Compact Micro-Bandwidth Bandpass Filter

Abstract

The present invention proposes a compact micro-bandwidth bandpass filter, which is formed by laminating three layers of dielectric substrates, with semi-solid sheets used as processing adhesives between the substrates; copper foil is applied to the upper layer of each dielectric substrate according to a designed pattern, and the bottom layer of the third dielectric substrate serves as a metal ground layer; the first layer of the upper surface coupling patch consists of two ports, two groups of tapered impedance matching sections, a group of symmetrical U-shaped branch lines, a central connecting microstrip line, and two pairs of quarter-wavelength open short stubs; the second layer of the upper surface coupling patch is a layer of broadside coupling patches; the third layer of the upper surface has two T-shaped microstrip branch lines; three equally spaced rectangular slots are etched on the metal ground layer, and two metalized blind holes are opened in the lower surface metal ground layer to the T-shaped microstrip branch lines on the upper surface; the mutual coupling of the three layers of the upper surface design patterns combined with the blind hole structure produces ultra-wideband bandpass filter characteristics.

Description

Technical Field

[0001] The present invention belongs to the field of microwave radio frequency technology, and in particular relates to a compact micro-bandwidth bandpass filter. Background Art

[0002] In recent years, ultra-wideband bandpass filters (UWBPFs) have attracted widespread attention in fields such as navigation, radar, satellites, and high-speed communications due to their wide bandwidth, low insertion loss, low and flat group delay within the passband, and compact size. Ultra-wideband characteristics can be achieved through design methods such as multimode resonators, cascaded high- and low-pass filters, coplanar waveguides, microstrip stubs, and microstrip / slotline structures, as well as processing techniques such as low-temperature co-fired ceramics, liquid crystal polymers, or other novel compound materials. Multilayer printed circuit board (PCB) design methods are frequently used in broadband and UWB bandpass filter design due to their simplicity, ability to support the design of dielectric substrates with low relative dielectric constants and vias, low cost, and excellent oxidation resistance.

[0003] In order to better match the large capacity, high-speed data transmission, low latency and small size required by the rapidly developing 5G ultra-wideband technology, the existing technology has proposed a variety of ultra-wideband bandpass filters based on multi-layer PCB structures. For example:

[0004] Document 1: Rao, Yunbo, et al. "Miniaturized 28-GHz Packaged BandpassFilter With High Selectivity and Wide Stopband Using Multilayer PCBTechnology." IEEE Microwave and Wireless Components Letters (2022) proposed a packaged millimeter-wave bandpass filter based on a multilayer printed circuit board structure. This filter exhibits ultra-wideband passband characteristics within the millimeter-wave frequency band, an ultra-wide stopband with good out-of-band rejection within the stopband, and a compact overall design. However, the filter exhibits high insertion loss and reflection loss within the passband.

[0005] Document 2: Yang, Shilin, et al. "A Structure Reuse Method for RealizingLarge Frequency Ratio Dual-Band Multi-Channel Integrated Filters." IEEE Transactions on Circuits and Systems II: Express Briefs69.4 (2022): 2101-2105. A dual-band bandpass filter based on substrate-integrated coaxial lines and semi-open transmission lines, constructed by laminating two different dielectric substrates, is proposed. The low-frequency passband exhibits ultra-wideband characteristics. This filter achieves low insertion loss and a wide passband. However, the press-fit structure used in this filter design is complex and large in size.

[0006] Ultra-wideband bandpass filters not only require bandwidth that meets ultra-wideband standards, but also require low insertion loss within the passband, low and flat group delay within the passband, and good reflection and stopband suppression characteristics within the passband. Furthermore, they place higher demands on the miniaturization and passband selectivity of the filters. Designing ultra-wideband bandpass filters that simultaneously possess wide bandwidth, low insertion loss, low group delay, and a small size remains a challenging problem for filter designers. Summary of the Invention

[0007] In view of the defects and shortcomings of the prior art, the present invention proposes a compact micro-wide bandpass filter.

[0008] The present invention specifically adopts the following technical solutions:

[0009] A compact micro-bandwidth bandpass filter characterized by:

[0010] It is made of three layers of dielectric substrates pressed together, with semi-solid sheets used as processing adhesives between the substrates; the upper layer of each dielectric substrate is copper-clad according to the designed pattern, and the bottom layer of the third dielectric substrate serves as the metal ground layer;

[0011] The first-layer upper surface coupling patch consists of two ports, two sets of tapered impedance matching sections, a set of symmetrical U-shaped branch lines, a central connecting microstrip line, and two pairs of quarter-wavelength open-circuit stubs.

