It is this directional property that makes circulators ideal for use as T/R switches (duplexers). For instance, in the example shown, there is little or no signal flow from Port 3 back to Port 1 from Port 2 back to Port 3 or Port 1 back to Port 2. Circulators are non-reciprocal devices, meaning there is no significant flow in the reverse direction. In the clockwise version of a circulator shown in Figure 1, a signal input at Port 1 propagates to Port 3 signals from Port 3 propagate to Port 2 and a signal from Port 2 is transmitted to Port 1. There is no significant flow in the reverse direction of each version-a characteristic that makes them ideal as T/R switches.
What does a transmit and receive switch do? This article looks at two main types-RF circulators and PIN diode switches-as well as a type used for voltage sensitive applications.Įach technology is matched to specific applications with example devices from Skyworks Solutions Inc. There are several technologies available for implementing T/R switches.
However, to use them effectively, designers must first understand their operation and key characteristics. T/R switches also handle the transmitted power while offering low insertion loss to prevent attenuation of the transmitted signal, and maintain a fixed characteristic impedance to prevent signal reflection and loss. These are designed to handle the task of rapidly switching an antenna or transducer between a transmitter and a receiver, while providing the required isolation between the T/R paths. To accomplish this, designers can turn to transmit/receive (T/R) switches, also referred to as duplexers. Additionally, the shared antenna or transducer has to be switched in rapidly after a transmission in order to allow the receiver time to acquire and measure the received RF or ultrasound echo. This requires a method for switching the antenna or transducer between the two devices while at the same time providing adequate attenuation between them to prevent damage to the high-sensitivity receiver components by the high-power transmitter. For many reasons, designers of echo ranging devices-such as radar, sonar, nuclear magnetic resonance (NMR), or ultrasonic ranging-as well as cell phone and satellite communications infrastructure are often in a situation where they must connect a common antenna or transducer to both a high-power transmitter and a sensitive receiver.