阅读说明：本技术 一种基于Pi型结构的柔性低通滤波器 (Flexible low pass filter based on Pi type structure ) 是由 韩宇南 袁靖 于 2019-10-30 设计创作，主要内容包括：本申请提供了一种基于Pi型结构的柔性低通滤波器,通过在酰亚胺薄膜基板设置10个级联非对称Pi型缺陷接地结构,等效于一个满足低通滤波功能的电感电容(LC)谐振滤波电路,能够获得比传统滤波器更锋利的过渡带。并且,该柔性低通滤波器为100mm×2.6mm×0.254mm的结构紧凑的柔性低通滤波器,具有良好的传输和滤波功能,有望在无线终端中取代传统的IPEX射频同轴电缆和LTCC滤波器。该柔性低通滤波器在2.2GHz下插入损耗小于1.9dB,在2.7GHz到12GHz之间插入损耗更低,抑制率大于50dB,与现有的滤波器相比,该基于Pi型结构的柔性低通滤波器具有更宽的阻带和更尖锐的过渡带。(The application provides a flexible low pass filter based on Pi type structure, sets up 10 and cascades asymmetric Pi type defect ground structure through at imide film substrate, is equivalent to an inductance-capacitance (LC) resonance filter circuit who satisfies the low pass filter function, can obtain the transition band sharper than traditional wave filter. In addition, the flexible low-pass filter is a flexible low-pass filter with a compact structure of 100mm multiplied by 2.6mm multiplied by 0.254mm, has good transmission and filtering functions, and is expected to replace the traditional IPEX radio frequency coaxial cable and LTCC filter in a wireless terminal. The flexible low-pass filter has the insertion loss of less than 1.9dB at 2.2GHz, is lower between 2.7GHz and 12GHz, has the suppression ratio of more than 50dB, and has a wider stop band and a sharper transition band compared with the existing filter.)

1. A flexible low-pass filter based on a Pi-type structure, wherein a low-pass filtering function is implemented by a Pi-type defected ground structure, the flexible low-pass filter comprising:

a flexible substrate;

the microstrip transmission line is arranged on the upper surface of the flexible substrate, and an etched gap is formed in the middle area of the microstrip transmission line;

the n cascaded Pi-type defect grounding structures are arranged on the lower surface of the flexible substrate;

wherein, the Pi type defected ground structure is an asymmetric Pi type defected ground structure.

2. A flexible low-pass filter according to claim 1, characterized in that the number of cascades of Pi-type defected ground structures is 10.

3. The flexible low-pass filter according to claim 1, wherein the flexible substrate is an imide film substrate or a liquid crystal polymer film substrate.

4. The flexible low pass filter according to claim 1, wherein the width of the slot is 0.1 mm.

5. The flexible low pass filter according to claim 1, characterized in that the length of the microstrip transmission line is 100 mm.

6. The flexible low pass filter according to claim 1, characterized in that the flexible low pass filter has a length of 100mm, a width of 2.6mm and a height of 0.254 mm.

7. The flexible low-pass filter according to claim 1, wherein the microstrip transmission line and the Pi-type defected ground structure each have a thickness of 18 μm.

8. The flexible low-pass filter according to claim 1, further comprising:

an insulating layer covering the upper and lower surfaces of the flexible substrate;

the insulation layer is used for protecting the microstrip transmission line and the Pi-type defect grounding structure.

9. The flexible low pass filter according to claim 8, characterized in that the thickness of the insulating layer is 25 μm.

Technical Field

The invention relates to the technical field of mobile terminal radio frequency connection, in particular to a flexible low-pass filter based on a Pi-type structure.

Background

The flexible microstrip filter is a filter manufactured by utilizing a flexible printed circuit board technology, is used for processing signals of a specific frequency band, is much cheaper compared with the traditional waveguide filter, a low-temperature co-fired ceramic filter and a hard PCB microstrip filter, and has a more compact structure and lighter weight.

