Analysis of Indirect Lightning Effects on Low-Noise Amplifier and Protection Design

Abstract

In order to analyze the interference mechanisms of indirect lightning effects on a low-noise amplifier (LNA), a circuit model of the LNA was constructed based on the advanced design system 2020 (ADS 2020) software. Lightning pulse injection simulations were conducted to explore the influence of lightning pulses on the performance of the LNA. A pin injection test was performed to investigate the interference and damage threshold of the LNA. A protective circuit incorporating the transient voltage suppressor (TVS) and Darlington structure was designed through simulation, employing the ADS 2020 for the LNA. The research findings reveal that the interference threshold for the LNA is 60 V, while the damage threshold is determined to be 100 V. The protective circuit demonstrates a measured insertion loss of 0.1 dB, a response time of 1.5 ns, and a peak output voltage of 20 V. The research results indicate that the protective circuit can effectively reduce the impact of lightning’s indirect effects on the LNA. In the future, we will continue the design work of the protective circuit and proceed with physical fabrication and experimental validation.

1. Introduction

It is inevitable for aircraft to encounter lightning strikes during flight. According to the International Air Transport Association (IATA), commercial aircraft have a potential risk of being struck by lightning approximately once every 10,000 flight hours [1]. The increasing complexity of the electromagnetic environment within aircraft can be attributed to the utilization of composite materials in contemporary aircraft structures, as well as the continuous expansion of onboard electronic systems [2,3]. Additionally, the existence of an external lightning environment presents a heightened potential for adversely impacting the performance of the electronic equipment installed onboard [4]. The effects of lightning on aircraft are categorized into direct and indirect effects. The direct lightning effects refer to the physical consequences caused by the direct attachment of the lightning channel to the aircraft [5]. The indirect lightning effects pertain to the interference caused by the coupling of the lightning environment with onboard electronics. Excessive voltage and current can induce disruptions in RF circuits and signal interfaces, consequently impacting signal transmission and potentially resulting in permanent equipment failure.

The low-noise amplifier (LNA), serving as a crucial component of communication receivers, is positioned at the forefront of the RF receiving link. The primary function of the LNA is to amplify the weak signals received from satellites to increase the reception range. Additionally, it determines the sensitivity of the receiver [6]. The nonlinear degradation of the LNA caused by an electromagnetic pulse (EMP) was investigated. The experimental results demonstrated that the real-time response and RF characteristics of the LNA showed nonlinear and permanent degradation features under the jamming of an EMP [7]. An empirical investigation was conducted to examine the effects of EMP radiation on the LNA [8], which illustrates that the semiconductor characteristics of the LNA make it more susceptible to interference. A high-performance electromagnetic protection circuit, based on the LC filter and transient voltage suppressor (TVS) diodes, was proposed in [9]. However, it was discovered that the power capacity of the protection circuit may be limited or insufficient. In [10], a high-intensity radiated-field (HIRF) protection circuit utilizing PIN diodes was introduced and subsequently validated through experimental verification. A protection circuit for a high-altitude electromagnetic pulse (HEMP) was designed based on heterojunction bipolar transistors in [11]. A comparison between two types of TVS diodes was conducted in [12], which obtained the relationship between dynamic resistance and input power. Based on the conducted analysis, five distinct topologies were designed for high-power microwave (HPM) protection. In [13], a dc–dc pulse-width modulation buck–boost converter was safeguarded against lightning’s indirect effects through the implementation of a metal oxide varistor and a series inductive blocking element. A protection circuit was devised by integrating iron core inductors and metal oxide varistors to provide protection against indirect lightning effects in avionic environments [14].

