JP7471587B2 - Split rectangular parallelepiped resonator and method for measuring dielectric constant using the same - Google Patents

Description

The present invention relates to a split rectangular parallelepiped resonator suitable for measuring the complex dielectric constant of a dielectric in the millimeter wave band and a measurement method using the same.

The fifth generation communication network (5G) has been proposed, and the development of communication equipment for it is progressing. Like the communication equipment used in the current fourth generation communication network (4G), 5G communication equipment will use materials such as plastic, ceramic, and glass for the printed circuit boards, antennas, cases, and displays. However, millimeter wave bands (28 GHz, 40 GHz) have been proposed for use in 5G, which are more than 10 times higher than the 1 to 2 GHz band used for 4G communication frequencies. It is necessary to investigate whether the above-mentioned materials for communication equipment used in 5G can be used without problems at 5G frequencies.

As the frequency increases, the dielectric constant becomes important as a material property. First, we define the term "dielectric constant" in this invention. The dielectric constant of a material is often expressed as a ratio to the dielectric constant of a vacuum, and strictly speaking, this should be called the "relative dielectric constant", but in this invention, following convention, the above "relative dielectric constant" is expressed as "dielectric constant". Furthermore, "dielectric constant" is a complex number, and in the following explanation, the "real part of the complex dielectric constant" is simply referred to as "dielectric constant", and the ratio of the "imaginary part of the complex dielectric constant" to the "real part of the complex dielectric constant" (imaginary part of the complex dielectric constant / real part of the complex dielectric constant) may be referred to as the "dielectric tangent".

As mentioned above, the frequency used in 5G will be more than 10 times higher than that of 4G. Even in 4G, it is important to know the dielectric constant of materials, and dielectric constant measurements have been made. However, in 5G, it has become necessary to measure the dielectric constant in the millimeter wave frequency band, and split cylinder resonators (cylindrical cavity resonators) and the like are beginning to be used. When measuring the dielectric constant of a material using a split cylinder resonator, it is common to process the material into a flat shape (film, sheet, plate, etc.) to use as a measurement sample.

Many of the materials used in 5G communication devices, such as those mentioned above, have anisotropic dielectric constants. Circuit patterns (electrical lines) and antennas on boards (flexible printed circuit boards = FPCs) that use anisotropic materials as the base material behave differently when placed in the orientation direction and when placed perpendicular to the orientation. In addition, when anisotropic materials are used for cases or displays, there is a concern that the efficiency of radio wave radiation will differ depending on the direction of radio wave irradiation and the direction of polarization, preventing uniform and stable radio wave radiation.

In order to design and manufacture stable, high-performance communications devices for 5G, it is necessary to know the dielectric constant in the orientation direction and the dielectric constant in the orientation and perpendicular directions separately, rather than simply the dielectric constant (which is generally the average value of the "orientation direction" and "orientation and perpendicular directions"). A similar problem existed with 4G, but with the frequency increasing by more than 10 times with 5G, there are concerns that the impact will become even greater.

Liquid crystal polymer (LCP), a promising material for use as the base material for 5G FPCs, has long, thin molecules that are strongly oriented, resulting in large anisotropy in the dielectric constant. In general, the dielectric constant in the oriented direction is greater than the dielectric constant perpendicular to the orientation. In this invention, we discuss the dielectric constant in the direction parallel to the plane of a flat material such as a film (hereinafter referred to as the "in-plane direction"), and do not take into account the dielectric constant perpendicular to the plane.

The method of measuring the dielectric constant by splitting a resonator in two and sandwiching a sample to be measured between them, such as a split cylinder resonator, allows for easy, accurate, and reproducible measurements in the millimeter wave band, and is expected to be most suitable for measuring the dielectric constant of high-frequency dielectric materials, the use of which is increasing in 5G applications. This method involves forming a resonator by combining two half cavities, which are formed by equally splitting a cylindrical cavity in half along a plane parallel to the bottom, so that they face each other, and then measuring the dielectric constant of the sample by sandwiching a film-like or thin plate-like sample to be measured between the two half cavities.

