Phased array antenna with optical beamforming device

0001The invention relates to an array antenna according to the preamble of claim 1.

0002The invention is particularly applicable to a Antenna system for satellite communications and radar applications in the micro and millimeter wave frequency range, increasingly as a (1 × N) - or two-dimensional (MxN), active antenna arrays can be realized.

0003An application of such antenna arrays are phased Antennas for ground-based and airborne radars, the aperture through several hundred to several thousand transmit / receive modules (T / R) modules with directly associated radiating elements is formed.

0004In conventional radar systems, the required, high transmit power generated centrally (eg by traveling wave tubes) and corresponding distributions (including any necessary slip rings) to the transmit antenna. The received signal of the antenna is via the same distribution network, the most as a waveguide structure is formed or as a tri-plate structure, transfer or a special reception distribution to the recipient.

0005Significant improvements to these conventional Radar systems provide active antenna arrays ( "active phased arrays ") with respect to its decentralized Power generation in the so-called T / R modules. Thereby cause some slight signal loss and a so-called gentle failure characteristic (failsoft characteristic). Addition takes place immediately behind the radiating elements low noise amplification of the received signals.

0006The RF signals required settings for molding and pivoting of the antenna pattern, polarization types and calibration for the transmission and reception by means of phase and amplitude controllers in the T / R modules.

0007From US 4,258,363 is a "phased array" radar system known which of a plurality of transmitter / receiver antenna elements (S / E lamps) is. Each S / E lamps is coupled to an associated transmitting / receiving module (T / R module) connected. Each T / R module has an optical input, which via an optical waveguide, an optical signal is supplied, which signal the transmission, at a Frequency of 725 MHz, and the oscillator signal at a Frequency of 750 MHz included as time-division multiplex signals. In each T / R module will transmit and oscillator signal by a common photodiode and a connected thereto electrical amplifier in an electric Multiplex signal is converted, which subsequently by a electrical diplexer in separate transmit and oscillator signal be split. These are each a Quadruple frequency multiplier with downstream phase adjuster supplied. There arise transmitting and oscillator signals at a frequency of 2.9 GHz, the emitted are (broadcast signal) or a mixer (oscillator signal) are supplied to the demodulation of the received signal. The demodulated in the mixer electrical reception signal is electrically amplified, and an electro-optical modulator supplied. This modulates the by a laser diode emitted light to an optical receive signal. This and the optical transmitter / oscillator signal are preferred via two separate optical distribution networks to central evaluation conducted.

0008Such an arrangement produces uncontrollable disadvantageously Error, eg phase error by the frequency multiplier, and makes no change in the amplitude adjustment (Amplitude distribution).

0009From US 4,814,773 is a radar installation with an antenna array is known in which each radiating element a is associated with transmission / reception module (T / R module). The Transmission of the transmitting and / or receiving signals between One central unit and the T / R modules is done using of optical fiber, optical multiplexers and a optical wavelength-division multiplexing method.

0010Here each T / R module is associated with a Lichtwel-optic cables directly connected to the central unit.

0011is from the US Patent 4,885,589 a generic array antenna known that over via a central laser arrangement a first optical beam-forming network modulated transmission signals or the unmodulated oscillator signal to the T / R modules passes, which in the transmission mode, the optical transmission signal means controlled phase shifter and amplifier to an associated Radiating element passes. In the receive mode, the above the received through the radiating element radar signal via controlled Receiving amplifier and phase shifter and processed by means of the unmodulated signal modulator and a modulator converted into an optical-modulated received signal that a second optical beam forming network of a remote Evaluation unit is supplied. The control of the T / R modules via a separate control line structure. This arrangement an array antenna proves very costly as and very vulnerable in the interconnect structure.

0012The invention is based on the object, a generic specify array antenna that reliably and cost is produced, the fast and precise changes Phase and / or amplitude and which in particular allows assignments is suitable for airborne radar application.

0013This object is achieved by the characterizing part of Claim 1 specified characteristics. Advantageous embodiments and / or further developments are in the dependent claims.

