Wireless module

Abstract

This wireless module comprises: an RFIC that processes an RF signal; a photoelectric conversion element that performs conversion processing between an optical signal transmitted through an optical fiber and an electric signal; a first substrate that has a first main surface and a second main surface, on which first main surface or second main surface the photoelectric conversion element is mounted, the first substrate having one or a plurality of first signal lines for transmitting an electric signal obtained by conversion by the photoelectric conversion element; a second substrate having a third main surface and a fourth main surface and being mounted on the first substrate with the third main surface facing the second main surface of the first substrate, on which third main surface the RFIC and one or a plurality of second signal lines connected to the RFIC and transmitting the RF signal are provided; and one or a plurality of antenna elements provided on the fourth main surface of the second substrate and supplied with power by means of the RFIC via the one or a plurality of second signal lines.

Description

Wireless Module

[0001] The present disclosure relates to a wireless module.

[0002] Conventionally, there has been an optical transmission device that includes a radio control station that converts an electrical signal into an optical signal and transmits it, an optical fiber that transmits the optical signal transmitted from the radio control station, and a radio base station that receives the optical signal transmitted by the optical fiber. The radio base station used in this optical transmission device includes an opto-electrical converter (optical / electrical converter) that converts the optical signal into an electrical signal, a mixer (frequency converter) that performs up-conversion, and the like (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2003-046444

[0004] However, with regard to conventional wireless base stations, there is no specific disclosure regarding the substrates on which the photoelectric conversion units, mixers, etc. are mounted. As the radio frequency increases, the signal transmission loss in the signal path from the photoelectric conversion unit to the antenna via the mixer increases, which has a significant impact on the communication performance of the wireless base station, particularly in the case of millimeter-wave band signals.

[0005] Therefore, an object of the present invention is to provide a wireless module for a wireless base station with improved communication performance.

[0006] a first substrate having a first main surface and a second main surface, the first substrate having the photoelectric conversion element mounted on the first main surface or the second main surface and one or more first signal lines transmitting electrical signals converted by the photoelectric conversion element; a second substrate having a third main surface and a fourth main surface, the second substrate being mounted on the first substrate with the third main surface facing the second main surface of the first substrate, the second substrate having the RFIC and one or more second signal lines connected to the RFIC and transmitting the RF signals provided on the third main surface; and one or more antenna elements provided on the fourth main surface of the second substrate and fed with power by the RFIC via the one or more second signal lines.

[0007] It is possible to provide a wireless module for a wireless base station with improved communication performance.

[0008] 1 is a diagram showing an example of the configuration of a wireless module 100 of an embodiment; FIG. 2 is a diagram showing an example of the configuration of a cross section taken along the line A-A in FIG. 1; FIG. 3 is a diagram showing an example of the configuration of a wireless module 100M of a modified embodiment; FIG. 4 shows a first modified embodiment of the embodiment; FIG. 5 shows a second modified embodiment of the embodiment; and FIG. 6 shows a third modified embodiment of the embodiment.

[0009] Hereinafter, embodiments to which the wireless module of the present disclosure is applied will be described. In the following, the same elements will be denoted by the same reference numerals, and duplicated descriptions may be omitted.

[0010] In the following description, the XYZ coordinate system is defined. The direction parallel to the X axis (X direction), the direction parallel to the Y axis (Y direction), and the direction parallel to the Z axis (Z direction) are perpendicular to one another. For ease of explanation, the -Z direction may be referred to as the lower side or bottom, and the +Z direction may be referred to as the upper side or top. Planar view refers to viewing from the XY plane. In the following description, the length, width, thickness, etc. of each part may be exaggerated to make the configuration easier to understand. Terms such as parallel, right angle, orthogonal, horizontal, vertical, and up and down may be misaligned to the extent that they do not impair the effects of the embodiments.

