A capacitively loaded substrate integrated waveguide equalizer

Abstract

The present invention relates to the technical field of microwave and millimeter-wave, and specifically to a capacitively loaded substrate integrated waveguide equalizer. It includes an SIW body, a tapered transition line, a 50Ω microstrip line, a ceramic substrate and an insulating pressing block. There is 1 slot on one side of the long side of the SIW body, which penetrates the surface metal layer of the SIW body. The ceramic substrate is arranged above the slot; the center point thereof is aligned with the center point of the slot in the vertical direction of the slot. A surface resistance layer is provided on the top surface or the bottom surface of the ceramic substrate and can completely cover the slot; the insulating pressing block is placed on the ceramic substrate, and the ceramic substrate and the SIW body are in close contact through the insulating pressing block, so that an equivalent capacitance is formed between the ceramic substrate and the metal layer of the SIW, which is equivalent to adding a part of capacitive reactance characteristics to the original loss surface resistance of the ceramic substrate. The introduction of the equivalent capacitance makes the loss at the low-frequency end (26 GHz) greater than the loss at the high-frequency end (40 GHz), thereby further improving the equalization amount.

Description

Technical Field

[0001] The present invention relates to microwave and millimeter-wave technologies, and particularly to a capacitively loaded substrate integrated waveguide equalizer. Background Art

[0002] As a new type of transmission line structure, substrate integrated waveguide (SIW) combines the advantages of rectangular waveguides and microwave planar circuits. It can achieve the transmission characteristics of traditional metal waveguides on a dielectric substrate and is compatible with existing PCB processing technologies. It has been widely used in microwave and millimeter-wave circuits and has the advantages of low radiation, low insertion loss, high Q value, high power capacity, miniaturization, and easy integration.

[0003] Equalizers are important components of microwave and millimeter-wave circuits and systems. As the frequency increases, most active and passive devices / circuits objectively tend to have a decrease in gain or an increase in insertion loss. Equalizers have the characteristic that the gain increases with the increase in frequency or the insertion loss decreases with the increase in frequency, and to a certain extent, they can compensate for this amplitude change caused by the increase in frequency.

[0004] The following reports mainly exist for existing equalizers operating in the microwave / millimeter-wave frequency band, such as:

[0005] An SIW equalizer designed by H. Peng et al. is fabricated on a ceramic substrate with surface resistance. The equalizer operates in the 26 - 40 GHz (Ka band). By introducing surface resistance at specific positions instead of the copper layer, excellent equalization characteristics are achieved. The actual test results show that in the entire Ka band, the SIW equalization values are 2.8 dB, 5.6 dB, and 9 dB respectively, and the return loss is better than -18.8 dB. See the literature H. Peng et al., "Substrate Integrated Waveguide Equalizers and Attenuators With Surface Resistance," in IEEE Transactions on Microwave Theory and Techniques, vol. 68, no. 4, pp. 1487 - 1495, April 2020, doi: 10.1109 / TMTT.2019.2958267.

[0006] A novel microwave resistor-based stepped SIW equalizer designed by H. Peng et al. The operating frequency range of this equalizer is 12 - 18 GHz (Ku band). When the number of microwave resistors is 4, 8, 12, 16, 20, and 24 respectively, the measured equalization values are 1.16 dB, 1.75 dB, 2.74 dB, 3.67 dB, 4.28 dB, and 4.95 dB respectively, and the return loss is better than -11.95 dB. See the reference H. Peng et al., "Step Substrate Integrated Waveguide Equalizer Based on Microwave Discrete Resistors for Feeding Network," 2021 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (APS / URSI), 2021, pp. 675 - 676, doi: 10.1109 / APS / URSI47566.2021.9704067.

[0007] An active equalizer based on PIN diodes designed by S.C. Bera. This equalizer is used for temperature and frequency compensation in microwave circuits and systems. By utilizing the characteristic that the impedance of PIN diodes changes with the set DC voltage, the equalization of the circuit amplitude is achieved. In the frequency range of 3 - 5 GHz, an attenuation characteristic of ±8 dB can be realized. See the reference S.C. Bera, "Amplitude Tilt Active Equalizer for Frequency and Temperature Compensation," in IEEE Microwave Wireless Component Letter, vol. 21, no. 7, pp. 344 - 346, Jul. 2011, doi: 10.1109 / LMWC.2011.2152385.