Prior academic contributions have indeed proposed design solutions for protective circuits against EMPs. However, with limitations associated with size, power capacity, and response time, these designs are not sufficiently suitable for effectively protecting the LNA against lightning pulses. In this paper, we evaluated the response characteristics of the LNA when exposed to lightning pulses and proposed a protective circuit for the LNA. The major contributions of our work are as follows [15,16]:

• We devised a circuit schematic for the LNA and conducted a lightning pulse injection simulation. We analyzed the variations in the gain and current values of the LNA under various conditions of lightning pulse injections.
• A pin injection test was conducted to evaluate the LNA’s transient susceptibility. Consequently, we ascertained the interference threshold and damage threshold of the LNA.
• We designed a lightning protection circuit specifically for the LNA, which can shield it from the indirect effects of lightning while not interrupting its normal operations. It is designed by combining TVS diodes and Darlington structures. TVS diodes are employed to trigger the conduction of the Darlington structures that are utilized to discharge the current.

The rest of this article is organized as follows. Section 2 provides an analysis of the waveform and power spectrum of the lightning pulses. Section 3 establishes an LNA circuit model and performs pulse injection simulations. Section 4 performs transient susceptibility experiments to investigate the effects of lightning induction. Section 5 presents the design of a protective circuit. Finally, Section 6 concludes this article.This research investigates the interaction mechanism of lightning pulses on the LNA, offering references and theoretical support for lightning’s indirect effects testing and protection measures of the LNA.

2. Methodology

This section presents the methodology employed in this study to analyze the interference mechanisms of indirect lightning effects on the LNA and propose an effective protective circuit design. The framework of the proposed method is illustrated in Figure 1. The research methodology encompasses the LNA circuit model design, lightning pulse data processing, LNA sensitivity analysis, and protective circuit design. This comprehensive approach allowed for a systematic analysis of the interference mechanisms and facilitated the development of an effective protective circuit design to mitigate the impact of indirect lightning effects on the LNA [17].

2.1. LNA Circuit Model Design

The LNA circuit was simulated using advanced design system 2020 (ADS 2020), with the GaAs PHEMT serving as the core component. Initially, a DC scan analysis was performed to determine the appropriate static operating point for the LNA. Subsequently, bias circuits were designed based on the identified static operating point. Following the principles of minimum noise and maximum gain, the input matching circuit and output matching circuit of the LNA were meticulously crafted. Moreover, to enhance circuit stability, a negative feedback circuit was incorporated between the source and gate of the LNA.

2.2. Lightning Pulse Data Processing

2.2.1. Lightning Pulse

Investigating the characteristics of the lightning pulse and spectrum enables a comprehensive analysis of the pulse in the time and frequency domains. This facilitates the examination of the interference mechanisms caused by lightning pulses on the LNA, as well as subsequent pulse injection simulations. SAE ARP 5412B defines the voltage waveform that characterizes the external lightning conditions encountered by aircraft. It also establishes a standardized transient voltage waveform that is anticipated to occur on wire bundles and equipment ports. For the purpose of analyzing lightning pulses, this study employs a damped sinusoidal wave to simulate the resonant oscillation voltage generated on cables due to the interaction between electric or magnetic fields and apertures [18]. The waveform of the damped sinusoidal wave is illustrated in Figure 2a. The mathematical expression of the damped sinusoidal wave is:

$$F\left(\mathrm{t}\right)={\mathrm{K}}_0{V}_{0}sin\left(\omega t\right)e^{-\alpha t}$$

(1)

where ${\mathrm{K}}_0$ represents the peak coefficient, $V_0$ represents the peak voltage, and $\alpha$ represents the damping coefficient, where $\alpha$ = 0.231f, $\omega$ = 2$\pi$f, and f = 1 MHz.

2.2.2. Power Spectrum Conversion

The damped sinusoidal wave was transformed into a power spectrum to analyze the energy distribution of the lightning pulse, which facilitated the subsequent simulation of injected lightning pulses. The time-domain signal, denoted as f(t), can be converted into its spectral representation through the process of Fourier transformation, as illustrated in (2) [19].

$$F\left(j\omega \right)={\int }_{-\infty }^{+\infty }f\left(t\right)e^{-j\omega t}dt$$

(2)

The energy and average power of the signal can be expressed as follows:

$$E={\int }_{-\infty }^{+\infty }{f}^2\left(t\right)dt=\frac{1}{2\pi }{\int }_{-\infty }^{+\infty }{\left|F\left(j\omega \right)\right|}^{2}d\omega$$