A network analyzer is often used for the measurement. The network analyzer is connected to the resonator to obtain a graph with frequency on the horizontal axis and transmitted signal strength (transmission coefficient) on the vertical axis, and the resonance characteristics are obtained. Here, "resonance characteristics" refers to the center frequency of resonance and the Q value (in this specification, the ratio of center frequency to 3 dB bandwidth is used). It is common to calculate or simulate the dielectric constant and dielectric tangent of the sample from the resonance characteristics with and without the sample.

Figure 12 is a schematic diagram of a cylindrical split cylinder resonator 50 according to the prior art. In Figure 12, two cylindrical half cavities 52, 62 formed in two housings, respectively, and a sample 30 sandwiched between the two half cavities 52, 62 are shown, and the shapes of the two housings are omitted. In this split cylinder resonator 50, the resonance mode used for measurement is the TE011 mode, and an electric field E is generated concentrically. Therefore, when the in-plane direction of the sample is set to a direction parallel to the XY plane as shown in Figure 12, the electric field strength in the plane of the sample is equally distributed in the X and Y directions, and the measured dielectric constant is the average value of the dielectric constant in the X direction and the dielectric constant in the Y direction.

To separate and measure the anisotropy of the dielectric constant of a dielectric in the high frequency band, a cavity resonator perturbation method using a cavity resonator 60 as shown in Figure 13 has been proposed. In the cavity resonator perturbation method, the sample 30 is processed into an elongated shape and inserted into the sample insertion hole 61 in the center of the cavity resonator 60 to measure the dielectric constant. At this time, the electric field E is generated perpendicular to the bottom surface of the cavity resonator 60, so it is applied in the longitudinal direction of the elongated sample 30. The anisotropy of the sample 30 can be measured by separately measuring the sample 30 processed into an elongated shape in the orientation direction and the sample 30 processed into an elongated shape perpendicular to the orientation.

In addition to the cavity resonator perturbation method, various methods for measuring the anisotropy of the dielectric constant have been proposed, such as those in Patent Document 1, Patent Document 2, and Non-Patent Document 1.

Patent Document 3 also proposes a method for measuring the dielectric constant of an anisotropic sample using a cylindrical cavity resonator (split cylinder resonator), which is suitable for measuring the dielectric constant in the millimeter wave frequency band. This method is characterized by using the TE111 mode or the higher order TE11n mode instead of the conventional TE011 mode. When the in-plane direction of the sample is set parallel to the XY plane as shown in Figure 12, the resonance of the TE111 mode of the cylindrical split cylinder resonator is in a state where the resonance in the X and Y directions is degenerated, so when an anisotropic sample is inserted, the degeneracy is released and the resonance is separated into two. This method makes use of this to measure the anisotropy of the dielectric constant.

The cavity resonator perturbation method of FIG. 13 requires processing the planar sample 30 into elongated strips in the orientation direction and in the direction perpendicular to the orientation. This is not only time-consuming, but also makes it difficult to determine whether the difference in the dielectric constant between the orientation direction and the direction perpendicular to the orientation is due to anisotropy or processing accuracy, since the processing accuracy affects the dielectric constant measurement. In addition, even within the same planar material, there is variation depending on the location where the sample is sampled, and the difference in the characteristics of two samples cut from different locations is included in the first place, so there is a possibility that differences will occur between the two even in materials that are not anisotropic. Furthermore, if a cavity resonator 60 is created at frequencies of 28 GHz or 40 GHz used in 5G, there is also the problem that the size will be too small and processing the measurement sample will be practically difficult.

In addition, the methods disclosed in Patent Document 1, Patent Document 2, and Non-Patent Document 1 are suitable for low frequencies, but are too small in size to be practical for use at millimeter wave frequencies, and can be said to be for different applications.

In addition, the method proposed in Patent Document 3 is difficult to measure accurately for the following reasons. It is practically impossible to process the cross section (radial direction) of the cavity in a cylindrical cavity resonator into a perfect circle, and the resonance in the TE111 mode should theoretically degenerate into one resonance, but as shown in Figure 14 (Figure 5 in Patent Document 3), even when no sample is inserted, the resonance is separated into two due to processing accuracy issues. To measure the dielectric constant, it is necessary to accurately obtain the resonance characteristics when no sample is inserted, but in such a state, the dielectric constant of the sample cannot be obtained accurately.

