Electro-optically controlled wideband multi-beam phased array antenna

Abstract: An optical network (46) for providing a wideband true time delay phased antenna array with simultaneous multiple beam capability is disclosed. The network (46) is provided for connection between plural beam ports (48-52M) and plural antenna elements (20-24N) for converting a received radio frequency (RF) planar wavefront to plural in-phase signals at one and only one beam port (48-52M). The converse is true for a transmitted wave. The network (46) includes a laser (30-34N) for each antenna element (20-24N) modulated by RF energy which is separated and delayed via optical dividers (35-39N) connected to optical combiners (40-44M) by optical fibers (46) of different lengths. Substantially all signals then arrive in-phase at one particular beam port (48-52M) for a receiver (56-60M) receiving a wave at one particular corresponding angle of inclination of the wavefront. In transmitted waves, appropriate radiations from the phased array differ by an amount to effect transmission in one particular direction corresponding to the beam port selected for energization by the transmitter.

Description: This invention relates to radiant energy systems and more particularly to such systems including electro-optical networks for phasing antenna arrays thereof for providing simultaneous multiple beams with true time delay wideband capability. Electro-optical apparatus for phased arrays are known in the prior art. For example, in Wright et al. U.S. Patent No. 3878520 issued April 15, 1975, there is disclosed an optical processing technique employed to optically generate a set of properly phase-controlled signals that are appropriate for forming and steering, in space, a beam from a two-dimensional phased array antenna. The set of properly phase-controlled signals are provided by first generating two optical beams having a differential frequency equal to the desired microwave frequency to be transmitted. The two beams are combined in a controlled manner to produce a two-dimensional optical pattern that contains the correct microwave phase and amplitude information to form and steer the final antenna beam in space. This two dimensional optical pattern is at any instant and optical analog of the microwave excitation applied to the antenna radiating elements. The optical pattern is converted to a two-dimensional microwave pattern in a transducer system called an optical-to-microwave converter, the output of which is a two-dimensional array of microwave signals. These signals are connected to a single radiating element of a phased array antenna. The elements then cooperate to radiate a beam in space. It is also known from U.S. Patent No. 4028702 to provide a radio frequency transmitter which provides a plurality of variable phase radio frequency signals at respective antenna elements of the system. Radio frequency modulated optical signals which are generated are divided and fed into sets of optical fibre delay lines in response to the operation of individual optical switches under the control of a phasing programmer to control the selection of individual radiating element phases for each successive beam pointing position. The optical fibre delay lines may be arranged in sets having delay lines of different lengths to provide discrete values of phase delay and one such set is provided in respect of each antenna element of the system. However, neither of the prior art patents referred to above disclose simultaneous plural beam ports combined with true time delay wideband capability. Moreover, both require optical switching. Additional efforts have occurred in the prior art to solve the problems of phased arrays. The Butler beam forming matrix and the Rotman lens are examples of these efforts. These examples have been used in microwave systems. The radio frequency signals are intercepted by receivers and coupled to a microwave (RF) structure designed to delay the signals. The Butler and Rotman apparatuses operate on the RF signal directly to provide the requisite delays to properly phase the incoming signals or the transmitted signals in case of a microwave RF transmitter. The major disadvantages are the size, weight and expense associated with this design in addition to the bandwidth limitaion inherent in a microwave RF beamforming system. The delay section of the phased array only operates over a limited frequency range. It is still further known from the Journal of Lightwave Technology, Vol. LT-3 No. 2, April 1985 pages 273 to 276 to provide a radiant energy receiving system in which radio signals received by a plurality of antenna elements of an array in response to the incidence of a wavefront are utilised to modulate respective laser light sources the optical outputs from which are conveyed to a common detector by optical fibres which are cut to different lengths to produce the requisite delays in the optical outputs from the laser light sources