A miniaturized ultra-wideband planar filter

Abstract

The application belongs to the field of thin film microstrip filter, and particularly relates to a miniaturized ultra-wideband planar filter. The application adopts a compact stub structure through an electric bridge, the stub length and interval are optimized according to the electromagnetic coupling characteristics of the 3.1-10.6 GHz frequency band, and the matching conditions of the characteristic impedance and the resonator and the dielectric substrate are strictly met; and further, the planar coupling path of the electric bridge is combined with the three-dimensional coupling of the gold wire to form a composite coupling mechanism of 'planar + three-dimensional', cooperating with the miniaturized configuration of the microstrip resonator, the overall size of the device is reduced by more than 30%, while the group delay is greatly reduced (from the traditional 0.68 ns to 0.33 ns @ 8.3 GHz), the coupling value between resonators is significantly improved, and finally the ultra-wideband coverage is realized, and the in-band interference signals can be effectively suppressed. The application effectively solves the problem in the prior art that the traditional electric bridge coupling only relies on the planar structure, the coupling path is single, the coupling value is limited, and it is difficult to balance the bandwidth and miniaturization.

Description

Technical Field

[0001] This invention relates to the field of thin-film microstrip filters, and more specifically to a miniaturized ultrawideband planar filter. Background Technology

[0002] The booming development of the communications industry has driven the progress of human civilization and profoundly impacted people's daily lives. At the same time, with the development of communication technology and the emergence of various communication systems, the bottleneck effect of radio spectrum resources has become increasingly apparent. While improving the utilization rate of existing spectrum, people also hope to develop wider bandwidths to adapt to this rapid development. Against this backdrop, ultra-wideband wireless communication technology has emerged and, with its advantages of system simplicity, low cost, low power consumption, high data transmission rate, and high security, has become a research hotspot in the field of communications.

[0003] The development history of ultra-wideband (UWB) wireless communication technology can be traced back to the 1960s, initially taking the form of impulse radio technology that directly uses pulses with pulse widths in the nanosecond or sub-nanosecond range as information carriers. Since the 1990s, with the rapid development of microelectronic device technology and processes, UWB communication technology has begun to be applied in the civilian field, sparking a surge of research, development, and application in the international academic and industrial communities, and is considered a revolutionary technology for next-generation wireless communication. In February 2002, the U.S. Federal Communications Commission (FCC) released preliminary specifications for UWB technology, allowing its civilian use and opening the 3.1 GHz to 10.6 GHz frequency band as a free civilian band. This move opened the door to the commercialization of UWB communication technology products, ushering in an era of rapid development for UWB wireless communication technology, and research on UWB systems and devices has received increasing attention.

[0004] Figure 1 shows the basic model of an ultra-wideband wireless communication system. As can be seen from the figure, the ultra-wideband filter is located at the radio frequency front end of the ultra-wideband system. It can be used to limit the radiation of high-power transmitters within a specified frequency band, and conversely, it can be used to prevent the receiver from being interfered with outside the operating frequency band. Therefore, the ultra-wideband microwave filter is a key passive component in the ultra-wideband system, and its performance has a significant impact on the overall performance of the system.

[0005] With the increasing integration of microwave devices, the miniaturization of filters has become increasingly urgent. Therefore, researching high-performance, miniaturized, and easily integrated microstrip filters is of great significance, which also presents some new challenges and difficulties for the design of ultra-wideband filters. Currently, the design of ultra-wideband bandpass filters mainly faces the following major difficulties: First, the FCC's requirements for ultra-wideband systems stipulate coverage of the 3.1 GHz to 10.6 GHz frequency band, requiring filters to have a relative bandwidth of 110%, making commonly used narrowband filter design methods infeasible; Second, the group delay of the ultra-wideband filter must be as small and stable as possible within the passband; Third, to reduce interference from ultra-wideband communication systems to existing wireless communication systems, ultra-wideband filters must have good suppression effects in the high and low stopbands and high selectivity in the sidebands; Fourth, the large frequency range of ultra-wideband systems makes them susceptible to interference from narrowband signals from other systems within the band (such as 5 GHz wireless local area networks, WLANs), and how to suppress interference signals is also a design challenge.

