Antenna module, communication device equipped with same, and method for manufacturing antenna module

Abstract

An antenna module (30) is provided with a transmission port (T1) and a reception port (T2), antenna elements (ANT1, ANT2) having the same resonant frequency, transmission lines (21, 22), a resistive circuit (R1), and a reactance circuit (LC1). The transmission line (21) is connected between the transmission port (T1) and the antenna element (ANT1). The transmission line (22) is connected between the reception port (T2) and the antenna element (ANT2). The resistive circuit (R1) is connected between the transmission line (21) and the transmission line (22). The reactance circuit (LC1) is connected in parallel to the resistive circuit (R1). A resistance value of the resistive circuit (R1) and a reactance value of the reactance circuit (LC1) are set so that a real part and an imaginary part of admittance between the transmission port (T1) and the reception port (T2) are cancelled out at the resonant frequency or in the vicinity of the resonant frequency.

Description

Antenna Module, Communication Device Equipped with the Same, and Method for Manufacturing Antenna Module

[0001] The present disclosure relates to an antenna module, a communication device equipped with the same, and a method for manufacturing an antenna module, and more particularly, to a technique for removing interference noise generated between two antenna elements.

[0002] In recent years, with the increase in communication devices, communication traffic has been rapidly increasing, and concerns about network bandwidth congestion have been spreading. As means for solving these problems, for example, expectations for full-duplex communication systems that enable communication at the same time and the same frequency have been increasing. As another example, expectations for technologies such as Massive-MIMO technology that mounts antennas at high density have also been increasing. In these examples, interference noise generated between a plurality of antennas during communication becomes a problem.

[0003] In International Publication No. 2023 / 106068 (Patent Document 1), a communication device is disclosed that includes a noise removal circuit including a coupling line that connects two transmission lines that respectively transmit high-frequency signals to two antenna elements, and a plurality of resonators connected in parallel to the coupling line.

[0004] In the communication device disclosed in International Publication No. 2023 / 106068 (Patent Document 1), a band-stop filter that blocks a predetermined frequency band is configured by the coupling line and the plurality of resonators included in the noise removal circuit, thereby reducing interference noise caused by the transmission signal generated in the received signal between the transmission lines.

[0005] International Publication No. 2023 / 106068

[0006] The noise removal circuit disclosed in International Publication No. 2023 / 1060 (Patent Document 1) tends to exhibit a noise removal effect in a configuration where the coupling between antennas is relatively strong, but is less likely to have an effect on a configuration where the coupling between antennas is relatively weak.

[0007] This disclosure was made to solve these problems, and its purpose is to enable the reduction of interference noise occurring between two transmission lines connected to two antenna elements, respectively.

[0008] The antenna module according to this disclosure comprises a transmitting port and a receiving port, a first antenna element and a second antenna element having the same resonant frequency, a first transmission line and a second transmission line, a resistor circuit, and a reactance circuit. The first transmission line is connected between the transmitting port and the first antenna element. The second transmission line is connected between the receiving port and the second antenna element. The resistor circuit is connected between the first transmission line and the second transmission line. The reactance circuit is connected in parallel with the resistor circuit. The resistance value of the resistor circuit and the reactance value of the reactance circuit are set so that the real and imaginary parts of the admittance between the transmitting port and the receiving port cancel each other out at or near the resonant frequency.

[0009] In the antenna module according to this disclosure, by providing a resistor circuit and a reactance circuit connected in parallel between two transmission lines, the antenna element itself can be used as a resonator and function as a bandstop filter. Therefore, interference noise generated between the two transmission lines connected to the two antenna elements can be reduced.

[0010] This is an overall schematic diagram of a communication device equipped with an antenna module according to Embodiment 1. This is an external perspective view of the antenna module in Figure 1. This is a plan view of the antenna module in Figure 1. This is a diagram for explaining the outline of the noise reduction principle in the comparative example. This is a diagram for explaining the problems in the noise reduction circuit of the comparative example. This is a diagram for explaining the outline of the noise reduction principle in the antenna module of Embodiment 1. This is a flowchart of the adjustment method in the manufacturing process of the antenna module of Embodiment 1. This is a diagram for explaining the change in antenna characteristics and admittance between ports when the length (phase) of the transmission line is changed. This is a diagram for explaining the change in antenna characteristics and admittance between ports when the resistance value of the resistor circuit is changed. This is a diagram for explaining the change in antenna characteristics and admittance between ports when the capacitance value of the capacitor circuit is changed. This is a diagram showing the antenna characteristics of the adjusted antenna module. This is an external perspective view of the antenna module according to Embodiment 2.

