Showing papers on "Chirp published in 1979"

Chirp-grating lens for guided-wave optics

Abstract: A high-throughput diffraction-limited Bragg diffraction grating having a variable periodicity functions as a lens for optical guided waves. The lens may be fabricated with planar photolithograhic techniques. It has predictable focusing properties which are insensitive to process variations making it particularly useful for mass production of integrated optical systems.

Transmitter-receiver system utilizing pulse position modulation and pulse compression

Abstract: Transmitter are receiver systems are disclosed including an encoder and a decorder, respectively. The encoder samples an incoming analog video signal and operates a periodic bipolar pulse pair whose phase separation is proportional to the amplitudes of the sampled data, thus pulse position modulation (PPM). In one embodiment of the invention the coded in-phase pulses are applied to a first channel having an intermediate frequency (IF) dispersive delay line with a positive-sloped transfer function. The out-of-phase pulses are applied to a second channel having a dispersive delay line with a negative-sloped, or conjugate, transfer function. The two channels of positive and negative dispersed pulses are added together resulting in a complex IF waveform. The complex IF waveform is frequency translated to a suitable time varying DC voltage waveform for controlling a transmitter. The receiver system includes a decoder having first and second channels with respective first and second conjugate pulse compression lines or chirp filters for recovering the original bipolar coded data. The first pulse compression line, with a negative-shaped transfer function recovers the in-phase PPM pulses of the bipolar pulse pair. The second pulse compression line, having the conjungate slope, recovers the out-of-phase PPM of the bipolar pulse pair pulses. The PPM pulses in the first and second channels are translated into pulse-width modulated pulses which are then demodulated. The demodulated pulses are subtracted and the original data is recovered while at the same time the sampling frequency is filtered out.

Ultrasonic ranging system for a camera

Abstract: An ultrasonic ranging system for a camera includes an ultrasonic transducer responsive to a keying pulse for transmitting a frequency modulated burst of ultrasonic energy toward a subject. The leading half of the burst is a chirp whose frequency varies from a higher to a lower value; during the trailing half of the burst, the frequency remains substantially constant. The system also includes a receiver for processing an echo signal produced by the transducer on receipt of an echo within a predetermined time interval following the burst, and producing a range signal with a characteristic linearly related to the distance of a subject being photographed from the camera. A variable Q filter in the receiver filters echo signals produced by the transducer eliminates the need for a matched filter. The filter Q has a relatively low value during the initial portion of said predetermined time interval causing the bandwidth of the filter to be wide enough to pass all the frequencies of the chirp returned from a subject relatively close to the camera. During the remaining portion of the interval, the Q increases narrowing the filter bandwidth and optimizing it, with regard to the signal-to-noise ratio, for the constant frequency of the burst returned from a relatively remote subject. This arrangement reduces sensitivity of the receiver to echo cancellation due to interference between waves reflected from a nearby subject without adversely affecting the signal-to-noise ratio for returns from remote subjects. An accompanying change in filter admittance reduces angular sensitivity of the receiver to off-axis echoes.

Spectral broadening of pulsating Al x Ga 1-x As double heterostructure lasers

Abstract: The longitudinal mode spectrum of stripe geometry double heterostructure (DH) lasers exhibits a spectral broadening of ∼ 0.8 A when the laser emits pulsations. The broadening results from a chirp to longer wavelengths which occurs during the ∼ 0.4 ns long pulse. The chirp is due to an increase of the refractive index resulting from the reduction in the carrier concentration during the pulse. Both plasma and band to band interactions affect the index change with the latter mechanism giving the dominant contribution. A comparison of the wavelength shift obtained during the pulse with the current dependent shift of the longitudinal modes at currents well below threshold confirms that the change in carrier concentration is responsible for the chirp.

Segmented chirp waveform implemented radar system

Abstract: In a radar system utilizing same, a segmented chirp waveform is built up by frequency hopping trains of simple chirp pulses. Each chirp pulse in a train is identical and is transmitted on one of a set of discrete carrier frequencies. The carrier frequencies are uniformly spaced in a predetermined bandwidth and are used in linear sequence. After transmitting on the last carrier frequency, the entire pattern is repeated, starting again at the first carrier frequency. The returns from the individual pulses are digitized and stored and the history thereof is then assembled by a digital signal processor into a high resolution image.

Surface Acoustic Wave Slanted Device Technology

Abstract: 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.

