Passive low pass filters and low pass filter circuits

Abstract

The present application belongs to the field of filtering electronic technology, and provides a passive low-pass filter and a low-pass filter circuit. The passive low-pass filter includes a radio frequency input module, a first resonant module, a first attenuating module, a plurality of second resonant modules connected in series, a plurality of second attenuating modules, and a radio frequency output module. Specifically, the frequency input module outputs a first radio frequency signal, the first resonant module outputs a second radio frequency signal with a predetermined passband frequency, the first attenuating module attenuates clutter signals in the second radio frequency signal, the plurality of second resonant modules connected in series adjust the frequency of the second radio frequency signal, each of the second attenuating modules attenuates clutter signals in the second radio frequency signal to generate a third radio frequency signal, and the radio frequency output module outputs the third radio frequency signal. The embodiment of the present application can solve the problem that the wide passband and frequency cutoff characteristics of the conventional low-pass filter do not meet the requirements and the volume is not sufficiently miniaturized.

Description

[Technical field]

[0001] This application claims priority to a Chinese patent application with application number 202210602935.1, filed with the China Patent Office on May 30, 2022, the entire contents of which are incorporated herein by reference. This application belongs to the field of filtering electronic technology, and in particular relates to a passive low-pass filter and a low-pass filter circuit. [Background technology]

[0002] In the rapidly developing modern wireless communication systems, such as Virtual Reality (VR), Wireless Local Area Network (WLAN), satellite communication, etc., the need for low-pass filters is increasing day by day. In these systems, low-pass filters are applied in radio frequency front-end receivers to suppress image frequencies, local oscillation frequencies, and harmonics.

[0003] At present, traditional low-pass filters have a self-capacitor due to the equivalent inductance, and the equivalent capacitor has a self-inductance, so in practical applications, it is easy to generate second harmonics, which affects the performance index of the filter. At the same time, with the miniaturization of electronic devices, the volume of the filter according to the traditional technology is large, which cannot meet the needs of miniaturization.

[0004] Therefore, conventional filters cannot satisfy the requirements for a wide passband and steep frequency cutoff characteristics of the filter circuit, and there is a problem that the miniaturization of the low-pass filter is insufficient. Summary of the Invention [Problem to be solved by the invention]

[0005] The present application aims to provide a passive low-pass filter and a low-pass filter circuit, and to solve the problems of the conventional low-pass filters, that is, the wide passband and frequency cutoff characteristics do not meet the requirements, and the volume is not sufficiently miniaturized. [Means for solving the problem]

[0006] A first aspect of an embodiment of the present application provides a passive low-pass filter, the passive low-pass filter comprising: a radio frequency input module for receiving a radio frequency signal, mixing and processing the radio frequency signal, and outputting a first radio frequency signal; a first resonator module coupled to the radio frequency input module, the first resonator module adjusting a frequency of the first radio frequency signal to output a second radio frequency signal at a predetermined passband frequency; a first attenuation module coupled to the first resonator module, the first attenuation module attenuating clutter signals in the second radio frequency signal; a plurality of second resonant modules connected in series and coupled to the first resonant module, the second resonant modules adjusting a frequency of the second radio frequency signal; a plurality of second attenuation modules, each having a first end coupled to a common node between adjacent second resonant modules and a second end grounded, the second attenuation modules attenuating clutter signals in the second radio frequency signal to generate a third radio frequency signal; a radio frequency output module connected to the plurality of series-connected second resonant modules and configured to output the third radio frequency signal.

[0007] In one embodiment, the first resonant module includes a first inductor and a first capacitor, a first end of the first inductor and a first end of the first capacitor are commonly connected to the radio frequency input module, and a second end of the first inductor and a second end of the first inductor are commonly connected to the second resonant module.

[0008] In one embodiment, each of the second resonant modules includes a second inductor and a second capacitor, the second inductor and the second capacitor being connected in parallel.

