A Ku-band miniaturized low-noise amplifier

Abstract

The present invention discloses a miniaturized low-noise amplifier for Ku band, comprising: a cascaded first-stage amplifier circuit, a second-stage amplifier circuit, and a bias circuit for biasing the first-stage amplifier circuit and the second-stage amplifier circuit respectively, an interstage low-pass filter is arranged between the first-stage amplifier circuit and the second-stage amplifier circuit, and an output low-pass filter is arranged at the output end of the second-stage amplifier circuit. The noise of the two-stage cascade amplifier of the present invention is only increased by 0.15dB, the gain is almost twice the original gain, the gain flatness is less than 0.65dB, and the input and output are well matched.

Description

Technical Field

[0001] The invention relates to the technical field of signal transmission and reception, and in particular to a miniaturized low-noise amplifier in the Ku band. Background Art

[0002] With the rapid development of communication technology and the improvement of technical means, the requirements for the integration, systematization and miniaturization of communication equipment are getting higher and higher. Low noise amplifier (LNA) is widely used in radar, communication and satellite receiving equipment, and is an important part of microwave receiving system. It is located at the front end of the receiver and requires a small noise factor and a certain gain. In the design of LNA, not only the stability and low noise factor of the amplifier must be considered, but also the gain and amplitude-frequency characteristics must be taken into account. It is a component that is difficult to design accurately.

[0003] This paper establishes an overall integrated miniaturized low-noise amplifier based on the microsystem design principles. It adopts a plastic-sealed amplifier die and an easy-to-process soft substrate. On the basis of a reasonable selection of matching structure, a low-pass filter is added to suppress out-of-band interference, and various indicators are optimized. The cost is low and the performance is stable and reliable. Summary of the invention

[0004] The purpose of the present invention is to provide a miniaturized low noise amplifier in Ku band, which is suitable for Ku band satellite communication receiving channel. The miniaturized low noise amplifier is established based on the microsystem design principle, adopts a two-stage heterojunction FET tube cascade structure, and adds a low-pass filter to suppress out-of-band interference on the basis of a reasonable selection of matching structure. The matching circuit is optimized and designed. The results show that the product has a noise figure of less than 1.55dB, a gain of more than 24dB, and good input and output matching in the working frequency band of 12GHz to 13GHz.

[0005] A miniaturized low-noise amplifier for Ku band comprises: a cascaded first-stage amplifier circuit, a second-stage amplifier circuit, and a bias circuit for biasing the first-stage amplifier circuit and the second-stage amplifier circuit respectively, an interstage low-pass filter is arranged between the first-stage amplifier circuit and the second-stage amplifier circuit, and an output low-pass filter is arranged at the output end of the second-stage amplifier circuit.

[0006] Furthermore, the bias circuit is powered by dual power supplies, that is, the negative gate voltage and the positive drain voltage of the transistor are provided by the negative power supply and the positive power supply respectively, and includes a transistor Q2, a first power supply SCR1, a second power supply SCR2, a resistor R3, a resistor R4, a resistor R6, a resistor R7, a resistor R1, a resistor R5, and a resistor R2. The base of the transistor Q2 is connected to the positive electrode of the first power supply SCR1 through the resistor R3, and the base of the transistor Q2 is also connected to the positive electrode of the second power supply SCR2 through the resistor R4. The collector of the transistor Q2 is connected to the negative electrode of the first power supply SCR1 through the resistor R6. The collector of the transistor Q2 is also connected to the input end of the first-stage amplifier circuit through the resistor R7 and the resistor R1 connected in series to form a negative bias. The emitter of the transistor Q2 is connected to the output end of the first-stage amplifier circuit through the resistor R5 and the resistor R2 connected in series to form a positive bias. The common point of the positive electrode of the first power supply SCR1 and the resistor R3 is connected to the ground, and the negative electrode of the second power supply SCR2 is connected to the ground. The common point of the resistor R7 and the resistor R1 is connected to the ground through the capacitor C5, and the common point of the resistor R5 and the resistor R2 is connected to the ground through the capacitor C6.

