NOVEL SLOW-WAVE STRUCTURE FOR NARROW-BAND QUASI-TRANSVERSAL FILTERS

Slow-wave transmission lines for producing large delays have employed multilayer patterning, increased width, or very fine features requiring accurate photolithography. A narrowband slow-wave structure with none of these disadvantages is proposed for use with tapped delay line (transversal) narrowband filters. This line has periodic discontinuities, resulting in a pass- and stopband structure in which the group delay in the passbands is several times that of an ordinary transmisson line. The discontinuities are spaced typically by one or two wavelengths so that fine details are avoided. A linear-phase transversal stripline filter in which delay is increased by a factor of five is demonstrated. Using a previously published design procedure to calculate the filter tap weights, multiple reflections, dispersion and frequency-dependent losses were allowed for and both amplitude and phase of the filter were synthesised. A wide range of both phase and amplitude characteristics should eventually be possible and superconducting delay lines should ultimately permit losses of only 1 or 2 dB.