JP6769817B2 - 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

In a transmitting antenna for broadcasting, in order to form antenna gain and directivity according to the broadcasting area, a plurality of twin loop antennas and the like are often arranged in multiple stages and in multiple surfaces to form a transmitting antenna system. In a transmitting antenna system using a plurality of antennas like this, in order for the combined radiated radio waves to obtain the gain and directivity as designed, each antenna emits radio waves with the intensity characteristics and phase characteristics as designed. It is necessary. However, in reality, the characteristics may not be as designed due to defects or failures during construction work. In particular, since it is necessary to finely adjust the relative phase difference between each antenna for the phase characteristic, it is essential to measure and monitor the phase characteristic for each antenna.

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 placed indoors together with the measuring equipment is several tens of meters to several hundreds of meters. It is connected by an optical fiber transmission line. When measuring the phase of radio waves radiated from an antenna, the phase of the radio wave signal obtained by converting the radio wave signal into an optical signal, transmitting it through an optical fiber, and performing O / E conversion is transmitted to each optical electric field sensor head. It depends on the length of the connected optical fiber and also on the temperature of the optical fiber. Therefore, some ingenuity is required to accurately measure the relative phase difference of the radio waves radiated from each antenna. For example, Patent Document 2 discloses a method in which an optical electric field sensor head is installed in the vicinity of a plurality of antennas, and the length of an optical fiber connected to all the optical electric field sensor heads is adjusted within an allowable set value. Has been done. Further, in Patent Document 3, one optical electric field sensor head connected to an optical fiber is used, and the heads are sequentially attached and detached in the vicinity of individual antennas for measurement, and the measurement data thereof are compared. The relative phase difference is measured.

However, when the installation locations of the individual antennas constituting the transmitting antenna system are separated or the degree of freedom in installing the optical electric field sensor head and the optical fiber is limited, as in Patent Document 2, the individual antennas are installed. It is not easy to accurately measure and adjust the length of the optical fiber connecting between the optical electric field sensor head arranged in the vicinity of the O / E converter and the O / E converter. Further, depending on the external environment, it may be difficult to attach / detach the optical electric field sensor head and install it, or it may take a large number of man-hours to attach / detach the optical electric field sensor head and lay the optical fiber. In such a case, Patent Document 3 It is not easy to use the method of.

An object of the present invention solves the above problems and does not require detailed measurement and adjustment of the length of the optical fiber connecting the optical electric field sensor head and the O / E converter, and attachment / detachment of the optical electric field sensor head. Therefore, it is an object of the present invention to provide an antenna characteristic measuring device capable of measuring the relative phase difference of a plurality of antennas.

In order to solve the above problems, from the first aspect, the antenna characteristic measuring device according to the present invention is arranged in the vicinity of at least two of the antennas in a transmitting antenna system that emits radio waves using a plurality of antennas, respectively, and emits light. At least two photoelectric field sensor heads that output modulated light obtained by modulating the intensity of input light input by the fiber according to the field strength of the electric field, and a modulation light source that supplies the input light to the photoelectric field sensor head. An O / E converter that converts the modulated light into an electric signal, at least two input optical fibers that transmit the input light from the modulation light source to the respective optical electric field sensor heads, and the respective optical electric field sensor. It has at least two output optical fibers that transmit the modulated light from the head to the O / E converter, and at least two by measuring the electric field strength based on the O / E converted electric signal. An antenna characteristic measuring device for measuring the phase of radio waves radiated from the antenna, which is a correction light source having a wavelength different from that of the modulation light source, and between the optical electric field sensor head and the output optical fiber, respectively. A correction optical signal obtained by modulating the intensity of the correction light source with a reference signal and having a reflective diffraction grid that passes through the wavelength of the installed modulation light source and reflects the wavelength of the correction light source. The correction optical signal that is input to the output optical fiber from the O / E converter side, is reflected by the reflection type diffraction grid, and returns to the O / E converter side is detected and compared with the reference signal. Therefore, it is characterized in that the measured value of the phase of the radio wave depending on each output optical fiber is corrected.

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 a correction optical signal is input to the output optical fiber from the O / E converter side and reflected. By detecting the correction optical signal that is reflected by the type diffraction grating and returns to the O / E converter side, the phase shift amount of the radio wave signal depending on the output optical fiber can be detected. The phase shift amount of the detected correction optical signal is the phase shift amount relative to the reference signal that is modulating the correction optical signal, and is the phase shift amount generated 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, for the output optical fiber of each optical electric field sensor head, the output optical fiber of the measured value of the phase of the radio wave of each optical electric field sensor head is detected by detecting the relative phase shift amount with respect to the same reference signal and comparing them. It is possible to grasp the part that depends on. 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.

