| A reconfigurable defected ground plane utilizing a micromachined, corrugated membrane is proposed and investigated as a phase shifter for phased array applications. The concept is based on etching slotted defects in the ground plane of the existing transmission line feed network of the antenna. Operation is regulated via control of the membrane electrode voltage, and thus a digital, analog and/or hybrid phase shifter is possible.; A parametric study is performed with a transmission line whose ground plane is defected by a single slot. For minimum return loss of 10 dB, up to 18° of phase shift is attainable, independent of substrate properties, with long, narrow rectangular slots promoting greater phase. Paired defects provide increased phase, and minimize return loss when defect separation promotes an impedance match. Phase shift figure of merit (FOM) of 500°/dB is possible with paired elements associated with 25O lines. Adopting a dumbbell shape for the defect pushes the paired defect FOM close to 600°/dB. An equivalent circuit model for the defect is presented, and is in agreement with its full wave analysis.; Fabricated prototypes of defected loaded line phase shifters, based on criteria of minimum size, yield measured FOMs of 334°/dB and 455°/dB, providing the required phase with a return loss of less than 10 dB as desired, in agreement with simulation. These structures are applied within a 3-element patch array, with beam scan in the far field computed for different element separations and phase shift progressions. Phase shifter designs based on minimum return loss by cascaded matched element pairs, require inter-pair spacing larger than 3 mm, at 10 GHz.; A cavity constructed beneath a ground plane defect is shown to influence phase shift, from 0° with zero cavity depth, up to the full defect phase, when the depth is twice the defect width. An electrostatically controlled membrane is selected to produce the cavity effect. Measured FOMs of 133°/dB and 143°/dB for defected transmission lines with and without a membrane backing, respectively, indicate that loss attributed to the membrane is negligible. Techniques for reducing the membrane electrode voltage are also studied and established. |