[0012] The second layer of upper surface coupling patches is a layer of broadside coupling patches;

[0013] The upper surface of the third layer is composed of two T-shaped microstrip branch lines;

[0014] Three equally spaced rectangular slots are etched on the metal ground layer, and two metalized blind holes are opened on the metal ground layer on the lower surface to the T-shaped microstrip branch line on the upper surface;

[0015] Ultra-wideband bandpass filter characteristics are produced by the mutual coupling of the three-layer upper surface design patterns combined with the blind hole structure.

[0016] Furthermore, the upper surface of the first dielectric substrate is designed with two sets of quarter-wavelength open-circuit stubs to extract energy at a specified frequency point, so that the insertion loss curve outside the passband can be quickly rolled off, thereby generating two zero points to improve the selectivity of the filter passband.

[0017] By changing the length of the wider side of the coupling patch on the upper surface of the second dielectric substrate, the coupling area between the two layers of patches and the branch line is affected, thereby adjusting the reflection loss characteristics within the passband;

[0018] By changing the diameter of the blind hole, the high-frequency cutoff frequency of the passband and the harmonic suppression characteristics of the high-frequency stopband can be adjusted;

[0019] Rectangular gaps etched on the metal ground layer are used to create two resonance points within the passband, further optimizing the filter's in-band reflection loss characteristics.

[0020] Furthermore, the dielectric substrate is an R04350 dielectric substrate, and the thicknesses of the three substrates are 0.1016 mm, 0.254 mm, and 0.508 mm respectively;

[0021] The copper thickness of the top layer and the metal ground layer is h=0.035mm, and the copper thickness of the upper surface of the second and third substrates is h=0.018mm. The three dielectric substrates are pressed together using two RO4450F semi-solid sheets through a processing technology. The thickness of the two semi-solid sheets is h=0.2032mm.

[0022] Furthermore, the first layer of coupling patch is provided with energy by a 50 Ω microstrip strip with a width of W0. The energy reaches the U-shaped branch line through tapered impedance matching and is split here. One path is coupled downward through the two outer branches of the U-shaped branch line, and the other path is transmitted to the symmetrical U-shaped branch line on the other side through the central connecting microstrip. Before the output signal, the energy of the corresponding frequency point is derived through two sets of quarter-wavelength open-circuit stubs, thereby achieving harmonic suppression in the stopband and introducing two zero points to optimize the passband selectivity of the filter.

[0023] Furthermore, the second layer of microstrip patch is a broadside coupling patch, which adjusts the coupling area with the upper microstrip patch and the lower branch line by adjusting the outer broadside length L6, thereby affecting the reflection loss characteristics within the passband.

[0024] Furthermore, the metallized blind hole is opened from the metal ground plane to the wider rectangle of the T-shaped microstrip branch line, and the high-frequency cutoff frequency and high-frequency stop-band harmonic suppression characteristics of the bandpass filter are adjusted by changing the diameter d0 of the blind hole.

[0025] Furthermore, the three rectangular slots etched in the metal grounding layer have a spacing of g1, and the three rectangular slots introduce two resonance points into the filter passband, further optimizing the reflection loss characteristics within the passband. The frequency and corresponding depth of the resonance point are affected by the spacing g1 between the rectangular slot resonators.

[0026] Compared to existing technologies, the present invention and its preferred embodiment utilize a 50Ω microstrip strip feed located at the port of the first layer of microstrip patches. The entire filter consists of a coupling patch layer with two ports, two sets of tapered impedance matching, two U-shaped stubs, a central connecting microstrip, and two pairs of open-circuit stubs, designed on three RO4350 dielectric substrates; a broadside coupling patch layer; two T-shaped microstrip stubs; two metallized blind vias; and a metal ground plane with three etched rectangular slots. The coupling between the two microstrip patches, the two T-shaped microstrip stubs, and the blind vias contributes to the filter's ultra-wideband passband characteristics. The two sets of open-circuit stubs loaded on the first layer of coupling patches optimize the out-of-band roll-off rate and stop-band harmonic suppression, and also introduce two zero points to optimize the passband selectivity; the length of the outer wide side of the second layer of wide-side coupling patches determines the coupling area between the first layer of coupling patches and the third layer of stub lines, thereby optimizing the reflection loss characteristics within the passband; the diameter of the blind hole affects the high-frequency cutoff frequency of the passband and the high-frequency stop-band harmonic suppression characteristics, and the parameters can be adjusted to obtain the optimal passband bandwidth and stop-band suppression characteristics; the three rectangular gaps etched in the metal ground layer introduce two resonance points into the filter passband, further optimizing the reflection loss characteristics within the passband.