Acoustooptic spectrum analysis: a high performance hybrid technique

Abstract: A hybrid technique for wide-bandwidth high-resolution acoustooptic spectrum analysis is described that combines features of 2-D space-integrating and time-integrating techniques. Performance features include extended small-signal detectability, improved optical efficiency, and insensitivity to high frequency laser noise. An optically transformed periodic chirp provides a distributed local oscillator that permits wide system bandwidth.

Mode-locking and chirping system for lasers

Abstract: A single electro-optic device is provided for simultaneously mode-locking and chirping the output of a laser by simultaneously applying to the electrodes of the electro-optic device a periodic signal superimposed on a voltage ramp. The electro-optic device in general utilizes a crystal of the type which changes refractive index in accordance with an applied voltage. As a result, FM mode-locking is achieved through the use of the periodic signal, whereas mode lines are displaced or shifted in frequency during the generation of the laser output by virtue of the changing bias supplied by the voltage ramp.

Side looking sonar beam forming utilizing the chirp Z-transform

Abstract: Apparatus which generates a plurality of sets of radially extending beams in a chirp Z-transform sonar beam former. Only a particular beam from each set is chosen for display.

Solitons created by chirped initial profiles in coherent pulse propagation

Abstract: If an incident pulse is chirped, the critical parameters for self-induced transparency to occur in coherent pulse propagation can no longer be obtained from the well-known McCall-Hahn area theorem. We have been able to obtain these parameters by solving the Zakharov-Shabat eigenvalue equation for the bound-state eigenvalues. We find that critical (threshold) areas will be increased for a chirped incident pulse in almost all cases, except for a box profile or for a pulse that is approximately box-like in shape. In these latter cases, the chirped critical areas will instead decrease for the second and all higher branches. The first branch’s critical area is always increased due to chirping.

Method for shaping and aiming narrow beams

Abstract: A method and apparatus is disclosed for use of a linear frequency chirp in a transmitter/receiver (14/16) having a correlator to synthesize a narrow beamwidth pattern from otherwise broadbeam transducers when there is relative velocity between the transmitter/receiver (14/16) and the target. The chirp is so produced in a generator (20) in bandwidth, B, and time, T, as to produce a time-bandwidth product, TB, that is increased for a narrower angle. A replica of the chirp produced in a generator (26) is time delayed and Doppler shifted for use as a reference in receiver (16) for correlation of received chirps from targets. This reference is Doppler shifted to select targets preferentially, thereby to not only synthesize a narrow beam but also aim the beam in azimuth and elevation.

On the use of pseudorandom codes for "Chirp" radar

Abstract: The effect of transmit/receive (T/R) switching on the amibiguity function of a radar signal whose complex modulation is long compared to the minimum target delay of interest is investigated theoretically, and the theory is then applied to the specific case on an ionospheric "chirp" sounder. Various pseudorandom T/R codes are compared for their suitability for this particular radar application, and one in particular is shown to have some advantageous properties.

Circuit for the adaptive suppression of narrow band interference

Abstract: Adaptive suppression of narrow band interference is realized by a filter that automatically makes estimates of interfering signals in the frequency domain and separates the interference from the desired signal. Received analog signals are Fourier transformed in accordance with a CHIRP Z algorithm, squared, and filtered by an N point serial structural CCD to provide a smoothed power spectral density signal. The smoothed power spectral density signal is utilized to cancel interfering signals by any one of three mechanizations. One mechanization comprehends a threshold circuit that generates binary signals in response to the CCD output. The binary signals control a gate that gates strong frequency components (the estimates of the interfering frequency coefficient) from the Fourier transformer through to an inverse Fourier transformer. The inverse Fourier transformed strong frequency components are then subtracted from the delayed received analog signal. A second mechanization transmits the full Fourier transformed spectrum to the inverse Fourier transformer and utilizes the gate to notch out the strong frequency components in response to the CCD output. The third mechanization weights the Fourier transformed frequency coefficients with the smoothed power spectral density signal, inverse transforms the weighted spectrum and subtracts it from the delayed analog signal.

A Satellite-Borne SAW Chirp-Transform System for Uplink Demodulation of FSK Communication Signals

Abstract: A SAW chirp-transform system employing reflective-array compressors (RACs) is being developed as an efficient low-power means for demodulation of frequency-shift- keyed (FSK) communication signals. The use of RAC devices allows the simultaneous demodulation of high-data-rate communications from many users. users each employing a 4-ary code (400 tones total) with a tone s eparation of 38 kHz (15.2-MHz overall bandwidth) and a tone or chip duration of 50 vsec. A convol ve-mu1 tiply-convolve chirp-transform configuration was chosen because weighting can be easily incorporated in the final RAC and because the excellent band-pass-filter ing characteristics of the initial RAC allow a system with only four RAC devices to operate at 100% duty factor with a minimum of out-of-band interference.

