JP6769818B2 - Antenna characteristic measuring device - Google Patents

Description

The present invention relates to an antenna characteristic measuring device that measures the intensity or phase of radio waves radiated from a transmitting antenna by an optical electric field sensor arranged near the transmitting antenna.

As a means for measuring and monitoring fluctuations in the characteristics of a transmitting antenna for broadcasting or communication, the intensity of input light input by an optical fiber is modulated according to the electric field strength in the field and output by the optical fiber. An optical electric field sensor is used in which an optical electric field sensor head and an O / E converter that converts the output light into an electric signal are used, and the electric field strength in the vicinity of the transmitting antenna is measured by the O / E converted electric signal. ing. An optical fiber sensor head, which is mainly composed of a dielectric material and has wideband characteristics capable of responding at radio frequency, is installed at a measurement point near the transmitting antenna, and is connected to a light source and measuring equipment such as an O / E converter. By connecting the antennas with an optical fiber, it is possible to measure the intensity and phase characteristics of the transmitted radio wave without being affected by the induction due to a lightning strike or the like, except for the influence on the characteristics of the transmitting antenna.

An example of an antenna monitoring system using such an optical electric field sensor is described in Patent Document 1. Further, Patent Document 2 describes a system using a plurality of optical electric field sensor heads capable of measuring the phases of radio waves at a plurality of locations with high reliability and high measurement accuracy, and a plurality of antennas using the optical electric field sensors. Patent Document 3 describes an antenna characteristic measurement system that measures the power level and phase difference of the antenna.

Japanese Unexamined Patent Publication No. 2005-86347 Japanese Unexamined Patent Publication No. 2014-2005 Japanese Unexamined Patent Publication No. 2014-35268

Normally, the distance between the optical fiber sensor head placed near the antenna installed in a high place such as a steel tower and the O / E converter installed indoors together with the measuring equipment is several tens of meters to several hundreds of meters. It is connected by the optical fiber transmission line of. In general, optical fiber transmission lines have propagation loss that attenuates the passing optical signal, connection loss at the connection between optical fibers, connector loss, loss due to bending stress to the optical fiber, and the like. The modulated light from the field sensor head passes through the optical fiber and is attenuated due to the above loss. Therefore, if the above loss changes due to some reason such as a failure, the intensity of the modulated light detected by the O / E converter changes, and as a result, the amplitude of the radio wave signal contained in the modulated light changes. It interferes with accurate measurement of radio field strength.

Conventionally, in order to correct the measured value of the radio wave intensity according to the change in the optical fiber loss over time after the optical electric field sensor head is installed, it is necessary to constantly measure the change in the loss in the optical fiber transmission line. there were. For this purpose, it is necessary to always provide a special loss measuring device such as an OTDR and measure the loss by separating the optical fiber transmission line from the measuring device of the radio wave intensity.

An object of the present invention is an antenna characteristic measurement capable of solving the above-mentioned problems, constantly measuring the radio wave intensity, measuring the change in loss of the optical fiber transmission line, and correcting the measured value of the radio wave strength. To provide the equipment.

In order to solve the above problems, from the first viewpoint, the antenna characteristic measuring device according to the present invention is arranged in the vicinity of the light source that emits radio waves, and the intensity of the input light input by the optical fiber is used as the local electric field strength. An optical electric field sensor head that outputs modulated light modulated accordingly, a light source for modulation that supplies the input light to the optical electric field sensor head, an O / E converter that converts the modulated light into an electric signal, and the input. It has an input optical fiber that transmits light from the modulation light source to the optical electric field sensor head, and an output optical fiber that transmits the modulated light from the optical electric field sensor head to the O / E converter. An antenna characteristic measuring device that measures the intensity of radio waves radiated from the antenna by measuring the electric field strength based on the E-converted electric signal, and is a reference light source having a wavelength different from that of the modulation light source. And a reflective diffraction grid that passes through the wavelength of the modulation light source installed between the photoelectric field sensor head and the output optical fiber and reflects the wavelength of the reference light source, and the reference light source. The reference light output from the light source is input from the O / E converter side to the output optical fiber, reflected by the reflective diffraction grid, and returned to the O / E converter side. The intensity of the reference light is measured. It is characterized in that the measured value of the intensity of the radio wave depending on the output optical fiber is corrected based on the measured light intensity.

As described above, in the present invention, a reflective diffraction grating is inserted between the optical electric field sensor head and the output optical fiber, and reference light is input to the output optical fiber from the O / E converter side to perform reflection type diffraction. The intensity of the reference light reflected by the grating and returned to the O / E converter side is measured. If the output of the reference light source is kept constant, the presence or absence of a change in the loss of the output optical fiber and the amount of the change can be detected by measuring the above intensity. As a result, it is possible to grasp the change in the intensity of the modulated light due to the change in the loss of the output optical fiber, and to correct the measured value of the measured radio wave intensity. As a result, the intensity of the radio wave radiated from the antenna can be measured with high accuracy.