to compensate for the time arrival differences of the incoming radio frequency signals of the wavefront at the antenna elements of the system. The prior art publication also discloses an experimental receiving system in which two matched delay filters are arranged to receive the R.F output from a sweep oscillator simulating a received wavefront. Each of these delay filters has two lasers with first and second optical fibres of different lengths connected to the outputs of each laser, the four first optical fibres of the two delay filters being connected to one photodetector and the four second optical fibres of the delay filters being connected to another photodetector. The present invention seeks to provide a radiant energy system which advantageously serves both as a receiving and transmitting system thereby resulting in an economy of components and which includes an improved optical beamforming network incorporating a minimum number of modulator/demodulator components for phased array antenna operation providing wideband operation with true time delay beamforming. According to the present invention there is provided a radiant energy system comprising an antenna having a plurality of antenna elements in respect of radio frequency signals of different phases as a function of the angle of inclination of a wavefront at the antenna and a plurality of first conversion means individually connected to the respective antenna elements and connected to second conversion means by an arrangement of optical fibres of different lengths defining sets of fibres, characterised in that the system comprises transmitter means and receiver means connected to the second conversion means so that beams are transmitted into, or received from, a particular number of predetermined directions, such number corresponding to the number of second conversion means and the directions being determined by the respective different lengths of optical fibres in the sets of optical fibres, each of the first conversion means and the second conversion means comprising a light modulator and a light demodulator connected in parallel, each light modulator including a laser for producing an intensity modulated light output and each de-modulator including a laser light intensity demodulator, and in that the first conversion means are individually connected to amplifier means while the first and second conversion means are coupled to the sets of optical fibres through optical dividers-combiners and optical combiners-dividers respectively, each first conversion means being coupled to a corresponding optical divider-combiner and each second conversion means being coupled to a corresponding optical combiner-divider while each optical divider-combiner is connected to all of the optical combiners-dividers by corresponding optical fibres and each optical combiner-divider is connected to all of the dividers-combiners by corresponding optical fibres, and in that the number of optical fibres of respective different lengths in the sets of optical fibres connected with the first conversion means corresponds to the number of first conversion means while the individual fibres of each set are coupled to the respective second conversion means, and in that the number of optical fibres of respective different lengths in the sets of optical fibres connected with the second conversion means corresponds to the number of second conversion means while the individual fibres of each set are coupled to the respective second conversion means, and in that corresponding optical fibres of the respective sets of fibres have different lengths so that when the system is operating as a receiver with the receiver means operative all the signals arriving at each of the light demodulators of the second conversion means arrive simultaneously and in phase for reception by the receiver means connected to the light demodulators of the second conversion means through beam ports and so that when the system is operating as a transmitter with the transmitter means operative signals arriving at the light demodulators of the first conversion means from the transmitter means connected to the second conversion means through beam ports arrive at different times and are out of phase so that RF signals applied to the antenna elements produce in respect of the transmitter means a plane wave propagated at the requisite angle. The system according to the invention may include linear, circular, planar, cylindrical, spherical and conformal arrays whilst the optical beamforming network is capable of employing either single axis beam steering or dual axis beam steering. The optical beamforming network may be lightweight and of compact size as compared with conventional radio frequency beamforming networks and provides multiple beamforming capabilities without employing switches or switched phase shifters in the beamforming network. In order that the invention and its various other preferred features may be