With the increasing demand of flexible and compact electronic devices such as wearable devices, intelligent electronic devices and portable wireless terminals, the development speed of the device is faster and faster, and the device has the advantages of flexibility, super-pulsation, super-lightness, low cost, low water absorption rate, good appearance, good electromagnetic compatibility and the like, and is expected to become a key component of wireless communication equipment.

In the past research, flexible microstrip filters have been attracting attention in high-frequency bandpass applications, and the main research directions are as follows: the filter is provided with a parallel coupling half-wavelength resonator to realize a broadband 60GHz band-pass filter; secondly, the performance of the flexible X-band-pass filter on the ultrathin LCP substrate is researched; designing two quadrupole quasi-elliptical X-band-pass filters on an LCP substrate, and stacking open-loop resonators; fourthly, designing a compact flexible band-pass filter operating at 5.15GHz-5.875GHz based on a 0-degree feeding structure of a LCP substrate with the thickness of 50 micrometers; fifthly, a 10GHz stepped impedance low-pass filter and a 9.5GHz band-pass filter are produced on the LCP substrate.

However, the research on the flexible microstrip filter has been mainly focused on the K-band or the X-band so far, the application of the flexible microstrip low-pass filter to the low-end band is very little, and the structural size of the flexible microstrip low-pass filter cannot meet the existing requirement.

Disclosure of Invention

In view of the above, in order to solve the above problems, the present invention provides a flexible low-pass filter based on Pi-type structure, and the technical solution is as follows:

a flexible low-pass filter based on a Pi-type structure, which implements a low-pass filtering function by a Pi-type defected ground structure, the flexible low-pass filter comprising:

a flexible substrate;

the microstrip transmission line is arranged on the upper surface of the flexible substrate, and an etched gap is formed in the middle area of the microstrip transmission line;

the n cascaded Pi-type defect grounding structures are arranged on the lower surface of the flexible substrate;

wherein, the Pi type defected ground structure is an asymmetric Pi type defected ground structure.

Preferably, in the flexible low-pass filter, the number of the cascades of the Pi-type defected ground structures is 10.

Preferably, in the flexible low-pass filter, the flexible substrate is an imide film substrate or a liquid crystal polymer film substrate.

Preferably, in the flexible low pass filter, a width of the slot is 0.1 mm.

Preferably, in the flexible low pass filter, the length of the microstrip transmission line is 100 mm.

Preferably, in the flexible low-pass filter, the flexible low-pass filter has a length of 100mm, a width of 2.6mm and a height of 0.254 mm.

Preferably, in the flexible low pass filter, the microstrip transmission line and the Pi-type defected ground structure each have a thickness of 18 μm.

Preferably, in the flexible low-pass filter, the flexible low-pass filter further includes:

an insulating layer covering the upper and lower surfaces of the flexible substrate;

the insulation layer is used for protecting the microstrip transmission line and the Pi-type defect grounding structure.

Preferably, in the flexible low-pass filter, the insulating layer has a thickness of 25 μm.

Compared with the prior art, the invention has the following beneficial effects:

according to the flexible low-pass filter based on the Pi-type structure, the flexible low-pass filter has the characteristics of thinness and good transmission and filtering functions by controlling the size of a plurality of cascaded asymmetrical Pi-type defect grounding structures, through experimental measurement results, the insertion loss is less than 1.9dB at 2.2GHz, the insertion loss is lower between 2.7GHz and 12GHz, the inhibition rate is greater than 50dB, and compared with the existing filter, the flexible low-pass filter based on the Pi-type structure has a wider stop band and a sharper transition band.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a schematic structural diagram of an upper surface of a flexible low-pass filter based on a Pi-type structure according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a lower surface of a flexible low-pass filter based on a Pi-type structure according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of an upper surface of a single Pi-type defected ground structure resonator according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of a lower surface of a resonator with a single Pi-type defected ground structure according to an embodiment of the present invention;

fig. 5 is an equivalent circuit diagram of a resonant cavity with a single asymmetric Pi-type defected ground structure according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Most of the techniques of the conventional microstrip filter can be directly used for designing a flexible microstrip filter, which can only realize a gentle Transition Band (TB) response and a narrow Stop Band (SB) of a butterworth characteristic or a chebyshev characteristic based on a stepped impedance resonator.

