GB1388318A - Networks - Google Patents

Abstract

1388318 All-pass networks WESTERN ELECTRIC CO Inc 13 Dec 1972 [15 Dec 1971] 57414/72 Heading H3U All pass transmission networks comprise a pair 10, 11 of hybrid quadrature couplers whose branches ; 1, 2; 3, 4; 1<SP>1</SP>, 2<SP>1</SP>; 3<SP>1</SP>, 4<SP>1</SP>; are conjugate within each pair, the transfer function 1 # 3; 2 # 4; 3<SP>1</SP> # 1<SP>1</SP>; 4<SP>1</SP> # 2<SP>1</SP> being t, that of 1 # 4; 2 # 3; 3<SP>1</SP> # 2<SP>1</SP>; 4<SP>1</SP> # 1<SP>1</SP> being ik i<SP>2</SP> = - 1, an input signal of unit value at branch 1 thus producing the quadrature pair t, ik at branches 3, 4. The transfer functions although having the frequency dependences displayed in Fig. 2 (not shown), satisfy the relation By connecting the couplers 10, 11 in cascade, with a 180 degrees shifting 1 : 1 transformer in line 12, a signal of values {1, 0} on brances 1, 2 leads to the pair {-1, 0} on branches 1<SP>1</SP>, 2<SP>1</SP> with a residual phase shift 0 degrees. The network of Fig. 1 has a larger pass band than that of transformer 14, which needs only to have the low frequency pass band of Fig. 2 (not shown), where t is substantial. By putting a 1 : 1 transformer (14<SP>1</SP>) Fig. 3 (not shown) having a high frequency pass band in the line 13, i.e. for frequencies whereat k is substantial, the same input pair {1, 0} leads to the pair {1, 0} at the output 1<SP>1</SP>, 21, with a residual phase shift # degrees. By placing 1 : N transformers in both lines (62, 63) Fig. 6 (not shown) connecting the couplers, one connected in a phase inverting sense, coupler (61) being adapted to correspondingly higher impedance levels, by a factor N<SP>2</SP>, than coupler (60), the network has the character of a transformer, whose bandwidth is greater than that of either transformers (64, 65), the former being designed for low pass, the latter for high pass. In a bootstrap arrangement to further increase band pass the transformer 14 is itself replaced by the network of Fig. 1, the network of Fig. 3 (not shown) being placed in line 13, see Fig. 5. This process can be iterated for further bandwidth increase, or combined with phase equalization techiques. By connecting the networks of Fig. 1 (Fig. 3) in parallel, Fig. 4 (not shown) the signals at the output branches (1<SP>1</SP>,1<SP>1</SP>), for a sigual applied to both input branches (1, 1) are precisely 180 degrees out of phase, both sharing the same residual phase shift # degrees. Each coupler may be a complex cascade of components, leading to the sharpened transfer functions of Fig. 7 (not shown), enabling the band pass of the transformers to be further reduced with respect to the network band pass.