[0009] In one embodiment, the first damping module includes at least one capacitor, the at least one capacitor having a first end connected to the first resonant module and a second end connected to ground.

[0010] In one embodiment, the first inductor and the second inductor are spiral inductors or rectangular inductors.

[0011] In one embodiment, the first capacitor and the second capacitor structure are metal-dielectric-metal structures.

[0012] In one embodiment, the passive low-pass filter further includes a base layer and a ground metal layer; The first resonant module and the second resonant module are formed on the base layer, and the first damping module and the second damping module are connected to the ground metal layer via a through-hole structure.

[0013] In one embodiment, the material of the base layer is a gallium arsenide material, and the thickness of the base layer is 100±5 μm.

[0014] In one embodiment, the radio frequency input module and the radio frequency output module are both coplanar port structures.

[0015] A second aspect of an embodiment of the present application provides a low-pass filter circuit, the low-pass filter circuit including the passive low-pass filter according to any one of the above aspects. Effect of the Invention

[0016] Compared with the prior art, the embodiments of the present application have the following advantages.

[0017] The low-pass filter circuit includes a radio frequency input module, a first resonant module, a first attenuating module, a plurality of second resonant modules connected in series, a plurality of second attenuating modules, and a radio frequency output module. The radio frequency input module receives a radio frequency signal and outputs a first radio frequency signal, the first resonant module outputs a second radio frequency signal with a predetermined passband frequency, the first attenuating module attenuates clutter signals in the second radio frequency signal, the plurality of second resonant modules connected in series adjust the frequency of the second radio frequency signal, each of the second attenuating modules attenuates clutter signals in the second radio frequency signal to generate a third radio frequency signal, and the radio frequency output module outputs the third radio frequency signal. The embodiment of the present application can solve the problem that the wide passband and frequency cutoff characteristics of the conventional low-pass filter do not meet the requirements and the volume is not sufficiently miniaturized. The gist of the present invention is that by installing the first attenuation module and the second attenuation module, the clutter signal in the radio frequency signal can be effectively attenuated, and by installing the first resonance module and the second resonance module, the frequency of the radio frequency signal can be adjusted, thus effectively avoiding the problems in the conventional filter that the wide pass band and the sharp frequency cutoff characteristics of the filter circuit cannot meet the requirements and the miniaturization of the low-pass filter is insufficient. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram illustrating the principle of a passive low-pass filter according to an embodiment of the present application. [Diagram 2] FIG. 2 is an equivalent circuit diagram of a passive low-pass filter according to an embodiment of the present application. [Diagram 3] FIG. 1 is an equivalent circuit diagram of another passive low-pass filter according to an embodiment of the present application. [Figure 4] FIG. 2 is a structural schematic diagram of another passive low-pass filter according to an embodiment of the present application. [Diagram 5]FIG. 2 is a schematic diagram of parameter test curves of an input port return loss S11 and an output port return loss S22 of a low-pass filter with a passband frequency of 0.5 GHz according to an embodiment of the present application. [Figure 6] FIG. 2 is a schematic diagram of a parameter test curve of stopband suppression S21 of a low-pass filter with a passband frequency of 0.5 GHz according to an embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In order to clarify the technical problems, technical solutions and advantages of the present application, the present application will be described in more detail below with reference to the drawings and examples. Note that the specific examples described herein are merely for the purpose of illustrating the present application and are not intended to limit the present application.

[0020] It should be noted that when an element is described as being "fixed" or "mounted" to another element, it may be directly or indirectly connected to the other element. When an element is described as being "connected" to another element, it may be directly or indirectly connected to the other element.

[0021] In addition, the orientations or positional relationships indicated by terms such as "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," and "outside" are based on the orientations or positional relationships shown in the drawings, and are merely intended to facilitate and simplify the explanation of the present invention, and are not intended to indicate or imply that such devices or parts must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be understood as limitations on the present application.

