A lossy filter based on an individually controllable transmission zero of an ltcc substrate

Abstract

The application belongs to the technical field of wireless communication, and discloses a lossy filter based on an individually controllable transmission zero point of an LTCC substrate, which comprises an LTCC substrate, a metal structure and a thick film resistor connected with the metal structure; the LTCC substrate is a one-piece multilayer ceramic structure and has 10 layers, which are ceramic L1 layer-L10 layer from top to bottom; the metal structure comprises a metal intermediate layer between the ceramic L5 layer and the ceramic L6 layer and a metal bottom layer arranged on the bottom surface of the ceramic L10 layer; the thick film resistor comprises a first resistor and a second resistor, and the first resistor and the second resistor are arranged on the upper surface of the ceramic L1 layer or between the ceramic L5 layer and the ceramic L6 layer. The application introduces resistive cross coupling between non-adjacent resonators, realizes the electrical performance of the lossy filter based on the LTCC substrate, and also considers the miniaturization demand.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless communication, and particularly relates to a lossy filter with individually controllable transmission zeros based on an LTCC substrate. BACKGROUND

[0002] In recent years, with the rapid development of science and technology, wireless communication has become one of the fastest growing branches in the electronic information industry. As an indispensable frequency selection device in the modern wireless communication industry, microwave passive filters are widely used in various fields of military and civilian, including satellite communication, navigation, radar, mobile communication, broadcast television communication field. In order to improve the performance of the whole communication system, the microwave filter with small size, high integration, high performance and high reliability has always been the goal pursued by people.

[0003] High-performance filters put forward higher requirements for the frequency selection characteristics of the filter and the distortionless transmission of the signal, that is, the insertion loss fluctuation and group delay fluctuation in the passband are as flat as possible, and the frequency suppression outside the passband is as steep as possible, which means that the quality factor Q that the filter can realize is as large as possible. At the same time, it is always a challenge to meet the filter with high Q value and small size. High Q value usually leads to the increase of the volume of the resonant cavity, while small size usually causes large in-band insertion loss fluctuation.

[0004] Low temperature co-fired ceramic (LTCC) substrate is a kind of multilayer circuit board manufacturing technology based on glass ceramic composite material. The radio frequency filter based on low temperature co-fired ceramic (LTCC) substrate has the advantages of small size, strong process compatibility, high integration and high reliability. However, the Q value that the LTCC filter can realize is only within 400, and the in-band flatness is large. The Q value that the cavity filter can realize is 1000-10000. For the indexes of in-band insertion loss fluctuation and group delay fluctuation, the LTCC filter scheme cannot be used, and only the large-size cavity filter can be used. SUMMARY

[0005] The application aims to provide a lossy filter with individually controllable transmission zeros based on an LTCC substrate, so as to solve the technical problem that the small-size LTCC filter cannot realize a high Q value.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is:

[0007] A lossy filter based on an individually controllable transmission zero point of an LTCC substrate includes an LTCC substrate and a metal structure, and further includes a thick-film resistor connected to the metal structure; wherein, the LTCC substrate is an integral multilayer ceramic structure with a total of 10 layers, which are sequentially labeled as ceramic L1 layer to ceramic L10 layer from top to bottom; the metal structure includes a metal intermediate layer 1 located between ceramic L5 layer and ceramic L6 layer, and a metal bottom layer 2 disposed on the bottom surface of ceramic L10 layer; the thick-film resistor includes a first resistor 3 and a second resistor 4, which are disposed together on the upper surface of ceramic L1 layer or between ceramic L5 layer and ceramic L6 layer.

[0008] Compared to existing implementations of LTCC filters, this invention achieves improved electrical performance of a lossy filter based on LTCC substrate by introducing resistive cross-coupling between non-adjacent resonators, thus meeting the requirements for miniaturization while enhancing the filter's electrical performance. Attached Figure Description

[0009] Figure 1 This is a side view of the lossy filter based on an individually controllable transmission zero point of an LTCC substrate according to the present invention.

[0010] Figure 2 This is an oblique axonometric view of the lossy filter based on an individually controllable transmission zero point of an LTCC substrate according to the present invention;

[0011] Figure 3 This is a top view of the lossy filter based on an individually controllable transmission zero point of an LTCC substrate according to the present invention.

