Reflection coefficient measurement device

Abstract

This reflection coefficient measurement device comprises: an antenna unit (110, 111) of which the end on the side in contact with a target sample is an open end; an open unit (112) of which the distal end is an open end; a short unit (113) in which a center conductor and the ground are electrically connected at the distal end; a load unit (16) that terminates a signal line; a switch (12); and a reflection coefficient measurement unit that controls the switch (12) to connect the antenna unit (110, 111), the open unit (112), and the short unit (113) to a port of the reflection coefficient measurement unit in the stated order, and measures a reflection coefficient. The electrical lengths of wiring from the open end of each antenna unit (110, 111) to the switch (12) are the same.

Description

Reflectance coefficient measuring device 【0001】 This invention relates to a reflection coefficient measuring device used in dielectric spectroscopy measurements. 【0002】 As the population ages, addressing lifestyle-related diseases is becoming a major challenge. Blood tests, such as those for blood glucose levels, require blood sampling, which places a significant burden on patients. For this reason, non-invasive device-based concentration measurement devices that do not require blood sampling are attracting attention. One such non-invasive device is one that utilizes dielectric spectroscopy. Dielectric spectroscopy involves irradiating the skin with electromagnetic waves, utilizing the interaction between the target blood component (e.g., glucose molecules) and water to cause the electromagnetic waves to be absorbed, and observing the amplitude and phase of the electromagnetic waves. 【0003】 Conventional devices include those using a coaxial probe that irradiates the object to be measured with electromagnetic waves in the microwave to millimeter wave range. Figure 16 shows the configuration of a dielectric spectroscopy measuring device using a coaxial probe. The dielectric spectroscopy measuring device consists of a coaxial probe 1000 with an open end on the end facing the object to be measured, a sensor unit 1001, and a vector network analyzer (VNA) 1002. 【0004】 In reflectance measurements, which calculate the reflection coefficient by measuring the incident voltage and reflected voltage, it is known that drift errors in the reflection coefficient occur due to fluctuations in ambient temperature and vibrations and stresses applied to the measurement cable. Generally, as shown in Figure 16, the sensor unit 1001 is connected to the coaxial probe 1000, and the sequential calibration function of the sensor unit 1001 is used to calibrate fluctuations occurring in the VNA 1002 and the measurement cable with each measurement. Such a sequential calibration function can reduce cable instability and system drift errors. 【0005】Furthermore, in addition to the antenna used to measure the sample, a device has been proposed that uses three types of calibration covers: an open type with an open end, a short-circuit type with a short-circuited open end, and a loaded type with a load connected to the open end (Patent Document 1). Also, a calibration device has been proposed that generates multiple states such as open, short-circuited, and loaded for the output port of a VNA, measures multiple states with the VNA, and calculates the calibration coefficient of the VNA based on the measurement results (Patent Document 2). Moreover, a planar dielectric spectroscopic sensor has been proposed in which a first via and a plurality of second vias arranged in a circle around the first via are formed on a dielectric substrate, and the reflection coefficient is measured using a pseudo-coaxial line structure made up of these vias as a coaxial probe (Patent Document 3). 【0006】 Furthermore, conventionally, a dielectric spectroscopy measuring device has been proposed that integrates a pseudo-coaxial sensor and a configuration for sequential calibration on the same substrate, with the aim of performing dielectric spectroscopy measurements with high accuracy while sequentially calibrating the drift error of the reflection coefficient (Patent Document 4). Figure 17 shows the configuration of the dielectric spectroscopy measuring device disclosed in Patent Document 4. 【0007】 The dielectric spectroscopy measuring device consists of a sensor unit 1 and a reflection coefficient measuring unit 2. A VNA is used in the reflection coefficient measuring unit 2, for example. The sensor unit 1 includes a dielectric substrate 10, a coaxial probe 11, a switch 12, an RF terminal 14, a control terminal 15, and a load unit 16. The coaxial probe 11, the switch 12, the RF terminal 14, the control terminal 15, and the load unit 16 are mounted on the dielectric substrate 10. The coaxial probe 11 includes antenna sections 110, 111, an open section 112, and a short section 113. In the example disclosed in Patent Document 4, a pseudo-coaxial line structure is adopted to form the antenna sections 110, 111, the open section 112, and the short section 113. 【0008】The antenna sections 110 and 111 have a pseudo-coaxial line structure with an open end on the side that contacts the sample to be measured. The open section 112 has a pseudo-coaxial line structure with an open end on the side that contacts the air. The short section 113 has a pseudo-coaxial line structure with conductivity between the central conductor and the ground at its tip. The load section 16 formed on the dielectric substrate 10 is composed of a resistor formed between the signal line and the ground and terminates the signal line. 