Principle of coaxial switching devices

The principle of a ferrite switch is to change the direction of the bias magnetic field, achieve a change in magnetic permeability, and alter the transmission constant of the signal to achieve the switching purpose.

PIN tubes have a switching effect on microwave signals under the action of forward and reverse low-frequency signals. When forward biased, the attenuation of microwave signals is very small (0.5dB), while when reverse biased, the attenuation of microwave signals is very large (25dB).

The principle of BJT and FET switches is the same as that of low-frequency transistor switches, where the control signal of the base (gate) determines the on/off state of the collector (drain) and emitter (source). The amplifier has gain and large reverse isolation, making it particularly suitable for MMIC switches.

MEMS micro mechanical circuits are a new type of device developed in recent years and can also be used as switching devices.

Microwave switch circuit

The combination of switch devices and microwave transmission lines constitutes a microwave switch component. The equivalent circuit of the connection form between various switching devices and microwave circuits is the same. Switches are defined according to the number of interfaces, with the code # P # T, such as single pole single throw (SPST), single pole double throw (SPDT), double pole double throw (DPDT), single pole six throw (SP6T), etc.

The microwave design of these circuits needs to consider the parasitic parameters of the switches and the matching network design, as well as the installation size of the devices.