: Phase shifters are important microwave devices. They are used in a wide variety of applications including wireless, satellite communications and radar systems. The most important application of phase shifter is found in phased array antennas, which are often part of radar systems. The number of phase shifters used in phased array antenna sometimes growsup to several thousands. The main parameters of a phase shifter based on the needs of a radar system are specified, such as operating frequency, angle beam scanning, transmitted power, cost ,and production facility. The most popular phase shifters used in phased array antennas are PIN diode phase shifters and ferrite phase shifters. Ferrit phase shifters have high power handling capability and low insertion loss but switching speeds are low also are temperature sensitive. PIN diode phase shifters have advantages such as fast switching times, low weights ,and low costs but in high frequency their insertion loss are high. Still to design of high power devices, rectangular waveguides preferred over planar transmission lines; such as microstrip and strip lines. The SIW structures are waveguides that built on microstrip lines. The SIW structures have the advantages of conventional metallic rectangular waveguide, such as high Q and high power capacity, and the advantages of microstrip lines, such as small volume and light weight. In last decade, several phase shifters based on SIW technology have been designed and fabricated that most of them are fixed phase shift. SIW has a closed structure, therefore semiconductor devices such as PIN diode can connect them through a slot and design controllable SIW phase shifter that have high power handling compared with the common transmission line phase shifters such switched line, loaded line and reflection type. In this thesis a PIN diode phase shifter based on SIW in X-band is designed, analyzed and simulated. The SIW phase shifter consists of two layers which two coupling transverse slots are used to connect them and the structure is loaded with PIN diodes. To achieve wider bandwidth transverse slots are used to couple the energy from bottom layer to the top layer. The designed phase shifter is able to produce phase shifts of 11 : 25 ? , 22 : 5 ? , 45 ? and 90 ? in 0.8 GHz bandwidth. In the frequency range from 11 to 12.5 GHz, return loss and insertion loss are better than 10 dB and 1.3 dB, respectively. The peak power handling capability of the proposed phase shifter is about 2 kW. Keywords: PIN Diode Phase Shifter , SIW Structure , Power Handling Capability Isfahan University of Technology Department of