A RF limiter is a two-port, variable attenuation device designed to be used as circuit protection and signal power limiting. The essential function of RF Limiters are, when exposed to signal power above a certain threshold the limiter attenuation is enhanced to ensure that the signal power level at the output of the limiter doesn’t exceed a certain threshold. RF Limiters are designed for a wide variety of applications and use cases, and hence there are a wide range of power levels and styles available, see Broadband High Power Coaxial RF Limiters.
One of the most common uses for RF Limiters is at the input of a low-noise amplifier (LNA). As LNAs are designed to amplify very weak signals, they can readily be damaged by unintended high power signal spikes or stray signals. Hence, having an RF limiter in between the antenna and the LNA can help to ensure that the LNA isn’t damaged during high signal transients. However, using an RF Limiter in this way can lead to desensitization of the RF receiver, as an RF Limiter attenuates all signals passing through the device.
As RF Limiters dissipate the excess incident power as heat, an RF Limiter will increase in temperature during use. Use of passive/active cooling measures, such as a heat sink is highly recommended to avoid excessive thermal conditions. RF Limiters may either be terminating/absorptive or reflecting typologies. With reflecting typologies, the excess incident signal energy is reflected instead of absorbed. Another note about RF Limiters is that they are not reciprocal devices, and there is a designated input and output.
RF Limiter Key Electrical Specification Performance Parameters
Frequency range [Hz]
Insertion loss [dB]
Input VSWR
Flat leakage, continuous wave (CW) [dBm]
Spike leakage [joules/nanojoules]
Response time [us]
Recovery time [us]
Input power maximum, continuous wave and peak [Watt]
Limiting threshold [dBm]
Interconnect type/style
When specifying a RF Limiter for an application, it is important to note the flat leakage and spike leakage characteristics. Flat leakage refers to the continuous wave (CW) leakage characteristics, where the spike leakage refers to short transient leakage events, such as pulses or spikes. As many RF Limiters are constructed using diodes, typically PIN diodes, there is a nonlinear response that needs to be taken into account along with the characteristics of the circuit being protected when properly designing or specifying a RF Limiter.