[0008] H. Peng et al. designed a novel substrate-integrated waveguide (SIW) equalizer based on absorbing materials. The operating frequency range of this equalizer is 26 - 40 GHz (Ka band), which can achieve lower insertion losses. The measured equalization values are 2.94 dB, 6.55 dB, 9.74 dB, 14.90 dB, 20.39 dB, and 24.01 dB respectively. The insertion losses at the maximum frequency point (40 GHz) are 2.32 dB, 2.30 dB, 2.77 dB, 3.61 dB, 4.60 dB, and 5.34 dB respectively, and the return losses are all better than -14.6 dB. See the literature H. Peng et al., "Low Cost / Insertion Loss Substrate-Integrated Waveguide Equalizer Based on Absorbing Materials," in IEEE Transactions on Components, Packaging and Manufacturing Technology, vol. 11, no. 11, pp. 1948 - 1954, Nov. 2021, doi: 10.1109 / TCPMT.2021.3113978.

[0009] Among the equalizers mentioned above, the first equalizer is designed based on a ceramic substrate with surface resistance, which has good return loss and insertion loss, but the equalization amount it provides is relatively low; the second equalizer realizes a stepped equalizer by changing the number of microwave resistors, but the equalization amount it provides is small and the operating frequency is not high (Ku band); the third equalizer dynamically adjusts the equalization amount through voltage change, but its operating frequency is low (not exceeding 7 GHz); the last equalizer is designed based on absorbing materials, but due to the softness of the absorbing materials themselves, there are certain fluctuations in the equalization amount under different pressure conditions. Summary of the Invention

[0010] The purpose of the present invention is to provide a substrate-integrated waveguide equalizer with equivalent capacitance loading, which utilizes the equivalent capacitance effect formed between the ceramic substrate and the metal layer of the SIW body, and increases the loss on the propagation channel by introducing capacitive reactance to overcome the problems existing in the equalizers operating in the microwave / millimeter-wave frequency band, such as low equalization amount, low operating frequency, or fluctuating equalization amount.

[0011] To achieve the above purpose, the present invention adopts the following technical solutions:

[0012] A substrate-integrated waveguide equalizer with equivalent capacitance loading, comprising an SIW body, a tapered transition line, a 50Ω microstrip line, a ceramic substrate, and an insulating pressing block for fixing the ceramic substrate;

[0013] Both ends of the SIW body are connected to 50Ω microstrip lines through a section of tapered transition line respectively;

[0014] On both sides of the central connection line of the wide side of the SIW body, four rows of metallized vias are arranged respectively. The center-to-center distance of the two rows of metallized vias closest to the central connection line of the wide side on both sides is W s , the center-to-center distance of two adjacent rows of metallized vias on one side of the long side of the SIW body is d, and the length of the long side of the SIW body is L s , the tapered transition line is located in the middle part of the wide side of the SIW body, and its length is L t , the length of the connection edge between the tapered line and the wide side of the SIW body is W t , the width of the end connected to the 50Ω microstrip line is W; the diameter of the metallized via is dvp, the center-to-center distance of two adjacent metallized vias on one side of the long side of the SIW body is svp, and the width of the 50Ω microstrip line is W;

[0015] One slot that penetrates the surface metal layer of the SIW body is opened on one side of the long side of the SIW body; the slot is located near the central connection line of the wide side of the SIW body. A ceramic substrate is provided above the slot. The center point of the ceramic substrate is aligned with the center point of the slot in the vertical direction of the slot. A surface resistance layer is provided on the top surface or bottom surface of the ceramic substrate, and its size is slightly larger than the slot so that it can completely cover the slot;

[0016] The insulating pressing block is placed on the ceramic substrate to make the ceramic substrate and the SIW body in close contact.

[0017] Furthermore, the slot is composed of two isosceles triangles and a rectangle; after the two isosceles triangles are connected by the rectangle, a spindle-shaped structure with small ends and a large middle is formed. The long side of the rectangle is parallel to the electromagnetic wave propagation direction. The two isosceles triangles are respectively located on the two wide sides of the rectangle, and their bases coincide with one wide side of the rectangle respectively, and the vertex angles point in opposite directions. Adopting this spindle-shaped structure can effectively improve the standing wave and further improve the overall performance of the equalizer.

[0018] Furthermore, the vertex angles of the two isosceles triangles forming the slot are all rounded, and the radius of the circle is R.