The direction of the electric field in the TE111 mode is not completely in one direction, but is curved as shown in Figure 11 of Patent Document 3 above, so even when an electric field is applied in the X direction, there is an electric field component in the Y direction. This means that the dielectric constant in the X direction and the dielectric constant in the Y direction cannot be measured completely separately. In the case of a sample with weak anisotropy, the resonance is not clearly separated into two, so the resonance characteristics cannot be measured accurately, and the measurement accuracy deteriorates or becomes impossible.

JP 2006-226963 A Japanese Patent Application Laid-Open No. 62-195568 JP 2007-248097 A

Shinichi Nagata, "Development and Demonstration Experiment of a New Online Fiber Orientation Meter Using Dielectric Anisotropy Measurement - Aiming for Future Automatic Control of Fiber Orientation -", Journal of the Japan Paper and Pulp Technology Association, Vol. 57, No. 2, pp. 58-64, February 2003.

As described above, there is an increasing demand for 5G to accurately measure the dielectric constant of a planar sample separately in the orientation direction and the direction perpendicular to the orientation, but no device or method that meets this requirement exists at millimeter wave frequencies. The object of the present invention is to provide a resonator that can measure the dielectric constant of a planar sample separately in the orientation direction and the direction perpendicular to the orientation, and a measurement method that can measure the anisotropy of the dielectric constant separately.

The split rectangular parallelepiped resonator of the first embodiment includes a first housing having a rectangular parallelepiped first half-cavity having a rectangular bottom surface and an opening facing the rectangular bottom surface, a second housing having a second half-cavity substantially identical to the first half-cavity and disposed relative to the first housing such that the opening of the first half-cavity faces the opening of the second half-cavity, a first loop antenna exposed from the bottom surface of the first half-cavity to the first half-cavity, and a second loop antenna exposed from the bottom surface of the second half-cavity to the second half-cavity. The ratio of the horizontal length to the vertical length of the rectangular bottom surface is 1.005 to 1.26.

The split rectangular parallelepiped resonator of the second embodiment has a configuration similar to that of the split rectangular parallelepiped resonator of the first embodiment, and the angle between the loop surfaces of the first loop antenna and the second loop antenna and the vertical direction of the bottom surface is approximately 45 degrees.

The dielectric constant measurement method disclosed herein is a dielectric constant measurement method that uses a split rectangular parallelepiped resonator of the first or second aspect to simultaneously measure the dielectric constant of a sample in two directions, and includes the steps of acquiring a first resonant frequency characteristic in a state where the sample is not inserted into the split rectangular parallelepiped resonator, acquiring a second resonant frequency characteristic in a state where the sample is inserted into the split rectangular parallelepiped resonator, and calculating the dielectric constant of the sample in two directions from the first and second resonant frequency characteristics.

According to the split rectangular parallelepiped resonator of the present invention, two resonances, TE011 mode resonance and TE101 mode resonance, are near the desired measurement frequency, and the TE011 mode resonance applies an electric field in the X direction to the sample, and the TE101 mode resonance applies an electric field in the Y direction to the sample. As a result, the TE011 mode resonance changes according to the dielectric constant of the sample in the X direction, and the TE101 mode resonance changes according to the dielectric constant of the sample in the Y direction.
The resonance characteristics of the TE011 mode resonance and the TE101 mode resonance are measured without inserting a sample, and the resonance characteristics of the two resonances are similarly measured with inserting a sample, and the dielectric constants in the X and Y directions can be measured independently and accurately by a specified calculation or simulation.

These measurements can be performed with a single sweep of the network analyzer, making the measurements simple. In addition, because the same location on the sample is measured, the measurements can be performed accurately without being affected by variations in the location of the sample sampling.

