JP7173544B6 - radio signal reception system - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Announced on May 15, 2018 at CLEO 2018 held from May 13 to 18, 2018.

TECHNICAL FIELD The present invention relates to a radio signal receiving system, and more particularly to a radio signal receiving system capable of receiving a radio signal in a wide frequency band such as a millimeter wave band or a terahertz band by filtering in the optical domain.

As one modulation method for an optical communication system, an external modulator method is employed in which a semiconductor laser is caused to continuously emit light and this light is turned on/off by an external modulator. The most popular external modulator is the Mach-Zehnder optical modulator.

The Mach-Zehnder optical modulator described above has a problem that the optical output characteristics relative to the drive signal drift with time due to changes in temperature or aging, and inter-symbol interference occurs in the on/off level of the optical output. there were. In order to solve this problem and stably control the operating point of the Mach-Zehnder optical modulator, it is necessary to change the bias voltage by the drive signal in accordance with the variation of the curve of the optical output characteristic with respect to the drive voltage. It is necessary to control the operating point that causes

A quadrature bias is generally used as a suitable method for controlling the operating point that changes the bias voltage (for example, Patent Document 1).

JP 2015-203737 A

However, when receiving a wide frequency band wireless signal in the millimeter wave band or terahertz band by filtering in the optical domain, if the orthogonal bias setting is used in the optical modulator, the wide frequency band wireless signal in the millimeter wave band or terahertz band was not able to be received by filtering in the optical domain.

Therefore, in view of the above problems, it is an object of the present invention to provide a radio signal receiving system capable of receiving radio signals in a wide frequency band such as the millimeter wave band or the terahertz band by filtering in the optical domain.

The above objects of the present invention are achieved by the following means. In addition, although the inside of parenthesis is attached with the reference code|symbol of embodiment mentioned later, this invention is not limited to this.

A radio signal receiving system according to claim 1 includes a receiving unit (receiving antenna unit 2) for receiving radio signals in the millimeter wave band or the terahertz band,
an electric signal conversion unit (first electric signal conversion unit 4A, second electric signal conversion unit 4B) that converts a radio signal received by the receiving unit (receiving antenna unit 2) into an electric signal;
An optical conversion unit (first optical conversion unit 6A, second optical conversion unit 6A, second optical conversion unit) that converts the electric signal converted by the electric signal conversion unit (first electric signal conversion unit 4A, second electric signal conversion unit 4B) into an optical signal Part 6B) and
The optical signal converted by the optical conversion section (first optical conversion section 6A, second optical conversion section 6B) is separated into bands equal to the frequency band of the radio signal received by the reception section (reception antenna section 2). and an optical filter unit (first optical filter 7A, second optical filter 7B),
The electric signal converted by the electrical signal conversion section (first electrical signal conversion section 4A, second electrical signal conversion section 4B) is supplied to the optical conversion section (first optical conversion section 6A, second optical conversion section 6B). It is characterized by using a null bias setting when converting the signal into an optical signal.

A radio signal receiving system according to claim 2 is the radio signal receiving system according to claim 1, wherein the electric signal conversion unit (first electric signal conversion unit 4A, second electric signal conversion unit 4B) includes: By taking the difference between the radio signal received by the receiving section (receiving antenna section 2) and the local oscillator signal, the carrier frequency of the radio signal received by the receiving section (receiving antenna section 2) is converted to an electrical signal down-converted to an intermediate frequency,
When the frequency band of the radio signal in the millimeter wave band or the terahertz band is Δf _t0 and the intermediate frequency is f _RF ,
The frequency band of the radio signal is characterized by satisfying the condition of Δf _t0 ≦2f _RF .

Further, the radio signal receiving system according to claim 3 is the radio signal receiving system according to claim 1 or 2, wherein a branching unit (receiving antenna unit 2) branches the radio signal received by the receiving unit (receiving antenna unit 2). 3) further comprising
The millimeter wave band or terahertz band radio signal is a division multiplexed signal having at least two channels of subcarrier signals, and is received by the receiving unit (receiving antenna unit 2),
The branching unit (3) branches the radio signal received by the receiving unit (receiving antenna unit 2),
The electric signal converter (first electric signal converter 4A, second electric signal converter 4B) obtains the difference between the radio signals branched by the branching unit (3) using different local oscillator signals. thereby converting the carrier frequency of the radio signal branched by the branching unit (3) into an electrical signal down-converted to an intermediate frequency,
The optical conversion section (first optical conversion section 6A, second optical conversion section 6B) converts the electrical signal converted by the electrical signal conversion section (first electrical signal conversion section 4A, second electrical signal conversion section 4B). into an optical signal,
The optical filter section (first optical filter 7A, second optical filter 7B) converts the optical signal converted by the optical conversion section (first optical conversion section 6A, second optical conversion section 6B) to each of the channels. It is characterized by being separated.

