Linear FM Chirp Research Articles

Surface Acoustic Wave Slanted Device Technology

Abmacr-The most common linear FM chirp surface acoustic wave devices used in radar employ the conventional in-line structure for the transducer. These devices have Fresnel ripple and interelectrode reflections in the time domain that, unless compensated for, will degrade the compressed pulse time sidelobes. Reported in this paper are techniques for constructing slanted transducers and slanted reflective arrays that minimize interelectrode reflections and Fresnel ripple. Utilizing the danted transducer structure, flat power response has been achieved for both wide-band lithium niobate devices and narrower band quartz devices. Weighting of the slanted transducers is also easily achieved and a pulse compression matched pair of the devices on lithium niobate has produced time sidelobes of -37 dB. The equivalent circuit model for lithium niobate and quartz slanted transducers is presented and equations for the beamwidth design are derived. The design of slanted reflective array correlators is presented along with some test results of the rust device.

Variable Format Radar Receiver Using a SAW Convolver

A technique for receiving radar pulse trains is presented [which can be of a variable format in the sense that they vary from pulse to pulse]. The heart of the receiver is a sufrace ascoustic wave (SAW) convolver. In addition to prsenting experimental results for variable format waveform reception, it is shown that the convolver can easily generate ambiguity functions for virtually any waveform, and specific results for signals such as Barker codes and linear FM (chirp) waveforms are presented.

Surface Acoustic Wave Memory Using Semiconductor Laser

A new method for storing both phase and amplitude of surface wave signals with large bandwidth in silicon surface states by a short light pulse emitted from a GaAs laser diode is presented. 87 MHz surface wave signals are stored by using a light pulse with a duration of 0.5 ns and the stored signal are read out as a correlation output signal at a delayed time after storage. Pulse compression experiments are also demonstrated by storing a linear FM chirp signal with this method.

Surface wave memory correlator with optical write-in

A surface wave memory device in which a light pulse emitted from a GaAs laser diode is used to store surface wave signals is described. The storage of 87-MHz surface wave signals in surface states in silicon is obtained by using a light pulse with a duration of 0.5 nsec. Pulse compression experiments are also demonstrated by storing linear FM chirp signals with this method.

SAW chirp filter performance above 1 GHz

The performance of a practical compact SAW dispersive filter with a bandwidth in excess of 500 MHz and centered at 1.3 GHz is described. The linear FM chirp filter was fabricated and serially reproduced by electron-beam microfabrication. The effect of an externally implemented weighting function on the time domain performance is discussed. The filter has been found suitable for pulse compression in a high-resolution monopulse radar. Replication of filter sets with identical characteristics is discussed.

Effects of Range-Doppler Coupling on Chirp Radar Tracking Accuracy

Attention is called to the phenomenon of "range-Doppler coupling," characteristic of linear FM (chirp) waveforms, and the strong effect this coupling may have on tracking accuracy. Numerical results are presented for simple three-state filters and for a realistic reentry vehicle tracking problem.

Taut-Wire Delay Lines

The audiofrequency delay line reported at the 63rd Meeting of the Acoustical Society has been improved and used to synthesize transfer functions with specified characteristics in the time and frequency domains. Time delays from 8 to 20 msec are obtained using a 0.4-mil-diam platinum-alloy wire with transverse wave velocities from 168 to 67 m/sec. Magnet boards with 64 and 256 magnets have been used for signal synthesis. The magnets can be magnetized with specified amplitudes (within 5%) and polarities with a push-button magnetizer in about 15 min. A linear FM chirp was set up with five 20-msec delay lines in series giving 75 msec differential delay between 800 and 1600 cps and approximately uniform amplitude response. Viscous damping in the liquid termination is obtained using liquid propane for long time delays and liquid pentane for short time delays. The delay lines cover a 10 to 1 frequency range, from about 200–2000 cps for a 20-msec delay line and 1500–15 000 cps for an 8-msec delay line. Each delay line has a Vernier adjustment permitting the time delay to be varied ±5%. The group delay phase errors are small and in good agreement with classical theory.