understood more easily, some embodiments therof will now be described, by way of example only, with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic view of a plane wave moving toward a linear array of antenna elements, Figure 2 is a perspective view of a planar array of antenna elements, Figure 3 is a perspective view of a cylindrical array of antenna elements, Figure 4 is a side elevational view of a spherical array of antenna elements, Figure 5 is a block diagram of a radiant energy receiver, Figure 6 is a block diagram of a transceiver constructed in accordance with the present invention, and Figure 7 is a block diagram of a radiant energy transmitter. In Figure 1 a plane wavefront is illustrated by a line 10 moving at an angle ϑ between the wavefront 10 and a linear array of equally spaced antenna elements 11,12,13,14 and 15 or more on a dotted line 16. Note that wavefront 10 reaches antenna element 11 a time Δt later than it reaches antenna element 12 where where d is the antenna element spacing shown in Figure 1 and c is the velocity of propagation. All this is old and well known in the prior art. The direction of propagation of the plane wavefront 10 in Figure 1 is then normal to wavefront line 10. The magnitude of Δt then is sine function of the magnitude of ϑ. If all the antenna elements 11-15 are equally spaced. Wavefront 10 reaches antenna element 11 at a time period Δt after it reaches antenna element 12, a time period 2 Δt after reaching antenna element 13, a time period 3 Δt after reaching antenna element 14, and a time period 5 Δt after reaching antenna element 16. In order to practise the present invention, as shown diagrammatically in Figures 1,23 and 4, antenna elements 11-15 may be mounted on line 16 (Figure 1), at a plurality of positions 17 on a plane surface (Figure 2), at a plurality of positions 18 on the surface of a cylinder (Figure 3), and at a plurality of positions 19 on the surface of a sphere (Figure 4). In Figure 5, identified by the general reference character 100, a plurality of conventional antenna elements are provided at 20-24N connected to a plurality of conventional radio frequency (RF) low noise amplifiers 25-29N, respectively. If desired, a conventional gallium arsenide monolithic amplifier chip may be employed for each of the RF low noise amplifiers 25-29N. The outputs of amplifiers 25-29N are respectively connected to a plurality of conventional solid state RF modulated diode lasers 30-34N. The outputs of modulated lasers 30-34N are connected respectively to a plurality of conventional optical dividers 35-39N. Also a plurality of conventional optical combiners 40-44M are provided. A network 46 having a plurality of optical fibers connects the plurality of optical dividers 35-39N to the plurality of optical combiners 40-44M. Network 46 and the direct connections of the plurality of optical fibers (which do not include a corresponding plurality of switches) in combination with the plurality of optical dividers 35-39N and the plurality of optical combiners 40-44M is one of the many novel features of the present invention. The optical fibers of network 46 are conventional except for their lengths. These lengths are chosen so that all the signals corresponding to a plane wavefront 10 of one direction are in phase at one and only one of a plurality of beam ports 48-52M connected to a respective plurality of receivers 56-60M via optical detectors 66-70M respectively. The lasers 30-34N may provide an RF amplitude modulated light by modulating the voltages thereof as is conventional. The plurality of diode lasers 30-34N are each a coherent light generator providing a light of a singular frequency. The lasers 30-34N each emit a high frequency light wave which acts as a carrier frequency in the light domain. The radio frequency voltages which include frequencies in the range of kilohertz to hundreds of gigahertz occupies only a small percentage of the optical frequency band. The high frequency electromagnetic wave emitted by the lasers 30-34N and acting as a carrier wave is modulated by the radio frequency voltages received at the plurality of antenna elements 20-24N. Once the RF signal voltages are carried into the optical domain the task of delaying the signals is easier to control. Lasers 30-34N may by of a type made by Ortel Corporation of Alhambra, California. Optical dividers 35-39N and optical combiners 40-44M may be conventional and may be of the type made by Canetar of Ontario, Canada including conventional bodies having a graded index of refraction. Optical dividers 35-39N divide each of their corresponding modulated laser signals into M output signals. Each optical combiner of the plurality of optical combiners 40-44M combines the light outputs of N optical fibers of the network 46. Note that "N" in the context above denotes the number of antenna elements 20-24N while "M" in the context above corresponds to the number of antenna beams simultaneously