Wide-band guided wave acoustooptic Bragg deflector using a tilted-finger chirp transducer

Abstract: A tilted-finger chirp transducer which had evolved from multiple tilted-tranducers was used to realize wide-band acoustooptic Bragg deflection in a Y -cut LiNbO 3 waveguide. A deflector bandwidth of 50 percent centered at 500 MHz and a diffraction efficiency of 16 percent at an RF drive power of 200 mw have been measured. Some comments on the relative merits of a tilted-finger chirp transducer versus multiple transducers for wide-band acoustooptic Bragg deflection are made.

Beamforming utilizing a surface acoustic wave device

Abstract: A beamforming apparatus is provided for processing the outputs of a linearrray of spaced apart receiving elements. The beamforming apparatus includes a surface acoustic wave device which has a pair of transducers mounted on a substrate in a spaced apart relationship. Each transducer is capable of receiving and converting an electrical chirp signal into an acoustic signal for propagation across the surface of the surface acoustical wave device. A plurality of taps are mounted on the substrate in a spaced apart relationship between the pair of transducers for receiving, sharing and converting the acoustic signals back into electric signals. Each tap is adapted to receive a bias voltage. A device is provided for mixing the signal from each tap with a signal from a respective receiving element so as to produce a plurality of mixed output signals, and another device is provided for summing the mixed output signals so as to provide a summed output signal. The summed output signal may then be processed by an upper sideband filter for controlling an indicating device. With this arrangement the beamforming is independent of the center frequency of the array from about 5 KHZ up to the millimeter frequency range.

Received signal encoding and correlating system

Abstract: An ultrasonic phased array imaging system having a received signal encoding and correlating system. Pulse echoes picked up by each of the plurality of transducers are passed by a timed gate signal only during a predetermined time interval when a return signal from a focal point is expected to arrive. The return signal is also encoded by a chirp waveform. All gated chirp signals are fed to a dispersive transversal filter where their sum occurs simultaneously.

Sonar beam forming utilizing the chirp Z-transform

Abstract: The chirp rate in a chirp Z-transform sonar beam former is varied as a function of range to form beams in the near field. The chirp rate may be varied with each range cell under examination or with each group of range cells.

Apparatus and method for locking a PLL onto a selected offset frequency sideband

Abstract: The output of a VCO, a referenced frequency signal and an offset frequency signal are mixed to provide a control signal for the VCO and a double offset frequency signal which is mixed with an output of the offset frequency source to provide a DC component having a positive polarity if the signals are inphase and the VCO is locked on one sideband and a negative polarity if the signals are out of phase and the VCO is locked on the other sideband. A sweep signal is activated and applied to the VCO in response to the VCO being locked onto the wrong sideband.

Surface acoustic wave time chirp devices

Abstract: Surface acoustic wave dispersive delay lines provide a chirp signal generator and filter capable of producing signals of which the frequency-time slope can be varied. The chirp signal generator includes two surface acoustic wave delay lines, means for impulsing the delay lines with a variable relative time delay, and a mixer for combining the outputs of the two delay lines. The variable dispersion filter includes two delay lines, means for impulsing the delay lines with a variable relative time delay, a first mixer for combining an input signal with the output of one delay line and a second mixer for combining the output of the first mixer with the output of the other delay line. Variation in the time delay between the impulsing of the two delay lines produces a variation in the chirp rate at the output signal. The amplitude frequency characteristics of the signal generator and filter may be made non-linear by amplitude weighting one delay line.

Broadband Chirp Transducers for Integrated Optics Spectrum Analyzers

Abstract: A broadband integrated optic spectrum analyzer IOSA requires a SAW transducer with a large bandwidth and low insertion loss. Several approaches have been investigated for this application including composite transducers made up of several transducers with staggered synchronous frequencies, phased array transducers, as well as chirp type transducers. A novel modification of the chirp transducer was employed in this study. In this design the electrode spacings and the electrode tilt angles are varied smoothly over a range of values that is synchronous with the range of frequencies in the desired response. By varying the tilt angle the Bragg condition can be met at all frequencies. As a result the Bmgg acousto-optic bandwidth is independent of the acoustic aperture. There are several additional advantages which result from using a chirp type transducer. The total number of electrodes can be selected primarily to satisfy impedance matching conditions to achieve low insertion loss instead of being determined by the required bandwidth, and using larger numbers of electrodes reduces electrode resistance effects. Also the chirp transducer can handle larger peak power levels which is particularly important for the IOSA.

