CN103414519B - Light control microwave beam shaper - Google Patents

Abstract

An optically controlled microwave beamformer comprising 2 ^N single-frequency DFB lasers with different wavelengths, 2 ^N electro-optical intensity modulators, 2 ^N x1 passive wavelength division multiplexers, optical fibers, 1x2 ^N optical beam splitters, 2 ^N fiber collimators, time-delay network modules, 2 ^N coupling lenses, 2 ^N photodetectors and 2 ^N low-noise amplifiers, wherein n is a positive integer greater than 2, and the present invention has high signal-to-noise ratio, It has the advantages of good dynamic characteristics, high delay precision, continuous adjustment, good stability, etc., and is convenient for expanding the scale of the system array.

Description

Optically controlled microwave beamformer

technical field

The invention relates to a broadband optically controlled phased array radar, in particular to an optically controlled microwave beamformer.

Background technique

The beamformer (BFN-Beam Forming Networks) is the core of phased array radar and smart antenna. It controls the phase difference or true delay difference of each microwave link in the array to make the radiation field of each microwave radiation source in the far field The specific direction of the interference is extremely large, and the purpose of energy directional emission (or reception) is achieved. Change the phase difference or true delay difference between microwave links to control the direction of the beam.

Beamforming, essentially processing multi-element reception (transmission) to obtain a specific pattern, is the premise and basis for good tactics and performance of modern radar and electronic countermeasure equipment.

The Optically Controlled Microwave Beamformer (abbreviated as OBFN) is a technology that combines Radio over Fiber (RoF) technology with Optically Controlled Phased Array Antenna (abbreviated as OPAA) technology. Among them, RoF technology uses optoelectronic devices to realize the modulation, transmission and frequency conversion of electrical signals, etc.; among them, optoelectronic devices and systems can solve traditional microwave problems due to their small size, light weight, low loss, anti-electromagnetic interference, large bandwidth, and high channel capacity. There are many problems in the millimeter wave system to meet the needs of future wireless communication systems; it can be applied to radio frequency signal transmission, remote antennas, wireless access and other fields; OPAA technology includes power distribution of broadband microwave signals, directional emission, etc., mainly used in smart antenna and phased array radar. The beamformer using a microwave phase shifter will have a beam tilt phenomenon when working in a broadband, while the beamforming network using a True Time Delay (TTD) can overcome the beam tilt effect in a broadband; early The TTD network is implemented with an electrical structure, which is bulky and susceptible to electromagnetic interference. With the development of wide-band, small-volume, light-weight optical devices and optical information processing technology, people began to seek ways to apply optics to solve the design of beamforming.

Traditional beamforming networks using phase shifters have beam tilt effects [see literature [1]MichaelY.Frankel and Ronald D.Esman,True Time-Delay Fiber-optic Control of anultrawideband Array Transmitted Receiver with Multibeam Capability]. The noise figure of the optical multi-beamformer of the spectrum light source is more than 30dB higher than that of the external modulation link using a single-frequency light source, which seriously affects the signal-to-noise ratio of the system and limits the dynamic range of the system. It is not suitable for the transmission of vector signals, etc. For occasions with higher requirements (see literature [2] Reconfigurable Optical Beamformer for Simplified Time SteeredArrays, US2002/0181874A1, Dec.5, 2002), so this system uses a single-frequency light source, and the signal modulation method adopts an external modulation method; the available beam The delay network part of the former mostly adopts the dispersion characteristics of the medium (see [3] Photonic dual RF beam reception of an X band phased array antenna using aphotonic crystal fiber-based true-time-delay beamformer, Harish subbaraman, Applied Optics , 47,6448,2008) and the time delay generated by the optical switch (see literature [2]Reconfigurable Optical Beamformer for Simplified Time Steered Arrays, US2002/0181874A1,Dec.5,2002; literature [4]Optical beam former for high frequency antenna arrays), For time-delay networks using dispersion characteristics, there are disadvantages such as difficult to effectively and quickly control beam scanning, slow beam scanning speed, slow response speed, low delay accuracy, poor real-time performance, and poor operability; For a 4x4 optical beamformer, the number of optical switches required is 16 to generate different delays, and the delay cannot be continuously adjusted. Using optical switches to form a delay array will result in high cost and complicated control structure. It can realize the scanning of some beams, and the practical value is not high;

Contents of the invention

The purpose of the present invention is to solve the deficiencies of the above-mentioned prior art, and provide an optically controlled microwave beamformer, which has the advantages of high signal-to-noise ratio, good dynamic characteristics, high delay precision, continuously adjustable, good stability, etc. Advantages, and it is easy to expand the scale of the system array.