generated. Thus, for each antenna element 20-24N, an optical divider 35-39N is required, necessitating "N" optical dividers. Since each optical divider 35-39N provides "M" laser signals, then "M" optical fibers must extend from each of the plurality of optical dividers 35-39N since each light signal requires one optical fiber. Each optical fiber extends from one of the "N" optical dividers 35-39N to one of the "M" optical combiners 40-44M since there must be one optical combiner 40-44 M for each of the "M" output signals that are generated. Thus, there are "N" optical fibers received by each of the "M" optical combiners 40-44M. The RF signal at each antenna element 20-24N is sampled by routing one of the "M" optical fibers carrying a signal sample from each of the "N" optical dividers 35-39N to each of the "M" optical combiners 40-44M. The optical fibers at the output of divider 35 are 35-1, 35-2, 35-3 ...35-M. These are connected to combiners 40,41,42,43,...44M, respectively. Dividers 35-39N and combiners 40-44M are all similarly connected by optical fibers. Dividers 36,37,38 ...39N have optical fibers 36-1, 37-1, ... 39-1 connected therefrom, respectively, to optical combiner 40, optical fibers 36-2, 37-2 ... 39-2 are connected to combiner 41 and so forth. Detectors 66-70M are conventional light intensity detectors, i.e. photodiodes. The selection of optical fiber lengths for the network 46 will be described only in connection with beam port 48. The remainder of network 46 may be constructed in an analogous way. In the case of Figure 5, if uniformly spaced antenna elements 20-24N were to assume the positions of antenna elements 11-15 (Figure 1), respectively, and the conditions in Figure 5 were the same as those in Figure 1, optical fibers 35-1, 36-1, 37-1 ... 39-1 must be of lengths to provide time delays of the RF signal envelope of Δt₅, Δt₆, Δt₇, ... Δt₉, respectively. where where Δ t₅ or the length of fiber 35-1 may provide one degree of freedom and may be chosen as a matter of convenience provided that the lengths of 36-1, 37-1, etc provide the time delay gradient appropriate for the beam direction as given by the above equations (2-4). Typically, the antenna element spacing d = λ / 2 for linear arrays with uniformly spaced elements. In Figure 5, it is a known advantage to determine the direction of propagation of the electromagnetic wave 10 by utilizing receiver means 56-60M to detect the beam selectively at the beam ports 48-52M. Each of the beam ports 48-52M is individually positioned to determine the direction of propagation of the approaching electromagnetic wave 10. Thus, each of the beam ports 48-52M that receive the wave 10 receive a portion of the RF signal which corresponds to a given beam direction. If the receiver 56 is connected to beam port 48, a first specific plurality of signals will be received from a first specific direction. Furthermore, if the receiver 57 is connected to beam port 49, a second specific plurality of signals will be received from a second specific direction. This design applies for each of the remaining receivers 58-60M. The angles of the specific RF signals received are determined from the length of the individual fibers of network 46 that connect optical dividers 35-39N to optical combiners 40-44M. Each of the fibers act as a time delay device to separately delay the RF signals from each of the antenna elements 20-24N. The goal is to collect each of the individual RF signals at a common point simultaneously. The network of optical fibers 46 is designed to deliver the sample of each of the RF signals received from each antenna element 20-24N to each of the optical combiners 40-44M. Suppose the waveform 10 illustrated in Figure 1 arrives at an angle 0 (where ϑ = 45 ). The RF signal of waveform 10 would be intercepted by the antenna elements 11-15 at different times. If the RF signal is intercepted by antenna element 15 prior to being intercepted by antenna elements 11 to 14, the optical fibers of network 46 extending between the divider and combiner associated with antenna element 15 will be longer than all the other optical fibers. This design permits the RF signal received by antenna element 15 to be delayed for a longer period. Then one of the fibers extending from each of the optical dividers 35-39N carrying a sample of the RF signal received at the particular angle ϑ by each antenna element 20-24N is routed to and combined at a common point. The common point is actually a plurality of common points comprised of optical combiners 40-44M. The output of each optical combiner 40-44M represents a signal arriving from a particular direction. This structure permits each of the beam ports 48-52M to concentrate on a specific beam direction. By generating a plurality of "M" simultaneous beams and by arranging the beams to slightly overlap, a continuous coverage is effected. Figures 6 and 7 are analogous to Figure 5. Figure 6 identified by the general reference character 300 