[0027] The present invention has a simple structure for each layer, small insertion loss in the passband, low reflection loss, low and flat group delay, wide 3dB fractional bandwidth, simple design structure, and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0029] Figure 1 This is a diagram of the filter pressing structure according to an embodiment of the present invention;

[0030] Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 These are respectively the design drawings of the copper cladding pattern, gaps and blind hole positions of each layer of the filter according to the embodiment of the present invention;

[0031] Figure 6 Graphs showing simulated and measured transmission coefficients and reflection coefficients of filters according to embodiments of the present invention;

[0032] Figure 7 is a curve diagram of the filter group delay according to an embodiment of the present invention;

[0033] Figure 8 This is a table of preferred structural parameters related to the filter according to the embodiment of the present invention (unit: mm);

[0034] Figure 9 This is a physical picture of the filter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] To make the features and advantages of this patent more clearly understood, the following embodiments are specifically described in detail as follows:

[0036] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this application belongs.

[0037] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0038] In this solution, the filter is constructed from three layers of RO4350 dielectric substrates laminated together, with RO4450F semi-solid sheets used as a processing adhesive between the substrates. Each dielectric substrate is coated with a copper foil according to a design pattern on the top layer. The bottom layer of the third dielectric substrate is a metal ground plane, with three rectangular slits etched into it.

[0039] Two metalized blind holes are opened from the metal grounding layer on the lower surface of the third dielectric substrate through the substrate to the copper foil of the branch line on the upper surface.

[0040] The upper surface of the first dielectric substrate is designed with two sets of quarter-wavelength open-circuit stubs to extract energy at specified frequency points, so that the insertion loss curve outside the passband can roll off quickly, thereby generating two zero points to improve the selectivity of the filter passband.

[0041] By changing the length of the wider side of the coupling patch on the upper surface of the second dielectric substrate, the coupling area between the two layers of patches and the branch lines is affected, thereby adjusting the reflection loss characteristics within the passband.

[0042] By changing the diameter of the blind hole, the high-frequency cutoff frequency of the passband and the harmonic suppression characteristics of the high-frequency stopband can be adjusted.

[0043] The rectangular gaps etched on the metal ground layer create two resonance points within the passband, further optimizing the filter's in-band reflection loss characteristics.

[0044] The ultra-wideband filter provided by the present invention has a compact size, a simple design pattern, a wide bandwidth and a low insertion loss, and a low and flat group delay in the passband.

[0045] As a possible implementation, it includes a layer of coupling patch containing two ports, two sets of tapered impedance matching, two U-shaped branch lines, a central connecting microstrip and two pairs of open short stubs; a layer of broadside coupling patch; two T-shaped microstrip branch lines; two metallized blind holes and a metal ground plane with three rectangular gaps etched in it.

[0046] The two layers of microstrip patches are above the first and second dielectric substrates, and there is no copper cladding under the two substrates; the two T-shaped microstrip branch lines are on the upper surface of the third dielectric substrate, the metal ground plane with etched rectangular gaps is the lower surface of the third dielectric substrate, and the metallized blind holes are opened from the metal ground plane to the wider rectangular branches of the T-shaped microstrip branch lines.

[0047] As a possible implementation, further, the first layer of coupling patch is provided with energy by a 50 Ω microstrip strip with a width of W0, which reaches the U-shaped branch line through tapered impedance matching and is split here. One path is coupled downward through the two outer branches of the U-shaped branch line, and the other path is transmitted to the symmetrical U-shaped branch line on the other side through the central connecting microstrip. Before the output signal, the energy of the corresponding frequency point is derived through two sets of loaded quarter-wavelength open-circuit stubs, thereby achieving harmonic suppression in the stopband and introducing two zero points, thereby optimizing the passband selectivity of the filter.

[0048] As a possible implementation, further, the second layer of microstrip patch is a layer of wide-side coupling patch. By adjusting the outer wide-side length L6, the coupling area with the upper microstrip patch and the lower branch line can be adjusted, thereby affecting the reflection loss characteristics within the passband.

