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Glossary

  • Absolute Attenuation: The reduction of RF power through a filter, referenced to 0 dB (filter removed from the circuit). This is measured in decibels referenced to absolute (dBa).
  • Amplitude Match: The absolute difference in the amplitude response between a reference filter and a filter under test.
  • Amplitude Track: The relative difference in the amplitude response between a reference filter and a filter under test with compensation for an insertion loss offset.
  • Average Power: Power averaged over time, which includes a complete on-off cycle. For example, a pulsed transmitter sends out RF energy in bursts. The peak power is averaged over the pulse time (duty cycle).
  • Bandwidth: The width of the passband or the stopband of a filter, normally referenced to the minimum insertion loss point in the passband. For example, the passband of a filter is normally stated as a -3 dB bandwidth and the stopband may be stated as a -40 dB bandwidth.
  • Bessel Response: A filter which exhibits a maximally flat group delay over a frequency range. The stopband is monotonic and not very selective.
  • Butterworth Response: A filter which exhibits a flat passband response. This means no or very little passband ripple. The stopband is moderately selective and monotonic.
  • Center Frequency: The midpoint of the bandpass filter passband, normally expressed as the arithmetic mean of the two -3 dB points. Also called F0 or FO.
  • Chebyshev Response: A filter which exhibits ripple in the passband. The stopband is highly selective and monotonic.
  • Cut-Off Frequency: The point where a lowpass or highpass filter makes a transition from the passband to the stopband. Normally given as a -3 dB point. Also called FC.
  • CW Power: CW is an acronym for continuous wave or carrier wave. With a CW transmitter, average power and peak power are the same.
  • dBa: This indicates the level of power in dB, referenced to 0 dB (absolute).
  • dBc: This indicates the level of power in dB, referenced to the loss of the carrier (typically the insertion loss of a filter).
  • Differential Group Delay: The peak-to-peak difference in group delay between two frequencies. This is typically used over a specified passband where the highest and lowest values are used to determine the differential group delay. Also referred to as delta group delay, group delay flatness, or differential time delay.
  • Diplexer: A form of a multiplexer consisting of one input and two outputs. The input is common to two individual filters with separate outputs. Also referred to as a duplexer.
  • Dissipation Loss: The transmission loss due to the resistance of the reactive and resistive elements in a filter.
  • Elliptic Response: A filter which is derived from a mathematical function to yield the sharpest roll-off response for a given number of circuit elements. The filter exhibits ripple in the passband and the stopband (not monotonic).
  • Flatness: Absolute limits of variation in loss through the passband of the filter. Includes ripple, slope, and rolloff at band edges.
  • FC: Cut-off frequency; the point where a lowpass or highpass filter makes a transition from the passband to the stopband. Normally given as a -3 dB point.
  • F0: Center frequency; the midpoint of the bandpass filter passband, normally expressed as the arithmetic mean of the two -3 dB points.
  • Gaussian Response: A filter which exhibits a zero or minimal overshoot when passing a step function. The stopband is monotonic and not very selective.
  • Group Delay: (absolute) The propagation time of a signal through the filter. Group delay is proportional to the slope of the phase shift versus frequency.
  • Input Impedance: The impedance measured at the input terminal of a filter when the output is properly terminated.
  • Insertion Loss: The loss of the filter, in decibels, measured at center frequency or at the minimum loss point of the passband relative to a thru line (0 dB). It is the combination of dissipation loss and reflection loss.
  • Insertion Phase: The amount of phase change from the input to the output of a filter. This is measured as the additional shift in phase when the filter is placed in the transmission line.
  • Linear Phase Response: A filter which exhibits a near constant change in degrees per unit of frequency. The plot of frequency versus phase is a straight line.
  • Monotonic Response: A band of frequencies where the transmission loss exhibits no slope reversals.
  • Multiplexer: A combination of two or more filters in a common package with one input and separate outputs for each of the individual filters.
  • Overshoot: The amount by which a signal exceeds its steady-state output on its initial rise, typically given as a percentage.
  • Passband: The frequency range that the filter is designed to pass with minimum attenuation. This is usually defined by the half power points (-3 dB).
  • Passband Flatness: The difference between the minimum loss point and the maximum loss point (usually in dB) over a specified passband or bandwidth. This value includes the ripple and the overall slope of the passband.
  • Passband Ripple: The variations in amplitude (transmission loss) in the passband of the filter, superimposed upon the fundamental shape of the passband.
  • Peak Power: The maximum power delivered. If this is in the form of a pulse, the peak power will be much greater than the average power.
  • Percent Bandwidth: This is defined for bandpass filters as the bandwidth divided by the center frequency times 100%. Typically the -3 dB bandwidth is used and the formula is (BW /FO)* 100%.
  • Phase Linearity: The deviation in the phase response from a straight line, usually expressed in degrees.
  • Phase Match: The absolute difference in the phase response between a reference filter and a filter under test.
  • Phase Track: The relative difference in the phase response between a reference filter and a filter under test with compensation for an electrical length offset.
  • Reflection Loss: The transmission loss due to the reflection of power at a discontinuity (mismatch).
  • Relative Attenuation: The reduction of RF power through a filter, referenced to the minimum insertion loss point of the filter. This is measured in decibels referenced to the carrier (dBc).
  • Return Loss: The ratio, in dB, of the power transmitted into the filter to the power reflected back toward the source.
  • Ripple: The deviation from a linear function or fundamental shape. This is usually applied to amplitude, phase, or group delay in filter terminology.
  • Rise Time: The length of time it takes a step function at the output of a filter to move from 10% to 90% of its steady state value on the initial rise.
  • Shape Factor: A ratio of two bandwidths. Typically, a comparison of the passband of a filter to its stopband. In bandpass filters, it is the stopband bandwidth divided by the passband bandwidth.
  • Step Function: A signal change in amplitude from one level to another which occurs in zero time. This usually refers to a rectangular waveform used in testing transient responses.
  • Stopband: The frequency range (or ranges) outside the passband of the filter where attenuation of signal is desirable. This region is normally specified at some attenuation value or values. The closer to the passband that attenuation is specified, the more complex the filter design becomes.
  • Transition Region: The frequency range between the passband and stopband.
  • Triplexer: A form of a multiplexer consisting of one input and three outputs. The input is common to three individual filters with separate outputs.
  • VSWR: (Voltage Standing Wave Ratio). The ratio of the maximum value of a standing wave to its minimum value, related to the return loss by the equation: R.L. = 20*log [(VSWR + 1)/(VSWR - 1)], Therefore, a VSWR of 1.5:1 corresponds to a return loss of 20*log(5) = 13.97 dB.