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RF filter terminologies | RF filter terms

This page describes RF filter terminologies or RF filter terms. The common terminologies or terms of RF filter include bandwidth, frequency range, shape factor, selectivity, attenuation, insetion loss, isolation, Q factor, passband, stopband, ripple, group delay etc.

RF Filter | Bandwidth, frequency range, shape factor, selectivity, attenuation, insertion loss, isolation, Q factor, passband, stopband, ripple, group delay

Following table mentions useful RF filter terms or RF filter terminologies.

RF filter shape factor and bandwidth
RF Filter terminologies or terms Description
Bandwidth Frequency range around center frequency over which filter can be used efficiently is known as bandwidth. Frequencies above and below the center frequency at which response fall down by 3 dB with reference to center frequency indicates limits of filter bandwidth.
Frequency Range The range of frequencies over which filter is useful for any application is known as frequency range.
Shape Factor It indicates selectivity of the filter. It is the ratio of filter's response at 60 dB to response at 6 dB attenuation as shown. Here shape factor can be expressed as (F4-F1)/(F3-F2). Lower the value of shape factor steeper the response of the rf filter.
Selectivity It is measure of capabilities of the filter to pass or to reject specific frequencies relative to center frequency. It is expressed as loss through the filter which occurs at some specific difference from center frequency of the filter. For example selectivity of cavity resonator at with center frequency of 150 MHz equals "15 dB down" at frequency of "1MHz above or below" the center frequency.
Attenuation It is the amplitude or magnitude loss incurred to the signal once it passes through the RF filter.
Insertion loss It is same as attenuation mentioned above. It is loss of signal power when it travels through the RF filter.
Isolation It is referred as separation of one signal from the other in order to prevent any undesired interaction between them.
Q-factor It is measure of selectivity of the resonant circuit. Q-factor is described as ratio of stored versus lost energy per oscillator cycle.
Passband The region in frequency response of the RF filter through which signal passes unattenuated.
Stopband The region in frequency response of the RF filter through which signal will be attenuated as per designed attenuation value. This is the band which stops i.e. attenuates the signal.
Ripple The variation in insertion loss of the filter in passband response. The difference between maximum and minimum attenuation is taken as ripple.
Group Delay It is measured in seconds. It is defined as propagation delay time of envelope of AM modulated signal when it passes through the RF filter.

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