GB1079285A - A two way non-reflective transmission device - Google Patents

Abstract

1,079,285. Duplex radio signalling. NIPPON ELECTRIC CO. Ltd. Dec. 2, 1964 [Dec. 4, 1963], No. 48966/64. Heading H4L. [Also in Division H1] A duplex system for transmission in opposite directions of signals occupying different frequency bands comprises multiple paths between junctions connected to a pair of input/ output ports, and a combination of filters, non- reciprocal devices and absorbers for directing the signals and absorbing reflections due to mismatch. As shown, two three-port circulators 105, 125 are used to connect a pair of input/output waveguides 101, 121 via two separate paths, the paths including filters (e.g. band-pass filters) 111,112 which in conjunction with the circulators (both circulating in the same sense) ensure transmission of the oppositely-directed signals in respective paths. Reflections due to mismatch of the load are directed by the appropriate circulator into a path difference from the path of the original signal, whereupon they suffer reflection by the corresponding filter and are again directed by the circulator into the other (original) path. However, the direction of propagation of the reflections being opposite to that of the original signals, they are absorbed by one of the isolators 113, 114. If one of the isolators is omitted, the circuit will still perform the same functions. In a modification (Fig. 2, not shown), both isolators are omitted and the three-port circulator (125) replaced by a four-port circulator (201) whose fourth port is connected to a dissipative load (206). It can be seen that all reflected signals are directed by the circulators to the dissipative load. In a further modification (Fig. 3, not shown), the circulators are replaced by T-junctions and separation of the oppositely-directed signals is achieved by four band-pass filters each arranged in a branch of a T one half-wavelength (at the appropriate frequency) from the junction. Reflections are absorbed by two isolators arranged in respective paths between the filters. In a third modification (Fig. 4, not shown), magic-T junctions are used and the symmetrical arms of the junctions are coupled by two paths each containing two band-pass filters and an intermediate isolator. In addition, the E-arms of the junctions are coupled by a third path which contains an isolator. In this case, pairs of filters in opposite paths are staggered by one quarterwavelength (at the appropriate frequency) from the corresponding common junction. The filters all have the same pass-band corresponding either to the forward or reverse signal, whereby one of the signals is transmitted simultaneously by both the symmetrical paths and the other is reflected back to the input junction with a phase appropriate for transmission to the third path whereby it is transmitted to the output junction. Reflections are absorbed by the isolators. In all the modifications it is possible to omit certain isolators when one of the signals is not subject to reflection.