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Computer based data acquisition and instrumentation control packages are becoming increasingly important tools in the field of research, development and industry. LabVIEW (National Instruments, USA) is a very popular and widely accepted graphical programming environment, using graphical programming language instead of the conventional text based language and is used extensively for developing automated measurement, test, and control systems. This article describes an automated test procedure based on LabVIEW software for the characterisation of a rotary field phase shifter (RFPS), using a vector network analyser (VNA).
This software has been developed keeping in mind the applicability of a phase shifter in a system such as a phased array radar. Rotary field phase shifters are key elements of multifunction phased array radars. A number of phase shifters with radiating elements are arranged in an array forming the antenna. By giving a suitable phase command to individual elements, the beam can be steered in any direction in space. The basic configuration of RFPS is shown in Figure 1.
Figure 1: C-band rotary field phase shifter
It consists of a metallised ferrite rod coupled at each ends to reciprocal polarisers and matching transformers . The polarisers convert the linear polarisation incident waves at either ends to circularly polarised TE11 mode waves. The matching transformers couple the phase shifter to standard rectangular waveguides. The ferrite rod is fitted with an 8-pole ferrite yoke which contains a set of windings to produce a transverse rotatable four pole magnetic field. This magnetic field provides a bias to the ferrite rod for creating a birefringence of 180° differential phase (that is a half wave plate) . This field can be rotated electronically by proper setting of the currents in the two orthogonal windings known as ‘sine’ and ‘cos’ windings. The differential phase shift is equal to twice the relative rotation of the magnetic field. The driver circuit does the interfacing between the control system and the phase shifter.