Q3Microwave Theory And Techniques

A phase shifter is a passive or active microwave component inserted in a transmission line or waveguide to change the phase of the transmitted signal by a controlled amount θ, ideally while keeping the transmitted amplitude (|S21|) close to unity (low insertion loss). Phase shifters can be fixed (a set, factory-determined phase shift, e.g. a fixed length of extra line or a dielectric slab of chosen thickness inserted into a waveguide) or variable/electronically controlled (using PIN diodes, varactor diodes, or ferrite elements whose electrical length or effective permeability can be tuned by an applied bias current or voltage). The most important application of variable phase shifters is in phased-array antennas, where independently controlling the phase fed to each radiating element steers the combined antenna beam electronically, without any mechanical movement of the antenna structure — the basis of modern electronically-scanned radar and satellite communication antennas.