[0012] Figure 4 This is a magnified view of the oblique axis of the resistive coupling branch;

[0013] Figure 5 The above is a simulation response curve of a preferred embodiment of the present invention. Detailed Implementation

[0014] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the embodiments are merely preferred embodiments of this invention. Based on this embodiment, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0015] like Figures 1-4 As shown, the lossy filter based on a individually controllable transmission zero of an LTCC substrate, as presented in this invention, includes an LTCC substrate, a metal structure, and a thick-film resistor; wherein:

[0016] The LTCC substrate is a single-layer ceramic structure with 10 layers, each with a thickness of 0.1 mm, which are numbered from top to bottom as ceramic L1 layer to ceramic L10 layer; the metal structure includes a metal intermediate layer 1 located between ceramic L5 layer and ceramic L6 layer, and a metal bottom layer 2 disposed on the bottom surface of ceramic L10 layer; the thick film resistor includes a first resistor 3 and a second resistor 4, which are disposed together on the upper surface of ceramic L1 layer or between ceramic L5 layer and ceramic L6 layer.

[0017] The metal interlayer 1 includes a first resonator 5, a second resonator 6, a third resonator 7, a fourth resonator 8, a fifth resonator 9, and a sixth resonator 10. Each of these resonators is a half-wavelength resonator with open ends. The first resonator 5 and the sixth resonator 10 are open-loop structures, and both are pole units whose transmission zero positions can be individually controlled to control the out-of-band rejection response of the filter. The perimeter of the open-loop structure determines the position of the transmission zero, and the number of pole units determines the number of out-of-band transmission zeros, independent of the other components of the invention. The number of pole units whose transmission zero positions can be individually controlled is not limited to the example number in this embodiment; 2 to 6 can be selected according to requirements, preferably 2 or 4. In this embodiment, the open-loop perimeter of the first resonator 5 is 16 mm, and the open-loop perimeter of the sixth resonator 10 is 16.7 mm.

[0018] The first resonator 5 is directly connected to the second resonator 6 via a straight or wall-type first main transmission line 11, or through parallel lines for energy coupling. The sixth resonator 10 is directly connected to the fifth resonator 9 via a straight or wall-type second main transmission line 12, or through parallel lines for energy coupling. The first resonator 5 and the sixth resonator 10 are respectively connected to the first main transmission line 11 and the second main transmission line 12 via tapped wires. The length of the first main transmission line 11 is determined by the phase electrical length between the first resonator 5 and the second resonator 6, and the length of the second main transmission line 12 is determined by the phase electrical length between the fifth resonator 9 and the sixth resonator 10. The second resonator 6, the third resonator 7, the fourth resonator 8, and the fifth resonator 9 are all hairpin-type open-circuit structures, and the energy coupling methods between the second resonator 6 and the third resonator 7, the third resonator 7 and the fourth resonator 8, and the fourth resonator 8 and the fifth resonator 9 are all interdigital structures.

[0019] A barbell-shaped first resistive coupling branch 13 is provided between the second resonator 6 and the fourth resonator 8, and the first resistive coupling branch 13 is connected to the first resistor 3; a barbell-shaped second resistive coupling branch 14 is provided between the third resonator 7 and the fifth resonator 9, and the second resistive coupling branch 14 is connected to the second resistor 4.

[0020] Preferably, the first resistive coupling branch 13 includes a first metal straight stub 15, a second metal straight stub 16, and two third metal straight stubs 17. If the first resistor 3 is disposed on the upper surface of the ceramic L1 layer, the first metal straight stub 15 and the second metal straight stub 16 are respectively led out from the open-circuit terminals on the same side of the second resonator 6 and the fourth resonator 8, and are respectively connected to the upper surface of the ceramic L1 layer through a first metal hole 18. Then, they are respectively connected to the two ends of the first resistor 3 through the two third metal straight stubs 17 disposed on the upper surface of the ceramic L1 layer to realize signal transmission. The first metal hole 18 vertically penetrates from the ceramic L1 layer to the ceramic L5 layer. If the first resistor 3 is disposed between the ceramic L5 layer and the ceramic L6 layer, the first metal straight stub 15 and the second metal straight stub 16 are respectively led out from the open-circuit terminals on the same side of the second resonator 6 and the fourth resonator 8, and are respectively connected to the two ends of the first resistor 3 through the two third metal straight stubs 17 disposed between the ceramic L5 layer and the ceramic L6 layer to realize signal transmission.