Here, the reference light source has a wavelength different from that of the modulation light source, and the reflection type diffraction grating installed between the optical electric field sensor head and the output optical fiber passes through the wavelength of the modulation light source and the wavelength of the reference light source. It is set to reflect only. As a result, the modulated light can be input to the O / E converter from the optical electric field sensor head through the output optical fiber.

Further, the optical electric field sensor head used in the present invention includes a substrate made of a material having an electro-optical effect, an optical waveguide formed on the substrate, and an electrode antenna installed in the vicinity of the optical waveguide. In the optical waveguide, an input optical waveguide extending from the incident side of light, two phase-shifted waveguides extending bifurcated from the input optical waveguide, and the two phase-shifted optical waveguides merge to form light. The electrode antenna is formed from an output optical waveguide connected to the exit side of the light, extends in the extending direction in parallel with the phase shift waveguide, and is an electric signal induced in the electrode antenna by a radio wave radiated from the antenna. Can be used for a branched interference type optical modulator having a drive electrode portion that changes the refractive index of the phase shift optical waveguide by applying the above to the phase shift optical waveguide. Lithium niobate crystals have been conventionally used as the substrate material, and since a compact, high-efficiency, wide-band optical modulator can be obtained, it is suitable for use in the optical electric field sensor head of the present invention. An electrode antenna for electric field detection integrated with the drive electrode is installed in this light modulator, and a voltage induced in the electrode antenna is applied to the phase shift waveguide via the drive electrode portion to form a phase shift optical waveguide. Change the refractive index.

From the second aspect, the present invention is characterized in that, in the antenna characteristic measuring apparatus of the first aspect, the reflective diffraction grating is an optical fiber Bragg grating. The reflective diffraction grating used in the present invention can be configured by combining individual parts such as a diffraction grating and a collimator, but it is smaller to use an optical fiber Bragg grating having a diffraction grating embedded in the optical fiber. Moreover, it can be realized at low cost.

From the third aspect, in the antenna characteristic measuring apparatus of the first or second aspect, the reference light from the reference light source is input to the output optical fiber via the first optical circulator. Then, the reference light reflected by the reflection type diffraction grid is output through the first optical circulator and then demultiplexed by the output WDM coupler for O / E conversion for the first reference light. The intensity of the reference light is detected by inputting to the device, and a second reference light source having a wavelength different from that of the modulation light source is installed between the optical electric field sensor head and the input optical fiber. It has a second reflective diffraction grid that passes through the wavelength of the modulation light source and reflects the wavelength of the second reference light source, and has a second reference light from the second reference light source and the modulation. The input light from the light source is combined by the input WDM coupler, then input to the input optical fiber via the second optical circulator, reflected by the second reflective diffraction grid, and reflected by the second reflective diffraction grid to be reflected by the modulation light source. Returning to the side The intensity of the second reference light is measured by inputting the second reference light to the O / E converter for the second reference light via the second optical circulator, and the measurement thereof is performed. It is characterized in that the measured value of the intensity of the radio wave depending on the input optical fiber is corrected based on the obtained light intensity.

In the invention of this aspect, in addition to correcting the measured value of the radio wave intensity depending on the loss fluctuation of the output optical fiber as in the invention of the first aspect, the second reference light and the second reflection type diffraction By using a grating, it is also possible to correct the measured value of the radio wave intensity that depends on the loss fluctuation of the input optical fiber. That is, when a transmissive optical electric field sensor head in which an input optical fiber and an output optical fiber are connected is used as the optical electric field sensor head, the invention from this viewpoint is effective. Further, in the invention of the present viewpoint, by using an optical circulator, the modulated light incident from the input optical fiber and the second reference light reflected from the second reference light are separated, or the light is incident from the output optical fiber. It facilitates the separation of the reference light to be reflected and the reference light to be reflected and returned and the modulated light.
By using the first optical circulator, the reference light input to the output optical fiber, the modulated light output from the output optical fiber, and the reflected light of the reference light can be easily separated and processed. The modulated light and the reflected light of the reference light output from the output optical fiber are separated by using the WDM coupler for output, and the reference light is input to the O / E converter for the first reference light and its intensity is detected. .. Further, a second reflective diffraction grating is also provided between the input optical fiber and the optical electric field sensor head so that the change in the intensity of the modulated light due to the change in the loss of the input optical fiber can be corrected. Therefore, by using the second optical circulator, the modulated light and the second reference light input to the input optical fiber and the reflected light of the second reference light output from the input optical fiber can be easily separated. Processing. The reflected light of the second reference light output from the input optical fiber is input to the O / E converter for the second reference light, its intensity is measured, and the input optical fiber is based on the measured light intensity. Understand the change in the intensity of the modulated light due to the change in the loss of. As a result, the measured value of the measured radio wave intensity can be corrected. From the above, the intensity of the radio wave radiated from the antenna can be measured with higher accuracy.