[0006] Currently, the main solutions for ultra-wideband filters in this field are as follows: 1) Using a multi-cascaded filter structure, multiple narrowband or medium-bandwidth filters are cascaded to cover the entire ultra-wideband frequency band. However, this method results in large filter size, high insertion loss, and difficulty in controlling group delay characteristics; 2) Using multi-mode resonator technology, multiple resonant modes of a single resonator are used to construct a wideband response, such as stepped impedance resonators (SIR) and defective ground structures (DGS). However, these designs usually require complex structural optimization and have limited out-of-band rejection performance; 3) Using special transmission line structures such as composite left-handed transmission lines (CRLH TL), which can achieve ultra-wideband characteristics, but the design is complex and has high process requirements; 4) Using parallel coupled lines and interdigital structures, although the structure is relatively simple, there is a contradiction between size and performance when achieving 110% relative bandwidth. Therefore, developing new coupling structures to achieve high-performance ultra-wideband filters remains a technical challenge that urgently needs to be solved. Summary of the Invention

[0007] To address the aforementioned problems or shortcomings, this invention provides a miniaturized ultra-wideband planar filter, which is an ultra-wideband planar filter with a special coupling structure, effectively solving the problems of miniaturization and ultra-wideband.

[0008] A miniaturized ultrawideband planar filter is disclosed, comprising a dielectric substrate, a first resonator, a second resonator, a bridge circuit, and gold wires; while maintaining a miniaturized overall filter size (overall area less than 0.35 square meters). ×0.25 ,in (with the center frequency guide wavelength), to achieve ultra-wideband characteristics of 3.1-10.6 GHz.

[0009] Both the first and second resonators are microstrip line resonators, positioned above the dielectric substrate.

[0010] The bridge is a low-impedance transmission line structure with a characteristic impedance of 15-25Ω and a physical length of 1 / 4 of the center frequency wavelength. Its two ends are connected to the coupling ends of the first resonator and the second resonator, respectively, forming a basic planar coupling path.

[0011] The gold wire is vertically arranged at the open-circuit point at the end of the first resonator, the open-circuit point at the end of the second resonator, and the two ends of the bridge to form a three-dimensional coupling channel. It forms a planar + three-dimensional composite coupling with the basic planar coupling path, which enhances the energy coupling strength between the first resonator and the second resonator and achieves ultra-wideband characteristics of 3.1GHz~10.6GHz, thereby realizing bandwidth expansion.

[0012] Furthermore, the gold wire bonding configuration has a gold wire diameter of 25μm and a vertical height of 0.15mm±0.05mm.

[0013] Furthermore, the dielectric substrate has a dielectric constant of 9.7 to 9.9, a thickness of 0.127 mm to 0.508 mm, and is made of ceramic.

[0014] Furthermore, the linewidth of the first resonator and the second resonator is 0.1mm~0.5mm, and the length is 1 / 4 wavelength or 1 / 2 wavelength at the corresponding center frequency.

[0015] Furthermore, the bridge is a compact stub structure, fabricated using microstrip lines with a linewidth of 0.05mm to 0.3mm. The stub spacing is optimized based on the electromagnetic coupling characteristics of the 3.1GHz to 10.6GHz frequency band and meets the 50Ω characteristic impedance matching condition with the resonator and dielectric substrate.

[0016] Furthermore, the first resonator, the second resonator, and the bridge are all fabricated on the upper surface of the dielectric substrate using a thin film deposition process, which includes sputtering, evaporation, or electroplating.

[0017] In summary, this invention utilizes the unique design of the bridge structure: the bridge employs a compact stub structure, with stub lengths and spacing optimized based on the electromagnetic coupling characteristics of the 3.1-10.6 GHz frequency band, and strictly satisfies the matching conditions between the characteristic impedance and the resonator and dielectric substrate (target characteristic impedance 50Ω); furthermore, it combines the planar coupling path of the bridge with the three-dimensional coupling of the gold wire, forming a "planar + three-dimensional" composite coupling mechanism. Combined with the miniaturized configuration of the microstrip resonator, this reduces the overall device size by more than 30% while significantly reducing the group delay (from the traditional 0.68 ns to 0.33 ns@8.3 GHz), significantly improving the coupling value between resonators, ultimately achieving ultra-wideband coverage, and effectively suppressing in-band interference signals. This invention effectively solves the problems of existing technologies where traditional bridge coupling relies solely on planar structures, has a single coupling path, limited coupling value improvement, and struggles to balance bandwidth and miniaturization. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a general model of an existing ultra-wideband (UWB) system.