[0011] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0012] [Embodiment 1] (Overall configuration of the communication device) Figure 1 is an overall schematic diagram of a communication device 10 equipped with an antenna module 30 according to Embodiment 1. Referring to Figure 1, the communication device 10 comprises an antenna module 30 and a signal processing circuit 50.

[0013] The antenna module 30 includes antenna elements ANT1 and ANT2, transmission lines 21 and 22, a transmitting port T1, a receiving port T2, a resistor circuit R1, a reactance circuit LC1, and matching circuits 61 and 62. The signal processing circuit 50 also includes a transmitting unit 51 and a receiving unit 52.

[0014] Antenna element ANT1 and transmission line 21 constitute the transmission signal transmission path (TX). Transmission line 21 is connected between antenna element ANT1 and transmission port T1. Antenna element ANT2 and transmission line 22 constitute the reception signal transmission path (RX). Transmission line 22 is connected between antenna element ANT2 and reception port T2.

[0015] In Embodiment 1, the antenna elements ANT1 and ANT2 are patch antennas having a flat plate shape and have the same resonant frequency.

[0016] The transmission line 21 is connected to the transmission unit 51 of the signal processing circuit 50 at the transmission port T1. The transmission signal sent from the transmission unit 51 is transmitted to the antenna element ANT1 via the transmission line 21 and radiated as radio waves from the antenna element ANT1 (arrow AR1). The transmission line 22 is connected to the receiving unit 52 of the signal processing circuit 50 at the receiving port T2. The received signal received by the antenna element ANT2 is transmitted to the receiving unit 52 via the transmission line 22 (arrow AR2). The receiving unit 52 processes the received signal and further transmits it to subsequent circuits (not shown).

[0017] Each of the resistor circuit R1 and the reactance circuit LC1 is connected between the transmission line 21 and the transmission line 22. In other words, the resistor circuit R1 and the reactance circuit LC1 are connected in parallel to each other between the transmission line 21 and the transmission line 22.

[0018] The reactance circuit LC1 can utilize either a capacitor or an inductor, depending on the admittance between the transmitting port T1 and the receiving port T2. More specifically, the imaginary part of the admittance between the ports is measured to determine whether the coupling between the antenna elements is odd or even. If the mode appearing on the low-frequency side is even, a capacitor is used as the reactance circuit LC1. On the other hand, if the mode appearing on the low-frequency side is odd, an inductor is used. In the following explanation, for the sake of simplicity, the case where a capacitor circuit C1 is used as the reactance circuit LC1 will be explained as an example.

[0019] The resistor circuit R1 may be a variable element whose resistance value can be changed. For example, a potentiometer or field-effect transistor that allows for continuous change can be used to make the resistance value variable. Alternatively, the resistor circuit R1 may be configured with multiple resistors connected in parallel, and the resistance value can be discretely changed by switching the resistors or disconnecting the paths of some of the resistors.

[0020] The capacitor circuit C1 may also be a variable element capable of changing its capacitance value. For example, a mechanical variable capacitor and a variable capacitance diode capable of continuous change can be used to make the capacitance value variable. Alternatively, the capacitor circuit C1 may be configured with multiple capacitors connected in parallel, and the capacitance value can be discretely changed by switching the capacitors or disconnecting the paths of some of the capacitors.

[0021] Furthermore, if the reactance circuit LC1 is an inductor circuit, the inductor circuit may be a variable element capable of changing its inductance value.

[0022] As will be described later, the resistor circuit R1 and the capacitor circuit C1 form a resonant circuit together with the transmission lines 21 and 22 and the antenna elements ANT1 and ANT2. This reduces the coupling between transmission line 21 and transmission line 22 and functions as a noise reduction circuit to suppress the propagation of noise between transmission line 21 and transmission line 22.