[0022] Moreover, the terms "first" and "second" are merely for explanatory purposes and should not be understood as indicating or implying relative importance or the number of such technical configurations. Thus, a configuration defined by "first" or "second" can explicitly or implicitly include one or more of the configurations. In the description of this application, "plurality" means two or more than two, unless otherwise specified.

[0023] The types and frequency coverage of existing filters in China basically meet the needs of various telecommunications equipment, but with the development of the electronics industry, the performance requirements for filters are becoming higher and higher, and the functions are becoming more and more numerous, which calls for the development of filters in the direction of integration. The development of passive filters in China is relatively slow overall, and in particular, low-pass filters developed using the thin-film integrated passive device (IPD) process have not yet been mass-produced and applied, so in order to meet the requirements, it is necessary to autonomously develop low-pass filters fabricated based on the thin-film integrated passive device process.

[0024] Radio frequency passive components (e.g. resistors, inductors, capacitors and filters) can be fabricated by several processes, for example, low temperature co-fired ceramic (LTCC) technology is used to integrate passive components into multi-layer substrates. The LTCC process is widely used due to its excellent electrical and mechanical properties, and traditional low-pass filters are often fabricated by the LTCC process, but the size of the ceramic substrate using the LTCC process faces a bottleneck in the development of miniaturization.

[0025] In recent years, compared with LTCC process and PCB (Printed Circuit Board) process, IPD semiconductor process can produce finer line width, higher density capacitor, high quality factor (Q-factor) inductor and high precision inductor, and can integrate each passive component by thin film integrated passive component process, which is of profound significance for realizing high integration and high performance in communication system. In order to meet the performance requirements of compact size, steep frequency cutoff characteristic and high out-of-band suppression transport characteristic of low pass filter, system integration technology such as system-in-a-package (SiP) has been widely applied in radio frequency system.

[0026] In this embodiment, a low pass filter is an electronic filter component that allows signals below a cutoff frequency to pass, but does not allow signals above the cutoff frequency to pass.

[0027] Inductor Q, also known as the quality factor of an inductor, is a key parameter for evaluating inductor components. Inductor Q is the ratio of the inductive resistance an inductor offers when operating at an AC voltage of a certain frequency to its equivalent loss resistance. The higher the inductor Q, the lower its losses and the higher its efficiency.

[0028] As shown in FIG. 1, the first embodiment of the present application provides a schematic diagram of the principle of a passive low-pass filter, and for ease of explanation, only the parts related to the present embodiment are shown.

[0029] As shown in FIG. 1, the passive low-pass filter in an embodiment of the present application includes a radio frequency input module 101, a first resonant module 103, a first attenuation module 105, a plurality of second resonant modules 104, a plurality of second attenuation modules 106 and a radio frequency output module 102.

[0030] In this embodiment, the radio frequency input module 101 receives a radio frequency signal, mixes and processes the radio frequency signal to output a first radio frequency signal. The first resonant module 103 is coupled to the radio frequency input module 101, adjusts the frequency of the first radio frequency signal, and outputs a second radio frequency signal of a predetermined passband frequency. The first attenuation module 105 is coupled to the first resonant module 103, and attenuates clutter signals in the second radio frequency signal. The plurality of second resonant modules 104 connected in series are coupled to the first resonant module 103, and adjusts the frequency of the second radio frequency signal. Each second attenuation module 106 has a first end coupled to a common node between adjacent second resonant modules 104, and a second end grounded, and attenuates clutter signals in the second radio frequency signal to generate a third radio frequency signal. The radio frequency output module is connected to the plurality of second resonant modules 104 connected in series, and outputs a third radio frequency signal.

[0031] In addition, in this embodiment, the received radio frequency signal may include interference frequencies of multiple amplitudes, and at the common junction between the first resonant module 103 and the first attenuating module 105, the first attenuating module 105 performs a shunting process on the radio frequency signal, and the first attenuating module 105 quickly attenuates the clutter signal at the cutoff frequency at the pole point for the clutter signal of the second radio frequency signal adjusted and output by the first resonant module 103.