0014A first advantage of the invention is that between the central control unit (BSU = "<u>b</u>eam <u>s</u>teering unit ") and the array antenna a tree and / or star-shaped optical waveguide structure is present, the part of the control unit is operable with a single semiconductor laser. such Optical waveguide structure can be produced inexpensively.

0015A second advantage is that in the light waveguide structure bidirectional data transmission of all signals takes place in time multiplex method.

0016A third advantage is that in each T / R module a digitally controllable T / R module control available is, with the highly accurate and fast phase and / or Amplitude distribution of the entire antenna is adjustable.

0017A fourth advantage is that all the signals, particularly the transmission signal, the LO signal and the IF signal in the original frequency range via the light waveguide structure be transmitted. This otherwise necessary electrical and / or optical mixer avoided.

0018A fifth advantage is that in each T / R module electro-optical and opto-electrical components, the cost as an integrated III-V semiconductor devices can be prepared, are present.

0019Further advantages result from the following description.

0020The invention will in the following by means of embodiments with reference to schematically illustrated Drawings explained in more detail. FIG. 1 to FIG. show 6 schematically illustrated block diagrams for explaining the Invention.

0021In an example of the selected on-board radar system for a Plane, signals in the X-band, for example, in the frequency domain of 9.5 GHz to 10.5 GHz, a frequency of about Central a distribution network to the individual T / R modules or of this to a signal processing with a central Receiver or antenna subsets associated receivers transfer. The conventional distribution structure (s) for the X-band signals are advantageously by Optical fiber and their combination to an optical Beamforming network replaced. This primarily single-mode Optical waveguide or distribution networks for their low attenuation and dispersion values ​​at wavelengths 0.8 <i>μ</i>m to 1.55 <i>μ</i>m used. For optical distribution to the T / R modules, the typical radar transmit signal, and LO-signal (in the time division multiplexing for transmission and reception) by means of an electro-optical converter, the advantageous is formed as a so-called distributed feedback laser, an optical modulated carrier signal directly. In each of the T / R modules is then carried out by means of an opto-electrical converter which advantageously embodied as photodiode, the implementation the transmission and the LO signal to the microwave range and its preparation for radiation by the associated Radiating element. In these signal conversions remain Amplitude and phase information obtained. During reception, Various types of transmission, such as analog, digital or optically, or uni- and bidirectional Beamforming networks applicable.

0022The invention combines the advantageous properties advantageous of opto-electrical and electro-optical converters for the implementation of microwave signals, eg up to a frequency of 12 GHz, and the optical signal distribution and management, creating a low-interference signal flow at low electrical losses and a high mechanical Flexibility is possible.

0023An arrangement of an active antenna array is shown in FIG. 1 shown. The radar typical transmission signal for the transmission case and the LO (local oscillator) signal for receiving case both in the microwave range, for example at a frequency of 9 GHz, depending on the operating mode (sending or receiving) of the frequency of the radar system to a central Transmitting / receiving change-over supplied. The signal, high-frequency analog signal is fed to a matching circuit for electro-optical converter, advantageously a laser diode, for example, as so-called DFB laser diode is trained. The matching circuit is minimal electrical losses and low noise, as well as on the required signal bandwidth, such as 7.5 GHz. to 10.5 GHz, optimized, with an additional network reaches the power supply of the electro-optical converter becomes. The matching circuit for the RF signal (transmitting or Received signal) and / or the network for the power supply is advantageously in microstrip or coplanar executed. The from the laser diode generated optical beat signal, for example at a wavelength of 1550 nm, is in a central optical waveguide (LWL) of beamforming (beamforming) network coupled. prevents A registered pleister optical isolator Repercussions of interfering reflected optical Signals to the laser diode. The subsequent optical Amplifiers, eg designed as a fiber optical amplifier or semiconductor optical amplifier increases, the Level of the optical signal, the optical then in a Beamforming network (optical splitter) linearly (One-dimensional array) or lines and columns (Two-dimensional array) and distributed to the respective performed T / R modules via corresponding optical waveguides becomes. Depending on the number of T / R modules in the antenna aperture may have a plurality of these optical amplifiers at the inputs of the row or column distributions required. The optical beam forming network based thereby to optical 1: 4-dividers or in a star Tree are connected via fiber optic cable. The 1: 4 signal division is called macro modules adapted 4 in which each T / R modules in a common mechanical housing are summarized. to produce of BITE (<u>b</u>uild <u>i</u>n <u>t</u>est) signals turn out optical 1: 5 Splitter beneficial, said fifth output for monitoring (Monitoring) are used for signal transmission can.

