Antenna having elements with programmable digitally generated time delays

• US 5,130,717 A
• Filed: 04/29/1991
• Issued: 07/14/1992
• Est. Priority Date: 04/29/1991
• Status: Expired due to Term

• Current Assignee: Loral Defense Systems (Martin Marietta Corporation)
• Original Assignee: Loral Defense Systems (Martin Marietta Corporation)
• Inventors: Ewen, Kenneth, Barrett, Fredrick W.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US07/692,681
• Time in Patent Office: 442 Days
• Field of Search: 342/375
• US Class Current: 342/375
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H01Q 3/2682 Time delay steered arrays

Abstract

An array antenna (12) in which dependent programmable and digitally generated time delays are imposed on signals passing through each antenna element (14) is disclosed. A beam steering computer (32) determines data values corresponding to delays needed at each element to form a desired beam angle. These data values are written into digital element signal processors (DESPs) (40) which are associated with each element in one-to-one correspondence. Each DESP (40) includes a waveform generator (30), which produces digitized samples synchronously with a reference clock signal. A stream of the digitized samples passes through and is delayed in a highly precise delay generator (54) before being converted to analog in a D/A converter (60). The analog signal is modulated (62), amplified (66), and then radiated at the associated element (14). Received signals are amplified (70), demodulated (72), converted to digital in an A/D converter (74), and then passed through the same delay generator (54). They are then re-converted to analog (60), modulated (62) back to RF, and combined (50) with other delayed RF signals. The delay generator (50) includes a register file (106) which receives a digitized waveform. A latch (86) receives delay data. The delay data programs a counter (80, 82) to delay the waveform for a variable, integral number of reference clock cycles. The delay data further programs a delay line (88) to impose a further fractional portion of a reference cycle delay on the waveform.

Claims

1. In an antenna array having a plurality of antenna elements, an elemental signal processor for association with one of said antenna elements and for inserting a programmable delay into an information signal passed through said one element, said element signal processor comprising:

means for providing a digitized waveform corresponding to said information signal, said digitized waveform comprising a sequence of samples exhibiting a predetermined period between adjacent ones of said samples;

means for supplying first and second delay values wherein said first and second delay values together specify a total relative delay to apply to said information signal in said one element;

first means, coupled to said providing means and to said supplying means, for delaying said digitized waveform by a first duration which is responsive to said first delay value, said first duration being substantially an integral number of said predetermined periods; and

second means, coupled to said supplying means, for delaying said digitized waveform by a second duration which is responsive to said second delay value, said second duration being less than said predetermined period.

2. An elemental signal processor as claimed in claim 1 wherein said second delaying means has a minimum delay value which is greater than zero, and said elemental signal processor comprises a third delaying means, coupled between said first and second delaying means, for delaying said digitized waveform by substantially said minimum delay value so that activation of said first delaying means is delayed to compensate for said minimum delay value of said second delaying means.

3. An elemental signal processor as claimed in claim 1 wherein said second delaying means comprises a delay line having a control input for specifying a discrete number of predetermined finite delays to impose on a signal passing therethrough, said predetermined finite delays being substantially more brief than said predetermined periods.

4. An elemental signal processor as claimed in claim 1 wherein said first delaying means comprises a register file having a predetermined number of registers coupled in series between a register file input and a register file output, said registers being clocked synchronously by a clock signal exhibiting said predetermined period.

5. An elemental signal processor as claimed in claim 4 wherein said first delaying means additionally comprises counter means coupled to said register file and responsive to a clock signal exhibiting said predetermined period, said counter means being configured to disable clocking of said register file for a variable period of time.

6. An elemental signal processor as claimed in claim 5 wherein said first delaying means is configured to operate in a first mode, in which said counter counts to a terminal count value and said register file is prevented from being clocked, and a second mode which occurs after said counter has reached its terminal count and in which said register file is clocked.

7. An elemental signal processor as claimed in claim 1 wherein said elemental signal processor additionally comprises means for supplying a reference clock exhibiting said predetermined period, and said second delaying means comprises:

means for imposing said second duration delay on said reference clock to generate a delayed reference clock; and

a register having a data input coupled to said first delaying means and a clock input adapted to receive said delayed reference clock from said imposing means, so that said register outputs said digitized waveform samples therefrom synchronously with said delayed reference clock.

8. An elemental signal processor as claimed in claim 1 additionally comprising:

a digital-to-analog converter having an input coupled to at least one of said first and second delaying means and having an output;

a modulator having an input coupled to said digital-to-analog output and having an output; and

a power amplifier having an input coupled to said modulator output and having an output adapted to provide an RF signal to said one element.

9. An elemental signal processor as claimed in claim 8 additionally comprising:

an RF amplifier having an input adapted to receive an RF signal from said one element and having an output;

a demodulator having an input coupled to said RF amplifier output and having an output;

an analog-to-digital converter having an input coupled to said demodulator output and having an output; and

switching means having input terminals coupled to said digitized waveform providing means and to said analog-to-digital converter output and having an output terminal coupled to at least one of said first and second delaying means.