[0011] In the following description, the term "millimeter wave" or "millimeter wave band" includes the quasi-millimeter wave band of 24 GHz to 30 GHz in addition to the frequency band of 30 GHz to 300 GHz.

[0012] The wireless module of the embodiment is, for example, a wireless communication device that can be used as a base station (wireless base station), CPE (Customer Premises Equipment), or terminal device. The radio waves transmitted and received by the wireless module of the embodiment are preferably in the millimeter wave band of the fifth generation mobile communication system (5G) or in the 1 GHz to 300 GHz frequency band including Sub-6. The radio waves transmitted and received by the wireless module of the embodiment may be Long Term Evolution (LTE), LTE-Advanced (LTE-A), or Ultra Mobile Broadband (UMB). The radio waves transmitted and received by the wireless module of the embodiment may be IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.20, UWB (Ultra-Wideband), Bluetooth (registered trademark), LPWA (Low Power Wide Area), WiGig (Wireless Gigabit), or the like. Generally, as the frequency of radio waves increases, signal transmission loss increases in wiring on printed circuit boards, etc. The wireless module of the embodiment improves communication performance by reducing transmission loss in the board, and is therefore more suitable for communication using relatively high frequencies (especially in the millimeter wave band).

[0013] 1 is a diagram showing an example of the configuration of a wireless module 100 according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of the configuration of a cross section taken along the line AA in FIG.

[0014] <Configuration of Wireless Module 100 > The wireless module 100 includes a first substrate 110 , a second substrate 120 , a control IC (Integrated Circuit) 130 , a photoelectric conversion element 140 , a converter 150 , an RF (Radio Frequency) IC 160 , and a plurality of antenna elements 170 .

[0015] In the wireless module 100, the photoelectric conversion element 140 is connected to a DU (Distributed Unit) 20 in the network center via an optical fiber 30, and the DU 20 is connected to a CU (Central Unit) 10.

[0016] An example of the present disclosure will be described using an analog radio-over-fiber (A-RoF) transmission method. The wireless module 100 is a wireless communication device that transmits analog optical signals to the DU 20 via an optical fiber 30 and transmits and receives radio signals (radio wave emission and reception) via multiple antenna elements 170. As an example, the optical signal transmitted via the optical fiber 30 is intensity-modulated with a radio signal called an intermediate frequency (IF) of 3.5 GHz, and the frequency of the radio signal transmitted and received via the multiple antenna elements 170 is 28 GHz.

[0017] In the following, the configuration of the wireless module 100 will be described using the operation (transmission operation) of the wireless module 100 to emit radio waves from the multiple antenna elements 170, but the reception operation is the reverse of the transmission operation.

[0018] <CU10, DU20, and Optical Fiber 30> The CU10, for example, controls the DU20, connects to the core network, encrypts packets, and performs other processes. The data handled by the CU10 is digital data. The DU20 performs signal processing such as modulation and demodulation on the digital signal transmitted from the CU10, and then converts it into an analog optical signal. The DU20 also converts the analog optical signal transmitted from the optical fiber 30 into a digital signal and outputs it to the CU10. The optical fiber 30 is an optical fiber that transmits an optical signal, and connects the DU20 and the photoelectric conversion element 140 of the wireless module 100.

[0019] <First Substrate 110> The first substrate 110 has a main surface 111, a main surface 112, an opening 113, and a plurality of signal lines 114. The main surface 111 is an example of a first surface, the main surface 112 is an example of a second main surface, and the signal line 114 is an example of a first signal line. Here, a form in which the first substrate 110 has a plurality of signal lines 114 will be described, but it is sufficient that the first substrate 110 has at least one signal line 114.

[0020] Furthermore, a control IC 130 and a photoelectric conversion element 140 are mounted on the first substrate 110, and a converter 150, an RFIC 160, and a plurality of antenna elements 170 are mounted on the second substrate 120.

