE WITHOUT A MI CROWAVE ENERG
11、Y ABSORB I NG LOAD ATTACHED. MEYER LOOK OR ANTENNA WHILE THE DEVICE IS INTO AN OPEN WAVEGU I DE ALUMINUM LETTERS I. PLACE HANDLINQ AND MOUNTING INSTRUCTIONS ON REVERSE SIDE 2, D = SCALINQ UNIT 3. LETTERINO: RATIO OF LETTER HEIGHT TO THICKNESS OF LETTER LINES UPPER TRIANGLE: 5 to 1 LARGE 6 to I MEDIU
12、M LOWER TRIANGLE; 4 to I SMALL 6 to I MEDIUM 4. SYMBOL IS SQUARE, TRIANOLES ARE RIOHT-ANGLE ISOSCELES FIGRE 1 i - -xxI f L 8 EIA TEP171 72 m 3234b00 0008498 O m APPE?3DJX I?JSPRU”TATICN CALIBRATICN F2OCEDURES LO INSIRWATICN = AN IN-HOUSE MFTHOD 1.1 1.2 1.3 The htrument should be calibrated in a know
13、n field where there is little likelihood of perturbation by kitrbduction of the instrument or of the observer. For assurance of the validity of the calibration, the field from the sourc6 is preferably unperturbed by reflections Prau fixed installations. A radiation source which has been found to be
14、ideally suited to this cafibration procedure is a /1/4 monopole whioh peers through an exten- sive metallic ground plane (3A to 5A X 3A to 5k ). The monopole is preferably located in a space which includes no structures for 100A in any direction. The monopole should be fed frm asuitable co-axial lhe
15、 from the unerside of the grouml plane. The diameter and length of the monopole should be adjusted so that the manopole is resonant and matched at the frequency of Interest. The power into the radiating element is measured by directional coupler and power meter, The calibration system is shown in bl
16、ock dgagram form in Figure 1. The power source must include some provision far variations 3n output level so as to permit measurement of lhearity. Frequency should be variable if accuracy of calibration is to be determined over a stated frequency band. It is often convenient to include a gimballed i
17、nstrument moqnt or clamp made from polystyrene foam or other suited na-metallic material of low dielectric constant. The design should permit the instrument to be moved through 180 of elevation angle an two orthogonal axes, while maintaining source-instrument range constant . Procedure 1.5.1 The ins
18、trument must be calibrated at the predetermined frequency of the rf leakage. For pulse applications, the instrument must be calibrated to correct for errar due to duty factor and pulse width, 1,5.2 The source of power to be used shall be of sufficient energey level and proper duty and pulse width fo
19、r pulse application, so as to permit direct use with sufficient accuracy. The energy source is coupled to an antenna through use of a carefully matched impedance transformer. The antenuia ground plane is to be rigid, measuring3 to 5 wavelengths in each direction. EIA TEP171 72 m 3234600 0008499 2 m
20、-2- 1.5.3 The power to be transetted (FT) to obtain a particular power O density is determined by where: G = Antenna gah - 1 for isotropic antama pD - Power density (milliwatts/cm2) B R Bistanoe in centimeters from the transmitting antenna to the probe fi = Average pmer to be transmitted (watts) The
21、 radihthg bergy density at EL fixed distance from .tihe antennaD is found by measuring the incident power to a matched antenna. 1,5,4 The probe is moved at many points on the surface of an imaginary hemisphere within the boundary of the ground plane. The average power density as indicated is observe
22、d, The instrunent calibra- tion potentiometer is adjusted for a meter indication showing the average power density established in 1.5,3 above. Measure- ments are made at several elevation angles and several azimuthal angles to ensure that the radiated field is not seriously per- turbed. The accumula
23、ted data is averaged at each elevations angle, and the caliration potentiometer set to correct for instrument non-linearity, Should the instrument calihration potentiometer reach its limit without adequate correction, the user mayt (a) establish a correction factar to be used with the scale reading
24、set at a convenient level, (b) consult the manufacturer far instructions regarding the replacemeat of the potentiometer with one of value such to give adequate range adjustment. 1.6 Factory Calibration The instrument can be calibrated by the factory for those frequency points of survey, 2.0 CALIBRAT
25、I(iBJ oF PROXXMXTY DISTANCE The hstrunent to be calibrated should be placed at a stated range (distance) greater than A and less than the mbimum dimension of the growd plane. Connections fron the sensing element to tho indicator should be positioned to lead essentially straight away from the monopol
26、e radiator so as to min,imiza field perturbation by the instrument and its leads. I . - EIA TEP171 72 3234600 O008500 5 2.1 Two Meter System e Power input to the dipole is adjusted to provide approximately 3/4 full scale hidication on the meter when the gimbals are adjusted to hold the meter at abou
27、t 30 elevation above the ground plane. A second identical ins-trument is maide to approach the first from either side and above and below, while mahtahhg the same range. The approach should continue until either the two instruments are in contact or the indication of the fhst instrument has changed
28、by 2 dB. The separation between the instru- ment whea this condition is achieved should be measured in each quadrant. The largest value so obtained, in terms of the center-ta-center spacing between the two instruments, is the proximity distance, 2.2 ne Meter System Since thefield above a ground plan
29、e from a rescerrant monopole is very nearly constant (relative to 2 dB) in the first 30 of elevation angle, the grom glane can be used as a mirror to determine Proximity Distance. In this situation, the meter is caused to approach the ground plane alang a spherical surface while maintahhg a fixed se
30、nsor orientation until the 2 dB change in reading is noted. All possible orientations of the jnstrunent relative to the ground plane shall be measured after a 2 dg change regardless of the initial change in sensitivity. The proximity distance shall be twice the largest measured value from center lin
