Integrated gradually-changing single-cone antenna system

Abstract

The invention discloses an integrated gradually-changing single-cone antenna system which is formed by cascading an unbalanced feed broadband oscillator antenna and a broadband matching network. The non-balanced feed broadband oscillator antenna is powered on based on an SMA interface, and is connected with an SMA inner core and an external ground respectively through a gradual change cone and a hemming disc in a screw mode, so that stable electrical and mechanical coupling is realized; the broadband matching network adopts a two-port structure of a coaxial interface, is composed of four sub-networks, and can carry out broadband matching on a plurality of load impedances changing along with frequency. The low-frequency performance and the high-frequency performance are both considered through the tapered gradual change design, the working frequency band is expanded, the impedance mismatch of the low-frequency band is effectively reduced, and the high-frequency radiation efficiency is improved; meanwhile, the broadband complex impedance matching unit formed by cascading the L-shaped network, the n-shaped network, the L-shaped network and the R-C network in four stages is adopted, accurate matching of a plurality of load impedances changing along with the frequency is achieved, and therefore the working efficiency and the radiation performance of the system are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic waves, and particularly relates to an integrated tapered monopole antenna system. BACKGROUND

[0002] In a conventional partial discharge detection device, an antenna is designed in a monopole, a spiral antenna or a logarithmic periodic antenna structure. The monopole antenna has a simple structure, but in a low frequency band (such as 30-300 MHz), impedance mismatch occurs due to insufficient electrical length, the voltage standing wave ratio (VSWR) is significantly increased, and the radiation efficiency is decreased. The spiral antenna can expand the low frequency response by increasing the number of turns, but the resonance point is deviated due to the parasitic capacitance effect in a high frequency band (such as 1 GHz or above), and the bandwidth is limited. The logarithmic periodic antenna has a wideband characteristic, but it is difficult to integrate into a ceiling-mounted device due to its large size, and the directivity diagram is easily distorted at low frequencies.

[0003] In terms of impedance matching, the conventional method mainly adopts a fixed LC matching network or a single-stage transformer matching, which can only be optimized for a narrow frequency band and is difficult to cover the wide frequency range (such as 300 MHz-3 GHz) required for partial discharge detection. When the load impedance changes nonlinearly with frequency, such methods will cause signal reflection loss to be intensified, dynamic range to be compressed, and weak signal detection sensitivity to be reduced. In addition, the conductor loss caused by the skin effect at high frequencies will further deteriorate the radiation efficiency, causing the signal-to-noise ratio (SNR) of the antenna to decrease in a strong interference environment.

[0004] The integrated tapered monopole antenna is an antenna structure combining tapered design and wideband impedance matching technology. Through the optimization design of geometric parameters, the antenna can effectively improve the working performance in a wide frequency range. By adjusting the height, bottom radius and taper angle of the cone, precise control of low and high frequency electromagnetic waves can be achieved, meeting the requirements of wideband, high gain and directivity. This design enables the antenna to have good frequency adaptability and electromagnetic performance in complex application environments.

[0005] In order to solve the problems of impedance mismatch at low frequencies and low radiation efficiency at high frequencies in conventional ceiling-mounted partial discharge detection devices, the integrated tapered monopole antenna adopts a tapered structure design. By optimizing the geometric parameters of the cone, the impedance matching capability at low frequencies is enhanced, and the radiation efficiency at high frequencies is improved. In addition, this design takes into account the wideband characteristics, ensuring stable operation of the antenna in a wide frequency range.

[0006] The linear response dynamic range of electromagnetic waves is an important parameter of partial discharge detection equipment, which directly affects the accuracy and stability of measurement. In view of the deficiency of traditional antenna in the linear response of strong and weak signals, the integrated tapered monopole antenna introduces a wideband complex impedance matching technology, through the four-stage cascade design of L-type, Π-type and R-C network, realizes the accurate matching of complex load impedance changing with frequency, and improves the linear dynamic response range of the equipment. SUMMARY

[0007] The present application aims to solve the problems in the prior art and provides an integrated tapered monopole antenna system. The system is designed for a gigahertz transverse electromagnetic wave (GTEM) cell, which can effectively enhance the effective height of the antenna, while meeting the demand of ceiling-mounted partial discharge detection probe for wideband adaptation, and significantly improving the performance and applicability of the system in a wide frequency range.