[0021] The frequency of the electrical signal transmitted through signal line 114 of first substrate 110 is 3.5 GHz, and the frequency of the electrical signal transmitted through signal line 124 of second substrate 120 is 28 GHz. In other words, the frequency of the electrical signal transmitted through signal line 114 of first substrate 110 is lower than the millimeter wave band, and the frequency of the electrical signal transmitted through signal line 124 of second substrate 120 is in the millimeter wave band.

[0022] When emitting radio waves in the millimeter wave band, it is particularly important to reduce transmission loss between the RFIC 160 and the plurality of antenna elements 170, and signal transmission loss between the converter 150 and the RFIC 160. On the other hand, if an attempt is made to reduce signal transmission loss in the entire section between the photoelectric conversion element 140 and the plurality of antenna elements 170, problems such as cost arise.

[0023] Furthermore, in the wireless module 100, signals transmitted in the section from the converter 150 via the RFIC 160 to the plurality of antenna elements 170 are in the millimeter wave band, but the frequency of signals transmitted between the photoelectric conversion element 140 and the converter 150 is lower than the millimeter wave band. In other words, even if the signal transmission loss in the section between the photoelectric conversion element 140 and the converter 150 is somewhat larger than that in the section from the converter 150 via the RFIC 160 to the plurality of antenna elements 170, it does not pose a major problem.

[0024] For these reasons, a printed circuit board that is less expensive and has a larger transmission loss than the second substrate 120 is used for the first substrate 110. For this reason, the dielectric loss tangent of the first substrate 110 is larger than the dielectric loss tangent of the second substrate 120. The dielectric loss tangent of the first substrate 110 is 0.0071 or more and 0.05 or less.

[0025] Furthermore, because a printed circuit board that is less expensive and has greater transmission loss than second substrate 120 is used for first substrate 110, the relative dielectric constant of first substrate 110 is greater than the relative dielectric constant of second substrate 120. The relative dielectric constant of first substrate 110 is 3.51 to 7.0.

[0026] In addition, the frequency of the electrical signal transmitted through the signal line 114 of the first substrate 110 is not limited to 3.5 GHz as long as it is lower than the millimeter wave band, and the frequency of the electrical signal transmitted through the signal line 124 of the second substrate 120 is not limited to 28 GHz as long as it is in the millimeter wave band.

[0027] The main surface 111 is the surface (bottom surface) on the -Z direction side, and the main surface 112 is the surface (top surface) on the +Z direction side. As an example, the first substrate 110 is a laminated substrate in which multiple insulating layers and multiple wiring layers are stacked between the main surfaces 111 and 112. As an example, such a first substrate 110 can be realized as an FR-4 (Flame Retardant type 4) standard printed circuit board, and as an example, can be made from a glass cloth substrate polyphenylene ether resin (PPE) or the like. As an example, the first substrate 110 is a substrate that is rectangular in plan view.

[0028] The opening 113 is a through-hole that penetrates the center of the first substrate 110 in the Z direction in a plan view. The opening 113 penetrates the first substrate 110 between the main surface 111 and the main surface 112. As an example, the opening 113 is an opening that is rectangular in a plan view. Since the first substrate 110 has a rectangular annular shape in a plan view, the first substrate 110 is divided into two in the cross section of FIG. 2 .

[0029] The signal line 114 connects the photoelectric conversion element 140 and the signal line 124 of the second substrate 120 , and transmits the electrical signal converted by the photoelectric conversion element 140 to the signal line 124 .

[0030] Furthermore, in the wireless module 100, a printed circuit board that is cheaper than the second substrate 120 is used for the first substrate 110, but in order to reduce the signal transmission loss between the photoelectric conversion element 140 and the converter 150, the sections of the signal line 114 other than the sections that need to be exposed on the main surface 111 or the main surface 112 are positioned as much as possible inside the insulating layer of the first substrate 110 and configured as strip lines.

