US5374903A
Expired / Lapsed
US
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Generation of wideband linear frequency modulation signals
Assignee: Raytheon Co
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Filing: 1988-04-22
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Granted: 1994-12-20
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Expires: 2008-04-22
Abstract
Abstract A low-frequency low bandwidth Linear Frequency Modulation (LFM) waveform, nominally a 1 MHz to 10 Mz swept frequency analog sinusoid or digital square wave, is produced by direct digital synthesis. This waveform is upconverted in frequency and expanded in bandwidth, nominally to microwave frequencies with bandwidths of nominally 160-360 MHz, in a multiplying offset phase locked loop. The phase locked loop also linearly frequency modulates a X-band carrier with the microwave frequency LFM waveform to produce an output signal suitable for Synthetic Aperture Radar. The phase locked loop induces low phase error, and may be closed around the radar transmitter to remove phase errors induced by that unit.
Inventors
- 👤 James L. Blanton
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 10:29
CPC Classifications
H; H03; H03C; H03C3/00; H03C3/02; H03C3/09; H03C3/0908; H03C3/0983; G; G01; G01S; G01S13/00; G01S13/02; G01S13/06; G01S13/08; G01S13/32; G01S13/34; G01S7/00; G01S7/02; G01S7/28; G01S7/282; H03C3/0966; H03L; H03L7/00; H03L7/06; H03L7/16; G01S13/88; G01S13/89; G01S13/90; H03B; H03B2200/00; H03B2200/006; H03B2200/0092
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
72 words
An apparatus for generating a wideband Linearly Frequency Modulated, LFM, carrier signal comprising: a generator of a low frequency, low bandwidth, baseband LFM signal; a variably offset phase locked loop (i) receiving the baseband LFM signal and also a fixed frequency reference signal in the band of a carrier signal, (ii) upconverting in frequency and expanding in bandwidth the received baseband LFM signal, to (iii) produce a wideband high frequency LFM signal.
Claim 2
Independent Claim
72 words
An apparatus for generating a wideband Linearly Frequency Modulated, LFM, carrier signal comprising: a generator of a low frequency, low bandwidth, baseband LFM signal; a variably offset phase locked loop (i) receiving the baseband LFM signal and also a fixed frequency reference signal in the band of a carrier signal, (ii) upconverting in frequency and expanding in bandwidth the received baseband LFM signal, to (iii) produce a wideband high frequency LFM signal.
Claim 3
Dependent Claim
124 words
The apparatus according to claim 1 wherein the variably offset phase locked loop comprises: a Voltage Controlled Oscillator, VCO, controllable to modulate the carrier signal in accordance with a modulation control signal; a mixer for mixing a portion of the modulated carrier wave output signal received from the VCO with the fixed frequency reference signal to produce a difference signal; a frequency divider circuit for receiving the difference signal from the mixer and reducing it in frequency to the low frequency range of the baseband LFM signal; and a phase detector for producing the modulation control signal responsive to a detected phase difference between the reduced frequency difference signal received from the frequency divider circuit and the received low frequency, low bandwidth, LFM signal.
Claim 4
Dependent Claim
57 words
The apparatus according to claim 2 further comprising: a transmit/receive switch disposed within the phase locked loop, said switch having a first position for communicating to the mixer a portion of a signal output from the VCO and a second position for communicating to the mixer a portion of the modulated carrier wave output signal being transmitted.
Claim 5
Dependent Claim
51 words
The apparatus according to claim 2 wherein the variably offset phase locked loop further comprises: a low pass filter disposed between the frequency divider circuit and the phase detector for substantially filtering harmonics above and including the third harmonic from the reduced frequency difference signal produced by the frequency divider circuit.
Claim 6
Dependent Claim
31 words
The apparatus according to claim 2 wherein the variably offset phase locked loop further comprises: a loop filter disposed within the phase locked loop between the phase detector and the VCO.
Claim 7
Dependent Claim
22 words
The apparatus according to claim 2 wherein the phase detector is an analog circuit, and wherein the received LFM signal is sinusoidal.
Claim 8
Dependent Claim
27 words
The apparatus according to claim 2 wherein the frequency divider circuit and phase detector are digital circuits, and wherein the received LFM signal is a square wave.
Claim 9
Dependent Claim
14 words
The apparatus according to claim 1 wherein the generator comprises: a direct digital synthesizer.
Claim 10
Dependent Claim
67 words
The apparatus according to claim 8 wherein the direct digital synthesizer comprises: an oscillator for producing clock signals a digital quadratic phase generator for receiving the clock signals and producing a series of binary numbers representing a quadratic progression; a memory for storing a sine look-up table and addressed by the series of binary numbers to produce digitalized data representations of the points upon a sinusoidal waveform.
Claim 11
Dependent Claim
32 words
The apparatus according to claim 9 wherein the direct digital synthesizer further comprises: a digital-to-analog converter, DAC, for receiving the digitalized data representations and converting them to a swept frequency sinusoid approximation.
