Design, fabrication, and application of precise delay lines at 2.45 GHz

For years linear optimization algorithms have been used successfully in bandpass filter design. This method has been adopted for the design of dispersive interdigital transducers (IDTs) for pulse compression filters with low time-bandwidth products, and for the design of delay lines with linear phase. Now this method has been extended to the design of dispersive IDTs operating at higher harmonics. As examples, delay lines at 2.45 GHz operating at the fundamental and third harmonic with relative bandwidths up to 30% are presented. The delay lines operating at the fundamental harmonics were fabricated on the rotated cut of LiNbO₃ and had normal fingers only. The relative height of the metallization was chosen for minimum reflections. Minimum linewidth of 0.3 μm was necessary, The delay lines operating at the third harmonic had split fingers for canceling reflections. Therefore minimum linewidths of approximately 0.45 μm had to be realized. Measured and calculated frequency responses of these delay lines are compared with each other. Taking advantage of the reported delay lines, a novel FMCW radar system incorporating a 2.45 GHz SAW reference path is established. The proposed SAW based system achieves a higher dynamic range than the conventional FMCW radar sensors