[0031] The first substrate 110 is not limited to a rectangular annular shape in a plan view. For example, the first substrate 110 may have a configuration in which one of the four sides of the opening edge of the opening 113 is closed in a plan view, thereby forming a notch cut from a part of the outer edge of the first substrate 110 toward the center in a plan view. Furthermore, the first substrate 110 may be divided into two pieces, as shown in FIG. 2 .

[0032] <Second Substrate 120> The second substrate 120 has a main surface 121, a main surface 122, and a plurality of signal lines 124. The main surface 121 is an example of a third surface, the main surface 122 is an example of a fourth main surface, and the signal line 124 is an example of a second signal line. Here, a form in which the second substrate 120 has a plurality of signal lines 124 will be described, but it is sufficient that the second substrate 120 has at least one signal line 124.

[0033] Furthermore, the converter 150, the RFIC 160, and a plurality of antenna elements 170 are mounted on the second substrate 120. A signal transmitted in the section from the converter 150 via the RFIC 160 to the plurality of antenna elements 170 is in the millimeter wave band, and it is preferable that the transmission loss is small.

[0034] For this reason, a printed circuit board with a smaller transmission loss than the first substrate 110 is used for the second substrate 120. The dielectric loss tangent of the second substrate 120 is smaller than the dielectric loss tangent of the first substrate 110. The dielectric loss tangent of the first substrate 110 is 0.0071 or more and 0.05 or less, and the second substrate 120 is a substrate with a dielectric loss tangent of less than 0.0071.

[0035] Furthermore, because a printed circuit board with lower transmission loss than the first substrate 110 is used for the second substrate 120, the second substrate 120 has a lower dielectric constant than the first substrate 110. The second substrate 120 has a dielectric constant of 1.01 to 3.50, which is lower than the dielectric constant of the first substrate 110 (3.51 to 7.0). The second substrate 120 may be made of glass with a high dielectric constant (e.g., 3.7) and a small dielectric dissipation factor (e.g., 0.001), such as synthetic quartz glass produced by the vapor phase axial deposition (VAD) method. Alternatively, the second substrate 120 may be made of ceramics with a high dielectric constant (e.g., 10.0) and a small dielectric dissipation factor (e.g., 0.001), such as fine ceramics.

[0036] The main surface 121 is the surface (bottom surface) on the -Z direction side, and the main surface 122 is the surface (top surface) on the +Z direction side. The second substrate 120 is, for example, a laminated substrate in which multiple insulating layers and multiple wiring layers are stacked between the main surfaces 121 and 122. For example, such a second substrate 120 can be realized as an FR-4 standard printed circuit board. From the viewpoint of transmission loss, the second substrate 120 is preferably a glass cloth-based polyphenylene ether resin (PPE) substrate, and more preferably a fluororesin substrate (PTFE). For example, the second substrate 120 is a rectangular substrate in a plan view, and for example, is larger than the opening 113 of the first substrate 110 in a plan view.

[0037] The second substrate 120 is mounted on the first substrate 110 with its main surface 121 facing the main surface 112 of the first substrate 110. The main surface 121 abuts against the main surface 112. The second substrate 120 is mounted on the first substrate 110 so as to cover the opening 113 of the first substrate 110 in a plan view. With the second substrate 120 mounted on the first substrate 110, the outer edge of the second substrate 120 encompasses the edge of the opening 113 in a plan view. Note that the second substrate 120 may be fixed to the main surface 112 of the first substrate 110 by adhesive or the like, for example.

[0038] In addition, the second substrate 120 may be mounted on the first substrate 110 with the main surface 122 facing the main surface 111 of the first substrate 110 .

[0039] By mounting the second substrate 120 so as to cover the opening 113 of the first substrate 110 in a plan view, the converter 150 and the RFIC 160 can be mounted on the main surface 121 , which is the lower surface of the second substrate 120 .