From the fourth aspect, the present invention is a reflection type optical electric fiber sensor head that modulates and reflects the input light and returns it in the antenna characteristic measuring device of the first or second aspect. The input optical fiber and the output optical fiber are the same optical fiber, and after the reference light from the reference light source and the input light from the modulation light source are combined by an input WDM coupler, the light is emitted. The reference light input to the output optical fiber via the circulator and reflected by the reflective diffraction grid is output via the optical circulator and then demultiplexed by the output WDM coupler to measure its intensity. It is characterized by doing.

By using the reflection type optical electric field sensor head, the input light and the output light are separated and input / output by the optical circulator. In this case, the modulated light output from the optical circulator and the reflected light of the reference light are separated by using a WDM coupler. The light intensity of the reference light is measured by an O / E converter for the reference light or the like.

As the reflection type optical electric field sensor head, a substrate made of a material having an electro-optical effect, an optical waveguide formed on the substrate, and light propagating on the substrate and propagating through the optical waveguide are reflected. A light reflecting portion and an electrode antenna installed in the vicinity of the optical waveguide are provided, and the optical waveguide extends bifurcated from the input / output optical waveguide extending from the light input / output side and the input / output optical waveguide. Formed from two phase-shifted waveguides that reach the light-reflecting portion, the electrode antenna extends in the extending direction in parallel with the phase-shifted waveguide, and the radio waves radiated from the antenna make the electrode antenna. A reflective branched interference type optical modulator having a driving electrode portion that applies an induced electric signal to the phase shift waveguide to change the refractive index of the phase shift optical waveguide can be used. By using such a reflection type light modulator configuration, light is transmitted twice as long as the same electrode length as compared with the transmission type optical modulator, so that the efficiency of the optical electric field sensor head is higher. It is possible to increase the size and bandwidth, and to reduce the size.

From the fifth aspect, the present invention is radiated from the antenna by measuring the electric field strength based on the O / E-converted electric signal in the antenna characteristic measuring apparatus of the first to fourth aspects. It is characterized by having a means for measuring the phase of radio waves. Since the optical signal from the optical electric field sensor head includes the amplitude and phase of the radio wave signal as they are, the phase of the radio wave signal can be measured. Usually, a reference signal source or the like is provided, and the phase of the radio wave signal is detected by comparison with the reference signal. Since the phase of the radio signal contained in the optical signal changes while passing through the optical fiber, some ingenuity is required to measure the absolute phase, but the fluctuation of the phase characteristic over time should be measured. Can be done. It is also possible to install optical electric field sensor heads on a plurality of antennas to detect the relative phase difference between the antennas. In this case, it is necessary to correct the measured value according to the length of the output optical fiber connected to each optical electric field sensor head. The antenna characteristic measuring device from this viewpoint can measure the phase of radio waves at the same time as measuring the intensity of radio waves radiated from the antenna.

From the sixth aspect, in the antenna characteristic measuring apparatus of the fifth aspect, the present invention modulates the intensity of the reference light with a reference signal, inputs it to the output optical fiber, and reflects it by the reflection type diffraction grating. It is characterized in that the measured value of the phase of the radio wave depending on the output optical fiber is corrected by detecting the signal of the reference light returning to the O / E converter side and comparing it with the reference signal.

As described above, the phase of the radio signal obtained by O / E conversion of the modulated light depends on the length of the output optical fiber connected to each optical electric field sensor head, and further depends on the temperature of the optical fiber. Dependent. It is not easy to accurately adjust the length of the optical fiber connecting the optical electric field sensor head and the O / E converter. In the invention of this aspect, the relative phase shift amount of the signal obtained by O / E conversion of the reference light modulated by the reference signal with respect to the reference signal includes the phase shift amount caused by the reciprocation of the output optical fiber. .. This value corresponds to the amount of phase shift depending on the length and temperature of the output optical fiber through which the radio signal converted into the optical signal passes. Therefore, by grasping the phase of the reference light, it is possible to correct the influence of the output optical fiber on the measured value. Further, when the optical electric field sensor heads are installed in a plurality of antennas and the relative phase difference between the antennas is detected, the phase shift of the output optical fiber of each optical electric field sensor head is relative to the same reference signal. By detecting the amounts and comparing them, it is possible to grasp the portion of the measured value of the phase of the radio wave of each optical electric field sensor head depending on the output optical fiber. That is, the relative phase difference portion of the radio wave radiated from each antenna and the phase difference portion depending on the difference in the output optical fiber can be separately grasped. By correcting the measured value of the phase of each optical electric field sensor head using the phase difference depending on the detected output optical fiber, the relative phase of the radio wave radiated from each antenna is measured with high accuracy. be able to. As described above, in the invention of the present viewpoint, it is possible to accurately measure the intensity of the radio wave radiated from the antenna and at the same time measure the relative phase of the radio wave.

As described above, according to the present invention, it is possible to obtain an antenna characteristic measuring device capable of constantly measuring the radio wave intensity and measuring the change in the loss of the optical fiber transmission line to correct the measured value of the radio wave strength. ..

