KR101236598B1 - Phased array antenna using dispersion compensating fiber and tunable multi-wavelength laser - Google Patents

Abstract

A phased array antenna is disclosed. A phased array antenna according to an embodiment of the present invention is an electro-optic modulator for modulating an electrical signal into an optical signal, a dispersion compensation optical fiber for causing the optical signal modulated signal to have a different delay time according to the wavelength, and fixed within the wavelength band. A thin film filter and a fixed time delay line for constituting the optical delay line, an optical receiver for demodulating the modulated optical signal into an electrical signal, and an antenna element for radiating the demodulated electrical signal with a linearly increasing delay time. Include. Accordingly, the phased array antenna can have a simple structure, thereby reducing costs.

Description

Phased array antenna using distributed compensation fiber and variable multi-wavelength laser {PHASED ARRAY ANTENNA USING DISPERSION COMPENSATING FIBER AND TUNABLE MULTI-WAVELENGTH LASER}

The present invention relates to a phased array antenna, and more particularly, to a structurally simple and stable phased array antenna using a distributed compensation optical fiber and a variable multi-wavelength laser.

Currently wireless communication technology is very useful because of the convenience of the portable terminal and the use in the mobile. However, the future wireless communication technology has a problem in that the performance degradation due to the multipath fading due to the increase in bandwidth is further increased and the visible distance is greatly reduced due to the increase in the carrier frequency. The problem is solved by the application of phased-array antenna (PAA) technology. In particular, the third-generation mobile communication systems such as China, Taiwan, and Japan have already commercialized the phased-array antenna technology to verify its performance and are currently providing trial services using the same. Phased array antenna technology is advantageous in that beam-forming using phased array antenna technology is advantageous in terms of price and transmit / receive signal power even though hardware complexity and power consumption are increased.

Phased array antennas for beam-forming provide high directionality and high gain and can perform a variety of beam pattern agileness. To adjust this antenna, a true-time delay (TTD) system is applied. The TTD system is an important technique for phase shifters that allows the beam radiation angle to be adjusted at a speed that adjusts the electronic circuits without moving the array antenna mechanically. With the recent expansion of wireless communication technology, problems of radio wave interference, fabrication cost, hardware stability, reliability, and weight of TTD systems have been highlighted. In addition, the electric beam-forming technology down-converts the high RF frequency to baseband to adjust the phase, which increases the volume and hardware cost of additional components.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a phased array antenna capable of not only having a simple structure but also reducing costs accordingly.

A phased array antenna according to an embodiment of the present invention for achieving the above object comprises an electro-optic modulator for modulating the electrical signal into an optical signal; A dispersion compensation optical fiber for causing the signal modulated by the optical signal to have a different delay time according to a wavelength; A thin film filter for forming an optical delay line fixed in the wavelength band; An optical receiver for demodulating the modulated optical signal into an electrical signal; And an antenna for radiating the demodulated electrical signal with a regular delay time.

And a variable multi-wavelength laser for generating light having a variable wavelength, wherein the generated wavelength can be used as a carrier wavelength for the electro-optic modulator to modulate an electrical signal into an optical signal.

In addition, the multi-wavelength laser includes at least one filter, such as a Lyot-Sagnac filter, a Fabry-Perot filter, a uniform FBG filter, and a sampling FBG, and the at least one filter may vary the generated wavelength.

The multi-wavelength laser may include a polarization controller of a Lyot-Sagnac filter or a PZT of a Fabry-Perot filter, a strain or a temperature of a uniform FBG filter or a sampling FBG for causing the at least one filter to adjust the variation of the wavelength. The apparatus may further include a device for change.

The multi-wavelength laser also generates a wavelength equal to the number N of antenna elements used. In this embodiment, four wavelengths can be generated in the C-band.

And a polarization controller for removing the polarization dependency of the electro-optic modulator.

The RF signal generator may further include an RF signal generator for generating an RF signal. In an actual system, a signal is replaced with a signal to be transmitted to an actual antenna, and the electro-optic modulator is provided with an RF signal generator when an optical signal is input from the multi-wavelength laser. The intensity modulation can be performed in the same form as the RF signal generated by the.

When the length of the fixed time delay line is defined by the following equation,

는 파장에 대한 선로의 지연시간이고, υ는 광 섬유 내 광속임)(Where i = 1,2,3… N,

Is the delay time of the line with respect to wavelength, and υ is the speed of light in the optical fiber)

The maximum time delay (± τ _max ) generated may satisfy the following equation.