[0040] The signal line 124 connects between the signal line 114 of the first substrate 110 and the converter 150, between the converter 150 and the RFIC 160, and between the RFIC 160 and the multiple antenna elements 170. Between the signal line 114 and the converter 150, the signal line 124 transmits an electrical signal transmitted from the signal line 114 to the converter 150. Between the converter 150 and the RFIC 160, the signal line 124 transmits an analog electrical signal up-converted by the converter 150 to the RFIC 160. Between the RFIC 160 and the multiple antenna elements 170, the signal line 124 transmits, to the multiple antenna elements 170, analog electrical signals that have been subjected to signal processing such as amplification and phase shift adjustment in the RFIC 160.

[0041] Furthermore, in the wireless module 100, a printed circuit board that is more expensive and has lower transmission loss than the first substrate 110 is used for the second substrate 120. In particular, to reduce the transmission loss of signals before and after the RFIC 160, sections of the signal line 124 other than the section that needs to be exposed on the main surface 121 or the main surface 122 are positioned as much as possible inside the insulating layer of the second substrate 120 and configured as striplines.

[0042] Furthermore, the converter 150 and the RFIC 160 can be mounted on the main surface 121, which is the lower surface of the second substrate 120. Therefore, the converter 150 and the RFIC 160 can be connected by a signal line 124 with small signal transmission loss, and the signal line 124 between the converter 150 and the RFIC 160 can be shortened. Furthermore, the RFIC 160 and the multiple antenna elements 170 can be connected by a signal line 124 with small signal transmission loss, and the signal line 124 between the RFIC 160 and the multiple antenna elements 170 can be shortened. In particular, the RFIC 160 and the multiple antenna elements 170 can be connected by a section of the signal line 124 that is formed by a stripline that passes through the inside of the second substrate 120. With this configuration, the signal transmission loss in the second substrate 120 can be efficiently reduced.

[0043] <Control IC 130> The control IC 130 is mounted on the main surface 112 of the first substrate 110, as an example. Although the control IC 130 is not shown, it is actually composed of a group of control ICs having various functions. The control IC 130 is connected to the converter 150, the RFIC 160, and the like via a control signal line 180, and performs overall control of the converter 150, control of the RFIC 160, and the like. The control IC 130 controls the power supply circuit 190 that supplies power to the converter 150 and the RFIC 160, thereby controlling the power supply. Furthermore, the control of the RFIC 160 performed by the control IC 130 includes control of the amount of phase shift and amplitude when performing beamforming with multiple antenna elements 170, and control of transmission / reception switching. Furthermore, when controlling the converter 150, the control IC 130 also controls the drive of a local signal oscillator (not shown) that inputs a local signal to the converter 150.

[0044] The control IC 130 may be provided on the main surface 111. In this case, the photoelectric conversion element 140 may be provided on the main surface 111 together with the control IC 130, but is preferably provided on the main surface 112. This is to reduce the effect of heat generated by the control IC 130 on the photoelectric conversion element 140.

[0045] <Photoelectric Conversion Element 140> The photoelectric conversion element 140 is mounted on the main surface 111 of the first substrate 110, for example. The photoelectric conversion element 140 has a terminal connected to the optical fiber 30 and a terminal connected to the signal line 114, and performs conversion processing between an analog optical signal and an analog electrical signal. For example, a photodiode or a laser diode can be used as the photoelectric conversion element 140. Although not shown, the photoelectric conversion element 140 also includes a function such as WDM (wavelength division multiplexing) and an optical modulator function such as MZM (Mach-Zehnder modulator).

[0046] The photoelectric conversion element 140 is provided on the main surface 112, and the control IC 130 is provided on the main surface 111 opposite to the main surface 112, thereby reducing the influence of heat generated by the control IC 130. Note that, as described above, the photoelectric conversion element 140 may be provided on the main surface 112.