[0021] Preferably, the second resistive coupling branch 14 includes a fourth metal straight stub 19, a fifth metal straight stub 20, and two sixth metal straight stubs 21. If the second resistor 4 is disposed on the upper surface of the ceramic L1 layer, the fourth metal straight stub 19 and the fifth metal straight stub 20 are respectively led out from the open terminals on the same side of the third resonator 7 and the fifth resonator 9, and respectively connected to the upper surface of the ceramic L1 layer via a first metal hole 18. They are then connected to the two ends of the second resistor 4 via the two sixth metal straight stubs 21 disposed on the upper surface of the ceramic L1 layer, thus achieving signal transmission. If the second resistor 4 is disposed between the ceramic L5 layer and the ceramic L6 layer, the fourth metal straight stub 19 and the fifth metal straight stub 20 are respectively led out from the open terminals on the same side of the third resonator 7 and the fifth resonator 9, and respectively connected to the two ends of the second resistor 4 via the two sixth metal straight stubs 21 disposed between the ceramic L5 layer and the ceramic L6 layer, thus achieving signal transmission.

[0022] Preferably, the horizontal gap between the first metal straight stub 15 and the second resonator 6 is equal to the horizontal gap between the second metal straight stub 16 and the fourth resonator 8, and the depth of the first metal straight stub 15 penetrating into the open end of the second resonator 6 is G1, which is equal to the depth of the second metal straight stub 16 penetrating into the open end of the fourth resonator 8; the horizontal gap between the fourth metal straight stub 19 and the third resonator 7 is equal to the horizontal gap between the fifth metal straight stub 20 and the fifth resonator 9, and the depth of the fourth metal straight stub 19 penetrating into the open end of the third resonator 7 is also G1, which is equal to the depth of the fifth metal straight stub 20 penetrating into the open end of the fifth resonator 9.

[0023] In this invention, the resistive cross-coupling strength is closely related to the resistance value r0, the depth G1 of the metal stub pendant within the open terminal of the hairpin resonator, and the horizontal gap between the metal stub and the hairpin resonator. In this embodiment, r0 is 300Ω, G1 is 1.2mm, and the horizontal gap is 0.15mm. Therefore, the lossy filter incorporating resistive cross-coupling achieves better in-band flatness and frequency selectivity by sacrificing some insertion loss.

[0024] The present invention also includes a first feed line 22 and a second feed line 23 serving as input / output interfaces. One end of the first feed line 22 and the second feed line 23 is disposed on the upper surface of the ceramic L1 layer for connecting to external circuits. The other end of the first feed line 22 and the second feed line 23 are respectively connected to the first main transmission line 11 and the second main transmission line 12 through a second metal hole 24 that vertically penetrates from the ceramic L1 layer to the ceramic L5 layer. The first feed line 22 and the second feed line 23 can also be replaced with surface-mount CPW interfaces disposed on the metal bottom layer 2 according to application requirements.

[0025] To reduce signal energy leakage, an electromagnetic shielding structure is needed at the edge of the LTCC substrate. Preferably, a continuous metal layer can be formed on the sidewall of the LTCC substrate, or multiple third metal holes 25 can be uniformly formed around the edge of the LTCC substrate. In addition, considering the process reliability requirements, the metal structure also includes a first metal frame along the edge of the upper surface of the ceramic L1 layer. The metal intermediate layer 1 also includes a second metal frame along the edge between the ceramic L5 and ceramic L6 layers. The third metal holes 25 can penetrate the first metal frame, ceramic L1 to ceramic L5 layers, the second metal frame, ceramic L6 to ceramic L10 layers, and the bottom metal layer to improve the far-band suppression effect of the filter. Specifically, the first metal frame and the second metal frame have two openings, which are used to ensure that the first metal frame and the second metal frame avoid the first feed line 22 and the second feed line 23.

[0026] In this embodiment, the linewidth of each resonator and the main transmission line is 0.45 mm. The distance between the second resonator 6 and the third resonator 7 is 1.92 mm, the distance between the third resonator 7 and the fourth resonator 8 is 1.87 mm, and the distance between the fourth resonator 8 and the fifth resonator 9 is 1.84 mm. The distance between the two arms of the hairpin resonator is 1.3 mm. The arm lengths of the second resonator 6 and the third resonator 7 are both 6.6 mm, the arm lengths of the fourth resonator 8 are 6.59 mm, and the arm lengths of the fifth resonator 9 are 6.52 mm. The diameters of the first metal hole 18 and the second metal hole 24 are both 0.15 mm, the diameter of the third metal hole 25 is 0.2 mm, and the spacing between adjacent holes of the third metal hole 25 is 0.5 mm. The resistance values ​​of the first resistor 3 and the second resistor 4 are both r0 = 300 Ω.