[0007] Furthermore, a high-resistance line and a fan-shaped open microstrip line are respectively used on the collector and emitter of the transistor Q2 of the bias circuit to form a first choke circuit and a first feeding circuit. The first choke circuit is used to choke and isolate the alternating current to prevent the influence of high-frequency signals on the DC circuit. The first choke circuit includes: a fan-shaped microstrip line TL1, a T-type microstrip line TL2, a microstrip transmission line TL3, and a combined transmission structure TL4. The ends 1 and 2 of the T-type microstrip line TL2 are respectively connected to one end of the fan-shaped microstrip line TL1 and the combined transmission structure TL4, and the end 3 of the T-type microstrip line TL2 is connected to one end of the microstrip transmission line TL3.

[0008] Furthermore, the combined transmission structure TL4 includes an arc-shaped microstrip line TL401, a middle microstrip transmission line LT402, and an arc-shaped microstrip line LT403. The two ends of the arc-shaped microstrip line LT401 are respectively connected to the two ends of the T-shaped microstrip line LT2 and one end of the middle microstrip transmission line LT402, and the two ends of the arc-shaped microstrip line LT403 are respectively connected to the other end of the middle microstrip transmission line LT402 and the three ends of the T-shaped microstrip line LT5.

[0009] Furthermore, the first-stage amplifier circuit adopts a heterojunction FET tube NB1, the gate and drain of the heterojunction FET tube NB1 are respectively connected to a first input matching circuit and a first output matching circuit, and the circuit structure of the first output matching circuit is the same as that of the first input matching circuit.

[0010] Furthermore, the first choke circuit is connected to the bias circuit via the microstrip transmission line TL3, and the first choke circuit is connected to the gate of the heterojunction FET tube NB1 via the first input matching circuit.

[0011] Furthermore, the first input matching circuit includes a microstrip transmission line TL8, a microstrip transmission line TL7, a T-type microstrip line TL5, a microstrip transmission line TL6, which are sequentially connected in series with the gate of the heterojunction FET tube NB1, and a short section of line TL9 connected in parallel between the microstrip transmission line TL7 and the microstrip transmission line TL8. The three ends of the T-type microstrip line TL5 are connected to the other end of the combined transmission structure TL4, and a T-type microstrip line TL10 is connected at the parallel connection to prevent large impedance jumps.

[0012] Furthermore, the source of the heterojunction FET tube NB1 is connected to the ground.

[0013] Furthermore, the second stage amplifier circuit adopts a heterojunction FET tube NB1, the gate and drain of the heterojunction FET tube NB1 are respectively connected to a second input matching circuit and a second output matching circuit, and the circuit structures of the second input matching circuit and the second output matching circuit are respectively the same as the first input matching circuit and the first output matching circuit.

[0014] Furthermore, the input end of the second-stage amplifier circuit is connected to the inter-stage low-pass filter through a first Γ-type matching circuit, and the output end of the second-stage amplifier circuit is connected to the output low-pass filter through a second Γ-type matching circuit.

[0015] Furthermore, the inter-stage low-pass filter and the output low-pass filter adopt a stump-type structure, including multiple sections of high-impedance microstrip lines, multiple sections of low-impedance microstrip lines and multiple matching blocks; wherein the high-impedance microstrip line is connected in series in the circuit as an inductive circuit; the low-impedance microstrip line is connected in parallel in the circuit as a capacitive circuit; the high-impedance microstrip line and the low-impedance microstrip line are alternately connected; and the matching block is formed at the connection between the high-impedance microstrip line and the low-impedance microstrip line.

[0016] Furthermore, the bias circuit, the second choke circuit, and the second feed circuit of the second stage amplifier circuit have the same circuit structures as the bias circuit, the first choke circuit, and the first feed circuit of the first stage amplifier circuit, respectively.

[0017] Furthermore, the input form of the low noise amplifier is a coaxial probe vertical input.

[0018] Furthermore, the feeding circuit includes two mutually perpendicular high-impedance microstrip lines, and a fan-shaped open-circuit branch is provided at the perpendicular intersection.

[0019] Because the bias circuit of the Ku-band miniaturized low noise amplifier is connected in parallel to the transmission line of the LNA, it will inevitably affect the signal transmission. Therefore, a choke circuit needs to be added near the transmission line. It is usually composed of a quarter-wavelength transmission line and a distributed fan-shaped capacitor to prevent the high-frequency signal from affecting the DC circuit and preventing it from entering the DC circuit, thereby affecting the performance of the circuit.