0024In each case, an output of an optical splitter (1: 4 or 1: 5) is via an optical waveguide with an associated T / R module coupled what. With reference to FIG 2 explained becomes.

0025According to FIG. 2, the optical signals via optical fibers to the respective opto-electronic converter, for example, a photodiode, a T / R Modules passed. To the Photodiodes these transducers are then the optical signals demodulated. The photodiodes are equal in terms of voltage biased and to optimize the transmission characteristics (Eg noise, insertion loss) high frequency technology adapted. About the output side RF line of matching network, eg with 50Ω impedance and executed in microstrip technology, are resulting from the demodulation electrical Transmission and LO signals a monolithic, low-noise Amplifier (LNA) is supplied. The operating frequency range this LNAs here includes, for example 7.5 GHz to 11.5 GHz, corresponding to the transmission frequency range of 9.5 GHz to 10.5 GHz and the LO frequency range of 7.5 GHz to 8.5 GHz. It affects the 7.5 GHz to 11.5 GHz limited bandwidth of the LNA advantageous to the Noise characteristics of the respective T / R module. The amplified microwave signal reaches a diplexer the combination of the two band-pass filter (BPF) is. One of the BPF is on the transmission signal, for example 9.5GHz to 10.5 GHz, optimized, the other on the LO signal, eg 7.5 GHz to 8.5 GHz. This passive Diplexerstruktur thus allows a simple, reliable Signalauftrennung with very low insertion attenuation, eg less than 1 dB, and a small footprint. This Signalauftrennung is according to the operating mode of the Radar system (sending or receiving) as an alternative to a Throw (SPDT) switch, for example, in monolithic form due to the highest by the operating frequency of 10.5 GHz predetermined mechanical T / R module width, executable. The Transmission signal then passes to transmit and Receiving case same control path consisting of two switches run (SPDT switch), an amplitude controller ( for example, as an adjustable amplifier VGA) and a 6-bit Phaser. The RF signal is thereby correspondingly the antenna-technical requirements, for example, beam shape, Beam steering, etc., weighted in amplitude and phase. After the required power amplification means of driver amplifier and power amplifier, preferably executed in a balanced amplifier configuration, the Transmission signal via a transmit / receive switch, for example a Circulator, and a low pass filter (LPF) of each Radiating element of the antenna array fed. The TPF and performed the highpass characteristic of the radiating element, eg in waveguide technology, realizing a bandpass characteristic, on the operating frequency range 9.5GHz is optimized to 10.5 GHz.

0026During reception, passes the incident electromagnetic Radar signal on the arrangement of the radiating elements of the Arrays. The respective RF signal in the X-band of the radiating element passes via the TPF and the transmit / receive soft to a non-reflecting limiter. This protects the subsequent low-noise amplifier (LNA) against too high, disturbing reception level and by his non-reflective structure and the output of the power amplifier. By means of the LNAs, the receiving signal amplified in the frequency range 9.5 GHz to 10.5 GHz, passes via the described control path (phase and Amplitude weighting) to a band pass filter BPF (9.5 GHz10,5 GHz). This band-limited signal and the LO signal (Diplexer and LO driver amplifier) ​​feed a monolithic mixer. The resulting IF signal, for example with a center frequency of 2 GHz, then stands for a Low pass filter (LPF) and an IF amplifier at the output of each T / R module.

0027also is on each T / R module a T / R module control available. This generates control signals St, which the press SPDT switch (transceiver switches) and Also the phaser and the amplitude controller according to the desired (antenna) Set chart. The control of the T / R module controller may, for example electrically be effected by means of a not shown electric Control cable network. particularly advantageous However, the control signals in coded digital form in the time-division multiplex method via the optical waveguide to transfer. The T / R module controller receives in this case a control input signal from the output of the low noise Amplifier LNA. This time-division multiplexing method will be reference to FIGS. 6 explained in more detail.

