A T-shaped dual-mode dielectric waveguide resonator and a dual-passband dielectric waveguide filter

Abstract

The application discloses a T-shaped dual-mode dielectric waveguide resonator and a dual-passband dielectric waveguide filter, and belongs to the technical field of microwave communication. The T-shaped dual-mode dielectric waveguide resonator is characterized in that the upper half of a dielectric block is symmetrically reduced inward to form a T-shaped dielectric ridge, a downward metallized blind hole is formed in the ridge, a through hole is formed in the side wall of the lower half, and the outer surface of the dielectric block is metallized. The T-shaped structure compresses the second high-order mode electric field and lifts the spurious resonance frequency; the through hole controls the main mode, the blind hole controls the high-order mode, and the dual-mode frequency decoupling is realized. The dual-passband dielectric waveguide filter adopts two resonators matched with T-shaped coupling windows, the low-frequency main mode and the high-frequency high-order mode are transmitted in the upper and lower parts of the coupling windows respectively, and the silver-plated microstrip feed structure is matched to realize independent adjustment of the dual-passband coupling coefficient and the external quality factor. The device is small in size, low in insertion loss, good in spurious suppression, and suitable for 5G Sub-6GHz base station radio frequency front ends.

Description

Technical Field

[0001] This invention relates to the field of microwave communication technology, and in particular to a dual-band ceramic dielectric waveguide filter for the radio frequency front-end of a mobile communication system base station. Background Technology

[0002] With the large-scale commercial deployment of 5G mobile communication systems, the Sub-6GHz band has become a core frequency resource for base station construction. The introduction of Massive MIMO technology has led to a significant increase in the number of antenna channels in base stations, requiring each RF channel to be equipped with an independent filter. This has resulted in a sharp rise in the total demand for filters and imposed stricter engineering constraints on the size, profile height, and electrical performance consistency of devices. Against this backdrop, ceramic dielectric waveguide filters, leveraging the spatial compression effect of high dielectric constant materials on the electromagnetic field and employing full-surface metallization processes to reduce conductor losses, have significantly reduced the electrical size of a single cavity while retaining the high power capacity and good heat dissipation characteristics of metal cavity filters. Therefore, they have become the mainstream technology solution for current base station RF front-ends.

[0003] However, multi-band co-location deployment has become the norm in communication network construction. Configuring an independent filter for each frequency band would lead to a doubling of the number of channels, accumulated insertion loss, and a significant increase in layout area, revealing the obvious shortcomings of single-band filters in terms of system integration. Therefore, filters with dual-band operation capabilities are evolving from an optional requirement to a fundamental constraint in engineering design, becoming a key technological path to improve the integration of RF front-ends.

[0004] In existing dual-band ceramic dielectric waveguide filter technology, multimode resonance and cross-coupling are typically used to achieve dual-passband response. However, the above-mentioned existing technical solutions still have the following shortcomings:

[0005] First, the independent controllability of dual-band bandwidth is limited. Since the coupling coefficients of the two passbands are jointly determined by the same physical coupling structure, adjusting the coupling strength of one band may cause unexpected effects on the other band due to boundary condition coupling effects. This severely restricts the freedom of bandwidth design and makes it difficult to meet the needs of differentiated bandwidth configuration for the two bands in engineering projects.

[0006] Secondly, the structure is complex to implement and difficult to debug. In order to simultaneously meet the requirements of multi-mode excitation and cross-coupling path construction, complex three-dimensional perturbation structures (such as irregular blind holes, asymmetric chamfers, etc.) must be introduced. Such structures are highly sensitive to machining tolerances, which significantly increases the design iteration and debugging cycle, and is not conducive to large-scale production and cost control.

[0007] Third, spurious suppression performance is limited. Higher-order spurious modes of dual-mode resonators are usually close to the operating passband, which easily introduces parasitic coupling channels in the stopband, restricting further improvement of the upper stopband suppression depth and affecting the system's anti-interference performance.