FIG. 6 is a block configuration diagram of a measurement system using the antenna characteristic measuring device according to the first embodiment. The perspective view which shows an example of the transmitting antenna system which is the object of measurement of Example 1. FIG. It is a figure which shows an example of the installation method of the optical electric field sensor head on the transmitting antenna, FIG. 3A is a plan view, and FIG. 3B is a side view. It is a figure which shows an example of the attachment structure of the optical electric field sensor head to the transmission antenna, FIG. 4A is a side view, and FIG. 4B is a back view. It is a figure which shows typically the structure of the reflection type light modulator built in the optical electric field sensor head, FIG. 5A is a plan view, and FIG. 5B is a sectional view. The plan view which shows the structure of the optical electric field sensor head. The block block diagram of the measurement system using the antenna characteristic measuring apparatus which concerns on Example 2. FIG.

Hereinafter, the antenna characteristic measuring apparatus of the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and the duplicated description will be omitted.

FIG. 1 is a block configuration diagram of a measurement system using the antenna characteristic measuring device according to the first embodiment. The measurement system 10 of this embodiment is a system that measures the intensity of radio waves radiated from a plurality of transmitting antennas. As shown in FIG. 1, each optical electric field sensor head 12 has a plurality of optical electric field sensor heads 12 that output modulated light obtained by modulating the intensity of input light input by an optical fiber according to the electric field strength in the field. Each of the 12 is installed in the vicinity of the transmitting antenna. The transmission / reception device 11 includes a modulation light source 14 that supplies input light to the optical electric field sensor head 12, and an O / E converter 15 that converts the modulated light into an electric signal. The optical electric field sensor head 12 used in this embodiment is a reflection type optical electric field sensor head, and the optical electric field sensor head 12 and a transmission / reception device are connected by a plurality of input / output optical fibers 21. The input / output optical fibers 21 transmit the input light from the modulation light source 14 to the respective optical electric field sensor heads 12, and the modulated light from the respective optical electric field sensor heads to the O / E converter 15. To. The modulation light source 14 includes two laser light sources that output polarized light orthogonal to each other and a polarization synthesizer connected via a polarization-holding optical fiber to synthesize the polarized light, and the polarization thereof. Light having polarization components orthogonal to each other from the synthesizer is output as input light to the optical electric field sensor head 12. Further, the O / E converter 15 includes an amplifier.

In this embodiment, the transmission / reception device 11 includes a reference light source 16 having a wavelength different from that of the modulation light source 14. The reference light source 16 is a laser light source and outputs reference light. Further, after the reference light from the reference light source 16 and the input light from the modulation light source 14 are combined by the WDM coupler 17, they are input to the optical switch 19 via the optical circulator 18. The optical switch 19 sequentially switches the input light and connects it to the input / output optical fiber 21 connected to each optical electric field sensor head 12.

FBG (optical fiber Bragg grating) is used as a reflective diffraction grating that passes the wavelength λ1 of the modulation light source 14 and reflects the wavelength λ2 of the reference light source 16 between the optical electric field sensor head 12 and the input / output optical fiber 21. ) 20 are installed respectively. That is, the FBG 20 allows the input light and the modulated light to the optical electric field sensor head 12 to pass through, and reflects the reference light. The modulated light and the reference light reflected by the FBG 20 return to the transmission / reception device 11 via the input / output optical fiber 21, pass through the optical switch 19, and are input to the WDM coupler 22 via the optical circulator 18 to have a wavelength of λ1. It is separated into modulated light and reference light with wavelength λ2. After that, the modulated light is input to the O / E converter 15 to detect the radio wave signal, and the reference light having the wavelength λ2 is input to the O / E converter 23 to detect the light intensity. These radio wave signals and light intensity signals are input to the antenna monitoring device 24.

In the antenna monitoring device 24, the light intensity of the reference light is compared with the reference light intensity preset for the output of the reference light source, and a correction value depending on the loss of the connected input / output optical fiber 21 is calculated. Will be done. On the other hand, from the radio wave signal obtained from the O / E converter 15, the intensity of the radio wave measured based on the intensity or amplitude thereof is calculated. At this time, the calculated value of the radio wave intensity is corrected according to the above-mentioned correction value. The measurement system 10 calculates the correction value due to the fluctuation of the loss of the input / output optical fiber 21 after installing the respective optical electric field sensor head 12 in each transmitting antenna, and periodically or constantly. The measured value of the radio wave intensity for each transmitting antenna is corrected. In the calculation of the above correction value, the light output intensity of the reference light source 16 as a reference may be kept constant at all times, or the light output intensity of the reference light source 16 may be constantly monitored and the monitor value may be used as a reference. ..

By sequentially switching by the optical switch 19 and measuring the input / output optical fibers 21 installed in each transmitting antenna, the light intensity of the reference light reflected and returned is detected, and the input / output optical fibers 21 of each input / output optical fiber 21 are detected. A correction value for the measured value of the radio wave intensity of each antenna can be obtained depending on the loss caused by deterioration, fluctuation, stress, etc. of the connection portion.

