Investigation On X-band Circulators And Its Array Package

X-band phased array radar is widely used in airborne,spaceborne and other communication fields as fire control and target tracking radars.Ferrite circulators are the key components in phased array radars,and thousands of circulators are integrated in a phased array radar system.With the development of miniaturization,lightweight and high performance,higher performance of ferrite circulators is desired.It is required that the circulator should have smaller volume and larger bandwidth,and also required that the circulator array has smaller package volume and higher performance.Therefore,two aspects are presented in this paper,one is for the miniaturization of the circulator,and the other is for the small package structure of the circulator array.Firstly,the X-band micro-strip circulator and the strip-line circulator with YIG ferrite substrates were designed and simulated,respectively,and the micro-strip circulator was fabricated.The circuit structure of micro-strip circulator has a fishbone type,the size of the YIG ferrite substrate is 7×7×0.4 mm³.The simulation results show that,at 8¹2 GHz,the insertion loss(S₂₁)is less than 0.4 dB,and both of the isolation degree(S₁₂)and return loss(S₁₁)are more than 20 dB.VSWR is less than1.15.The fabricated circulator was measured.The results show that,at 9.5¹0.5 GHz,both of S₁₁ and S₁₂ are greater than 20 dB,and S₂₁ is less than 1.2 dB.The outline dimension of strip-line circulator is 9×9×3.2 mm³.The simulation results reveal that,at 8¹2 GHz,S₂₁ is less than 0.3dB and VSWR is less than 1.15,while S₁₁ and S₁₂2 are both greater than 20 dB.Secondly,investigation on the x-band circulator package structure was presented,Basing on HFSS software,design and simulation for the micro-strip circulator array and the strip-line circulator array were carried out,respectivly.A tiled package structure with small volume and high integration was demonstrated.Four layers of PTFE dielectric substrate were selected as the package substrates because of its excellent properties applied at high frequency.The vertical interconnection circuit acts as the connection of circulators with the antenna and T/R module.A reasonable layout of the circulators and microwave transmission lines was designed.The 4×4 array of micro-strip circulators and 4×4 array of strip-line circulators were packed in a size of80×80×4 mm³,respectively.The simulation results for the micro-strip circulator array unit show that,at 8.7¹2 GHz,the insertion loss of the circulator array is less than0.52 dB while the isolation degree and return loss are both greater than 20 dB.And the simulation for the strip-line circulator array unit shows,at 8.7¹1.7 GHz,the insertion loss of the circulator array is less than 0.6 d B while the isolation degree and return loss are both greater than 20 dB.Finally,the X-band micro-strip circulator array was fabricated,and the circulator unit in the array was measured.The results show that,at 8.7-9.8 GHz,the return loss and isolation degree are both greater than 20 dB and the insertion loss is less than 2.1dB.