는 필터의 대역폭, L_DCF는 분산 보상 광섬유의 길이임)
Where D (ps / nm-km) is the variance,

Is the bandwidth of the filter, L _DCF is the length of the dispersion compensation fiber)

The phased array antenna according to the above configuration has not only a simplified structure but also an effect of reducing the cost required for producing the phased array antenna.

1 is a conceptual diagram of a true-time delay (TTD) line beam for a phased array antenna;
2 is a block diagram showing the configuration of a phased array antenna according to an embodiment of the present invention;
3 is a diagram illustrating a configuration of a multi-wavelength laser 110 that is one configuration of a phased array antenna according to an embodiment of the present invention.
4 is a view showing the transmission characteristics of the Lyot-Sagnac filter,
5 is a diagram showing an output spectrum of a variable wavelength laser;
6 shows measured group velocity delay and loss of dispersion compensation fiber;
7 shows loss and time delay as a function of wavelength,
8 shows the variance measured by ODA,
9A to 9D are graphs showing the spectrum of each part of the TTD while measuring the time delay of the phased array antenna according to the embodiment of the present invention;
10 is a graph showing superimposed results of measuring time delay and intensity as a function of wavelength in four optical receivers,
11 is a view showing a time delay characteristic of a phased array antenna with respect to the number of antenna elements expressed based on element 1;
FIG. 12 is a diagram showing a radiation pattern obtained by simulation from the time delay of the phased array antenna shown in FIG.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "comprises" or "having" and the like refer to the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

In the following description of the present invention with reference to the accompanying drawings, the same components are denoted by the same reference numerals regardless of the reference numerals, and redundant explanations thereof will be omitted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

Hereinafter, with reference to the accompanying drawings will be described in more detail with respect to the present invention. 1 illustrates a conceptual diagram of a true time-delay (TTD) line beam for a phased array antenna. Through this, the basic principle of the phased array antenna will be described.

In a phased array antenna, if the normalized array factor (AF) is a linear antenna array interval,

(1)

(One)

(2)

(2)

Where N is the number of elements, β = 2πf / c is the propagation constant of the RF signal, c is the speed of light, f is the frequency of the electrical RF signal, d is the distance between two consecutive antenna elements, and Is the spatial angle between the axis of the elements and the radial axis. The electrical current supplied to the nth antenna element is

(3)

(3)

(4)

(4)

과

은 각각 전기 전류와의 진폭과 위상이다. τ_n은 n번째 요소의 군속도 지연이다. 식 (2)-(4)를 식 (1)에 대입하면 정규화 배열인수는,When displayed as

and

Are the amplitude and phase with electrical current, respectively. τ _n is the group speed delay of the nth element. Substituting equations (2)-(4) into equation (1), the normalized array argument is

(5)

(5)

Is displayed as:

As a result, TTD technology is a technique for adjusting the angle of radiation by varying the delay time.

2 is a block diagram showing the configuration of a phased array antenna 100 according to an embodiment of the present invention. As shown in FIG. 2, the phased array antenna 100 according to an exemplary embodiment of the present invention may include a multi-wavelength laser 110, an RF signal generator 120, an electro-optic modulator 130, a polarization controller 140, Distributed compensation fiber 150, band select filters 160-1, 160-2, 160-3, 160-4, fixed time delay lines 170-1, 170-2, 170-3, 170-4, Optical receivers 180-1, 180-2, 180-3, 180-4 and antenna elements 190-1, 190-2, 190-3, 190-4.

Multi-wavelength laser 110 generates wavelengths. In this case, the generated wavelength is used as a carrier wavelength for modulating an optical signal by the electro-optic modulator 130 to be described later. This will be described with reference to FIG. 3.

3 is a diagram illustrating a configuration of a multi-wavelength laser 110 that is one configuration of a phased array antenna according to an embodiment of the present invention. Here, an optical fiber ring laser using a PMF Lyot-Sagnac filter was assumed. Polarization maintaining fiber (PMF) and coupler 1 consist of a Lyot-Sagnac filter. The length of the PMF is about 1m, and the coupler 1 may be a 2 × 2 3dB coupler.