[0020] The power supply of the Ku-band miniaturized low-noise amplifier is fed through the microstrip line of the output port of each stage of the amplifier circuit. Therefore, similar to the choke circuit, it is also necessary to design a combination of high-impedance lines and fan-shaped capacitors to prevent microwave signals from entering the power line. This structure has a very small impact on the transmission of the main signal.

[0021] The invention has the following beneficial effects:

[0022] 1. During the design, interdigital capacitors are used to isolate DC between the input and output and between the two stages; a high-resistance line and a fan-shaped open-circuit microstrip line are used in the DC bias circuit to form a choke circuit to choke and isolate the alternating current to prevent the influence of high-frequency signals on the DC circuit; and negative feedback is used to increase the stability of the amplifier;

[0023] 2. The results show that compared with the single-stage amplifier, the noise of the two-stage cascade amplifier increases by only 0.15dB, the gain is almost twice the original gain, the gain flatness is less than 0.65dB, and the input and output are well matched. Therefore, the overall performance meets the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the amplifier cascade of the present invention;

[0025] Figure 2 The stability judging circuit diagram of the present invention;

[0026] Figure 3 This is a schematic diagram of the stability judgment result of the present invention;

[0027] Figure 4 Schematic diagram of an LNA active bias circuit of the present invention;

[0028] Figure 5 It is a schematic diagram of parallel admittance matching of the present invention;

[0029] Figure 6 It is a schematic diagram of the noise matching result of the present invention;

[0030] Figure 7 It is a schematic diagram of the gain matching result of the present invention;

[0031] Figure 8 A schematic diagram of the topology of a low-pass filter of the present invention;

[0032] Fig. 9 It is a schematic diagram of a simulation curve of a single low-pass filter of the present invention;

[0033] Fig.10 It is a schematic diagram of a cascade simulation curve of two low-pass filters of the present invention;

[0034] Fig.11 The coaxial to microstrip vertical transition structure of the present invention;

[0035] Fig.12 It is a schematic diagram of the S11 curve of the coaxial to microstrip vertical transition structure of the present invention;

[0036] Fig.13 It is a schematic diagram of the structure of the feeding circuit of the present invention;

[0037] Fig.14 It is a schematic diagram of the S11 curve of the feeding circuit of the present invention;

[0038] Fig.15 is a complete LNA circuit schematic diagram of the present invention;

[0039] Fig.16 It is a schematic diagram of simulation results of a two-stage cascade amplifier of the present invention;

[0040] Fig.17 A schematic diagram of a low noise amplifier according to an embodiment of the present invention;

[0041] Fig.18 A schematic diagram of a first-stage amplifier based on biasing and matching according to an embodiment of the present invention;

[0042] Fig.19 A schematic diagram of a second-stage amplifier based on biasing and matching according to an embodiment of the present invention;

[0043] Fig. 20 is a schematic diagram of a choke circuit according to an embodiment of the present invention;

[0044] Fig.21 A schematic diagram of a combined transmission structure of an embodiment of the present invention;

[0045] Reference numerals: 1 - coaxial probe head, 2 - microstrip line, 3 - fan-shaped open-circuit branch, 4 - mutually perpendicular high-impedance microstrip lines. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0047] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "longitudinal", "lateral", "horizontal", "inside", "outside", "front", "back", "top", "bottom" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation to the present invention.

[0048] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "disposed", "opened", "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] Example

[0050] The amplifier introduced in this article is a two-stage cascade structure. The input end uses a coaxial connector to a microstrip line vertical transition structure. Low-pass filters are added between stages and at the output to suppress out-of-band interference. The power supply is fed from the output microstrip line. Figure 1 As shown, it consists of an amplifier die, a matching network, a bias circuit, a transition structure, a feeding circuit and a low-pass filter.

[0051] (1) Select appropriate devices and DC operating points

[0052] The actual indicators that LNA can achieve depend largely on the selected amplifier core. According to the requirements for gain and noise, as well as the frequency band of application, the heterojunction FET tube NE3210S01 with a very low noise coefficient is selected here. Its minimum noise typical value at 12GHz is 0.35dB, and the gain is 13.5dB, which is a very good one. At the same time, the manufacturer provides a design toolbox for the amplifier tube, which can be used to call the tube model for DC and microwave circuit design, which is very convenient.