Here, the correction 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 correction 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. When measuring the correction data for each output optical fiber, if the reference signal has the same frequency as the radio wave signal radiated from the antenna, the phase of the radio wave signal converted into the optical signal by the output optical fiber The difference in shift amount can be directly grasped. Further, if the frequency of the reference signal is made higher, the change in the phase shift amount with respect to the difference in the length of the output optical fiber becomes larger, so that the measured value of the phase can be corrected with higher accuracy.

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 an optical fiber Bragg grating (FBG) having a diffraction grating embedded in the optical fiber is used. It is smaller and less costly to achieve.

From the third aspect, in the antenna characteristic measuring apparatus of the first or second aspect, the correction optical signal from the correction light source is input to the output optical fiber via an optical circulator. The modulated light and the correction optical signal reflected by the reflective diffraction grating are input to the O / E converter via the optical circulator. By using the optical circulator, the correction optical signal input to the output optical fiber, the modulated light output from the output optical fiber, and the reflected light of the correction optical signal can be easily separated and processed. In this case, the modulated light output from the output optical fiber and the reflected light of the correction light signal may be separated by using a WDM coupler and then input to separate O / E converters. Alternatively, if the input light from the modulation light source is blocked when the correction light signal is detected so that the modulation light and the correction light signal are not detected at the same time, the reflected light of the modulation light and the correction light signal can be detected. Can be input to the O / E converter without separating.

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 correction optical signal from the correction light source and the input light from the modulation light source are combined by a WDM coupler, the light is emitted. The feature is that the modulated light and the correction optical signal reflected by the reflective diffraction grid are input to the input optical fiber via the circulator and input to the O / E converter via the optical circulator. To do.

By using the reflective 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 correction light signal may be separated by using a WDM coupler and then input to separate O / E converters. Alternatively, if the input light from the modulation light source is blocked when the correction light signal is detected so that the modulation light and the correction light signal are not detected at the same time, the reflected light of the modulation light and the correction light signal can be detected. Can be input to the O / E converter without separating.

The reflective optical electric field sensor head includes a substrate made of a material having an electro-optical effect, an optical waveguide formed on the substrate, and light that is installed on the substrate and reflects light propagating through the optical waveguide. The optical waveguide is provided with a reflecting portion and an electrode antenna installed in the vicinity of the optical waveguide, and the optical waveguide extends bifurcated from the input / output optical waveguide 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 is induced in the electrode antenna by radio waves radiated from the antenna. A reflection type branch interference type optical modulator having a driving electrode portion for applying the generated 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 a fifth aspect, the present invention is characterized in that, in the antenna characteristic measuring device of the third or fourth aspect, when the correction optical signal is detected, the input light from the modulation light source is blocked. .. In this way, if the input light from the modulation light source is blocked when the correction optical signal is detected so that the modulation light and the correction optical signal are not detected at the same time, the modulation light and the correction optical signal are reflected. Light can be input to the same O / E converter for detection.

From the sixth 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 fifth aspects. It is characterized by having a means for measuring the intensity of radio waves. Since the intensity or amplitude of the radio wave signal converted into an optical signal by the optical electric field sensor head depends on the electric wave strength in the field, if the intensity or amplitude of the detected radio wave signal is measured using a comparator or the like, the antenna The intensity of radio waves radiated from can be measured. That is, the antenna characteristic measuring device from this viewpoint can measure the strength of radio waves at the same time as measuring the relative phases of radio waves radiated from a plurality of antennas.

From the seventh aspect, the present invention measures the light intensity of the correction optical signal that is reflected by the reflection type diffraction grating and returns to the O / E converter side in the antenna characteristic measuring device of the sixth aspect. Then, based on the measured light intensity, the measured value of the radio wave intensity depending on the output optical fiber is corrected. The optical fiber transmission line has propagation loss that attenuates the passing optical signal, connection loss at the connection portion between the optical fibers, connector loss, and the like, and the modulated light from the optical electric field sensor head passes through the optical fiber. This causes some attenuation. Since the above loss depends on the length of the optical fiber, the connection state, etc., the strength of the measured radio wave signal also changes due to the loss of the output optical fiber connected to the optical electric field sensor head, and the accurate radio wave strength No measurement is available. Therefore, in the present invention, the measured value depending on the loss of the output optical fiber can be corrected by measuring the optical intensity of the correction optical signal that reciprocates and passes through the same output optical fiber as the modulated light. .. That is, if the optical intensity of the correction optical signal input to the output optical fiber changes with a constant intensity, the loss of the output optical fiber changes, and the measured value of the radio wave intensity is based on this change amount. Can be corrected. This makes it possible to accurately measure the intensity of radio waves at the same time as measuring the relative phases of radio waves radiated from a plurality of antennas.