The transmission characteristics of the Lyot-Sagnac filter are shown in Figure 4, where the Lyot-Sagnac filter using PMF is characterized by a variable Fabry-Perot filter with a free-spectral range of 7.2 nm, uniform FBGs or variable sampling FBG. Can be used. Looking at the loss spectrum of Figure 4 it can be seen that it has a uniform wavelength interval of 900GHz (~ 7.2nm). Polarization regulators are used to vary the selected wavelength of the filter. Erbium-doped fiber (EDF) is used as a gain medium for oscillation of the optical fiber ring laser. EDF has a gain spectrum throughout the C-band. EDF can be replaced by Raman fiber amplifier. Multiwavelength lasers can also be replaced by semiconductor Fabry-Perot semiconductor lasers operating in multiple modes.

A variable optical attenuator (VOA) is used to adjust the gain of the fiber laser, and combiner 2 is a 1 × 2 10dB combiner that sends some back to the gain medium for lasing and some to the output. The output spectrum of the variable wavelength laser is shown in FIG. 5.

The RF signal generator 120 has a function of generating an RF signal and is replaced by an RF signal to be radiated through an antenna in an actual system.

The electro-optic modulator 130 modulates the electrical signal into an optical signal. When an optical signal generated by the multi-wavelength laser 110 is input, an electro-optic modulator (EOM) is intensity modulated in the same form as the signal generated by the RF signal generator 120. The signal of the RF signal generator 120 is a signal emitted by the antenna elements.

The dispersion compensation optical fiber 150 allows the signal modulated by the optical signal to have a different delay time according to the wavelength. When a light pulse is transmitted in a single mode optical fiber, a pulse spreading occurs, which is called dispersion. The dispersion of single-mode fiber is also called in-mode dispersion, and the cause is caused by structural dispersion and material dispersion, which are a function of wavelength. Because of this dispersion, it is difficult to transmit a large amount of information far, so to compensate for this, dispersion compensating fiber (DCF) is used in the present invention, and this dispersion compensating fiber is used as a time delay element in the present invention. As a result, the dispersion value varies depending on the wavelength, and thus, even if each wavelength travels the same distance, it has a different delay time. DCF can be used to compensate for Lucent Technology's Truewave fiber.

The group velocity delay τ _d (λ) and the loss of the dispersion compensation optical fiber were measured using an optical dispersion analyzer (ODA, Agilent 86038A) and are shown in FIG. 6.

Where the dotted line represents the group velocity delay and the solid line represents the loss with wavelength. The loss is about -3.9 dB and the time delay has a difference in time delay of about 18 ns between 1525 and 1565 nm. The length of DCM is about 5.5 km.

The band select filters 160-1, 160-2, 160-3, and 160-4 perform only the drop function of the band select filter or the wavelength add / drop filter used to obtain a fixed optical delay in each wavelength band together with the optical delay lines. do. Filters have the advantages of lower phase ripple and more balanced losses within the bandwidth of the selected wavelength than FBG filters. In the present invention, the band select filters 160-1, 160-2, 160-3, and 160-4 are DWDM 9-skip-filters having a bandwidth of about 7.2 nm in the C-band and continuous in the DWDM 100G system. A thin film filter that selects eight channels is used. In order to achieve the same delay time, a filter having a long wavelength interval is required to minimize the length of the dispersion compensation optical fiber.

The fixed time delay lines 170-1, 170-2, 170-3, and 170-4 from the dispersion compensation optical fiber 150 to the optical receivers 180-1, 180-2, 180-3, and 180-4 are After passing through the band select filter 160-1, 160-2, 160-3, 160-4, it can be fully realized by the addition of an appropriate length of optical fiber. At this time, when it is difficult to accurately match the physical length of the optical fiber, the optical variable delay line (optical variable delay line) 170-1, 170-2, 170-3, 170-4 and the optical receiver (180-1, 180-2, 180-3, 180-4) can be added

In order to accurately measure the time delay over the wavelength of the TTD, a 1 × 4 optical coupler is used to combine all the optical signals input to the PDs. The input of the DCF and the output of the 1X4 optocoupler were connected to the input and output ports of the ODA, respectively.

7 is a diagram illustrating loss and time delay as a function of wavelength. The modulated optical signal is separated by a band select filter and the lengths of the fixed time delay lines 170-1, 170-2, 170-3, 170-4 composed of SMF have the same time delay at the center wavelength of the wavelength band. Adjusted.

Where i = 1,2,3... N.