[0008] In summary, existing dual-band ceramic dielectric waveguide filters still have technical problems that need to be solved in terms of independent bandwidth control, structural manufacturability, and spurious suppression. It is necessary to propose a new technical solution to overcome the above-mentioned defects. Summary of the Invention

[0009] Purpose of the invention: In view of the above-mentioned prior art, a T-type dual-mode dielectric waveguide resonator and a dual-passband filter containing the resonator are proposed, which have the characteristics of miniaturization, harmonic control and low insertion loss.

[0010] Technical solution: A T-type dual-mode dielectric waveguide resonator includes a dielectric block, which is divided into a lower half and an upper half along the height direction; the upper half is symmetrically reduced inward along the width direction of the dielectric block to form a dielectric ridge structure with a T-shaped cross-section; a metallized blind via is etched downward at the top center of the dielectric ridge structure, and a through-hole is etched at the center of the sidewall of the lower half of the dielectric block; the outer surface of the dielectric block is covered with a metallization layer.

[0011] Furthermore, the dielectric block is made of ceramic dielectric material and the metallization layer is a silver-plated metal layer.

[0012] Furthermore, the via is used to adjust the resonant frequency and unloaded quality factor of the resonator's main mode (TEM mode), and the metallized blind via is used to adjust the resonant frequency and unloaded quality factor of the resonator's first higher-order quasi-TEM mode; wherein, when the via length is increased, the resonant frequency of the main mode (TEM mode) decreases, the unloaded quality factor decreases, and the resonant frequency of the first higher-order quasi-TEM mode remains basically unchanged; when the blind via depth is increased, the resonant frequency of the first higher-order quasi-TEM mode decreases, the unloaded quality factor decreases, and the resonant frequency of the main mode (TEM mode) remains basically unchanged.

[0013] Furthermore, the T-shaped dielectric ridge structure affects the second higher-order mode TE of the resonator. 101 The electric field distribution of the mode produces a spatial compression effect, causing the second higher-order mode TE to... 101 The equivalent electrical length of the mode is shortened and the resonant frequency is shifted to a higher frequency, thus improving the spurious suppression capability of the resonator.

[0014] A dual-passband dielectric waveguide filter includes a PCB board, a first T-type dual-mode dielectric waveguide resonator, a second T-type dual-mode dielectric waveguide resonator, and a T-type coupling window; the first T-type dual-mode dielectric waveguide resonator and the second T-type dual-mode dielectric waveguide resonator are both T-type dual-mode dielectric waveguide resonators, and are arranged side by side on the PCB board; the T-type coupling window is disposed between the two resonators and connects the internal dielectrics of the two resonators; a feed microstrip structure is respectively disposed on the outer side of the two resonators that are far apart.

[0015] Furthermore, the T-shaped coupling window is divided into an upper coupling window and a lower coupling window along the height direction; the upper coupling window corresponds to the height of the dielectric ridge structure of the resonator and is used to transmit the first higher-order quasi-TEM mode signal, forming a coupling path in the high-frequency passband; the lower coupling window corresponds to the height of the lower half of the resonator and is used to transmit the main mode TEM mode signal, forming a coupling path in the low-frequency passband; the coupling paths of the two modes are partially separated in space to reduce cross-interference between the two passbands.

[0016] Furthermore, by adjusting the length of the upper coupling window, the coupling coefficient of the quasi-TEM mode corresponding to the high-frequency passband can be independently controlled: the larger the length of the upper coupling window, the larger the coupling coefficient of the quasi-TEM mode, and it has no significant effect on the coupling coefficient of the low-frequency passband main mode TEM mode; by adjusting the height of the lower coupling window, the coupling coefficient of the low-frequency passband main mode TEM mode can be controlled: the larger the height of the lower coupling window, the larger the coupling coefficient of the main mode TEM mode, while the coupling coefficient of the quasi-TEM mode decreases slightly.

[0017] Furthermore, the feed microstrip structure includes silver-plated microstrip lines disposed on the outer and lower surfaces of the resonator and interconnected with each other, and the dielectric region on the resonator corresponding to the silver-plated microstrip lines is in a non-metallic state; the silver-plated microstrip lines are electrically connected to a transmission line on the PCB board with a characteristic impedance of 50 ohms.

