ANSI C63.5:2006 pdf download.Electromagnetic Compatibility-Radiated Emission Measurements in Electromagnetic Interference (EMI) Control- Calibration of Antennas (9 kHz to 40 GHz).
5.3.1.1 Procedure
I) Allow the signal gcnerator. amplifier or prc-ainpliticr and measuring Instrument to warm up ax specilied by the manufacturer of the equipment. (‘are should be taken if multiple band amplifiers are used. These amplifiers may require additional time to warm up whcn switching bands, since different components may be used in each band and those components are not nccessanly stable when the band is switchcd. Thc signal at the generator output V1. is held constant throughout the measurement. Ensure that the instrumentation has sufficient dynamic range available to record the difference between the direct cable measurement [step 3)) and the indirect measurement through the atitennas Istep 2)). It is recommended that high quality calibrated attenuators be used dwing the direct measurement that are neaxly equal to the anticipated antenna losses. The use of these attenuators will ensure accuracy during a relatise amplitude measurement, by reducing the uncertainty due to nun-lineanty of the instnimentatitm, (See Annex I for uncertainties associated with the selection of the substitution attenUator.) The frequency response of the attenuators, if used. must be normalized from the direct measurement since they are not used during the indirect measurement If attenuators arc not used, the difference between the direct and indirect measurement can be as much as 60 dB or more,
2) At the selected distance. transmitting height and frequency, connect the first pair of antenna.’. (antennas I and 2) via cables and any attenuators to their respective signal source (transmitting antenna) and measurement in’trument (spectrum anaIy’cr or receiver), Tune the measurement instrument to receive the maximum received signal. Adjust the height of the receiving antenna for the maximum received signal. Ensure that the recorded maximum signal is at least 16 dH above the ambient signals and noise floor (see 4,3). Adjust the substitution attenuator for reference indication on the measuring instrument. Record thcsc data as in Figure H. I.
3) Disconnect the cables and attenuators from the antennas and connect the cables and attenuators directly together with the substitution attenuator and a siraight.ihrough adapter. Adjust or select the substitution attenuator to give the same receiver reference indication as in step 2) and record the data as V11.,,, in Figure 8.1. (See Annex I or uncertainties associated with the selection of the substitution attenuator) The signal genciator output attenuator may be used in place of an external substitution attenuator in the path between the generator and the transmit antenna. This direct measurement shall be repeated anytime the temperature at the site changes by S C or more.
4 Find the difference in attenuation by subtracting the “attenuation for antenna-to-antenna modc”in step 2) from the “attenuation for direct connection mode” in step 3) in Figure H. I and record this as 4, in Figure B.3.
5) Change the frequency (see Table 2 or Table 3) and repeat step 2) through step 4).
6) After all frequencies are measured, repeat step 2) through step 4) twice more, once for each of the remaining antenna painngs (antennas I and 3, antennas 2 and 3) to get the values for 42 and A. respectively. Enter the results in Figure 8.3, Calculate the resulting antenna factors at each frequency using Equation (4) through Equation (b) and Table 2 or Table 3 depending upon frequency.
The values of’ E1 listed in Table 2 were calculated for metal ground planes assuming K I. a
(perfectly conducting) as defined in Annex A. This table has data up to I 6Hz. Use Table 3 to calibrate horn antennas. Frequency coverage shall be every 300 MHz from I 6th through 12 6Hz. evcly I 6Hz from 12 6Hz through IX 6Hz, and every 2 6Hz from IX 6Hz through 40 6Hz.
5.3.2 Swept frequency method
For the swept frequency method. measurements using broadband antennas may be made using automatic measuring equipment having a peak hold (maximum hold), storage capability, and a tracking generator. In this method, the frequency is scanned or swept over the desired range. holding the maximum signal.