Next, the effects of the present invention will be described with reference to the drawings. In addition, although the inside of parenthesis is attached with the reference code|symbol of embodiment mentioned later, this invention is not limited to this.

According to the first aspect of the invention, the optical conversion section (the first optical conversion section 6A, the second optical conversion section 6B) is the electrical signal conversion section (the first electrical signal conversion section 4A, the second electrical signal conversion section 4B). ) is used to convert the converted electrical signal into an optical signal, a null bias setting is used, so that it is possible to receive radio signals in a wide frequency band in the millimeter wave band or the terahertz band by filtering in the optical domain.

In using the null bias setting, it is preferable to use it when the condition of Δf _t0 ≦2f _RF shown in the second aspect of the invention is satisfied.

Furthermore, according to the third aspect of the invention, a radio signal that is a division multiplexed signal having at least two channel subcarrier signals is received by the receiving section (receiving antenna section 2), and the received radio signal is sent to the branching section ( 3), and by taking the difference using different local oscillator signals, the carrier wave frequency of the radio signal branched by the branching unit (3) is converted to an electric signal conversion unit (first electric signal conversion unit 4A , second electrical signal conversion unit 4B) into an electrical signal down-converted to an intermediate frequency, and the electrical signal converted by the electrical signal conversion unit (first electrical signal conversion unit 4A, second electrical signal conversion unit 4B) The signal is converted into an optical signal by the optical conversion section (first optical conversion section 6A, second optical conversion section 6B), and converted by the optical conversion section (first optical conversion section 6A, second optical conversion section 6B). An optical signal is separated for each channel using an optical filter unit (first optical filter 7A, second optical filter 7B). This makes it possible to receive even a radio signal that is a division multiplexed signal having at least two channels of subcarrier signals.

1 is a block diagram showing an embodiment of a radio signal receiving system according to the present invention; FIG. (a) shows a millimeter wave band or terahertz band wide frequency band radio signal transmitted from a base station, mobile station, etc., (b-1) shows a local oscillator signal f _L2 , (b- 2) shows the local oscillator signal f _L1 , (c-1) shows the intermediate frequency down-converted by the first electrical signal converter according to the same embodiment, and (c-2) shows the same embodiment. (d-1) represents the second channel separated by the first optical filter according to the embodiment, and (d-2) represents the intermediate frequency down-converted by the second electrical signal conversion unit according to 3 is a diagram showing a first channel separated by a second optical filter according to the same embodiment; FIG. 3 is a conceptual block diagram of a first optical modulator and a second optical modulator according to the embodiment; FIG. FIG. 3 is a graph showing characteristics of a Bessel function of the first kind; (a) shows the spectrum of the optical signal with protrusions, (b) shows the eye pattern of the optical signal with intersymbol interference (overlapping between adjacent pulses), and (c) shows the code FIG. 10 is a diagram showing an eye pattern of an optical signal in which occurrence of inter-interference (overlapping between adjacent pulses) is reduced;

Hereinafter, a radio signal receiving system according to the present invention will be specifically described with reference to the drawings. In the following description, when the directions of up, down, left, and right are indicated, they refer to up, down, left, and right when viewed from the front of the drawing.

As shown in FIG. 1, a radio signal receiving system 1 includes a receiving antenna unit 2 capable of receiving radio signals in a wide frequency band such as a millimeter wave band or a terahertz band, and a radio signal received by the receiving antenna unit 2. a first electrical signal conversion unit 4A that converts one of the radio signals branched by the branching unit 3 into an electrical signal; and the other radio signal that is branched by the branching unit 3 into an electrical signal. a second electrical signal converter 4B, a first linear amplifier 5A for amplifying the voltage of the electrical signal converted by the first electrical signal converter 4A, and the electrical signal converted by the second electrical signal converter 4B a second linear amplifier 5B that amplifies the voltage of the first linear amplifier 5A, a first optical conversion unit 6A that converts the electrical signal whose voltage is amplified by the first linear amplifier 5A into an optical signal, and the voltage is amplified by the second linear amplifier 5B a second optical converter 6B that converts the converted electrical signal into an optical signal; a first optical filter 7A that separates the optical signal converted by the first optical converter 6A; and a second optical filter 7B for separating the optical signal.

