This article presents the design and implementation of a mechanically controlled, series-fed antenna array featuring wide-angle beamsteering at the X-band. A theoretical model of a series-fed array, including phase shifters inserted between consecutive elements, is initially developed to derive design rules and gain insight into crucial performance tradeoffs. Subsequently, a mechanically controlled, reflection-type phase shifter consisting of a branch line coupler and two Pi-network reflective loads is presented. A movable metallic overlay tunes the impedance of the reflective loads, thus effectively modifying the output phase. While requiring a minimal linear displacement of only 0.06λ _0 , this topology provides a maximum phase shift of 300° with an average insertion loss of 1 dB and is exploited for synthesizing a series-fed patch array. Based on simulations and measurements, the proposed antenna offers an almost constant realized gain of about 15 dBi within a wide scanning range of ±50°, and the sidelobe level is better than -12 dB. The average total efficiency is 50%, and the cross-polarization levels are at least 11 dB below the maximum realized gain. The main weaknesses are the narrow bandwidth of 2.5% and the slight beam squint as the frequency varies. The proposed design is ideal for radars due to its excellent performance and high power-handling capability.