FIG. 1 is a schematic diagram (perspective view) of a split rectangular parallelepiped resonator according to a first embodiment; FIG. 2 is a schematic diagram showing a cross section of a split rectangular parallelepiped resonator taken along a plane parallel to the XZ plane including line 2-2 in FIG. FIG. 2 is a front view showing a first housing of the split rectangular parallelepiped resonator according to the first embodiment; 1A and 1B are a front view and a side view showing a loop antenna of a split rectangular parallelepiped resonator according to a first embodiment of the present invention; 1 is a table showing calculated values of the resonant frequencies in each mode of the split rectangular parallelepiped resonator according to the first embodiment. Graph showing the resonance frequency characteristics of an LCP film (when the orientation direction is the X-axis direction) measured using a split rectangular parallelepiped resonator according to the first embodiment. Graph showing the resonance frequency characteristics of an LCP film (when the orientation direction is the Y-axis direction) measured using a split rectangular parallelepiped resonator according to the first embodiment. Table showing the dielectric constant of LCP film calculated from Figs. 6 and 7 Graph showing the resonance frequency characteristics of a PI film (V direction) measured using a split rectangular parallelepiped resonator according to the first embodiment. Graph showing the resonance frequency characteristics of a PI film (H direction) measured using a split rectangular parallelepiped resonator according to the first embodiment. Table showing the dielectric constant of the PI film calculated from Figs. 9 and 10 FIG. 1 shows a split cylinder resonator according to the prior art. FIG. 1 shows a conventional cavity resonator perturbation method. FIG. 1 is a diagram showing the resonant frequency characteristic (TE111 mode) of a split cylinder resonator according to the prior art;

(Embodiment 1)
FIG. 1 is a schematic diagram (perspective view) of a split rectangular parallelepiped resonator, FIG. 2 is a schematic diagram showing a cross section of the split rectangular parallelepiped resonator along a plane parallel to the XZ plane including the line 2-2 in FIG. 1, and FIG. 3 is a front view of the first housing of the split rectangular parallelepiped resonator seen from the +Z direction. For the sake of later explanation, an XYZ orthogonal coordinate system is defined as shown in FIG. 1. As shown in FIGS. 1 to 3, the split rectangular parallelepiped resonator 10 has a housing 11 having a half cavity 12, a housing 21 having a half cavity 22, and two loop antennas 13 and 23. In the split rectangular parallelepiped resonator 10, the two half cavities 12 and 22 each having a rectangular parallelepiped shape in the two housings 11 and 21 function as resonators, so in FIG. 1, the half cavities 12 and 22 formed in the housings 11 and 21 are shown, and the outer shapes of the housings 11 and 21 are omitted.

The semi-cavities 12, 22 formed in the two housings 11, 21 respectively have substantially the same rectangular parallelepiped shape, each having a rectangular bottom surface and an opening facing the bottom surface. The bottom surface is parallel to the XY plane, and has a rectangular shape with a vertical length (side in the X direction) of a and a horizontal length (side in the Y direction) of b. The housings 11, 21 are made of copper.

The loop antennas 13, 23 are provided at the tips of the coaxial cables 14, 24, respectively, and are arranged exposed inside the semi-cavities 12, 22 from the bottom surfaces of the semi-cavities 12, 22. An insertion hole is provided in the center of the bottom surface of each of the semi-cavities 12, 22, through which the coaxial cables 14, 24 are inserted.

Figure 4 shows (A) a front view and (B) a side view of the loop antenna of the split rectangular parallelepiped resonator according to the first embodiment. As shown in Figure 4, the loop antennas 13 and 23 are formed so as to draw a loop from the center to the end at the tip of the coaxial cable 14 and 24, respectively. The surface formed by the loop of the loop antennas 13 and 23 is defined as the "loop surface". The loop antennas 13 and 23 of the split rectangular parallelepiped resonator 10 according to the first embodiment are attached to the housings 11 and 21 so that the angle θ between the loop surface and the X direction is 45 degrees, as shown in Figure 4. Although Figure 4 shows an example in which the angle θ is 45 degrees, the angle θ may be any of 45 degrees, 135 degrees, 225 degrees, and 315 degrees. That is, the "loop surface" of each of the loop antennas 13 and 23 may have an angle of 45 degrees with respect to the vertical direction (X direction) or horizontal direction (Y direction) of the bottom surface of the semi-cavity. In the first embodiment, the two "loop planes" of the loop antennas 13 and 23 are on the same plane, and the loop antennas 13 and 23 are arranged in positions that are point-symmetrical with each other (when the angle θ of the loop plane of the loop antenna 13 is 45 degrees, the angle θ of the loop plane of the loop antenna 23 is 225 degrees). This is to minimize the deviation from ideal resonance caused by the finite size of the loop antennas 13 and 23.