Broadband radio signals in the millimeter wave band or the terahertz band use the Nyquist WDM (Wavelength Division Multiplexing) method, as shown in FIG. 2(a). More specifically, as shown in FIG. 2(a), a millimeter-wave or terahertz-band wide frequency band radio signal has a carrier frequency f _T , a frequency band Δf of each channel, and a total frequency band Δf _t0 =2Δf. It has subcarrier signals of a plurality of channels (FIG. 2(a) shows subcarrier signals of two channels, a first channel CH1 and a second channel CH2). The interval between subcarrier signals of the plurality of channels is Δf.

Note that the millimeter wave band of the radio signal refers to the range of 30 GHz to 100 GHz or 300 GHz, and the terahertz band refers to the range of 100 GHz or 300 GHz to 10 THz. Moreover, a wide frequency band means 25 GHz or more.

Thus, a radio signal in a wide frequency band such as the millimeter wave band or the terahertz band is transmitted from a base station, a mobile station, or the like (not shown) and received by the receiving antenna section 2 shown in FIG. A wide frequency band radio signal in the millimeter wave band or the terahertz band received by the receiving antenna unit 2 is divided by the branch unit 3 shown in FIG. Then, one of the branched millimeter wave band or terahertz band wide frequency band radio signals is converted into an electric signal by the first electric signal conversion unit 4A, and the branched millimeter wave band or terahertz band wide frequency band The other of the radio signals in the band is converted into an electric signal by the second electric signal converter 4B.

The first electrical signal converter 4A, as shown in FIG. 1, comprises a first local oscillator signal generator 4Aa, a first multiplier 4Ab, and a first mixer 4Ac. The first local oscillator signal generator 4Aa is for generating a local oscillator signal, and the generated local oscillator signal is multiplied by the first multiplier 4Ab as shown in FIG. 2(b-1). Thus, the local oscillator signal _fL2 close to the carrier frequency _fT of the wide frequency band radio signal in the millimeter wave band or the terahertz band is generated. As an example of a specific value, if the carrier wave frequency fT of a wide frequency band radio signal in the millimeter wave band or the terahertz band is 300 GHz and the frequency band _Δf is 40 GHz, the local oscillator signal f _L2 is generated at 350 GHz. becomes.

Thus, the local oscillator signal _fL2 generated as described above is subtracted from the carrier wave frequency fT of the wide frequency band radio signal in the millimeter wave band or the terahertz band by the first mixer _4Ac . 2(c-1), it is converted into an electric signal down-converted to the intermediate frequency |f _T −f _L2 |. As an example of a specific value, the intermediate frequency |f _T −f _L2 | is 50 GHz.

On the other hand, as shown in FIG. 1, the second electrical signal converter 4B is composed of a second local oscillator signal generator 4Ba, a second multiplier 4Bb, and a second mixer 4Bc. The second local oscillator signal generator 4Ba generates a local oscillator signal, and the generated local oscillator signal is multiplied by a second multiplier 4Bb to produce the signal shown in FIG. 2(b-2). Thus, the local oscillator signal _fL1 close to the carrier wave frequency _fT of the wide frequency band radio signal in the millimeter wave band or the terahertz band is generated. As an example of a specific value, if the carrier wave frequency fT of a wide frequency band wireless signal in the millimeter wave band or the terahertz band is 300 GHz and the frequency band _Δf is 40 GHz, the local oscillator signal f _L1 is generated at 250 GHz. becomes.

Thus, the local oscillator signal _fL1 generated as described above is subtracted from the carrier wave frequency fT of the wide frequency band radio signal in the millimeter wave band or the terahertz band by the second mixer _4Bc . 2(c-2), it is converted into an electric signal down-converted to the intermediate frequency |f _T −f _L1 |. As an example of a specific value, the intermediate frequency |f _T −f _L1 | is 50 GHz.