【0009】 Furthermore, a switch 12, an RF terminal 14, and a control terminal 15 are mounted on the dielectric substrate 10. The antenna sections 110, 111, the open section 112, the short section 113, and the load section 16 are each connected to the selection terminal of the switch 12. This allows the switch 12 to select one of the antenna sections 110, 111, the open section 112, the short section 113, and the load section 16. The control terminal of the switch 12 is connected to the control terminal 15. 【0010】 The reflection coefficient measurement unit 2 outputs a control signal to the switch 12 via the control terminal 15. As a result, the reflection coefficient measurement unit 2 switches the switch 12 so that one of the short section 113, the open section 112, and the load section 16 is connected to the RF terminal of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 connects the short section 113, the open section 112, and the load section 16 to the RF terminal of the reflection coefficient measurement unit 2 in order and performs reflection measurements for each. Then, the reflection coefficient measurement unit 2 calculates a calibration coefficient (S-parameter of the error circuit present in the reflection coefficient measurement unit 2) from the results of the reflection measurements. By calculating the calibration coefficient in this way, it becomes possible to calculate the reflection coefficient with the measurement error of the reflection coefficient measurement unit 2 removed. 【0011】With the open ends of the antenna sections 110 and 111 in contact with the sample, the reflection coefficient measurement unit 2 switches switch 12 so that either of the antenna sections 110 or 111 is connected to the RF terminal of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 applies an electric field to the sample from the antenna section 110 or 111 and calculates the reflection coefficient of the sample based on the voltage amplitude and phase of the reflected wave reflected by the sample and the voltage of the incident wave measured by the reflection coefficient measurement unit 2. 【0012】 Figure 18 is a plan view of the dielectric substrate 10, and Figure 19 is a bottom view of the same part as in Figure 18, viewed from below. Figure 20 is a cross-sectional view of the dielectric substrate 10 where the switch 12, RF terminal 14, and coaxial probe 11 (multilayer wiring board) are mounted. The switch 12, RF terminal 14, control terminal 15, and resistor 160 constituting the load section 16 are mounted on the bottom surface of the dielectric substrate 10. The pad of the antenna section 110 and the first select terminal of the switch 12 are connected by a microstrip line 120. The pad of the antenna section 111 and the second select terminal of the switch 12 are connected by a microstrip line 121. The pad of the open section 112 and the third select terminal of the switch 12 are connected by a microstrip line 122. The pad of the short section 113 and the fourth select terminal of the switch 12 are connected by a microstrip line 123. The pad of the load section 16 and the fifth select terminal of the switch 12 are connected by a microstrip line 124. The RF terminal 14 and the input terminal of the switch 12 are connected by a microstrip line 125. The control terminal 15 and the control terminal of the switch 12 are connected by a microstrip line 126. 【0013】In conventional devices, multiple reflections occur between the reflection coefficient measuring unit 2 and the antenna section 110, 111 during reflection measurement, which is performed by switching between multiple antenna sections 110, 111. If the electrical lengths of the microstrip lines 120, 121 are different, different frequency ripples occur in the received signal between the switch 12 and the open ends of the antenna sections 110, 111. Thus, in conventional devices, the electrical length between the open end and the switch 12 differs for multiple antenna sections 110, 111. For this reason, even when measuring the dielectric constant of the same sample, the phase of the received signal changes due to the effect of frequency ripple, and the reflection coefficient calculated from the received signal becomes a different value, making it impossible to accurately measure the dielectric constant. 【0014】 Japanese Patent Publication No. 5499379, Japanese Unexamined Patent Publication No. 2005-99038, Japanese Patent Publication No. 6771372, International Publication WO2023 / 223541 【0015】 The present invention was made to solve the above problems and aims to provide a reflection coefficient measuring device that can accurately measure the reflection coefficient. 【0016】 The reflection coefficient measuring device of the present invention comprises a plurality of antenna sections, each having an open end on the side in contact with the sample to be measured; an open section, each having an open tip; a short section, where the central conductor and ground are electrically connected at the tip; a load section configured to terminate a signal line; a switch configured to select one of the plurality of antenna sections, the open section, the short section, and the load section; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the plurality of antenna sections, the open section, and the short section to its own port and measure the reflection coefficient of each, wherein the electrical length of the wiring from the open end of each of the plurality of antenna sections to the switch is the same. 【0017】 According to the present invention, by making the electrical length of the wiring from the open end of each of the multiple antenna sections to the switch the same, the reflection coefficient can be accurately measured. As a result, in the present invention, the dielectric constant of the sample can be accurately measured using the measurement result of the reflection coefficient. 