GB966629A - Improvements in or relating to decoupling circuit arrangements for high frequency sources - Google Patents

Abstract

966,629. Impedance matching. TELEFUNKEN PATENTVERWALTUNGS G.m.b.H. April 25, 1962 [April 26, 1961], No. 15741/62. Heading H1W. [Also in Division H4] A bridge circuit for connecting two sources operating at the same frequency to a single load, e.g. an aerial, comprises two line sections each of length (2n+1)#/8, one connected between one source and the load, the other connected between the other source and a dummy load of the same value as the output load, and two reactances of value equal to the line surge impedance and the two loads, connecting the input and the output ends of the line sections. Isolation between the sources is obtained if the phase difference between the inputs is #/2. An analysis of the circuit given in the Specification shows that if n is odd (or zero) the reactances must be capacitative to obtain isolation and Fig. 3 shows an arrangement using two Lecher lines of length #/8 coupled by capacitances X. The conductors of each line section are arranged on the opposite edges of a parallelepiped to obtain isolation between the two lines. In the construction shown in Fig. 4, n is even (e.g. the lines are of length 3#/8) and the lines comprise two adjustable coaxial trombone sections 3, 4. In this case, the coupling reactances must be inductive and are shown in the form of two loops 5, 6 at the junctions between the trombone sections and the input and output lines 1, 2, 1<SP>1</SP>, 2<SP>1</SP>. The loops may be adjustable telescopically within the inner conductors of the input and output lines. In order to reduce the physical lengths of the lines when these are coaxial, the inner conductors may be formed as iterative structures having alternate thin and thick sections affording the equivalent of a series of #-sections. In this case, in order to adjust the lengths of the lines, it is necessary to arrange tapping points for one of the reactances adjustable over the electrical length of the last iterative component of the line. A circuit using lumped impedances is shown in Fig. 7 where X L =Z/#2 and X c = (1+#2)Z. In order to reduce the effect of stray capacitance at the ends of lines, they may be connected to earth through inductors which form with the capacitances parallel LC circuits antiresonant at the operating frequency. Where use is made of iterative line sections, these may be dimensioned to have cut-off frequencies below the frequencies of undesired harmonics.