Cochlea-Inspired Channelizing Filters for Wideband Radio Systems.

Abstract

RF and microwave multiplexers with a large number of output ports--called channelizers--have always posed a challenging design problem. Typical multiplexer designs use a set of channel filters connected at either a common port or through a manifold consisting of transmission lines (or waveguide) and tuning elements at the junction of, or between, separate channel filters. Nearly all modern multiplexer design methods rely on optimization of the individual channel filters and/or compensation networks used to reduce channel-to-channel interactions. Even with computer optimization, solutions for certain multiplexer topologies with more than about ten channels are often not possible, especially for units covering a wide bandwidth.

The work presented here approaches the problem of designing wide bandwidth, contiguous-channel, multiplexing filters by implementing a model of the mammalian cochlea. The cochlea is an amazing channelizing filter, covering three decades of bandwidth with over 3,000 channels in a very small physical space. Using a simplified mechanical cochlear model and its electrical analogue, a design method is demonstrated for RF and microwave channelizers that retain the desirable features of the cochlea including multiple-octave frequency coverage, a large number of output channels, and an enhanced, high-order upper stop-band response. In addition, improved cochlea-like channelizing filters are demonstrated that use conventional, higher-order bandpass filters with prescribed input impedance characteristics. Versions are presented that cover 20-90 MHz, with both constant fractional bandwidth and constant absolute bandwidth channels, planar microwave channelizers covering 2-7 GHz, and higher-order cochlea-like channelizers covering 200 MHz to 1 GHz. Applications of these channelizing filters include wideband, contiguous-channel receivers for signal intelligence or spectral analysis as well as transmit multiplexing.