Crystal bandpass filter

The crystal bandpass filter is a filter that utilizes piezoelectric quartz crystals in its realization. Anatol Zeverev defines a bandpass filter as a filter that "passes the package of waves from certain lower to upper frequency limits and stops all energy out side these two limits. This filter is by far the most important and most commonly used filter in electronic equipment." Bandpass crystal filters are used as IF Filters, SSB Filters, Microwave Filters, Preselector Networks, Multiplexing Filters, Anti-Jam Filters, Channel Filters and Font End Filters.

The crystal bandpass filter is used when a narrow bandpass filter with low insertion loss is required. This is due to the crystal’s high, unloaded Q factor, which is in the range of 10,000 to 100,000. Discrete crystal filter bandwidths from 0.005% to 2.0% of the center frequency are achievable. Moreover center frequencies are available from 4 KHz to 600 MHz. Monolithic bandpass crystal filters (MCF) are typically restricted to bandwidths less than 0.4% of center frequency and a center frequency less than 150 MHz.

Filtronetics has designed and built discrete and monolithic crystal filters that utilize from 1 to 22 crystals. Discrete crystal filters have the advantage of complex and custom designs as well as wider bandwidths, however they are larger and more expensive than monolithic crystal filters. Filtronetics, Inc utilizes flat, polished, fundamental, overtone, and inverted mesa crystals in its crystal bandpass filters. We supply crystal bandpass filters with monotonic or elliptic designs. Some of the realizations include and with characteristic responses of Buterworth, Chebyshev, Cauer, Gaussian, Bessel (maximally flat delay), Equal ripple delay, Legendre as well as custom responses. These filters can be group delay equalized, amplitude equalized, phase equalized, amplitude matched, delay matched, phase matched, amplitude tracked, delay tracked, or phase tracked. We have special designs for good ring-down or overshoot response as well as good IP3 or third order intermodulation characteristics and IP2 or second order intermodulation characteristics.

Our crystal filters have been utilized in systems in space, military, undersea, airborne, testing, and commercial applications. We can produce from one to millions of crystal bandpass filters for your application. Crystal bandpass filters can be packaged in surface mount (SMD), through-hole, and with connector (BNC, TNC, SMA or N) versions.