Abstract
In the present paper, a unified analysis is given for studying the characteristics of surface wave delay lines using interdigital transducers or phase-coded transducer configurations for dc pulse transmission based on equivalent circuits and Laplace transform calculus. A general idea of the transmission characteristics of a delay line using an interdigital transducer may be obtained by calcuulating the short circuit transfer admittance Y_<TS>. If the number of exciting and detecting electrode pairs is one, the transfer admittance is expressed by Eq. (1). Fig. 2 shows the characteristics of a line in the time domain expressed in terms of Laplace transforms by replacing (jω) with the by operator p in Eq. (1). If the number of exciting and detecting electrode pairs is large, the transfer admittance is obtained from the superposition of the transfer admittance denoted by Eq. (1). For an interdigital exciting transducer composed of M periodic sections and a detecting transducer composed of N periodic sections, the transfer admittance can be expressed by Eq. (6), where a_n, b_n=±1 denote the polarity of the electrode pair. Transducer configurations of a normal type and a phase-coded type will be discussed with a view of applying the surface wave transducer to a digital delay line. Fig. 8, 10 and 13 show the experimental impluse response of transducers using the normal sequence, Baker sequence and Golay sequence. With respect to the impulse response, a transducer that is phase-coded may be applicable to digital devices because the amplitude ratio of the main peak to the second sidelobed peak is large. Fig. 14 shows the experimental response of these transducers for random input pulses. Fig. 15 shows the eye-patterns which are obtained from a superposition of each impulse response corresponding to the random input pulses shown is Fig. 14 . From Fig. 15, it is seen that the transducer using the Golay sequence is more applicable to digital devices. In order to obtain the design method of the surface wave transducer for actual digital devices, the relations between several external conditions, such as the width of the input pulse and the load admittance, and the output response should be considered by computing the Fourier transform of the transmission characteristics as expressed in Eq. (20). Fig. 16 shows the maximum amplitude and the variation of peak position of the main response as a function of the width of the input pulse. From this figure, it is seen that the maximum output amplitude and the minimum variation of peak position are obtained for t=T(T=L/2V). Fig. 17 shows the experimental and calculated output response patterns as a function of the load admittance obtained from Eq. (20). Fig. 18 shows the instantaneous power (e_0(t)^2/R_<out>)as a function of the load admittance. From these figures, it is seen that(w_0C_tR_<out>)^<-1> is nearly equal to the maximum instantaneous power of the main response. Analysis gives a convenient means of calculating the relation between the input signals and the output response patterns, thus concisely demonstratig how transducer configurations using phase-coding, such as the Golay code, are useful for digital devices.