【0018】Figure 1 is a cross-sectional view of a sensor section according to an embodiment of the present invention. Figure 2 is a cross-sectional view of a sensor section according to an embodiment of the present invention. Figure 3 is a plan view of an antenna section according to an embodiment of the present invention. Figure 4 is a plan view of an antenna section according to an embodiment of the present invention. Figure 5 is a plan view of an open section according to an embodiment of the present invention. Figure 6 is a plan view of a short section according to an embodiment of the present invention. Figure 7 is a cross-sectional view of an antenna section according to an embodiment of the present invention. Figure 8 is a bottom view of an antenna section according to an embodiment of the present invention. Figure 9 is a bottom view of a microstrip line according to an embodiment of the present invention. Figure 10 is a plan view of a dielectric substrate according to an embodiment of the present invention. Figure 11 is a bottom view of a dielectric substrate according to an embodiment of the present invention. Figure 12 is a cross-sectional view of a portion of the dielectric substrate in which a switch, an RF terminal, and a multilayer wiring board are mounted in an embodiment of the present invention. Figure 13 is a diagram showing the reflection characteristics of a conventional coaxial probe. Figure 14 is a diagram showing the reflection characteristics of a coaxial probe according to an embodiment of the present invention. Figure 15 is a block diagram showing an example of the configuration of a computer that realizes the reflection coefficient measurement section according to an embodiment of the present invention. Figure 16 is a block diagram showing the configuration of a conventional dielectric spectroscopy measuring device. Figure 17 is a block diagram showing another configuration of a conventional dielectric spectroscopy measuring device. Figure 18 is a plan view of the dielectric substrate of a conventional dielectric spectroscopy apparatus. Figure 19 is a bottom view of the dielectric substrate of a conventional dielectric spectroscopy apparatus. Figure 20 is a cross-sectional view of the portion of the dielectric substrate of a conventional dielectric spectroscopy apparatus in which the switch, RF terminal, and coaxial probe are mounted. 【0019】 Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment as well, the configuration of the reflection coefficient measuring device (dielectric spectroscopy measuring device) is the same as in Figure 17, so the reference numerals in Figure 17 will be used for explanation. The reflection coefficient measuring device consists of a sensor unit 1 and a reflection coefficient measuring unit 2. The sensor unit 1 includes a dielectric substrate 10, a coaxial probe 11, a switch 12, an RF terminal 14, a control terminal 15, and a load unit 16. 【0020】Figures 1 and 2 are cross-sectional views of the sensor unit 1. The coaxial probe 11, switch 12, RF terminal 14, control terminal 15, and load unit 16 are mounted on the dielectric substrate 10. However, the switch 12, RF terminal 14, and control terminal 15 are omitted from the description in Figures 1 and 2. The coaxial probe 11 includes antenna sections 110 and 111, an open section 112, and a shorted section 113. 【0021】 The antenna section 110 has a pseudo-coaxial cable structure in which the end on the side in contact with the sample to be measured (upper side in Figure 1) is an open end. In the antenna section 110, a land 1100 made of a conductor is formed on the upper surface of the uppermost insulating layer 22 of the multilayer wiring board 21, a land 1107 made of a conductor is formed on the upper surface of the insulating layer 23, a land 1108 made of a conductor is formed on the upper surface of the insulating layer 24, a land 1109 made of a conductor is formed on the upper surface of the insulating layer 25, and a land 1101 made of a conductor is formed on the lower surface of the insulating layer 25. The lands 1100, 1101, 1107-1109 are connected by vias 1102, which are conductors that penetrate perpendicularly through the insulating layers 22-25 along the stacking direction of the conductor layers 26-30. Figure 3 is a plan view of the antenna section 110, and Figure 4 is a plan view of the land 1101 layer of the antenna section 110. In Figure 4, multiple conductor layers and insulating layers are shown through the material. 【0022】 A conductor layer 26, which serves as a ground conductor, is formed in the same layer as land 1100 but outside of land 1100. Land 1100 and the conductor layer 26 are separated by a conductor-free circular area 1103 in plan view. Similarly, a conductor layer 30, which serves as a ground conductor, is formed in the same layer as land 1101 but outside of land 1101. Land 1101 and the conductor layer 30 are separated by a conductor-free circular area 1104 in plan view. 【0023】Multiple conductor layers 27-29, which serve as ground conductors, are formed inside the multilayer wiring board 21. The conductor layers 27-29 and the lands 1107-1109 are separated by a circular conductor-free region 1105 in plan view, which is a region without conductors and filled with dielectric material. Via 1102 passes through the center of the conductor-free regions 1103-1105. In the antenna section 110, the conductor layers 26-30 are connected by through-vias (through-holes) 1106. 