[0019] Figure 2 This is a schematic diagram of coupling values ​​based on group delay;

[0020] Figure 3 This is a schematic diagram of a traditional filter coupling structure;

[0021] Figure 4 This is a schematic diagram of the time delay parameters of a traditional filter coupling structure group.

[0022] Figure 5 This is a schematic diagram of the filter coupling structure of the present invention;

[0023] Figure 6 This is a schematic diagram of the group delay parameters of the filter coupling structure in the embodiment.

[0024] Figure 7 This is a schematic diagram showing the specific dimensions of the filter in the embodiment;

[0025] Figure reference numerals: 1-Dielectric substrate, 2-First resonator, 3-Second resonator, 4-Bridge circuit, 5-Gold wire. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0027] In filter design, the resonant cavity is a fundamental component. Its material, structure, and size determine core parameters such as the filter's center frequency, while the coupling value (i.e., the strength of energy coupling between resonators) directly controls key response indicators such as the filter's bandwidth, in-band ripple, and stopband attenuation. The mainstream microwave filter design process follows a "low-pass prototype → band-pass converter → anti-phase coupled resonator" flow, the core of which is adjusting the coupling value between the resonators (…). ) and external quality factors ( To achieve the target response (such as Chebyshev, linear phase). Additionally, the reflection coefficient group delay... It can replace the coupling coefficient, which contains all the key information for filter design and tuning—the group delay at the center frequency can be directly correlated with the low-pass prototype parameters, band-pass LC elements, and coupling coefficient.

[0028] Group delay fundamental formula: Input reflection coefficient Group delay definition ( for Phase, (Angular frequency). Low-pass to band-pass converter: using the standard conversion formula. ( For the center frequency, To convert the group delay of the low-pass prototype into the group delay of the band-pass filter (for the upper and lower sidebands), the final result of the band-pass circuit is derived. Normalization with low-pass prototype The direct correlation between value and bandwidth. The correlation between group delay and design parameters is as follows:

[0029] Single resonator: center frequency Location, group time delay With the outside The relationship between the LC elements is as follows:

[0030] ( It is a band-pass capacitor. (characteristic impedance).

[0031] Two coupled resonators: When the second resonator is short-circuited, the group delay of the center frequency. Coupling coefficient between two resonators The relationship is: = ;

[0032] Coupling value of a coupled resonator filter The reflection coefficient can be input. Group delay ( (Direct derivation.) The formula shows that increasing the group delay filter resonator coupling value decreases, thus reducing the filter bandwidth; conversely, decreasing the group delay filter coupling value increases, thus increasing the filter bandwidth.

[0033] Traditional coupled filters mostly achieve coupling through the resonator itself (as shown in the attached image). Figure 3 As shown), the coupling value between the resonators is finite, and its group delay parameter is 0.68ns@8.3GHz (as shown in the attached figure). Figure 4 (As shown).

[0034] This invention reduces the group delay of the filter resonator through an innovative coupling structure, thereby increasing the coupling value between the resonators and achieving a bandwidth extension effect.

[0035] The specific miniaturized ultrawideband planar filter designed in this embodiment (as shown in the attached document) Figure 5 As shown in the figure, it consists of a dielectric substrate (1), a first resonator (2), a second resonator (3), a bridge (4), and gold wires (5). Resonators A (2) and B (3) adopt a microstrip resonator configuration and are placed on a dielectric substrate (1) with a dielectric constant of 9.8 and a thickness of 0.254 mm. The bridge (4) is a microstrip line with a width of 0.05 mm and a length of 1 / 4 of the wavelength corresponding to the center frequency of 8.3 GHz, connecting the first resonator (2) and the second resonator (3). Gold wires with a diameter of 25 μm are bonded to the open-circuit point at the end of the first resonator (2), the open-circuit point at the end of the second resonator (3), and both ends of the bridge (4). The vertical height of the gold wires is 0.15 mm ± 0.05 mm, forming a three-dimensional coupling channel to significantly enhance the coupling effect and achieve ultra-wideband characteristics of 3.1-10.6 GHz. For the specific dimensions of the coupling structure in this embodiment, please refer to the attached figure. Figure 7 For details on the group delay parameters of the filter coupling structure in the embodiment, please refer to the appendix. Figure 6 .

