Phased array antenna with optical beamforming device.

p0001The invention relates to an array antenna according to the preamble of claim 1.

p0002The invention is particularly applicable to an antenna system for satellite communications and radar applications, the micro- and millimeter wave frequency range, which is increasingly as a (1 × N) - are realized or two-dimensional (MxN), active antenna arrays.

p0003An application of such antenna arrays are phased arrays for ground-based and airborne radar antennas whose aperture is formed by a few hundred to several thousand transmit / receive modules (T / R) modules with directly associated radiating elements.

p0004In conventional radar systems, the required, high transmit power generated centrally (eg by traveling wave tubes) and corresponding distributions (including any necessary slip rings) is transmitted to the antenna. The received signal of the antenna is transmitted via the same distribution network, which is usually formed as a waveguide structure or as a triplate structure, or a special receiving distribution to the receiver.

p0005Significant improvements to these conventional radar systems provide active antenna arrays ( "active phased arrays") with respect to their decentralized power generation in the so-called T / R modules. This results in low signal losses and a so-called soft breakdown characteristics (failsoft characteristic). Addition takes place immediately behind the radiating elements, a low-noise amplification of the received signals.

p0006The RF signals required settings for shaping and tilting 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.

p0007From US 4,258,363 is a "phased array" radar system is known which consists of a plurality of transmitter / receiver antenna elements (S / E-emitters). Each T / R emitter is connected to an associated transmitting / receiving module (T / R module). Each T / R module has an optical input, which via an optical waveguide, an optical signal is supplied which contain the transmission signal, at a frequency of 725 MHz, and the oscillator signal at a frequency of 750 MHz as a time-division multiplex signals. In each T / R module and transmit oscillator signal can be converted by a common photodiode and an electrical amplifier connected thereto into an electrical multiplex signal which is then split by an electrical diplexer in separate transmit and oscillator signal. These are each fed a quadruple frequency multiplier with downstream phase adjuster. There arise transmitting and oscillator signals having a frequency of 2.9 GHz, the transmitted (transmission signal) and a mixer (oscillator signal) are supplied to the demodulation of the received signal. The mixer in the demodulated reception electric signal is electrically amplified and supplied to an electro-optical modulator. This modulates the light emitted from a laser diode light into an optical receive signal. This as well as the optical transmitter / oscillator signal are preferably conducted via two separate optical distribution networks to a central evaluation unit.

p0008Such an arrangement produces disadvantageously uncontrollable error, eg phase error by the frequency multiplier, and allows no change in the amplitude adjustment (amplitude distribution).

p0009From US 4,814,773 a radar system with an array antenna is known in which each radiating element, a transmit / receive module is assigned (T / R) module. The transmission of the transmitting and / or receiving signals between a central processing unit and the T / R modules is effected by means of optical fiber, optical multiplexers and an optical wavelength division multiplexing.

p0010Here each T / R module is connected to an associated fiber optic cable directly to the central unit.

p0011The invention addresses the problem of providing a generic array antenna, which is reliable and inexpensive to manufacture, enables rapid and highly accurate changes in phase and / or amplitude assignment and which is particularly suitable for an airborne radar application.

p0012This object is achieved by the features specified in the characterizing part of patent claim 1. Advantageous embodiments and / or refinements are the subclaims.

p0013A first advantage of the invention is that between the central control unit (BSU = "<u>b</u>eam <u>s</u>teering <u>u</u>nit ") and the array antenna a tree and / or star-shaped optical waveguide structure is present, which is part of the control unit with a single semiconductor laser operated. Such optical waveguide structure can be produced inexpensively.

p0014A second advantage is that in the optical waveguide structure is a bidirectional data transmission of all signals in the time division multiplex method.

p0015A third advantage is that a digitally controllable T / R module control is available in each T / R module, with the phase and / or amplitude distribution of the entire antenna is highly accurate and quickly adjustable.

p0016A fourth advantage is that all the signals, particularly the transmission signal, the LO signal and the IF signal may be transmitted in their original frequency range via the light waveguide structure. This necessary electrical and / or optical mixers are avoided otherwise.

p0017A fifth advantage is that electro-optic and opto-electric devices that can be manufactured inexpensively as integrated III-V semiconductor devices, are provided in each T / R module.

p0018Further advantages result from the following description.

p0019The invention is explained in more detail below with reference to embodiments with reference to drawings schematically illustrated. FIG. 1 to FIG. 6 show block diagrams schematically shown to illustrate the invention.

