A HYBRID JUNCTION

Abstract: A hybrid junction device formed by an intermediate conductor located between and spaced from an outer conductor and a central conductor. The conductors are all about λ/4 in length. A first port is connected between the central conductor and the outer conductor at one end of the device and a second port is connected between the interme­ diate conductor and the outer conductor at the other end of the device. A third port is connected between the intermedi­ ate and the outer conductor at one end of the device while a fourth port is connected between the central conductor and outer conductor at the other end. The conductors may be co-axial type or formed by stripline type conductors.

Description: The invention relates to four port hydbrid junction networks which may be used as attenuators, phasers, signal combiners and splitters, mixers or modulators for high frequency or microwave apparatus. These hybrid junctions are known in the prior art and belong to a class of hybrids in which ring and branch lines are used. A particular characteristic of these hybrid junctions is that there are two possible paths, from any port to any other port, differing so that signals arriving at a destination port oppose each other. This can be achieved by either insertion of a λ/2 long transmission line in one path or by use of an electrical reversal connection. The insertion of a λ/2 long transmission line in one path has an advantage of allowing a simple and inexpensive design but has the disadvantage of operating over a narrow frequency range due to the λ/2 long transmission line. The insertion of an electrical reversal connection performs better over a wider frequency range since the electrical reversal connection is, by itself, an item which is independent of the frequency. However, the designs involving an electrical reversal connection require a more complex type of arrangement. U.S. Patent 3,504.304 describes a hybrid network in which 4 sections of suitable transmission medium such as transmission lines, co-axial cables, waveguides or striplines are connected in a ring network with one of arms connected so as to provide the needed 180 o phase shift. This U.S. Patent further describes a compensation circuit, such as variable reactance circuits, which is connected to each of the four junctions of the network to compensate the ring in a manner to increase the operating bandwidth and/or decrease the input voltage standing wave ratio(VSWR) with decreasing isolation between conjugate arms of the network, U.S. Patent 3,654,570 describes an improvement on U.S. Patent 3,358,248 which is directed to a four port coaxial hybrid junction in which a pair of insulated centre conductors extend side-by-side for a quarter wavelength in a manner permitting this pair of centre conductors to be substantially co-axial with an outer conductor, the improvement being an improved means for coupling signals into and out of hybrid junction device. U.S. Patent 3,497,832 describes a four port magic tee type hybrid apparatus with a pair of sub members λ/4 long having inner conductor portions co-axial with respective tubular intermediate conductor members which are aligned parallel to and equidistant from outer ground plate members. This U.S. Patent 3,497,832 illustrates in Figure 6 a stripline configuration which is analogous to the pair of co-axial type stub members illustrated in Figure 4. It is an object of the present invention to provide an improved four port hybrid junction device which is extremely compact, simple in design and as a result low in manufacturing cost. It is further object of the present invention to provide a hybrid junction device with an improved operating frequency range. These objects are achieved in the present invention by a four port hybrid junction device consisting of an intermediate conductor located between and spaced from an outer conductor and a central conductor, all conductors being λ/4 long with a first port connected at one end of the device between the central conductor and outer conductor, a second port connected at an opposite end of the device between the intermediate conductor and the outer conductor, a third port connected at said one end between the intermediate conductor and outer conductor and a fourth port connected at said opposite end between the central conductor and the outer conductor. In one embodiment of the present invention the conductors are co-axial conductors. In a further embodiment of the present invention the conductors are stripline conductors with two intermediate conductors being connected together at said one and at said opposite ends and two outer conductors being connected together at said one and at said opposite ends. The invention can be better understood by reference to the following detailed description when considered together with the accompanying drawings in