Technical solution of the present invention is as follows:

An optically controlled microwave beamformer is characterized in that its composition includes 2 ^N single-frequency DFB lasers of different wavelengths, 2 ^N electro-optic intensity modulators, 2 ^N x1 passive wavelength division multiplexers, optical fibers, 1x2 ^N optical division Beamers, 2 ^N fiber collimators, time-delay network modules, 2 ^N coupling lenses, 2 ^N photodetectors and 2 ^N low-noise amplifiers, where n is a positive integer greater than 2, and the positions of the above components The relationship is as follows:

The output terminals of 2 ^N single-frequency lasers with different wavelengths are respectively connected to the optical signal input terminals of 2 ^N electro-optic intensity modulators, and the RF signal captured by the phased array radar array unit is connected to the electrical signal input terminals of the electro-optic intensity modulators, The output terminals of the 2 ^N electro-optical intensity modulators are respectively connected to the 2 ^N input terminals of the 2 ^N x1 passive wavelength division multiplexing device, and the output terminals of the 2 ^N x1 passive wavelength division multiplexing device are connected to One end of the optical fiber, the other end of the optical fiber is connected to the input end of the 1x2 ^N optical beam splitter, and the 2 ^N output ends of the 1x2 ^N optical beam splitter are respectively connected to the input ends of 2 ^N optical fiber collimators The output ends of the 2 ^N fiber collimators correspond to the 2 ^N input ends of the delay network module, which includes 2 ^N delay network units with adjustable optical path differences, each The output terminals of each time delay network unit are sequentially connected through a coupling lens, a photodetector and a low noise amplifier.

The time delay network module is composed of 45° angle right-angle prisms, and the number of right-angle prisms comprising the first right-angle prism group is respectively 2n-1, 2n-2, ... 2, 1, 0; the right-angle prisms of the second right-angle prism group The number of prisms is 0, 1, 2, ... 2n-1; the number of right-angle prisms in the third right-angle prism group is 2n-1, 2n-1, ... 2n-1; The prism group and the third right-angle prism group are arranged from top to bottom, and the hypotenuse of the right-angle prism in the second right-angle prism group is opposite to the hypotenuse of the right-angle prism in the third right-angle prism group and fixed on the same horizontal plane with an interval of 0 , the abscissa corresponding to the midpoint of the hypotenuse of the right-angled prism in the second right-angled prism group is consistent with the abscissa corresponding to the endpoint of the hypotenuse of the right-angled prism in the third right-angled prism group, and the hypotenuse of the right-angled prism of the first right-angled prism group is consistent with The hypotenuses of the right-angled prisms in the third right-angled prism group are opposite, the spacing is d, and the abscissa corresponding to the midpoint of the hypotenuse of the right-angled prisms of the first right-angled prism group is the endpoint of the hypotenuse of the right-angled prisms in the third right-angled prism group The corresponding abscissas are consistent, the first right-angle prism group is driven by the motor to adjust the distance d between the first right-angle prism group and the third right-angle prism group, and the incident parallel light beam first enters the corresponding right-angle prism of the third right-angle prism group , after the third right-angle prism group, the second right-angle prism group and the first right-angle prism group’s right-angle prism light return and the optical path delay compensation in the glass medium, it is output by the second right-angle prism group or the first right-angle prism group, and sent into the coupling lens.

The microwave signal RF sent by the phased array antenna array is input from the RF electrical signal input end of the electro-optical modulator, and the output light of the DFB laser is input to the optical signal input end of the EOM. Due to the electro-optic effect, the output beam of the EOM will be loaded With the information of the RF signal, 2 ^N channels of light wave signals modulated with RF signals are multiplexed onto one optical fiber through a dense wavelength division multiplexer, transmitted through the optical fiber, and separated by passive beam splitting devices at the far end The 2 ^N light wave signals, the 2 ^N light wave signals are then passed through the fiber collimator to change the fiber light into 2 ^N beams of free space light with the same intensity, and then sent to the 2 ^N prism groups of the delay network module to generate different Time delay; the parallel light containing 2 ^N wavelengths emitted by the prism group is coupled into the photosensitive surface of the photodetector by the lens; the detected signal is amplified and output by the low noise amplifier LNA. Continuous scanning of multiple beams in space can be realized by adjusting the relative position of the lens group;

