Delay Line Secondaries in Phase-Modulated Sweep Integrators

A video sweep integrator is a device for adding successive radar returns of transmitted pulses. One type of sweep integrator uses an ultrasonic delay line for storage, requiring that the delay line transmission be in the form of a modulated carrier. Addition is obtained by means of a closed regenerative loop that operates for a finite time to provide uniformly weighted addition or operates continuously with exponentially decaying memory. The former type of operation is called iteration to distinguish it from the continuous operation called integration. This paper treats the case of phase modulation imposed upon the carrier. Delay line secondary, or spurious, responses result from multipath propagation through the delay line. The cumulative effect of these secondaries after circulation in the sweep integrator or iterator may set a severe limitation on dynamic range. This paper treats two cases of secondary buildup: 1) the coherent buildup case in which relative buildup of secondaries is much greater than that of the signal, and 2) noncoherent buildup in which the built-up secondary effect is less than in the coherent case. It is suggested that it is possible to assure noncoherent secondary buildup by changing the carrier frequency in an irregular manner upon each circulation around the regenerative loop.