[0027] Figure 5 The simulation response curve of a lossy filter based on a controllable transmission zero on an LTCC substrate provided in this embodiment of the invention shows that the designed filter has a center frequency of 3.72 GHz and a design bandwidth of 76 MHz. The insertion loss fluctuation within the 50 MHz bandwidth is less than 0.25 dB, the out-of-band rejection at the center frequency ±100 MHz is more than 40 dB, and the effective Q value is about 1500. The in-band characteristics are significantly improved compared with the electrical performance of conventional LTCC filters.

[0028] The fabrication process of the lossy filter based on LTCC substrate with individually controllable transmission zeros according to the present invention is as follows: Prepare 10 green ceramic sheets according to design requirements. Drill holes in the 1st to 10th layers of green ceramic sheets according to the corresponding positions of the first metal hole 18, the second metal hole 24, and the third metal hole 25. Fill all the holes with copper to achieve metallization, resulting in the first metal hole 18, the second metal hole 24, and the third metal hole 25. Then, screen print the patterned ceramic layers (i.e., ceramic L1 layer and ceramic L6 layer) to obtain the metal patterns and thick-film resistors for each layer. Next, stack the 10 green ceramic sheets together and perform isostatic pressing, followed by hot cutting to remove excess material. Afterward, perform end coating and sintering to form a single unit. Finally, perform electroplating or electroless nickel-gold plating to obtain the lossy filter based on LTCC substrate with individually controllable transmission zeros according to the present invention. The various steps involved in the above process, such as drilling, copper filling, screen printing, isostatic pressing, hot cutting, end coating, sintering, and plating, are all conventional LTCC processing methods and will not be detailed here.

[0029] The above describes the implementation of the lossy filter based on a individually controllable transmission zero of an LTCC substrate provided by this invention. For those skilled in the art, based on the ideas of the embodiments of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A lossy filter based on an individually controllable transmission zero of an LTCC substrate, comprising an LTCC substrate and a metal structure, characterized in that, It also includes a thick-film resistor connected to the metal structure; wherein, the LTCC substrate is an integral multilayer ceramic structure with a total of 10 layers, which are sequentially labeled as ceramic L1 layer to ceramic L10 layer from top to bottom; the metal structure includes a metal intermediate layer (1) located between ceramic L5 layer and ceramic L6 layer, and a metal bottom layer (2) disposed on the bottom surface of ceramic L10 layer; the thick-film resistor includes a first resistor (3) and a second resistor (4), which are disposed together on the upper surface of ceramic L1 layer or between ceramic L5 layer and ceramic L6 layer; the metal intermediate layer (1) includes a first resonator (5) and a second resonator (6). The first resonator (5), the second resonator (6), the third resonator (7), the fourth resonator (8), the fifth resonator (9), and the sixth resonator (10) are all half-wavelength resonators with open ends. The first resonator (5) and the sixth resonator (10) are open-loop structures, and they are all pole units whose transmission zero positions can be controlled individually to control the out-of-band rejection response of the filter of the present invention. The first resonator (5) is directly connected to the second resonator (6) through a straight or wall-type first main transmission line (11) or through a parallel line. Energy coupling is achieved through a form where the sixth resonator (10) is directly connected to the fifth resonator (9) via a straight or wall-shaped second main transmission line (12) or through a parallel line; the first resonator (5) and the sixth resonator (10) are respectively connected to the first main transmission line (11) and the second main transmission line (12) via a tapped wire; the length of the first main transmission line (11) is determined by the phase electrical length between the first resonator (5) and the second resonator (6), and the length of the second main transmission line (12) is determined by the phase electrical length between the fifth resonator (9) and the sixth resonator (10); the second resonator (6), the third resonator (7), and the fifth resonator (9) are connected to the fifth resonator (9) and the sixth resonator (10) via a tapped wire. The fourth resonator (8) and the fifth resonator (9) are both hairpin open circuit structures, and the energy coupling mode of the second resonator (6) and the third resonator (7), the third resonator (7) and the fourth resonator (8), and the fourth resonator (8) and the fifth resonator (9) are all interdigital structures; a barbell-shaped first resistance coupling branch (13) is provided between the second resonator (6) and the fourth resonator (8), and the first resistance coupling branch (13) is connected to the first resistor (3); a barbell-shaped second resistance coupling branch (14) is provided between the third resonator (7) and the fifth resonator (9), and the second resistance coupling branch (14) is connected to the second resistor (4).