[0049] As a possible implementation, further, a metallized blind hole is opened from the metal ground plane to the wider rectangle of the T-shaped microstrip branch line. Changing the diameter d0 of the blind hole will affect the high-frequency cutoff frequency and high-frequency stopband harmonic suppression characteristics of the bandpass filter.

[0050] As a possible implementation method, further, the three rectangular gaps etched in the metal ground layer have a spacing of g1, and the three rectangular gaps introduce two resonance points into the filter passband, thereby further optimizing the reflection loss characteristics within the passband. The frequency and corresponding depth of the resonance point are affected by the spacing g1 between the rectangular gap resonators.

[0051] As a specific design, a compact micro-bandwidth bandpass filter based on a multi-layer printed circuit board (PCB) structure is provided, including: three R04350 dielectric substrates (substrate, sub) with copper cladding (copper) according to a designed pattern on the top surface. The thickness of the three substrates is h = 0.1016mm, 0.254mm, and 0.508mm, respectively. The bottom surface of the third dielectric substrate is copper clad and three rectangular slits are etched. Blind vias (Blind Vias) are opened in the metal ground layer to the rectangular area with wider branch lines on the top surface of the third dielectric substrate.

[0052] The top layer and metal ground layer copper thickness is h = 0.035mm, and the top surface copper thickness of the second and third substrates is h = 0.018mm. The three dielectric substrates are laminated using two RO4450F semi-solid sheets, each with a thickness of h = 0.2032mm.

[0053] The three-layer top surface design patterns are coupled with each other and combined with the blind hole structure to produce ultra-wideband bandpass filter characteristics.

[0054] The first layer of top surface coupling patches consists of two ports, two sets of tapered impedance matching sections, a set of symmetrical U-shaped branch lines, a central connecting microstrip line, and two pairs of quarter-wavelength open-circuit stubs. The second layer of top surface coupling patches is a layer of broadside coupling patches.

[0055] The top surface of the third layer is made up of two T-shaped microstrip branches. Three equally spaced rectangular slots are etched on the metal ground layer, and two metalized blind vias are opened on the bottom surface of the metal ground layer to the two wider T-shaped branches.

[0056] Combining the above solutions, such as Figures 1-9 As shown, the following is a complete example of the ultra-wideband bandpass filter provided by the present invention: including a first layer of coupling patches with two ports ①, two sets of tapered impedance matching ②, two U-shaped branch lines ③, a central connecting microstrip ④ and two pairs of open-circuit short stubs ⑤ and ⑥, as shown Figure 2 As shown; the broadside coupling patch of the second layer, as Figure 3 As shown; the two T-shaped microstrip branch lines on the third layer, as shown Figure 4 As shown in Figure 1, there are two metalized blind holes and a metal ground layer with three rectangular gaps etched in it. Figure 5 As shown in the figure, two layers of coupling patches and T-shaped microstrip stubs are located on three dielectric substrates, with a metal ground layer located below the third dielectric substrate. Blind vias are drilled from the metal ground layer through the third dielectric substrate to the wider rectangle of the T-shaped stub. The substrates are bonded together using RO4450F semi-solid sheeting.

[0057] The filter designed by the present invention has ultra-wideband bandpass characteristics. In order to produce ultra-wideband characteristics, two layers of coupling patches, one layer of branch lines and two blind holes are designed. The two pairs of open-circuit stubs loaded on the first layer of coupling patches derive the energy of the corresponding frequency points within the stopband range, so that the insertion loss curve can achieve a rapid roll-off outside the passband, thereby obtaining a good stopband harmonic suppression characteristic. At the same time, two zero points are introduced to improve the filter passband selectivity. The diameter change of the blind hole can adjust the high-frequency cutoff frequency and the high-frequency out-of-band harmonic suppression. The three rectangular gaps etched by the metal ground layer provide two resonance points in the filter passband. By adjusting the distance between the rectangular gaps, the surface current path on the metal ground layer can be changed to adjust the frequency and corresponding depth of the two resonance points.

[0058] The insertion loss and reflection loss of the designed filter are as follows Figure 6 As shown in the test, the insertion loss at the center frequency of 12.795 GHz in the passband is -0.58 dB, the frequency range where the insertion loss is less than -3 dB is 10.215 GHz to 15.375 GHz, the -3 dB fractional bandwidth reaches 40.33%, and the in-band reflection loss is less than -18 dB.

[0059] The designed filter group delay curve is as follows: Figure 7 As shown in the figure, the passband group delay within the -3 dB frequency range is flat and less than 0.1 ns, which means the group delay is extremely low.

