Optimizing The Design Of Your RF Switch Network

This article is part 2 of the Guide to Selecting an RF Switch. This 5-part guide is an accumulation of insightful content that will arm you with the necessary knowledge to design your RF switch network. This section will discuss the importance of switch system design by explaining how choosing the right topology for your application can increase its performance incrementally.

Click here for Understanding Key RF Switch Specifications, part 1 of this 5-part series.

Introduction

The previous chapter discussed how and why signal degradation occurs in high-frequency signals. It also discussed the two main reasons for this degradation: power dissipation in the line, and power loss due to reflections in the transmission line. However all discussions and explanations thus far have been made from a single module perspective. In a typical RF system, the switch network consists of multiple modules and cables. These networks may be constructed in numerous arrangements with modules of varying topologies. To understand the how to design the best arrangement for your RF system, it is important to understand the different RF switch topologies.

Before discussing available topologies and the effects they have on the insertion loss and voltage standing-wave ratio (VSWR) specification of the system, let's recap the key concepts from the previous chapter. Insertion loss is a cumulative measure of total power loss that takes place in the line. It is the logarithmic ratio of the power of the signal that leaves the transmission line to the power of the signal that enters the transmission line. Voltage attenuation and power loss that a transmission line will cause on a signal of a particular frequency can be calculated using its insertion loss specifications. The following graph, which can be found in the specifications document of the NI PXI-2548 Quad SPDT Relay module, displays its insertion loss performance.