[0008] The technical solution for achieving the purpose of the present application is an integrated tapered monopole antenna system, which is powered by an SMA interface and consists of a tapered cone and a rolled edge disc. The matching network adopts a two-port structure with a coaxial interface, which is composed of four sub-networks.

[0009] The length and taper angle of the tapered cone are optimized, with a half taper angle of about 8°, and the impedance matching is improved through the tapered structure of the tapered monopole antenna.

[0010] The height h of the monopole antenna, the angle θ between the side of the monopole antenna and the height of the monopole antenna, and the radius r of the bottom surface of the monopole antenna are related as shown in the formula: h

[0011]

[0012] Where θ h satisfies the following relationship:

[0013]

[0014] Where Zc is the characteristic impedance, with a value of 50 ohms; η0 is the wave impedance of free space, about 377 ohms.

[0015] According to the angle θ between the generatrix of the monopole antenna and the height of the monopole antenna h and the height h, the length of the generatrix of the monopole antenna is determined as shown in the formula:

[0016]

[0017] ​The radius of the crimped disc is optimally designed as 13.67 times the diameter of the outer grounding part of the SMA interface. Through this optimal design, the uniformity of the electromagnetic field distribution is significantly improved, thereby enhancing the performance of the antenna in a wide frequency range. This uniform electromagnetic field distribution not only effectively improves the working efficiency of the antenna, but also improves its radiation performance, ensuring efficient signal transmission and radiation characteristics in a wide frequency band.

[0018] An insulating gasket is arranged at the connection between the tapered cone and the crimped disc to enhance mechanical stability, prevent electrical short circuit, and ensure the stability and reliability of the system when working at high frequencies.

[0019] The tapered cone and the crimped disc are connected with the inner core and the outer grounding part of the SMA interface respectively through screw joints to form a firm mechanical coupling structure, ensuring high reliability and stability of the antenna during use.

[0020] A broadband complex impedance matching network includes network 1, network 2, network 3 and network 4 connected in sequence, which can accurately match the complex load impedance varying with frequency in a wide frequency range.

[0021] The network 1 is an L-shaped network composed of a parallel short-circuit microstrip line and a series transmission line;

[0022] The network 2 is a Π-shaped network composed of a first capacitor connected in parallel, a first inductor connected in series and a second capacitor connected in parallel;

[0023] The network 3 is an L-shaped network composed of a second inductor connected in series and a third capacitor, a fourth capacitor and a third inductor connected in parallel in sequence;

[0024] The network 4 is an R-C network composed of a first resistor connected in series and a fifth capacitor connected in parallel.

[0025] Compared with the prior art, the present application has the following beneficial effects. By designing the tapered structure of the tapered monopole antenna and the broadband complex impedance matching network, the lower limit of the frequency of the antenna can be effectively reduced, and the antenna can work in a wider frequency range. The tapered structure adjusts the geometric shape of the antenna (such as the taper angle and the taper radius), which helps to improve the impedance matching at low frequencies, reduce low-frequency reflection, and improve the low-frequency response capability of the antenna. The broadband network structure is simple to implement, can realize broadband impedance matching for complex load impedance, and has good matching effect. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a schematic diagram of an integrated tapered monopole antenna system in one embodiment.

[0027] Figure 2 It is a top view and a side view of a disc bottom plate in one embodiment.

[0028] Figure 3 Top view and side view of a tapered cone for one embodiment;

[0029] Figure 4 Top view and side view of an insulating spacer for one embodiment;

[0030] Figure 5 Top view and side view of a circular fence for one embodiment;

[0031] Figure 6 Comparison of effective height of a tapered single cone antenna and a double monopole probe for one embodiment;

[0032] Figure 7 Circuit schematic of a wideband complex impedance matching network transmission line structure for one embodiment.

[0033] Figure 8 Circuit schematic of a wideband complex impedance matching network transmission line lumped element hybrid structure for one embodiment.