The most basic principle of this device is the interference theory. The optical path difference between two adjacent beams after passing through the phased array antenna is d sinθ, where d is the spacing of the antenna array, and θ is the polarization angle (or azimuth angle) of the beam. . When the difference between the optical path difference and d·sinθ of the two beams transmitted in the prism group is an integer multiple of the wavelength, the interference is strengthened, and the azimuth angle of the beam can be adjusted according to the detected signal. Since the signal received by the phased array radar is on the order of GHz, the feasible operation is to make the two equal, that is, the optical path difference is zero;

Compared with the prior art, the present invention has the following advantages:

1. Although the existing optical multi-beamformer using a wide-spectrum light source has no beam tilt, the link noise is more than 30dB higher than that of a single-frequency optical link, which seriously affects the signal-to-noise ratio of the system and limits the dynamics of the system. range, it is not suitable for transmission of vector signals and other occasions that have high requirements for noise, and the stability of the signal of the wide-spectrum light source in the broadband range is lower than that of the single-frequency light source. Adjustment, it is convenient to adjust the gain balance of each channel;

2. The present invention uses the adjustable optical path difference as the time delay, which has higher delay precision and the function of continuously adjustable delay compared with other dispersion technologies, and can perform rapid and continuous scanning of the beam, and has a fast response speed , strong real-time performance, more suitable for the application of the actual field environment; compared with the use of optical switches to achieve delay, it can greatly reduce the cost of the system, reduce the structural complexity of the system, and achieve a wider range of beams and continuous azimuth angles The scanning has smaller delay error, the corresponding azimuth angle measurement error is smaller, and has higher practical value;

Description of drawings

Fig. 1 is the structural block diagram of optical beamformer device of the present invention

Fig. 2 is the spectroscopic technical solution adopted by the embodiment of the present invention

This method divides a beam of multiplexing beams into 4 beams, the purpose of which is to facilitate the generation of different time delays according to different light waves loaded with RF signals in the delay network later;

Fig. 3 is the schematic diagram of the optical delay of the delay network module embodiment of the present invention

detailed description

First please refer to Fig. 1, Fig. 1 is the structural block diagram of the optical beam former device of the present invention, as can be seen from the figure, the optically controlled microwave beam former of the present invention, its composition comprises 2 ^N single-frequency DFB lasers 101, 2 ^N different wavelengths 1 electro-optic intensity modulator 102, 2 ^N x 1 passive wavelength division multiplexer 103, optical fiber 104, 1 x 2 ^N optical beam splitter 105, 2 ^N fiber collimators 106, time delay network module 107, 2 ^N coupling lenses 108, 2 ^N photodetectors 109 and 2 ^N low-noise amplifiers 110, wherein n is a positive integer greater than 2, and the positional relationship of the above-mentioned components is as follows:

The output terminals of 2 ^N single-frequency lasers 101 with different wavelengths are respectively connected to the optical signal input terminals of 2 ^N electro-optical intensity modulators 102, and the RF signal captured by the phased array radar array unit is input via the electrical signal of the electro-optical intensity modulator 102 The output terminals of the 2 ^N electro-optical intensity modulators 102 are respectively connected to the 2 ^N input terminals of the 2 ^N x1 passive wavelength division multiplexing device 103, and the 2 ^N x1 passive wavelength division multiplexing The output end of the device 103 is connected to one end of the optical fiber 104, and the other end of the optical fiber 104 is connected to the input end of the 1x2 ^N optical beam splitter 105, and the 2 ^N output ends of the 1x2 ^N optical beam splitter 105 are respectively connected to The input ends of 2 ^N fiber collimators 106 are connected, and the output ends of these 2 ^N fiber collimators 106 are connected with the input ends of the time delay network 107, and the time delay network 107 includes 2 ^N road optical path differences An adjustable delay network unit, the output end of each delay network unit is connected through a coupling lens 108 , a photodetector 109 and a low noise amplifier 110 in sequence.