(3)

$$P=\underset{T\to \infty }{lim}\frac{1}{T}{\int }_{-\frac{T}{2}}^{\frac{T}{2}}{f}^2\left(t\right)dt=\frac{1}{2\pi }{\int }_{-\infty }^{+\infty }\underset{T\to \infty }{lim}\frac{{\left|F\left(j\omega \right)\right|}^2}{T}d\omega$$

(4)

The ℘($\omega$) is defined as the power spectrum of the signal, which characterizes the distribution of power across various frequencies. It provides the frequency-domain characteristics of the signal. Consequently, the power of the signal can be determined as follows:

$$P={\int }_{-\infty }^{+\infty }\wp \left(\omega \right)df=\frac{1}{2\pi }{\int }_{-\infty }^{+\infty }\wp \left(\omega \right)d\omega$$

(5)

Based on (4) and (5), the power spectrum of the signal can be derived as:

$$\wp \left(\omega \right)=\underset{T\to \infty }{lim}\frac{{\left|F\left(j\omega \right)\right|}^2}{T}$$

(6)

where T represents the period of the signal and F(j$\omega$) represents the frequency spectrum of the signal.

Based on (1) and (2), the frequency spectrum of the lightning pulse can be derived as:

$$F\left(jw\right)=j\left(\frac{K_0{V}_{0}w}{w^2-{\left(w+V_0\right)}^2+\frac{0.231w}{2\pi }}\right)-j\left(\frac{K_0{V}_{0}w}{w^2-{\left(w-V_0\right)}^2+\frac{0.231w}{2\pi }}\right)$$

(7)

Based on (6) and (7), the power spectrum of the lightning pulse can be derived as:

$$S\left(f\right)=\left(\frac{K_0^2{V}_0^2}{4\pi }\right)\left(\frac{{\left(2\pi f\right)}^2}{\left({\left(2\pi f\right)}^2-{\left(2\pi f+V_0\right)}^2+0.0526{\left(2\pi f\right)}^2\right)\left({\left(2\pi f\right)}^2-{\left(2\pi f-V_0\right)}^2+0.0526{\left(2\pi f\right)}^2\right)}\right)$$

(8)

According to (8), the power spectrum of the lightning pulse with a peak voltage of 100 V is depicted in Figure 2b. The analysis reveals that the energy of the lightning pulse is primarily concentrated at 1 MHz. Furthermore, it is observed that the distribution of power is solely dependent on the peak voltage of the lighting pulses.

2.3. LNA Sensitivity Analysis

2.3.1. Pulse Injection Simulation

To assess the interference conditions of the LNA under indirect lightning effects, a pulse injection simulation was conducted. This simulation involved applying both the lightning pulse and RF signals to the input port of the LNA using a power combiner. The objective of this simulation was to analyze the transient response and performance of the LNA when subjected to lightning-induced pulses. The transient simulation provided insights into the dynamic behavior and effects of lightning pulses on the LNA, while the power scan analysis established the interference threshold and characterized the LNA’s robustness against lightning-induced stress levels. The results from these simulations contributed to a comprehensive understanding of the LNA’s susceptibility to interference and facilitated the development of effective protective measures.

2.3.2. Pin Injection Test

To investigate the interference condition of the LNA and evaluate its resilience to lightning-induced interference, a pin injection test was conducted. This test involved injecting lightning pulses directly into the LNA circuit using pin probes. The primary objective was to meticulously monitor and analyze crucial parameters, including the LNA’s output power, as well as the input and output currents, across various peak lightning pulse injection scenarios. Additionally, an in-depth calculation of the LNA’s gain during the test was performed. The pin injection test provided invaluable insights into the LNA’s response to lightning-induced interference, thereby facilitating the determination of both the interference and damage thresholds.