[0019] Furthermore, the length of the long side of the rectangle is L sr , the length of the wide side is W sr , and W sr <W s / 2; the height of both isosceles triangles is L srt , L srt should satisfy L sr +2*L srt <L s .

[0020] Further, the insulating pressing block material is an insulating material such as polytetrafluoroethylene.

[0021] The working principle of the substrate integrated waveguide equalizer with equivalent capacitance loading provided by the present invention is as follows: Electromagnetic waves propagate in the SIW body in the TE 1.0 mode. The front and back sides in the SIW, together with the eight rows of metallized vias in the SIW body through the metal layers covering them, jointly confine the propagation boundary of the electromagnetic waves. Using a polytetrafluoroethylene pressing block to fix the ceramic substrate can make the ceramic substrate and the SIW body in close contact, keep the equivalent capacitance stable, and also prevent electromagnetic wave leakage. In the traditional SIW structure, the losses mainly come from dielectric losses and the losses caused by the skin effect of the metal walls. To increase the losses on the propagation path, we introduce a ceramic substrate with a single-sided GaN material coating, and an equivalent capacitance is formed between the ceramic substrate and the metal layer of the SIW, which is equivalent to adding a part of capacitive reactance characteristics (1 / ωC0) to the original loss surface resistance R s of the ceramic substrate. The capacitive reactance brought by the equivalent capacitance is frequency-dependent. The lower the frequency, the greater the capacitive reactance. The introduction of the equivalent capacitance makes the losses at the low-frequency end (26 GHz) greater than those at the high-frequency end (40 GHz), thereby further improving the equalization amount.

[0022] In summary, the present invention provides a novel capacitance-loaded SIW equalizer structure implemented on a ceramic substrate. This SIW equalizer can be used in microwave and millimeter-wave circuits and systems to perform different attenuations on signals of different frequencies. Brief Description of the Drawings

[0023] Figure 1 is a top view of the equalizer structure of the embodiment of the present invention.

[0024] Figure 2 is a physical diagram of the SIW body of the embodiment of the present invention.

[0025] Figure 3 is a schematic diagram of the 3D model of the SIW body of the embodiment of the present invention - with the surface resistance layer facing down.

[0026] Figure 4 is a schematic diagram of the 3D model of the SIW body of the embodiment of the present invention - with the surface resistance layer facing up.

[0027] Figure 5 is a schematic diagram of the equivalent capacitance model and current flow direction of the embodiment of the present invention.

[0028] Figure 6 is the resistance region division of the RW sidewall of the embodiment of the present invention.

[0029] Figure 7 is a simulation diagram of different normalized attenuation values between k and k + Δk of the embodiment of the present invention.

[0030] Figure 8 It is the overall physical diagram of the equalizer structure of the embodiment of the present invention.

[0031] Figure 9 It is the 3dB - S parameter curve of the embodiment of the present invention: among which, (a) is the simulation / measurement comparison diagram with the surface resistance layer facing upward, and (b) is the simulation / measurement comparison diagram with the 3dB - surface resistance layer facing downward.

[0032] Figure 10 It is the 4.1dB - S parameter curve of the embodiment of the present invention: among which, (a) is the simulation / measurement comparison diagram with the - surface resistance layer facing upward, and (b) is the simulation / measurement comparison diagram with the surface resistance layer facing downward.

[0033] Figure 11 It is the 6dB - S parameter curve of the embodiment of the present invention: among which, (a) is the simulation / measurement comparison diagram with the surface resistance layer facing upward, and (b) is the simulation / measurement comparison diagram with the surface resistance layer facing downward.

[0034] Figure 12 It is the 10dB - S parameter curve of the embodiment of the present invention: among which, (a) is the simulation / measurement comparison diagram with the surface resistance layer facing upward, and (b) is the simulation / measurement comparison diagram with the surface resistance layer facing downward.

[0035] Reference numerals: SIW equalizer body - 1, slot line - 2, metallized via - hole - 3, tapered line - 4, microstrip line - 5. Detailed implementation manners

[0036] The present invention will be further described in detail below with reference to the drawings and embodiments.

[0037] The EM field distribution characteristics in SIW and rectangular waveguide (RW) are similar. To simplify the analysis process, the equalizer in RW is analyzed first. The ideal RW is filled with vacuum / air. The surface resistance Rs of the ideal RW is 0. The distribution of the surface resistance of the side wall part of the equalizer body is as Figure 6 , which can be divided into two parts: region one and regions two and three.