illustrates a possible implementation of a transmit and receive capability using a common optical beamforming network. Also shown is a means of commutating a single transmitter and receiver among the plural beam ports. A transmitter is shown at 80 with a receiver shown at 82 in Figure 6. A plurality of antenna elements 84-87N are provided including a plurality of RF low noise transmit amplifiers 92-95N and a plurality of RF low noise receive amplifiers 96-99N. A plurality of modulated lasers 102-105N and a plurality of light photodiode demodulators 108-111N are connected to a plurality of optical divider-combiners 114-117N with, for example, antenna element 84 in line with divider-combiner 114 through the parallel paths of amplifier 96/modulated laser 102 and amplifier 92/demodulator 108 via one of a plurality of fiber optic "Y's" identified by 119 to 122N. Each of the divider-combiners 114-117N functions as a divider in the receiver mode but also serves as a combiner in the transmitter mode of operation. Each of the optical divider-combiners 114 to 117N are connected to one of a plurality of optical combiner-dividers 125 to 128M through a network of optical fibers 130. Conversely, each of the combiner-dividers 125 to 128M functions as a combiner in the receiver mode but also serves as a divider in the transmitter mode of operation. The network 130 shown in Figure 6 may be identical to the network 46 shown in Figure 5. A plurality of modulated laser diodes 132 to 135M and a plurality of photodiode demodulators 138-141M are respectively connected to a pair of beam selector switches 143 and 144 via a plurality of transmit beam ports 146 to 149M and a plurality of receiver beam ports 150 to 153M respectively. Transmitter 80 and receiver 82 are connected respectively to switches 143 and 144 while the optical combiner-dividers 125 to 128M are connected to the modulated laser diodes 132-135M and the demodulator photodiodes 138-141M via a plurality of fiber optic "Y's" 155-158M. The receiver mode of operation in Figure 6 operates in a similar manner as was described for Figure 5. The RF signal wavefront 10 is received by the antenna elements 84 to 87N and amplified by amplifiers 96-99N. The amplified RF signals modulate the conventional laser diodes 102 to 105N. In the receiver mode, the RF modulated light signal passes through the plurality of fiber optic "Y's" 119 to 122N to the "N" optical divider-combiners 114 to 117N which functions as optical dividers. A plurality of "M" simultaneous beams are formed as described in Figure 5 by the optical fiber delay network 130, the optical combiner-dividers 125 to 128M (which function as optical combiners) and the photodiode demodulators 138 to 141M which demodulate the combined phased optical signal. Switch 144 can be used to select the desired beam port if only single beam reception is desired. If simultaneous reception of multiple beams is desired, separate receivers can be connected to each beam port. In essence, the RF waveform 10 is converted from the radio frequency domain to the optical domain for beam forming purposes and then the optical signal is converted back to the radio frequency domain after beamforming. This results in a beamforming system which is lightweight and compact in size since the optical components (consisting of laser diodes, combiner/dividers, optical fibers and detector photodiodes) are very small and lightweight. Further, the beamforming system results in a very wide bandwidth capability for two reasons. First, the use of an optical carrier frequency and optical components intrinsically provide operating bandwidths which are much wider than are generally possible at radio or microwave frequencies. Second, the beamforming system described herein is a true time-delay system wherein the time delays provided by the optical fibers remain constant independent of radio or microwave modulating frequencies. Thus, the antenna and beamforming system provides not only a broad operating frequency range but also provides capability for distortion-free processing of signals having wide instantaneous bandwidth. The bandwidth of a phased array antenna system as described herein is limited only by the bandwidths of the RF and microwave components such as the RF radiator elements, RF amplifiers and their interface connections to the optical beamforming system and not by the optical beamformer. Monolithic gallium arsenide RF amplifiers currently available today, however, are capable of bandwidths of several octaves, Thus, the ultimate bandwidth limit is controlled by the antenna RF radiating elements. In the transmit mode of operation, the transmitter 80 delivers a desired RF waveform signal to one of the plurality of convention RF modulated laser diodes 132 to 135M via beam selector switch 143 and transmit beam ports 146 to 149M. The RF signal is modulated by the selected modulator 132 to 135M, converting the RF signal into a modulated light signal in the optical