An EMI Calibration Device Based On Wide Band Comb Spectrum Signal Generator

When conducting EMI(Electromagnetic Interference)tests,in order to ensure the accuracy of the measurement results,the measurement instruments need to be regularly calibrated.However,calibrating before each test will waste a lot of time and effort,using the stability of the comb spectrum signal generator,which can be used as a standard noise source when testing.The design mainly includes a comb spectrum signal pulse generator,a power amplifier and two Vivaldi antennas.This paper first introduces the principle of comb spectrum signal generation,analyzes the structure of the pulse generation circuit and the calculation of key component parameters.And then,the most important device of the pulse generating circuit is step recovery diode(SRD).I chosed a MMDB45-B11 SRD which produced by METELICS company.It can output 0.2-16GHz comb spectrum signal.According to the output power requirements of the comb spectrum signal generator,a power amplifier needs to be designed.The power amplifier adopts a two-stage cascading manner,in which the first stage uses the SPF-5043 chip of SERINZA,and the second stage selects the SGA-9189 chip of SERINZA.After two stages are cascaded,the measured gain can reach 35dB at a frequency of 200MHz.In addition,two Vivaldi antennas have been designed for this text,one frequency band is 0.5-2GHz,and the other frequency band is 1.6-20GHz,which can cover the entire output frequency band of the frequency comb generator.The 0.5-2GHz antenna has a gain of 1.5dB at a low frequency of 0.5GHz and a gain of 5.5dB at a high frequency of 2GHz.The 1.6-20GHz antenna has the highest gain at 14 GHz,which can reach 11.1 dB.The gain in the whole frequency band is 1.5-11.1 dB.Finally,the radiation level test is performed on the entire system.The test results show that the frequency comb generator works well and the output is stable and reliable.It can be used for EMI test calibration.