[0053] Assume Fn is the noise coefficient of the nth stage and Gn is the power gain of the nth stage, then the noise coefficient cascade formula is as follows:

[0054]

[0055] From the above formula, we can conclude that the noise of the first stage has the greatest impact on the noise of the entire link, and the impact becomes smaller as time goes on. Therefore, the first stage circuit should select the best operating point based on the minimum noise coefficient, and the second stage should consider the optimal gain condition while taking noise into account.

[0056] (2) Determine stability

[0057] One of the first conditions that the amplifier circuit must meet is its stability within the operating frequency band. Stability is divided into absolute stability and conditional stability. In the design, we try to ensure that the amplifier is absolutely stable. If it is difficult to achieve, we must use appropriate matching circuits to avoid the unstable area of ​​the amplifier.

[0058] The criteria for absolute stability are as follows:

[0059] The amplifier is considered as a two-port network, which is determined by the input reflection coefficient ΓIN, the source signal reflection coefficient ΓS, the output reflection coefficient ΓOUT and the load reflection coefficient ΓL. These four reflection coefficients are independent of each other and are determined by S parameters.

[0060] There is feedback S12 inside the amplifier, and the feedback system will inevitably cause stability problems. If the reflection coefficient > 1, the amplitude of the reflected wave exceeds the incident wave, which means that the circuit has positive feedback, resulting in instability. The stability of the amplifier can be judged by the reflection coefficient. Stability means that the modulus of the reflection coefficient is less than 1. Therefore:

[0061] |Γ S |<1

[0062] |Γ L |<1

[0063]

[0064]

[0065] in:

[0066] Δ=S 11 S 22 -S 21 S 12

[0067] The necessary and sufficient conditions for unconditional stability are:

[0068] 1-|S 11 | 2 >|S 12 S 21 |

[0069] 1-|S 22 | 2 >|S12 S 21 |

[0070] K>1

[0071] in:

[0072]

[0073] Further deduction can be obtained

[0074]

[0075] The stability of the tube can be easily seen using EDA tools, such as Figure 2 As shown, NE3210S01 is stable within the working frequency band of this design.

[0076] (3) Design of DC bias circuit

[0077] The function of the bias circuit is to feed direct current to the amplifier core while minimizing the impact on microwave transmission. There are many types of bias circuits and biasing methods. This article selects source grounding, positive and negative dual power supply, and adding a triode for active bias. Although the structure is more complex than passive bias, it can provide a more stable operating point and protect the amplifier core from damage when negative voltage is not applied.

[0078] Because the bias circuit is connected in parallel to the transmission line of the LNA, it will inevitably affect the signal transmission. Therefore, a choke network needs to be added near the transmission line, which is usually composed of a quarter-wavelength transmission line and a distributed fan-shaped capacitor.

[0079] (4) Design matching network

[0080] The design of LNA is mainly about the design of matching network, and the main requirements for the matching network are:

[0081] 1. Match the input and output impedance of active devices with external impedance. Mainly divided into noise matching and gain matching.

[0082] 2. Use the matching network to adjust the transfer function to compensate for the gradual decrease in gain of the amplifier tube within a wide bandwidth.

[0083] First of all, we need to reasonably select the topology of the matching network according to the location of the matching point. The corresponding matching structures of different matching points will be very different. The Ku-band is suitable for using a distributed parameter branch structure. This article first uses a series microstrip transmission line for admittance transformation, and then connects a microstrip open-circuit branch in parallel, using its input admittance as the compensation admittance to achieve circuit matching. This is the commonly used parallel admittance type matching.

[0084] The following model is established for each stage of the amplifier. The matching and bias choke circuits are all implemented on the microstrip board. The DC blocking capacitors are interdigitated capacitors. Different optimization targets are set for the noise of the first stage and the gain of the second stage. After the initial optimization, better simulation results for a single stage can be obtained.