domain. The optical signal is then transmitted to the selected optical combiner-divider 125 to 128M via one of the fiber optic "Y's" 155 to 158M. The selected optical combiner-divider 125 to 128M functions as a divider and divides the light modulated signal into "N" light signals. The "N" light signals are transmitted through the optical fiber delay network 130 to the plurality of optical divider-combiners 114 to 117N which function as combiners in the transmit mode. The divider-combiners 114 to 117N transmit the "N" light signals to the plurality of demodulator photodiodes 108 to 111N which provide the RF waveform signal 10 to the plurality of transmit amplifiers 92 to 95N and to antenna elements 84-87N. Figure 7 identified by the general reference character 400 illustrates a transmit antenna implementation using the optical beamforming system. The transmission system of Figure 7 may be identical to the transmit portion of Figure 6 except that certain components have been omitted. The components that have been omitted are the receiver 82, the receiver amplifiers 95 to 99N, the modulator laser diodes 102 to 105N, the demodulator photodiodes 138 to 141M and the beam selector switch 144. The transmit system of Figure 7 is a special implementation of the transmitter-receiver (transceiver) of Figure 6. The transmit system of Figure 7 includes a plurality of antenna elements 160 to 164N connected to a plurality of RF power transmit amplifiers 168-172N. Each amplifier 168 to 172N is connected to one of a plurality of demodulator photodiodes 176 to 180N which are in turn each connected to one of a plurality of optical combiners 184 to 188N. Each of the plurality of optical combiners 184 to 188N is connected to a plurality of optical dividers 192 to 196M through a network of optical fibers 200. Each of the plurality of optical dividers 192 to 196M is in turn connected to one of a plurality of laser diode modulators 202-206M which are in turn each connected to one of a plurality of beam ports 208 to 212M connected within a transmit beam selector switch 216 in series with a trannmitter 218. The transmitter 218 provides an RF transmission signal to the transmit beam selector switch 216 which selects which of the plurality of beam ports 208 to 212M is connected to the plurality of antenna elements 160 to 164N. The selected beam ports 208 to 212M transmits the RF signal to the corresponding laser diode modulator 202 to 206M where the RF signal modulates the laser optical carrier frequency signal and delivers the modulated light signal to the corresponding optical divider of the "M" optical dividers 192 to 196M. The selected optical divider 192 to 196M divides the modulated light signal into "N" optical signals, one signal sample to be transmitted to each of the "N" optical combiners 184 to 188N via the network of optical fibers 200. The optical fibers at the output of divider 192 are 192-1, 192-2, 192-3 ....192-N individually connected to combiners 184,185,186 ....188N respectively. Further, dividers 193-196M are individually connected to the "N" optical combiners 184 to 188N via optical fibers 193-1 to 193-N, 194-1 to 194-N, 195-1 to 195-N and 196-1 to 196-N. Each of the "N" optical combiners 184 to 188N receives "M" optical fibers and combines the "M" light signal samples fromt the "M" optical fibers. Then each optical combiner 184 to 188N delivers a combined sample light signal to each of the photodiode demodulators 176 to 180N. Each demodulator 176-180N demodulates the combined sample light signal providing an RF signal which is amplified by the power amplifiers 168-172N and radiated by antenna elements 160 to 164N. Although the transmit system shown in Figure 7 with a single transmitter commutated among the several beam ports 208-212M is capable of generating only one single beam at a time, it is easily seen that the use of multiple transmitters, one at each beam port, would provide the capability of generating simultaneous multiple transmit beams if so desired. In the latter case, each of the transmitters could operate at a different frequency to enhance beam to beam isolation and selectivity. Further, it is evident that although the diagrams of Figures 5, 6 and 7 show a uniform amplitude weighting for the described beamforming system, special amplitude weightings are easily provided to yield beam patterns with low sidelobes by providing appropriate attenuators in the optical fiber lines to achieve optimal signal amplitude weightings on transmit and receive. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. While the above description of the optically controlled phased array has been illustrated for linear arrays providing multiple beams along one axis only, the basic principle can be readily applied to two axis beamforming antennas having various configurations such as planar, circular, cylindrical, spherical and conformal arrays. Such arrangements are considered to fall within the scope of this invention.