Table 1 shows an example of the measurement results using the antenna characteristic measuring device of this embodiment. The frequency of the radio signal used for the measurement is 473.143 MHz. Here, an attenuator was inserted into the input / output optical fiber 21 to give a loss of 0 to 7 dB, and the measurement was performed. The light receiving level in the table is the light receiving level of the modulated light of wavelength λ1 in the O / E converter 15, and the O / of the modulated light of wavelength λ1 when the RF output level measurement value does not consider the loss of the input / output optical fiber 21. It is an RF output value from the E converter 15, that is, a measured value corresponding to the radio wave intensity. The RF output reference value is a value that serves as a reference for the radio wave intensity obtained in consideration of the light receiving level. The RF output measured value correction result is a result of correcting the RF output level measured value by the correction value calculated by using the light intensity in the O / E converter 23 of the reference light having the wavelength λ2.
As shown in Table 1, by comparing the RF output measured value correction result and the RF output reference value, the measurement accuracy of the radio wave intensity is 0.09 by correcting the measured value for the loss fluctuation of the input / output optical fiber 21. A high value of ~ 0.17 dB degree was obtained.

FIG. 2 is a perspective view showing an example of the transmitting antenna system to be measured in this embodiment. Four transmitting antennas 30, each facing a different direction, are used in two upper and lower stages to radiate radio waves in all directions. The optical electric field sensor head 12 is installed at the same position relative to each transmitting antenna 30. 3A and 3B are views showing an example of a method of installing an optical electric field sensor head on a transmitting antenna, FIG. 3A is a plan view, and FIG. 3B is a side view. As shown in FIG. 3, the transmitting antenna 30 is a transmitting antenna having a reflector 32 on the back surface of the antenna body 31 that radiates radio waves, and the front surface and the side surface are covered with a radome 33 which is a waterproof cover. In FIG. 3, a 4L type twin loop antenna element is used as the antenna main body 31. The optical electric field sensor head 12 is inserted into a predetermined position between the antenna body 31 and the reflector 32 through a hole 34 provided in the reflector 32.

In FIG. 3, the optical electric field sensor head 12 is housed in a housing made of an insulating material together with a part of an input / output optical fiber pigtail connected to the photoelectric field sensor head 12, and the housing is housed in a reflector 32. It is detachably fixed to the fixing box installed on the outside of the.

4A and 4B are views showing an example of a structure for attaching an optical electric field sensor head to a transmitting antenna, FIG. 4A is a side view, and FIG. 4B is a back view. In FIG. 4, the cylindrical housing 35 incorporates a part of the optical electric field sensor head 12 and the input / output optical fiber pigtail 36 connected to the optical electric field sensor head, and is fixed to the back surface of the reflector 32. It is fixed to the mounting portion 38 of 37. The fixing box 37 has a hole corresponding to the hole 34 of the reflector 32, and a mounting portion 38 is formed on the back side of the hole. Further, the position of the hole 34 is set at the position between the antenna main body 31 and the reflector 32 of the optical electric field sensor head 12 so that the sensitivity to the target electric field component can be obtained, and the housing The body 35 is configured to be inserted obliquely with respect to the reflector 32. When the housing 35 is fixed, most of the portion protruding inward from the reflector 32 is made of an insulating material such as fluororesin, and the connecting portion 35A to be bonded to the mounting portion 38 is made of metal. A screw is formed on the outer periphery of the end portion of the connecting portion 35A, and the mounting portion 38 has a cylindrical portion in which a screw that fits the screw is formed on the inner circumference. An optical fiber connector is formed at the tip of the optical fiber pigtail 36, and is inserted into a receiving side optical fiber connector 39 installed on the side surface of the fixing box 37 through the bottom of the mounting portion 38. After fixing the optical electric field sensor head 12, the fixing box 37 is sealed from the back side by the lid 37A, and the periphery of the lid 37A is fixed by screws.

Here, in the configuration of FIG. 4, the FBG 20 is built in the optical connection connector 40 inserted in the optical fiber connector 39. The input / output optical fiber 21 is connected to the outside of the optical connector 40. With such a configuration, the FBG 20 can be compactly inserted without requiring an extra space between the optical electric field sensor head 12 and the input / output optical fiber 21.

The transmitting antenna of this embodiment emits radio waves in the UHF band, that is, a frequency of 470 to 710 MHz, and the diameter of the hole 34 is about 20 to 50 mm. Therefore, the diameter of the hole 34 is about 1/10 or less of the wavelength of the radio wave. Therefore, the influence of the presence of the hole 34 on the antenna characteristics is very small.

5A and 5B are views schematically showing the configuration of a reflection type optical modulator built in the optical electric field sensor head of this embodiment, FIG. 5A is a plan view, and FIG. 5B is a sectional view. is there. In FIG. 5,
The light modulator 25 includes a substrate 26 made of X-cut lithium niobate (LiNbO ₃ ) crystal, which is a crystal substrate having an electro-optical effect, and a branched interference type optical circuit board made by Ti diffusion on the upper surface side of the substrate 26. The waveguide 27, the buffer layer 28 formed on the upper surface side of the substrate 26, the electrode antenna 29 formed on the buffer layer 28, and the light reflecting portion 43 installed at one end of the substrate 26. It is composed of.

