Propagation of transverse bulk and surface acoustic waves in LiNbO (3) variable time-delay devices

Experimental measurements are reported on voltage-controlled acoustic time-delay lines operating at 1 GHz in the nearly pure shear-horizontal (S-H) mode in 38 degrees rotated Y-cut LiNbO(3). The high-acoustic velocity (4800 m/s) in conjunction with the large electroacoustic effect exhibited by this orientation allows high-frequency operation and optimum time-delay tuning sensitivity with a planar, single surface, device geometry. The authors demonstrate fractional time delay of 0.3x10(-6) V(-1 ) for surface electrodes that produce an in-plane E-field. However, the simultaneous excitation and propagation of both a leaky surface-acoustic wave (LSAW) and surface skimming bulk wave (SSBW), both as (nearly pure) S-H waves in these devices, seriously restricts the extent to which it is possible to maximize the time delay modulation sensitivity by reducing electrode gap spacing as done in similar SAW devices. The LSAW and surface-skimming body wave (SSBW) propagate at nearly the same velocity on a free surface, and perturbation of their velocity and relative attenuation rates by surface electrodes causes pronounced interference effects between the two modes for some device geometries.     

Experimental 6-GHz frozen wave generator with fiber-optic feed

Experimental results from an optically activated 6 GHz frozen wave generator (FWG) test device are presented. The several system components needed to produce a low-cost monolithic pulsed power source suitable for large phased arrays are demonstrated. Static electric energy stored in 50 ohm microstrip transmission lines is released by fast GaAs photoconductive (PC) switches activated by 50 picosecond laser pulses distributed over fiber-optics. The present device is of hybrid construction, using commercial fiber-optic pigtailed integrated optic couplers and semi-insulating (SI) GaAs metal-semiconductor-metal (MSM) photoconductive switch chips bonded into microstrip. However, exclusive of the laser, the design lends itself to monolithic microwave and integrated optic techniques especially at high frequencies. Experimental test results compare well with circuit simulation predictions, showing that hybrid techniques introduce negligible parasitics at the design frequency. Lower resistance PC switches are needed to fully demonstrate the high power performance capabilities of this type of device