Antenna system and method for operating same

• US 6,466,167 B1
• Filed: 07/30/2001
• Issued: 10/15/2002
• Est. Priority Date: 07/30/2001
• 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: Steinbrecher, Donald H.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US09/917,586
• Time in Patent Office: 442 Days
• Field of Search: 342/378, 342/372
• US Class Current: 342/378
• 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

Abstract

An antenna apparatus (and corresponding innate method) comprises an array of antenna elements each having a phase center. An “observable signal” that contains a low-frequency component and a high-frequency component is generated. The high-frequency component is summed with the signal received by each antenna element near its phase center, forming a plurality of sum signals. These are fed into a signal processing arrangement that processes these signals with the low frequency component of the observable signal, including analog to digital conversion to (i) remove the high frequency component of the observable signal, (ii) normalize the effects of the signal transfer characteristics on the digital sum signals, (iii) synchronously re-sample the digital sum signals, and (iv) differentially time-reference each digital sum signal to the phase center of the corresponding antenna element. The thusly, processed digital signals are combined into a single composite signal.

Claims

1. A method for processing electromagnetic signals impinging on a given area comprising the steps of:

providing an antenna system comprising an array of antenna elements spatially distributed over said given area for providing received signals, each antenna element having a phase center;

generating an observable signal that contains a low-frequency component and a high-frequency component;

summing the high-frequency component with the signal received by each antenna element near the phase center of each antenna element to form a plurality of sum signals;

feeding each sum signal into an analog signal path that modifies the sum signal;

converting each modified sum signal into a digital sum signal;

processing the digital sum signals with the low frequency component of the observable signal to (i) remove the high frequency component of the observable signal from each digital sum signal, (ii) normalize the effects of the signal transfer characteristics of the analog signal paths on each digital sum signal, (iii) synchronously re-sample all digital sum signals, and (iv) differentially time-reference each digital sum signal to the phase center of the corresponding elements so as to provide a plurality of processed digital signals wherein each processed digital signal is a low-frequency replica of the signal received by the corresponding antenna element; and

combining the processed digital signals into a single composite signal;

to thereby enhance the spurious-free dynamic range of the array.

2. The method according to claim 1 wherein the generating step comprises the step of performing an aliasing function on the observable signal to produce the low and high frequency components.

3. The method according to claim 1 wherein the processing step further comprises the step of determining the differential time of arrival of each received signal at the phase center of the corresponding antenna element.

4. The method according to claim 1 wherein in the processing step, each digital sum signal is normalized to the relative amplitude and relative phase of the corresponding received signal when such received signal was at the phase center of the corresponding antenna element.

5. The method according to claim 4 wherein the normalizing step further includes the step of delaying each digital sum signal by a uniform time delay.

6. The method according to claim 1 wherein the combining step comprises the step of forming a beam emphasizing the direction of arrival of one of the signals incident on one of the antenna elements so that the composite signal represents the total signal received from the emphasized direction of arrival.

7. An antenna system for capturing electromagnetic radiation impinging upon a given area, comprising:

an array of antenna elements for receiving signals, each antenna element having a capture area such that the sum of the capture areas of the elements is generally equal to said given area, each antenna element having a phase center;

a circuit for generating an observable signal that contains a low-frequency component and a high-frequency component;

a plurality of signal processing channels, each channel comprising an input for receiving a signal received from a corresponding antenna element, a summing circuit located at each element near the phase center of the corresponding antenna element for summing the high-frequency component of the observable signal with the received signal to form a sum signal, an analog signal path for modifying the sum signal, an analog-to-digital converter for converting each modified sum signal into a digital sum signal, and a digital signal processor having inputs for receiving the digital sum signal and the low-frequency component, the digital signal processor configured to (i) remove the high frequency component from the digital sum signal, (ii) normalize the effects of the signal transfer characteristics of the analog signal paths on the digital sum signal, (iii) re-sample the digital sum signal synchronously with the digital signal processors of the other signal processing channels, and (iv) differentially time-reference each re-sampled digital sum signal to the phase center of the corresponding antenna elements so as to provide a processed digital sum signal that is a low-frequency replica of the signal received by the corresponding antenna element;

a control circuit for effecting synchronous operation of the digital signal processors of the signal processing channels; and

a system digital signal processor for combining the processed digital sum signal outputted by each signal processing channel into a single composite signal.

8. The antenna system according to claim 7 wherein the control circuit is in electronic data communication with the analog-to-digital converter and digital signal processor of each signal processing channel so as to synchronize the functions of the analog-to-digital converters and digital signal processors.

9. The antenna system according to claim 8 wherein the control circuit comprises a computer.

10. The antenna system according to claim 7 wherein the circuit for generating the observable signal comprises a frequency synthesizer.

11. The antenna system according to claim 7 wherein the circuit for generating the observable signal generator is configured to implement an aliasing function on the observable signal so as to produce the low and high frequency components.

12. The antenna system according to claim 7 wherein the digital signal processor of each channel includes means for determining the differential time of arrival of the signals at the phase centers of each antenna element.

13. The antenna system according to claim 7 wherein the digital signal processor of each signal processing channel includes means for delaying each digital sum signal by a uniform time delay.

14. The antenna system according to claim 7 wherein the system digital signal processor is configured to form a beam emphasizing the direction of arrival of a particular one of the signals incident on one of the antenna elements so that the composite signal represents the total signal arriving from the emphasized direction of arrival.

15. An article of manufacture comprising a computer processor usable medium having computer processor readable program code embodied therein for processing signals received from an antenna system that comprises an array of antenna elements for receiving signals wherein each antenna has a phase center, a circuit for generating an observable signal that contains a low-frequency component and a high-frequency component, a plurality of signal processing channels wherein each channel comprises an input for receiving a signal received from a corresponding antenna, a summing circuit located element near the phase center of the corresponding antenna, an analog signal path for modifying the sum signal, an analog-to-digital converter, a digital signal processor having inputs for receiving the digital sum signal and the low-frequency component, the antenna system further comprising a control circuit for synchronously controlling the digital signal processor of each signal processing channel, and a system digital signal processor having a plurality of inputs wherein each input is connected to the output of a corresponding signal processing channel, the computer processor readable program code in the article of manufacture comprising:

computer processor readable program code configured to cause the antenna system to enable the circuit to generate the observable signal;

computer processor readable program code configured to cause the antenna system to enable each summing circuit to sum the high-frequency component of the observable signal with a received signal to form a sum signal;

computer processor readable program code configured to cause the antenna system to enable the analog signal path of each channel to modify the sum signal to produce a modified sum signal;

computer processor readable program code configured to cause the antenna system to enable the analog-to-digital-converter to convert each modified sum signal into a digital sum signal;

computer processor readable program code configured to cause the antenna system to enable the digital signal processor of each channel to (i) remove the high frequency component from the digital sum signal, (ii) normalize the effects of the signal transfer characteristics of the analog signal path on the digital sum signal, (iii) re-sample the digital sum signal synchronously with the digital signal processors of the other signal processing channels, and (iv) differentially time-reference each re-sampled digital sum signal to the phase center of the corresponding antenna elements so as to provide a processed digital sum signal that is a low-frequency replica of the signal received by the corresponding antenna element; and

computer processor readable program code configured to cause the antenna system to enable the system digital signal processor to combine all of the processed digital signals into a composite signal.