Digital monopulse

• US 5,315,304 A
• Filed: 07/02/1993
• Issued: 05/24/1994
• Est. Priority Date: 07/02/1993
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Stokes, Michael, Ghaleb, Sam
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/086,424
• Time in Patent Office: 326 Days
• Field of Search: 342/165, 342/173, 342/174, 342/151, 342/152
• US Class Current: 342/165
• CPC Class Codes: G01S 13/4418 with means for eliminating radar-dependent errors in angle measurements, e.g. multipath effects
• CPC Class Codes: G01S 7/4004 of parts of a radar system
• CPC Class Codes: G01S 7/4052 by simulation of echoes
• CPC Class Codes: G01S 7/4073 involving an IF signal injection

Abstract

A digitally formed monopulse radar employing dynamic real-time calibrationuring operation. The invention has a transmitter section, timing circuit, RF section, IF section, in-phase and quadrature section and a digital signal processor. A portion of the transmit signal is diverted from the transmitter section for preparation of calibration factors during the calibration period between receive signals. The calibration factors prepared by the digital signal processor are applied by the processor to antenna received signals during the receive mode and to produce the corrected sum and delta pitch, and delta yaw signals and the tracking errors ε_y and ε_p.

Claims

1. A digitally formed monopulse system having a transmission/calibration cycle and a receive cycle, said system comprising:

means for signal transmission to and return signal reception from an environment external to said system;

means for producing signals for external transmission and internal signal processing, said producing means connected to said means for signal transmission and reception, and to said means for internal signal processing;

means for diverting a portion of said signal produced for external transmission to said means for internal signal processing during said transmission/calibration cycle; and

means for internal signal processing comprising four signal processing channels for simultaneous processing of four-quadrant antenna transmit and receive signal information connected to said means for transmission and reception, said signal processing channels for calculating calibration factors reflecting system characteristics during the transmission/calibration cycle of said system, for calculating corrected signals received during the immediately following receive cycle, and for calculating the monopulse information derived therefrom and

wherein each of said channels provides in-phase and quadrature signals to a digital signal processor for production of calibration factors, where said in-phase and quadrature signals in one channel are used as the standard for correcting the other three channels to that standard in accordance with the following equations;

space="preserve" listing-type="equation">K(I2)=I(1)/I(2)

space="preserve" listing-type="equation">K(Q2)=Q(1)/Q(2)

space="preserve" listing-type="equation">K(I3)=I(1)/I(3)

space="preserve" listing-type="equation">K(Q3)=Q(1)/Q(3)

space="preserve" listing-type="equation">K(I4)=I(1)/I(4)

space="preserve" listing-type="equation">K(Q4)=Q(1)/Q(4)

where K(I2), K(Q2), K(I3), K(Q3), K(I4), K(Q4) are the calibration factors calculated as the ratio of the standard channel I(1) and Q(1) divided by each of the other channels I(2), Q(2), I(3), Q(3), I(4), and Q(4), and where during said receive cycle said means for digital signal processing uses the correction factors calculated during the calibration cycle to calculate the corrected signals received in accordance with the following equations;

space="preserve" listing-type="equation">I'"'"'(1)=I(1)

space="preserve" listing-type="equation">Q'"'"'(1)=Q(1)

space="preserve" listing-type="equation">I'"'"'(2)=I(2)×

K(I2)

space="preserve" listing-type="equation">Q'"'"'(2)=Q(2)×

K(Q2)

space="preserve" listing-type="equation">I'"'"'(3)=I(3)×

K(I3)

space="preserve" listing-type="equation">Q'"'"'(3)=Q(3)×

K(Q3)

space="preserve" listing-type="equation">I'"'"'(4)=I(4)×

K(I4)

space="preserve" listing-type="equation">Q'"'"'(4)=Q(4)×

K(Q4)

where the primes are the corrected values then used by said digital signal processing means to calculate the sum (Σ

)

space="preserve" listing-type="equation">Σ

=+ + + 4

where 1, 2, 3, and 4 are the complex I and Q values for each channel, and where said digital signal processing means calculates

the delta pitch (Δ

p)

space="preserve" listing-type="equation">Δ

p=(1+2)-(3+4) and

the delta yaw (Δ

y)

space="preserve" listing-type="equation">Δ

y=(1+3)-(2+4); and

the delta diagonal (Δ

d)

space="preserve" listing-type="equation">Δ

d=(1+4)-(2+3).