To obtain a sharpened tb characteristic, more stepped impedance resonant cells are required, thereby increasing the insertion loss in the pass band (pb) and the geometry of the filter.

In order to improve the frequency response performance of the microstrip filter, a Defected Ground Structure (DGS) resonator with symmetrical geometric structures such as dumbbells, circles, triangles and rectangles is widely adopted in the design of the microstrip filter.

In recent years, improvements in DGS resonators, such as asymmetric structures, have attracted considerable attention in filter design to achieve better performance. Also, a microstrip filter having several Photonic Band Gap (PBG) structure periodic units is proposed.

Therefore, the DGS resonator with the periodic defect grounding structure is used in the design of the flexible microstrip filter to obtain better performance, such as size reduction, Tb sharpening, Sb widening and the like.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Referring to fig. 1, fig. 1 is a schematic structural diagram of an upper surface of a flexible low-pass filter based on a Pi-type structure according to an embodiment of the present invention. Referring to fig. 2, fig. 2 is a schematic structural diagram of a lower surface of a flexible low-pass filter based on a Pi-type structure according to an embodiment of the present invention.

The flexible low-pass filter realizes a low-pass filtering function through a Pi type defect grounding structure, and comprises:

a flexible substrate 11;

a microstrip transmission line 12 disposed on the upper surface of the flexible substrate 11, wherein the middle region of the microstrip transmission line 12 has an etched slot;

n cascaded Pi-type defected ground structures 13 disposed on the lower surface of the flexible substrate 11;

wherein the Pi-type defected ground structure 13 is an asymmetric Pi-type defected ground structure.

Further, based on the above-described embodiment of the present invention, the number of the cascades of the Pi-type defected ground structures 13 is 10.

It should be noted that the out-of-band rejection effect can be increased by increasing the number of stages, and in the embodiment of the present invention, the number of cascades of the Pi-type defected ground structures 13 is preferably 10.

Further, according to the above embodiment of the present invention, the flexible substrate 11 is an imide film substrate or a liquid crystal polymer film substrate.

Further, according to the above embodiment of the present invention, the flexible low pass filter has a length of 100mm, a width of 2.6mm, and a height of 0.254 mm.

In the above embodiments, the present application successfully designs, simulates, manufactures and measures a grounding structure with 10 cascaded asymmetric Pi-type defects on an imide thin film substrate, optimizes the grounding structure by using electromagnetic simulation software, and is equivalent to an inductance-capacitance (LC) resonant filter circuit satisfying a low-pass filtering function, thereby obtaining a sharper transition band than that of a conventional filter.

In addition, the flexible low-pass filter is a flexible low-pass filter with a compact structure of 100mm multiplied by 2.6mm multiplied by 0.254mm, has good transmission and filtering functions, and is expected to replace the traditional IPEX radio frequency coaxial cable and LTCC filter in a wireless terminal.

The flexible low-pass filter has an insertion loss of less than 1.9dB at 2.2GHz, a lower insertion loss between 2.7GHz and 12GHz and a suppression rate of more than 50dB, and compared with the existing filter, the flexible low-pass filter based on the Pi type structure has a wider stop band and a sharper transition band.

It is noted that in the present application, an imide film substrate or a liquid crystal polymer film substrate is used for radio frequency, microwave or millimeter scale applications because they combine excellent electrical properties with good processability. The material of the flexible dielectric substrate is uniform, and thus the dielectric properties of the flexible substrate are very uniform. For different material formulas, the relative dielectric constant of the polyimide film may be between 2.2 and 3.8, and the dielectric loss tangent may be less than 0.008. The relative dielectric constant of the commercial liquid crystal polymer film was 3.3, and the dielectric loss tangent was less than 0.005. In addition, the water absorption of the flexible medium substrate material is very low (23 ℃, and less than 0.04% at 50% relative humidity), so that the size and dielectric property do not change greatly under the humid condition. Based on these properties, different types of microstrip lines can be easily designed and manufactured by using the flexible dielectric substrate to verify the applicability of the microstrip lines in microwave device applications.