The first linear amplifier 5A amplifies the voltage of the intermediate frequency |f _T −f _L2 | down-converted by the first electrical signal conversion section 4A. amplifies the voltage of the intermediate frequency |f _T −f _L1 | down-converted at . Note that the first linear amplifier 5A and the second linear amplifier 5B are unnecessary if there is no need to amplify the intermediate frequency voltage.

The first optical converter 6A converts the electric signal of the intermediate frequency |f _T −f _L2 | whose voltage is amplified by the first linear amplifier 5A into an optical signal. Specifically, as shown in FIG. 1, the first optical converter 6A is composed of a first semiconductor laser 6Aa and a first optical modulator 6Ab. Light is output from the first semiconductor laser 6Aa, and the light output from the first semiconductor laser 6Aa is an electrical signal with an intermediate frequency |f _T −f _L2 | whose voltage is amplified by the first linear amplifier 5A. is modulated by the first optical modulator 6Ab. As a result, the electric signal of the intermediate frequency |f _T −f _L2 | whose voltage is amplified by the first linear amplifier 5A is converted into an optical signal.

On the other hand, the second optical converter 6B converts the electric signal of the intermediate frequency |f _T −f _L1 | whose voltage is amplified by the second linear amplifier 5B into an optical signal. Specifically, as shown in FIG. 1, the second optical converter 6B is composed of a second semiconductor laser 6Ba and a second optical modulator 6Bb. Light is output from the second semiconductor laser 6Ba, and the light output from the second semiconductor laser 6Ba is an electrical signal with an intermediate frequency |f _T −f _L1 | whose voltage is amplified by the second linear amplifier 5B. is modulated by the second optical modulator 6Bb. As a result, the electric signal of the intermediate frequency |f _T −f _L1 | whose voltage is amplified by the second linear amplifier 5B is converted into an optical signal.

The first optical filter 7A filters the optical domain and separates the optical signal converted by the first optical converter 6A. As a result, the second channel CH2 is separated as shown in FIG. 2(d-1).

On the other hand, the second optical filter 7B filters the optical domain and separates the optical signal converted by the second optical converter 6B. As a result, the first channel CH1 is separated as shown in FIG. 2(d-2).

Thus, in receiving a wide frequency band radio signal in the millimeter wave band or the terahertz band having subcarrier signals of a plurality of channels using the Nyquist WDM (Wavelength Division Multiplexing) method as described above, The signal is down-converted to an intermediate frequency by the first electrical signal converter 4A or the second electrical signal converter 4B and then received.

However, the higher the frequency, the more the amplitude deteriorates due to the band limitation of the first mixer 4Ac or the second mixer 4Bc. Therefore, of the first channel CH1 and the second channel CH2 shown in FIG. 2(a), the amplitude of the second channel CH2, which is a high frequency signal, is degraded, making it difficult to separate the second channel CH2. This causes a problem that only the first channel CH1 can be received.

Therefore, in the present embodiment, a wide frequency band radio signal in the millimeter wave band or the terahertz band having subcarrier signals of a plurality of channels using the Nyquist WDM (Wavelength Division Multiplexing) method as described above is used. When receiving, the radio signal is branched by the branching unit 3, and the carrier wave of the radio signal branched by the branching unit 3 is obtained by taking the difference between the radio signals branched by the branching unit 3 using different local oscillator signals. The frequency is down-converted to an intermediate frequency.

Thus, when the first electrical signal converter 4A down-converts the electrical signal of the intermediate frequency |f _T −f _L2 | as shown in FIG. 2(c-1), the high frequency Although the amplitude of the first channel CH1 is degraded, the second channel CH2 whose amplitude is not degraded can be separated by using the first optical filter 7A. Then, in the second electrical signal converter 4B, when down-converted into an electrical signal of intermediate frequency |f _T −f _L1 | as shown in FIG. The first channel CH1 whose amplitude is degraded but whose amplitude is not degraded can be separated by using the second optical filter 7B. This makes it possible to receive both the first channel CH1 and the second channel CH2 shown in FIG. 2(a). Also, by using the first optical filter 7A and the second optical filter 7B, various shapes can be obtained with good characteristics (no characteristic deterioration on the high frequency side). becomes possible. Furthermore, by introducing optical processing, it is possible to eliminate an electronic circuit for performing complicated received signal processing, so that power consumption can be reduced.

By the way, in order to receive a wide frequency band radio signal in the millimeter wave band or the terahertz band, it is necessary to use the null bias setting in the first optical modulator 6Ab and the second optical modulator 6Bb. This point will be described in detail below.

