Design of a Hybrid Radar Sensor for Smart Ammunitions

Abstract

With the recent development of smart shells, it is necessary to install electronic com- ponents such as drive systems, GPS (Global Positioning System), guidance systems, and electronic fuses in shells similar to guided missiles. However, unlike guided missiles, which have a backward inertia of a few tens of grams (acceleration due to gravity), smart munitions require high impact resistance because they are subjected to high backward inertia forces of up to 15,000 g at initial launch. Therefore, smart sensors for electronic fuzes must be smaller, more precise, and even indestructible at high impacts of 15,000 g than those applied to guided munitions. For this purpose, sensors for smart munitions have been developed in the direction of reducing the size and increasing the target detection ability by using a combination of millimeter-wave radar sensors and IR sensors. In addition, the developed sensors have to be proven to be impact-resistant through high-impact tests such as the SRS test. In this thesis, I will discuss a hybrid sensor that uses a combination of FMCW radar and TPR as a representative sensor for smart munitions, and a hybrid sensor as a device that can monitor the behavior of test munitions during the SRS test, which is necessary for conducting an impact resistance test of shells equipped with the developed sensor. First, as a representative sensor for smart munitions, I propose a hybrid sensor that combines FMCW radar and TPR. The frequency-modulated continuous-wave (FMCW) radar is generally applied in ground target detecting devices mounted on small shells or projectiles because of its compact size. However, the FMCW radar often produces false alarms when detecting ground targets surrounded by heavy clutter. To overcome this problem, this paper proposes a ground target detection system based on both the miniaturized FMCW radar and the total power radiometer (TPR), consisting of the common millimeter-wave (MMW) front ends and an antenna. However, its intermediate frequency (IF) parts are separated using different frequency bands to miniaturize the entire system. The minimum detectable temperature (MDT) increases and the sensitivity is thus degraded because the TPR for the hybrid sensor inevitably includes an undesirable transmitter section owing to the widespread usage of the front ends with the radar. The proposed system employs optimization of the physical path delay and duplexing the IF band for the TPR and FMCW radar to improve the sensitivity of the TPR in the proposed hybrid sensors and reduce the system noise. The system includes a matching circuit and a voltage doubler to improve the sensitivity of the detector. Therefore, the MDT of TPR in the proposed hybrid system can be reduced to 47.5 K from 734.6 K in the initial design. The drop test demonstrates that the proposed hybrid sensor can reduce false alarms when compared to using either the FMCW radar or only the TPR. Next, I propose a hybrid radar sensor capable of monitoring the behavior of projectiles in a soft recovery system (SRS) in near real-time to validate the high-impact characteristics of key components in smart munitions. The sensor consists of a FMCW radar mode to check whether the soft recovery of the projectile after being launched is normal and a CW Doppler radar mode to estimate the projectile velocity, distance traveled, and deceleration characteristics during the test. Because the proposed sensor is installed inside a 155.8 mm circular tube, 1.4 GHz is chosen as the operating frequency, where only the dominant mode in the tube can exist. In addition, the radar equations in free space are modified to consider the operation inside the tube and ensure accurate calculations. A hybrid radar sensor is installed and operated inside an SRS test device. The position of the projectile after the test can be determined from the positions of the peaks of the receiving signals in the FMCW mode. The projectile velocity, traveling distance, and decay velocity are accurately predicted using the CW Doppler mode.