which : Figure 1 illustrates a hybrid junction device according to the present invention using co-axial conductors. Figure 2 illustrates a hybrid junction device according to the present invention using stripline conductors, Figure 3 shows an equivalent electrical diagram for the devices illustrated in Figures 1 and 2. Figure 1 shows a hybrid junction device according to the present invention with a central conductor 1, an intermediate tubular conductor 2 co-axial with the central conductor and an outer tubular conductor 3 co-axial with the central and intermediate conductor. The conductors 1, 2 and 3 all have a length of 1/4 λ . A first port # 1 is connected to the central and outer conductor at the left end of the device while a second port # 2 is connected to the intermediate and outer conductor at the opposite (right) end of the device. A third port # 3 is connected to the intermediate and outer conductor at the left end and a fourth port # 4 is connected to the central and outer conductor at the opposite end of the device. Figure 2 shows an equivalent type of hybrid device similar to that shown in Fig. 1 using stripline conductors rather than co-axial tubular conductors. In this case the outer conductor 3 shown in Figure 1 is replaced by two outer stripline conductors 3' and 3'' which are electrically interconnected at the left end and at the opposite or right end of the device. In a similar manner, the intermediate tubular conductor 2 in Figure 1 is replaced by two intermediate stripline conductors 2' and 2'' which are electrically connected at the ends of the device. The central conductor is formed by a single stripline conductor 1'. All these conductors are 1/4 λ in length and are positioned with respect to each other in the manner shown in Figure 2. In order to provide a fuller description of the operation of the hybrid junctions shown in Figures 1 and 2, an equivalent electric circuit diagram is shown in Figure 3. In this circuit diagram, ports # 1 and # 2 are symmetrical if terminations to ports # 3 and # 4 meet certain requirements. Also ports # 3 and # 4 are symmetrical if terminations to ports # 1 and # 2 meet certain requirements. For instance, the characteristic impedance of the transmission structure from port # 1 to port # 2 (or vice versa) equals Zo if terminations to ports # 3 and # 4 have a ratio 1 : 4. In this case, if both terminations at ports # 3 and # 4 are real impedances, an attenuator is formed from port # 1 to port # 2 and if the terminations are imaginary impedances, then a phase shifter is formed from ports # 1 to # 2. When the terminations to ports # 3 and # 4 shown in Figure 3 are short circuited or open circuited, a phase shift of ± 90 o is obtained, with no attenuation involved, between ports # 1 and # 2, However, if the termination to port # 3 is real and equal to Zo/2 while the termination to port # 4 is also real and equals 2Zo, then ports # 1 and # 2 are mutually isolated, i.e. an infinite attenuation is obtained. It can be shown that admittance matrix, [ y ] of the hybrid junction shown in Figure 3 is: where: ϑ is electrical length in radians or degrees, Yo is characteristic admittance equal to 1/Zo, as defined per Figures 1, 2 and 3, and assuming negligible transmission losses in the junction hybrid as defined per Figure 3. Selecting electrical length of ϑ = 90 o (physical length equal to λ/4) derived are properties of the hybrid junction described above.

Claims: A hybrid junction device electrically comprising an intermediate conductor (2; 2', 2'') located between and spaced from an outer conductor (3; 3', 3'') and a central conductor (1; 1'), all conductors being λ/4 long with a first port (#1) connected at one end of the device between the central conductor (1; 1') and the outer conductor (3; 3', 3''), a second port (#2) connected at an opposite end of the device between the intermediate conductor (2; 2', 2'') and the outer conductor (3; 3', 3''), a third port (#3) connected at said one end between the intermediate (2; 2', 2'') and the outer conductor (3; 3',3'') and a fourth port (#4) connected at said opposite end between the central conductor (1; 1') and the outer conductor (3; 3', 3''). A hybrid junction device as claimed in Claim 1, characterized in that the central condcutor (1), the intermediate conductor (2) and the outer conductor (3) are co-axial. A hybrid junction device as claimed in Claim 1, characterized in that the conductors are stripline conductors with the intermediate conductor formed by two intermediate stripline conductors (2', 2'') connected together at said one end and at said opposite end and the outer conductor formed by two outer stripline conductors (3', 3'') connected together at said one end and at said opposite end.

Inventors: MILETIC, IGOR
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1984
Main classification: H01P5
IPC codes: H04B3, H01P5