[0047] The wireless module 100 transmits analog optical signals to and from the DU 20 via the optical fiber 30. Because the wireless module 100 does not require digital conversion of electrical signals, it does not require an A / D (Analog to Digital) converter or a D / A (Digital to Analog) converter, making it possible to simplify the configuration, reduce the size of the device, and reduce power consumption. This makes it possible to provide a wireless module 100 that can be used as a base station (base station), and that has a simplified configuration, a smaller size of the device, and low power consumption.

[0048] Furthermore, because the wireless module 100 is connected to the DU 20 via the optical fiber 30 using an analog optical signal, the analog-to-digital conversion function can be transferred from the wireless module 100 to the DU 20. This also makes it possible to simplify the configuration, reduce the size of the device, and reduce power consumption. Therefore, it is possible to provide a wireless module 100 that can be used as a base station (base station), has a simplified configuration, is a smaller device, and consumes less power.

[0049] The photoelectric conversion element 140 that converts between analog optical signals and analog electrical signals can be realized by, for example, a photodiode or a laser diode.

[0050] 2 shows a single converter 150 for simplicity, but the converter 150 actually includes a converter 150 that performs upconversion in a transmission (Tx) circuit and a converter 150 that performs downconversion in a reception (Rx) circuit. Between the photoelectric conversion element 140 and the RFIC 160, the connection with the transmission (Tx) circuit or the reception (Rx) circuit is switched by a switch (not shown). The control IC 130 controls the switching of this switch via signal lines 114 and 124.

[0051] <RFIC 160> The RFIC 160 is connected between the converter 150 and the multiple antenna elements 170. The RFIC 160 is connected to the multiple antenna elements 170 via multiple signal lines 124, respectively, and has built-in phase shifters that adjust the phase shift amount of signals transmitted from the multiple antenna elements 170 and amplifiers that control the amplitude. The RFIC 160 is controlled by the control IC 130 and sets the phase shift adjustment amount and amplitude amount of each phase shifter. Note that one antenna element 170 may be connected to one phase shifter and amplifier, or the multiple antenna elements 170 may be divided into several groups, with one phase shifter and amplifier provided for each group.

[0052] <Multiple Antenna Elements 170> Multiple antenna elements 170 are provided on the main surface 122 of the second substrate 120. Each antenna element 170 is formed from a metal layer of copper, aluminum, or the like provided on the main surface 122, and is configured as a patch antenna, for example. Each antenna element 170 is connected to the RFIC 160 and is fed power via the RFIC 160. By using a printed circuit board, which is more expensive and has smaller transmission loss than the first substrate 110, for the second substrate 120, the radiation performance of the multiple antenna elements 170 can be improved.

[0053] The antenna elements 170 are arranged in an array along the X and Y directions, for example, and radiate beams formed by beamforming. The angle of the beam is variably controlled by controlling the phase adjustment amount of the phase shifter inside the RFIC 160. Note that, in order to perform beamforming, it is sufficient that a plurality of antenna elements 170 are provided, and they may be configured to be arranged along either the X or Y direction.

[0054] <Effects> The wireless module 100 includes an RFIC 160 that processes RF signals, a photoelectric conversion element 140 that converts between optical signals transmitted through the optical fiber 30 and electrical signals, a first substrate 110 having a main surface 111 and a main surface 112, where the photoelectric conversion element 140 is mounted on the main surface 111 or the main surface 112, and where the first substrate 110 has one or more signal lines 114 that transmit electrical signals converted by the photoelectric conversion element 140, and a main surface 121 and a main surface 122. 2 and is mounted on the first substrate 110 with its main surface 121 facing the main surface 112 of the first substrate 110, the second substrate 120 including an RFIC 160 and one or more signal lines 124 connected to the RFIC 160 and transmitting RF signals provided on the main surface 121, and one or more antenna elements 170 provided on the main surface 122 of the second substrate 120 and fed by the RFIC 160 via the one or more signal lines 124. In this way, by separating the first substrate 110, on which the photoelectric conversion element 140 is mounted and on which the frequency of the electric signal is low, from the second substrate 120, on which the RFIC 160 is mounted and on which the frequency of the electric signal is high, it is possible to separately select the characteristics of the first substrate 110 and the second substrate 120 according to the frequency of the electric signal, thereby improving communication performance.