2.4. Protective Circuit Design

The protective circuit design for the LNA was developed using ADS software. It incorporates a combination of TVS diodes and Darlington structures to ensure reliable surge protection. The TVS diodes serve the purpose of clamping the output voltage and triggering the conduction of the Darlington structures, while the Darlington structures are responsible for the current’s dissipation. The design process involved optimizing the performance of the protective circuit by appropriately adjusting the clamping voltage of the TVS diodes. This adjustment was critical in achieving the desired conduction of the Darlington current dissipation circuit, thereby reducing the response time of the protective circuit and enhancing its power capacity.

3. Pulse Injection Simulation

3.1. Circuit Mode of the LNA

Figure 3a shows the physical diagram of the LNA. Within the core component of the LNA, highlighted by the red circle, lies a pseudomorphic high-electron-mobility transistor (GaAs PHEMT). The aforementioned chip offers advantages such as high electron mobility, high gain, and low noise, rendering it highly suitable for the amplification of small signals. The circuit of the LNA was modeled utilizing ADS 2020, as shown in Figure 3b [20]. The primary objective of this research is to analyze the L1 band of the GPS satellite, which operates at a frequency of 1575 MHz [21]. According to the datasheet of ATF54143, the LNA was designed to operate with a drain-source voltage of 4V and a drain-source current of 65 mA. This configuration ensured that the gain and noise figures were compliant with the design requirements. Additionally, a biasing circuit was designed for the LNA. The design of the impedance-matching circuit was tailored to the operating frequency of the LNA. The input matching circuit was designed based on the principle of minimum noise matching, while the output matching circuit followed the principle of maximum gain matching.

The input port of the LNA was configured with an excitation signal. Harmonic balance analysis and transient simulation controls were incorporated to obtain the noise figure, input voltage ($U_{in}$), and output voltage ($U_{out}$). The gain of the LNA was calculated according to (9).

$$G=20log\left(\frac{U_{out}}{U_{in}}\right)$$

(9)

Figure 4a shows the simulation results of the LNA. The LNA exhibited a gain of 18.3 dB and a noise figure of 0.34 dB at a frequency of 1575 MHz. Figure 4b depicts the gate current, source current, and drain current of the LNA. During typical operation, the gate current of the LNA exhibited fluctuations around 0 A, whereas the source current and drain current remained equal and fluctuated around 25 mA.

3.2. Simulation of the Interference Effects

In order to accurately simulate the coupling process of lightning and effectively demonstrate its interference effect, a power combiner was utilized to simultaneously inject the lightning pulse and RF signal into the input port of the LNA. A high-power single-pulse with a frequency of 1 MHz was employed to replicate the lightning pulse, while a small-signal wave at 1575 MHz was used to simulate the RF signal of the LNA [22]. The small-signal wave was modulated by a square wave with a pulse width of 10 ns, a pulse power of −30 dBm, and a period of 10 ns. The high-power single-pulse exhibited a pulse width of 2 ns and a period of 20 ns. To evaluate the influence of power levels on the LNA, a comprehensive analysis was performed by sweeping the power of the high-power pulse [23]. The variation in the gain with pulse power is shown in Figure 5.

It was apparent that the amplification of the LNA decreased when the injected pulse power exceeded 9 dBm. This can be attributed to the nonlinear effects of the LNA, which represent a deviation from linearity in which the output signal of the amplifier no longer maintains a direct proportionality to its input signal. When the injected power exceeded 32 dBm, it exceeded the simulation range. According to (8), the high-power single-pulse with a power of 9 dBm corresponds to an attenuated sinusoidal waveform with a peak voltage of 30 V. Similarly, the pulse with a power level of 32 dBm corresponds to a peak voltage of 270 V.

The RF susceptibility testing procedures in RTCA DO-160G are widely applied to airborne equipment in the indirect lightning effects research field. According to RTCA DO-160G, the test level should be determined based on the installation environment of the LNA and the exposure level of its interconnected cables [24]. Therefore, the lightning pulse peak voltages ranging from 0 to 300 V were sampled with a step size of 10 V. The power of the high-power single-pulse at 1 MHz was calculated utilizing the sampled peak voltage values. The high-power single-pulse injection simulations were conducted based on the calculated power values. Figure 6a illustrates the currents of the LNA when a high-power single-pulse with a power level of 3.3 dBm (equivalent to a lightning pulse with a peak voltage of 10 V) was injected. Following pulse injection, the gate current experienced a rapid increase to 2.2 mA, while the drain and source currents simultaneously rose to 63.6 mA, maintaining equality. The currents returned to their initial state after a time interval of 6.6 ns.

