Designing of Feeding Networks for TCAS Antenna

Abstract

The Traffic Alert And Collision Avoidance System (TCAS) has had extraordinary success in reducing the risk of mid air collisions. Now mandated on all large transport aircraft, TCAS has been in operation for more than a decade and has prevented several catastrophic accidents. TCAS is unique decision support system in the sense that it has been widely deployed and is continuously exposed to a high tempo, complex air traffic systems. This report presents the designing of feeding network for TCAS system.We have designed the feeding network where input power will be switched between two ports of antenna equally and in different ratio and this can be implemented by terminating two stubs of the design with varactor diodes which works as avariable capacitor and switched on and off according to the condition .with correct choice of bias voltage it is possible to realize equal as well as unequal power division ratios between four output ports. The design frequency is chosen 1.06GHz as centre frequency. Simulation part is done on HFSS with Rogersduroid 5880 substrate with dielectric constant(ξ) = 2.2 .Varactor diodes are simulated by fixing the value of junction capacitance corresponding to maximum reverse bias which is 0.16 pF and capacitance corresponding to maximum forward bias will be 2.25 pF and value of R= 4.8Ω and inductor (L)= 1 nH where R and L will be same for both of the cases. We have simulated the design and analyzed the reflection coefficients(S55,S22,S33,S44,S11) and transmission coefficients (S15,S12,S13,S14 etc) where the values of these coefficients are according to the condition.