Excitation of magnetostatic surface waves in an arbitrary direction on a tangentially magnetied YIG film

While magnetostatic surface waves (MSSW´s) can propagate over a range of angle in the plane of the YIG film, the treatment of MSSW excitation has so far considered only the simplest case of propagation at right angles to a tangential bias field[1]. Away from the latter direction, the phase and group velocity vectors are noncollinear, with the beam steering angle variable by the bias field. MSSW´s localized at a metallized YIG surface exist for all propagation directions except along the bias field[2], while MSSW´s localized at an unmetallized YIG surface exist only for propagation directions outside of an angle zone bisected by the bias field[3]. This paper reports a theory for the excitation of MSSW´s in an arbitrary direction in the allowed angle zones by the most basic electromagnetic transducer, namely, an electric line-current source, and various ramifications thereof, e.g., microstrip and meander-line couplers. The excitation characteristics are compared to the special case of propagation at right angles to the bias field, and transducer impedance characterization in terms of radiation resistance and reactance is obtained.