【0024】 The insulator layers 22-25, the lands 1100, 1101, 1107-1109, the via 1102 that penetrates the insulator layers 22-25 perpendicularly, the conductor layers 26-30 surrounding the via 1102, and the through via 1106 connecting the conductor layers 26-30 constitute a pseudo-coaxial line. The via 1102 and the conductor removal regions 1103-1105 are circular in plan view, and the impedance of the pseudo-coaxial line can be designed according to the sample being measured by the diameter of the via 1102, the diameter of the surrounding conductor removal regions 1103-1105, and the dielectric constant of the dielectric of the insulator layers 22-25. 【0025】 The antenna section 111 has a pseudo-coaxial cable structure in which the end on the side in contact with the sample to be measured (upper side in Figure 2) is an open end. In the antenna section 111, a land 1110 made of a conductor is formed on the upper surface of the uppermost insulating layer 22 of the multilayer wiring board 21, a land 1117 made of a conductor is formed on the upper surface of the insulating layer 23, a land 1118 made of a conductor is formed on the upper surface of the insulating layer 24, a land 1119 made of a conductor is formed on the upper surface of the insulating layer 25, and a land 1111 made of a conductor is formed on the lower surface of the insulating layer 25. The lands 1110, 1111, 1117-1119 are connected by vias 1112, which are conductors that penetrate perpendicularly through the insulating layers 22-25 along the stacking direction of the conductor layers 26-30. The plan view of the antenna section 111 when viewed from above is the same as in Figure 3. 【0026】A conductor layer 26, which serves as a ground conductor, is formed in the same layer as land 1110, but in a region outside of land 1110. Land 1110 and the conductor layer 26 are separated by a conductor-free circular region 1113 in plan view. Similarly, a conductor layer 30, which serves as a ground conductor, is formed in the same layer as land 1111, but in a region outside of land 1111. Land 1111 and the conductor layer 30 are separated by a conductor-free circular region 1114 in plan view. 【0027】 The conductor layers 27-29 and lands 1117-1119 of the multilayer wiring board 21 are separated by a circular conductor-free region 1115 in plan view, which is a region without conductors and filled with dielectric material. The via 1112 passes through the center of the conductor-free regions 1113-1115. In the antenna section 111, the conductor layers 26-30 are connected by through-vias (through-holes) 1116. 【0028】 The insulating layers 22-25, the lands 1110, 1111, 1117-1119, the via 1112 that penetrates the insulating layers 22-25 perpendicularly, the conductor layers 26-30 surrounding the via 1112, and the through via 1116 connecting the conductor layers 26-30 constitute a pseudo-coaxial line. The via 1112 and the conductor removal regions 1113-1115 are circular in plan view, and the impedance of the pseudo-coaxial line can be designed according to the sample being measured by the diameter of the via 1112, the diameter of the surrounding conductor removal regions 1113-1115, and the dielectric constant of the dielectric of the insulating layers 22-25. The shape of the antenna section 111 may be formed differently from that of the antenna section 110 to accommodate different samples. 【0029】The open section 112 has a pseudo-coaxial line structure in which the end on the side in contact with the dielectric (insulating layer 22) (upper side in Figure 1) is an open end. In the open section 112, the uppermost conductor layer 26 of the multilayer wiring board 21 has an opening 1127, which is a circular removal area in plan view, so that the lower insulating layer 22 is exposed to the air. A land 1120 made of a conductor is formed on the upper surface of the insulating layer 23, a land 1128 made of a conductor is formed on the upper surface of the insulating layer 24, a land 1129 made of a conductor is formed on the upper surface of the insulating layer 25, and a land 1121 made of a conductor is formed on the lower surface of the insulating layer 25. The lands 1120, 1121, 1128, and 1129 are connected by vias 1122, which are conductors that penetrate perpendicularly through the insulating layers 23 to 25 along the stacking direction of the conductor layers 26 to 30. Figure 5 is a plan view of the open section 112. In the open section 112, the open end is shielded by an insulating layer 22 to prevent water, dust, and other contaminants from entering the open end. 【0030】 Land 1121 and the conductor layer 30 are separated by a circular conductor-free region 1123 in plan view, which has no conductors. Land 1120 and the conductor layer 27 are separated by a circular conductor-free region 1124 in plan view, which has no conductors. Conductor layers 28 and 29 and lands 1128 and 1129 are separated by a circular conductor-free region 1125 in plan view, which has no conductors and is filled with dielectric material. Via 1122 passes through the center of conductor-free regions 1123 to 1125. In the open section 112, conductor layers 27 to 30 are connected by through vias 1126. 【0031】 The insulating layers 23-25, the lands 1120, 1121, 1128, and 1129, the via 1122 that penetrates the insulating layers 23-25 ​​perpendicularly, the conductor layers 27-30 surrounding the via 1122, and the through via 1126 connecting the conductor layers 27-30 constitute a pseudo-coaxial line. In the open section 112, the incident signal is almost totally reflected in phase. 