Bandpass Filter

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A bandpass filter transfers energy from the source to its load in a select band of frequencies between the lower cutoff frequency and the upper cutoff frequency. The transition and stopband regions occur both below and above the cutoff frequencies. 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 filters are used as IF Filters, RF Filters, SSB Filters, Microwave Filters, Preselector Networks, Multiplexing Filters, Anti-Jam Filters, Channel Filters or Front End Filters.

Filtronetics, Inc. supplies bandpass filters that utilize a wide array of technologies. The LC or lumped element bandpass filter is comprised of inductors and capacitors. These are available for low pass, high pass, band stop and bandpass topologies. We also offer crystal bandpass and monolithic bandpass filters, as well as crystal band stop filters. For higher frequency applications, microwave structures are utilized. These, like LC are available in low pass, high pass, band stop and bandpass topologies. Finally, for commercial applications we offer a full line of SAW, Helical and ceramic filters in bandpass and bandstop topologies.

The type of technology employed is determined by the center frequency and bandwidth. A crystal filter is used when a narrow band filter is required. This is due to the crystal’s high, unloaded Q-factor, which is in the range of 10,000 to 100,000. Narrowband crystal filters with low insertion loss are achievable for bandwidths from 0.005% to 2% of the center frequency. Moreover, center frequencies are available from 4 KHz to 600 MHz. Monolithic filters are typically restricted to bandwidths of less than 0.4% of the center frequency. In addition, the center frequency is typically less than 150 MHz.

SAW filters are effectively constructed with center frequencies of 20 to 2500 MHz. Bandwidths can be from 1% to 10% of the center frequency. Ceramic and Helical filters have the same bandwidth limitations but are limited to frequencies greater than 200 MHz. All three have good reproducibility and are thus excellent for low cost commercial products. Filtronetics, Inc. provides custom, LC, Crystal, SAW, Helical and ceramic bandpass filters to the above limitations.

Microwave bandpass filters can be designed as low as 50 MHz. Conversely, LC bandpass structures start at DC and end about 2 GHz. The bandwidth is mathematically limited to twice the center frequency. At this upper bandwidth, it becomes a low pass filter. The lower bandwidth limit is determined by insertion loss limitations and stability. In extreme cases, filters can be as narrow as 0.5% of the center frequency. Filtronetics, Inc. offers custom filters from DC to over 3 GHz.

Filtronetics Inc. supplies bandpass filters with monotonic, elliptic and custom designs. Characteristic responses are 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 IP2 or 2nd order intermodulation characteristics and IP3 or 3rd order intermodulation characteristics.

Our filters have been utilized in systems in space, military, undersea, airborne, testing, and commercial applications. We can produce from one to over a million filters to suit your application. bandpass filter packages include Surface mount (SMD), Through-hole, and with connectors (BNC, TNC, SMA or N) versions.