The split rectangular parallelepiped resonator 10 is constructed by arranging the openings of the semi-cavities 12, 22 of the two housings 11, 21 so that they face each other, as shown in Figure 1. When measuring the dielectric constant of the sample 30, the resonance characteristics are measured with the sample 30 sandwiched between the two housings 11, 21, as shown in Figure 1.

When the sample 30 is not inserted, the half cavities 12 and 22 form a cavity in the shape of a rectangular parallelepiped (referred to as a "rectangular parallelepiped cavity"). The cavity functioning as a resonator is a rectangular parallelepiped with a side length in the X direction, b in the Y direction, and c in the Z direction. That is, the length (side length in the Z direction) of the half cavities 12 and 22 is c/2, as shown in FIG. 2. In this embodiment, in order to set the measurement frequency to 28 GHz, which is the frequency used in 5G, the shape of the cavity (shape 1) is a = 7.1 mm, b = 7.3 mm, and c = 8 mm. At this time, the calculated resonant frequency of the TE011 mode resonance is about 27.7983 GHz, and the resonant frequency of the TE101 mode resonance is about 28.2283 GHz. In addition, other resonance modes also exist, but by making c>b, the resonance frequencies (calculated values) of the other modes are higher than the resonance frequencies of the TE0110 mode and TE101 mode, as shown in Figure 5, and do not affect the measurement.

As shown in Figure 1, the electric field E is applied only in the X direction in the TE011 mode resonance, and only in the Y direction in the TE101 mode resonance.

The signal is excited by loop antennas 13 and 23 attached near the center of the bottom of the half cavities 12 and 22, respectively, as shown in Figure 2. In the TE011 mode resonance, the magnetic field is excited parallel to the YZ plane, so it is necessary to orient the opening of the loop antenna in the Y direction (loop surface is parallel to the XZ plane) and excite the magnetic field in the Y direction. Similarly, in the TE101 mode resonance, the magnetic field is excited parallel to the XZ plane, so it is necessary to orient the opening of the loop antenna in the X direction (loop surface is parallel to the YZ plane) and excite the magnetic field in the X direction. Since these two requirements are contradictory, in this embodiment, the orientation of the opening of the loop antennas 13 and 23 is set to an intermediate direction, that is, a direction that forms an angle of 45 degrees with respect to the X and Y directions (loop surface is 45 degrees with respect to the XZ and YZ planes), as shown in Figures 3 and 4. This excites the TE011 mode resonance and the TE101 mode resonance to the same intensity, making it easier to find the resonance peak during measurement, and allowing the two resonances to be measured well without one peak having a strong effect on the other.

The resonance of the TE011 mode is affected by the dielectric constant of the sample in the X direction, and moves to a lower frequency. Similarly, the resonant frequency of the TE101 mode is affected by the dielectric constant of the sample in the Y direction, and moves to a lower frequency. The amount of resonance frequency shift between the TE011 mode and the TE101 mode will be different if the sample is anisotropic. Because the resonance frequencies of each resonance mode are different, the resonance characteristics of each can be accurately measured without a sample. Also, when the resonance frequency is measured with a sample inserted, the two resonances are clearly separated, so the dielectric constant in the X direction and the dielectric constant in the Y direction of the sample can be accurately separated and measured.

Figures 6, 7, 9, and 10 show the resonance characteristics of the TE011 mode and the TE101 mode when the sample 30 is not inserted and when it is inserted, and the dashed lines in each figure show the resonance characteristics when the sample 30 is not inserted. The actual measured values of the resonance frequencies of the TE011 mode and the TE101 mode when the sample 30 is not inserted were Fte011 = 27.788 GHz and Fte101 = 28.216 GHz, respectively. The difference from the calculated values is due to the error caused by the cutting process and the influence of the R processing (R = 0.5 mm) formed on the corners of the half cavity.

The solid line in Figure 6 shows the resonance characteristics when a highly anisotropic LCP film (thickness 64 μm) is inserted into the split rectangular parallelepiped resonator 10 as a sample. The insertion direction is such that the orientation of the LCP is parallel to the X direction of the resonator. In this case, the resonance frequencies of the TE011 mode and the TE101 mode are Fte011 = 26.995 GHz and Fte101 = 27.676 GHz, respectively, and while the resonance of the TE011 mode shifts significantly to the lower frequency side, the resonance of the TE101 mode shifts to the lower frequency side, but not by as much as the resonance of the TE011 mode.