As shown in FIG. 3, the first optical modulator 6Ab and the second optical modulator 6Bb transmit light incident on an optical waveguide 60 on the input side to two optical waveguides (arms) 61a and 61b at an intensity of 1:1. After being branched and propagating the branched light for a certain length, it is combined again and output from the optical waveguide 62 on the output side. The two branched optical waveguides (arms) 61a and 61b are provided with phase modulation sections 61a1 and 61b1, respectively.

Here, if the electric field of the incident light is E _in , the electric field of the output light is E _out , and the modulator driving RF signal is φ(t), the following formulas 1 and 2 are established.

Here, φ(t) is defined as shown in Equation 3 below.

Substituting Equation 3 defined above into Equation 2 gives Equation 4 below.

The real part of Equation 4 above can be expressed by Equation 5 below.

Here, when the null bias setting is used as the setting of the modulator drive bias, φ ₀ =π, so the following formula 6 is established.

From Equation 6, it can be seen that signals are generated in the band waves of f=f ₀ ±f _RF , f ₀ ±3f _RF , f ₀ ±5f _RF , . . . That is, the adjacent channel frequency spacing is 2f _RF .

Here, the k-order Bessel function of the first kind has the characteristics shown in FIG. The vertical axis _Jn of the graph shown in FIG. 4 corresponds to the optical electric field output, and the horizontal axis z corresponds to the voltage. As a result, from the amplitude characteristic of J ₁ at f = f ₀ ±f _RF , when the total frequency band Δf _to of the wide frequency band radio signal in the millimeter wave band or the terahertz band is 2f _RF or less (Δf _to ≤ 2f _RF ) If so, it can be seen that the intermediate frequency signal can be linearly converted into an optical signal without spectral overlap. In particular, if the amplitude of d(t) is 1.74 rad or less, linear conversion can be performed within an error of 10%.

On the other hand, when the quadrature bias setting is used as the setting of the modulator drive bias, φ ₀ =−π/2, so the following formula 7 holds.

From Equation 7, it can be seen that signals are generated in the carrier wave or survey band wave of f=f ₀ , f ₀ ±f _RF , f ₀ ±2f _RF , . . . . That is, the adjacent channel frequency spacing is _fRF .

Here, from the amplitude characteristics of J ₁ at f=f ₀ ±f _RF (see FIG. 4), the total frequency band Δf _to of the wide frequency band radio signal in the millimeter wave band or the terahertz band is f _RF or less (Δf _to ≤f _RF ), the intermediate frequency signal can be linearly converted into an optical signal without spectral overlap. However, since the signal power concentrates on the carrier wave of f=f ₀ , there is a drawback that the signal strength of the band wave of f=f ₀ ±f _RF becomes weak.

Thus, since the wide frequency band radio signal in the millimeter wave band or the terahertz band is a signal having a total frequency band Δf _to (e.g., 80 GHz) greater than the intermediate frequency f _RF (e.g., 50 GHz), the first optical modulator The use of quadrature bias settings in 6Ab and second optical modulator 6Bb results in the inability to linearly convert intermediate frequency signals to optical signals without spectral overlap, as described above. Therefore, there arises a problem that it is impossible to receive radio signals in a wide frequency band such as the millimeter wave band or the terahertz band by filtering in the optical domain.

Therefore, in the present embodiment, null bias setting is used in the first optical modulator 6Ab and the second optical modulator 6Bb when receiving a radio signal in a wide frequency band such as the millimeter wave band or the terahertz band. . However, if the null bias setting is used, even if the total frequency bandwidth Δf _to (eg, 80 GHz) is greater than the intermediate frequency f _RF (eg, 50 GHz), the intermediate frequency signal becomes the optical signal, spectrally can be linearly transformed without overlapping. In particular, when using the null bias setting, it is preferable when the total frequency band Δf _to of the radio signal in the broad frequency band of the millimeter wave band or the terahertz band satisfies the condition of Δf _to ≦2f _RF , and more preferably, This is the case where the condition of f _RF <Δf _to ≦2f _RF is satisfied.

Thus, according to this embodiment, it is possible to receive a radio signal in a wide frequency band in the millimeter wave band or the terahertz band by filtering in the optical domain.

