Showing papers on "Stopband published in 1971"

On maximally flat sharp cutoff low-pass filters

Abstract: Maximally flat (MF) low-pass filters with multiple pairs of coincident or distinct imaginary axis zeros are investigated and compared with the all pole Butterworth filters. It is shown that for the same order n , finite zero filters provide much sharper cutoff than Butterworth filters, and that the cutoff slope increases with increasing number of zeros. Expressions for cutoff slope and minimum attenuation in the stopband are derived in terms of n , the number of pairs of zeros ( m ) and their locations. In the case of coincident multiple zeros, the stopband performance is found to be an optimum for a particular value of m . The information required for design of finite zero filters is provided in the form of universal graphs and use of these graphs is illustrated by a design example.

Characteristics and element values of equally terminated Achieser-Zolotarev quasi-low-pass filters

Abstract: Achieser-Zolotarev filters are similar to the familiar Chebyshev low-pass filters except for a large-amplitude first ripple (near dc). If a low-pass filter is required for operation only over the upper frequency portion of the band, an Achieser-Zolotarev filter may be used to give greater attenuation in the stopband for a given ripple level. The new filters give increased flexibility in the choice of impedance level within the filter, leading to improved design for distributed-element filters. The design tables for filters of 5, 7, 9, and 11 elements include the coefficients of the Zolotarev polynomials, the comparative stopband attenuation relative to the Chebyshev case, and the element values of lumped-element quasi-low-pass filters for various pass bandwidths and ripple levels of 0.01, 0.1, 0.2, 0.5, and 1.0 dB.

Multilayer dielectric stacks of coupled filters.

Abstract: The variety of optical filter characteristics obtainable with periodic stacks of two dielectric materials having simply commensurate optical thicknesses can be greatly increased when the basic section consists of more than one pair of layers. Although no more difficult to monitor in coating than stacks of two-layer sections, coupled-filter stacks have stopband spectra which differ considerably from those of their components in much the same way as the transmission characteristics of closely coupled resonators differ from those of their component resonators. The utility of periodic coupled-filter multilayers is illustrated by several examples: one for mirrors of doubly resonant parametric oscillators, which helps close a gap in signal-to-idler frequency ratios not filled by simply periodic multilayers; and two which permit the construction by band-nesting of wide band high-reflectance mirrors for near-ir and visible wavelengths, as well as MacNeille-Banning prisms for the uv region, with lower index ratios than previously envisaged.