【0032】The short section 113 has a pseudo-coaxial line structure in which the central conductor (via) and the ground are electrically connected at the tip. In the short section 113, the uppermost conductor layer 26 of the multilayer wiring board 21 has an opening 1137, which is a circular removal area in plan view, so that the lower insulating layer 22 is exposed to the air. A land 1138 made of a conductor is formed on the upper surface of the insulating layer 24, a land 1139 made of a conductor is formed on the upper surface of the insulating layer 25, and a land 1131 made of a conductor is formed on the lower surface of the insulating layer 25. The conductor layer 27 and the lands 1131, 1138, and 1139 are connected by vias 1132, which are conductors that penetrate perpendicularly through the insulating layers 23 to 25 along the stacking direction of the conductor layers 26 to 30. Figure 6 is a plan view of the short section 113. 【0033】 Land 1131 and the conductor layer 30 are separated by a circular conductor-free region 1133 in plan view, which has no conductors. Conductor layers 28 and 29 and lands 1138 and 1139 are separated by a circular conductor-free region 1135 in plan view, which has no conductors and is filled with dielectric material. Via 1132 passes through the centers of conductor-free regions 1133 and 1135. In the shorted section 113, conductor layers 27 to 30 are connected by a through via 1136. 【0034】 The insulating layers 23-25, the lands 1131, 1138, 1139, the via 1132 that penetrates the insulating layers 23-25 ​​perpendicularly, the conductor layers 27-30 surrounding the via 1132, and the through via 1136 connecting the conductor layers 27-30 constitute a pseudo-coaxial line. In the short-circuit section 113, the phase of the incident signal is inverted and almost total internal reflection occurs. 【0035】On the upper surface of the dielectric substrate 10, pads 40 to 43 made of a conductor and a conductor layer 46 serving as a ground conductor are formed. The pads 40 to 43 and the conductor layer 46 are separated from each other by circular conductor removal regions 47 to 50 having no conductor in plan view. On the lower surface of the dielectric substrate 10, pads 51 to 55 made of a conductor and a conductor layer 56 serving as a ground conductor are formed. The pads 51 to 54 and the conductor layer 56 are separated from each other by circular conductor removal regions 57 to 60 having no conductor in plan view. As shown in FIG. 2, the pad 55 and the conductor layer 56 are connected by a resistor 160 that constitutes the load portion 16. The load portion 16 is better as the signal reflection is smaller. For this reason, the resistor 160 is selected so as to match the impedance of the signal line. 【0036】 The pads 40 and 51 are connected by a via 61 which is a conductor vertically penetrating the dielectric substrate 10. The conductor layers 46 and 56 are connected by a through-via (through hole) 65 which is a conductor vertically penetrating the dielectric substrate 10. The dielectric substrate 10, the pads 40 and 51, the via 61, the conductor layers 46 and 56 around the via 61, and the through-via 65 connecting the conductor layers 46 and 56 constitute a pseudo coaxial line. FIG. 7 is a cross-sectional view when the antenna portion 111 is viewed from a direction different from that in FIG. 1, and FIG. 8 is a bottom view when the antenna portion 110 is viewed from below. In FIGS. 4, 7, and 8, reference numeral 120 denotes a microstrip line connecting the pad 51 of the antenna portion 110 and the switch 12. FIG. 9 is a bottom view when the microstrip line 120 at a position away from the antenna portion 110 is viewed from below. 【0037】 The pads 41 and 52 are connected by a via 62 which is a conductor vertically penetrating the dielectric substrate 10. The dielectric substrate 10, the pads 41 and 52, the via 62, the conductor layers 46 and 56 around the via 62, and the through-via 65 connecting the conductor layers 46 and 56 constitute a pseudo coaxial line. 【0038】The pads 42 and 53 are connected by a via 63 which is a conductor vertically penetrating the dielectric substrate 10. The dielectric substrate 10, the pads 42 and 53, the via 63, the conductor layers 46 and 56 around the via 63, and the through-via 65 connecting the conductor layers 46 and 56 constitute a pseudo coaxial line. 【0039】 The pads 43 and 54 are connected by a via 64 which is a conductor vertically penetrating the dielectric substrate 10. The dielectric substrate 10, the pads 43 and 54, the via 64, the conductor layers 46 and 56 around the via 63, and the through-via 65 connecting the conductor layers 46 and 56 constitute a pseudo coaxial line. The bottom view of the antenna portion 111, the open portion 112, and the short portion 113 when viewed from below is the same as that in FIG. 7. 【0040】 Between the land 1101 and the pad 40, between the land 1111 and the pad 41, between the land 1121 and the pad 42, between the land 1131 and the pad 43, and between the conductor layer 30 and the conductor layer 46 are connected by solder 66. Thus, the multilayer wiring substrate 21 in which the antenna portions 110 and 111, the open portion 112, and the short portion 113 are formed is mounted on the dielectric substrate 10. 【0041】 Furthermore, a switch 12, an RF terminal 14, and a control terminal 15 are mounted on the dielectric substrate 10. FIG. 10 is a plan view of the dielectric substrate 10 of the present embodiment, and FIG. 11 is a bottom view of the same portion as FIG. 10 when viewed from below. FIG. 12 is a cross-sectional view of a portion where the switch 12, the RF terminal 14, and the multilayer wiring substrate 21 (coaxial probe 11) are mounted on the dielectric substrate 10. In FIG. 11, the description of the conductor layer 56 is omitted. 