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RF Limiter basics

This page of RF Wireless World covers RF Limiter basics and Limiter application note as well as RF power Limiter manufacturers.

Typically Limiter is any device which limits the input signal above certain limit set by the manufacturer. For example, conventional class-A amplifier can also acts as limiter if the input signal is very high in magnitude. With a very large input signal being applied to the transistor, it will drive transistor between saturation and cutoff.

RF Limiter is specially designed to limit the signals in the radio frequency or RF spectrum range.

As mentioned limiter operates in saturated mode, its output spectrum is composed of harmonics of the applied input signal. The harmonic contents will depend on the applied power level as well as bias current.

RF Limiters are mainly designed and developed using diodes such as PIN diode and schottky diode.

RF Limiter Application note

RF Limiter application

In FM receiver, one or more IF amplifiers are used as limiters. As mentioned, limiters remove any undesired amplitude variations from the received FM signal. This signal is later fed to the FM demodulator portion. The same have been depicted in the figure-1 above.

Mini circuits provide RF limiters in wide range of frequencies from 3KHz to 900MHz with dynamic range between 3 to 20dBm. This RF limiter produces 0.05 dB output change for 1 dB input change. The benefits of these RF limiters is that they introduce very little phase variations to the input signal while doing limiting operation.

As we know dynamic range is the range from minimum to maximum amplitude over which limiter is useful for using in the electronic circuit. What if RF signal level provided as input is outside the dynamic range of limiter, there are two scenarios that will exist here. If the input level is very high, an attenuator will be utilized. If the input level is very low, an amplifier will be utilized. Both the components are used so that RF input signal level remains within the designed dynamic range of the RF limiter.

RF Power Limiter Manufacturers

Following specifications are considered for selecting the right RF power limiter.
• Frequency range of operation
• Input power (Maximum)
• Input peak power (Maximum)
• Insertion loss: loss to signal as it travels from input to the output.
• Packet type: connectorized or in the form of drop in module

Following table lists out RF limiter manufacturers.

RF Power Limiter Manufacturer
Mini Circuits power limiters are available upto 3 GHz, handles power in magnitude of watts
Fairview Microwave: Available in GHz frequency band from 12GHz to 18GHz.
API Technologies
Planar Monolithics Industries
Aeroflex control components
G.T.Microwave Inc.
Penta Laboratories
Conectec International
Cap Wireless
Satellink, Inc.

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