[0036] As can be seen from the above embodiments, the present invention introduces a specially designed low-impedance bridge structure between the couplers (as shown in the attached figure). Figure 5 As shown in the attached diagram, this bridge structure employs the λ / 4 wavelength impedance transformation principle, with its characteristic impedance controlled within the range of 15-25Ω. The width and length have been rigorously optimized, reducing the resonator group delay parameter to 0.33ns@8.3GHz (as shown in the attached diagram). Figure 6As shown, this invention significantly improves the coupling value between resonators, enabling a large bandwidth design. In particular, the bridge structure of this invention differs fundamentally from traditional bridge filters: traditional bridges are mainly used for power distribution or combining, typically with a characteristic impedance of 50Ω, and are not directly coupled to the resonators; while the bridge of this invention, acting as a coupling medium, employs low impedance characteristics. By precisely controlling the electrical length, width, and connection position with the resonators, strong coupling between resonators is achieved, while maintaining the miniaturization of the filter. Furthermore, this invention innovatively introduces gold wire bonding technology into the bridge structure. By placing gold wires at specific locations (the open-circuit points at the ends of the first and second resonators, and the two ends of the bridge), a three-dimensional coupling channel is formed, further optimizing the electric field distribution and significantly improving coupling efficiency.

Claims

1. A miniaturized ultrawideband planar filter, characterized in that: It consists of a dielectric substrate, a first resonator, a second resonator, a bridge circuit, and gold wires; the overall area of ​​the filter is less than 0.35 square meters. ×0.25 ,in With the center frequency guide wavelength as the standard, the entire filter operates in the ultra-wideband range of 3.1-10.6 GHz; Both the first and second resonators are microstrip line resonators, which are disposed above the dielectric substrate; The bridge is a low-impedance transmission line structure with a characteristic impedance of 15-25Ω and a physical length of 1 / 4 of the center frequency wavelength. Its two ends are connected to the coupling ends of the first resonator and the second resonator, respectively, forming a basic planar coupling path. The gold wire is vertically arranged at the open-circuit point at the end of the first resonator, the open-circuit point at the end of the second resonator, and the two ends of the bridge to form a three-dimensional coupling channel. It forms a composite coupling of planar and three-dimensional elements with the basic planar coupling path.

2. The miniaturized ultrawideband planar filter as described in claim 1, characterized in that: The gold wire bonding configuration has a gold wire diameter of 25μm and a vertical height of 0.15mm±0.05mm.

3. The miniaturized ultrawideband planar filter as described in claim 1, characterized in that: The dielectric substrate has a dielectric constant of 9.7 to 9.9, a thickness of 0.127 mm to 0.508 mm, and is made of ceramic.

4. The miniaturized ultrawideband planar filter as described in claim 1, characterized in that: The linewidth of the first resonator and the second resonator is 0.1mm~0.5mm, and the length is 1 / 4 wavelength or 1 / 2 wavelength at the corresponding center frequency.

5. The miniaturized ultrawideband planar filter as described in claim 1, characterized in that: The bridge is a compact stub structure, fabricated using microstrip lines with a linewidth of 0.05mm to 0.3mm. The stub spacing is optimized based on the electromagnetic coupling characteristics of the 3.1GHz to 10.6GHz frequency band and meets the 50Ω characteristic impedance matching condition with the resonator and dielectric substrate.

6. The miniaturized ultrawideband planar filter as described in claim 1, characterized in that: The gold wire is made of gold or a gold alloy, and there are a total of 4 gold wires. The vertical height of each gold wire is 0.15mm ± 0.05mm, which correspond to the open point at the end of the first resonator, the open point at the end of the second resonator, and the two ends of the bridge, respectively.

7. The miniaturized ultrawideband planar filter as described in claim 1, characterized in that: The first resonator, the second resonator, and the bridge are all fabricated on the surface of a dielectric substrate using a thin film deposition process, which includes sputtering, evaporation, or electroplating.

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