[0034] Figure 9 Corresponding layout for one embodiment Figure 8 Corresponding layout for one embodiment Corresponding layout for one embodiment

[0035] Corresponding layout for one embodiment Figure 10 Corresponding layout for one embodiment Corresponding layout for one embodiment

[0036] Corresponding layout for one embodiment Figure 11 Corresponding layout for one embodiment Corresponding layout for one embodiment

[0037] Corresponding layout for one embodiment Figure 12 Corresponding layout for one embodiment Figure 7 Corresponding layout for one embodiment Figure 8 Corresponding layout for one embodiment DETAILED DESCRIPTION

[0038] This invention proposes an integrated tapered monoconical antenna system, primarily used to enhance the effective antenna height in a gigahertz transverse electromagnetic wave (GTEM) chamber and meet the broadband adaptation requirements of ceiling-mounted partial discharge detection probes. Addressing the shortcomings of current ceiling-mounted partial discharge detection equipment in terms of broadband characteristics at high effective heights and the limited dynamic range of linear response to strong and weak signals, this invention employs a tapered tapered design to balance low-frequency and high-frequency performance. This expands the operating frequency band, effectively reduces impedance mismatch in the low-frequency band, and improves high-frequency radiation efficiency. Simultaneously, a broadband complex impedance matching unit composed of four cascaded stages of L-type, Π-type, L-type, and RC networks is used to accurately match the complex load impedance that varies with frequency, thereby significantly improving the system's operating efficiency and radiation performance. To further enhance low-frequency response, improve antenna radiation directivity, and reduce sidelobes and environmental interference, this invention also utilizes a circular base plate and surrounding plate structure within the GTEM chamber, significantly improving measurement accuracy and field distribution consistency. The above design not only ensures system stability under complex operating conditions and meets the requirements of high effective height and wide bandwidth, but also significantly extends the dynamic range of linear response for strong and weak signal detection, thereby ensuring more accurate measurement and analysis. This invention has wide applications in electromagnetic compatibility testing, sensor calibration, electromagnetic radiation research, and performance evaluation of radar and communication systems. It can significantly improve antenna performance from low to high frequencies and achieve more accurate measurement and calibration results in practical applications.

[0039] The integrated tapered monocone antenna system of this invention, through its optimized tapered cone and rolled-edge disk structure combined with a broadband matching network, effectively improves the antenna's effective height and radiation performance. In traditional antenna design, broadband impedance matching and high-frequency radiation efficiency often present performance bottlenecks. This invention, through the optimized design of the tapered cone, solves the impedance mismatch problem in the low-frequency band and improves radiation efficiency in the high-frequency band. Combined with a four-stage cascaded broadband matching network, the system can accurately match the complex load impedance that varies with frequency, significantly improving operating efficiency and broadband response, further ensuring the antenna's stable performance in high-frequency electromagnetic field measurements.

[0040] This invention provides an integrated monoconical antenna system to enhance the effective antenna height, consisting of an unbalanced fed broadband dipole antenna and a broadband matching network cascaded together.

[0041] The unbalanced fed broadband dipole antenna is powered by an SMA interface. It consists of a tapered cone and a rolled-edge disk connected to the inner core of the SMA and the external ground via screw threads, respectively, to achieve stable electrical and mechanical coupling.

[0042] The broadband matching network adopts a two-port structure of a coaxial interface, is composed of four sub-networks, and can match complex load impedance varying with frequency in a broadband manner to meet the needs of high-frequency electromagnetic field measurement and analysis.

[0043] Further, the length and the taper angle of the tapered cone are designed and optimized, and the half taper angle is about 8° to realize broadband impedance matching and low return loss.

[0044] Further, the height h of the tapered cone, the angle θ between the side of the tapered cone and the height of the tapered cone, and the radius r of the bottom surface of the tapered cone satisfy the following formula: h

[0045] (1) ;

[0046] Further, θ h satisfies the following relationship:

[0047] (2) ;

[0048] wherein Zc is the characteristic impedance, and the value is 50 ohms; η0 is the wave impedance of free space, and is about 377 ohms.

[0049] Further, the length of the generatrix of the single-cone antenna is determined according to the angle θ between the generatrix of the single-cone antenna and the height of the single-cone antenna and the height h, as shown in the following formula: h

[0050] (3) ;

[0051] Through the cooperative optimization of the formulas (1) to (3), it is ensured that the tapered cone can provide stable electrical performance and broadband impedance matching.

[0052] Further, the radius of the crimped disc is about 13.67 times the diameter of the outer grounding part of the SMA interface, which is determined by full-wave simulation to optimize the uniformity of electromagnetic field distribution.

