Patent GB-1269412-A (GB)
Title: Hybrid-coupled fan-out and fan-in circuits
Inventor: SEIDEL HAROLD
IPC: H01P5/12
Filed: 1969-03-27
Abstract: 1,269,412. Amplifiers. WESTERN ELECTRIC CO. Inc. 27 March, 1969 [29 March, 1968], No. 16000/69. Heading H3W. [Also in Division H1] Comprises a method of power-equalizing or " tempering " a power-dividing or " fan-out " network using quadrature hybrid couplers by providing further such couplers in which the signals from symmetrical branches are mixed, the sense of " symmetrical " being explained below. The known hybrid fan-out circuit comprises an input quadrature coupler whose outputs form the inputs of two further couplers and so forth, whereby, in general, 2<SP>n</SP>-1 hybrid couplers provide 2<SP>n</SP> branches. Equal division of power is only attained if the transmission coefficient t of each coupler is equal to the coupling coefficient k over a sufficient band, and departure from equality causes an unequal power division which becomes more intolerable as n increases. The powers of the output signals from the first coupler are proportional to t and ik respectively (where i = #-1 represents a 90 degrees phase-shift), those of the (two) couplers in the second bank being proportional to t<SP>2</SP>, ikt, ikt and - k<SP>2</SP>, and so forth. Fig. 3 represents the n = 16 outputs of a four-bank fan-out, the power levels being marked against the corresponding output terminals 41-56. All the levels are of the same degree n and "symmetrical " refers to pairs of the type tpk<SP>n-p</SP> and t<SP>n-p</SP>k<SP>p</SP>, signals from such pairs being coupled to 2<SP>n-1</SP> = 8 further hybrids where they are mixed and fed to sixteen outputs. The resuit of such tempering is: (a) the power in all branches is the same at the crossover frequency of the couplers (i.e. the frequency at which t = k); and (b) the slope of the power v frequency curve is zero at the crossover frequency. The signals are fed to separate amplifiers and then recombined in a fan-in which is the conjugate of the fan-out network. The modification necessary to form such a conjugate network involves the insertion of 180 degrees phase-shifters in selected branches of the fan-out, the first phaseshifter being inserted in the B branch of the first hybrid 70, Fig. 5. Of the 2<SP>n</SP> branches of the untempered fan-out half are derived from the A and half from the B branch of hybrid 70, the A- and B-derived outputs being combined in symmetrical pairs by the tempering hybrids 77, 78, 79 &c. If the exponent of the signal coupled from an A-derived output is even, a phaseshifter is added to the B branch of the corresponding tempering hybrid, e.g. assuming p is even, a phase-shifter is added to branch 83 of tempering hybrid 79. If the said exponent is odd, nothing is added. Thus, half the tempering hybrids are provided with phase-shifters. The tempered hybrid suffers from the disadvantage that reflections due to discontinuities may return to the input. This may be avoided by using the parallel channel arrangement of Fig. 7 in which the signal is divided and recombined respectively by 180 degrees hybrids 104, 105, the fan-out network N of one channel being identical to the fan-in network of the other, and the conjugate networks N* being likewise identical. All reflections are coupled to the termination 106. In a more general form of the fan-out network, different couplers may be used at each binary level. Thus, the coefficients of the first coupler may be t 1 , k 1 , those of the first bank t 2 , k 2  and so forth. The signals in the output branches are then of the form t 1 t b  ... t c .k i k l  ... k m  where the subscripts are all different integers between 2 and n, the number of t factors being p and the number of k factors (n-p). A " symmetrical " branch is now one of the form k 1 k b  ... k c .t j t l  ... t m  where the k factors number p and the t factors (n-p). In a preferred form of the fan-out, the couplers in the first few binary banks are of wider bandwidth than those in the remaining banks. Attenuators may be used to equalize the signals in the few branches in which the power level is intolerably higher than the average.