Development Of Dedicated Signal Source For Electromagnetic Shielding Effectiveness Of Cabinets

Electromagnetic shielding is an effective technology used to solve the problems of electromagnetic interference and electromagnetic susceptibility of electronic equipment.Metal materials are used to make cabinets of various electronic equipment for electromagnetic shielding.Electromagnetic shielding effectiveness of cabinets is closely related to material,structure and manufacturing technique of cabinets.In some application which require high performance of electromagnetic shielding,strict requirements are put forward for electromagnetic shielding effectiveness of cabinets."GJB5240-2004 Requirement and measurement method for electromagnetic shielding effectiveness of cabinets,recks and subracks of military electronic equipment." has made clear regulations on the measurement method,measurement frequency band,shielding effectiveness requirements and measurement process of electromagnetic shielding effectiveness of the cabinets.The signal source with small volume,wide frequency range and sufficient transmission strength is the key to measure electromagnetic shielding effectiveness of the cabinets.Under this background,it is of great practical significance and application prospects to develop a signal source suitable for cabinet shielding effectiveness test.A dedicated signal source for cabinet shielding effectiveness test in the range of 100 MHz-800 MHz is made,which includes signal source,RF amplifier and antenna.The specific work is as follows:Firstly,A signal source is designed with ADF4351 phase-locked loop chip.It cover the frequency from 100 MHz to 800 MHz.Test result indicates that the signal source can output four frequency points at the same time: 100 MHz,300MHz,500 MHz,700MHz.Its frequency is stable,the phase noise is low,and the output level is about-1.5d Bm.Secondly,SBB-2089 RF power amplifier chip is selected for RF power amplifier.Test result indicate that the operating frequency range of the amplifier is from 50 MHz to 850 MHz,which covers the frequency range of the output signal of the signal source,and its gain remains stable at 20 d B in this frequency range.Thirdly,Three methods are used to design the broadband compact antenna separately.The first method is using a non-Foster matching circuit on the basis of the monopole antenna.The simulation results show that the matching circuit improves the impedance characteristics of the antenna effectively in the low frequency band;the second method is using monopole capacitive loaded antenna which has a disk mounted at the top of monopole antenna,its resonant frequency is moved from 700 MHz to 300 MHz,which makes the antenna smaller,but the bandwidth does not change greatly;the third method is using a Disk-cone antenna,The bandwidth of the Disk-cone antenna is greatly improved after the 700 MHz resonance frequency,which makes the antenna broadband,but does not contribute much to the miniaturization.It was found by actual measurement that the monopole antenna with non-foster matching circuit not does not enhance the radiation efficiency of the antenna.On the contrary,the capacitive loaded antenna can greatly improve the radiation efficiency of the antenna in the designed frequency range.The resulting signal source can produce signals that meet the requirements of the GJB5240-2004 standard at frequency 100 MHz,300MHz,500 MHz,and 700 MHz,which can be used to measure the electromagnetic shielding effectiveness of the cabinets.There are 80 pictures,6 tables and 50 references in this paper.