[0023] The resistor circuit R1 and the capacitor circuit C1 may be arranged on the main surface 32 of the dielectric substrate 31, or they may be composed of a combination of wiring patterns, flat electrodes, and vias in the inner layers of the dielectric substrate 31.

[0024] As described above, when two transmission lines are located in close proximity, electromagnetic field coupling can occur between them. In this case, noise originating from the transmitted signal passing through transmission line 21 may be superimposed on the receiving transmission line 22 due to electromagnetic field coupling (arrow AR3). Similarly, noise originating from the received signal passing through transmission line 22 may be superimposed on the transmitting transmission line 21 due to electromagnetic field coupling (arrow AR4). Furthermore, in a circuit like the one in Figure 1, there is a path (arrow AR5) between transmission line 21 and transmission line 22 that is coupled in space due to electromagnetic field coupling.

[0025] In the antenna module 30 of Embodiment 1, the parameters (length of the transmission line, resistance value of the resistor circuit R1, and capacitance value of the capacitor circuit C1) are designed so that the real and imaginary parts of the admittance between the transmission line 21 and the transmission line 22 cancel each other out, taking into account the path via the resistor circuit R1 and the capacitor circuit C1, and the path coupled in space by electromagnetic field coupling as shown by arrow AR5. This makes it possible to reduce noise caused by the transmission signal from the transmission line 21 to the transmission line 22, and noise caused by the reception signal from the transmission line 22 to the transmission line 21.

[0026] As will be described later in Figure 8, in the example of Embodiment 1, the phase of the signal transmitted through the transmission lines is adjusted by changing the length of the transmission lines 21 and 22. However, instead of adjusting the length of the transmission lines 21 and 22, or in addition to adjusting the length of the transmission lines 21 and 22, the phase may be adjusted by phase adjustment circuits 71 and 72 provided on the transmission lines 21 and 22. By using phase adjustment circuits, the length of the transmission lines 21 and 22 can be shortened, which is suitable for miniaturizing the device.

[0027] (Antenna Module Configuration) Next, the detailed configuration of the antenna module 30 will be described using Figures 2 and 3. Figure 2 is an external perspective view of the antenna module 30 shown in Figure 1. Figure 3 is a plan view of the antenna module 30 shown in Figure 1.

[0028] Referring to Figures 2 and 3, the antenna module 30 includes, in addition to the antenna elements ANT1, ANT2, transmission lines 21, 22, transmission port T1, reception port T2, and matching circuits 61, 62 described above, a dielectric substrate 31 and a ground electrode GND. In Figures 2 and 3, the direction normal to the main surfaces 32, 33 of the dielectric substrate 31 is defined as the Z-axis direction, the direction along one side of the main surfaces 32, 33 is defined as the X-axis direction, and the direction along the other side perpendicular to it is defined as the Y-axis direction.

[0029] Antenna elements ANT1 and ANT2 are arranged adjacent to each other with a gap in the Y-axis direction on the main surface 32 of the dielectric substrate 31. One end of the transmission line 21 is electrically connected to a transmission port T1 located on the positive X-axis side surface 34 of the dielectric substrate 31, and the other end is connected to antenna element ANT1. One end of the transmission line 22 is electrically connected to a reception port T2 located on the side surface 34, and the other end is connected to antenna element ANT2.

[0030] As shown in Figure 3, transmission lines 21 and 22 are connected to each other by a resistor circuit R1. In this case, if the distance between the two transmission lines is greater than the dimension of the resistor circuit R1, they may be brought closer together in the intermediate portion. A capacitor circuit C1 is connected in parallel to the resistor circuit R1. The capacitor circuit C1 may be composed of individual discrete elements, but as will be explained below, capacitive coupling between transmission line 21 and transmission line 22 may also be utilized. Specifically, in the antenna module 30 of Embodiment 1, the transmission line 211 going from the connection point with the resistor circuit R1 in transmission line 21 to the transmission port T1 is close to the transmission line 221 going from the connection point with the resistor circuit R1 in transmission line 22 to the reception port T2. Between these transmission lines 211 and 221, transmission line 21 and transmission line 22 are capacitively coupled. That is, the capacitor circuit C1 is configured in the portion of transmission lines 211 and 221.

[0031] In transmission line 21, a matching circuit 61 is located in the path from line 211 to transmission port T1. Similarly, in transmission line 22, a matching circuit 62 is located in the path from line 221 to receiving port T2.

