GB590474A - Improvements in wave transmission networks - Google Patents

Abstract

590,474. Impedance networks ; electric resonators. WESTERN ELECTRIC CO., Inc. Aug. 17, 1944, No. 15775. Convention date, May 15, 1943. [Class 40 (iii)] Signals in two different bands of frequency pass from or to a common transmission line 1 to or from two separate transmission lines 2, 3, and are separated or combined by a pair of band-pass filters 8, 9, constructed of sections of transmission line. The filter 9, which passes the band of higher frequency, comprises two short-circuited stubs 17, 18, which are shunt arms anti-resonant at the mid-band frequency, and an intervening length 19, which is equivalent to a low-pass pi section, the whole being equivalent to a band-pass pi section with series inductance and shunt anti-resonant arms, Fig. 2 (not shown). The lengths of the stubs 17, 18 and connecting section 19 are determined from the desired cut-off frequencies to give an impedance match with the outside line 3 at the mid-band frequency. This calculation determines also the characteristic impedance which the connecting section 19 must have, but alternatively, coaxial lines of uniform construction may be used throughout the filter, the two cut-off frequencies being determined in that case with only one degree of freedom. The building-out section 20 is of such a length that at its junction with the line I it presents a high impedance at the mid-band frequency of the pass-band of the lower-frequency filter 8. The stub 13 of the latter is constructed to be anti-resonant at the mid-band frequency of the filter 8, but resonant at that of the filter 9, and the connecting length 15 is a quarter of a wave length at the mid-band frequency of the filter 9, so as to present a high impedance at that frequency to the junction 10. In order that the resonant and anti-resonant frequencies of the stub 13 may be widely spaced, Fig. 4 (not shown), the inner conductor is made in two sections of different diameters, the edge 34 being rounded to prevent corona discharge, and the mid-band frequency of the filter 9 may coincide with the third or a higher resonance of the stub 13. The stub 12 is similar and the intervening length 14 is such that the filter 8, like the filter 9, is equivalent to a band-pass pi section with series inductance and shunt anti-resonant arms, Fig. 3 (not shown). The lengths of the intervening sections are corrected to allow for interruption by the mouths of the stubs. Specification 487,282 is referred to.