In fig. 1 and 2, the structure following the parallel slashes indicates a plurality of cascaded Pi-type defective ground structures 13.

Further, based on the above-mentioned embodiment of the present invention, as shown in fig. 1, the length of the microstrip transmission line 12 is Lsub ═ 100 mm.

Further, according to the above embodiment of the present invention, as shown in fig. 1, the width of the substrate 11 is 2.6 mm.

Further, based on the above embodiments of the present invention, referring to fig. 3, fig. 3 is a schematic structural diagram of an upper surface of a resonator with a single Pi-type defected ground structure according to an embodiment of the present invention.

As shown in fig. 3, the width of the slot is Wslot ═ 0.1 mm.

Optionally, the length of the slot-free portion at each end of the microstrip transmission line 12 is L0-1 mm.

Further, according to the above embodiment of the present invention, as shown in fig. 3, the width of the microstrip transmission line 12 is Wtran ═ 0.46 mm.

Based on the above embodiment, the microstrip transmission line with the above dimensions can realize a characteristic impedance of 50 Ω.

Further, based on the above embodiments of the present invention, referring to fig. 4, fig. 4 is a schematic structural diagram of a lower surface of a resonator with a single Pi-type defected ground structure according to an embodiment of the present invention.

With reference to fig. 3 and 4, a Pi-type defected ground structure with a preset size is provided, and a flexible low-pass filter is realized by cascading 10 same Pi-type defected ground structures.

Wherein, the parameters in fig. 3 and 4 are: lr is 10.7mm, L1 is 9.3mm, L2 is 0.7mm, L3 is 3.9mm, L4 is 0.3mm, L5 is 1.5mm, W1 is 0.4mm, W2 is 1mm, W3 is 0.4mm, W4 is 0.35mm, and W5 is 0.45 mm.

Further, according to the above embodiments of the present invention, the thicknesses of the microstrip transmission line and the Pi-type defected ground structure are both 18 μm.

In this embodiment, the metal layers of the microstrip transmission line and the Pi-type defected ground structure are composed of copper 18 μm thick.

Further, based on the above embodiment of the present invention, the flexible low-pass filter further includes:

an insulating layer covering the upper and lower surfaces of the flexible substrate;

the insulation layer is used for protecting the microstrip transmission line and the Pi-type defect grounding structure.

The thickness of the optional insulating layer is 25 μm.

In this example, in order to protect the copper layers, a PI film insulating layer with a thickness of 25 μm was provided to cover each of them, where ∈ r was 3.6 and a loss tan δ was 0.03.

Further, referring to fig. 5 based on the above embodiments of the present invention, fig. 5 is an equivalent circuit diagram of a single asymmetric Pi-type defected ground structure resonator according to an embodiment of the present invention.

A single asymmetric Pi-type DGS resonator can be equivalent to a resonant LC resonant circuit, which satisfies the LPF function of a low pass filter having a sharp transition band Tb and a wide stop band Sb.

Through structural analysis, current analysis and S parameter curve fitting, an equivalent circuit can be realized. The current at the edge of the DGS of the asymmetrical Pi-type defected ground structure can be equivalent by a capacitor and an inductor.

By adjusting the geometrical parameters of the proposed asymmetric Pi-type defected ground structure DGS, the flexible low pass filter LPF can realize different inductances, capacitances, pass bands and stop bands.

In order to replace the IPEX radio frequency coaxial cable, the structure of the resonator must be as narrow as possible, on the other hand its length can be much longer.

Based on an equivalent circuit model and simulation optimization, the DGS resonator structure of the asymmetric Pi-type defected ground structure of the flexible low-pass filter LPF is realized, as shown in FIG. 1. For 10 cascaded resonators, the equivalent circuit is also cascaded as an equivalent circuit of a single resonator.

The flexible low-pass filter based on Pi-type structure provided by the present invention is described in detail above, and the principle and the embodiment of the present invention are explained herein by applying specific examples, and the description of the above examples is only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.

It should be noted that, in the present specification, the embodiments are all described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments may be referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include or include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.