Next, the LCP film was rotated 90 degrees, and the orientation was set parallel to the Y direction, and the results of the same measurement are shown by the solid line in Figure 7. At this time, the resonance frequencies of the TE011 mode and the TE101 mode were Fte011 = 27.276 GHz and Fte101 = 27.444 GHz, respectively, with the resonance shift of the TE011 mode being small and the resonance shift of the TE101 mode being large.

Figure 8 shows the dielectric constant and dielectric tangent in the orientation direction of the LCP film and in the direction perpendicular to the orientation calculated from the resonance characteristics in each case. It was confirmed that there is a large difference between the dielectric constant and dielectric tangent in the orientation direction and the dielectric constant and dielectric tangent in the direction perpendicular to the orientation. Furthermore, despite the measurements being taken in different resonance modes, the dielectric constant and dielectric tangent in the orientation direction and the direction perpendicular to the orientation are almost the same.

For comparison, similar measurements were performed on a polyimide (PI) film, which is said to have almost no anisotropy. Since the orientation direction of a non-anisotropic polyimide film cannot be determined, an arbitrarily selected direction was defined as the vertical (V) direction, and a direction rotated 90 degrees from the V direction was defined as the horizontal (H) direction. The solid line in Figure 9 shows the resonance characteristics when the polyimide film is inserted vertically. In this case, the resonance frequencies of the TE011 mode and the TE101 mode are Fte011 = 27.330 GHz and Fte101 = 27.753 GHz, respectively, and the amount of movement in the resonance frequency and the change in the Q value in the TE011 mode resonance and the TE101 mode resonance are almost equal.

Similarly, the resonance characteristics when the polyimide film is inserted horizontally and measured are shown by the solid line in Figure 10. In this case, the resonance frequencies of the TE011 mode and the TE101 mode are Fte011 = 27.326 GHz and Fte101 = 27.754 GHz, respectively, and there is almost no change in the amount of movement in the resonance frequency and the change in the Q value in the TE011 mode resonance and the TE101 mode resonance.

From these measurement data, the dielectric constant and dielectric dissipation factor of the polyimide film in the longitudinal direction were calculated, and the results are shown in Figure 11. It can be seen that there is no significant difference between the dielectric constant and dielectric dissipation factor in the longitudinal and transverse directions.

In the split rectangular resonator 10 having a rectangular cavity according to the present embodiment, it was confirmed that in the highly anisotropic LCP film, the dielectric constant obtained varies greatly depending on the direction of the electric field measured, while in the PI film, which has almost no anisotropy, the dielectric constant obtained is approximately the same regardless of the direction of the electric field measured.

The split rectangular parallelepiped resonator 10 includes a housing 11 having a rectangular parallelepiped half cavity 12 with a rectangular bottom surface and an opening facing the bottom surface, a housing 21 having a half cavity 22 that is substantially identical to the half cavity 12 and arranged relative to the housing 11 so that the opening of the half cavity 12 faces the opening of the half cavity 22, a first loop antenna 13 exposed from the bottom surface of the half cavity 12 to the half cavity 12, and a second loop antenna 23 exposed from the bottom surface of the half cavity 22 to the half cavity 22. The loop surfaces of the first loop antenna 13 and the second loop antenna 23 are at an angle of about 45 degrees with respect to the vertical direction of the bottom surface. The loop surfaces of the first loop antenna 13 and the second loop antenna 23 are located substantially on the same plane. In this way, by positioning the two loop antennas 13 and 23 at angles of approximately 45 degrees to the X-axis and Y-axis, it is possible to excite the resonances of both the TE011 and TE101 modes in a balanced manner when measuring the complex dielectric constant of an anisotropic dielectric, and to simultaneously measure the dielectric constant in two axial directions with a single sweep using a single split rectangular resonator.

In addition, the dielectric constant of an anisotropic sample 30 can be measured simultaneously in two directions by a method for measuring the dielectric constant using the split rectangular parallelepiped resonator 10. This measurement method includes a step of acquiring a first resonant frequency characteristic in a state where the sample 30 is not inserted in the split rectangular parallelepiped resonator 10, a step of acquiring a second resonant frequency characteristic in a state where the sample 30 is inserted in the split rectangular parallelepiped resonator 10, and a step of calculating the dielectric constant of the sample 30 from the first and second resonant frequency characteristics. Each of the first resonant frequency characteristic and the second resonant frequency characteristic includes the resonant characteristics of the TE011 mode and the TE101 mode.