[0018] Furthermore, by adjusting the length of the silver-plated microstrip line, the external quality factor corresponding to the two working modes can be controlled respectively: when the length of the bottom microstrip line is increased, the external quality factor of the quasi-TEM mode decreases, while the external quality factor of the main TEM mode remains basically unchanged; when the length of the side microstrip line is increased, the external quality factor of the quasi-TEM mode decreases significantly, while the external quality factor of the main TEM mode increases slightly.

[0019] Beneficial Effects: This invention utilizes two T-shaped dielectric waveguide resonators to construct a miniaturized dual-mode dual-passband dielectric waveguide bandpass filter. The designed resonator is based on a traditional rectangular dielectric waveguide, divided into upper and lower parts along its height. The upper waveguide is symmetrically reduced inward along its width, forming a T-shaped structure in the plane. Simultaneously, a metallized blind via is etched downward at the center of the upper part, and a through-hole is etched at the center of the lower part, thus forming a dual-mode dielectric waveguide resonator. This design effectively controls the dominant mode and higher-order modes by adjusting the through-hole and blind via, respectively. Furthermore, this T-shaped structure generates a spatial compression effect on the electric field distribution of the second higher-order mode (used to construct the high-frequency band), which affects the first higher-order mode, shortening its equivalent electrical length and shifting the resonant frequency to higher frequencies. This helps reduce the interference of spurious modes on the passband performance.

[0020] Based on this resonator, a miniaturized dual-mode dual-passband dielectric waveguide bandpass filter was designed. The bandpass filter can control the frequency of the dominant mode by using the via length and adjust the frequency of higher-order modes by using the height of the blind via. At the same time, it can also use the coupling window length to coordinately control the coupling coefficients of low and high frequencies, achieving a small size while also providing independent dual-mode control. Attached Figure Description

[0021] Figure 1 This is a three-dimensional structural diagram of the T-type dual-mode dielectric waveguide resonator used in this invention;

[0022] Figure 2 A three-dimensional structural diagram of an embodiment of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by the present invention;

[0023] Figure 3 This is a top view of an embodiment of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by the present invention;

[0024] Figure 4 The electric field distribution diagrams for the first three modes of a traditional rectangular dielectric waveguide resonator are shown.

[0025] Figure 5 The electric field distribution diagrams for the first three modes of the T-type dual-mode dielectric waveguide resonator provided by this invention;

[0026] Figure 6 The via length 'a' of the T-type dual-mode dielectric waveguide resonator provided by this invention affects the resonant frequencies and unloaded quality factor Q of the first two modes. u The impact of simulation results;

[0027] Figure 7 The blind aperture height h1 of the T-type dual-mode dielectric waveguide resonator provided by this invention affects the resonant frequencies and unloaded quality factor Q of the first two modes. u The impact of simulation results;

[0028] Figure 8 S-parameter simulation results of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by this invention;

[0029] Figure 9 The coupling topology diagram of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by the present invention;

[0030] Figure 10 The simulation results of the frequency variation with the via length a of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by the present invention are shown, where (a) corresponds to low frequency and (b) corresponds to high frequency.

[0031] Figure 11 The simulation results of the frequency variation of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by the present invention with the blind hole depth h1 are shown, where (a) corresponds to low frequency and (b) corresponds to high frequency.

[0032] Figure 12 The coupling coefficient k between the DR1 and DR2 resonators provided by this invention 12 (Low frequency), k 34 (High frequency) curves as a function of parameters, where (a) corresponds to the upper half coupling window length w. cw1 (b) The corresponding parameter is the height c1 of the lower half of the coupling window;

[0033] Figure 13 The external quality factor Q of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by this invention e With the width l of the bottom microstrip line ms1 The curve of change;

[0034] Figure 14 The external quality factor Q of the miniaturized T-type dual-mode dual-passband dielectric waveguide filter provided by this invention e With the length l of the side microstrip line ms2 The curve showing the change. Detailed Implementation

[0035] The invention will now be further explained with reference to the accompanying drawings.

