JPH04220003A - Expanded phased array with digital beamforming network - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This invention relates to phased array antenna systems, and more particularly to an expanded phased array antenna system with digital beamforming circuitry.

0002

2. Description of the Related Art A typical phased array antenna system includes a large number of antenna elements. A large number of antenna elements are generally required to obtain sufficient gain. Furthermore, many such conventional phased array antenna systems are generally reconfigurable. The beam profile used in such conventional antennas is easily maneuverable and, due to its nimble nature, is not subject to interference. For large aperture array antennas where even larger scan volumes are required, the beamforming process generally includes the use of phase shifters as necessary to provide time delays between different antenna elements. In conclusion, beamforming processing does not involve simple coefficient multiplication of signal vectors to perform signal detection and beam steering.

0003

SUMMARY OF THE INVENTION In order to overcome the limitations of conventional phased array antenna systems, namely the need to use a large number of elements and a large number of phase shifter sets as well as complex feed arrangements, the present invention provides: An enlarged phased array antenna system is provided that incorporates digital beamforming circuitry that can significantly reduce the number of antenna elements compared to conventional antennas.

0004

SUMMARY OF THE INVENTION The present invention provides an expanded phased array antenna system that incorporates digital beamforming circuitry. The inclusion of digital beamforming circuitry allows multiple simultaneous beamforming that can be distinguished and steered in various selected directions. Although the field of view according to the invention is therefore limited, the gain of the system is increased by utilizing its enlarged portion. The magnified portion may be a telescope, such as a Cassegrain telescope, and may include a transfer lens used to provide an intermediate focal plane at which an image of the output of the antenna element is formed. The enlarged phased array antenna has a focal plane located on the flat radiating surface of the transfer lens, which radiates the transferred signal to a remote location or focuses the incoming signal to be processed by the feed array system. to tie.

[0005] In a terrestrial satellite communicating with a terrestrial link with a limited field of view, the present invention provides an arrangement that uses a minimum number of antenna elements to provide adequate gain. Digital beamforming networks effectively provide multiple beam capability. The network provides a rapid scanning spot beam and a reconfigurable area coverage beam.

[0006] Therefore, when the present invention is compared to conventional phased array antenna systems, the number of elements is reduced and therefore manufacturing costs are reduced. Redundancy in the array improves reliability when compared to conventional multi-beam antenna systems. Compared to a normal antenna array,
The use of digital beamforming circuitry provides multiple, simultaneous, reconfigurable beams. Furthermore, optimal efficiency of the present invention is achieved by dynamically allocating spatial (beamforming) and temporal (waveform detection) processing sequences.

Particularly in accordance with the present invention, there is provided an enlarged phased array antenna system having an array of antenna elements and an enlarged portion having a predetermined field of view coupled to the array of antenna elements for increasing the gain of the antenna system. be done. A conversion device is coupled to the antenna element array to convert the analog output signal derived from each element in the array into a digital signal when the antenna system operates in a receive mode and converts the analog output signal derived from each element in the array into a digital signal when the antenna system operates in a transmit mode. Each element converts the digital signal into an analog signal that can be transmitted.

Digital beamforming circuitry is coupled to the conversion device to convert each digital signal derived from each element in the array into a
Multiply the separated directional vector and each digital signal,
Each multiplied digital signal is processed by combining each multiplied digital signal into a single digital signal in which the signal components are in phase. This digital signal represents a beam formed in the direction of the signal received by the array. The digital beamforming network also includes a phase vector associated with each digital signal generated such that when the antenna system operates in a transmit mode, the phase vector associated with each digital signal is predetermined such that upon transmission by the array, a beam is generated in a predetermined direction. The digital signal is processed to generate a beam that can be transmitted in a predetermined direction by multiplying it by a separate directional vector having a defined phase relationship.

Multiple simultaneous beams are selectively formed in multiple directions simultaneously by multiplying the transmitted signal by a plurality of separate sets of beam coefficients. A beam expanding section is optionally coupled to the antenna element array to expand each beam provided by the digital beamforming circuitry.