31、e of hstrment Co %he ground plane. 3.0 LINEARITY 3.1 Uith the instrument held as In 2.0, increment the Input poner to the antenna so as to note indicated pawer density at several stated values of radiated power, in ascending and descending power until it is clear that the hdicated power density valu
32、e which corresponds to each stated level of power is free from errors caused by meter problems (stickiness, hysteresis, etc.) and that an accurate value of power density has been obtained at each stated power level. 3.2 The data shoul then be plotted in suitable coordinates so thrtt the result- ant
33、plot would be a straight line if the data were fully linear, Two curves should be drawn: passing from adjacent point to adjacent point; (b) the best fit straight lhe, The maxiinum deviations between these curves should be within the linearity limits o Excursions through the power range should be rep
34、eated (a) one consisthg of a series of straight lines 4.0 SENSDIVlYY CALIBRATICM 4.1 With the instrument mounted as in 2.0 and the elevation angle adjusted so that the instrument axis is one proximity distance above the ground plane, adjust the sensor range to a stated value between Aand 3A . Then a
35、djust frequencyto mid-band and input power to obtain full scale hdication, thereafker holding both constant. Increment the elevation fmgle through severalostated values relative io the antenna axis (usually So, 60, 450, 30, O , -30, 45O, -60, -75 ) and reoard the corres- ponding instrument indicatio
36、ns. Then repeat with the instrument incre- mented through the same values for the orthogonal elevation axis. e / P EIA TEP171 72 m 3234b00 0008501 7 m 1 / -4- 4.2 Thus, for each elevation angle above the groun plane, four data points O have bem obtained. Average these values and correct, using the c
37、alibra- tion non-smooth curve of 3.0. The corrected values are used to arith- netioally integrate the power density over the area of the stated hemis- phere, The power value obtained from this integration, Pc, is related to the instrument correction factor by K, K - P radiated/P, Actual power densit
38、y thus becomes indicated density multiplied by the carreCCion factor K. 5.0 CALTBIIATIW AT VARIOUS FREQDI!NC 5.1 The steps of 4.0 are to be repeated h full far frequencies at both ends of any band for which oabration is to be asstared. 6.1 When the instrument ia placed at a fixed position in a steay
39、 far field of mgnitude suck as to produce approximately a full scale defleotion of the indicatar, there shall be less than ldb difference in indicatian when (a) the instrument is held i31 the normal manner (hand or otherwise), and (b) aupported on an extenaive polyethylene foam plane. 7,O DmmATIW OF
40、 EFFECTIVE APERTURE 7.1 The ;Instrument is mounted as in 3.0 and input is adjusted to provide EI stated known power density at the sensor. The detector (see note) is removed from the sensor (with the sensor remining in the same position), The actual power absorbed by the sensor is thtm measured by a
41、 power meter whose input impedance is idediGa1 to that of the detector. Dividing (3.) the measured power by (2) the stated power deasity gives (3) the effective aperture of the instrument in square centimeters. N(YTE: Some instrumenta directly connect sensor and detector, When this - ia done, do not
42、 attempt to measure effective aperture. 8.0 MAXIMM DIMENSI? OF TPHE: APEENJRE 8.1 The physical length of the langest element of the antenna is measured irect3.y or determined from an x-ray of the sensor. Materials which dielectrically load the sensor must be hcluded but non-participathg. materials c
43、an be excluded. 9.0 CALIBRATIW ACCURACY 9.1 The calibration error is the maximum value of the algebraic sum of the linearity error (from 3.0) expressed Ul dB and the worst case correction factor K (from 4.0 and 5.0) expressed in B. a -5- 10,O DETERMINATION OF CALIBRATION INACCURACY ARISING FROM STRA
44、Y PICK-UP NOTE: Instruments which detect leakage energy by a sensor which is remote from the indicators generally will have less difficulty from proximity 10.1 effects than those which combine indicator and sensor in an integral arrangement. indicated value is derived from unintended coupling to the
45、 instrument. Since the effect of such coupling will vary with the spatial distri- bution of the field being measured, the error introduced by such unintended coupling cannot be calibrated out. As a consequence, a test for unintended leakage is important. When the indicator is seperate from the senso
46、r, it is often necessary to cover connecting cables with lossy materials and to ensure that all openings be shielded or screened. Explore the field over an extensive polyethylene foam (or equivalent material of dielectric susceptibility approaching zero), and mark on the surface a constant energy de
47、nsity profile. sensor in the normal manner at one end of the sector marked out. Then, in turn, position the indicator box so that: all its surfaces, in turn, are parallel to the constant energy profile and at least 30cm from the sensor. Likewise, expose all cables, line cords needed in normal use, e
48、tc., at the same distance. Under no conditions shall the indicated value change by more than 1 dB. In either case, it is possible that a portion of the men position the CAUTION: THIS MEASUREMENT CANNOT BE MADE TOO CLOSE TO THE SOURCE MONOPOLE OR REFLECTIONS FROM THE INDICATOR BOX MAY AFFECT FIELDS A
49、T THE SENSOR. IF MOVEMENT OF THF, INDICATOR BOX TOWARD OR AWAY FROM THE SOURCE MONOPOLE CAUSES THE INDI- CATED FIELD STRENGTH To RISE AND FALL PERIODICALLY, SIMILAR TO A STANDING WAVE PATTERN, THE INDICATOR BOX IS TOO CLOSE TO THE SOURCE. 11.0 DETERMINATION OF RESPONSE TIME 11.1 Mount the sensor as in 4.0. Adjust the power source to give full scale indication on the test instrument and measure source power calorimetrically. with nominally 10% duty. taining average power constant as determined calorimetrically by the wate