[0032] Furthermore, the second radio frequency signal directly enters the plurality of second resonant modules 104, where the plurality of second resonant modules 104 are coupled to the first resonant module 103, and the plurality of second resonant modules 104 adjust the frequency at which the passband frequency in the second radio frequency signal deviates from a predetermined value. Furthermore, the plurality of second attenuation modules 106 each have a first end coupled to a common node between adjacent second resonant modules 104 and a second end grounded, and attenuate other clutter frequency widths at the cutoff frequency to generate a third radio frequency signal. When the radio frequency signal reaches a predetermined signal and the clutter is attenuated to a predetermined range, the radio frequency signal enters the radio frequency output module 102 connected to the plurality of second resonant modules 104 connected in series. The radio frequency output module 102 outputs the third radio frequency signal to a coplanar port.

[0033] In one embodiment, the radio frequency input module 101 includes a radio frequency (RF) port, and the radio frequency signal received by the radio frequency port may be one or more of a digital analog signal, an audio signal, and a video signal, and the corresponding signal is mixed and processed to output a signal frequency that matches a predetermined value. For example, the radio frequency port receives a digital analog signal, and the radio frequency port is mixed and processed to output a stable digital analog signal, and triggers a subsequent module to realize a corresponding function. It should be noted that the radio frequency input module 101 may further include multiple other radio ports, and the radio frequency port may be correspondingly replaced according to the corresponding function that the device needs to realize, and the specific port type and model number are not limited.

[0034] In one embodiment, the first resonant module 103 includes at least one of an inductor component or a capacitor component.

[0035] In this embodiment, as shown in FIG. 2, the first resonant module 103 includes a first inductor L1 and a first capacitor C1, and a first end of the first inductor L1 and a first end of the first capacitor C1 are commonly connected to the radio frequency input module 101, and a second end of the first inductor L1 and a second end of the first inductor L1 are commonly connected to the second resonant module 104.

[0036] In one embodiment, one second resonant module 104 includes a second inductor L2 and a second capacitor C2, and the second inductor L2 is connected in parallel with the second capacitor C2. Each of the second resonant modules 104 includes a first inductor L1, a second inductor L2, a third inductor L3, a fourth inductor L4, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4, and the inductors and capacitors are connected correspondingly. For example, the first capacitor C1 has a first end connected to the radio frequency input module 101, a second end connected to the first end of the second capacitor C2, the second capacitor C2 has a second end connected to the first end of the third capacitor C3, the third capacitor C3 has a second end connected to the first end of the fourth capacitor C4, and the fourth capacitor C4 has a second end connected to the radio frequency output module 102, the first inductor L1 is connected in parallel to the first capacitor C1, the second inductor L2 is connected in parallel to the second capacitor C2, the third inductor L3 is connected in parallel to the third capacitor C3, and the fourth inductor L4 is connected in parallel to the fourth capacitor C4.

[0037] In one embodiment, the first damping module 105 includes at least one capacitor, the first end of which is connected to the first resonating module 103 and the second end of which is grounded.

[0038] For example, the first damping module 105 includes a fifth capacitor C5, and the second damping module 106 includes a sixth capacitor C6 and a seventh capacitor C7. Specifically, the fifth capacitor C5 has a first end connected to the second end of the first capacitor C1 and a second end grounded, the sixth capacitor C6 has a first end connected to the second end of the second capacitor C2 and a second end grounded, and the seventh capacitor C7 has a first end connected to the second end of the third capacitor C3 and a second end grounded.

[0039] In another embodiment, as shown in FIG. 3, when the first resonant module 103 includes only an inductor, the inductor serves to pass AC but block DC, and the corresponding function is realized as the first part in the circuit that connects the parallel-connected inductor and capacitor with the grounded capacitor.

