Ultra wide-band low-loss band-pass filter constructed from piezo-electric crystal or crystals and stabilized negative impedance element or elements, for radio and television systems

摘要

537,797. Impedance networks. CHAKRAVARTI, S. P. March 19, 1940, No. 5119. [Class 40 (iii)] A filter for passing a wide frequency band with low attenuation comprises one or more combinations of a piezo-electric crystal with a stabilized negative resistance element. A two-terminal filter consists of a crystal C in series, Fig. 1, or in parallel with a tetrode Y-Z or other device acting as a negative resistance. The latter, which may or may not be tuned by external capacitance to the resonant frequency of the crystal, presents an effective impedance made up of the negative resistance -Ra shunted by a total capacitance Cs and by the inductance L of a blocking choke. In one form of symmetrical lattice filter, Fig. 3, the series combination of Fig. 1 is employed as one pair of arms and the shunt combination as the other pair. In other forms, the series or shunt combination is used in both pairs of arms, Figs. 4, 5 (not shown), or the series or shunt combination is used in one pair of arms, while a series or parallel tuned circuit is used in the other pair of arms, Figs. 6-9 (not shown). In all these arrangements, each negative resistance element may be tuned to the resonant frequency of the crystal in the same arm or in the conjugate arm. The individual elements and leads are screened, and an earthed screen E encloses the whole system. The Specification compares the band-width, attenuation and cut-off properties of the various embodiments with those of the ordinary lattice-type crystal filter.