Referring to FIG. 3, FIG. 3 is a schematic diagram of the optical delay of the delay network module embodiment of the present invention, n=2 in the embodiment,

The 4-way time-delay network module 107 is made up of 45 ° angle right-angle prisms, including the number of right-angle prisms of the first right-angle prism group I respectively 3,2,1,0; the number of the second right-angle prism group I 0, 1, 2, 3 respectively; the number of right-angle prisms in the third right-angle prism group III is 3, 3, 3, 3 respectively; the first right-angle prism group I, the second right-angle prism group II and the third right-angle prism group III is set from top to bottom, the hypotenuse of the right-angle prism in the second right-angle prism group II is opposite to the hypotenuse of the right-angle prism in the third right-angle prism group III and fixed on the same horizontal plane with an interval of 0, the second right-angle prism The abscissa corresponding to the middle point of the hypotenuse of the right-angled prism in group II is consistent with the abscissa corresponding to the endpoint of the hypotenuse of the right-angled prism in group III of the third right-angled prism. The hypotenuses of the right-angled prisms in the right-angled prism group (Ⅲ) are opposite, and the distance is d, and the abscissa corresponding to the midpoint of the hypotenuse of the right-angled prisms in the first right-angled prism group I is the same as the oblique The abscissas corresponding to the endpoints of the sides are the same, the first right-angle prism group I adjusts the distance d between the first right-angle prism group I and the third right-angle prism group III under the drive of the motor, and the incident parallel beam first enters the third right-angle The corresponding right-angle prism of prism group III, after the light return of the right-angle prism of the third right-angle prism group III, the second right-angle prism group II and the first right-angle prism group I, and the optical path delay compensation in the glass medium, the second right-angle prism group II Or the output of the first right-angle prism group I is sent to the coupling lens.

By continuously stepping and adjusting the distance between the first prism group and the third prism group by the stepping motor, the scanning of the light waves modulated with RF signals can be realized, that is, the measurement of the RF signal amplitude and azimuth angle parameters can be realized; Adding some prisms to the prism group II for optical path delay is to eliminate the optical path difference generated by the transmission of each light wave in the prism, so that the optical path difference only depends on the distance d between the boundaries of prism group I and II and III; For a 2nx2n network, the numbers of right-angle prisms in the first prism group I, the second prism group II, and the third prism group III are 2n-1, 2n-2, ... 2, 1, 0 and 0, 1, 2, ... 2n- 1 and 2n-1, 2n-1, ... 2n-1;

The microwave signal RF received by the phased array antenna array is modulated by the electro-optic modulator 102 onto the outgoing light of the DFB laser 101, and the 4 channels of single-frequency optical carriers with a wavelength interval of 100 GHz are modulated with RF signals of different frequencies. The light wave signal of the RF signal is multiplexed onto one optical fiber through a dense wavelength division multiplexing (DWDM) device 103, transmitted through a length of optical fiber 104, and split by a passive splitter device (Splitter) 105 at the far end to obtain 4 separate beams. Then, the fiber optic light is transformed into free-space light through the fiber collimator 106, and then sent to the time delay network module 107 to generate different time delays; Coupled into the photosensitive surface of the photodetector 109; the detected signal is amplified by the low noise amplifier LNA110. By adjusting the relative position of the lens group 111, continuous scanning of multiple beams in space can be realized; the delay network module 107 uses integrated optical technology to realize an optical multi-beam delay network, which can realize precise adjustment and continuous change of the delay of each channel, and It is not sensitive to the temperature change of the environment, and can realize the measurement of RF signals at different azimuth angles, which is very suitable for the application in the actual battlefield environment.

In the time-delay network module, some prisms are added to the second prism group and the third group prism group to eliminate the time delay caused by the transmission of each group of light in the prism, so that the time delay is only determined by the path transmitted in the air medium;

To generate a delay of 23.92ps, then 2d/c=t,d=ct/2=3*10^8*23.92*10^(-12)/2=3.6mm; corresponding to an incident RF signal angle of 11.5°;

The resulting delay is 59.82ps, then d1=ct/2=3*10^8*59.82*10^(-12)/2=9mm; corresponding to 29.9°RF signal incident angle;

For module assembly and calibration, the prism group of group II (the lower group) is fixed and adjusted, and the prism group of group I is fixed on the same horizontal line (horizontal), and the vertical direction is continuously adjustable. The size of d in the vertical direction is adjusted by driving the motor, resulting in Continuously adjustable time delay, capable of detecting RF signals at different azimuth angles.