[0053] Further, the tapered cone is placed upside down in the center of the crimped disc, and an insulating gasket is arranged between the tapered cone and the crimped disc through the screw joint to enhance the mechanical stability and prevent electrical short circuit.

[0054] Further, the tapered cone and the crimped disc are connected with the inner core and the outer grounding part of the SMA interface through screw joints respectively, forming a firm mechanical coupling structure to ensure that the antenna has high reliability and stability during use.

[0055] ​​In view of the deficiency of the traditional antenna in linear response of strong and weak signals, the integrated gradually changing single cone antenna introduces a broadband complex impedance matching technology, and through four-stage cascade design of L-type, Π-type and R-C network, the complex load impedance varying with frequency is accurately matched.

[0056] Further, TL1 and TL2 in the network 1 are sequentially cascaded transmission lines, TL3 is a short-circuit stub line and is connected with the transmission line TL1. One end of the transmission line TL2 is connected with the transmission line TL1 in series, and the other end is connected with the network 2.

[0057] Further, the network 2 is a Π-type network composed of a first capacitor C1 in parallel, a first inductor L1 in series, and a second capacitor C2 in parallel. The common end of the first capacitor C1 and the first inductor L1 is connected with the network 1, the other end of the first capacitor C1 is grounded, the common end of the first inductor L1 and the second capacitor C2 is connected with the network 3 as an output end of the network 2, and the other end of the second capacitor C2 is grounded.

[0058] Further, the network 3 is composed of a second inductor L2 in series and a third capacitor C3, a fourth capacitor C4 and a third inductor L3 in parallel. One end of the second inductor L2 in series is connected with the network 2, and the other end is connected with the common end of the third capacitor C3, the fourth capacitor C4 and the third inductor L3. The parallel common end of the third capacitor C3, the fourth capacitor C4 and the third inductor L3 is connected with the network 4 as an output end of the network 3, and the other end is grounded respectively.

[0059] Further, the network 4 is an R-C network composed of a first resistor R1 in series and a fifth capacitor C5 in parallel. One end of the first resistor R1 is connected with the output end of the network 3, the other end is connected with one end of the fifth capacitor C5 as an output end, and the other end of the fifth capacitor C5 is grounded.

[0060] Embodiment

[0061] The embodiment provides an integrated single cone antenna system, which is composed of a non-balanced feeding broadband dipole antenna and a broadband matching network in cascade, and has high efficient broadband performance. Specifically, the non-balanced feeding broadband dipole antenna is powered through an SMA interface, adopts a structure design of a gradually changing cone and a curled edge disc, and is connected with the inner core and the outer ground of the SMA interface through a screw port respectively, so as to realize stable and reliable electrical and mechanical coupling, and ensure the stability of signal transmission and the mechanical strength of the structure. In addition, the broadband matching network adopts a two-port structure of a coaxial interface, is composed of four sub-networks in cascade, accurately matches the complex load impedance varying with frequency, and significantly improves the adaptability and working efficiency of the system in high-frequency electromagnetic field measurement and analysis.

[0062] In the embodiment, the top view and the side view of the circular bottom plate of the non-balanced feeding broadband dipole antenna are as followsFigure 2 As shown, the structure of the circular base plate is designed as a uniform thickness conductive metal plate with a diameter of 260 mm, which has good mechanical strength and conductivity. A surrounding plate is installed outside the base plate and is fixed by mechanical connection. The surrounding plate extends uniformly along the edge of the base plate and is used to improve the mechanical stability of the structure and optimize the electromagnetic field distribution. Various types of through holes are provided on the base plate, including a through hole with a central diameter of 10 mm for the interface of the feed cable, a plurality of M3 through holes with a diameter of 3 mm for bolt fixation, and six through holes with a diameter of 8.2 mm and four through holes with a diameter of 7 mm uniformly distributed on the periphery, wherein the 7 mm through holes are designed with a 90° counterbore for bolt head embedding.