It should be noted that the content illustrated in the present embodiment is merely an example, and various modifications and changes are possible within the scope of the gist of the invention described in the scope of claims. For example, in the present embodiment, a radio signal of a wide frequency band in the millimeter wave band or the terahertz band is exemplified as having subcarrier signals of a plurality of channels. Anything you have is fine. In this case, the branch portion 3 becomes unnecessary.

Any optical filter may be used as the first optical filter 7A and the second optical filter 7B shown in this embodiment. As such, there is the possibility of separating optical signals in which a spectral protrusion P1 is present. In this case, as shown in FIG. 5(b), intersymbol interference (overlapping between adjacent pulses) occurs, degrading the optical signal. The signal shown in FIG. 5 is a 40 Gbit/s binary modulated signal.

Therefore, as the first optical filter 7A and the second optical filter 7B, a grating+LCoS (Liquid crystal on silicon) type optical filter, or a configuration in which a rectangular optical filter is combined with a variable coupling ratio asymmetric Mach-Zehnder interferometer type optical filter is used. is preferably used to remove peaks P1 in the spectrum and flatten the top of the spectrum as indicated by the dashed line P2 shown in FIG. 5(a). In this way, intersymbol interference (overlapping between adjacent pulses) can be reduced as shown in FIG. Signals can be separated.

Further, in the present embodiment, an example in which the first semiconductor laser 6Aa and the second semiconductor laser 6Ba are provided in the first light conversion section 6A and the second light conversion section 6B, respectively, has been described, but the present invention is not limited to this. A laser may be used to split the light output from the semiconductor laser and enter the first optical modulator 6Ab and the second optical modulator 6Bb for modulation.

On the other hand, when the first semiconductor laser 6Aa and the second semiconductor laser 6Ba are provided in the first optical conversion section 6A and the second optical conversion section 6B, respectively, the received radio signal in a wide frequency band in the millimeter wave band or the terahertz band is converted to , is suitable for transmission to another location. That is, the first semiconductor laser 6Aa and the second semiconductor laser 6Ba output light beams having different wavelengths, and the first optical filter 7A filters the light region to produce a second light beam as shown in FIG. 2(d-1). The second channel CH2 is separated, the second optical filter 7B performs filtering in the optical region, and the first channel CH1 is separated as shown in FIG. 2(d-2). Then, the separated first channel CH1 and second channel CH2 are combined and transmitted to another location.

1 Radio signal receiving system 2 Receiving antenna (receiving unit)
3 branching portion 4A first electrical signal conversion portion (electrical signal conversion portion)
4B Second electrical signal converter (electrical signal converter)
6A first optical conversion unit (optical conversion unit)
6Ab First optical modulator 6B Second optical converter (optical converter)
6Bb Second optical modulator 7A First optical filter 7B Second optical filter

Claims (3)

a receiving unit that receives radio signals in the millimeter wave band or the terahertz band;
an electrical signal converter that converts a radio signal received by the receiver into an electrical signal;
an optical conversion unit that converts the electrical signal converted by the electrical signal conversion unit into an optical signal;
an optical filter unit that separates the optical signal converted by the optical conversion unit into bands equal to the frequency band of the radio signal received by the reception unit;
The radio signal receiving system, wherein the optical conversion section uses a null bias setting when converting the electrical signal converted by the electrical signal conversion section into an optical signal. The electrical signal converter down-converts the carrier frequency of the radio signal received by the receiver to an intermediate frequency by finding the difference between the radio signal received by the receiver and the local oscillator signal. converted into an electrical signal,
When the frequency band of the radio signal in the millimeter wave band or the terahertz band is Δf _t0 and the intermediate frequency is f _RF ,
2. The radio signal receiving system according to claim 1, wherein the frequency band of said radio signal satisfies the condition of ?f _t0 ≤ 2f _RF . further comprising a branching unit for branching the radio signal received by the receiving unit;
The millimeter wave band or terahertz band radio signal is a division multiplexed signal having at least two channels of subcarrier signals, and is received by the receiving unit,
The branching unit branches the radio signal received by the receiving unit,
The electrical signal conversion unit converts the carrier frequency of the radio signal branched by the branching unit to an intermediate frequency by taking a difference between the radio signals branched by the branching unit using different local oscillation signals. converted to an electrical signal down-converted to
The optical conversion unit converts the electrical signal converted by the electrical signal conversion unit into an optical signal,
3. The radio signal receiving system according to claim 1, wherein the optical filter section separates the optical signal converted by the optical conversion section for each channel.

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