0028also has a T / R Module (fine) on each T / R module power supply available, with which, for example, the electrical generates voltages for the components described and are stabilized.

0029The T / R module according to FIG. 3 differs from that of FIG. 2 only in that, after the IF amplifier an analog / digital converter to the IF range is inserted. Thereby, the reception signals (IF section) in digital form for further transmission and processing in the receiver (conventional radar) or multiple receivers (Adaptive Array) available.

0030The signal transmission in the receiving case according to FIG. 2 via coaxial cable and / or distributions in Stripline form or according to FIG. 3 via a Data bus. In addition to these conventional and per se known electrical transmission types is also an optical signal transmission possible. For this purpose, within the T / R modules, the analog or digital reception signals (IF section) for direct modulation of a Laser diode (low lasing threshold) used and the resulting respective optical signal to specific FO an optical receiving distribution coupled. The required Demodulation is performed by optoelectrical Converter at the / the corresponding evaluation units (receivers).

0031FIG. 4 shows an embodiment, wherein the reference of FIG. 1 described optical beamforming (beamforming) network by a bidirectional use is advantageously exploited. This is the effort with respect the optical beam forming network and the optical Receiving distribution minimized, particularly for a active antenna array. According to the time-sequential Radar operation are within a Radarzyklusses first the initialization of a in the radar system existing beam-shaping unit ( "Beam Steering Unit ") (BSU) to the individual T / R modules of one or transmitted two-dimensional antenna array. Here are the setting of the phase and amplitude controller according to the technical requirements for the antenna Transmission and reception transmitted and cached, for example in a digital memory in the T / R modules, is available. Time then takes place Transmission of the transmitted signal, followed by the LO signal in the Microwave range for conversion of the received signal in the IF section. After A / D conversion and a corresponding Caching can in the fourth part of the Radarzyklusses the digital data is retrieved. Notwithstanding the in FIG. Architecture 1 described are Here the optical-electrical conversion of the control signals for the T / R modules via an additional second laser diode (Laser diode 2), with corresponding matching circuit and Bias network. The resulting optical signals via an optical coupler in the optical beam-forming network (FIG. 4) and coupled to the T / R modules transfer.

0032Alternatively, it is possible to omit the laser diode 2 and instead, the (main) laser diode (for transmission of transmitting and / or LO-signal) electrically connected to a Signal corresponding to the control signals (initialization signals) to modulate, so that a time-division multiplexing method emitted corresponding optical signal is produced.

0033It is advantageous for a T / R module according to FIG. 3 the illustrated there analog / digital converter ADC a digital latch downstream of. This may in each T / R module which are present in digital form in the IF range Received signals are cached.

0034It is advantageous that with in the figures 2 and 3 optoelectric Converter characteristic arrangement in each module to the invention by an electro-optical transmit / receive arrangement FIG. 5 to replace. The arrangement includes a first electrical branch, consisting of the already using the Fig. 2, 3 described opto-electrical transducer (photodiode), an associated electrical matching network and the downstream low-noise amplifier LNA, at its Starting the transmission or LO signal is produced.

0035The described analog IF signal (received signal) (FIG. 2) or the corresponding digital IF signal (FIG 3)., The was advantageously buffered to be laid the electrical input of the second branch. This includes an electrical matching network and a downstream electro-optical transducer, such as a laser diode. The documents belonging to the transducers optical signal guides are using eiens optical directional coupler to coupled leading to each module optical waveguide.

0036Such an arrangement according to FIG. 5 is advantageously fully as opto-electrical component in integrated Form as a semiconductor device, preferably in so-called III-V technology, such as GaAs technology, to manufacture. there the illustrated optical signal and guides the optical coupler by known per se diffusion and doping processes produce. It is advantageous to that the electro-optical transducer as possible a low so-called laser threshold has, so that a direct Modulation is possible. The resulting optical signal is then via the optical directional coupler in the optical Beamforming network fed, in the central unit demodulates (BSU) and there in a known manner evaluated.