Progressive augmentation of the injection power resulted in a gradual convergence of the gate current and source current in the LNA. Specifically, when a high-power single-pulse power of 18.3 dBm (equivalent to a lightning pulse with a peak voltage of 50 V) was applied, both the gate current and source current exhibited a significant increase compared to the previous stage, as depicted in Figure 6b. A disconnection between the gate and the source resulted in the formation of a low-impedance pathway. The LNA current returned to normal within a time period of 9.6 ns. When a high-power single-pulse with a power level of 23.3 dBm (equivalent to a lightning pulse with a peak voltage of 100 V) was injected, a strong correlation between the gate current and source current was observed. As shown in Figure 6c, reversal was observed in the drain current at 1.1 ns. A breakdown between the gate and drain forms a low-impedance path. Following pulse cessation, the currents failed to return to their initial state, indicating that the LNA suffered irreversible damage.

3.3. Analysis of Results

According to the pulse injection simulation, the damage evaluation curve of the LNA is shown in Figure 7. The LNA operated normally, with a steady gain of 18.3 dB when the power level of the injected pulse was less than 9 dBm. The gain of the LNA decreased, and the current recovery time progressively prolonged as the injected power exceeded 9 dBm. Surpassing a power level of 18.6 dBm, the LNA demonstrated recoverable damage, characterized by the emergence of a low-impedance path between the gate and source terminals. Observably, the LNA sustained irreversible damage, discernible as a low-impedance path between the gate and drain terminals when the power level exceeded 23.3 dBm. The interference mechanism of lightning pulses on the LNA operates as follows: The LNA achieves amplification by regulating the gate voltage, thereby controlling the two-dimensional electron gas between the drain and source terminals. Simultaneously, a short circuit forms between the source and drain terminals. Meanwhile, the gate remains non-conductive to both the source and drain, exhibiting a negligible gate current [7]. As the injected pulse power escalates, both the gate current and source current surge, consequently compromising the gain of the LNA. A subsequent augmentation in power thus results in an overcurrent across the gate’s metallic band, leading to both a gate–source and gate–drain breakdown [25,26].

4. Lightning-Induced Transient Susceptibility

4.1. Experiment Platform

To validate the simulation results and scrutinize the effects of genuine lightning pulses on the LNA, we adhered to the guidelines in Section 22 of RTCA DO-160G and performed a pin injection test to assess the transient sensitivity of the LNA [27]. The pin injection test is an experimental method that directly applies the produced transient signals to the signal pins of the device. This test was utilized to assess the LNA’s fault tolerance capabilities. Figure 8a illustrates the schematic diagram of the pin injection test for the LNA, while Figure 8b shows the experimental platform.

The types and functions of the test equipment are presented in

Table 1. Types and functions of the test equipment.

Test Equipment	Type	Function
DC power supply	E3631A	Power supply
Line impedance stabilization network	DN-LISN160	Prevents interference
Vector signal generator	E8267D	Provides RF signal
Spectrum analyzer	N9020B	Monitors output power
Oscilloscope	RTO2044	Monitors currents
Pulse generator	AG-MIG-OS-MB	Generates pulses
Injection probe	CN-MIG-TT	Injects pulses

. The testing platform comprises two sections: injection and receiving. The injection section encompassed a pulse generator, a vector signal generator, a filter, and an injection probe. The receiving section included a DC power supply, a line impedance stabilization network (LISN), an oscilloscope, two current loops, an attenuator, and a spectrum analyzer. The filter operates within the frequency range of 1570–1580 MHz, exhibiting an insertion loss of 1 dB, while the attenuator was calibrated to provide a 10 dB attenuation [28].