The branch interference type optical waveguide 27 is formed of one input / output optical waveguide 27a extending to the incident side of the input light and two phase shift waveguides 27b and 27c extending bifurcated from the input / output optical waveguide 27a. Has been done. The input / output optical waveguide 27a and the phase shift optical waveguides 27b and 27c have the same width dimension W in the direction perpendicular to the stretching direction. The phase-shifted optical waveguides 27b and 27c have substantially the same length dimension in the extending direction.

The width dimension W of the optical waveguides 27a to 27c is in the range of 5 to 10 μm. The length dimension of each phase shift optical waveguide 27b, 27c in the stretching direction is in the range of 10 to 30 mm. The central portions of the phase-shifted optical waveguides 27b and 27c are separated by a predetermined dimension in the width direction and extend in parallel with each other. The distance between the optical waveguides 27b and 27c in the central portion is in the range of 20 to 50 μm. The width dimension W of the optical waveguides 27a to 27c, the length dimension of the phase-shifted optical waveguides 27b, 27c, and the separation dimension of the optical waveguides 27b, 27c are not particularly limited, and these dimensions can be set arbitrarily.

The buffer layer 28 is provided for the purpose of preventing a part of the light propagating through the optical waveguide 27 from being absorbed by the electrode antenna 29. The buffer layer 28 is made of silicon dioxide (SiO ₂ ) and has a thickness dimension of about 100 to 1000 nm. The electrode antennas 29, which function as detection antennas similar to the dipole antenna, are arranged in the extending direction so that one is located on the side of the input / output optical waveguide 27a and the other is located on the side of the light reflecting portion 43. The electrode antenna 29 is a two-layer film of chromium (Cr) and gold (Au) formed by sputtering or the like. The electrode antenna 29 receives radio waves propagating in space and induces an electric signal proportional to the electric field strength of the radio waves.

The electrode antenna 29 located on the side of the light reflecting portion 43 has a driving electrode portion 29a arranged between the phase shift optical waveguide 27b and 27c, and the electrode antenna 29 located on the side of the input / output optical waveguide 27a has a phase. It has drive electrode portions 29b and 29c arranged on both sides of the drive electrode portion 29a with the shift optical waveguides 27b and 27c interposed therebetween. The drive electrode portions 29a, 29b, 29c extend in the extending direction in parallel with the optical waveguides 27b, 27c. The length between both ends of the electrode antenna 29 in the extending direction is about 5 to 10 mm.

A light input / output end of the input / output optical waveguide 27a is formed at one end of the substrate 26, and a light reflecting portion 43 is installed at the other end. The input / output end face of the optical fiber 41 is coupled to the optical input / output end of the input / output optical waveguide 27a. The light reflecting unit 43 reflects the light incident from the input / output optical waveguide 27a and propagating through the phase-shifted optical waveguides 27b and 27c, and returns the light from the phase-shifted optical waveguides 27b and 27c to the input / output optical waveguide 27a and propagates the light. A voltage induced by receiving radio waves from the electrode antenna 29 is applied between the drive electrodes 29a, 29b, and 29c in opposite directions, so that the phase-shift optical waveguides 27b and 27c are refracted in opposite directions. The rate change occurs, and the light passing through them undergoes phase shifts of opposite polarities to each other, so that when the light merges, they interfere with each other and the intensity changes. As a result, modulated light having a light intensity change corresponding to the electric field strength change of the radio wave received by the electrode antenna 29 can be obtained.

In this embodiment, a reflection type light modulator is used, and the same drive electrode portion is folded back to allow light to pass through twice, so that higher modulation efficiency can be obtained. Alternatively, since the length of the drive electrode portion for obtaining the same modulation efficiency may be short, the electrode capacitance can be reduced and a wider band can be obtained. Further, the output optical waveguide can be integrated with the input optical waveguide, and the length of the phase shift optical waveguide can be shortened, so that the optical electric field sensor head can be miniaturized.

FIG. 6 is a plan view showing the configuration of the optical electric field sensor head. The coupling portion between the light modulator 25 and the optical fiber 41 is built in the sensor package 42 and sealed. FIG. 6 shows a state before the sensor package 42 is covered with the lid. The sensor package 42 is made of an insulating material such as glass or fluororesin so as not to affect the detected electric field, and its shape is about 10 to 20 mm in width and height and about 50 to 100 mm in length. Is.

In this embodiment, as the laser light source of the modulation light source 14, for example, a semiconductor laser light source having a wavelength of 1.55 μm and an output of 50 mW can be used. The laser beam used for the optical electric field sensor head may have a wavelength in the range of 1.26 to 1.68 μm, and its electric energy may be in the range of 1 to 100 mW. This is because when the wavelength of the laser light exceeds 1.68 μm, unnecessary noise is generated in the optical fiber, and a loss occurs due to propagation in the optical fiber. When the electric energy of the laser light exceeds 100 mW, the laser light having an unnecessary electric energy is supplied to the optical electric field sensor head 12, and as a result, the power consumption of the transmission / reception device 11 cannot be reduced.