As described above, according to the present invention, there is no need for detailed measurement and adjustment of the length of the optical fiber connecting the optical electric field sensor head and the O / E converter, and attachment / detachment of the optical electric field sensor head. An antenna characteristic measuring device capable of measuring the relative phase difference of the antenna can be obtained.

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 relative phase difference 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 correction light source 16 having a wavelength different from that of the modulation light source 14. The correction light source 16 is a laser light source, and outputs a correction optical signal whose intensity is modulated by the reference signal generated from the reference signal source 22. Further, after the correction optical signal from the correction 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 couples 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 correction 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 the correction optical signal is reflected. The modulated light and the correction optical signal 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 O / E converter 15 via the optical circulator 18. To do.

In this embodiment, after installing each optical electric field sensor head 12 on each transmitting antenna, the measured value of the phase for each transmitting antenna is corrected. At this time, the input light from the modulation light source 14 is blocked, and the correction optical signal input to the O / E converter 15 is detected. The reference signal from the reference signal source 22 is split into two by the demultiplexer 23, one is used for modulation of the correction light source 16, and the other monitors the intensity and phase of the radio wave emitted from the transmitting antenna. It is input to the reference port P1 of the antenna monitoring device 24. The correction optical signal output by the O / E converter 15 is input to the measurement port P2 of the antenna monitoring device 24, compared with the reference signal input to the reference port P1, and the relative phase difference between them is detected. To.

By sequentially switching by the optical switch 19 and measuring the input / output optical fiber 21 installed in each transmitting antenna, the relative phase difference with the reference signal is detected. This relative phase difference is a phase difference caused by a difference in the length, temperature, stress, etc. of each input / output optical fiber 21, and is a correction value for the measured value of the radio wave phase of each antenna.

After grasping the above correction value, the output from the correction light source 16 is cut off, the modulation light source 14 is driven, and the phase of the radio wave radiated from each transmitting antenna is measured. By sequentially switching the optical switches 19, input light is supplied to the input / output optical fibers 21 to the optical electric field sensor head 12 of each transmitting antenna, and the modulated light from the optical electric field sensor head 12 is O / O / via the optical circulator 18. Input to the E converter 15. The radio wave signal output by the O / E converter 15 is input to the measurement port P2 of the antenna monitoring device 24, compared with the reference signal input to the reference port P1, and the relative phase difference between them is detected. This detected phase difference is corrected by the above correction value. By measuring for each transmitting antenna, the relative phase difference of radio waves between the transmitting antennas can be measured.

Table 1 shows an example of the measurement results using the antenna characteristic measuring device of this embodiment. The relative phase difference measurement values in the table are for cases where there is a difference of 0.023 m and 1.076 m in the lengths of the input / output optical fibers 21 connected to the optical electric field sensor heads 12 installed in the two transmitting antennas, respectively. It is a value obtained by correcting the measured value by the modulated light of the wavelength λ1 by using the result of comparing the detected correction optical signal of the wavelength λ2 with the reference signal. It has been confirmed that the relative phase difference of the radio waves actually emitted is as designed. As shown in Table 1, in the case of a radio signal having a frequency of 473.143 MHz or 485.143 MHz, the difference in length of the input / output optical fiber 12 is relative to 0.023 to 1.076 m due to the correction of the measured value. A high measurement accuracy of −0.1 to 0.6 degrees was obtained.

FIG. 2 is a perspective view showing an example of the transmitting antenna system to be measured in this embodiment. This transmitting antenna system radiates radio waves in all directions by using four transmitting antennas 30 facing different directions in two upper and lower stages. 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 correction 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 correction 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. Further, the output of the correction 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. In FIG. 7, the measurement system 50 of the present embodiment measures antenna characteristics capable of measuring the strength of radio waves radiated from a transmitting antenna by measuring the electric field strength based on the O / E-converted electric signal. It is a device. 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, in the transmission / reception device 51, the modulated light from the optical circulator 18 and the correction optical signal are separated by the WDM coupler 52, and the correction optical signal is input to the O / E converter 53 and the light thereof. Detect intensity. The light intensity signal of the detected correction light signal is input to the level measuring device 54, and the correction value is calculated by comparing with the reference light intensity set in advance for the output of the correction light source, and the antenna monitoring device. It is sent to 24 and the measured value of the intensity of the radio wave signal is corrected.