0037In the optical waveguides of the beamforming (beamforming) network according to FIG. 4 is then a two-way optical data transmission in the above-mentioned Time multiplex operation possible.

0038FIG. 6a shows a schematically illustrated optical Time division multiplexed signal for a radar cycle n (n = integer Number) for a single T / R module. The time division multiplex signal contains a transmission signal, which is for example 1.0 microseconds long and as a transmission frequency of a frequency range of 9.5 GHz to 10.5 GHz contains. Subsequent to the transmission signal is for example in a period of 0.5 microseconds n for the subsequent radar cycle + 1 needed Initialization message sent. Launched by the Beam-shaping unit (BSU) emitted initialization message contains in digital form at least data terminating the SPDT switch, phase and Amplitude controller (FIG. 2, 3) as well as an identifier for identifying of the associated T / R module. such a Initialization message is from the T / R module controller (FIG. 2, 3) are evaluated and then the corresponding generates control signals. Subsequent to the initialization message is transmitted from the T / R module of the Radar cycle n-1 herrührendes received signal, eg during a time of about 0.5 <i>μ</i>s transfer. The received signal contains preferably present in digital form IF received data relating to the radar in the cycle n-1 Initialization message contained in the radar cycle n relate. Subsequent to the transmission of the digital IF received data occurs in a period of about 5 microseconds, the transmission of the LO signal to the T / R module, which is needed for conversion of the received signal, and the example, a frequency of a frequency range of 7.5 GHz contains up to 8.5 GHz. There now follows the transmission of the Time division multiplexed signal for the radar cycle n + 1, which is provided with the transfer of the associated transmission signal n + 1 starts.

0039In FIG. 6b is alternatively another time-division multiplex signal shown for a single T / R module. The time division multiplex signal contains a so-called initialization message, the example a total of about 0.5 microseconds long is. Launched by the beam-shaping unit (BSU) emitted Initialization message contains in digital form at least Data for setting the SPDT switch and the Phase and amplitude controller (FIG. 2, 3) and an identifier for identification of the associated T / R module. On Such initialization message is from the T / R module controller (FIG. 2, 3) are evaluated and then the corresponding generates control signals. Subsequent to the initialization message the transmission signal is emitted, the eg 1.0 microseconds is long and as a transmission frequency of includes a frequency range of 9.5 GHz to 10.5 GHz. At the transmission signal is then for example in a time period of 5 microseconds, the transposing of the received signal required LO signal, for example, a frequency of a frequency range contains from 7.5 GHz to 8.5 GHz, the T / R module transfer. This is followed by a Period of approximately 0.5 microseconds of the by Initialization message mentioned T / R module a Transmission of digital form present IF received data.

0040These are summarized in the optical beam forming network, transmitted to the central unit (BSU) and before there the optical isolator has an optical directional coupler a central photodiode (with a corresponding matching circuit and bias network) coupled. The optical signal is detected (demodulated) and as a conventional Data telegram delivered to a recipient, and there in a known Way evaluated.

0041With the described arrangement it is possible within an antenna arrangement, a plurality, for example, 1000 Transmitting / receiving antenna elements and associated T / R modules may contain all T / R modules on the basis of FIG. 1 and / or FIG. 4 described to Fiber Optic Network couple and then only a single optical fiber for connection to the associated central processing unit (BSU) to use. Otherwise necessary RF transmission lines, eg Coaxial cables and / or waveguide, are advantageously Manner not needed.

0042The in the central processing unit (BSU) existing laser diode enables spatially via optical waveguides several mutually remote radar sensors, eg so-called multi-surface arrays and / or so-called back / forward radar sensors (Forward / reverse sensors) and / or so-called look-up / look down-range radar sensors (up / down directional sensors), in advantageously inexpensive and reliable coupling.

0043It is also possible that the in the central unit existing photodiode (FIG. 4) generated electric receiving signal multiple (reception) supply evaluation, creating a very versatile and fast evaluation (Parallel processing) is made possible.

0044The invention is not limited to the described embodiments restricted but apply mutatis mutandis to other, eg on an antenna array for a much lower frequency range.