Research And Design Of Transition Structure And Switch Circuit Based On SISL Platform

As communication technology is constantly changing,RF transceiver systems have placed increasing demands on the performance of transmission lines.Due to the limitations of the structure,the electromagnetic field of conventional planar circuits such as microstrip lines and strip lines are mainly distributed in the medium which contribute to large transmission loss and serious dispersion in the millimeter wave frequency.The substrate integrated suspended line(SISL)is a new transmission line based on the traditional waveguide suspended line and multilayer printed circuit board stacking technology.It can not only retain the low loss and high quality factor of the waveguide suspended line,but also overcome the limiting of waveguide suspended line such as large volume,heavy weight,difficulty in integration,and high processing cost.Therefore,the circuit based on the substrate integrated suspended line platform has broad prospects.At present,there are active circuits such as low noise amplifier,power amplifier,voltage controlled oscillator,and passive circuit such as high gain antenna,low loss multiplexer,coupler have proven the excellent characteristics of the substrate integrated suspended line.In order to solve the testing problem of the substrate integrated suspended line,the former studied the transition structure of the substrate integrated suspended line to the microstrip line or the coplanar waveguide,but affected by the characteristics of the microstrip line and the coplanar waveguide,its frequency can only cover the microwave frequency.In the millimeter wave band,because the rectangular waveguide has low loss,high quality factor and large power capacity property,it is often used as the input and output port of the test instrument.Therefore,three millimeter wave band(including Ka band,V band and E band)transition structures of substrate integrated suspended line to rectangular waveguide are designed in this paper.Among them,in the frequency from 24.6 GHz to 38.5 GHz,that is,within 44% of the relative bandwidth,the measured return loss of Ka-band transition structure is basically better than 15 dB,and the insertion loss of a single transition structure is less than 0.34 dB.The V-band back-to-back transition structure has a simulated return loss better than 18 dB and an insertion loss less than 0.57 dB(including a 18.6 mm SISL transmission line)in the 44% relative bandwidth of 48-75 GHz.The E-band transition structure is a very low-cost transition structure with low-cost FR4 for all printed circuit boards.The transition structure uses dielectric excavation,double-layer metal,and multi-row metal via technologies to reduce losses in three aspects include dielectric loss,metal loss and radiation loss.The simulation results show that in the frequency from 60 GHz to 95 GHz,that is,within the relative bandwidth of 45.2%,the insertion loss of the entire back-to-back low-cost transition structure is reduced from 2.45 dB to 1.7 dB and the overall loss is reduced by 30.6%.It can be seen that the above three methods have a significant effect on reducing the loss of the transition structure.Subsequently,this paper designed a 24 GHz SPST switching circuit based on PIN diode by using the low loss and easy-to-integrate characteristics of the substrate integrated suspended line platform.The switching circuit adopts a topology structure in which four stages of parallel PIN diodes are cascaded,where short circuit branches are used to resonate in series with the parasitic reactance of the PIN diode to offset the parasitic inductance to improve the isolation of the switching circuit.At the same time,the doublelayer metal and medium excavation technologies are used to reduce the loss.By using such technologies,the simulation insertion loss of the switching circuit is reduced by 25%.The insertion loss of the final switching circuit is less than 1.25 dB,the return loss is better than 15 dB,and the off state isolation is greater than 30 dB.Finally,a 24 GHz SP4 T switching circuit is designed based on the SP4 T switch chip.The insertion loss of each channel is about 3 dB in the on state,the insertion loss introduced by its peripheral circuit is about 0.2 dB,and the isolation of each channel are greater than 30 dB in the off state.Based on the substrate integrated suspended line platform,three ultra-wideband SISL-to-rectangular waveguide transition structures with a relative bandwidth greater than 44% and a 24 GHz low loss switching circuit are designed in this paper.Both of the switching circuit and the transition structures are based on SISL platform thus have the characteristics of low loss,small size,light weight,and high integration.