[0038] In the direction of +z of the electric field amplitude E, assuming the attenuation constant in RW is α and propagating in the form of a wave, it can be expressed as

[0039] E = E0e -αz (1)

[0040] The transmitted power P can be expressed as

[0041] P = P0e -2αz (2)

[0042] The power loss per unit length is

[0043]

[0044] where R s , Z s , Js, and respectively represent the surface resistance of the metal in RW, the surface impedance in the lossy material, the surface current density, the unit normal vector pointing to the perfect conductor and the surface impedance, and the magnetic field strength in RW.

[0045] where Z S is the complex impedance composed of the surface resistance R s ' of the lossy material and the equivalent capacitive reactance 1 / jωC0.

[0046]

[0047] To simplify the analysis, compared with the surface impedance of the lossy ceramic substrate, the surface resistance of the metal wall can be approximately equal to 0 Ω. Then,

[0048]

[0049] η, Z TE , f c are the characteristic impedance of SIW, the wave impedance of the transverse electromagnetic wave and the magnetic field, and its cut-off frequency, and β is the phase constant..

[0050] Substitute equations (8) and (9) into equation (6)

[0051]

[0052] Therefore, the attenuation constant α is given by the following equation

[0053]

[0054] where a is the side length of RW along the x-axis, and b is the side length of RW along the y-axis, as shown in the appendix Figure 6 . Let c = k·a (0 ≤ k ≤ 1), from equation (13), the attenuation constant α can be rewritten as

[0055]

[0056] Let F = f c / f (0.5 < F < 0.85), substituting equation (7) into equation (14), the attenuation constant α can be written as

[0057]

[0058] Furthermore, the magnitude of the attenuation constant, i.e., |α|, is given by the following formula

[0059]

[0060] It can be seen from Equation (16) that when the frequency becomes lower, the capacitive reactance becomes larger, and thus the attenuation constant α becomes larger. This indicates that the loss at the low-frequency end is greater than that at the high-frequency end. The equalization amount is defined as the difference in the insertion loss |S21| between the high-frequency end (40 GHz) and the low-frequency end (26 GHz). That is, the insertion loss at the 26 GHz frequency point is higher than that at the 40 GHz frequency point, so the equalization amount becomes higher. This shows that the additional equivalent capacitance introduced by the capacitor-loaded equalizer adds a part of capacitive reactance loss on the basis of the loss resistance, and the capacitive reactance loss decreases with the increase of frequency, thus further increasing the attenuation constant at the low-frequency end and further improving the equalization amount.

[0061] According to CN201910977726.3, the conclusion disclosed in the invention named "A substrate integrated waveguide equalizer" is that the distribution of the surface resistance of the side wall part of the equalizer body is as Figure 6 shown, which can be divided into Region 1, Region 2, and Region 3. The simulation results of different normalized attenuation values between k and k+Δk are as Figure 7 . In Region 1: the difference in insertion loss between the high- and low-frequency points increases with the increase of k. In Region 2 and Region 3: the difference in insertion loss between the high- and low-frequency points decreases with the increase of k. Starting from the RW attenuation characteristic, in order to achieve the maximum slope, the scaling factor k is selected to be about 0.8, and the position of the surface resistance should be placed in Region 2 and Region 3.

[0062] In this embodiment, the capacitor-loaded SIW equalizer based on a ceramic substrate operates in the Ka band, on a Rogers 5880 dielectric substrate with a thickness of 0.254 mm, a dielectric constant of 2.2, a tangent loss of 0.0009, a copper thickness of 18 um, and the front and back metal layers are gold-plated, and the final thickness is about 43 um. The ceramic substrate is placed at the center position of the SIW body, and the center line of its wide side coincides with the center line of the wide side of the SIW body. Moreover, the width of the ceramic substrate is slightly larger than the width of the SIW body (the width of the body = the distance between the two rows of metal holes close to the center) by about 2 mm, so that the ceramic substrate can cover the SIW body, and the width of the raised part of the polytetrafluoroethylene pressing block is the same as the width of the ceramic substrate.