Further, as the reference light source 16, for example, when the wavelength λ1 of the modulation light source is 1.55 μm, a semiconductor laser light source having a wavelength of 1.53 μm can be used. When the light is combined with the input light of the modulation light source by a general WDM coupler and separated from the modulation light by a general FBG, the wavelength λ2 of the reference light source 16 is the wavelength λ1 of the modulation light source 14 and 0.01 to 0. The distance may be about 05 μm. The output of the reference light source 16 may be about 1 to 10 mW.

FIG. 7 is a block configuration diagram of a measurement system using the antenna characteristic measuring device according to the second embodiment. The measurement system 50 of this embodiment is an antenna characteristic measuring device capable of measuring the phase of radio waves radiated from a transmitting antenna by measuring the electric field strength based on the O / E-converted electric signal. The basic configuration of the measurement system 50 of the present embodiment is the same as that of the measurement system 10 of the first embodiment. However, in this embodiment, the antenna monitoring device 54 includes a radio wave intensity measuring circuit and a radio wave relative phase measuring circuit based on the detected radio wave signal. Further, in order to correct the measured value of the phase of the radio wave depending on the output optical fiber, the light intensity of the reference light source 16 is modulated by the reference signal generated from the reference signal source 52. The reference signal from the reference signal source 52 is split into two by the demultiplexer 53, one is used for modulation of the reference light source 16, and the other is input to the phase measurement circuit of the antenna monitoring device 54 as a reference reference. Will be done. The O / E converter 23 to which the reference light is incident detects the reference signal included in the reference light at the same time as detecting the light intensity of the reference light. The detected reference signal is input to the phase measurement circuit of the antenna monitoring device 54, compared with the reference signal input from the demultiplexer 53, and the relative phase difference between them is detected.

Since the radio wave signal included in the modulated light faithfully includes the time change of the electric field strength in the place, the phase of the radio wave radiated from the antenna can be measured by measuring the phase of the detected radio wave signal. Here, the relative phase difference between the phase of the radio wave signal included in the modulated light and the reference signal input from the demultiplexer 53 is detected. If the phase characteristic of the reference signal source 52 is stable, the reference signal detected from the above reference light has a phase characteristic corresponding to the phase change generated when the input / output optical fibers 21 reciprocate. There is. The difference in relative phase difference between the reference signal input from the demultiplexer 53 and the reference signal detected from the reference light is caused by the difference in the length, temperature, stress, etc. of each input / output optical fiber 21. The phase difference. This relative difference in phase is the correction value for the measured value of the radio wave phase of each antenna.

As described above, in this embodiment, it is possible to accurately measure the intensity of the radio wave radiated from the transmitting antenna and at the same time measure the relative phase of the radio wave.

Needless to say, the present invention is not limited to the above embodiment, and various modifications such as the configuration of the measurement system and the configuration of the optical electric field sensor head to be used are possible.

In the above embodiment, the input / output optical fiber 21 connected to each optical electric field sensor head 12 and the transmission / reception device 11 or 51 are sequentially switched and connected by the optical switch 19, but the number of transmitting antennas to be measured is 1. If there are only a few, the optical switch 19 is not an essential component. A plurality of modulation light sources 14 and reference light sources 16 may be provided, or the light of the modulation light source 14 and the light of the reference light source 16 may be distributed and supplied to each optical electric field sensor head 12.

In the above embodiment, the reflection type light modulator 25 is used as the light modulator of the optical electric field sensor head 12, but a transmission type light modulator may also be used. As a configuration example of the transmissive light modulator, for example, the same substrate as the above-mentioned optical modulator 25 can be used, and an optical waveguide or an electrode antenna having the same shape can be formed on the substrate. However, in the case of a transmissive optical modulator, in FIG. 5A, instead of the light reflecting portion 43, an output optical waveguide that joins from the phase-shifted optical waveguide 27 symmetrically with the incident side is provided, and the output light is provided on the output end face thereof. The fibers are coupled and output. Further, when a transmissive optical modulator is used, the input optical fiber and the output optical fiber are separately installed, so that the input light from the modulation light source 14 is coupled to the input optical fiber and only the reference light is used. Is input to the output optical fiber via the optical circulator 18. The modulated light from the output optical fiber and the reflected light of the reference light are incident on the O / E converter 15 via the optical circulator. When a transmission type optical modulator is used, a second reference light source having a wavelength different from that of the modulation light source, an optical electric field sensor head, and an input optical fiber are used, as in the invention of the third aspect described above. Use a second reflective diffraction grid installed between the two, an input WDM coupler and a second optical circulator for combining the modulated light and the second reference light and inputting them to the input optical fiber. Therefore, it is desirable to simultaneously correct the measured value of the intensity of the radio wave, which depends on the loss fluctuation of the input optical fiber. Further, when an optical switch is used in this configuration, an optical switch having a function of switching between an input optical fiber and an output optical fiber at the same time is required.