[0040] In this embodiment, as shown in Fig. 3, the first resonant module 103 includes a first inductor L1. The plurality of second resonant modules 104 includes a second inductor L2, a third inductor L3, a fourth inductor L4, a first capacitor C1, a second capacitor C2 and a third capacitor C3, and the inductors and capacitors are connected correspondingly. For example, the first inductor L1 has a first end connected to the radio frequency input module 101, a second end connected to the first end of the first capacitor C1, the first capacitor C1 has a second end connected to the first end of the second capacitor C2, and a second end connected to the first end of the third capacitor C3, and the third capacitor C3 has a second end connected to the radio frequency output module 102. The second inductor L2 is connected in parallel to the first capacitor C1, the third inductor L3 is connected in parallel to the second capacitor C2, and the fourth inductor L4 is connected in parallel to the third capacitor C3. The first damping module 105 includes a fourth capacitor C4, and the second damping module 106 includes a fifth capacitor C5 and a sixth capacitor C6. Specifically, the fourth capacitor C4 has a first end connected to the first end of the first capacitor C1 and a second end grounded, the fifth capacitor C5 has a first end connected to the first end of the second capacitor C2 and a second end grounded, and the sixth capacitor C6 has a first end connected to the first end of the third capacitor C3.

[0041] Preferably, when only one inductor is installed in the first resonant module 103, the radio frequency signal received from the radio frequency input module 101 passes through the inductor, and the non-passband frequency loss of the radio frequency signal is first processed by the first attenuation module 105, and then resonated by the first resonant module of the plurality of second resonant modules 104 to stabilize the passband frequency at a predetermined value interval. This allows the low-pass filter to have a steep cutoff frequency characteristic and a good high out-of-band suppression characteristic.

[0042] Preferably, regarding the number of series resonant circuits of the multiple second resonant circuits 104, one or more second resonant circuits are selected and connected according to the effect to be implemented by the equipment and the actual cost, and the specific number is not limited.

[0043] Here, regarding the number of attenuation circuits of the multiple second attenuation modules 106, one or more second attenuation circuits are selected and connected based on the effect that the equipment needs to achieve and the actual cost, and the specific number is not limited.

[0044] In this embodiment, the radio frequency input module 101 further includes a plurality of through holes, where if the radio frequency input module 101 includes two through holes, the two through holes are respectively connected to the ground end Via of the radio frequency coplanar end, where if the radio frequency output module 102 includes two through holes, the two through holes are respectively connected to the ground end Via of the radio frequency coplanar end, the capacitors in the branch circuit consisting of the first attenuation module 105 and the plurality of second attenuation modules 106 are respectively connected to the corresponding through hole Via, and the capacitors of each branch circuit are respectively connected to the ground metal layer through the through hole.

[0045] Preferably, the dimension of the through hole on the back surface of the ground is 84±5 μm. Note that the dimension of the through hole is not limited to the dimension installed in this embodiment, and the specific dimension can be selected from the perspective of realizing the equipment function, large-scale of the through hole, convenience of industrialized production and economy.

[0046] In one embodiment, the first damping module 105 includes at least one capacitor, the first end of which is connected to the first resonating module 103 and the second end of which is grounded.

[0047] Specifically, the capacitor of each branch circuit has a first end connected to the common contact and a second end connected to the ground metal layer.

[0048] In one embodiment, the first inductor L1 and the second inductor L2 are spiral inductors or rectangular inductors.

[0049] Preferably, the inductor of the passive low-pass filter is an inductor made of annular magnetic material, and the shape of the finished inductor is a multi-spiral inductor or a rectangular inductor, where the inductor can only use annular magnetic material, and cannot use polygonal material, and when using polygonal material, the manufactured inductor is a hollow inductor. Preferably, the shape of the finished product is not limited to annular or rectangular, and the specific shape and shape can be set according to the size of the plate and the needs of realizing the corresponding function.