2. A digitally formed monpulse system having a calibration cycle and a receive cycle, and having four signal processing channels for simultaneous processing of four-quadrant antenna transmit and receive information, said system comprising:

means for producing a high power RF signal, an IF reference signal, a 90°

phase-shifted IF signal, and a local oscillator signal;

means connected to said producing means for transmitting a high power portion of said RF signal to said antenna and a low power portion of said RF signal as an output during said calibration cycle, and receiving an RF return signal from said antenna as an output during said receive cycle;

means connected to said transmitting and receiving means for amplifying and bandpass filtering the RF signal coupled from said transmitting and receiving means;

means for heterodyning the RF signal from said amplifying and filtering means with the local oscillator signal from said producing means and filtering the resultant IF signal to eliminate the sidebands;

means for creating four baseband digital in-phase signals and four baseband digital quadrature signals from said IF signal from said heterodyning and filtering means and the IF reference signal and the 90°

phase-shifted IF signal from said producing means, said creating means providing said digital in-phase and quadrature signals as an output;

means for digital signal processing, said means calculating and storing calibration factors for the system during said calibration cycle for use in correcting signals received from said antenna for phase mismatches, amplitude mismatches, and low noise amplifier drift within the system during said receive cycle, said calibration factors calculated using the digital in-phase signals from one of said channels as the standard and correcting the other three channels to that standard in accordance with the following equations;

space="preserve" listing-type="equation">K(I2)=I(1)/I(2)

space="preserve" listing-type="equation">K(Q2)=Q(1)/Q(2)

space="preserve" listing-type="equation">K(I3)=I(1)/I(3)

space="preserve" listing-type="equation">K(Q3)=Q(1)/Q(3)

space="preserve" listing-type="equation">K(I4)=I(1)/I(4)

space="preserve" listing-type="equation">K(Q4)=Q(1)/Q(4)

where K(I2), K(Q2), K(I3), K(Q3), K(I4), K(Q4) are the calibration factors calculated as the ratio of the standard channel I(1) and Q(1) divided by each of the other channels I(2), Q(2), I(3), Q(3), I(4), and Q(4), and where during said receive cycle said means for digital signal processing uses the correction factors calculated during the calibration cycle to calculate the corrected signals received in accordance with

space="preserve" listing-type="equation">I'"'"'(1)=I(1)

space="preserve" listing-type="equation">Q'"'"'(1)=Q(1)

space="preserve" listing-type="equation">I'"'"'(2)=I(2)×

K(I2)

space="preserve" listing-type="equation">Q'"'"'(2)=Q(2)×

K(Q2)

space="preserve" listing-type="equation">I'"'"'(3)=I(3)×

K(I3)

space="preserve" listing-type="equation">Q'"'"'(3)=Q(3)×

K(Q3)

space="preserve" listing-type="equation">I'"'"'(4)=I(4)×

K(I4)

space="preserve" listing-type="equation">Q'"'"'(4)=Q(4)×

K(Q4)

where the primes are the corrected values then used by said digital signal processing means to calculate the sum (Σ

)

space="preserve" listing-type="equation">Σ

=+ + + 4

where 1, 2, 3, and 4 are the complex I and Q values for each channel, and where said digital signal processing means calculates

the delta pitch (Δ

p)

space="preserve" listing-type="equation">Δ

p=(1+2)-(3+4) and

the delta yaw (Δ

y)

space="preserve" listing-type="equation">Δ

y=(1+3)-(2+4); and

the delta diagonal (Δ

d)

space="preserve" listing-type="equation">Δ

d=(1+4)-(2+3).

means for producing and providing timing signals to said transmitting and receiving means and to said digital signal processing means.

3. A digitally formed monpulse system having a calibration cycle and a receive cycle, and having four signal processing channels for simultaneous processing of four-quadrant antenna transmit and receive information, said system comprising:

means for producing a high power RF signal, an IF reference signal, a 90°

phase-shifted IF signal, and a local oscillator signal;

means connected to said producing means for transmitting a high power portion of said RF signal to said antenna and a low power portion of said RF signal as an output during said calibration cycle,

means connected to said transmitting and receiving means for amplifying and bandpass filtering the RF signal coupled from said transmitting and receiving means;

means for heterodyning the RF signal from said amplifying and filtering means with the local oscillator signal from said producing means and filtering the resultant IF signal to eliminate the sidebands;

means for creating four baseband digital in-phase signals and four baseband digital quadrature signals from said IF signal from said heterodyning and filtering means and the IF reference signal and the 90°

phase-shifted IF signal from said producing means, said creating means providing said digital in-phase and quadrature signals as an output;