[0055] Therefore, it is possible to provide a wireless module 100 for a wireless base station with improved communication performance.

[0056] Furthermore, the dielectric loss tangent of second substrate 120 may be smaller than the dielectric loss tangent of first substrate 110. By making the dielectric loss tangent of second substrate 120 smaller than the dielectric loss tangent of first substrate 110, the transmission loss of electrical signals in second substrate 120 can be reduced more than that in first substrate 110. By setting the relationship of the dielectric loss tangents in this way, it is possible to provide a wireless module 100 for a wireless base station with improved communication performance.

[0057] The first substrate 110 is a substrate having a dielectric loss tangent of 0.0071 or more and 0.05 or less, and the first substrate 110 may be a substrate having a dielectric loss tangent of less than 0.0071. When the second substrate 120 has a dielectric loss tangent of less than 0.0071, the transmission loss of electrical signals in the second substrate 120 can be reduced compared to the first substrate 110. By setting the relationship of the dielectric loss tangents in this way, it is possible to provide a wireless module 100 for a wireless base station with improved communication performance.

[0058] Furthermore, the relative dielectric constant of the second substrate 120 may be smaller than the relative dielectric constant of the first substrate 110. By making the relative dielectric constant of the second substrate 120 smaller than the relative dielectric constant of the first substrate 110, it is possible to improve the radiation characteristics of the antenna in the second substrate 120 compared to the first substrate 110. By setting the relationship between the relative dielectric constants in this way, it is possible to provide a wireless module 100 for a wireless base station with improved communication performance.

[0059] The first substrate 110 may have a relative dielectric constant of 3.51 to 7.00, and the second substrate 120 may have a relative dielectric constant of 1.01 to 3.50. By making the second substrate 120 have a relative dielectric constant of 1.01 to 3.50, the radiation characteristics of the antenna in the second substrate 120 can be improved compared to the first substrate 110. By setting the relationship between the relative dielectric constants in this way, it is possible to provide a wireless module 100 for a wireless base station with improved communication performance.

[0060] Furthermore, at least some sections of one or more signal lines 114 may be configured with striplines formed on the first substrate 110, or at least some sections of one or more signal lines 124 may be configured with striplines formed on the second substrate 120. By configuring at least some sections of one or more signal lines 114 or at least some sections of one or more signal lines 124 with striplines, noise from other signal lines, etc. can be reduced, and a wireless module 100 for a wireless base station with further improved communication performance can be provided.

[0061] 3 is a diagram illustrating an example of the configuration of a wireless module 100M according to a modification of the embodiment. The wireless module 100M has a configuration in which the converter 150 of the wireless module 100 shown in FIG. 2 is moved to the main surface 111 of the first substrate 110.

[0062] In the wireless module 100M, as an example, a photoelectric conversion element 140 and a converter 150 are mounted on the main surface 111 of the first substrate 110, and the photoelectric conversion element 140 and the converter 150 are connected by a signal line 114. The converter 150 is connected to an RFIC 160 mounted on the main surface 111 of the first substrate 110 via a portion of the signal line 114 that is configured as a strip line that passes through the inside of the first substrate 110 and a signal line 124 of the second substrate 120.

[0063] Even if the converter 150 is mounted on the main surface 111 of the first substrate 110, electrical signals can be transmitted between the RFIC 160 and the multiple antenna elements 170 via the signal line 124 of the second substrate 120, which has low signal transmission loss, so that a wireless module 100M for a wireless base station with improved communication performance can be provided.