p0020In one example the selected on-board radar system for an aircraft, signals at X-band, for example in the frequency range of 9.5 GHz to 10.5 GHz, a frequency center via a distribution network to the individual T / R modules or from these to a signal processing transmitted associated with a central receiver or antenna subsets receivers. The conventional distribution structure (s) for the x-band signals are advantageously replaced by optical fiber and their combination to an optical beam-forming network. Above all, single-mode optical fiber or distribution networks are used because of their low attenuation and dispersion values ​​at wavelengths of 0.8 microns to 1.55 microns. For optical distribution to the T / R modules, the radar typical transmission signal and LO signal (time division multiplexed for transmission and reception) by means of an electro-optical converter which is advantageously constructed as a so-called DFB laser modulated an optical carrier signal directly. In each of the T / R modules then takes place by means of an opto-electrical converter, which is advantageously implemented as a photodiode, the implementation of the transmit and LO signal in the microwave range as well as its preparation for radiation by the associated radiating element. In these implementations, the signal amplitude and phase information are preserved. During reception, various types of transmission, as are analog, digital or optical, or uni- and bi-directional beamforming networks applicable.

p0021The invention combines advantageous the favorable properties of the opto-electric and electro-optical converters for converting microwave signals, for example up to a frequency of 12 GHz, and the optical signal distribution and management, whereby a low-interference signal flow with low electrical losses and high mechanical flexibility is possible.

p0022An arrangement of an active antenna array is shown in FIG. 1 shown. The radar typical transmission signal for the case of transmission, and the LO (local oscillator) signal for the case of reception, both in the microwave range, for example at a frequency of 9 GHz, depending on the mode of operation (transmit or receive) on the frequency center of the radar system to a transmitting / receive switch supplied. The applied high-frequency analog signal is passed to a matching circuit for an electro-optical converter, advantageously a laser diode, for example, is formed as a so-called distributed feedback laser diode. The matching circuit is for minimum electrical losses and low noise, as well as to the required signal bandwidth, such as 7.5 GHz. to 10.5 GHz, optimized, wherein an additional network, the power supply of the electro-optical converter is achieved. The matching circuit for the RF signal (transmit or receive signal) and / or the network for the power supply is advantageously carried out in microstrip or coplanar technology. The generated by the laser diode optical beat signal, for example at a wavelength of 1550 nm is coupled into a central optical waveguide (LWL) of beamforming (beamforming) network. A registered pleister optical isolator prevents reactions from interfering reflected optical signals to the laser diode. The subsequent optical amplifier, for example, implemented as optical fiber amplifier or semiconductor optical amplifier, increases the level of the optical signal, which is then in an optical beam-forming network (optical splitter) distributes the form of lines (one dimensional array), or rows and columns (two-dimensional array) and the respective T / R modules is conducted via corresponding optical waveguides. Depending on the number of T / R modules in the antenna aperture a plurality of these optical amplifier to the inputs of the row or column distributions may be required. The optical beam-forming network is based on optical 1: 4 splitters connected in a star or tree structure via optical waveguides. The 1: 4 signal distribution is adapted to so-called macro-modules in each of which four T / R modules are combined in a common mechanical housing. To generate BITE (<u>b</u>uild <u>i</u>n <u>th</u>st) signals prove to optical 1: 5 Splitter beneficial, said fifth output for monitoring (monitoring) can be used for signal transmission.

p0023In each case, an output of an optical splitter (1: 4 or 1: 5) is connected via an optical waveguide with an associated T / R module, which with reference to FIG. 2 is explained in more detail.

p0024According to FIG. 2, the optical signals via optical fibers to the respective opto-electronic converter such as a photodiode, a T / R modules to be routed. Then, the optical signals are demodulated at the photodiodes of these transducers. The photodiodes are biased terms of DC voltage and to optimize the transmission characteristics (eg noise, insertion loss) adjusted high frequency technology. About the output-side RF line of matching network, eg with 50Ω impedance and executed in microstrip technology, resulting from the demodulation electric transmission and LO signals are fed to a monolithic, low-noise amplifier (LNA). The operating frequency range of 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 from 7.5 GHz to 8.5 GHz. It's limited to 7.5 GHz to 11.5 GHz bandwidth of the LNA has an advantageous effect on the noise characteristics of each T / R module. The amplified microwave signal is fed to a diplexer, which consists of the combination of two band-pass filter (BPF). One of the BPF is on the transmission signal, for example, 9.5 GHz to 10.5 GHz optimized, and the other on the LO signal, for example, 7.5 GHz to 8.5 GHz. This passive Diplexerstruktur thus enables easy, 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), alternatively with a throw (SPDT) switch, for example, in monolithic form executable because of the predetermined by the maximum operating frequency of 10.5 GHz mechanical T / R module width. The transmission signal then passes to a same for transmission and reception control path consisting of two switches (SPDT switch), an amplitude controller (eg executed as adjustable amplifier VGA) and a 6-bit phase shifter. The RF signal is weighted according to the antenna-technical requirements, such as beam shape, beam steering, etc., in amplitude and phase. After the required power amplification means of driver amplifier and power amplifier, preferably carried out in a balanced amplifier configuration, the transmission signal via a transmit / receive switch, for example a circulator, and a low pass filter (LPF) is supplied to the respective radiating element of the antenna array. The LPF and the high-pass characteristic of the radiating element, as set forth in waveguide technology, realize a band paßcharakteristik, which is optimized for the operating frequency range 9.5 GHz to 10.5 GHz.