[0050] In one embodiment, the structure of the first capacitor C1 and the second capacitor C2 is a metal-dielectric-metal structure.

[0051] In addition, the intermediate dielectric layer of the capacitor can select different material media. Specifically, the dielectric can include one or more of aluminum oxide, capacitor paper, and ceramic sheet. The specific dielectric material is selected according to the functional demands and manufacturing costs, and the specific type is not limited.

[0052] In one embodiment, the passive low-pass filter further includes a base layer and a ground metal layer; Here, the first resonant module 103 and the second resonant module 104 are formed on a base layer, and the first damping module 105 and the second damping module 106 are connected to a ground metal layer via a through-hole structure.

[0053] Specifically, the capacitors in the low-pass filter are all formed on the base layer using a thin-film integrated passive device (IPD) process, and are composed of a top metal layer, a bottom metal layer, and an intermediate insulating layer added between the top metal layer and the bottom metal layer.

[0054] Optionally, the bottom metal surface is further fitted with a ground metal layer to form a sheath or shield layer, and adopts one or more of the following grounding schemes: single point grounding, mid-point grounding, both ends grounding, and cross-connected interconnections.

[0055] Preferably, the interlayer dielectric may be, but is not limited to, a silicon nitride interlayer dielectric.

[0056] In one embodiment, the base layer is a conductive surface layer of semiconductor material arsenide, and the thickness of the base is 100±5 μm. Specifically, the base layer is a single-layer substrate, and the base layer may be a gallium arsenide (GaAs) substrate, or may be other semiconductor materials such as silicon. When the thickness of the base layer is ≦200 μm, the thickness of the base layer 10 is preferably 100 μm, but the specific base thickness is selected according to the function.

[0057] In another embodiment, the passive low-pass filter chip is composed of the passive low-pass filter, the base layer and the ground metal layer, and the passive low-pass filter chip has a length of 1.8±0.05 mm, a width of 0.9±0.05 mm, and a height of 0.1±0.05 mm. The low-pass filter of the above size formed based on the thin-film integrated passive component process realizes ultra-miniaturization of the low-pass filter, and is easily applied to various electronic devices that require surface mounting.

[0058] In another embodiment, as shown in FIG. 4 and FIG. 5, FIG. 4 is a curve diagram of the input port return loss S11 and the output port return loss S22 of the low-pass filter having a passband frequency of 0.5 GHz according to an embodiment of the present application, and FIG. 5 is a curve diagram of the stopband suppression S21 of the low-pass filter having a passband frequency of 0.5 GHz according to an embodiment of the present application. The input port return loss S11 of the low-pass filter is less than -16.0 dB in the entire 0 to 0.5 GHz band, which indicates that the low-pass filter of this embodiment has a small loss of reflection and return after passing through the main circuit and each resonant branch circuit, and the low-pass filter has reached impedance matching. The stopband suppression S21 of the low-pass filter is greater than -1.82 dB in the entire 0 to 0.5 GHz band, which indicates that the insertion loss of the low-pass filter is small and the transmission characteristics are good. At 1.068GHz, S21<-20dB, at 1.3GHz, S21<-40dB, which indicates that the low-pass filter has good rectangular coefficient and steep cutoff frequency. At 1.25~8GHz, S21<-35dB, which indicates that the low-pass filter has high out-of-band suppression characteristics.

[0059] In one embodiment, the low-pass filter circuit includes a radio frequency input module 101, a radio frequency output module 102, a plurality of resonant modules and a plurality of attenuation modules, and the radio frequency input module 101, the radio frequency output module 102, the plurality of resonant modules and the plurality of attenuation modules are respectively connected to a passive low-pass filter.

[0060] In the above embodiments, the description of each embodiment is focused on, and for the parts that are not detailed or described in an embodiment, reference can be made to the relevant descriptions of other embodiments.