In the above embodiment, the optical electric field sensor head 12 is inserted into the hole 34 of the reflector 32 of the transmitting antenna 30 and installed, but the installation location of the optical electric field sensor head 12 is a certain size due to the radio waves radiated from the transmitting antenna. It may be in another place as long as the electric field is present.

The reflection type diffraction grating can be configured by combining not only the FBG but also individual parts such as a diffraction grating and a collimator. Further, the installation location is not limited to the built-in connector, and may be installed at the incident end or the outgoing end of the optical fiber pigtail of the optical electric field sensor head.

10, 50 Measurement system 11, 51 Transmitter / receiver 12 Optical electric field sensor head 14 Modulation light source 15, 23 O / E converter 16 Reference light source 17, 22 WDM coupler 18 Optical circulator 19 Optical switch 20 FBG
21 Input / output optical fiber 24, 54 Antenna monitoring device 25 Optical modulator 26 Substrate 27 Branch interference type optical waveguide 27a Input / output optical waveguide 27b, 27c Phase shift optical waveguide 28 Buffer layer 29 Electrode antenna 29a, 29b, 29c Drive electrode
30 Transmitting antenna 31 Antenna body 32 Reflector 33 Redome 34 Hole 35 Housing 35A Coupling 36 Optical fiber pigtail 37 Fixed box 37A Lid 38 Mounting part 39 Optical fiber connector 40 Optical connection connector 41 Optical fiber 42 Sensor package 43 Optical reflection part 52 Reference signal source 53 Demultiplexer

Claims (6)

An optical electric field sensor head that is arranged in the vicinity of an antenna that emits radio waves and outputs modulated light in which the intensity of input light input by an optical fiber is modulated according to the electric field strength in the field, and the optical electric field sensor head described above. A modulation light source that supplies input light, an O / E converter that converts the modulated light into an electric signal, an input optical fiber that transmits the input light from the modulation light source to the optical electric field sensor head, and the modulation. It has an output optical fiber that transmits light from the optical electric field sensor head to the O / E converter, and is radiated from the antenna by measuring the electric field strength based on the O / E converted electric signal. It is an antenna characteristic measuring device that measures the intensity of radio waves.
It passes through the wavelength of the reference light source having a wavelength different from that of the modulation light source and the wavelength of the modulation light source installed between the optical electric field sensor head and the output optical fiber, and reflects the wavelength of the reference light source. It has a reflective diffraction grid and
The reference light output from the reference light source is input from the O / E converter side to the output optical fiber, reflected by the reflection type diffraction grating, and returned to the O / E converter side. An antenna characteristic measuring device, characterized in that the measured value of the intensity of the radio wave depending on the output optical fiber is corrected based on the measured light intensity. The antenna characteristic measuring apparatus according to claim 1, wherein the reflective diffraction grating is an optical fiber Bragg grating. The reference light from the reference light source is input to the output optical fiber via the first optical circulator, and the reference light reflected by the reflection type diffraction grating is passed through the first optical circulator. After the output, the intensity of the reference light is detected by demultiplexing it with the WDM coupler for output and inputting it to the O / E converter for the first reference light.
It passes through the wavelength of the second reference light source having a wavelength different from that of the modulation light source and the wavelength of the modulation light source installed between the optical electric field sensor head and the input optical fiber, and is used for the second reference. It has a second reflective diffraction grating that reflects the wavelength of the light source.
The second reference light from the second reference light source and the input light from the modulation light source are combined by the input WDM coupler and then input to the input optical fiber via the second optical circulator. The second reference light that is reflected by the second reflective diffraction grid and returns to the modulation light source side is input to the O / E converter for the second reference light via the second optical circulator. 1. The second reference light intensity is measured, and the measured value of the radio wave intensity depending on the input optical fiber is corrected based on the measured light intensity. Or the antenna characteristic measuring device according to 2. The optical electric field sensor head is a reflection type optical electric field sensor head that modulates and reflects the input light and returns it. The input optical fiber and the output optical fiber are the same optical fiber, and are derived from the reference light source. After the reference light and the input light from the modulation light source are combined by the input WDM coupler, the reference light is input to the output optical fiber via an optical circulator, and the reference light reflected by the reflective diffraction grid is used. The antenna characteristic measuring apparatus according to claim 1 or 2, wherein after outputting through the optical circulator, the light is demultiplexed by a WDM coupler for output and the intensity thereof is measured. Any one of claims 1 to 4, wherein the means includes means for measuring the phase of the radio wave radiated from the antenna by measuring the electric field strength based on the O / E converted electric signal. The antenna characteristic measuring device according to. The intensity of the reference light is modulated by the reference signal, input to the output optical fiber, reflected by the reflection type diffraction grating, and returned to the O / E converter side. The reference light signal is detected and the reference signal is detected. The antenna characteristic measuring apparatus according to claim 5, wherein the measured value of the phase of the radio wave depending on the output optical fiber is corrected by comparing with the above.

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