The core of active phased array antenna design is t / R module. The main factors considered in the design of T / R module are: the number of different forms of integrated circuits, the level of power output, the size of received noise coefficient, the accuracy of amplitude and phase control. At the same time, the design of radiation element array is also very important.
1 chip design
Ideally, the circuits of all modules need to be integrated into one chip. In the past decades, everyone has been working hard for this goal. However, due to the different requirements of different functional units in the system, the existing engineering technology has made a compromise between the system performance and the difficulty of implementation, so the common practice is to classify the circuits according to their functions, then place them on different chips, and then connect them through hybrid microcircuits, as shown in the figure.
The basic chip setup of a T / R module includes three MMICs and one digital large scale integrated circuit (VLSI), as shown in the figure.
High power amplifier (MMIC)
Low noise amplifier plus protection circuit (MMIC)
Gain adjustable amplifier and phase shifter (MMIC)
Digital control circuit (VLSI)
According to different application requirements, the T / R module may need some other circuits, such as the pre power amplifier circuit, which needs to amplify the input signal to meet the high peak power requirements.
Most T / R modules in X band and above adopt MMICs technology based on GaAs technology. One disadvantage of this technology is that the thermal conductivity is very low, so the circuit based on GaAs needs to be designed for heat dissipation.
In the future, the development direction of T / R module is based on the design process of GaN and SiGe.
The power amplifier based on GaN can achieve higher peak power output, so as to improve the sensitivity or detection distance of the radar. The output power is more than 5 times of the process circuit based on GaAs. Although the power transmitted by SiGe process is not as high as that of GaAs, the cost of this material is relatively low, which is suitable for the design of low-cost, low-power density radar system in the future.
2 power output
In general, the average power output required by the radar system is basically determined after the aperture of the array is given. The maximum average power that the antenna can achieve is related to the output power of each TR module, the number of T / R modules, the efficiency of T / R modules and heat dissipation. When the input power is determined, the higher the efficiency of the T / R module, the greater the corresponding output power.
In the design of high power amplifier, the peak power required is an important index, which is defined as the average power divided by the minimum duty cycle. The peak power of radar system is realized by the whole antenna array, that is to say, when the peak power is determined, the minimum number of T / R components required is also determined.
The design of TR module of radar system needs to consider antenna aperture, output power of T / R module and layout of T / R module. For example, in order to achieve the same radar detection performance and the same number of T / R modules, for 4m2 caliber antenna, assuming the output power of each T / R module is p, then for 2M2 caliber antenna, the output power of each T / R module is 2p, as shown in the figure.
3 transmitter noise limit
Generally, the radar system uses a central transmitter to work, so it is necessary to reduce the noise as much as possible. In the active phased array antenna, the main noise source is DC ripple or input voltage fluctuation. Due to the low voltage and high current of each T / R module, it is necessary to filter the input power adaptively.
4 receiver noise coefficient
The received noise coefficient is an important index of active ESA antenna. It is usually necessary to make the received noise coefficient low to improve the radar performance. In general, the received noise coefficient of T / R module refers to the noise coefficient of the whole module, including LNA and the insertion loss caused by the previous circuit (circulator, receiving protection circuit, transmission line), as shown in the figure.
5 amplitude and phase control
The accuracy of amplitude and phase control is related to the requirements of the radar system for the sidelobe of the whole antenna array. If the radar system needs the antenna to achieve low sidelobe, then it needs to reduce the quantization step of the phase and amplitude control circuit, and at the same time improve the range of the amplitude and phase control to realize the weighting of the real antenna array, and it needs to strictly control the error of the amplitude and phase.
6 array physical structure design
The performance and cost design of active ESA antenna is not only related to t / R components, but also closely related to the integrated design of array.
In general, each antenna array radiation unit must ensure its exact position in the array and be installed on the rigid backplane. When the RCS of the antenna is required to be reduced, the distortion of the antenna array will cause the enhancement of random scattering, and the influence cannot be eliminated.
Each T / R module is usually installed on a backplane with a heat sink to timely dissipate the heat generated by the T / R module. For each phased array antenna, the specific T / R layout is different. One of the common layout is brick layout, as shown in the figure.
Another layout of active phased array antenna is tile structure, as shown in the figure. Each T / R module consists of three layers of circuit boards stacked vertically, and each layer of circuit board includes four tr circuits. The heat generated by the circuit in the T / R module is transmitted through the circuit board to the surrounding metal structure for emission.
The phased array antenna with chip T / R module also includes the coupling gap of DC power, control signal and RF signal, as shown in the figure.
For wideband or digital beamforming radar system, the active phased array antenna usually needs to adopt subarray layout. When the sub array layout is adopted, the production and processing cost of the whole phased array antenna will be greatly reduced, and the analog beam scanning ability will be formed by adjusting the phase shifter at the back of each sub array.
For the analog radar system, each subarray needs to scan the beam through the time delay unit, as shown in the figure. For the digital radar system, the echo of each sub array is directly collected by the receiver.

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This paper is from radar communication electronic warfare