Method for computing return losses requirements of devices from system specifications

Coaxial networks like satellite master antenna television (SMATV) or Cable antenna television (CATV) there are a lot of devices on serial connections, and it is very important to compute return loss performance of the complete system. When there are many devices in cascade connection, each output of individual device is connected to the input of other. Then the matching depends of both individual impedances and length of interconnection coaxial cables, so that it is possible to evaluate the performance through uncertainty mismatch expression based in S parameters of the devices. Therefore, the overall prediction of the return loss of the system is hard without an accurate characterization of the interconnections. In this paper we propose an analytical solution for individual devices specifications to ensure the return loss performance in all points of the network. The solution is independent of the length of connections. In addition, we present a practical graphic to calculate the solution and a very simple expression with less than 0.61 dB of error for devices return losses specifications bigger or equal than 10 dB.