[0060] Preferred parameters such as Figure 8 shown.

[0061] The actual filter picture is as follows Figure 9 As shown, the total size is 20.8mm*20mm.

[0062] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of compact micro-bandwidth bandpass filters based on the inspiration of this patent. All equivalent changes and modifications made within the scope of the patent application of this invention should be covered by this patent.

Claims

1. A compact micro-bandwidth bandpass filter, characterized by: It is made of three layers of dielectric substrates pressed together, with semi-solid sheets used as processing adhesives between the substrates; the upper layer of each dielectric substrate is copper-clad according to the designed pattern, and the bottom layer of the third dielectric substrate is copper-clad as the metal ground layer; The surface coupling patch on the first dielectric substrate consists of two ports, two sets of tapered impedance matching sections, a set of symmetrical U-shaped branch lines, a central connecting microstrip line, and two pairs of quarter-wavelength open-circuit stubs. The coupling patch on the upper surface of the second dielectric substrate is a layer of broadside coupling patches; The upper surface of the third dielectric substrate is provided with two T-shaped microstrip branch lines; Three equally spaced rectangular slots are etched on the metal ground layer, and two metalized blind vias are opened in the metal ground layer on the lower surface of the third dielectric substrate to the T-shaped microstrip branch line on the upper surface of the third dielectric substrate; Ultra-wideband bandpass filter characteristics are produced by the mutual coupling of the designed patterns on the surface of the three-layer dielectric substrate combined with the blind hole structure.

2. The compact micro-bandwidth bandpass filter according to claim 1, characterized in that: The first dielectric substrate is designed with a pattern on its upper surface, which loads two sets of quarter-wavelength open-circuit stubs to extract energy at a specified frequency point. This allows the insertion loss curve outside the passband to roll off quickly, thereby generating two zero points to improve the selectivity of the filter passband. By changing the length of the wider side of the coupling patch on the upper surface of the second dielectric substrate, the coupling area between the two layers of patches and the branch line is affected, thereby adjusting the reflection loss characteristics within the passband; Adjust the passband high-frequency cutoff frequency and high-frequency stopband harmonic suppression characteristics by digging the blind hole diameter; Rectangular gaps etched on the metal ground layer are used to create two resonance points within the passband, further optimizing the filter's in-band reflection loss characteristics.

3. The compact micro-bandwidth bandpass filter according to claim 1, characterized in that: The dielectric substrate is an RO4350 dielectric substrate, and the thicknesses of the three substrates are 0.1016 mm, 0.254 mm, and 0.508 mm respectively; The copper thickness of the top layer and the metal ground layer is h=0.035mm, and the copper thickness of the upper surface of the second and third substrates is h=0.018mm. The three dielectric substrates are pressed together using two RO4450F semi-solid sheets through a processing technology. The thickness of the two semi-solid sheets is h=0.2032mm.

4. The compact micro-bandwidth bandpass filter according to claim 2, characterized in that: The first layer of coupling patch is provided with energy by a 50 Ω microstrip with a width of W0. The energy reaches the U-shaped branch line through tapered impedance matching and is split here. One path is coupled downward through the two outer branches of the U-shaped branch line, and the other path is transmitted to the symmetrical U-shaped branch line on the other side through the central connecting microstrip. Before the output signal, the energy at the corresponding frequency point is derived through two sets of quarter-wavelength open-circuit stubs, thereby achieving harmonic suppression in the stopband and introducing two zeros, optimizing the passband selectivity of the filter.

5. The compact micro-bandwidth bandpass filter according to claim 4, characterized in that: The second layer of microstrip patch is a broadside coupling patch. By adjusting the outer broadside length L6, the coupling area with the upper microstrip patch and the lower branch line is adjusted, thereby affecting the reflection loss characteristics within the passband.

6. The compact micro-bandwidth bandpass filter according to claim 5, characterized in that: The metalized blind hole is opened from the metal ground plane to the wider rectangle of the T-shaped microstrip branch line. The high-frequency cutoff frequency and high-frequency stop-band harmonic suppression characteristics of the bandpass filter are adjusted by changing the diameter d0 of the blind hole.

7. The compact micro-bandwidth bandpass filter according to claim 6, characterized in that: The three rectangular slots etched in the metal ground layer have a spacing of g1. The three rectangular slots introduce two resonance points into the filter passband, further optimizing the reflection loss characteristics within the passband. The frequency and corresponding depth of the resonance point are affected by the spacing g1 between the rectangular slot resonators.

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