10. An elemental signal processor as claimed in claim 1 wherein said digitized waveform providing means comprises an analog-to-digital converter, and said element signal processor additionally comprises:

an RF amplifier having an input adapted to receive an RF signal from said one element and having an output; and

a demodulator having an input coupled to said RF amplifier output and having an output coupled to said analog-to-digital converter.

11. An electronically steerable antenna array for passing wideband RF signals without squinting an antenna beam, said array comprising:

array computing means for specifying a beam angle;

array oscillator means for providing timing signals;

array transmission signal identifying means;

a multiplicity of substantially identical digital elemental signal processors (DESPs), wherein each of said DESPs comprises;

means for providing a digitized waveform in response to said transmission signal identifying means, said digitized waveform comprising a sequence of samples exhibiting a predetermined period between adjacent ones of said samples, said predetermined period being responsive to said oscillator means,

means for supplying first and second delay values wherein the combination of said first and second delay values specifies a delay to apply to said digitized waveform, and said first and second delay values are responsive to said computing means,

first means, coupled to said providing means and to said supplying means, for delaying said digitized waveform by a first duration, said first duration being substantially an integral number of said predetermined periods,

second means, coupled to said supplying means, for delaying said digitized waveform by a second duration, said second duration being less than said predetermined period; and

a multiplicity of radiating elements, wherein each of said radiating elements couples to a corresponding one of said second delaying means.

12. An electronically steerable antenna array as claimed in claim 11, wherein each of said DESPs additionally comprises:

a digital-to-analog converter having an input coupled to at least one of said first and second delaying means and having an output;

a modulator having an input coupled to said digital-to-analog output and having an output; and

a power amplifier having an input coupled to said modulator output and having an output adapted to provide an RF signal to said corresponding one of said multiplicity of radiating elements.

13. An electronically steerable antenna array as claimed in claim 12, wherein:

each of said DESPs additionally comprises;

an RF amplifier having an input adapted to receive an RF signal from said one element and having an output,

a demodulator having an input coupled to said RF amplifier output and having an output,

an analog-to-digital converter having an input coupled to said demodulator output and having an output, and

switching means having input terminals coupled to said waveform generator and to said analog-to-digital converter output and having an output terminal coupled to at least one of said first and second delaying means; and

said antenna array additionally comprises an array combining means, coupled to said modulator outputs of each of said DESPs, for combining information signals received at each of said multiplicity of radiating elements into a single signal received by said antenna.

14. An electronically steerable antenna array as claimed in claim 11 wherein said first delaying means comprises a register file having a predetermined number of registers coupled in series between a register file input and a register file output and clocked substantially in synchronism by a clock signal exhibiting said predetermined period.

15. An electronically steerable antenna array as claimed in claim 14 wherein:

said first delaying means of each DESP additionally comprises counter means coupled to said register file and responsive to a clock signal exhibiting said predetermined period, said counter means being configured to disable clocking of said register file for a variable period of time; and

said first delaying means of each DESP is configured to operate in a first mode, in which said counter counts to a terminal count value and said register file is prevented from being clocked, and a second mode which occurs after said counter has reached its terminal count and in which said register file is clocked.

16. An electronically steerable antenna array as claimed in claim 11 wherein each DESP additionally comprises means for receiving a reference clock exhibiting said predetermined period from said oscillator means, and said second delaying means of each DESP comprises:

means for imposing said second duration delay on said reference clock to generate a delayed reference clock; and

a register having a data input coupled to said first delaying means and a clock input adapted to receive said delayed reference clock from said imposing means, so that said register outputs said digitized waveform samples therefrom synchronously with said delayed reference clock.

17. A method for inserting a digitally programmable time delay into an information signal passed through one of a multiplicity of antenna elements in an antenna array to form a squintless electronically steerable antenna array, said method comprising the steps of:

providing a digitized waveform corresponding to said information signal, said digitized waveform comprising a sequence of samples exhibiting a predetermined period between adjacent ones of said samples;

receiving first and second delay values, wherein said first and second delay values together specify a delay to apply to said information signal in said one element;

delaying said digitized waveform by a first duration which is substantially an integral number of said predetermined periods, said first duration being responsive to said first delay value; and

delaying said digitized waveform by a second duration which is less than said predetermine period, said second duration being responsive to said second delay value.

18. A method as claimed in claim 17 wherein, when said second delay value specifies a delay substantially equal to zero, said second duration delaying causes a minimum delay which is greater than zero, and said method additionally comprises the step of delaying said digitized waveform by substantially said minimum delay so that performance of said first duration delaying step is delayed to compensate for said minimum delay associated with said second duration delaying step.

19. A method as claimed in claim 17 additionally comprising the steps of:

converting said digitized waveform, after said delaying steps, into an analog waveform;

modulating said analog waveform into an RF waveform; and

amplifying said RF waveform to provide an amplified RF signal, said amplified RF signal being routed to said one antenna element.

20. A method as claimed in claim 19 additionally comprising the steps of:

receiving an RF signal at said antenna element;

amplifying said received RF signal to provide a received, amplified RF signal;

demodulating said received, amplified RF signal to provide an analog signal;

converting said analog signal into a second digitized waveform; and

selecting one of said digitized waveform and said second digitized waveform for delay in said delaying steps.