Tunable Electromagnetic bandgap (EBG) structures are used as variable surface impedance in the sidewall of waveguides to provide three generations of agile analog phase shifters for low cost ESA applications. A design methodology is discussed using a periodic unit cell approach. Three unique millimeter wave varactor diodes (heterojunction barrier varactor, Schottky varactors and flip chip Schottky varactor diode) have been developed. They have been introduced in monolithic form for the first two-generations and flipchip varactors for the last generation of EBG phase shifters. Results from each generation are reported with a phase shift of 36 to 16.8 deg/mm and the lowest insertion loss of 0.3 dB/mm at 38 GHz. A surface impedance model predicts the increase in the inductance/capacitance ratio of the unit cell components provides the lowest insertion loss. This is validated from the measured results from the three generations of the phase shifter circuits. Our results indicate that the approach of the electronically tuned EBG waveguide phase shifters could provide the low cost-high performance components for an ESA architecture without the need for TR modules.