In this embodiment, the wavelength of the 4=2 ² -way single-frequency lasers we adopt is the standard channel specified by ITU, which is convenient to adopt the dense wavelength division multiplexing device DWDM with ITU channel spacing of 100 GHz; by selecting the number of channels of the wavelength division multiplexing device and Increasing the number of single-frequency light sources can easily expand the number of arrays, resulting in 16x16, 32x32 beamformers.

Claims (1)

1. a light control microwave beam shaper, is characterised by that its composition includes 2^NThe single-frequency laser (101) of individual different wave length, 2^NIndividual electro-optic intensity modulator (102), 2^NThe passive wavelength division multiplexer of x1 (103), optical fiber (104), 1x2^NSolve wavelength division multiplexer (105)、2^NIndividual optical fiber collimator (106), time-delay network (107), 2^NIndividual coupled lens (108), 2^NIndividual photodetector (109) With 2^NIndividual low-noise amplifier (110), wherein N is the positive integer of more than 2, and the position relationship of above-mentioned component is as follows:

2^NThe output of the single-frequency laser (101) of individual different wave length is respectively with 2^NThe optical signal of individual electro-optic intensity modulator (102) Input is connected, and the RF signal of phased-array radar array element capture sends into the signal of telecommunication input of electro-optic intensity modulator (102) End, described 2^NThe output of individual electro-optic intensity modulator (102) is respectively with described 2^NThe passive wavelength division multiplex device of x1 (103) 2^NInput is connected, and these are 2 years old^NOne end of the optical fiber (104) described in output termination of the passive wavelength division multiplexer of x1 (103), this optical fiber (104) another 1x2 described in termination^NSolve the input of wavelength division multiplexer (105), this 1x2^NSolve the 2 of wavelength division multiplexer (105)^N Output is respectively with 2^NThe input of individual optical fiber collimator (106) is connected, and these are 2 years old^NThe output of individual optical fiber collimator (106) and institute The input of the time-delay network (107) stated is connected, and this time-delay network (107) comprises 2^NRoad optical path difference adjustable time-delay network list Unit, the most coupled lens of the output (108) of each time-delay network unit, photodetector (109), by low-noise amplifier (110) output microwave signal；

Described time-delay network (107) is made up of 45° angle right-angle prism, including the right-angle prism number of the first right-angle prism group (I) Mesh is respectively 2n-1,2n-2 ... 2,1,0；The right-angle prism number of the second right-angle prism group (II) is respectively 0, and 1,2 ... 2n-1； And first right-angle prism group (I) right-angle prism number and the right-angle prism number of the second right-angle prism group (II) there is 2n-1 pair Answer 0,2n-2 correspondence 1 ... 2 corresponding 2n-3,1 corresponding 2n-2, the corresponding relation of 0 corresponding 2n-1, the 3rd right-angle prism group (III) The number of right-angle prism is respectively 2n-1,2n-1 ... 2n-1；First right-angle prism group (I), the second right-angle prism group (II) and Three right-angle prism groups (III) are arranged from top to bottom, the hypotenuse of right-angle prism and the 3rd right-angle prism in the second right-angle prism group (II) In group (III) hypotenuse of right-angle prism relative and longitudinally spaced be that 0 ground is fixed on same horizontal plane, the second right-angle prism group (II) end of the hypotenuse of right-angle prism in abscissa that in, the hypotenuse midpoint of right-angle prism is corresponding and the 3rd right-angle prism group (III) The abscissa that point is corresponding is consistent, straight in the hypotenuse of the right-angle prism of the first right-angle prism group (I) and the 3rd right-angle prism group (III) The hypotenuse of angle prism is relative, and spacing is d, and the horizontal stroke that the midpoint of the hypotenuse of the right-angle prism of the first right-angle prism group (I) is corresponding The abscissa that coordinate is corresponding with the end points of the hypotenuse of right-angle prism in the 3rd right-angle prism group (III) is consistent, the first described right angle Prism group (I) adjusts spacing d of the first right-angle prism group (I) and the 3rd right-angle prism group (III) under motor drives, incidence Collimated light beam first incides the corresponding right-angle prism of the 3rd right-angle prism group (III), through the 3rd right-angle prism group (III), second straight The right-angle prism light of angle prism group (II) and the first right-angle prism group (I) turn back and glass medium in light path compensation of delay after Exported by the second right-angle prism group (II) or the first right-angle prism group (I), send into coupled lens.