Digital beamforming circuitry includes circuitry that provides a plurality of directional vectors corresponding to the directions in which multiple simultaneous beams are respectively transmitted and received. Multiple multipliers are used to combine the multiple directional vectors with corresponding signals provided by the antenna element array. Each multiplier provides a plurality of output signals that are substantially in phase. A summing circuit is coupled to the plurality of multipliers to combine the plurality of output signals into a single digital output signal sequence for each beam direction.

Comparing the present invention to conventional arrays, although conventional arrays are very nimble, each beam requires a set of phase shifters to achieve such nimbleness. To further explain, typical arrays have large fields of view and large numbers of elements, multiple sets of phase shifters are required for multiple beams, and the system needs to have reasonable gain. The expanded phased array of the present invention has a limited field of view and an appropriate number of elements can form multiple beams using digital beamforming circuitry without phase shifters, yet still Has a high gain in comparison.

Various features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an enlarged phased array antenna system 10 in accordance with one embodiment of the present invention. System 10 includes a magnification system 12, shown as a Cassegrain antenna in FIG. 1, comprising a transfer lens 14, a first reflector 16, and a second reflector 18. Other magnification systems, including confocal lens systems or confocal reflector systems, or a single reflector with a transfer lens, well known to those skilled in the art can also be used. An antenna array 20 composed of a plurality of antenna elements is arranged in a conventional manner on the focal plane of the transfer lens 14. An array of 16 or fewer antenna elements can be used in the expanded phased array antenna system 10 of the present invention. Each antenna element of array 20 is coupled to a digital beamforming network (DBN) 22.

FIG. 2a shows the digital beamforming circuitry 22 of the system of FIG. 1 in receive mode. As shown, the antenna elements of array 20 are designated elements 20a-20n. Each antenna element 2
0a - 20n are coupled to a down conversion circuit 26 used to convert the signals received by the antenna array 20 to intermediate frequency (IF) signals that can be processed by the digital beamforming circuitry 22. .

The down conversion circuit 26 includes a buffer amplifier 34a.
A local oscillator circuit 30a is provided which includes a local oscillator 32a coupled to a frequency multiplier 36a (in the embodiment multiplied by eight as indicated by x8). The output of the local oscillation circuit 30a is sent to the mixer 4.
0a and the other input of mixer 40a is coupled to the first antenna element 20a. The output of the mixer 40a is a band pass filter (BPF) 4.
2a and a buffer amplifier 44a to an analog-to-digital conversion section 50.

Each antenna element 20a to 2 of the array 20
0n are each coupled to converter 50 by a separate down converter circuit 26. The conversion device 50 is composed of a plurality of analog-to-digital converters 50a to 50n,
Each portion 26a to 2 of the downward conversion circuit 26 is separately connected to the lower conversion circuit 26.
The output signal from 6n is converted to a digital signal, which is processed by digital beamforming circuitry 22.

As shown in FIG. 2(a), the analog-to-digital converters 50a to 50n include a decimating/estimating circuit 5 including a digital circuit including an accumulator, a sign detector, etc.
2a to 52n. This estimation operation typically increases dynamic range and reduces processing bandwidth.

Decimate/estimate circuits 52a to 52n
The outputs of are coupled to respective inputs of digital beamforming network 22. The digital beamforming network 22 comprises a plurality of digital multipliers 60a-60n, each having one input fed to the output of each decimating/estimating circuit 52a-52n and the other input being a beam coefficient for calculating the beam direction vector. It is coupled to generation circuits 62a-62n. The output of each digital multiplier 60a-60n is coupled to a summing circuit 64 that combines the digital output signals into a single digital signal. The output of the summing circuit 64 is the output of the digital beamforming circuitry 22, which may be used, for example, in a communications receiver as well as the temporal processing circuit 6.
6, and processing circuitry 66 performs processing such as demodulation, channelization decoding, data storage and transmission, etc. Referring to FIG. 2B, digital beamforming circuitry 22 of system 10 of FIG. It is shown. In the circuit of FIG. 2B, the conversion device 50 uses a plurality of digital-to-analog converters 50a' to 50n', does not use the decimate/estimation circuits 52a to 52n, and the adder circuit 64 uses a 1:N multiplexer 50. replaced by
The circuit is substantially the same as that shown in FIG. Same as above.

