GB1433862A - Four port networks synthesized from interconnection of coupled and uncoupled sections of line lengths - Google Patents

Abstract

1433862 Coupling circuits MERRIMAC INDUSTRIES Inc 9 April 1973 [16 May 1972] 16932/73 Heading H1W Directional couplers, phase-shifting circuits and impedance-matching circuits are made from circuit elements comprising combinations of coupled and uncoupled lines having a common characteristic impedance equal to that of the system in which they are incorporated. The elements are combined together to make the above-mentioned devices. The two basic elements are shown in Figs. 1 and 2. In the Fig. 1 element, two identical coupled lines 31, 32 are joined by uncoupled lines 33, the characteristic impedances of all the lines being equal. When terminated in the characteristic impedance Z t , the coupled lines exhibit even and odd mode impedances. Z e , Z o where Z t =#Z e Z o , and the phase velocities of these modes are made equal. The total length of the Fig. 1 element is less than one quarter-wavelength and it has the amplitude but not the phase characteristics of a directional coupler. It is shown mathematiccally in the Specification that the element may be used to match unequal impedances Z e and Z o . The element of Fig. 2 has an overall length of one quarter-wavelength and has both the amplitude and phase characteristics of a directional coupler. It consists of coupled lines 31, 32 and uncoupled lines 36, 37; 33, 34; 38, 39. The prior-art directional coupler of Fig. 3 consists of a quarter-wave central section 47 having a different geometry and hence a different geometry and hence a different impedance from quarter-wave sections 46, 48. The method by which this circuit may be realized from the structural elements of Figs. 1, 2 is apparent from Fig. 4. The Specification discusses the frequency response of circuits realized by the method of the invention, e.g. a combination of elements which realizes a five-section coupler with an odd response function is described (Fig. 9, not shown). Fig. 12 shows a known kind of differential phase shifter in which a power divider 90 drives output lines 92, 93 and the line 92 contains a quarter-wave reflective phaseshifter. This is realized by the circuit 99 which is a modification of the element of Fig. 1. Other examples of reflective phase-shifters having desired frequency-response are given (Figs. 13, 14, not shown).