[0036] A T-type dual-mode dielectric waveguide resonator, the three-dimensional structure of which is as follows: Figure 1As shown. The specific design method is as follows: For a rectangular dielectric block with width a and length b, the waveguide of the upper half of the dielectric block with height c2 is first symmetrically reduced inward along its width direction to form a dielectric ridge structure with a T-shaped cross-section. The width of the ridge on both sides is w. On this basis, a metallized blind hole with a depth h1 is further etched downward at the center of the upper half of the dielectric ridge structure. The lower half of the dielectric block has a height of c1, and a through hole is etched at the center of the side wall in the width direction of the lower half. This constructs a complete T-shaped dual-mode dielectric waveguide resonator unit. The dielectric block can be made of dielectric ceramic material and the outer surface is silver-plated.

[0037] A miniaturized dual-passband filter based on a T-type dual-mode dielectric waveguide resonator, its three-dimensional structure is as follows: Figure 2 As shown, the top view is as follows Figure 3 As shown. This miniaturized dual-passband filter includes a PCB board, on which two T-shaped dual-mode dielectric waveguide resonators DR1 and DR2 are mounted, along with a T-shaped coupling window 3 connecting them. The T-shaped coupling window 3 is divided into upper and lower parts in the vertical direction: the upper part is a dielectric block coupling window with a length of w. cw1 The height is c2, and the length of the lower half of the dielectric block coupling window is w. cw2 The height is c1. The through holes D1 and D2 located in the lower half of the resonators DR1 and DR2 are used to adjust the main mode frequency, and the blind holes C1 and C2 located in the upper half of the resonators DR1 and DR2 are used to adjust the higher-order mode frequency.

[0038] A silver-plated microstrip line 1 is connected to the outer and lower surfaces of resonator DR1, and a silver-plated microstrip line 2 is connected to the outer and lower surfaces of resonator DR2. The dielectric near the microstrip lines is non-metallized. The silver-plated microstrip lines 1 and 2 are used for power feeding. The silver-plated microstrip lines are respectively connected to transmission lines with a characteristic impedance of 50 ohms on the PCB board, and the width of the transmission lines is w. ms1 By controlling the lengths l of silver-plated microstrip lines 1 and 2 ms1 l ms2 The port coupling strength can be precisely adjusted, thereby achieving control over the external quality factor Q. e The adjustment and optimization were performed. The widths of the silver-plated microstrip lines 1 and 2 are w. ms2 To facilitate coupling between the tuning source and load and various modes, the width w of the transmission line in contact with the medium is... ms2 The width w of the microstrip line at the port ms1 Inconsistent.

[0039] The operation of this miniaturized dual-passband filter is as follows: The signal is input through a silver-plated microstrip line 1, which excites the dominant mode and the first higher-order mode in resonator DR1. The two modes are coupled to their corresponding modes in DR2 through a T-shaped coupling window 3. The dominant mode mainly propagates along the lower half of the window, while the higher-order mode mainly propagates along the upper half. Although they share the same window, their coupling paths are partially separated in space, thus reducing cross-interference between the two passbands. Finally, the two modes are output through resonator DR2 and the silver-plated microstrip line 2, completing the entire filtering and transmission process.

[0040] Figure 4 The diagram shows the electric field distribution of the first three modes of a conventional rectangular dielectric waveguide resonator with blind vias etched at the top and through-holes etched on the sidewalls. The electric field of the dominant TEM mode is concentrated in the center of the through-hole, while the electric field of its first higher-order quasi-TEM mode is concentrated at the bottom of the blind via. The electric field of the second higher-order TE mode is concentrated in the center of the through-hole. 101 The electric field of the mode is concentrated at the center of the xoz plane. Based on a traditional rectangular waveguide, it is divided into upper and lower parts along its height, and the sidewalls of the upper resonator are symmetrically reduced inwards, thus forming... Figure 5 The T-shaped dielectric waveguide resonator is shown. The electric field distribution of the T-shaped dielectric waveguide resonator is as follows. Figure 5 As shown, the electric field of the master mode (TEM) is concentrated in the center of the via, the electric field of its first higher-order mode (quasi-TEM) is concentrated at the bottom of the blind via, and the electric field of the second higher-order mode is concentrated at the center of the xoz plane. However, due to the T-shaped structure, the electric field of the second higher-order mode (TEM) in the xoz plane is concentrated at the center of the via. 101 The electric field of the mode is compressed, causing its frequency to increase, thereby enhancing harmonic suppression.