Other Embodiments
In order to accurately measure the dielectric constant of an anisotropic dielectric, it is necessary to make the difference between the resonance frequency of the TE011 mode and the resonance frequency of the TE101 mode sufficiently large so that the resonance characteristics of each mode can be accurately obtained when a sample is not inserted, and the two resonances do not overlap when an anisotropic sample is inserted. In the first embodiment, the shape of the rectangular parallelepiped cavity is a = 7.1 mm, b = 7.3 mm, c = 8.0 mm (shape 1), and the difference between the two resonance frequencies is 428 MHz when no sample is inserted. However, by inserting the LCP film sample, the difference between the two resonance frequencies is reduced to 168 MHz (when the orientation direction is the Y direction) as shown in FIG. 7. If the resonance frequency shifts due to the insertion of the sample, and the resonance of the TE011 mode and the TE101 mode overlap after the shift, the resonance characteristics cannot be measured. In addition, the resonance of the TE011 mode and the TE101 mode may be switched, in which case it is not clear which resonance is which. In the split rectangular parallelepiped resonator 10 of the first embodiment, the same thing can occur when the sample has a stronger anisotropy or is thicker.

The difference in dielectric constant due to the anisotropy of the sample is Δε, the thickness of the sample is t, and in this case, the amount of shift in the center frequency when the resonance of the TE011 mode shifts is ΔF011, and the amount of shift in the center frequency when the resonance of the TE101 mode shifts is ΔF101. If the difference between ΔF011 and ΔF101 is ΔF, then ΔF is approximately proportional to Δε x t.

In the first embodiment, the difference in the resonant frequencies of both resonant modes when no sample was inserted was 428 MHz. By using an LCP film with a thickness of 64 μm and a dielectric constant difference due to anisotropy of approximately 1.17, the difference in the resonant frequencies of both resonant modes was reduced to 168 MHz (when the orientation direction is the Y direction). In this case, ΔF011 is 512 MHz, ΔF101 is 772 MHz, and ΔF is 260 MHz.

If a sample that is thicker and more anisotropic than the LCP film used in embodiment 1 is to be measured, for example, if the shape of the rectangular cavity is a = 6.2 mm, b = 7.8 mm, and c = 8.5 mm (shape 2), the resonance frequencies (calculated values) of the TE011 mode and the TE101 mode will be 26.08 GHz and 29.93 GHz, respectively, which is a separation of nearly 4 GHz, making it possible to measure samples with stronger anisotropy or thickness. On the other hand, as the resonance frequency moves away from 28 GHz, the deviation from the measurement in a state that reflects the characteristics of the material used near 28 GHz increases, and there is a possibility that the difference from the characteristics in actual use in the market will increase. In addition, the frequency when measuring the dielectric constant in the same direction as the orientation will be significantly different from the frequency when measuring the dielectric constant perpendicular to the orientation.

Conversely, if the shape of the rectangular cavity is a = 7.18 mm, b = 7.22 mm, c = 8 mm (shape 3), the resonant frequencies (calculated values) of the TE011 mode and TE101 mode are 27.967 GHz and 28.053 GHz, respectively, which is sufficient for measurements that reflect the characteristics of the material used around 28 GHz. However, the difference between the two resonant frequencies is only 86 MHz, and even for samples with small anisotropy, there is a high possibility that the two resonances will overlap, making it impossible to measure the dielectric constant. This is considered to be the limit of practical use.

From the above considerations, it can be seen that the width of the front and back can be assumed for the selection of a, b, and c that define the shape of the rectangular parallelepiped cavity in this embodiment. If c is about 10% larger than b (c/b is 1.08 or more, more preferably 1.09 or more), the resonance frequency of the TE110 mode, which is an unnecessary mode, does not affect the measurement. If c is unnecessarily large, the size of the resonator will be unnecessarily large, so it is practical to keep c about 10% larger than b (c/b is 1.15 or less, more preferably 1.11 or less). The important thing is the ratio of a to b, but in the case of embodiment 1 (shape 1), the ratio of a to b is a:b = 7.1:7.3, which has a difference of about 3%. In the above considerations, in the minimum case (shape 3), the ratio of a to b is considered to be a:b = 7.18:7.22, which is a difference of about 0.5%. Conversely, in the maximum case (shape 2), the ratio of a to b is a:b = 6.2:7.8, which is a difference of about 26%.