4.2. Experimental  Results

To reflect the actual operating conditions of the LNA, the vector signal generator produced a modulated RF signal, operating at a power level of −30 dBm and a frequency of 1575 MHz. The output power of the LNA, which was monitored utilizing a spectrum analyzer, is depicted in Figure 9. The gain of the LNA can be calculated based on the input and output powers utilizing the following formula:

$$G_1=P_{\mathrm{out}}-P_{\mathrm{in}}-G_2-G_3$$

(10)

where $P_{in}$ represents the power of the RF signal, $P_{out}$ represents the power of the output signal, $G_2$ represents the in-band loss of the filter, and $G_3$ represents the attenuation of the attenuator. The gain of the LNA was calculated to be 15.8 dB.

To evaluate the effects of lightning pulses on the LNA, a pin injection test was performed by incrementally increasing the peak voltage of the lightning pulses in 10 V increments. The evaluation of the effects of lightning pulses on the LNA was based on the variations in LNA gain, input current, and output current. Each test was repeated a minimum of five times to ensure the validity and precision of the results. The relationship between the LNA’s gain and the peak voltage of injected pulses is presented in

Table 2. The gain of the LNA varies with the peak voltage.

Peak Voltage/V		10	20	30	40	50	60	70	80	90	100	110	120
Gain/dB	LNA1	15.8	15.6	15.6	15.5	15.3	11.2	10.9	10	9.8	−15.4	−15.4	−15.4
	LNA2	15.7	15.7	15.7	15.6	15	14.8	11.5	11	10	−15.8	−15.8	−15.8
	LNA3	15.8	15.8	15.7	15.8	15.4	12	10.9	11	10	9.8	−16	−16
	LNA4	16	16.1	15.8	15.6	15.2	12.5	11.2	10.7	9	−16.5	−16.5	−16.5
	LNA5	15.9	15.8	15.6	15.7	15.4	10.9	10	9.6	9.4	9	−15.9	−15.9

. There was no significant change in the LNA gain when the peak voltage of the pulse was set to 10 V. The input and output currents of the LNA are illustrated in Figure 10a, indicating that the output current significantly surpasses the input current. LNA1, LNA3, LNA4, and LNA5 exhibited significant gain degradation when the peak voltage of the injected pulse was 60 V. Similarly, LNA2 exhibited evident gain degradation when the peak voltage reached 70 V [29]. The input and output currents of the LNA are depicted in Figure 10b, showing the input current approaching the output current. This finding aligns with the trends of the gate and source variations observed in the simulation results. After cessation of the pulse injection, the gain of the LNA recovered to approximately 16 dB, suggesting that the LNA experienced recoverable damage. LNA1, LNA3, and LNA5 demonstrated a rapid shift towards negative gains when the peak voltage of the injected pulse was 100 V. Identical behavior was observed in LNA2 and LNA4 when the pulse peak voltage reached 110 V. Following the cessation of the pulse injection, the gains of the LNAs could not recover, indicating permanent damage to the LNA. When the GaAs PHEMT chip of the LNA was replaced, the gain of the LNA recovered to 15.8 dB, demonstrating that the main cause of the lightning pulse damage to the LNA was the damage to the GaAs PHEMT chip [30].

The experimental results exhibit significant consistency across various samples under identical pulse injection conditions. Coupling lightning pulses into the LNA leads to a reduction in gain. Specifically, the LNA’s gain experiences a significant decrease when the peak voltage of the pulse exceeds 60 V. Additionally, the input current and output current of the LNA are nearly equal, impeding its effective functioning. When the peak voltage of the pulse exceeds 100 V, it results in irreversible damage to the GaAs PHEMT chips. The interference and damage patterns on the LNA caused by lightning pulses, as observed in the pin injection tests, aligned with the simulation results. The gain of the LNA decreases while the peak voltage of the injected lightning pulse increases. Furthermore, the gate current and source current progressively increase and approach equality. The phenomenon of gate–source breakdown and gate–drain breakdown occurs while the pulse level exceeds the threshold voltage. However, the damage threshold obtained from the simulation is marginally lower than the experimental damage threshold. This discrepancy can be attributed to the simulation process, which evaluates the LNA disturbance based on the alterations in the gate, source, and drain currents of the LNA. In practical scenarios, the device is susceptible to damage only when its temperature exceeds a specific melting point [31].