[0041] When the through-hole length 'a' is changed while other parameters remain constant, the simulation results of the resonant frequency and unloaded quality factor of the resonator are as follows: Figure 6 As shown, the longer the via, the lower the resonant frequency of the TEM mode, while the resonant frequency of the quasi-TEM mode remains essentially unchanged. At this point, the unloaded quality factor of the quasi-TEM mode increases, while the unloaded quality factor of the TEM mode decreases. The simulation results of the resonant frequency and unloaded quality factor of the resonator when the blind via depth h1 is changed while other parameters remain constant are as follows: Figure 7 As shown, the deeper the blind via, the resonant frequency and unloaded quality factor of the TEM mode remain essentially unchanged, while the resonant frequency and unloaded quality factor of the quasi-TEM mode both decrease significantly. This demonstrates that the length of the through-hole and the depth of the blind via in the resonator can control the resonant frequency and quality factor of the first two modes.

[0042] The present invention proposes a miniaturized T-type dual-mode dual-passband dielectric waveguide filter, the simulation results of which are as follows: Figure 8As shown in the figure, the filter's passbands are 3320MHz~3360MHz for low frequencies and 4140MHz~4200MHz for high frequencies, covering the n77 band (3300MHz~4200MHz). The low-frequency center frequency is 3340MHz, with a maximum insertion loss of 0.68dB, an operating bandwidth of 40MHz, and a relative bandwidth of 1.2%. The high-frequency center frequency is 4170MHz, with a maximum insertion loss of 0.58dB, an operating bandwidth of 60MHz, and a relative bandwidth of 1.4%. The second higher-order spurious mode shifts from 4732MHz in the traditional rectangular structure to 5500MHz in the T-structure.

[0043] To further illustrate the filter's ability to be independently controllable in both modes, Figure 9 The coupling topology of the dual passband filter is given. Figure 10 It shows that as the resonator aperture length 'a' increases, the low-frequency passband of the filter shifts significantly to lower frequencies overall, while the high-frequency passband remains basically unchanged. Figure 11 This demonstrates that as the blind aperture depth h1 of the resonator increases, the high-frequency passband of the filter shifts generally towards lower frequencies, while the low-frequency passband remains essentially unchanged. (Summary) Figure 10 and Figure 11 This demonstrates that the two passband frequencies of the dual passband filter are independently controllable by the length of the via and the depth of the blind via in the resonator.

[0044] Figure 12 The graphs show the variation curves of some parameters that affect the coupling coefficient between resonators. Figure 13 , Figure 14 This corresponds to the external quality factor increasing with the length l of the bottom microstrip line. ms1 and the length l of the side microstrip line ms2 The curve that changes. k 12 It is the coupling coefficient of the TEM modes between resonators DR1 and DR2 at low frequencies, k 34 It is the coupling coefficient of the quasi-TEM mode between resonators DR1 and DR2 at high frequencies, derived from... Figure 12 It can be seen that as the length w of the upper coupling window increases... cw1 The increase of k 34 Significantly larger, k 12 It remains essentially unchanged; as the height c1 of the lower half coupling window increases, k 12 It increases, at which point k 34 Decrease.

[0045] Theoretically, when the coupling coefficient between resonators changes, the corresponding external quality factor will also change. Figure 13 , Figure 14 These are the external quality factors of the filter as a function of the length l of the bottom microstrip line. ms1and the length l of the side microstrip line ms2 The curve showing the change in length l of the bottom microstrip line. ms1 Variable length, Q in TEM mode e Basically unchanged, Q in quasi-TEM mode e Continuously decreasing; side microstrip line length l ms2 Increase, Q in TEM mode e Slightly increased, at this point the Q of the quasi-TEM mode e Significantly reduced. Overall Figure 13 , Figure 14 This demonstrates that the dual-passband dielectric waveguide filter is capable of independent control of both modes.