[0063] In this embodiment, the top view and side view of the circular base plate of the non-balance feed broadband dipole antenna are as shown in Figure 3 As shown, the structure of the tapered cone is designed as a truncated cone with a linearly tapered side surface. The overall height of the tapered cone is 37 mm, the lower base diameter is 14 mm, the upper base diameter is 3.6 mm, and the half-cone angle of the tapered cone is about 8°. The upper base is a small circular flat surface with a diameter of 3.6 mm, and a M3 threaded hole is provided in the center with a threaded depth of 10 mm for fixed connection with the inner core of the SMA interface to ensure mechanical stability and feed signal transmission. The lower base is a large circular flat surface with a diameter of 14 mm for mechanical connection and electrical grounding with the flanged disc.

[0064] In this embodiment, the top view and side view of the gasket of the non-balance feed broadband dipole antenna are as shown in Figure 4 As shown, the structure of the gasket is designed as a circular flat plate with an outer diameter of 9.8 mm, an inner diameter of 3 mm, and a thickness of 3 mm. The gasket is fixed with other components through the center through hole to provide mechanical support and electrical isolation, ensuring the stability and reliability of the connection.

[0065] In this embodiment, the top view and side view of the surrounding plate of the non-balance feed broadband dipole antenna are as shown in Figure 5 As shown, the structure of the surrounding plate is designed as a circular ring-shaped metal plate with a height of 37 mm, an outer diameter of 268 mm, and an inner diameter of 260 mm. Six M3 threaded holes are uniformly distributed on the inner side of the surrounding plate with a threaded depth of 6 mm for fixed connection with the base plate through bolts. The ring-shaped structure of the surrounding plate provides good mechanical strength and effectively improves the mechanical stability and electromagnetic performance of the overall system in cooperation with the base plate.

[0066] In this embodiment, the effective height of the tapered single-cone antenna is as shown in Figure 6 As can be seen, the effective height of the high-frequency band of the single-cone antenna with a tapered structure is effectively improved, thereby effectively improving the high-frequency working characteristics of the single-cone antenna.

[0067] In this embodiment, the antenna input impedance as a function of frequency is shown in the figure. Figure 10 As shown, the curve of S11 before matching as a function of frequency is as follows: Figure 11 As shown, the present invention provides a... Figure 8 The broadband complex impedance matching network shown has a return loss of less than 17 dB for the matched antenna S11 in the frequency band of 1.5 GHz to 2.5 GHz.

[0068] First, the antenna impedance is cascaded sequentially with a low-impedance microstrip line and a small resistor to obtain a relatively smooth impedance change curve. Then, a broadband matching network consisting of transmission lines TL1, TL2, TL3, TL4, and TL5 is cascaded, as follows: Figure 7 As shown. The specific parameter calculation process is as follows: The poles of the passband (1.5 GHz to 2.5 GHz) Inner Chebyshev filter are selected as sampling points, and impedance matching is performed at each sampling point. Then, the following parameters are calculated: Figure 1 Characteristic impedance and electrical length of transmission lines: Z1=53.5Ω, Z2=26.3Ω, Z3=8.3Ω, Z4=74.6Ω, Z5=4Ω, Z6=1.5Ω. =180° 2 = 90.8° 3 = 90° 4 = 90° 5 = 90° 6 = 90°. The antenna passes through... Figure 7 The return loss curve S11 after the transmission line circuit matching is shown in the figure. Figure 12 As shown by the blue line.

[0069] Furthermore, since smaller characteristic impedances (such as TL3, TL5, TL6) are difficult to realize on microstrip lines, TL3 is equivalent to... Figure 8 The Π-shaped network in the diagram, i.e., network 2, has L1 = 1.2 nH, C1 = 8.3 pF, and C2 = 8.5 pF; TL5 is equivalent to... Figure 8 The L-shaped network in the diagram, i.e., network 3, has L2 = 1.2nH, L3 = 1.5nH, C3 = 12pF, and C4 = 10pF; TL6 is equivalent to an LC network, and after circuit simplification, it forms a network with resistor R1. Figure 8 Network 4 in the diagram, where C5 = 7pF. The antenna passes through... Figure 8 The return loss S11 curve after matching the hybrid circuit of the lumped element transmission line shown is as follows: Figure 12 As shown by the red line, it can be seen that after transforming the difficult-to-implement small characteristic impedance transmission line into an easily implemented lumped element, the matching effect remains almost unchanged. The center frequency of the matching circuit is 1 GHz, and S11 is below -17 dB in the 0.5 GHz-1.5 GHz frequency band.