5. Protection Circuit of the LNA

5.1. Design of the Protection Circuit

Based on the simulation and experimental results, it is imperative to design a protective circuit for the LNA. The protective circuit is required to provide effective protection against lightning pulses while simultaneously minimizing any potential interference with the reception of RF signals by the LNA. Surge protection devices, including gas discharge tubes (GDT), TVS diodes, and voltage-dependent resistors (MOV), are typically incorporated for protective purposes [32]. GDT and MOV devices, despite their high power capacity, are limited by their extended response times and larger parasitic capacitance [33]. TVS diodes, in contrast, exhibit shorter response times and smaller parasitic capacitance, albeit with a lower power capacity [34]. The Darlington structure, on the other hand, provides the advantage of reduced parasitic capacitance and excellent protection against electromagnetic pulses. Therefore, this paper proposes a protective circuit that integrates TVS diodes and Darlington pairs in parallel, as illustrated in Figure 11. The protective circuit is comprised of two stages, purposefully designed to re-route currents and confine voltage within a secure range. The first stage consists of two series-connected bidirectional TVS diodes, D1 and D2. The clamping voltage of D2 operates as the trigger voltage for the second stage. The output voltage of the protection circuit corresponds to the cumulative clamping voltages of D1 and D2. The second stage includes two parallel-connected Darlington structures, which enhance the dissipation capacity. The Darlington structure primarily comprises a field-effect transistor (FET) and a high-power bipolar transistor.The device selection method for protective circuits is shown in Appendix A.

5.2. Simulation of the Protection Circuit

To verify the effectiveness of the protection circuit, we conducted transient and S-parameter simulations, applying a 100 V peak voltage lightning pulse at the input port of the protection circuit. The input and output voltages of the protection circuit are shown in Figure 12a. Significantly limiting the peak output voltage to 20 V—lower than the input voltage—the protection circuit demonstrated effective protection. The S-parameter and the voltage standing-wave ratio (VSWR) of the protection circuit are depicted in Figure 12b. The protective circuit exhibited an insertion loss of 0.106 dB and a VSWR of 1.017 at a frequency of 1575 MHz, indicating that it had a negligible effect on the LNA.

To verify the current dissipation capability of the protective circuit, high-power single-pulse injections were carried out for the proposed protection circuit, TVS protection circuit, and parallel TVS-MOV protection circuit [35]. The power level for the injection was set at 23.3 dBm. The response time and output power of the protective circuit are depicted in Figure 13. The protective effects of different circuits are presented in

Table 3. Comparison of protective circuit effects.

Protection Circuit	Response Time/ns	Output Power/W	Output Power/dBm
TVS	1.3	0.14	21.4
TVS and MOV	7.8	0.05	16.9
Proposed circuit	1.5	0.02	13.0

. The proposed protection demonstrates superior power handling capabilities, while its response time is comparable to that of the TVS protection circuit. When compared to the parallel TVS-MOV protection circuit, the proposed protection configuration shows significant advancements in response time and power capacity.

6. Conclusions

This paper conducted pulse injection simulations and transient sensitivity tests to investigate the impact of lightning-induced transients on the LNA. Based on the observed interference patterns, a protective circuit of the LNA was devised. The primary findings of the research are as follows:

(1)

The coupling of lightning pulses with the LNA leads to a decrease in gain. Exceeding the predetermined damage thresholds, the LNA experiences gate–source and gate–drain breakdown.

(2)

Recoverable damage occurs to the LNA when the peak voltage of the coupled lightning pulse surpasses 60 V. Conversely, when the peak voltage surpasses 100 V, the GaAs PHEMT chip sustains irreversible damage.

(3)

The protection circuit exhibits a response time of 1.5 ns, ensuring that the output voltage remains below 20 V. This effectively mitigates the interference caused by lightning pulses without interrupting normal operations.