Claims: A radiant energy system comprising an antenna having a plurality of antenna elements (84,85,86....87N) in respect of radio frequency signals of different phases as a function of the angle of inclination of a wavefront at the antenna and a plurality of first conversion means (102,108;103,109;104,110;..;105N,111N) individually connected to the respective antenna elements and connected to second conversion means (132,138;133,139;134,140;...;135M,141M) by an arrangement of optical fibres (130) of different lengths defining sets of fibres, characterised in that the system comprises transmitter means (80) and receiver means (82) connected to the second conversion means (132,138;...135M,141M) so that beams are transmitted into, or received from, a particular number of predetermined directions, such number corresponding to the number of second (132,138;...135M,141M) conversion means and the directions being determined by the respective different lengths of optical fibres (130) in the sets of optical fibres, each of the first conversion means and the second conversion means comprising a light modulator (102,132;103,133;104,134;...;105N,135M) and a light demodulator (108,138;109,139;110,140;...;111N,141M) connected in parallel, each light modulator including a laser for producing an intensity modulated light output and each de-modulator including a laser light intensity demodulator, and in that the first conversion means are individually connected to amplifier means (92,96;93,97;94,98;...;95N,99N) while the first and second conversion means are coupled to the sets of optical fibres (130) through optical dividers-combiners (114,115,116,...117N) and optical combiners-dividers (125,126,127;...;128M), respectively, each first conversion means being coupled to a corresponding optical divider-combiner and each second conversion means being coupled to a corresponding optical combiner-divider while each optical divider-combiner is connected to all of the optical combiners-dividers by corresponding optical fibres and each optical combiner-divider is connected to all of the dividers-combiners by corresponding optical fibres, and in that the number of optical fibres of respective different lengths in the sets of optical fibres connected with the first conversion means corresponds to the number of first conversion means while the individual fibres of each set are coupled to the respective second conversion means, and in that the number of optical fibres of respective different lengths in the sets of optical fibres connected with the second conversion means corresponds to the number of second conversion means while the individual fibres of each set are coupled to the respective second conversion means, and in that corresponding optical fibres of the respective sets of fibres have different lengths so that when the system is operating as a receiver with the receiver means operative all the signals arriving at each of the light demodulators (138,139,140;...;141M) of the second conversion means arrive simultaneously and in phase for reception by the receiver means (82) connected to the light demodulators of the second conversion means through beam ports (150,151,152...153M) and so that when the system is operating as a transmitter with the transmitter means operative signals arriving at the light demodulators (108,109,110,...111N) of the first conversion means from the transmitter means (80) connected to the second conversion means through beam ports (146,147,148,...149M) arrive at different times and are out of phase so that RF signals applied to the antenna elements produce in respect of the transmitter means a plane wave propagated at the requisite angle. A radiant energy receiver and transmitter system as claimed in claim 1, characterised in that each of the plurality of optical dividers-combiners (114,115,116,...117N) provides an optical divider during the receive mode of operation of the system and provides an optical combiner during the transmit mode of operation of the system. A radiant energy receiver and transmitter system as claimed in claim 1 or 2, characterised in that each of the plurality of optical combiners-dividers (125,126,127,...128M) provides an optical divider in the transmit mode of operation of the system and provides an optical combiner in the receive mode of operation of the system. A radiant energy receiver and transmitter system as claimed in any one of claims 1 to 3, characterised in that a plurality of light splitters (119,120,121,...122N) are provided, each light splitter being connected between one of the plurality of optical dividers-combiners (114,115,116,...117N) and the parallel combination (102,108;103,109;104,110;...105N,111N) of light modulator and light demodulator of the first conversion means. A radiant energy receiver and transmitter system as claimed in any one of claims 1 to 4, characterised in that a plurality of light splitters (155,156,157;...;158M) are provided, each light splitter being connected between one of the plurality of optical combiners-dividers (125,126,127;...128M) and the parallel combination (132,138;133,139;134,140;...135M,141M) of light modulator and light demodulator of the second conversion means.

Inventors: CHAVEZ JOSEPH DAVID, CHAVEZ, JOSEPH DAVID
Applicants: INT STANDARD ELECTRIC CORP, INTERNATIONAL STANDARD ELECTRIC CORPORATION
Application year: 1987
Main classification: H01Q3
IPC codes: H01Q3