【0042】A switch 12, an RF terminal 14, a control terminal 15, and a resistor 160 are mounted on the lower surface of the dielectric substrate 10. The pad 51 of the antenna section 110 and the first select terminal of the switch 12 are connected by a microstrip line 120 made of a conductor. The pad 52 of the antenna section 111 and the second select terminal of the switch 12 are connected by a microstrip line 121 made of a conductor. The pad 53 of the open section 112 and the third select terminal of the switch 12 are connected by a microstrip line 122 made of a conductor. The pad 54 of the short section 113 and the fourth select terminal of the switch 12 are connected by a microstrip line 123 made of a conductor. The pad 55 of the load section 16 and the fifth select terminal of the switch 12 are connected by a microstrip line 124 made of a conductor. The RF terminal 14 and the input terminal of the switch 12 are connected by a microstrip line 125. The control terminal 15 and the control terminal of the switch 12 are connected by a microstrip line 126. 【0043】 In this embodiment, the electrical length of the microstrip lines 120 and 121 (wiring) connecting the pads 51 and 52 of the antenna sections 110 and 111 to the switch 12 is made the same. Also in this embodiment, the switch 12 is positioned so that the microstrip lines 120 and 121 are as short as possible. 【0044】 Furthermore, in this embodiment, the open end of the open section 112 and the tip of the short section 113 are shielded by the insulating layer 22, and the distance from the open end of the open section 112 to the switch 12 and the distance from the tip of the short section 113 to the switch 12 are different from the distance from the open ends of the antenna sections 110 and 111 to the switch 12. Therefore, the microstrip lines 122 and 123 are made longer than the microstrip lines 120 and 121 by an amount equivalent to the electrical length of the insulating layer 22. As a result, in this embodiment, the electrical length from the open end of the open section 112 to the switch 12 and the electrical length from the tip of the short section 113 to the switch 12 can be made the same as the electrical length from the open ends of the antenna sections 110 and 111 to the switch 12. 【0045】Next, the measurement of the reflection coefficient and dielectric constant will be described. The reflection coefficient measurement unit 2 outputs a control signal to the switch 12 via the control terminal 15. As a result, the reflection coefficient measurement unit 2 switches the switch 12 so that one of the antenna sections 110, 111, the open section 112, the short section 113, and the load section 16 is connected to the port of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 outputs an RF signal by connecting the open section 112 to the port of the reflection coefficient measurement unit 2, and calculates the reflection coefficient of the open section 112 (dielectric) based on the voltage amplitude and phase of the reflected wave reflected by the open section 112 and the voltage of the incident wave measured by the reflection coefficient measurement unit 2. 【0046】 Similarly, the reflection coefficient measurement unit 2 connects the short section 113 to its port and outputs an RF signal, and calculates the reflection coefficient of the short section 113 (the metal constituting the conductor layer 27) based on the voltage amplitude and phase of the reflected wave reflected by the short section 113 and the voltage of the incident wave measured by the reflection coefficient measurement unit 2. In addition, with the open end of the antenna section 110 or 111 in contact with a known liquid sample (e.g., pure water), the reflection coefficient measurement unit 2 connects the antenna section 110 or 111 to its port and outputs an RF signal, and calculates the reflection coefficient of the liquid sample based on the voltage amplitude and phase of the reflected wave reflected by the liquid sample and the voltage of the incident wave measured by the reflection coefficient measurement unit 2. 【0047】 Next, the reflection coefficient measurement unit 2 outputs a control signal to the switch 12 via the control terminal 15 while the open end of the antenna unit 110 or 111 is in contact with the sample to be measured. As a result, the reflection coefficient measurement unit 2 switches the switch 12 so that the antenna unit 110 or 111 is connected to the port of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 outputs an RF signal to apply an electric field to the sample from the antenna unit 110 or 111, and calculates the reflection coefficient of the sample to be measured based on the voltage amplitude and phase of the reflected wave reflected by the sample and the voltage of the incident wave measured by the reflection coefficient measurement unit 2. The complex permittivity can be calculated from the measured reflection coefficient as follows. 【0048】 【0049】 Here, ε ＊ is the dielectric constant of the sample to be measured, ε Ａ ＊ is the known dielectric constant of the dielectric (insulating layer 22), ε Ｂ ＊ is the known dielectric constant of the metal constituting the conductor layer 27, ε Ｃ ＊ is the known dielectric constant of the liquid sample. ρ ＊ is the complex reflection coefficient, and when the reflection coefficient obtained by measurement is Γ ｉ and the phase is φ ｉ it is expressed by the following formula (2). 【0050】 【0051】 ρ Ａ ＊ is the measurement result in the case of the open part 112, ρ Ｂ ＊ is the measurement result in the case of the short part 113, ρ Ｃ ＊ is the measurement result when the open end of the antenna part 110 or 111 is in contact with the liquid sample, ρ ＊ respectively corresponds to the measurement result of the sample to be measured. Thus, the reflection coefficient measurement unit 2 can calculate the complex dielectric constant of the sample to be measured from the measurement results of the reflection coefficients of the dielectric, metal, and liquid sample measured in advance, the measurement result of the reflection coefficient of the sample to be measured, and the known complex dielectric constants of the dielectric, metal, and liquid sample respectively. 