Referring to FIG. 3, (a) and (b) of FIG.
) The operation of the digital beamforming circuitry 22 used in the circuit shown in FIG. Digital beamforming network 2
2 includes a plurality of digital multipliers 60a to 60n,
Their inputs are provided by a plurality of antenna elements 20a to 20n.
and beam coefficients from beam coefficient generation circuit 62. The outputs of the plurality of digital multipliers 60a-60n are coupled to a summing circuit 64. The beam coefficients are determined by the central processing unit (CPU), for example.
) is given by

As shown in FIG. 3, the relative amount of phase difference in the signals output from a single signal source in the field of view of the antenna array 20 and received by the plurality of antenna elements 20a to 20n changes with angular rotation. This is represented by an arrow 78 indicating. Each signal received by antenna elements 20a-20n is combined separately with a beam coefficient to accommodate the multiplication of each signal to produce signals that are in phase with each other. These signals are combined into a single signal by a summing circuit 70 to output a signal representative of the formed beam with the beam direction vector pointing in the direction of the radiation source.

Referring again to FIG. 1, expanded phased array antenna system 10 is shown operating in a receive mode. For example, a 4×4 array of antenna elements with an operating frequency centered at 60 GHz is used. The signals received by antenna array 20 are amplified and downconverted by downconversion circuit 26 to a processing intermediate frequency. The reduced intermediate frequency analog signal is then converted to a digital signal in a down-conversion post-conversion device 50. The conversion device 50 in this case consists of a plurality of analog-to-digital converters 50a to 50n. Typically the downconversion has a hopping bandwidth of 2 GHz and an instantaneous bandwidth of 50 MHz6.
For example, a 0 GHz signal is converted into a 1 GHz signal with a bandwidth of 50 MHz. Decimating/estimating circuits 52a-52n can be processed by digital beamforming circuitry 22 and used to increase the dynamic range of the digital signal and reduce bandwidth requirements.

The signals entering antenna array 20 are sequentially rotated such that the phase vectors of the signals received by adjacent antenna elements 20a-20n are more clearly shown in FIG. The angle of spatial rotation per element spacing depends on the arrival angle of the input radio waves. When the signal provided by a mechanical boresight or other reference signal source is processed, its rate of rotation is zero. The farther the angle of arrival of a particular signal is from the boresight, the faster its rate of rotation. Each antenna element 20a-20n is sampled separately and each signal can be represented as a signal vector. The digital signal vector is then multiplied by the beam coefficients (directional vectors) in the digital beamforming network 22 so that the products are all in phase. These in-phase signals are then summed together by summing circuit 64 to provide a single output signal.

In conclusion, the digital beamforming process digitally aligns the signals received by each antenna element 20a-20n. The beam is therefore formed pointing in the direction of the incoming signal. Similarly, multiple beams can be formed simultaneously by independently multiplying the signal vector by different direction vectors. In this way multiple receive beams can be processed simultaneously and multiple transmit beams can be processed simultaneously. Alternatively, the transmitted beam can be quickly redirected to any desired direction by appropriately selecting the beam direction coefficient.

Referring to FIGS. 1 and 2, an enlarged phased array antenna system 10 can be constructed in a variety of ways, including the use of a Cassegrain reflector 12 and transfer lens 14 arrangement. Transfer lens 14 is placed in the focal plane of Cassegrain reflector 12 .

In the transmit mode of operation, antenna array 20 concentrates radiated power into a small spot at the rear surface of transfer lens 14. This spot acts as a virtual image of the light source illuminating the Cassegrain reflector 12 which produces a spot beam in a remote area. As the antenna array 20 focuses its radiated power to different spots on the transfer lens 14, the remote area beam moves correspondingly. If two spots are created on the transfer lens 14, two spot beams will be generated simultaneously in the remote area. As more spot beams are generated, they are summed to form an area coverage beam with instantaneous reconfiguration capability.