As described above, the split rectangular parallelepiped resonator 10 has a cavity formed by combining two half cavities 12, 22, which are formed by dividing a rectangular parallelepiped into two by a plane parallel to the XY plane, facing each other. If the length of the vertical (side in the X direction) of the rectangular parallelepiped cavity is a and the length of the horizontal (side in the Y direction) is b, then the length b is 100.5% to 126% of the length a. This makes it possible to measure the dielectric constant in a state close to actual use at 28 GHz, which is the frequency band for 5G, while ensuring a sufficient difference between the resonant frequencies of the TE011 mode and the TE101 mode.

In addition, the length of the cavity (the length of the side in the Z direction) c (the sum of the two half cavities 12, 22) is 108% (more preferably, 109%) or more of the length b. This makes it possible to suppress the influence of resonance modes other than these on the TE0110 mode and the TE0101 mode.

The split rectangular resonator of the present invention is suitable for measuring the complex dielectric constant of dielectric materials in the millimeter wave band.

10 Split-type rectangular parallelepiped resonator 11, 21 Housing 12, 22, 52, 62 Half cavity 13, 23 Loop antenna 14, 24 Coaxial cable 30 Sample 50 Split cylinder resonator 60 Cavity resonator 61 Sample insertion hole E Electric field

Claims (5)

a first housing having a rectangular parallelepiped first half-cavity with a rectangular bottom surface and an opening facing the rectangular bottom surface;
a second housing having a second half cavity substantially identical to the first half cavity, the second housing being disposed relative to the first housing such that an opening of the first half cavity faces an opening of the second half cavity;
a first loop antenna exposed to the first half cavity from a bottom surface of the first half cavity;
a second loop antenna exposed to the second half cavity from a bottom surface of the second half cavity,
the ratio of the width to the length of the rectangular base is from 1.005 to 1.26;
a sum of a length from the bottom surface of the first half cavity to the opening and a length from the bottom surface of the second half cavity to the opening is 1.08 or more relative to the lateral length of the bottom surface;
The first loop antenna and the second loop antenna simultaneously excite resonance in a TE011 mode and a TE101 mode.
Split rectangular resonator. a first housing having a rectangular parallelepiped first half-cavity with a rectangular bottom surface and an opening facing the rectangular bottom surface;
a second housing having a second half cavity substantially identical to the first half cavity, the second housing being disposed relative to the first housing such that an opening of the first half cavity faces an opening of the second half cavity;
a first loop antenna exposed to the first half cavity from a bottom surface of the first half cavity;
a second loop antenna exposed to the second half cavity from a bottom surface of the second half cavity,
the ratio of the width to the length of the rectangular base is from 1.005 to 1.26;
a sum of a length from the bottom surface of the first half cavity to the opening and a length from the bottom surface of the second half cavity to the opening is 1.08 or more relative to the lateral length of the bottom surface;
the angle between the loop plane of the first loop antenna and the loop plane of the second loop antenna and the vertical direction of the bottom surface is about 45 degrees;
Split rectangular resonator. The first loop antenna and the second loop antenna are arranged symmetrically with respect to a point.
The split rectangular parallelepiped resonator according to claim 2 . A method for simultaneously measuring the dielectric constant of a sample in two directions using the split rectangular parallelepiped resonator according to any one of claims 1 to 3 , comprising the steps of:
acquiring a first resonant frequency characteristic in a state where the sample is not inserted into the split rectangular parallelepiped resonator;
acquiring a second resonant frequency characteristic in a state in which the sample is inserted into the split rectangular parallelepiped resonator;
calculating the dielectric constants of the sample in two directions from the first and second resonant frequency characteristics;
Method for measuring dielectric constant. Each of the first resonant frequency characteristic and the second resonant frequency characteristic includes a resonant characteristic of a TE011 mode and a TE101 mode.
The method for measuring a dielectric constant according to claim 4 .