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Triple stub circuit topology as simultaneous insertion phase, amplitude and impedance control circuit for phased array applications

This study shows that the well-known triple stub circuit topology can also be used for controlling the insertion phase and amplitude of a given signal simultaneously, as well as preserving its impedance transformation ability. The triple stub circuit topology, which is nothing but an extension of the conventional double stub loaded-line phase shifter, results in one more degree of freedom to its solution when it is solved for its insertion phase. This additional degree of freedom not only brings the impedance transformation ability, but also allows tuning the circuit into a resonator at the frequency of interest whose quality factor can also be adjusted. This result is employed for controlling the amplitude of the output signal to any desired level, which is achieved using only low-loss transmission lines and shown to be true for any non-zero transmission line losses. The measurements of the fabricated sample circuits verify that it is possible to control simultaneously the insertion phase between 0 and 360 degrees and the amplitude from -0.8 to < -15 dB, whereas the input return loss is always kept better than -15 dB as an example of their impedance transformation capabilities.