The loss curve is slightly different because the path of light passage is different. The relationship between DCF dispersion and group speed delay

,

그리고 D( ps / nm - km )는 각각 그룹 지연 차이, 대역 선택 필터의 대역폭과 DCF의 분산이다. Since D ( ps / nm - km ) is a function of wavelength, the time delay slope varies between bands. here

,

And D ( ps / nm - km ) is the group delay difference, the bandwidth of the band select filter, and the variance of the DCF, respectively.

The maximum time delay caused by TTD (± τ _max ) satisfies the following equation.

는 필터의 대역폭, L_DCF는 분산 보상 광섬유의 길이이다.Where D (ps / nm-km) is the variance,

Is the bandwidth of the filter, and L _DCF is the length of the dispersion compensation fiber.

8 is a diagram showing dispersion measured by ODA. The dispersion of the DCF · D used as shown in Figure 8 in accordance with the band L _DCF is -443.3, -459.9, -478.3, and reduced to -498.4 ps / nm, and the loss is 13.2 dB in the band pass filter the pass band. If you want to use a short DCF, you should choose a DCF with a large dispersion slope, ΔD (λ _i ) / Δλ · L _DCF . And in order to change the scanning angle from 0 ° to 180 ° in a 10 GHz system, the delay time between antenna elements should have a maximum of -150 to +150 ps.

The optical receivers 180-1, 180-2, 180-3, and 180-4 have a function of demodulating the modulated optical signal into an electrical signal. That is, the optical signal is converted into an electrical signal by a photo detector (PD). In the present invention, 10 GHz may be used as the frequency of the RF signal. In this case, the reception frequency of the optical preamplifier should detect 10 GHz. The same number of photodetectors may be required for TTDs for 4-A PAAs. At this time, when the light input to the optical receiver is different from the loss due to the wavelength selection filter and the optical fixed time delay line, the light intensity applied to the optical receiver may be different. The variable optical attenuator may be added between the fixed time delay lines 170-1, 170-2, 170-3, 170-4 and the optical receivers 180-1, 180-2, 180-3, 180-4. Can be.

The configuration of the phased array antenna 100 according to the embodiment of the present invention described above will be summarized with reference to FIG. 2 again.

2 shows a TTD beamformer for 4-element PAA proposed by the present invention. The laser is a multi-wavelength laser 110 for generating four wavelengths in the C-Band, a plurality of uniform FBG in series in the multi-wavelength laser 110 in order to change the wavelength or use a variable SFBG (sampled- fiber Bragg grating) and variable Fabry-Perot filters to vary the wavelength.

In the electro-optic modulator 130 the wavelengths are modulated into an RF signal to be radiated by the antenna elements. The wavelengths passing through the dispersion compensation optical fiber 150 have different delay times. The thin-film filters 160-1, 160-2, 160-3, 160-4 are used to separate the wavelengths of the multi-wavelength lasers and fixed delay lines are used to achieve the same delay time for the wavelengths within the bandwidth of the band select filter. to provide. The total time delay consists of a dispersion compensation fiber 150 having wavelength dependence in the band and fixed time delay lines 170-1, 170-2, 170-3, 170-4, which do not depend on the wavelength in the band. The optical signal is converted into an electrical signal by the optical receivers 180-1, 180-2, 180-3, 180-4.

9A to 9D illustrate a result of measuring spectra at respective portions of a phased array antenna according to an embodiment of the present invention when only two wavelengths of four wavelengths are used. As shown in FIG. 9A, the time difference between two wavelengths having different bands was measured using two wavelengths. The optical power of the two wavelengths is about -25 dBm and shows about 5 dB loss in the electro-optic modulator 130 as shown in FIG. 9B. 9C and 9D show that this light is amplified by about 20 dB in EDFA and about 20 dB in loss in the dispersion compensation fiber 150 and the band pass filter.

In this experiment, when one of the two wavelengths is used and only the other wavelength is changed, the time delay of the two light waves input to the optical receivers 180-1, 180-2, 180-3, and 180-4 is measured. It was for the purpose. As shown in Figs. 10A and 10B, the two wavelengths are 1530.5 and 1553.5 nm, varying the light waves of 1553.5 nm and measuring the time delay between the two wavelengths. In this measurement, the RF signal uses a 1 GHz square wave, and a lower frequency than the actual RF signal is used to avoid confusion in delay measurement when the delay time is longer than one period of the RF signal. A digital communication analyzer is used to measure the time delay.

When the four-wavelength laser is used, the results measured by the four optical receivers based on the RF signal are superimposed and shown in FIG. 10.