p0025During reception, the incident electromagnetic radar signal reaches the arrangement of the radiating elements of the array. The respective RF signal in the X-band of a radiating element passes through the LPF, and the transmit / receive soft to a non-reflecting limiter. This protects the subsequent low-noise amplifier (LNA) plant against a large, disturbing reception level and through its non-reflective structure and the output of the power amplifier. Using the LNA, the received signal in the frequency range is amplified 9.5 GHz to 10.5 GHz, passes through the above-described control path (phase and amplitude weighting) to a band pass filter BPF (9.5 GHz-10.5 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 the respective T / R module.

p0026On each T / R module also a T / R module controller is present. This generates control signals St, which actuate the SPDT switch (transceiver switches) and also set the phasers and the amplitude controller according to the desired (antenna) diagram. The control of the T / R module control may be performed electrically by means of an electric control line network not shown for example. , It is particularly advantageous to transmit the control signals in coded digital form in time division multiplexing on the optical waveguide. The T / R module-controller receives a control input signal from the output of the low noise amplifier LNA in this case. This time-division multiplex method is hereinafter with reference to FIG. 6 explained in more detail.

p0027On each T / R module also a T / R Module (fine) power supply is present, with which for example generates and stabilizes the voltages for the described components.

p0028The T / R module according to FIG. 3 differs from that of FIG. 2 only in that, after the IF amplifier, an analog / digital converter is inserted for the IF range. Thus, the received signals (IF section) are available in digital form for further transmission and processing in the receiver (conventional radar) or more receivers (Adaptive Array).

p0029The 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 known electrical transmission types optical signal transmission is also possible. For this purpose, the analog or digital reception signals (IF range) (with a low laser threshold) used for the direct modulation of a laser diode and is coupled the resulting respective optical signal on an optical receiving special fiber optic distribution within the T / R modules. The required demodulation is performed by means of opto-electrical converters at the / the corresponding evaluation units (receivers).

p0030FIG. 4 shows an embodiment, wherein the reference to FIG. 1 described optical beamforming (beamforming) network is advantageously exploited by a bidirectional use. Thereby, the effort with respect to the optical beamforming network or the optical receiving distribution is minimized, in particular for an active antenna array. In accordance with the time-sequential radar operation are within a Radarzyklusses first initialization data from an existing in the radar beam forming unit ( "<u>B</u>eam<u>st</u>eering <u>U</u>nit ") transferred (BSU) to the individual T / R modules of one or two dimensional antenna array. The setting of the phase and amplitude controller according to the antenna technical requirements for the transmission and reception are transmitted and cached, for example in a a digital memory which is present in the T / R modules. meantime followed by the transmission of the transmitted signal, followed by the LO signal in the microwave range for conversion of the received signal to the IF range. After the a / D conversion and a corresponding caching the digital data can be retrieved in the fourth part of Radarzyklusses. Notwithstanding done by the architecture described in FIG. 1 here, the opto-electric conversion of the control signals for the T / R modules via an additional second laser diode (laser diode 2), with a corresponding matching circuit and bias network. the resulting optical signals via an optical coupler in the optical beam-forming network (FIG. 4) coupled and transmitted to the T / R modules.

p0031Alternatively, it is possible to omit the laser diode 2 and, instead, the (main) to modulate laser diode (For the transmission of the transmitting and / or LO-signal) electrically connected to a signal corresponding to the control signals (initialization signals), so that a time-division multiplexing method emitted corresponding optical signal is produced.

p0032It is advantageous for a T / R module according to FIG. 3 the illustrated there analog / digital converter ADC downstream of a digital latch. Thus, the present in digital form in the IF range reception signals can be stored in each T / R module.

