microwave filter

microwave filter

[′mī·krə‚wāv ‚fil·tər]
(electromagnetism)
A device which passes microwaves of certain frequencies in a transmission line or waveguide while rejecting or absorbing other frequencies; consists of resonant cavity sections or other elements.

Microwave filter

A two-port component used to provide frequency selectivity in satellite and mobile communications, radar, electronic warfare, metrology, and remote-sensing systems operating at microwave frequencies (1 GHz and above). Microwave filters perform the same function as electric filters at lower frequencies, but differ in their implementation because circuit dimensions are on the order of the electrical wavelength at microwave frequencies. Thus, in the microwave regime, distributed circuit elements such as transmission lines must be used in place of the lumped-element inductors and capacitors used at lower frequencies. This can make microwave filter design more difficult, but it also introduces a variety of useful coupling and transmission effects that are not possible at lower frequencies.

The majority of modern microwave filters are designed by using the insertion-loss method, whereby the amplitude response of the filter is approximated by using network synthesis techniques that have been extended to accommodate microwave distributed circuit elements. A general four-step procedure is followed: determination of filter specifications, design of a low-pass prototype filter, scaling and transforming the filter, and implementation (conversion of lumped elements to distributed elements).

Microwave filters are implemented in many ways. Waveguide cavity band-pass filters have very low insertion loss, making them preferred for frequency multiplexing in satellite communication systems. Coaxial low-pass filters, made with sections of coaxial line with varying diameters, are compact and inexpensive. Planar filters in microstrip or stripline form (see illus.) are important for integration with hybrid or monolithic microwave integrated circuits. While planar filters are usually more cost effective than waveguide versions, their insertion loss is usually greater. Computer-aided design procedures are used in the synthesis of more sophisticated amplitude and phase responses, and active microwave devices (field-effect transistors) are used to provide filters with gain or tunable response characteristics. See Coaxial cable, Computer-aided design and manufacturing, Microwave solid-state devices

References in periodicals archive ?
As well as frequency tunability, a microwave filter must be lightweight and compact [4].
Noise reduction using photonic microwave filter for radio over fiber system.
Thicknesses of external layers were increased in order to obtain properties of microwave filter in models of periodical SDWs.
Some tunable filters are implemented by RF-MEMS capacitors with low insertion loss and high Q at RF, but RF-MEMS capacitors are relatively expensive which blocks them from wide applications in microwave filter. Compared with RF-MEMS capacitors, varactor diodes have the advantage of higher reliability, lower cost and faster tuning speed, so they are widely used in the tunable microstrip filters [6-13].
Gowanda Holdings LLC, an Addison Capital portfolio company, has acquired the business of TTE Inc, a company involved in specialty RF and microwave filter manufacturer.
T Johns, "Properties of some common microwave filter elements," in Microwave Filters, Impedance-Matching Networks, and Coupling Structures, pp.
Lancaster, Microwave Filter for RF/Microwave Application, John Wiley &Sons, New York, NY, USA, 2001.
Such an electronically switchable microwave filter is also desirable for multi-band telecommunication system, radio-meters, wide-band radar or electronically welfare communication systems, because of their diversity and high integration.
Neural network inverse modeling and applications to microwave filter design, IEEE Microwave Theory and Techniques 56(4): 867-879.
In a separate announcement, Smiths said it had acquired US firm Lorch Microwave - adding microwave filter technology to its electronic components and subsystems Interconnect business -in a deal valued at pounds 14.1 million.
The microwave filter uses a silicon carbide fiber that converts microwave energy to heat, allowing the filter to operate at high enough temperatures either while running or during unavoidable cold starts.
Therefore, a general overview of each tuning element in the realization of a tunable microwave filter is only presented.

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