Claim 12
Dependent Claim
40 words
The apparatus according to claim 10 wherein the direct digital synthesizer further comprises: a low pass filter for receiving the swept frequency sinusoid approximation and filtering the frequency of the clock signals therefrom to produce a true swept frequency sinusoid.
Claim 13
Independent Claim
193 words
An apparatus receiving a Linear Frequency Modulated, LFM, signal and concurrently (i) upconverting in frequency the received LFM signal (ii) expanding the modulation bandwidth of the upconverted LFM signal to produce a wideband LFM carrier signal, the apparatus comprising: a Voltage Controlled Oscillator, VCO, controllable to produce a frequency modulated carrier wave output signal in accordance with a received modulation control signal; a reference signal source for producing a fixed frequency reference signal in the band of the carrier signal; a mixer for mixing a portion of the frequency modulated carrier wave output signal received from the VCO with the reference signal received from the reference signal source to produce a difference frequency signal; a frequency divider circuit for receiving the difference signal from the mixer and reducing it in frequency to a frequency range of the received baseband LFM signal; and a phase detector for producing the modulation control signal responsive to a detected phase difference between a reduced frequency difference signal received from the frequency divider circuit and the received baseband LFM signal; wherein the VCO, reference signal source, mixer, frequency divider, and phase detector operate as a phase locked loop.
Claim 14
Independent Claim
193 words
An apparatus receiving a Linear Frequency Modulated, LFM, signal and concurrently (i) upconverting in frequency the received LFM signal (ii) expanding the modulation bandwidth of the upconverted LFM signal to produce a wideband LFM carrier signal, the apparatus comprising: a Voltage Controlled Oscillator, VCO, controllable to produce a frequency modulated carrier wave output signal in accordance with a received modulation control signal; a reference signal source for producing a fixed frequency reference signal in the band of the carrier signal; a mixer for mixing a portion of the frequency modulated carrier wave output signal received from the VCO with the reference signal received from the reference signal source to produce a difference frequency signal; a frequency divider circuit for receiving the difference signal from the mixer and reducing it in frequency to a frequency range of the received baseband LFM signal; and a phase detector for producing the modulation control signal responsive to a detected phase difference between a reduced frequency difference signal received from the frequency divider circuit and the received baseband LFM signal; wherein the VCO, reference signal source, mixer, frequency divider, and phase detector operate as a phase locked loop.
Claim 15
Dependent Claim
42 words
The apparatus according to claim 12 further comprising: a low pass filter between the frequency divider circuit and the phase detector for substantially filtering harmonics above and including the third from the reduced frequency difference signal produced by the frequency divider circuit.
Claim 16
Dependent Claim
23 words
The apparatus according to claim 12 further comprising: a loop filter within the phase locked loop between the phase detector and the VCO.
Claim 17
Dependent Claim
22 words
The apparatus according to claim 12 wherein the phase detector is an analog circuit, and wherein the received LFM signal is sinusoidal.
Claim 18
Dependent Claim
27 words
The apparatus according to claim 12 wherein the frequency divider circuit and phase detector are digital circuits, and wherein the received LFM signal is a square wave.
Claim 19
Dependent Claim
102 words
A phase locked loop for a transmitter circuit CHARACTERIZED IN THAT the phase locked loop is variably offset in frequency for modulating a transmitted carrier signal to be Linearly Frequency Modulated (LFM) in response to a modulation control signal; and the modulation control signal is developed within the phase locked loop from (i) a fixed frequency reference signal in the band of the carrier signal, and from (ii) a received LFM signal that is both of lessor frequency and lessor modulation bandwidth than the control-LFM signal, to effect (1) a frequency upconversion and (2) a bandwidth expansion of the received LFM signal.
Claim 20
Dependent Claim
102 words
A phase locked loop for a transmitter circuit CHARACTERIZED IN THAT the phase locked loop is variably offset in frequency for modulating a transmitted carrier signal to be Linearly Frequency Modulated (LFM) in response to a modulation control signal; and the modulation control signal is developed within the phase locked loop from (i) a fixed frequency reference signal in the band of the carrier signal, and from (ii) a received LFM signal that is both of lessor frequency and lessor modulation bandwidth than the control-LFM signal, to effect (1) a frequency upconversion and (2) a bandwidth expansion of the received LFM signal.
Claim 21
Dependent Claim
62 words
The phase locked loop according to claim 17 FURTHER CHARACTERIZED IN THAT: a portion of the LFM carrier signal is mixed with the fixed frequency reference signal to form a difference signal; the difference signal is frequency divided; and the frequency divided difference signal is phase detected relative to the received LFM baseband signal in order to generate the modulation control signal.
References Cited (Backward Citations)
US4160958A
Cited
US4546328A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1997-12-19 | 1998-06-20 | 1998-12-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2001-12-19 | 2002-06-20 | 2002-12-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2005-12-19 | 2006-06-20 | 2006-12-20 | $7700.00 | Window Closed / Lapsed |