On the other hand, in order to verify the performance of the phased array antenna according to an embodiment of the present invention, an optical dispersion analyzer (ODA) was used. The input and output terminals of the dispersion compensation optical fiber 150 were connected to the laser output and the input port of the ODA, respectively. The result is a loss of about 3.9 dB and a time delay of about 18 ns between 1525 and 1565 nm, with the result shown in FIG.

In order to accurately measure the time delay according to the wavelength, a 1x4 optical coupler is used to combine all optical signals inputted to the optical receivers, and the input of the dispersion compensation optical fiber 150 and the output of the 1x4 optical coupler are input to the optical scatterometer. And output ports, respectively. The modulated optical signal is separated by a thin film band selection filter, and the length of the fixed delay line composed of SMF can be adjusted to have the same time delay at the center wavelength of the wavelength band.

FIG. 11 shows time delay characteristics of a phased array antenna with respect to the number of antenna elements indicated on the basis of element 1. FIG. As the wavelength of a multichannel laser increases, the time delay decreases.

The radiation pattern obtained by simulation from the time delay of the phased array antenna shown in FIG. 11 is shown in FIG. This was calculated using the above equation (5). It can be seen that the radiation angle varies from 0 ° to 180 ° with respect to the antenna axis when the wavelengths of the multi wavelength laser are varied. For the simulation, the RF frequency is 10 GHz, four elements and the distance between the elements is 15 mm. According to the simulation result, sufficient time delay can be obtained to make the radiation angle more than 180 degrees. Gain also shows a characteristic that the error range is limited to within 1dB.

As described above, it can be seen that the phased array antenna according to the embodiment of the present invention has an excellent radiation pattern and is capable of emitting beams at all radiation angles of 0 ° to 180 °.

In the foregoing description, each component and / or function described in various embodiments may be implemented in combination with each other, and those skilled in the art may recognize the present invention described in the claims below. It will be understood that various modifications and variations can be made in the present invention without departing from the spirit and scope.

100 ................. Phase array antenna
110 ...................... Multiwavelength Laser
120 ...................... RF Signal Generator
130 ................................. An electro-optic modulator
140 ...................... Polarizer
150 ...................... Distributed Compensation Fiber
160-1 to 160-4 ........... bandpass filter
170-1 ~ 170-4 ..................... Fixed time delay line
180-1 to 180-4 ........ Optical receiver
190-1 to 190-4 ..................... Antenna

Claims (8)

An electro-optic modulator for modulating the electrical signal into an optical signal;
A multi-wavelength laser generating a wavelength used as a carrier wavelength for the electro-optic modulator to modulate the electrical signal into the optical signal;
A dispersion compensation optical fiber for causing the signal modulated by the optical signal to have a different delay time according to a wavelength;
A thin film filter and a fixed time delay line for forming an optical delay line fixed in the wavelength band;
An optical receiver for demodulating the modulated optical signal into an electrical signal; And
And an antenna radiating the demodulated electrical signal with a linearly increasing delay time. delete The method of claim 1,
The multi-wavelength laser includes any one of a Lyot-Sagnac filter, a variable sampled-fiber bragg grating (SFBG), and a variable Fabry-Perot filter using PMF,
The at least one filter is a phased array antenna, characterized in that for varying the generated wavelength. The method of claim 3,
The multi-wavelength laser,
A polarization controller of a Lyot-Sagnac filter for adjusting the variation of the wavelength by the at least one filter; Phased array antenna, characterized in that. The method of claim 3,
The multi-wavelength laser,
A phased array antenna which generates a number of wavelengths equal to the number of antenna elements. The method of claim 1,
And a polarization controller for removing the polarization dependence of the electro-optic modulator. The method of claim 1,
It further comprises an RF signal generator for generating an RF signal,
When the optical signal is input from the multi-wavelength laser, the electro-optic modulator is characterized in that the intensity modulation in the same form as the RF signal generated by the RF signal generator, in the actual system is replaced by the RF signal to be transmitted to the antenna A phased array antenna. The method of claim 1,
When the length of the fixed time delay line is defined by the following equation,

(Where i = 1,2,3…),

Is the delay of the line with respect to wavelength,

Is the speed of light in the optical fiber.)
The maximum delay time ± _{τ max} generated by the antenna is characterized by the following equation.

Where D (ps / nm-km) is the variance,

Is the bandwidth of the filter, and L _DCF is the length of the dispersion compensation fiber.)

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