[0032] The ground electrode GND is positioned across the entire surface of the dielectric substrate 31, either on the main surface 33 or in an inner layer close to the main surface 33. The ground electrode GND faces the antenna elements ANT1 and ANT2. By arranging the equipment in this manner, the transmission lines 21 and 22 function as microstrip lines, and the antenna elements ANT1 and ANT2 function as microstrip antennas.

[0033] (Principle of Noise Reduction) The principle of noise reduction between transmission lines in the antenna module 30 of Embodiment 1 will be explained using Figures 4 to 6. The configuration of the noise reduction circuit disclosed in International Publication No. 2023 / 106068 (Patent Document 1) will be explained as a comparative example.

[0034] The noise reduction circuit in the comparative example consists of a coupling line connecting two transmission lines and a bandstop filter including multiple resonators connected in parallel to the coupling line. In the comparative example, the admittance of the noise reduction circuit (line LN11 in Figure 4(B)) is set to a value that cancels out the admittance between the transmission lines (i.e., between the antennas) (line LN10 in Figure 4(A)) at the desired frequency. Then, by adding the admittance of the noise reduction circuit to the admittance between the antennas, the admittance at the desired frequency is canceled out, as shown by line LN12 in Figure 4(C). In other words, the comparative example uses a different resonator than the antenna to remove noise.

[0035] Here, the configuration shown in the comparative example tends to exhibit noise reduction effects when the coupling between antenna elements is relatively strong, such as with a monopole antenna, but it is less effective when the coupling between antenna elements is relatively weak, such as with a patch antenna.

[0036] Figure 5 is a diagram illustrating why the noise reduction effect is less pronounced in the comparative example when the coupling between antenna elements is relatively weak. In Figure 5, the upper panel shows the change in admittance between antenna elements when the frequency changes, and the lower panel shows the change in admittance required for the bandstop filter of the comparative example. The left column of Figure 5 shows the case where the coupling between antenna elements is relatively strong, and the right column shows the case where the coupling between antenna elements is relatively weak.

[0037] When the coupling between antenna elements is relatively strong, generally, the frequencies of the two poles originating from the antenna in the admittance are far apart from each other, as shown by line LN10 in the upper left column of Figure 5 (W1 in Figure 5). In this case, the admittance changes slowly in response to the frequency change from the two poles toward the antenna's center frequency. Therefore, as shown by line LN11 in Figure 5, the admittance of the bandstop filter by the noise reduction circuit can also change slowly.

[0038] On the other hand, when the coupling between antenna elements is relatively weak, as shown by line LN20 in the upper right column of Figure 5, the frequencies of the two poles originating from the antenna in the admittance occur closer to each other than when the coupling between antenna elements is strong (W2 in Figure 5). In other words, the change in admittance becomes steeper with respect to the change in frequency from the two poles toward the center frequency of the antenna.

[0039] In this case, as shown by line LN21 in the lower right column of Figure 5, the admittance required for the bandstop filter also needs to be changed abruptly.

[0040] Here, in order to make the change in admittance steep in the configuration of the band-stop filter of the comparative example, it is necessary to increase the Q value of the inductor that constitutes the resonator included in the band-stop filter. However, since there are non-negligible resistance components and capacitance components in an actual inductor, when a signal passes through, loss due to the resistance component and leakage current due to the capacitance component may occur. Therefore, in reality, it is difficult to realize an inductor having a high Q value. Therefore, when the configuration of the noise removal circuit of the comparative example is applied to a configuration in which the coupling between antenna elements is relatively weak, there is a possibility that a sufficient effect cannot be exhibited.

[0041] Therefore, in the antenna module 30 according to the first embodiment, a resistance circuit R1 and a reactance circuit LC1 connected in parallel are connected between two transmission lines 21 and 22 to which the antenna elements ANT1 and ANT2 are respectively connected, and a resonance circuit is formed by each antenna element, the resistance circuit R1, and the reactance circuit LC1.

[0042] And in such a configuration, the resistance value of the resistance circuit R1 and the reactance value of the reactance circuit LC1 are adjusted so that the real part and the imaginary part of the admittance between the antenna elements become zero. As a result, as shown in FIG. 6, by shifting the admittance itself between the antenna elements in the zero direction, the propagation of noise between the transmission lines at a desired frequency can be suppressed.