[0064] In the above-described embodiment, an analog radio-over-fiber (RoF) transmission system has been described as an example, but the present disclosure is not limited to analog RoF. For example, a ΔΣ RoF transmission system as shown in FIG. 4 may also be used. In the wireless module 100 using the ΔΣ RoF transmission system shown in FIG. 4, the CU 10 and DU 20 convert ΔΣ modulated signals into optical signals using optical modulators, transmit the signals via optical fiber 30, and receive them at the photoelectric conversion element 140. The configuration from the photoelectric conversion element 140 to the antenna 170 can be substantially the same as in the above-described embodiment. The converter 150 may be located on the first substrate 110 or, as in the case of the analog RoF transmission system described above, on the second substrate 120.

[0065] The present disclosure also includes a case where a 1-bit RoF transmission method as shown in Fig. 5 is used. In the wireless module 100 using the 1-bit RoF transmission method of Fig. 5, the CU 10 and DU 20 perform digital signal processing on high-frequency analog signals, then convert the signals into 1-bit pulse signals in a 1-bit pulse converter, and further convert the 1-bit pulse signals into optical signals in an optical converter (EO) for transmission over the optical fiber 30. The converter 150 may be located on the first board 110 or the second board 120, as in the case of Fig. 4.

[0066] The present disclosure also includes a case where a digital RoF (D-RoF) transmission method is used, as shown in FIG. 6. In a wireless module using the D-RoF transmission method of FIG. 6, the waveform of the wireless signal can be sampled and quantized in the CU and DU 20 to convert it into digital data, and then transmitted over the optical fiber 30. As shown in FIG. 6, a method can also be used in which an optical signal is converted into an electrical signal by the photoelectric conversion element 140, and then the digital signal is converted into an analog signal. In this case, the converter 150 may be located on either the first board 110 or the second board 120.

[0067] While exemplary wireless modules of the present disclosure have been described above, the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and variations are possible without departing from the scope of the claims.

[0068] REFERENCE SIGNS LIST 100 Wireless module 110 First substrate 111 Main surface (an example of a first surface) 112 Main surface (an example of a second main surface) 113 Opening 114 Signal line (an example of a first signal line) 120 Second substrate 121 Main surface (an example of a third surface) 122 Main surface (an example of a fourth main surface) 124 Signal line (an example of a second signal line) 130 Control IC 140 Photoelectric conversion element 150 Converter 160 RFIC 170 Antenna element 180 Control signal line 190 Power supply circuit

Claims

1. A wireless module comprising: an RFIC that processes RF signals; a photoelectric conversion element that converts optical signals transmitted through an optical fiber into electrical signals; a first substrate having a first main surface and a second main surface, wherein the photoelectric conversion element is mounted on the first main surface or the second main surface and has one or more first signal lines that transmit electrical signals converted by the photoelectric conversion element; a second substrate having a third main surface and a fourth main surface, wherein the second substrate is mounted on the first substrate with the third main surface facing the second main surface of the first substrate, and wherein the RFIC and one or more second signal lines connected to the RFIC that transmit the RF signals are provided on the third main surface; and one or more antenna elements that are provided on the fourth main surface of the second substrate and are fed with power by the RFIC via the one or more second signal lines.

2. The wireless module according to claim 1, wherein the dielectric loss tangent of the second substrate is smaller than the dielectric loss tangent of the first substrate.

3. A wireless module according to claim 2, wherein the first substrate is a substrate having a dielectric dissipation factor of 0.0071 or more and 0.05 or less, and the second substrate is a substrate having a dielectric dissipation factor of less than 0.0071.

4. The wireless module according to claim 1, wherein the second substrate has a lower dielectric constant than the first substrate.

5. The wireless module according to claim 4, wherein the first substrate has a relative dielectric constant of 3.51 to 7.0, and the second substrate has a relative dielectric constant of 1.01 to 3.

50.

6. A wireless module according to any one of claims 1 to 5, wherein the one or more first signal lines are formed as striplines formed on the first substrate, or the one or more second signal lines are formed as striplines formed on the second substrate.

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