means for digital signal processing, said means calculating and storing calibration factors for the system during said calibration cycle for use in correcting signals received from said antenna for phase mismatches and low noise amplifier drift within system during said calibration cycle for use in correcting signals received from said antenna for phase mismatches and low noise amplifier drift within the system during said receive cycle, said calibration factors calculated using the signals in the four channels

space="preserve" listing-type="equation">(1)=α

.sub.1 e.sup.jδ

.sbsp.1

space="preserve" listing-type="equation">(2)=α

.sub.2 e.sup.jδ

.sbsp.2

space="preserve" listing-type="equation">(3)=α

.sub.3 e.sup.jδ

.sbsp.3

space="preserve" listing-type="equation">(4)=α

.sub.4 e.sup.jδ

.sbsp.4

where α

_i and δ

_i for i=1 to 4 are amplitude and phase, respectively, of the calibration signal which contains the amplitude and phase mismatches and drift effects and are used to calculate the Sum (Σ

) and delta (Δ

) error values during the calibration cycle as;

space="preserve" listing-type="equation">Σ

.sub.e =(1)+(2)+(3)+(4)=α

.sub.1 e.sup.jδ

.sbsp.1 +α

.sub.2 e.sup.jδ

.sbsp.2 +α

.sub.3 e.sup.jδ

.sbsp.3 +α

.sub.4 e.sup.jδ

.sbsp.4

and

space="preserve" listing-type="equation">Magnitude of Σ

.sub.e =((I.sub.Σ

.sup.2)+(Q.sub.Σ

.sup.2)).sup.1/2

where I is the in-phase and Q is the quadrature component of the calibration signal

and ##EQU1## where

space="preserve" listing-type="equation">I.sub.Σ

=I.sub.1 +I.sub.2 +I.sub.3 +I.sub.4 and Q.sub.Σ

=Q.sub.1 +Q.sub.2 +Q.sub.3 +Q.sub.4

and

space="preserve" listing-type="equation">Δ

.sub.pe =((1)+(2))-((3)+(4))

and

space="preserve" listing-type="equation">Magnitude of Δ

.sub.pe =[{(I.sub.1 +I.sub.2)-(I.sub.3 +I.sub.4)}.sup.2 +{(Q.sub.1 +Q.sub.2)-(Q.sub.3 +Q.sub.4)}.sup.2 ].sup.1/2

and ##EQU2## and

space="preserve" listing-type="equation">Δ

.sub.ye =((1)+(3))-((2))+(4))

space="preserve" listing-type="equation">Magnitude of Δ

.sub.ye =[{(I.sub.1 +I.sub.3)-(I.sub.2 +I.sub.4)}.sup.2 +{(Q.sub.1 +Q.sub.3)-(Q.sub.2 +Q.sub.4)}.sup.2 ].sup.1/2

and ##EQU3##

space="preserve" listing-type="equation">Δ

.sub.de =((1)+(4))-((2))+(3))

space="preserve" listing-type="equation">Magnitude of Δ

.sub.de =[{(I.sub.1 +I.sub.4)-(I.sub.2 +I.sub.3)}.sup.2 +{(Q.sub.1 +Q.sub.4)-(Q.sub.2 +Q.sub.3)}.sup.2 ].sup.1/2

and ##EQU4## from which correction factors the tracking errors ε

_y and ε

_p are calculated during the receive cycle as the negative of the imaginary part of the quotient Delta divided by Sum ##EQU5## means for producing and providing timing signals to said transmitting and receiving means and to said digital signal processing means.

4. A digitally formed monopulse system having a transmission/calibration cycle and a receive cycle, said system comprising:

means for signal transmission to and return signal reception from an environment external to said system;

means for producing signals for external transmission and internal signal processing, said producing means connected to said means for signal transmission and reception, and to said means for internal signal processing;

means for diverting a portion of said signal produced for external transmission to said means for internal signal processing during said transmission/calibration cycle; and

means for internal signal processing connected to said means for transmission and reception, said means for internal signal processing comprising four signal processing channels for simultaneous processing of four-quadrant antenna transmit and receive signal information, for calculating calibration factors reflecting system characteristics during the transmission/calibration cycle of said system, for calculating corrected signals received during the immediately following receive cycle, and for calculating the monopulse information derived therefrom; and

wherein the tracking errors in said monopulse information are calculated by said digital signal processing means during the receive cycle as the Sum shifted by 90°

in phase and multiplying (dot product) by the Delta (where there is a 90°

phase shift between the Sum and Delta) and dividing the magnitude of the sum squared, such that ##EQU6##