[0043] In the configuration of the antenna module 30 of the first embodiment, a high Q value is not required for noise removal, and realistic reactance elements can be used. Therefore, not only when the coupling between antenna elements is relatively strong, but also when the coupling between antenna elements is relatively weak, the interference noise generated between the transmission lines can be reduced.

[0044] (Parameter Adjustment Method) Next, a method (design method) for adjusting various parameters of the configuration of the antenna module 30 in the manufacturing process will be described with reference to FIGS. 7 to 11.

[0045] FIG. 7 is a flowchart showing an adjustment method in the manufacturing process of the antenna module 30. First, in step (hereinafter, steps are abbreviated as S) 100, the lengths of the transmission lines 21 and 22 are adjusted. As will be described later with reference to FIG. 8, when the line length of the transmission line is changed, the phases of the real part and the imaginary part of the admittance shift accordingly. In S100, the line length is set such that the imaginary part of the admittance between the transmission port T1 and the reception port T2 has an extreme value near the center frequency of the desired frequency band (i.e., the resonance frequency of the antenna elements ANT1 and ANT2).

[0046] At this time, it can be seen that the resonance poles of the odd mode and the even mode at the phase of 0° in FIG. 8 are 2.45 GHz and 2.52 GHz, respectively. On the other hand, by rotating the phase, the interval between the resonance poles can be widened. For example, at the phase of 120°, each resonator can be adjusted to about 2.3 GHz and 2.7 GHz, respectively. Since these resonance poles finally contribute to wideband attenuation as attenuation poles, it is preferable to set the phase so that the interval between the two poles becomes as wide as possible.

[0047] When the phase adjustment circuits 71 and 72 are provided in the antenna module 30, instead of or in addition to adjusting the line lengths of the transmission lines 21 and 22, by adjusting the parameters of the phase adjustment circuits 71 and 72, near the resonance frequencies of the antenna elements ANT1 and ANT2, the imaginary part of the admittance between the ports has an extreme value.

[0048] Then, in S110, the resistance value of the resistance circuit R1 is adjusted. As will be described later with reference to FIG. 9, by adjusting the resistance value of the resistance circuit R1, the real part of the admittance between the antenna elements changes. Therefore, in S110, the resistance value of the resistance circuit R1 is adjusted so that the real part of the admittance between the ports becomes zero near the resonance frequencies of the antenna elements ANT1 and ANT2 or near the resonance frequencies.

[0049] Furthermore, depending on the circuit configuration of the antenna module 30, if the resistance value of resistor circuit R1 is zero, that is, in a configuration in which transmission lines 21 and transmission lines 22 are essentially directly connected, the actual part of the admittance between ports may be approximately zero. Also, if the ideal resistance value of resistor circuit R1 exceeds 1 kΩ, resistor circuit R1 may be essentially omitted.

[0050] Now, let's consider the reactance circuit LC1. Looking at the admittance shown in Figure 8, we can see that even modes appear on the low-frequency side and odd modes appear on the high-frequency side. Therefore, in this embodiment, a capacitor circuit C1 is used as the reactance circuit LC1. Next, in S120, the capacitance value of the capacitor circuit C1 is adjusted. As will be described later in Figure 10, by adjusting the capacitance value of the capacitor circuit C1, the imaginary part of the admittance between the antenna elements changes. Therefore, in S120, the capacitance value of the capacitor circuit C1 is adjusted so that the imaginary part of the admittance between the antenna elements becomes zero at or near the resonant frequency of the antenna elements ANT1 and ANT2.

[0051] Since the real and imaginary parts of the admittance between antenna elements can be adjusted independently, the order of adjusting the resistor circuit R1 (S110) and the capacitor circuit C1 (S120) can be reversed.

[0052] Subsequently, in S130, the parameters of matching circuits 61 and 62 are adjusted to match the impedance between the antenna module 30 and the signal processing circuit 50.

[0053] By adjusting the parameters using the method described above, the real and imaginary parts of the admittance between ports become approximately zero, thereby suppressing the propagation of interference noise between transmission lines.

