In a typical back-pocket model (Landy & Oruc, 2002, their Figure 1), the input image goes through a set of linear, band-pass, spatial filters (first-order channels); then, a point-wise non-linearity (full-wave rectification) is applied to the outputs; and finally, a second-order, linear, low-pass or lower spatial-frequency tuned
band-pass filter is used (see the flowchart in Figure 2B).
A
band-pass filter chooses the coefficients [c.sub.j] to isolate (or "pass") a specific range (or "band") of cyclical components.
This causes a peak in the noise spectrum, which is excluded effectively by the 25-45 kHz
band-pass filter.
Like the HP filter, the
band-pass filter is a two-sided filter.
The seeker could use two different detectors to monitor the energy levels in the two bands (for example, lead sulfide for the short band and indium antimonide for the long band) or use a single detector with different
band-pass filters on the reticle spokes.
Note that the dual-band
band-pass filter is directly connected to the antenna, and the mismatch loss is correspondingly reduced.
Chen, "Miniaturized dual-mode substrate integrated waveguide (SIW)
band-pass filters loaded by double/single T-shaped structures," Progress In Electromagnetics Research Letters, Vol.
Wavelet transform is widely applied for temporal and frequency analyses of signals as well as a
band-pass filter. The latter case is called wavelet decomposition.
A repeater cannot be designed to comply with the above specifications by using a common RF
band-pass filter unless cost is no object.