An L-band SiGe HBT active vector modulator using lookup tables of the control voltage for high stability and small amplitude/phase errors

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