[0054] Figure 8 shows an example of adjusting the transmission line length as described in S100. Figure 8 shows the simulation results of the changes in antenna characteristics and admittance between ports when the transmission line length (phase) is changed. In this simulation, the target frequency bandwidth is 2.4 GHz to 2.5 GHz. Also, in Figure 8, the resistance value of the resistor circuit R1 is ∞Ω, and the capacitance value of the capacitor circuit C1 is 0 pF.

[0055] The left column of Figure 8 shows examples of reflection losses at each port (solid lines LN31, LN33, LN35, LN37) and isolation between ports (dashed lines LN32, LN34, LN36, LN38) when the phase is changed to 0°, 100°, 120°, and 160°. The right column of Figure 8 shows the real part (solid lines LN41, LN43, LN45, LN47) and the imaginary part (dashed lines LN42, LN44, LN46, LN48) of the admittance between ports at each phase.

[0056] Referring to Figure 8, even when the transmission line length is changed to alter the phase, the reflection loss and isolation between ports remain largely unchanged. On the other hand, with respect to admittance, as the phase change increases, both the real and imaginary parts of the waveform shift in the direction of decreasing frequency. In Figure 8, when the phase is 120°, the imaginary part of admittance reaches an extreme value (local minimum) near the target frequency band. At this time, the shape, width, and / or length of the transmission line are adjusted so that the spacing between the poles of the even and odd modes is wider than before the transmission line was added (i.e., phase 0°). In this embodiment, a phase of 128° was adopted so that the extreme value occurs at the center frequency of the frequency band (2.45 GHz).

[0057] Figure 9 shows an example of adjusting the resistance value of the resistor circuit R1 described in S110. In Figure 9, the simulation results of the changes in antenna characteristics and admittance between ports are shown when the resistance value of the resistor circuit R1 is changed, while the length of the transmission line is adjusted to have a phase of 128° as adopted in Figure 8.

[0058] The left column of Figure 9 shows examples of reflection losses at each port (solid lines LN51, LN53, LN55, LN57) and isolation between ports (dashed lines LN52, LN54, LN56, LN58) when the resistance values ​​are varied to 100Ω, 300Ω, 600Ω, and 900Ω. The right column of Figure 9 shows the real part (solid lines LN61, LN63, LN65, LN67) and the imaginary part (dashed lines LN62, LN64, LN66, LN68) of the admittance between ports at each resistance value.

[0059] Referring to Figure 9, as the resistance value of resistor R1 is increased, the reflection loss of each port in the target frequency bandwidth gradually increases. On the other hand, the isolation between ports remains almost unchanged.

[0060] On the other hand, regarding admittance, as the resistance value increases, the real admittance approaches zero, and becomes almost zero when it exceeds 300 Ω. This is because as the resistance value increases, it becomes more difficult for current to flow. In this embodiment, a resistance value of 600 Ω was used.

[0061] Figure 10 shows an example of adjusting the capacitance value of the capacitor circuit C1 described in S120. In Figure 10, the simulation results of the changes in antenna characteristics and admittance between ports are shown when the capacitance value of the capacitor circuit C1 is changed, while the phase and resistance values ​​used in Figures 8 and 9 are adjusted.

[0062] The left column of Figure 10 shows examples of reflection losses at each port (solid lines LN71, LN73, LN75, LN77) and isolation between ports (dashed lines LN72, LN74, LN76, LN78) when the capacitance values ​​are varied to 0.2 pF, 1.0 pF, 1.2 pF, and 2.0 pF. The right column of Figure 9 shows the real part (solid lines LN81, LN83, LN85, LN87) and the imaginary part (dashed lines LN82, LN84, LN86, LN88) of the admittance between ports at each capacitance value.

[0063] Referring to Figure 10, the reflection loss at each port increases as the capacitance value increases. On the other hand, the isolation between ports increases or decreases depending on the capacitance value.

[0064] Regarding admittance, the real part hardly changes even when the capacitance value is changed. On the other hand, the imaginary part decreases as the capacitance value increases. In this embodiment, around 1.0 pF, the extreme value of the imaginary part of admittance is zero at the center frequency of the target frequency band.

