To protect the RF front end from electronic warfare, many studies have focused on damage phenomena of the low-noise amplifiers (LNAs). Existing studies have focused on the damage points of semiconductor devices because the peripheral circuit elements of LNAs are less susceptible to breakdown than nonlinear elements. However, their theoretical analysis is insufficient to explain the damage mechanism of LNAs under conditions such as changes in input power, frequency, and design parameters. To analyze the relationship between damage rate and parameters of the peripheral circuit of an LNA, this paper proposes a new definition of the power absorbed to a nonlinear element when input power to an LNA is very high by high-power electromagnetic pulses. In addition, LNAs having different input impedances and output impedances are designed to verify the power absorption. From the results, this paper identified parameters that increase the damage rate of LNAs, and suggested designs to reduce the damage rate.

For driving multichannel underwater acoustic transducers, the integrated design of the transmitter based on the analysis of the widely distributed impedance should be considered. Previous studies focused on either the matching circuit or the fast resonant tracking control. This paper proposes the design and control methods of a sonar transmitter based on the analysis of the impedance distribution. For the transmitter design, the optimization method based on the particle swarm optimization (PSO) algorithm is proposed for estimating the equivalent and matching circuit parameters. The equivalent circuits of the transducer are more precisely designed by using the measured data in both air and water. The fitness function proposed in the matching includes special functions, such as the limitation and parasitic inductances. A comparison of the experimental and simulation results shows that the optimized matching design improved the power factor, and was similar to the experimental result. For the transmitter control, the constant power and voltage control (CPVC) and instant voltage and current control (IVCC) methods are proposed for the variable impedance load. The impedance variation range affects the rated power and rated voltage of the transmitter, and the rating range determines the initial modulation index (MI) of the pulse-width modulation (PWM) control. To verify the control method, an experimental setup including the multichannel acoustic transducers was established. As a result, the constant power and constant voltage were verified with the proposed control, and the instant voltage and current control also worked in the event that the instant voltage or current exceed their threshold values.

The electrical equivalent model of an underwater acoustic transducer must be exactly defined in the operating frequency band to improve the driving efficiency between a sonar transmitter and a transducer. This paper used the PSO (particle swarm optimization) algorithm to estimate electrical equivalent circuit parameters of a transducer that has multiple resonant modes. The proposed method used a new fitness function to minimize the estimation error between the measured impedance of the transducer and the estimated impedance. The difference to the previous method is that the proposed method considered interference effects of the adjacent resonant modes. Additionally, this paper analyzed the effective power and separated the mechanical and acoustical resistance by considering the acoustic radiation efficiency of the transducer. As a result, the proposed method estimated all parameters at the resonance points which are influenced by the adjacent resonant modes.

RF system plays an important role in many applications such as military, telecommunication and etc. Especially an antenna used in the RF system is essential in modern society because it transmits and receives a variety of information by wireless. However it is susceptible to unwished microwaves such as noise and electromagnetic shock wave. Compared to the conventional microwave, electromagnetic shock wave can reach up to 100 MW in peak power and span within the range of frequencies between 1 and 300 GHz, which could destroy the electronic equipment. Therefore it is important to analyze the damage of the RF system affected by electromagnetic shock wave. The damage of RF system falls into four types: (1) Deception, (2) Jamming, (3) Upset, (4) Burnout. Among these, the burnout, which means physical damage to RF system, is fatal. There are two main coupling paths in microwave couplings. One is the front-door coupling which is through intentional receptors such as antennas and sensors and the other is the back-door coupling which is through apertures intended for other purposes or incidental coupling to the construction of the target system such as seams, cracks and etc. The former could strongly give affection the target. In this paper, we predict damages of the radar system by electromagnetic shock wave. Main damage type considered is the burnout and only the front-door coupling is covered. It is simulated from electromagnetic shock wave propagation to coupling the radar system via circuit modeling method. We modeled the equivalent circuit for antenna and sub-electronic equipment. The energy induced by electromagnetic shock wave through antenna flows to weak parts of the radar system. The affected parts are analyzed by EMTP (Electro Magnetic Transient Program). Using the damage prediction, the protection plans can be established.