BEAM STEERING SYSTEM FOR PHASED ARRAY ANTENNA

• US 3,611,401 A
• Filed: 09/24/1968
• Issued: 10/05/1971
• Est. Priority Date: 09/24/1968
• Status: Expired due to Term

• Current Assignee: Terrence E. Connolly
• Original Assignee: Terrence E. Connolly
• Inventors: Connolly, Terrence E.
• Primary Examiner(s): Lieberman, Eli
• Application Number:
  US04/762,030
• Time in Patent Office: 1,106 Days
• Field of Search: 343/778,853,854,1SA
• US Class Current: 342/377
• CPC Class Codes: H01Q 3/34 by electrical means active lenses or reflecting arrays H01Q3/46

Abstract

A beam-steering system for phased array antennas is disclosed, wherein the phases of the signals fed to the individual elements of the array are varied by phase shifters in selectable discrete steps to obtain directivity or steering of the array for transmitting and/or receiving. Special circuitry monitors the roundoff phasing errors of the phase shifters, and alters the settings of certain of the phase shifters at certain times in order to compensate for and eliminate the effects of the accumulated roundoff phasing errors. Thus, improvements in beamsteering accuracy and other characteristics are obtained, and/or the system is simplified and reduced in cost because fewer (and coarser) steps of selectable phase shifts can be employed.

Claims

1. A phased array antenna system having a plurality of radiation elements, a plurality of phase shifters respectively associated with said radiation element, antenna-steering means including a source of successive steering command signals each indicative of phase shift values providing a desired antenna radiation characteristic and further including phase shifter control means connected to said phase shifters and to said command signal source to receive therefrom said steering command signals, said phase shifter control means being responsive to said steering command signals to set said phase shifters at phase shift values approximating said desired values of phase shifts whereby roundoff errors occur for the settings of at least some of said phase shifters, monitoring means connected to said antenna steering means for deriving therefrom a roundoff error signal indicative of the value of phase shifter setting error, and Compensating means connected with said monitoring means to receive said roundoff error signal therefrom and to recirculate the error signal to said antenna steering means for addition thereby to the next successive steering command signal thus accumulating roundoff errors for providing an adjusted phase setting of at least one of said phase shifters to at least partially compensate for said accumulated roundoff errors.

2. A system as claimed in claim 1, in which the amplitude characteristics of said radiation elements are given a nonuniform distribution, and including storage means for storing the amplitude distribution of said radiation elements, and weighting means connected with said storage means and with said monitoring means, said weighting means being adapted to apply to said accumulated roundoff errors a weighting factor based on the relative amplitude characteristics of adjacent radiation elements.

3. A phased array antenna system having a plurality of radiation elements, a plurality of phase shifters respectively associated with said radiation elements, each of said phase shifters being adapted to shift phase in a limited number of discrete step-values, antenna-steering means including a source of digital steering command signals for providing successive sets of multibit digital signals each comprising a number of bits greater than said number of phase shifter step-values and being indicative of desired step-values for said phase shifters to obtain desired radiation characteristics of said array of radiation elements, said antenna-steering means further including control means responsive to a number of the more significant bits of each set of multibit digital signals of respectively setting said phase shifters to discrete phase-shift settings adjacent to said desired phase-shift values whereby roundoff errors occur in the settings of the phase shifters, monitoring means responsive to a number of the less significant bits of each set of multibit digital signals thereby to obtain a measure of the value of said roundoff errors and to output a roundoff error signal, and compensating means connected to receive said roundoff error signal from said monitoring means and to recirculate the error signal to said antenna-steering means for addition thereby to the next successive steering command signal for providing an adjusted phase setting of at least on e said phase shifters to at least partially compensate for said roundoff errors.

4. A system as claimed in claim 3, in which the amplitude characteristics of said radiation elements are given a nonuniform distribution, and including storage means for storing the amplitude distribution of said radiation elements, and weighting means connected with said storage means and with said monitoring means, said weighting means being adapted to apply to said accumulated roundoff errors a weighting factor based on the relative amplitude characteristic of adjacent radiation elements.

5. A system as claimed in claim 4, in which said amplitude distribution is characterized by the greatest amplitude being at the center of said array of radiation elements and tapering to minimum amplitudes at the outer edges of said array, said source of digital-steering command signals being adapted to provide said successive sets of digital signals first for the center elements of the array and thence for elements successively outwardly from the center, whereby said weighting factor is successively based on ratios of lesser amplitude characteristics.

6. A system as claimed in claim 3, in which said control means, said monitoring means and said compensating means comprise, in combination, an adder having first and second inputs with said first input connected to receive said multibit digital signals from said source of digital steering command signals, a phase signal channel connected to the output of said adder and adapted to receive only the relatively more significant bits of said digital signals outputted thereby and further adapteD to control said phase shifter step values in accordance with these relatively more significant bits, a roundoff error channel connected to the output of said adder to receive therefrom only the relatively less significant bits of said digital signals and connected to output a roundoff error signal to said second input of said adder thereby to temporarily circulate and accumulate said roundoff errors until the value thereof is sufficiently great to affect the value of said relatively more significant bits of the digital signals outputted by the adder to thus provide said adjusted phase setting.

7. A system as claimed in claim 6, in which the amplitude characteristics of said radiation elements are given a nonuniform distribution, and including a recirculating shift register loaded with the amplitude characteristics of successive radiation elements, delay means interposed in the recirculating path between the input and output of said recirculating shift register, a divider having inputs respectively connected to the input and output of said recirculating shift register so as to provide a weighting factor based on relative amplitudes of said radiation elements, a multiplier interposed in the roundoff error recirculating path between said roundoff error channel and said second input of the adder, and means connecting said weighting factor output of the divider to an input of said multiplier, whereby said roundoff errors are altered by said weighting factor.