[0065] Furthermore, when adjusting the capacitance value, it is desirable that the imaginary part of the admittance be near zero across the entire range of the target frequency bandwidth. As shown in Figures 8 to 10, the imaginary part of the admittance has an extremum near the target frequency bandwidth. Rather than trying to make this extremum zero, it is possible to bring the imaginary part of the admittance closer to zero across the entire range of the target frequency bandwidth by making the imaginary part of the admittance zero at two frequencies on either side of the center frequency within the range of the target frequency bandwidth.

[0066] In other words, in the example shown in Figure 10, it is preferable to use a capacitance value between 1.0 pF and 1.2 pF. In this embodiment, a capacitance value of 1.086 pF was adopted so that the imaginary part of the admittance is in the range of ±0.002 S in the target frequency bandwidth.

[0067] Figure 11 shows the antenna characteristics of the antenna module 30 after impedance matching was performed in S130 by adjusting matching circuits 61 and 62, with the phase adjusted to 128°, the resistance to 600Ω, and the capacitance to 1.086pF, as explained in Figures 8 to 10. In Figure 11, the solid line LN91 shows the reflection loss at each port, and the dashed line LN92 shows the insertion loss (i.e., isolation) between ports.

[0068] As shown in Figure 1, the reflection loss is reduced to 20 dB at the center frequency (2.45 GHz), and isolation of 23 dB or more is secured across the target frequency bandwidth BW. Furthermore, the attenuation pole originating from the resonant pole of the antenna coupling can be adjusted by changing the phase due to the transmission line length, and attenuation poles can be obtained around 2.2 GHz and 2.7 GHz. In this way, by utilizing the attenuation pole generated by the coupling of the antennas as described above, in addition to the attenuation pole generated by the resistor circuit R1 and the reactance circuit LC1 (capacitor circuit C1), a wideband decoupling bandwidth can be realized.

[0069] As described above, in the antenna module 30 of Embodiment 1, a resistor circuit R1 and a reactance circuit LC1 are connected in parallel between transmission lines 21 and 22 connected to antenna elements ANT1 and ANT2, respectively. The line lengths of transmission lines 21 and 22, the resistance value of resistor circuit R1, and the reactance value of reactance circuit LC1 are adjusted so that the real and imaginary parts of the admittance between ports cancel each other out in the target frequency band. With this configuration, the antenna elements themselves can be used as resonators and function as bandstop filters. Therefore, even in the case of patch antennas with relatively weak coupling between antenna elements, isolation between the transmitting port T1 and the receiving port T2 can be ensured, thereby reducing interference noise between transmission lines.

[0070] In Embodiment 1, "antenna element ANT1" and "antenna element ANT2" correspond to "first antenna element" and "second antenna element" in this disclosure. In Embodiment 1, "transmission line 21" and "transmission line 22" correspond to "first transmission line" and "second transmission line" in this disclosure.

[0071] [Embodiment 2] Embodiment 2 describes the case in which a monopole antenna is used as the antenna element.

[0072] Figure 12 is an external perspective view of the antenna module 30A according to Embodiment 2. In the antenna module 30A, the antenna elements ANT1 and ANT2 in the antenna module 30 of Embodiment 1 shown in Figure 2 are replaced with straight lines. Furthermore, in the antenna module 30A, the dimension of the ground electrode GND arranged in the dielectric substrate 31 in the X-axis direction is shortened, and the ground electrode GND is arranged only in the region from the side surface 34 to the ends of the transmission lines 21 and 22. The other configurations in Figure 12 are the same as in Figure 2, and the explanation of overlapping elements will not be repeated.

[0073] With this configuration, the transmission lines 21 and 22 function as microstrip lines, and the antenna elements ANT1 and ANT2 function as monopole antennas.

[0074] Even in the case of a monopole antenna, such as antenna module 30A, where the coupling between antenna elements is relatively strong, interference noise between transmission lines can be reduced by connecting a resistor circuit and a capacitor circuit in parallel between the transmission lines connected to the antenna elements, and adjusting the transmission line length, the resistance value of the resistor circuit, and the reactance value of the reactance circuit so that the real and imaginary parts of the admittance between ports become approximately zero.

[0075] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included.

