Ultra-wideband active electronically scanned antenna

Abstract

The architecture of this invention makes multiple use of switched time-delay circuits to reduce the complexity of both series and parallel feed antenna arrays. Each time-delay circuit can give a delay that can be switched to values between 0 and 2d/c, where d is the inter-element spacing and c is the velocity of light. At the highest frequency of the series feed array, the elements are spaced by lambda /2 to avoid grating lobes and the maximum delay corresponds to 360 DEG of phaseshift. When the time-delays are set half way (d/c), the various lines feeding the elements of the array at the aperture have bias delays that make them all equal in length, thereby giving a broadside beam, independent of frequency. At the highest frequency, the switchable time delay gives some excess in available delay. If additional excess time-delay is needed it can be obtained by increasing the time delay circuit range. Insertion loss is proportional to the number of bits used. This could become high in large antennas, however, this loss may be compensated by the addition of two-way amplification in the branch lines with an appropriate bias length adjustment. Also the insertion loss may be reduced by dividing the array into subarrays which are then combined by a series feed combiner network.

What is claimed is: 
     
       1. An apparatus for beamforming in a broadband antenna array having a plurality of antenna elements comprised of: a plurality of electromagnetic transmission lines forming a at least two branches;   means for splitting a broadband electromagnetic signal, in a transmit mode, into a plurality of electromagnetic signals applied, respectively, to each branch of the plurality of branches, or, in a receive mode, combining a plurality of electromagnetic signals from each branch into a composite electromagnetic signal;   a plurality of antenna feed lines coupled to each branch and an associated antenna element; and   means for selectively inserting a finite amount of line-delay in at least two of the branch lines prior to each antenna feed line for varying the amount of time-delay in each antenna feed line to selectively delay the electromagnetic signal to the associated antenna element, thereby directing the beam of the array in a predetermined direction by selectively adjusting the time-delay to each antenna.   
     
     
       2. An apparatus, as in claim 1, wherein one or more antenna feed lines are further comprised of one or more lengths of electronic transmission feed line forming a fixed bias delay. 
     
     
       3. An apparatus, as in claim 1, further comprising: means for amplifying the delayed electromagnetic signal in each antenna feed line prior to the electromagnetic signal being applied to the associated antenna element;   means for amplifying an electromagnetic signal received by the antenna element and applying the amplified electromagnetic signal to an associated antenna feed line; and   means for switching each antenna element from a receive to a transmit, or vice versa, mode of operation.   
     
     
       4. An apparatus, as in claim 1, further comprised of a means for amplifying and switching the electromagnetic signal in at least two branches of the plurality of branches to compensate for an insertion loss of electromagnetic signal introduced into the branch by the line delay. 
     
     
       5. An apparatus, as in claim 1, wherein the means for selectively inserting a finite time-delay is further comprised of a plurality of feed line segments of varying length, selectively switchable, coupled together in sequence. 
     
     
       6. An apparatus for beamforming a broadband antenna array having a plurality of antenna elements comprised of: an electromagnetic signal transmitter and receiver for selectively generating and receiving a broadband electromagnetic signal;   a plurality of electromagnetic transmission lines forming a at least three branches;   means for splitting the electromagnetic signal, in a transmit mode, into a plurality of electromagnetic signals applied, respectively, to each branch of the plurality of branches, or, in a receive mode, combining a plurality of electromagnetic signals from each branch into a composite electromagnetic signal;   a plurality of antenna feed lines coupled to each branch and an associated antenna element;   means for selectively inserting a finite amount of line-delay in at least two of the branch lines prior to each antenna feed line for varying the amount of delay in each antenna feed line to selectively delay the electromagnetic signal to the associated antenna element, comprised of a plurality of feed line segments of varying length selectively switchable, coupled together in sequence, thereby directing the beam of the array in a predetermined direction by selectively adjusting the time-delay to each antenna;   at least one amplifier, configurable to the same mode of operation as the electromagnetic signal transmitter and receiver, located in at least two branches of the plurality of branches to compensate for a loss of electromagnetic signal caused by the insertion of the line delay;   an amplifier located in each antenna feed line prior to the antenna element, in the transmit mode, to amplify the delayed electromagnetic signal prior to the electromagnetic signal being applied to the associated antenna element and, in the receive mode, for amplifying an electromagnetic signal received by an associated antenna element; and   a switch in each antenna feed line to select the same mode of operation for the amplifier as the electronic signal transmitter and receiver.   
     
     
       7. An apparatus for beamforming a broadband antenna array having a plurality of antenna elements comprised of: an electromagnetic signal transmitter and receiver for selectively generating and receiving a broadband electromagnetic signal;   a plurality of electromagnetic transmission lines forming a plurality of branches comprised of at least a right branch and a left branch;   a plurality of antenna feed lines coupled to each branch and an associated antenna element of the array;   one or more antenna feed lines are which further comprised of one or more lengths of electronic transmission feed line forming a fixed bias delay;   an electronic signal splitter which, in the transmit mode, selectively splits the generated electromagnetic signal into a plurality of electromagnetic signals applied, respectively, to each branch of the plurality of branches and which, in the receive mode, the electronic signal splitter combines a plurality of electromagnetic signals received by the elements of the antenna array into a single electromagnetic signal;   the electronic signal splitter being further comprised of a switch to selectively configure the electronic signal splitter to the same mode of operation as the electromagnetic signal transmitter and receiver;   a plurality of line-delay modules located in the branch lines at least one of which is prior to each antenna feed line comprised of a plurality of feed line segments of varying length, selectively switchable, coupled together, in sequence, to selectively delay the electromagnetic signal in the antenna feed line of the associated antenna element so as to orient the transmitted or received electromagnetic beam in a predetermined direction by selectively adjusting the time-delay to each antenna;   at least one amplifier, configurable to the same mode of operation as the electromagnetic signal transmitter and receiver, located in at least two branches of the plurality of branches to compensate for a loss of electromagnetic signal caused by the insertion of the line delay;   an amplifier located in each antenna feed line prior to the antenna element, in the transmit mode, to amplify the delayed electromagnetic signal prior to the electromagnetic signal being applied to the associated antenna element and, in the receive mode, for amplifying an electromagnetic signal received by an associated antenna element; and   a switch in each antenna feed line to select the same mode of operation for the amplifier as the electronic signal transmitter and receiver.   
     
     
       8. A method for beamforming in an antenna array having a plurality of antenna elements comprising the steps of: selecting a predetermined time-delay for an electromagnetic signal applied to each antenna element of antenna elements; and   adjusting the line-delay to each antenna feed line so as to cause a composite electromagnetic signal emitted from the plurality of antenna elements to be directed in a predetermined direction.