Between a satellite and a terrestrial link where the field of view is limited, the present invention can use a minimum number of antenna elements to obtain adequate gain. Digital beamforming networks efficiently provide multiple beam capability. The network provides a fast scanning spot beam and a reconfigurable area coverage beam.

Compared to conventional phased array antenna systems, the present invention therefore reduces the number of elements and therefore reduces manufacturing costs. Compared to conventional multi-beam antennas, the present invention improves reliability due to redundancy in the array. Compared to regular antenna arrays, the use of digital beamforming provides multiple, simultaneous, reconfigurable beams. Furthermore, optimal efficiency of the present invention is achieved by dynamically allocating spatial (beamforming) and temporal (waveform detection) processing sequences.

The new and improved phased array antenna system of the present invention has been described. It should be understood that the above embodiments are merely some of the many embodiments, and that those skilled in the art can make various modifications and changes without departing from the technical scope of the present invention. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an expanded phased array antenna system according to the invention.

FIG. 2 is a block diagram of the digital beamforming circuitry of the system of FIG. 1 operating in receive mode and transmit mode.

FIG. 3 is a detailed diagram illustrating the operation of the digital beamforming circuitry of the present invention.

Claims (7)

[Claims] 1. An array of antenna elements; a magnifying means having a predetermined field of view coupled to the array of antenna elements for increasing the gain of the antenna system; coupled to the array of antenna elements; (a) converting the analog output signal output from each element in the array into a digital signal when the antenna system is operated in receive mode;
(b) converting means for converting a digital signal into an analog signal transmittable by each element in the array when the antenna system is operated in a transmitting mode, coupled to the converting means; In operation, each digital signal is multiplied by a separate directional vector, and each multiplied digital signal is combined into a single digital signal whose signal components are in phase and represent a beam formed in the direction of the signal received by the array. Process each digital signal output from an element of the array by combining the signals (b
) When the antenna system operates in transmit mode, each digital signal generated and its associated phase vector is a separate signal having a predetermined phase relationship such that the beam is formed in a predetermined direction for transmission by the array. digital beam forming means for processing the digital signals to generate a beam transmitted in a predetermined direction by multiplying each digital signal by a directional vector. Zudo array antenna system. 2. The digital beam forming means includes a coefficient generating means for generating a plurality of directional vectors corresponding to the directions in which the signal is received by the array and the beam is transmitted, and a correspondence between the signal provided by the array of antenna elements. a plurality of multiplier means for combining the plurality of directional vectors with a corresponding signal transmitted by the antenna system; and a plurality of outputs coupled to the plurality of multiplier means, when the antenna system operates in a receive mode. 4. Adding means for combining the signals into a single output signal and multiplexing the digital signals to be transmitted into a plurality of individual signals that are summed with the plurality of directional vectors in the multiplication means. 1. The expanded phased array antenna system according to 1. 3. A transfer device in which the expanding means is arranged between reflector means for transmitting and receiving the beam and for focusing the beam on a remote area, and reflector means for combining the beam with the array of antenna elements. Claim 1 comprising a lens.
The enlarged phased array antenna system described. 4. The expanded phased array antenna system of claim 1, wherein the reflector means comprises a Cassegrain reflector and transfer lens means for expanding each beam provided by the digital beam forming means. 5. coupled to digital beam forming means;
2. The expanded phased array antenna system of claim 1, further comprising computer means for generating beam direction coefficients for determining the direction in which the beam is received or transmitted. 6. The expanded phased array antenna of claim 1, further comprising down conversion means coupled between the array of antenna elements and the conversion means to reduce the data rate at which the signals are processed by the system. system. 7. The down conversion means is coupled to each antenna element of the array of antenna elements to reduce the data rate at which the signal is processed by the system and increase the dynamic range at which the signal is processed by the digital beamforming means. 7. The extended phased array antenna system of claim 6, further comprising separate down-conversion and estimating means.