[0076] 10 Communication device, 21, 22 Transmission line, 30, 30A Antenna module, 31 Dielectric substrate, 32, 33 Main surface, 34 Side surface, 50 Signal processing circuit, 51 Transmitter, 52 Receiver, 61, 62 Matching circuit, 71, 72 Phase adjustment circuit, 211, 221 Line, ANT1, ANT2 Antenna element, C1 Capacitor circuit, GND Ground electrode, LC1 Reactance circuit, R1 Resistor circuit, T1 Transmitter port, T2 Receiver port.

Claims

1. An antenna module comprising: a transmitting port and a receiving port; a first antenna element and a second antenna element having the same resonant frequency; a first transmission line connected between the transmitting port and the first antenna element; a second transmission line connected between the receiving port and the second antenna element; a resistor circuit connected between the first transmission line and the second transmission line; and a reactance circuit connected in parallel to the resistor circuit, wherein the resistance value of the resistor circuit and the reactance value of the reactance circuit are set such that the real and imaginary parts of the admittance between the transmitting port and the receiving port cancel each other out at or near the resonant frequency.

2. The antenna module according to claim 1, wherein the length of the first transmission line and the second transmission line is set such that the imaginary part of the admittance between the transmitting port and the receiving port becomes an extremum at or near the resonant frequency.

3. The antenna module according to claim 1 or 2, wherein the resistor circuit is set to a resistance value such that the real part of the admittance between the transmitting port and the receiving port becomes zero at or near the resonant frequency.

4. The antenna module according to any one of claims 1 to 3, wherein the reactance circuit is set to a reactance value such that the imaginary part of the admittance between the transmitting port and the receiving port is zero at or near the resonant frequency.

5. The antenna module according to claim 4, wherein the reactance value of the reactance circuit is set such that the imaginary part of the admittance between the transmitting port and the receiving port is zero at the first and second frequencies, and the resonant frequency is between the first and second frequencies.

6. The antenna module according to claim 5, wherein the first transmission line and the second transmission line are set to lengths such that attenuation poles are formed at frequencies lower than both the first frequency and the second frequency, and at frequencies higher than both the first frequency and the second frequency.

7. The antenna module according to any one of claims 1 to 6, wherein the transmitting port and the receiving port are connected to a signal processing circuit, and the antenna module further comprises a first matching circuit located in the first transmission line for adjusting the impedance between the first antenna element and the signal processing circuit, and a second matching circuit located in the second transmission line for adjusting the impedance between the second antenna element and the signal processing circuit.

8. The antenna module according to any one of claims 1 to 7, further comprising a phase adjustment circuit provided in each of the first transmission line and the second transmission line and configured to adjust the phase of a high-frequency signal transmitted to a corresponding antenna element.

9. The antenna module according to any one of claims 1 to 8, wherein at least one of the resistor circuit and the reactance circuit is a variable element.

10. The antenna module according to any one of claims 1 to 9, further comprising a dielectric substrate on which the first antenna element, the second antenna element, the first transmission line, and the second transmission line are arranged, wherein at least one of the resistive circuit and the reactance circuit is arranged within the dielectric substrate.

11. The antenna module according to any one of claims 1 to 10, wherein each of the first antenna element and the second antenna element is a patch antenna having a flat plate shape.

12. The antenna module according to any one of claims 1 to 10, wherein each of the first antenna element and the second antenna element is a monopole antenna.

13. A communication device equipped with an antenna module according to any one of claims 1 to 12.

14. A method for manufacturing an antenna module, wherein the antenna module comprises: a transmitting port and a receiving port; a first antenna element and a second antenna element having the same resonant frequency; a first transmission line connected between the transmitting port and the first antenna element; a second transmission line connected between the receiving port and the second antenna element; a resistor circuit connected between the first transmission line and the second transmission line; and a reactance circuit connected in parallel to the resistor circuit, the manufacturing method comprising: adjusting the lengths of the first transmission line and the second transmission line such that the imaginary part of the admittance between the transmitting port and the receiving port becomes an extremum at or near the resonant frequency; and adjusting the resistance value of the resistor circuit such that the real part of the admittance between the transmitting port and the receiving port becomes zero at or near the resonant frequency. A method for manufacturing an antenna module, comprising the step of adjusting the reactance value of the reactance circuit such that the imaginary part of the admittance between the transmitting port and the receiving port becomes zero at or near the resonant frequency.

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