[0046] The T-type dual-mode dual-passband dielectric waveguide filter designed in this invention, by introducing a T-type resonator, can independently control both modes while reducing the filter size, reducing manufacturing costs, and having low insertion loss, thus possessing high practicality.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A T-type dual-mode dielectric waveguide resonator, characterized in that, The device includes a dielectric block, which is divided into a lower half and an upper half along the height direction; the upper half is symmetrically reduced inward along the width direction of the dielectric block to form a dielectric ridge structure with a T-shaped cross-section; a metallized blind hole is etched downward at the top center of the dielectric ridge structure, and a through hole is etched at the center of the side wall of the lower half of the dielectric block; the outer surface of the dielectric block is covered with a metallized layer.

2. The T-type dual-mode dielectric waveguide resonator according to claim 1, characterized in that, The medium block is made of ceramic medium material and the metallization layer is a silver-plated metal layer.

3. The T-type dual-mode dielectric waveguide resonator according to claim 1, characterized in that, The via is used to adjust the resonant frequency and unloaded quality factor of the resonator's primary mode (TEM mode), and the metallized blind via is used to adjust the resonant frequency and unloaded quality factor of the resonator's first higher-order quasi-TEM mode. Specifically, increasing the via length reduces the resonant frequency and unloaded quality factor of the primary mode (TEM mode); increasing the blind via depth reduces the resonant frequency and unloaded quality factor of the first higher-order quasi-TEM mode.

4. The T-type dual-mode dielectric waveguide resonator according to claim 1, characterized in that, The T-shaped dielectric ridge structure affects the second higher-order mode TE of the resonator. 101 The electric field distribution of the mode produces a spatial compression effect, causing the second higher-order mode TE to... 101 The equivalent electrical length of the mode is shortened and the resonant frequency is shifted to a higher frequency, thus improving the spurious suppression capability of the resonator.

5. A dual-passband dielectric waveguide filter, characterized in that, The device includes a PCB board, a first T-type dual-mode dielectric waveguide resonator, a second T-type dual-mode dielectric waveguide resonator, and a T-type coupling window; the first T-type dual-mode dielectric waveguide resonator and the second T-type dual-mode dielectric waveguide resonator are both T-type dual-mode dielectric waveguide resonators as described in any one of claims 1 to 4, and are arranged side by side on the PCB board; the T-type coupling window is disposed between the two resonators and connects the internal dielectrics of the two resonators; and a feed microstrip structure is respectively disposed on the outer sides of the two resonators that are far apart.

6. The dual-passband dielectric waveguide filter according to claim 5, characterized in that, The T-shaped coupling window is divided into an upper coupling window and a lower coupling window along the height direction. The upper coupling window corresponds to the height of the dielectric ridge structure of the resonator and is used to transmit the first higher-order quasi-TEM mode signal, forming a coupling path in the high-frequency passband. The lower coupling window corresponds to the height of the lower half of the resonator and is used to transmit the main mode TEM mode signal, forming a coupling path in the low-frequency passband. The coupling paths of the two modes are partially separated in space to reduce cross-interference between the two passbands.

7. The dual-passband dielectric waveguide filter according to claim 6, characterized in that, By adjusting the length of the upper coupling window, the coupling coefficient of the quasi-TEM mode corresponding to the high-frequency passband can be independently controlled: the larger the length of the upper coupling window, the larger the coupling coefficient of the quasi-TEM mode; by adjusting the height of the lower coupling window, the coupling coefficient of the low-frequency passband main mode TEM mode can be controlled: the larger the height of the lower coupling window, the larger the coupling coefficient of the main mode TEM mode.

8. The dual-passband dielectric waveguide filter according to claim 5, characterized in that, The feed microstrip structure includes silver-plated microstrip lines disposed on the outer and lower surfaces of the resonator and interconnected with each other, and the dielectric region on the resonator corresponding to the silver-plated microstrip lines is in a non-metallic state. The silver-plated microstrip line is electrically connected to the transmission line on the PCB with a characteristic impedance of 50 ohms.

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