【0052】 Incidentally, the load unit 16 is used for calibration of the VNA. The one-port calibration method of the VNA using an open standard, a short standard, and a load standard as calibration standards is known as SOL calibration. In SOL calibration, three standards, an open standard, a short standard, and a load standard, are connected to the port of the VNA to measure calibration data. By this calibration data, frequency response reflection tracking, directivity, and source match of the measurement system can be eliminated in the reflection measurement using the port to be calibrated. 【0053】In this embodiment, the reflection coefficient measurement unit 2 outputs a control signal to the switch 12 via the control terminal 15. As a result, the reflection coefficient measurement unit 2 switches the switch 12 so that one of the open section 112, short section 113, and load section 16 is connected to the port of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 connects the open section 112, short section 113, and load section 16 to the port of the reflection coefficient measurement unit 2 in order and performs reflection measurements for each. Then, the reflection coefficient measurement unit 2 calculates a calibration coefficient (S-parameter of the error circuit present in the reflection coefficient measurement unit 2) from the results of the reflection measurements. By calculating the calibration coefficient in this way, it becomes possible to calculate the reflection coefficient with the measurement error of the reflection coefficient measurement unit 2 removed. The method of calculating the calibration coefficient by SOL calibration is a well-known technique. 【0054】 As described above, in this embodiment, by making the electrical length of the microstrip lines 120 and 121 the same and making the electrical length of the wiring from the open ends of the antenna sections 110 and 111 to the switch 12 the same, the antenna characteristics can be made the same among multiple antenna sections 110 and 111. 【0055】 Figure 13 shows the reflection characteristics of a conventional coaxial probe (S parameter S). １１ This is a diagram showing the reflective characteristics of the antenna section 110 when the tip is open, 131 when the tip of the antenna section 111 is open, 132 when the open section 112 is open, and 133 when the short section 113 is short. In the conventional configuration, the antenna sections 110, 111 and the open section 112 have different reflective characteristics regardless of the same reflection conditions. 【0056】 Figure 14 shows the reflection characteristics of the coaxial probe 11 of this embodiment. Figure 140 shows the reflection characteristics of the antenna section 110 of this embodiment when the tip is open, 141 shows the reflection characteristics of the antenna section 111 of this embodiment when the tip is open, 142 shows the reflection characteristics of the open section 112 of this embodiment, and 143 shows the reflection characteristics of the shorted section 113 of this embodiment. In this embodiment, since the electrical lengths are the same, the antenna sections 110, 111 and the open section 112 show similar reflection characteristics. The difference in the characteristics of the shorted section 113 is due to the difference in reflection conditions. 【0057】 Furthermore, in this embodiment, by arranging the switch 12 so that the microstrip lines 120 and 121 are as short as possible, the frequency ripple generated in the received signal of the antenna section 110 and 111 can be made to have a gentle characteristic. In this embodiment, the signal fluctuation based on the frequency ripple characteristic is also gentle in response to changes in electrical length due to environmental temperature fluctuations, etc., so it is possible to measure the reflection coefficient relatively stably. 【0058】 Note that the multilayer wiring board 21 and the dielectric board 10 may be the same board. In this case, mounting of different boards using solder or the like becomes unnecessary. 【0059】 The reflection coefficient measuring unit 2 described in this embodiment can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 15. 【0060】 The computer comprises a CPU 300, a storage device 301, a communication device 303, a transmitter 302, a receiver 304, a directional coupler 305, a power supply 306, a transformer 307, and a regulator 308. The transmitter 302 and the receiver 304 are connected to the sensor unit 1 via the directional coupler 305. Electromagnetic waves in the microwave band generated by the transmitter 302 are irradiated onto the sample to be measured. The signal reflected from the sample is input from the sensor unit 1 to the receiver 304 via the directional coupler 305, converted into a digital signal, and then read by the CPU 300. The CPU 300 outputs a control signal to the sensor unit 1 and controls the switch 12 to sequentially read the reflected signals from the antenna units 110, 111, the open unit 112, the short unit 113, and the load unit 16. 【0061】In such a computer, the program for implementing the reflection coefficient measurement method (dielectric spectroscopy measurement method) of the present invention is stored in the storage device 301. The CPU 300 executes the control and arithmetic processing described in this embodiment according to the program stored in the storage device 301. The reflection coefficient and dielectric constant obtained by the processing are transmitted to an external computer by a communication device 303 connected to the CPU 300. As the transmitter 302, for example, a frequency synthesizer using a phase-locked circuit is used. As the receiver 304, for example, a double-balanced mixer is used. A circulator may be used instead of the directional coupler 305. 