2. The lossy filter based on a individually controllable transmission zero of an LTCC substrate as described in claim 1, characterized in that, The first resistive coupling branch (13) includes a first metal straight stub (15), a second metal straight stub (16), and two third metal straight stubs (17). If the first resistor (3) is disposed on the upper surface of the ceramic L1 layer, the first metal straight stub (15) and the second metal straight stub (16) are respectively led out from the open terminals on the same side of the second resonator (6) and the fourth resonator (8), and respectively connected to the upper surface of the ceramic L1 layer through a first metal hole (18), and then respectively through two third metal straight stubs (17) disposed on the upper surface of the ceramic L1 layer. 7) Connect to both ends of the first resistor (3) to realize signal transmission; the first metal hole (18) vertically penetrates from the ceramic L1 layer to the ceramic L5 layer; if the first resistor (3) is set between the ceramic L5 layer and the ceramic L6 layer, the first metal straight stub (15) and the second metal straight stub (16) are respectively led out from the open end on the same side of the second resonator (6) and the fourth resonator (8), and respectively connected to both ends of the first resistor (3) through two third metal straight stubs (17) set between the ceramic L5 layer and the ceramic L6 layer to realize signal transmission; The second resistive coupling branch (14) includes a fourth metal straight stub (19), a fifth metal straight stub (20), and two sixth metal straight stubs (21). If the second resistor (4) is disposed on the upper surface of the ceramic L1 layer, the fourth metal straight stub (19) and the fifth metal straight stub (20) are respectively led out from the open terminals on the same side of the third resonator (7) and the fifth resonator (9), and respectively connected to the upper surface of the ceramic L1 layer through a first metal hole (18), and then respectively through the terminals disposed on the ceramic L1 layer. The two sixth metal straight stubs (21) on the surface are connected to the two ends of the second resistor (4) to realize signal transmission; if the second resistor (4) is set between the ceramic L5 layer and the ceramic L6 layer, the fourth metal straight stub (19) and the fifth metal straight stub (20) are respectively led out from the open end on the same side of the third resonator (7) and the fifth resonator (9), and respectively connected to the two ends of the second resistor (4) through the two sixth metal straight stubs (21) set between the ceramic L5 layer and the ceramic L6 layer to realize signal transmission.

3. The lossy filter based on a individually controllable transmission zero of an LTCC substrate as described in claim 2, characterized in that, The horizontal gap between the first metal straight stub (15) and the second resonator (6) is equal to the horizontal gap between the second metal straight stub (16) and the fourth resonator (8), and the depth of the first metal straight stub (15) into the open end of the second resonator (6) is equal to the depth of the second metal straight stub (16) into the open end of the fourth resonator (8); the horizontal gap between the fourth metal straight stub (19) and the third resonator (7) is equal to the horizontal gap between the fifth metal straight stub (20) and the fifth resonator (9), and the depth of the fourth metal straight stub (19) into the open end of the third resonator (7) is equal to the depth of the fifth metal straight stub (20) into the open end of the fifth resonator (9).

4. The lossy filter based on a individually controllable transmission zero of an LTCC substrate as described in claim 3, characterized in that, It also includes a first feed line (22) and a second feed line (23) as input / output interfaces; one end of the first feed line (22) and the second feed line (23) is disposed on the upper surface of the ceramic L1 layer for connecting external circuits, and the other end of the first feed line (22) and the second feed line (23) are respectively connected to the first main transmission line (11) and the second main transmission line (12) through a second metal hole (24) that runs vertically through the ceramic L1 layer to the ceramic L5 layer.

5. The lossy filter based on a individually controllable transmission zero of an LTCC substrate as described in claim 4, characterized in that, A continuous metal layer is provided on the sidewall of the LTCC substrate, or multiple third metal holes (25) are uniformly opened around the edge of the LTCC substrate.

6. The lossy filter based on a individually controllable transmission zero of an LTCC substrate as described in claim 5, characterized in that, The metal structure also includes a first metal frame disposed along the edge of the upper surface of the ceramic L1 layer; the metal intermediate layer (1) also includes a second metal frame disposed along the edge between the ceramic L5 layer and the ceramic L6 layer, and the third metal hole (25) can penetrate the first metal frame, the ceramic L1 layer to the ceramic L5 layer, the second metal frame, the ceramic L6 layer to the ceramic L10 layer and the metal bottom layer.

Images