Magnetostatic delay lines for group delay equalization in millimetric waveguide communication systems

This paper considers the application and performance of magnetostatic surface wave delay lines as adjustable group delay equalisers in the high data rate, long haul millimetric waveguide system under study by the British Post Office. The initial 14.58 km link requires differential delays between 42 nsec and 12 nsec over a 500 MHz bandwidth for 32 channels in the 32- 48 GHz band. Test group delay equalisers have been fabricated from narrow linewidth yttrium iron garnet films, grown by liquid phase epitaxy in the 5 μm to 50 μm thickness range. These have been operated at the system IF, 1.0-1.5 GHz, in the magnetostatic surface wave mode utilising microstrip input and output couplers. Theory as well as experimental results for this frequency range are presented. Investigations have been carried out on magnetostatic wave terminations, and the effect that residual mismatches from these terminations, as well as input-output electromagnetic mismatches from the transducer 3-port networks, have on the phase and amplitude ripple of the equaliser. The effects of anisotropy field on the minimum operating frequency have been studied and optimum crystallographic orientations chosen.