[0085] 2.2 Design of Passive Components

[0086] (1) Low-pass filter

[0087] In this paper, a low-pass filter needs to be added to the LNA to suppress out-of-band interference signals. The microstrip line with high characteristic impedance (inductive) is connected to the microstrip line with low characteristic impedance (capacitive), and a low-pass filter with series inductance and parallel capacitance can be obtained. The tree stump circuit structure is selected to establish the following model:

[0088] A low-pass filter includes: a tree stump structure, including a characteristic high-impedance microstrip line, a characteristic low-impedance microstrip line and a matching block; wherein the high-impedance microstrip line is connected in series as an inductive circuit; the low-impedance microstrip line is connected in parallel as a capacitive circuit; the high-impedance microstrip line and the low-impedance microstrip line are alternately connected; the matching block is formed at the connection between the high-impedance microstrip line and the low-impedance microstrip line. The device has a small size, a simple design process, high performance indicators, saves materials, is easy to process, and is easy to integrate with other microwave circuits.

[0089] like Figure 8 Described, wherein: 1-1, a first high impedance microstrip line, 1-2, a second high impedance microstrip line, 1-3, a third high impedance microstrip line, 1-4, a fourth high impedance microstrip line, 2-1, a first low impedance microstrip line, 2-2, a second low impedance microstrip line, 2-3, a third low impedance microstrip line, 3-1, a first matching block, 3-2, a second matching block.

[0090] The simulation results are as follows Fig. 9 , we can see that the in-band return loss is below -20dB, and the suppression of the right-end stopband is above 15dB, which meets the use requirements. In the actual circuit, two identical filters are placed separately. Through simulation, the cascaded stopband suppression can reach more than 35dB.

[0091] (2) Vertical transition from coaxial to microstrip

[0092] For the convenience of physical connection with the antenna, the input form of LNA is a coaxial probe vertical input. In order to minimize the introduction of mismatch and reduce insertion loss, this paper specifically analyzes and optimizes this transition structure. The following model is established and good results are obtained. The return loss is kept below -20dB in the working frequency band.

[0093] (3) Vertical transition from coaxial to microstrip

[0094] The power supply of the LNA amplifier is fed through the microstrip line of the output port. Therefore, similar to the bias circuit, it is also necessary to design a combination of high-impedance lines and fan-shaped capacitors to prevent microwave signals from entering the power line. The corresponding circuit model is established separately as follows. It can be seen that this structure has a very small impact on the transmission of the main signal.

[0095] 2.3 Overall circuit design

[0096] Although the simulation results of each discrete unit are very good, there may be resonance points when the parts are cascaded, and the performance is deteriorated. Therefore, we need to build a model of the overall circuit. The models of the filter, feed structure and transition structure are imported using the S2P file, and each variable is fine-tuned. The model and simulation results are as follows:

[0097] After simulation, the performance parameters of the two-stage cascade amplifier are as follows: Fig.16 The results show that compared with the single-stage amplifier, the noise of the two-stage cascade amplifier increases by only 0.15dB, the gain is almost twice the original gain, the gain flatness is less than 0.65dB, and the input and output are well matched. Therefore, the overall performance meets the requirements.

[0098] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. According to the technical essence of the present invention, within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A Ku-band miniaturized low-noise amplifier, characterized in that: include: A cascaded first-stage amplifier circuit, a second-stage amplifier circuit, and a bias circuit for biasing the first-stage amplifier circuit and the second-stage amplifier circuit respectively; an interstage low-pass filter is arranged between the first-stage amplifier circuit and the second-stage amplifier circuit; an output low-pass filter is arranged at the output end of the second-stage amplifier circuit; the interstage low-pass filter and the output low-pass filter adopt a stump-type structure, including multiple sections of high-impedance microstrip lines, multiple sections of low-impedance microstrip lines and multiple matching blocks; wherein the high-impedance microstrip line is connected in series in the circuit as an inductive circuit; the low-impedance microstrip line is connected in parallel in the circuit as a capacitive circuit; the high-impedance microstrip line and the low-impedance microstrip line are alternately connected; and the matching block is formed at the connection between the high-impedance microstrip line and the low-impedance microstrip line.