[0061] The above examples are for illustrating the technical solutions of the present application, but are not limited thereto. Although the present application has been described in detail with reference to the above examples, those skilled in the art may still modify the technical solutions described in the above examples or make equivalent substitutions for some technical features therein. These modifications or substitutions shall all be included within the protection scope of the present application, without departing from the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

[0062] For convenience and simplicity of explanation, only the division of each of the above functional units and circuits is given as an example. In actual applications, the above functions can be assigned to different functional units and circuits as necessary, that is, the internal structure of the device can be divided into different functional units or circuits to complete all or part of the above-described functions. Each functional unit and circuit in the embodiment may be integrated into one processing unit, each unit may exist physically alone, or two or more units may be integrated into one unit. The integrated unit may be realized as hardware or as a software functional unit. In addition, the specific names of each functional unit and circuit are used to distinguish each other, and do not limit the scope of protection of the present application. For the specific operation process of the units and circuits in the above system, reference may be made to the corresponding process in the embodiment of the above method, and the description will be omitted here.

[0063] In the above embodiments, the description of each embodiment is focused on, and for the parts that are not detailed or described in an embodiment, reference can be made to the relevant descriptions of other embodiments. [Explanation of symbols]

[0064] 101 Radio Frequency Input Module 102 Radio Frequency Output Module 103 First Resonant Module 104 A plurality of second resonant modules 105 First damping module 106 Multiple Secondary Attenuation Modules

Claims

1. A passive low-pass filter, a radio frequency input module for receiving a radio frequency signal, mixing and processing the radio frequency signal, and outputting a first radio frequency signal; a first resonator module coupled to the radio frequency input module, the first resonator module adjusting a frequency of the first radio frequency signal to output a second radio frequency signal at a predetermined passband frequency; a first attenuation module coupled to the first resonator module, the first attenuation module attenuating clutter signals in the second radio frequency signal; a plurality of second resonant modules connected in series and coupled to the first resonant module, the second resonant modules adjusting a frequency of the second radio frequency signal; a plurality of second attenuation modules, each having a first end coupled to a common node between adjacent second resonant modules and a second end grounded, the second attenuation modules attenuating clutter signals in the second radio frequency signal to generate a third radio frequency signal; a radio frequency output module connected to the plurality of series-connected second resonant modules and configured to output the third radio frequency signal. Passive low pass filter.

2. the first resonant module includes a first inductor and a first capacitor, a first end of the first inductor and a first end of the first capacitor are commonly connected to the radio frequency input module, and a second end of the first inductor and a second end of the first inductor are commonly connected to the second resonant module; 2. The passive low-pass filter of claim 1.

3. Each of the second resonant modules includes a second inductor and a second capacitor, and the second inductor and the second capacitor are connected in parallel.

3. The passive low-pass filter of claim 2.

4. The first damping module includes at least one capacitor, the at least one capacitor having a first end connected to the first resonant module and a second end connected to ground.

4. The passive low-pass filter of claim 3.

5. the first inductor and the second inductor are spiral inductors or rectangular inductors; 4. The passive low-pass filter of claim 3.

6. the first capacitor and the second capacitor have a metal-dielectric-metal structure; 4. The passive low-pass filter of claim 3.

7. The passive low-pass filter further includes a base layer and a ground metal layer; the first resonant module and the second resonant module are formed on the base layer, and the first damping module and the second damping module are connected to the ground metal layer through a through-hole structure; 2. The passive low-pass filter of claim 1.

8. The material of the base layer is a gallium arsenide material, and the thickness of the base layer is 100±5 μm; 8. A passive low-pass filter according to claim 7.

9. The radio frequency input module and the radio frequency output module are both coplanar port structures; 9. A passive low-pass filter according to claim 8.

10. A low-pass filter circuit comprising the passive low-pass filter according to any one of claims 1 to 9.

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