An L-Band SiGe HBT Vector Modulator Using Lumped-Element 180°/90°Hybrids and Wilkinson Power Dividers for High Stability and Small Amplitude/Phase Errors

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An L-band SiGe HBT vector modulator has been developed for the next generation wireless radiosusing active phased array antennas and adaptive beam forming networks. It employs 180°/90° hybridsfor achieving quadrature phase shifting, four variable gain amplifi ers for controlling gain, and Wilkinsonpower dividers for combining vectors. The amplitudes of two of the four signal paths with a phaseoff set of 90° are weighed and combined to obtain a full 360° phase shifting. High stability and smallamplitude/phase errors can be expected since the 180°/90° hybrids and Wilkinson power dividersprovide high isolation between ports. A collector drive is used for switching amplifi ers to achieve highimpedance and low insertion loss. Lumped elements are employed in the design of the 180°/90° hybridsand Wilkinson power dividers for achieving a miniaturized size. Lookup tables of the control voltagesare generated from calibrating four signal paths. This lookup table can be easily extended to theelectrical, environmental or process changes. The vector modulator shows a maximum gain error ofless than 1dB and a maximum phase error of less than 2° for a full 360° phase shifting at 1GHz.

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