Microwave & RF filter products

Coleman Microwave

Coleman Microwave offers Cavity and Waveguide filters types of filters include Low Pass, High Pass, Band Pass, Band Reject, Duplexers, Diplexers, Multiplexers from 500 MHz to 40.0GHz. Coleman specializes in  high power CW and pulse applications.  Tunable bandpass filters in both Co-Ax and waveguide are available in sub-bands from 500MHz to 18GHz.  Tunable Diplexers are available over the same frequency range.  The filter products can be integrated with couplers, terminations, combiners. switches and branching networks to create subsystems.


Co-Axial ceramic resonatorBand Pass, Band Reject, Multiplexers from 500MHz to 6GHz using Chebyshev, Bessel and Elliptic responses in surface mount packages.  These Co-Axial resonator filters are TEM coaxial structures using quarter wave resonators and either capacitive or magnetic coupling. The quarter wave resonator is formed from a block (usually square) of ceramic material with a hole in the middle parallel to it’s length. The outside, one end, and the hole are coated with a conductive material (usually silver) to form a shorted quarter wave length of transmission line. The length -vs- frequency of the line is determined by the dielectric constant of the ceramic. Essentially, ceramic filters are a form of distributed filters. They are much more rugged than LC filters which are susceptible to vibration and microphonics. Ceramic filters are much less expensive to produce than either LC or cavity type filters, due to the reduced labor, material, and machining costs. In addition, most modern ceramic materials are extremely temperature stable with temp coefficients of < 5ppm. Typically ceramic filters are much less temperature sensitive than either LC or Cavity filters, even after compensation.

Co-Axial resonator filters with Magnetic coupled resonators, the bandwidth is limited to about 8%, but magnetic coupling allows broad and deep stopbands, with 80 dB or more to 6 GHz not uncommon. Capacitively coupled filters can achieve bandwidths of 20% or more, but the stopband attenuation is limited to about 40 dB due to parasitic coupling at the front of the resonator. This problem becomes more pronounced with smaller resonators and higher frequencies.