[0070] As a specific example, an FR4 dielectric substrate with a dielectric constant of 4.6 and a thickness of 0.508 mm was selected.

[0071] In summary, the broadband transmission line lumped element hybrid circuit matching structure proposed in this invention is simple, can realize a broadband matching network with a fractional bandwidth of up to 100%, and has high integration and is easy to implement.

[0072] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An integrated tapered monocone antenna system, characterized in that, The system includes an unbalanced-fed broadband dipole antenna cascaded with a broadband matching network. The unbalanced-fed broadband dipole antenna is powered by an SMA interface and is connected to the SMA inner core and external ground via screw threads, respectively, to achieve stable electrical and mechanical coupling. The broadband matching network adopts a two-port structure with a coaxial interface and includes four sub-networks, which can perform broadband matching of complex load impedances that vary with frequency.

2. The integrated tapered monocone antenna system according to claim 1, characterized in that: The length and cone angle of the gradient cone have been optimized, and the height of the gradient cone... The angle between the side of the gradient cone and the height of the gradient cone. and the base radius of the gradient cone The relationship is shown in formula (1): （1）； in The following relationship must be satisfied: （2）； Among them, Z c η is the characteristic impedance, with a value of 50 ohms; η0 is the free space wave impedance; the impedance characteristics of the tapered cone are determined by the parameter design of formula (1) and formula (2).

3. The integrated tapered monocone antenna system according to claim 2, characterized in that: Based on the angle between the generatrix of the gradient cone and the height of the gradient cone and height The generatrix length of the gradient single cone is determined as shown in formula (3): （3）。 4. The integrated tapered monocone antenna system according to claim 1, characterized in that: The radius of the rolled-edge disk is 13.67 times the diameter of the external grounding portion of the SMA interface, determined by full-wave simulation, to optimize the uniformity of the electromagnetic field distribution.

5. The integrated tapered monocone antenna system according to claim 1, characterized in that: An insulating gasket is provided at the threaded connection between the tapered cone and the rolled-edge disk to enhance mechanical stability and prevent electrical short circuits.

6. The integrated tapered monocone antenna system according to claim 1, characterized in that: The tapered cone and rolled-edge disk are connected to the inner core and outer grounding part of the SMA interface respectively via screw threads, forming a robust mechanical coupling structure to ensure high reliability and stability of the antenna during use.

7. The integrated tapered monocone antenna system according to claim 1, characterized in that: The broadband matching network includes network 1, network 2, network 3 and network 4 cascaded in sequence. Network 1 is an L-shaped network composed of parallel short-circuited microstrip lines and series transmission lines. TL1 and TL2 are cascaded transmission lines, and TL3 is a short-circuited stub line connected to transmission line TL1. One end of transmission line TL2 is connected to the series transmission line TL1, and the other end is connected to network 2.

8. The integrated tapered monocone antenna system according to claim 7, characterized in that: Network 2 is a Π-shaped network formed by a first capacitor C1 connected in parallel, a first inductor L1 connected in series, and a second capacitor C2 connected in parallel. The common terminal of the first capacitor C1 and the first inductor L1 is connected to network 1, and the other terminal of the first capacitor C1 is grounded. The common terminal of the first inductor L1 and the second capacitor C2 is connected to network 3 as the output terminal of network 2, and the other terminal of the second capacitor C2 is grounded.

9. The integrated tapered monocone antenna system according to claim 8, characterized in that: Network 3 includes a second inductor L2 connected in series and a third capacitor C3, a fourth capacitor C4, and a third inductor L3 connected in parallel. One end of the second inductor L2 is connected to network 2, and the other end is connected to the common terminal of the third capacitor C3, the fourth capacitor C4, and the third inductor L3. The common terminal of the third capacitor C3, the fourth capacitor C4, and the third inductor L3 is connected to network 4 as the output terminal of network 3, and the other end is grounded.

10. The integrated tapered monocone antenna system according to claim 9, characterized in that: Network 4 consists of an RC network composed of a first resistor R1 connected in series and a fifth capacitor C5 connected in parallel; one end of the first resistor R1 is connected to the output terminal of network 3, and the other end is connected to the load as the output terminal along with one end of the fifth capacitor C5, while the other end of the fifth capacitor C5 is grounded.

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