[0063] After simulation and optimization using the electromagnetic simulation software Ansoft HFSS, the optimal parameter dimensions are obtained, as shown in Table 1 specifically:

[0064] Table 1

[0065]

[0066]

[0067] When the surface resistance layer of the ceramic substrate faces downward, the equalization amounts of the equalizer are set to 3 dB, 4.1 dB, 6 dB, and 10 dB; then the surface resistance layer of the ceramic substrate faces upward to simulate and measure the equalization amount of the capacitively loaded equalizer. The simulation results and the measured results are respectively as Figure 9 (a) and Figure 9 (b), Figure 10 (a) and Figure 10 (b), Figure 11 (a) and Figure 11 (b), Figure 12 (a) and Figure 12 (b) shown, and the specific analysis results are shown in Table 2.

[0068] Table 2

[0069]

[0070]

[0071] The test and simulation results are as Figure 9 、 10 、11、12 shown, and the test results are in good agreement with the simulation results. The measured return loss value is better than -15.2 dB in the range of 26 GHz - 40 GHz, covering the entire Ka band. Compared with the simulation results, the actual measured equalization values are 3.5 dB, 4.5 dB, 7 dB, and 11.5 dB respectively when the surface resistance layer of the ceramic substrate faces downward close to the PCB metal layer, and the equalization errors are 0.5 dB, 0.4 dB, 0.9 dB, and 1.5 dB respectively; when the surface resistance layer of the ceramic substrate faces upward, the actual measured equalization values are 6.2 dB, 8.4 dB, 12.4 dB, and 22.6 dB respectively, and the equalization errors are 1.2 dB, 1.8 dB, 2.5 dB, and 3.9 dB respectively. The simulation and measured results show that the SIW equalizer can attenuate signals of different frequencies differently. By introducing a ceramic substrate and assembling it with the surface resistance layer facing upward, an equivalent loading capacitance is achieved with the PCB metal layer to obtain a higher equalization value.

Claims

1. A substrate integrated waveguide equalizer with equivalent capacitance loading, comprising an SIW body, a tapered transition line, a 50Ω microstrip line, a ceramic substrate, and an insulating pressing block for fixing the ceramic substrate; both ends of the SIW body are connected to the 50Ω microstrip line through a section of tapered transition line respectively, and it is characterized in that: On both sides of the center line of the wide side of the SIW body, four rows of metallized vias are arranged, and the center-to-center distances of the two rows of metallized vias closest to the center line of the wide side on both sides are both W s , the center-to-center distance between two adjacent rows of metallized vias on one side of the long side is d, and the length of the long side of the SIW body is L s , the tapered transition line is located in the middle part of the wide side of the SIW body, and its length is L t , the length of the connection edge between the tapered line and the wide side of the SIW body is W t , the width of the end connected to the 50Ω microstrip line is W; the diameter of the metallized via is dvp, the center-to-center distance between two adjacent metallized vias on one side of the long side of the SIW body is svp, and the width of the 50Ω microstrip line is W; A slot penetrating the surface metal layer of the SIW body is opened on one side of the long side of the SIW body; the slot is located at the position of the center connection line close to the wide side of the SIW body, and a ceramic substrate is arranged above the slot; the center point of the ceramic substrate is aligned with the center point of the slot in the vertical direction of the slot; a surface resistance layer is arranged on the top surface or bottom surface of the ceramic substrate, and its size is slightly larger than the slot so that it can completely cover the slot; The insulating pressing block is placed on the ceramic substrate to make the ceramic substrate and the SIW body in close contact.

2. The equivalent-capacitance-loaded substrate integrated waveguide equalizer according to claim 1, wherein: The slot is composed of two isosceles triangles and a rectangle; after the two isosceles triangles are connected by the rectangle, a shuttle-shaped structure with small ends and a large middle is formed. The long side of the rectangle is parallel to the electromagnetic wave propagation direction. The two isosceles triangles are respectively located on the two wide sides of the rectangle, and their bases coincide with one wide side of the rectangle respectively, and the vertex angles point in opposite directions.

3. An equivalent capacitance loaded substrate integrated waveguide equalizer according to claim 2, characterized in that: The vertex angles of the two isosceles triangles forming the slot are all rounded, and the radius of the circle is R.

4. An equivalent-capacitance-loaded substrate integrated waveguide equalizer according to claim 2, characterized in that: The long side length of the rectangle is L sr , and the short side length is W sr , and W sr <W s / 2; the heights of the two isosceles triangles are both L srt , L srt should satisfy L sr +2*L srt <L s .

5. An equivalent-capacitance-loaded substrate integrated waveguide equalizer according to any one of claims 1 to 4, characterized in that: The material of the insulating pressing block is polytetrafluoroethylene.

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