Acousto-Optic Devices Applied To Image Processing

Abstract: Two recently reported optical processing concepts can be exploited for realtime linear shift-invariant processing of 2-D imagery with acoustooptic devices: (1) space coordinate-to-temporal frequency conversion, and (2) time-integration spectral analysis. A pair of crossed acoustooptic cells, driven by periodic chirp wave-forms, can be used for both operations. State-of-the-art acoustooptic devices appear suitable for gigahertz rate processing of images with spacebandwidth products approaching 106.

Sidelobe rejection filter

Abstract: Disclosed is a Sidelobe Rejection Filter for reducing the time sidelobes seen in the auto-correlation output signals from a matched filter. Such matched filters are used with radars utilizing pulse compression techniques, for example. The sidelobe rejection filter may be utilized whenever the time response of the auto-correlation signals includes a plurality of sidelobes each having a period τ and having essentially the same amplitude. Accordingly, the disclosed sidelobe rejection filter is particularly useful for pulse compression radars employing linear FM (i.e., Chirp) or Barker phase coded waveforms. The matched filter includes a delay circuit coupled to receive the time response of the auto-correlation signal, which delay circuit inserts a delay of τ, and a subtraction circuit for finding the difference between the delayed and undelayed time FM pulse compression techniques, the output of the subtraction circuit need merely be rectified to obtain an output signal whose sidelobes are substantially reduced in amplitude. In the case of phase coded pulse compression techniques using Barker codes, on the other hand, the output of the subtraction circuit is supplied to both positive and negative rectification circuits, one of whose outputs is then delayed by Nτ, where N is the number of bits in the Barker code. The output of the Nτ delay circuit is well as the output of the other rectification circuit is then applied to an adder for further reducing time sidelobes. The output of the adder is applied to yet another rectification circuit for providing an auto-correlation response which is substantially free of time sidelobes.

Real‐time Fourier transformation via acousto‐optics

Abstract: An implementation of the chirp transform algorithm for performing a real‐time Fourier transform is described. The implementation is based upon an acousto‐optic convolver with a large time‐bandwidth product An instantaneous bandwidth of about 75 MHz was achieved for the Fourier transformer with a dynamic range in excess of 60 dB for a cw time‐gated waveform. By using an almost‐uniform light‐beam intensity across the device, the measured sidelobe amplitudes were within 0.5 dB of the theoretical values. The corresponding measured phase errors were less than 5°. The adaptability of this acousto‐optic implementation is demonstrated by the ease with which one can vary both the sidelobe weighting function and the time rate of the transform.

Coherent Optical Hybrid Techniques For Spectrum Analysis

Abstract: A hybrid optical approach to coherent spectrum analysis realizes gains associated with time-integrating techniques while still retaining some of the advantages of space-integrating techniques. Measurement of large time-bandwidth spectra is performed with high sensitivity, efficiency, and range of detectable signal power levels, particularly in large bandwidth applications, where an optically transformed periodic chirp forms a distributed local oscillator as a reference for time integration.

A monolithic 512 point chirp Z transform processor

Abstract: A monolithic analog 512 point chirp Z transform processor which calculates the discrete time Fourier transform will be described. A 6.1 × 5.5mm N-channel MOS chip includes premultiply, convolution and postmultiplication functions. Dynamic range of 63dB with operation from 1kHz to 1.5MHz has been measured.

Temperature detecting unit

Abstract: PURPOSE: To make it possible that a temperature detecting part is arranged in an arbitrary position by the wireless system and the temperature detecting part has no electric power source, by utilizing change of the resonance frequency for temperature change to detect temperatures. CONSTITUTION: A temperature detecting unit is constituted by main body 1 having transmission part 11, receiving part 12, and so on and temperature detecting part 2 having resonator 21 which changes the resonance frequency for temperature change and so on, and the sweep signal generated in transmission part 11 is first modulated, and interrogation signal A is transmitted to temperature detecting part 2 through antenna 13. This signal is led to detecting part 23 through antenna 24, and interrogation signal A is modulated to take out sweep signal components. These sweep signal components are applied to resonator 21 to generate a resonance signal. This resonance signal is modulated by detecting part 23 and is transmitted as response signal B to main body 1 and is input to receiving part 12 to take out the resonance signal, and after that, this signal is operated as a temperature by the signal processing. COPYRIGHT: (C)1980,JPO&Japio