Since the amplitude or intensity of the radio wave signal contained in the modulated light depends on the electric field strength in the place, if the intensity or amplitude of the detected radio wave signal is measured, the intensity of the radio wave radiated from the antenna can be measured. it can. In this embodiment, the antenna monitoring device 24 includes a radio wave intensity measuring circuit, and the radio wave intensity is measured by the radio wave signal detected by the O / E converter 15. The intensity of the correction optical signal input to the O / E converter 53 corresponds to the loss of each input / output optical fiber 21 if the output of the correction light source 16 is constant. Therefore, it is possible to calculate a correction value for the measured value of the radio wave intensity depending on the loss of the input / output optical fiber 21 based on the light intensity of the correction optical signal.

The loss of the optical fiber transmission line includes a connection loss at a connection portion between optical fibers, a connector loss, and the like, which may fluctuate due to a failure or deterioration. Therefore, the measurement of the radio wave intensity of this embodiment is performed. The correction in the above may be set not only when the optical electric field sensor head is installed but also on a steady basis. In this case, it is possible to configure a circuit in which the loss fluctuation of the input / output optical fiber is constantly measured, and the strength of the radio wave signal measured by the value is automatically corrected and output.

If the intensity of the reference signal that modulates the correction light source 16 is constant, the intensity of the reference signal included in the correction optical signal is measured instead of measuring the optical intensity of the correction optical signal as described above. Then, it is also possible to obtain the amount of loss fluctuation of the input / output optical fiber 21 from the fluctuation and correct the measured value of the intensity of the radio wave. Further, when only the measured value of the radio wave intensity is corrected by measuring the light intensity of the correction optical signal, it is not necessary to modulate the correction light source with the reference signal.

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 small. In this case, a plurality of modulation light sources 14 and correction light sources 16 may be provided, or the light of the modulation light source 14 and the light of the correction light source 16 may be distributed and supplied to each optical electric field sensor head.

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 transmission type optical modulator is used, since the input optical fiber and the output optical fiber are separately installed, the input light from the modulation light source 14 is coupled to the input optical fiber, and the correction light is used. Only the signal 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 correction light signal are incident on the O / E converter 15 via the optical circulator. 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, 53 O / E converter 16 Correction light source 17, 52 WDM coupler 18 Optical circulator 19 Optical switch 20 FBG
21 Input / output optical fiber 22 Reference signal source 23 Demultiplexer 24 Antenna monitoring device 25 Optical modulator 26 Board 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 fiber 54 level measuring instrument

Claims (7)

In a transmitting antenna system that emits radio waves using a plurality of antennas, modulated light that is arranged in the vicinity of at least two of the antennas and that modulates the intensity of the input light input by the optical fiber according to the field strength of the electric field. At least two optical electric field sensor heads that output the above, a modulation light source 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 light. At least two input optical fibers that are transmitted from the modulation light source to each of the optical electric field sensor heads, and at least two output optical fibers that transmit the modulated light from each of the optical electric field sensor heads to the O / E converter. An antenna characteristic measuring device that measures the phase of radio waves radiated from at least two antennas by measuring the electric field strength based on the O / E-converted electric signal.
It passes through the wavelength of the correction 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 correction light source. Has a reflective diffraction grating and
The correction optical signal obtained by modulating the intensity of the correction light source with a reference signal is input to the output optical fiber from the O / E converter side and reflected by the reflection type diffraction grating to perform the O / E conversion. An antenna characteristic measuring device, characterized in that it corrects a measured value of a radio wave phase depending on each output optical fiber by detecting the correction optical signal returning to the device side and comparing it with the reference signal. The antenna characteristic measuring apparatus according to claim 1, wherein the reflective diffraction grating is an optical fiber Bragg grating. The correction optical signal from the correction light source is input to the output optical fiber via the optical circulator, and the modulated light and the correction optical signal reflected by the reflection type diffraction grating are transmitted via the optical circulator. The antenna characteristic measuring apparatus according to claim 1 or 2, wherein the light is input to the O / E converter. 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 the light source for correction is used. The correction optical signal and the input light from the modulation light source were combined by a WDM coupler, then input to the input optical fiber via an optical circulator, and reflected by the modulated light and the reflective diffraction grid. The antenna characteristic measuring apparatus according to claim 1 or 2, wherein the correction optical signal is input to the O / E converter via the optical circulator. The antenna characteristic measuring apparatus according to claim 3 or 4, wherein when the correction optical signal is detected, the input light from the modulation light source is blocked. Any one of claims 1 to 5, further comprising means for measuring the intensity of radio waves 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 light intensity of the correction optical signal reflected by the reflective diffraction grating and returned to the O / E converter side is measured, and the intensity of the radio wave depending on the output optical fiber is measured based on the measured light intensity. The antenna characteristic measuring apparatus according to claim 6, wherein the measured value of the above is corrected.

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