GB611982A - Improvements relating to balanced-to-unbalanced circuit connectors - Google Patents

Abstract

611,982. Impedance transformers. HAZELTINE CORPORATION. May 22, 1946, No. 15536. Convention date, June 5, 1945. [Class 40 (viii)] [Also in Group XL (c)] A circuit connector for connecting a balanced and an unbalanced circuit has two sections of equal characteristic impedance. The inner and outer conductors of the connector each comprises two sections, the second section of the outer conductor having two longitudinal slots, the first sections of the inner and outer conductors forming an unbalanced transmission line, and the second section of the inner conductor and the other conductive portion of the outer conductor forming a balanced transmission line of the same characteristic impedance. Fig. 1 shows a connector connecting a signal generator 26 to antennae 25, which is suitable for operation over a wide frequency band. The first section consists of conductors 10 and 12 which may be provided by a normal coaxial cable of any desired length. The second section. consists of conductors 11 and 13, the length of these sections being equal to one quarter of the mean operating wavelength. The outer conductor 11 is divided into two conducting portions 11a and 11b by two' diametrically opposed slots 15. A semicircular conducting member 17 connects the inner conductor 13 to portion 11b. The dipole antennae 25 are connected to 11a and to eonductor 13. In order that the characteristic impedance of the balanced section 11a, 13 shall be equal to that of the unbalanced section 10, 12, the diameter d2 of inner conductor 13 is made equal to the geometric mean of the diameters d1, d0 of the inner and outer conductors 12 and 10. An equivalent circuit is described, in which the arrangement is shown to behave as having a short-circuited quarterwave stub line connected at each end of the second section. For optimum wide-band operation, the characteristic impedance of the stub line across the free end of the second section should be equal to that of the other effective stub line, and also that of the balanced section 11a, 13 of the connector. This may be arranged by appropriately selecting the width of slots 15. The connector may be constructed so as to compensate for impedance changes in the balanced circuit coupled thereto. Flanges extending along the lengths of the slots 15 may be introduced, which reduce the impedance of the stub line effectively connected across the free end of the second section, and thereby compensate impedance changes introduced by a series resonant antenna circuit. In the case of a parallel resonant antenna circuit, the loading of this equivalent stub line may be increased. In a modification (Fig. 6, not shown) the inner conductor 13 has a hollow semicircular cross-section. ' This is shown'to have the effect of increasing the characteristic. impedance of the equivalent stub line connected at the lower end of the second section. The relative dimensions of the conductors in any of the examples may be modified by employing different dielectric materials.