Tunable RF filters have significant utility in
software-defined radio applications. Often, these applications require wideband
frequency coverage that may differ greatly from frequency coverage used in
civilian telecommunication systems. Most commonly, tuning response is a product
of changes made to capacitors and inductors in the resonators of a bandpass
filter; however, the higher order resonances and spurious pass-bands induced by
the periodic nature of the distributed elements present in the filter structure
limit the utility of this method of tuning.
Researchers at Arizona State University have developed a
multi-resolution filter comprising a number of cascaded bimodal filter stages
that takes advantage of the periodic response of the individual stages to
achieve a selectable high-resolution bandpass response. Designing each stage as
a bimodal switchable filter allows the device to act as a channel-select filter
operating over a range from near DC up to a maximum frequency of several GHz.
Potential Applications
- Ultra-Wideband Tunable Filters may provide substantial
utility to applications requiring RF band select functions. The following
examples illustrate some potential applications of this technology:
- Software-Defined Radio Transceivers (e.g. Joint Tactical
Radio System)
- Multi-Functional Radio Transceivers
- Wideband RF Sensors
- Ad-Hoc Wireless Sensor Networks
Benefits and Advantages
- Ultra-Wideband Coverage – A tunable frequency response
between DC and RF is a very desirable capability that is not afforded by any
other technology
- Equal Channel Widths – All bands have equal absolute
bandwidths
- Reduced Size – Significantly smaller and less complicated
than filters banks. It can be miniaturized through using synthetic
transmission lines
- Versatility – possible to implant topology using PIN
diode, FET, or MEMS switches
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