A filter allows desired frequencies to pass while unwanted frequencies are suppressed. A perfect filter would allow all desired frequencies to pass (in the passband) and all unwanted frequencies would be completely rejected (in the reject or stopband). However, in the real world there is a transition area between the passband and the reject band. The narrower the transition area, the steeper the slope(s) of the filter. Also, there will always be some loss of signal in the passband (insertion loss) due to dissipation in the filter and reflection caused by impedance mismatch of the filter (return loss). The degree of suppression in the reject band can vary depending on the filter design.
Most of the electrical characteristics are interdependent. One may be improved at the cost of another. For Example, the insertion loss varies inversely with band width and directly with steepness of slope.
The mechanical dimensions of a filter largely depend on the electrical specifications. For example, the frequency of a cavity filter determines the length of its resonators. The width of the passband and reject band, the reject band attenuation, and the steepness of slope determine the diameter and number of resonators. Therefore the electrical specifications determine the overall dimensions of the filter.
The filter designs we specialize in are:
LC-Filters: Filters constructed with inductors & capacitors. This type of design allows for great flexibility in filter responses (such as Chebyshev or Cauer/Elliptic) and allows for smaller build-up sizes.
Cavity Filters: Filters constructed with resonators within conducting enclosures. This type of design achieves steeper slopes and narrower stopbands (higher selectivity). However, the design is limited by spurious resonances and VSWR considerations.
Helical Filters: Filters constructed with helical resonators. This type of design allows for lower frequency filters to be built in smaller housings.