In the operation of electronic systems and circuits, the basic function of a filter is to selectively pass, by frequency, desired signals and to suppress undesired signals. The amount of insertion loss and phase shift encountered by a signal passing through the filter is a function of the filter design. Similarly, the amount of rejection of an undesired signal is a function of the filter design.

Mini-Circuits’ filters are passive, they contain inductors and capacitors. Three types of filters, low-pass, high-pass, and band-pass are available. Two different low-pass filters have been designed to (1) provide high rejection of undesired signals very close to the pass-band and (2) to provide a linear phase vs. frequency characteristic across the pass-band frequency range. A linear phase characteristic is essential when passing a pulse waveform in order to preserve the pulse shape and avoid a distorted waveform. High-pass filters have similarly been designed to provide high rejection of undesired signals very close to the pass-band. Constant impedance band-pass filters have been designed to allow signals to pass within the pass-band and to be rejected outside of this band. However, these filters provide a matched 50Ω impedance both within and outside the pass-band. This is a very important characteristic especially when inter-modulation distortion and non-linear devices. such as mixers and oscillators, are to be considered. Refer to the article “Constant Impedance IF Band-pass Filters Improve Performance” for more details.

Mini-Circuits’ filters are available in a variety of packages and connector styles. Pin plug-in and surface-mount packages are available to accommodate both commercial and military applications. In addition to the catalog models described on the specification sheets, Mini-Circuits designs and manufactures filters to specific customer requirements. Consult our applications department for your specific needs.

The basic filter designs offered by Mini-Circuits utilizes a modified butterworth or “maximally flat” design, a modified Bessel-Thomson or flat delay design, and an elliptic function design. All filters are specified by their amplitude response, both in the pass-band and reject-band, also by their VSWR and phase characteristic where applicable. For convenience, the 20 dB and 40 dB reject-bands are specified. The cut-off frequency, fco, of each filter is also given. This frequency corresponds to the 3 dB insertion loss point of the filter response. This frequency point easily allows the filter response to be normalized to fco.

The CAPD data given in the handbook for each filter has a significant amount of data points to clearly describe the filter performance characteristic. The data curves show the overall filter performance curves. Any resonances that would be available can easily be observed. The data and curves present a very accurate description of each filter and may be used in conjunction with various software programs designed to analyze system performance.

Figure 1

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