Rf filter design pdf

Using a methodology means that all the necessary requirements are taken on board, the right design approach used, and ultimately the correct RF filter is designed. In general terms, filters modify the amplitudes and phases of sinusoidal waveforms that pass through them.

This change varies according to the frequency of the individual sinusoids within the overall waveform. Most filters are what is termed linear filters. As such they have no non-linear actions in which the response is proportional to the input. Instead the signals pass through and their amplitude and phase is altered in a linear fashion according to their frequency. These two functions represent the magnitude response often referred to as the frequency response and the phase response of the filter respectively.

These two functions govern the major features that need to be known about the filter. In being able to determine the functions it is possible to design the RF filter. Normally the example of the low pass RF filter design is used in the first instance and then this is expanded to include other forms of filter.

Accordingly we will look at low pass filter design first. When designing an RF filter it would be ideal if the filter would allow signals within the pass-band through without any change in amplitude or phase. Filters like this could have a rectangular response, falling straight to their stop-band and giving the required level of stop-band attenuation.

Unfortunately it is not possible to design RF filters like this, and real RF filter designs can only approximate to the ideal response curves and parameters. These approximations can then be used as the different types of filter that exist. Using a mathematical approach for RF filter design, it is possible to use a mathematical relationship. It can be proved that the square of the response for all realisable filters can be expressed as the ratio of two even, i. This means that a generic mathematical expression for all RF filter designs is:.

While relatively straightforward equations are available for Butterworth filters and constant-K filters, other forms of filter require more complicated calculations. The approach to RF filter design that has been used for many years uses what are termed normalised filters. A set of variables is calculated for a standard set of conditions and these and tabulated ready for use and scaling to the required conditions. A normalised filter would have a cut-off frequency of 1 radian per second, i. These values can then be scaled very easily for use at the required frequency and impedance.

In this way the tedious and involved mathematics required for RF filter design was reduced to little more than determining the requirements and then finding the relevant table of values.

Download S2P File. LTSpice is a free circuit simulator available for download on analog. For more info on how to export and use LTSpice for filter simulation click here. Export LTSpice. Qucs is an open-source circuit simulator available for download on qucs. For more info on how to export and use Qucs for filter simulation click here.

Export Qucs. Privacy Policy. Toggle navigation. LC Filter Design Tool. Calculate LC filters circuit values with low-pass, high-pass, band-pass, or band-stop response. Select Chebyshev, Elliptic, Butterworth or Bessel filter type, with filter order up to 20, and arbitrary input and output impedances. Filter Properties Response. Lowpass Highpass Bandpass Bandstop. Shunt First Series First. Cutoff Frequency. Lower Cutoff Frequency. Upper Cutoff Frequency.