【0062】 In the example shown in Figure 15, a direct conversion type transmit / receive configuration is shown, but a low IF (Intermediate Frequency) type transmit / receive configuration may be adopted by adding a transmitter with a slightly different transmission frequency. Power supply 306 supplies power to each device. For example, a DC-DC converter is used as the transformer 307. Regulator 308 converts the input voltage from transformer 307 to a desired voltage. A linear regulator that operates even with a low input / output potential difference is used as the regulator 308. A lithium-ion battery or the like is used as the power supply 306. 【0063】 Some or all of the above examples may also be described as follows, but are not limited to the following: 【0064】(Note 1) The reflection coefficient measuring device of the present invention comprises a plurality of antenna sections, each having an open end on the side in contact with the sample to be measured; an open section, each having an open tip; a short section, where the central conductor and ground are electrically connected at the tip; a load section configured to terminate a signal line; a switch configured to select one of the plurality of antenna sections, the open section, the short section, and the load section; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the plurality of antenna sections, the open section, and the short section to its own port and measure the reflection coefficient of each, wherein the electrical length of the wiring from the open end of each of the plurality of antenna sections to the switch is the same. 【0065】 (Note 2) In the reflection coefficient measuring device described in Note 1, the switch is arranged such that the wiring from each of the open ends of the plurality of antenna sections to the switch is as short as possible. 【0066】 (Note 3) In the reflection coefficient measuring device described in Note 1, the electrical length of the wiring from the open end of the open section to the switch and the electrical length of the wiring from the tip of the short section to the switch are the same as the electrical length of the wiring from the open end of each of the plurality of antenna sections to the switch. 【0067】 (Note 4) In the reflection coefficient measuring device described in Note 1, the plurality of antenna sections, the open section, the short section, the load section, and the switch are arranged on the same circuit board. 【0068】 (Note 5) In the reflection coefficient measuring device described in Note 1, each of the plurality of antenna sections, the open section, and the short section has a coaxial line structure in which a ground conductor is arranged around a central conductor which is a signal line. 【0069】 (Note 6) In the reflection coefficient measuring device described in Note 1, the reflection coefficient measuring unit calculates the dielectric constant of the sample based on the measurement result of the reflection coefficient. 【0070】1...Sensor unit, 2...Reflection coefficient measurement unit, 10...Dielectric substrate, 11...Coaxial probe, 12...Switch, 14...RF terminal, 15...Control terminal, 16...Load unit, 21...Multilayer wiring board, 110, 111...Antenna unit, 112...Open unit, 113...Short unit, 120-126...Microstrip line, 160...Resistor.

Claims

1. A reflection coefficient measuring device comprising: a plurality of antenna sections, each having an open end on the side in contact with the target sample; an open section, each having an open tip; a short section, where the central conductor and ground are electrically connected at the tip; a load section configured to terminate a signal line; a switch configured to select one of the plurality of antenna sections, the open section, the short section, and the load section; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the plurality of antenna sections, the open section, and the short section to its own port and measure the reflection coefficient of each, wherein the electrical length of the wiring from the open end of each of the plurality of antenna sections to the switch is the same.

2. A reflection coefficient measuring device according to claim 1, characterized in that the switch is arranged such that the wiring from each of the open ends of the plurality of antenna sections to the switch is as short as possible.

3. A reflection coefficient measuring device according to claim 1, characterized in that the electrical length of the wiring from the open end of the open section to the switch and the electrical length of the wiring from the tip of the short section to the switch are the same as the electrical length of the wiring from the open end of each of the plurality of antenna sections to the switch.

4. A reflection coefficient measuring device according to claim 1, characterized in that the plurality of antenna sections, the open section, the short section, the load section, and the switch are arranged on the same substrate.

5. A reflection coefficient measuring device according to claim 1, characterized in that each of the plurality of antenna sections, the open section, and the short section is a coaxial line structure in which a ground conductor is arranged around a central conductor which is a signal line.

6. A reflection coefficient measuring device according to claim 1, characterized in that the reflection coefficient measuring unit calculates the dielectric constant of the sample based on the measurement result of the reflection coefficient.

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