p0033It is advantageous that in Figures 2 and 3 characteristic with the optoelectric transducer arrangement in each module through an electro-optic transmitter / receiver arrangement according to FIG. 5 to replace. The arrangement includes a first electric branch consisting of the opto-electric converter, already described with reference to FIGS. 2, 3 (Photo Diode), an associated electrical matching network, and the downstream low-noise amplifier LNA, the transmitter or LO signal is produced at its output.

p0034The described analog IF signal (received signal) (FIG. 2) or the corresponding digital IF signal (FIG. 3), which has been cached advantageously be applied to 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 coupled using eiens optical directional coupler at leading to each module optical waveguide.

p0035Such an arrangement according to FIG. 5 is advantageously completely as opto-electrical component in an integrated form as a semiconductor device, preferably in so-called III-V technology, such as GaAs technology, to manufacture. The illustrated optical signal and guides the optical directional coupler by known per se diffusion and doping processes are produced. It is advantageous that the electro-optical converter has a low as possible, so-called laser threshold, so that a direct modulation is possible. The resulting optical signal is then fed via the optical directional coupler in the optical beamforming network is demodulated in the central unit (BSU) and evaluated there in a known manner.

p0036In the optical waveguides of the beamforming (beamforming) network according to FIG. a bidirectional optical data transmission in the above-mentioned time-division multiplex mode 4 is then possible.

p0037FIG. 6a shows a schematically illustrated optical time division multiplexed signal for a radar cycle n (n = integer) for a single T / R module. The time division multiplex signal contains a transmission signal, which is, for example, 1.0 microseconds long, and the example includes a transmitting frequency from a frequency range from 9.5 GHz to 10.5 GHz. Subsequent to the transmission signal, for example, a n for the subsequent radar cycle + 1 needed initialization message is sent out in a time period of 0.5 microseconds. That of 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) as well as an identifier for identification of the associated T / R module. Such initialization message is from the T / R module controller (Fig. 2, 3) is evaluated and then generates the corresponding control signals. Subsequent to the initialization message from the T / R module a herrührendes from the radar cycle n-1 reception signal, for example, is transmitted during a time of approximately 0.5 microseconds. The received signal preferably contains in digital form IF received data relating to the contained in the radar cycle n-1 initialization message for the radar cycle n. Subsequently, to the transmission of the digital IF received data in a time 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 for 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 begins with the transmission of the corresponding transmit signal n + 1st

p0038In FIG. 6b is shown another alternative, time division multiplexed signal for a single T / R module. The TDM signal contains a so-called initialization message, which is for example a total of about 0.5 microseconds long. That of 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) as well as an identifier for identification of the associated T / R module. Such initialization message is from the T / R module controller (Fig. 2, 3) is evaluated and then generates the corresponding control signals. Subsequent to the initialization message the transmission signal is emitted, which is, for example, 1.0 microseconds long, and the example includes a transmitting frequency from a frequency range from 9.5 GHz to 10.5 GHz. Subsequent to the transmission signal, for example, the transposing of the received signal required LO signal, which for example includes a frequency from a frequency range from 7.5 GHz to 8.5 GHz is transmitted to the T / R module in a period of 5 microseconds. This is followed by a period of about 0.5 microseconds to transfer the digital form of the present initialization message addressed by the T / R module receive IF data.

p0039These are summarized in the optical beamforming network is transmitted to the central unit (BSU) and coupled there via an optical coupler to a central photodiode in front of the optical isolator (with a corresponding matching circuit and bias network). The optical signal is detected (demodulated) and is supplied as a conventional data telegram to a receiver and evaluated in a known manner.

p0040With the described arrangement it is possible within an antenna array, which may contain a plurality, eg 1000, the transmitting / receiving antenna elements and associated T / R modules, all T / R modules on the basis of FIG. 1 and / or FIG. couple 4 described fiber optic network, and then only a single optical fiber for connection to the associated CPU to use (BSU). Otherwise required RF transmission lines, such as coaxial cables and / or waveguide, are not needed in an advantageous manner.

p0041The in the central processing unit (BSU) allows existing laser diode, via optical fiber a plurality of mutually spatially remote radar sensors, eg so-called multi-surface arrangements and / or so-called back / forward radar sensors (up / down) sensors and / or so-called look-up / look down radar sensors (up / down directional sensors) to pair inexpensive and reliable in an advantageous manner.

p0042It is also possible that of the present in the central unit photodiode (FIG. 4) generated electric reception signal multiple (reception) supply evaluation, creating a very versatile and fast evaluation (parallel processing) is made possible.

p0043The invention is not limited to the disclosed embodiments but, mutatis mutandis applicable to other, for example to an antenna array for a much lower frequency range.