2. The Ku-band miniaturized low noise amplifier according to claim 1, characterized in that: The bias circuit is powered by a dual power supply, including a transistor Q2, a first power supply SCR1, a second power supply SCR2, a resistor R3, a resistor R4, a resistor R6, a resistor R7, a resistor R1, a resistor R5, and a resistor R2. The base of the transistor Q2 is connected to the positive electrode of the first power supply SCR1 through the resistor R3, and the base of the transistor Q2 is also connected to the positive electrode of the second power supply SCR2 through the resistor R4. The collector of the transistor Q2 is connected to the negative electrode of the first power supply SCR1 through the resistor R6. The collector of the transistor Q2 is also connected to the input end of the first-stage amplifier circuit through the resistors R7 and R1 connected in series in sequence. The emitter of the transistor Q2 is connected to the output end of the first-stage amplifier circuit through the resistors R5 and R2 connected in series in sequence. The common point of the positive electrode of the first power supply SCR1 and the resistor R3 is connected to the ground, and the negative electrode of the second power supply SCR2 is connected to the ground.

3. The Ku-band miniaturized low noise amplifier according to claim 2, characterized in that: A high-resistance line and a fan-shaped open microstrip line are respectively used on the collector and emitter of the transistor Q2 of the bias circuit to form a first choke circuit and a first feeding circuit. The circuit structure of the first choke circuit is the same as that of the first feeding circuit. The first choke circuit includes: a fan-shaped microstrip line TL1, a T-type microstrip line TL2, a microstrip transmission line TL3, and a combined transmission structure TL4. The ends 1 and 2 of the T-type microstrip line TL2 are respectively connected to one end of the fan-shaped microstrip line TL1 and the combined transmission structure TL4, the end 3 of the T-type microstrip line TL2 is connected to one end of the microstrip transmission line TL3, and the other end of the microstrip transmission line TL3 is connected to one end of the resistor R1.

4. The Ku-band miniaturized low noise amplifier according to claim 3, characterized in that: The combined transmission structure TL4 includes an arc-shaped microstrip line TL401, a middle microstrip transmission line LT402, and an arc-shaped microstrip line LT403. The two ends of the arc-shaped microstrip line LT401 are respectively connected to the two ends of the T-shaped microstrip line LT2 and one end of the middle microstrip transmission line LT402, and the two ends of the arc-shaped microstrip line LT403 are respectively connected to the other end of the middle microstrip transmission line LT402 and the three ends of the T-shaped microstrip line LT5.

5. The Ku-band miniaturized low noise amplifier according to claim 3, characterized in that: The first-stage amplifier circuit adopts a heterojunction FET tube NB1, the gate and drain of which are respectively connected to a first input matching circuit and a first output matching circuit, and the circuit structure of the first output matching circuit is the same as that of the first input matching circuit.

6. The Ku-band miniaturized low noise amplifier according to claim 5, characterized in that: The first choke circuit is connected to the bias circuit through the microstrip transmission line TL3, and the first choke circuit is connected to the gate of the heterojunction FET tube NB1 through the first input matching circuit.

7. The Ku-band miniaturized low noise amplifier according to claim 6, characterized in that: The first input matching circuit includes a microstrip transmission line TL8, a microstrip transmission line TL7, a T-type microstrip line TL5, a microstrip transmission line TL6, which are sequentially connected in series with the gate of the heterojunction FET tube NB1, and a short section of line TL9 connected in parallel between the microstrip transmission line TL7 and the microstrip transmission line TL8. The three ends of the T-type microstrip line TL5 are connected to the other end of the combined transmission structure TL4, and a T-type microstrip line TL10 is connected at the parallel connection to prevent large impedance jumps.

8. The Ku-band miniaturized low noise amplifier according to claim 3, characterized in that: The second-stage amplifier circuit adopts a heterojunction FET tube NB1, and the gate and drain of the heterojunction FET tube NB1 are respectively connected to a second input matching circuit and a second output matching circuit, and the circuit structures of the second input matching circuit and the second output matching circuit are respectively the same as the first input matching circuit and the first output matching circuit.

9. The Ku-band miniaturized low noise amplifier according to claim 8, characterized in that: The input end of the second-stage amplifier circuit is connected to the inter-stage low-pass filter through a first Γ-type matching circuit, and the output end of the second-stage amplifier circuit is connected to the output low-pass filter through a second Γ-type matching circuit.

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