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Industry News

Then: A Helical Phase Shifter For VHF

June 16, 2008
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I. Introduction

An antenna beam scanner which uses the principle of phasing for beam steering a linear array has been designed. Essentially it is a slow wave helical structure with a coupled non-contracting outer helix. The directionally coupled outer helix can be varied mechanically along the axis of the inner helix to change the line length between two terminals. A series of single coupled helices can be used to program the phase to an array of elements and, in turn, to steer the beam of the array.

II. Theory of Coupled Helix

As show in Figure1, the phase shifting device operates on the principle of coupled helices. The energy incident on T2 is electromagnetically transferred to the inner helix in the direction of T1, thereby producing a non-contracting unity transmission device. With translational motion of the outer helix, this device becomes a phase shifter.

The electric design of the phase shifter was undertaken according to the theory proposed by Kompfner, et al, 1 which states that if the helices are contrawound and the phase velocities on each helix are equal, complete unidirectional power transfer takes place when the helices are coupled over some appropriate length.

The properties of a concentric helix structure may be investigated by means of field theory; however, interesting properties can be deduced more simply by considering two transmission lines with uniformly distributed self and mutual susceptances and reactances. The use of field theory


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