Hejun Yin

TEM Horn Antenna Loaded With Absorbing Material for GPR Applications

A novel exponentially tapered TEM horn antenna is presented. It is fed directly by a coax through a compact transition section and possesses a wide bandwidth, good radiation characteristic, and easy integration with microwave circuits. Two specially tapered metal flares have been designed to make a wideband characteristic and reduce the reflection. To overcome aperture reflections at low frequencies and unbalanced aperture field at higher frequencies, an arc surface is added at the end of the flare plates, and an absorbing material is loaded on the outer surface of the flare section. Measured results show that the presented antenna has a wide bandwidth from 0.83 to more than 12.8 GHz under a return loss <;-10 dB, small input reflection, a moderate gain from 0 dBi at 0.83 GHz to 10 dBi at 12 GHz, and a good radiation characteristics in the time domain, which can be suitable for ground penetrating radar (GPR) applications.

A Novel Compact Tapered-Slot Antenna for GPR Applications

A novel compact planar tapered-slot antenna for ground penetrating radar (GPR) system is proposed. The antenna is fed by a coplanar waveguide (CPW) and evolved from one slotline of the compact CPW. Another slotline of the compact CPW forms a magnetic antenna as a supplement to the tapered-slot antenna. Some discontinuous points on the compact antenna structure will produce a relatively strong reflection, so the resistive loading is introduced. In order to validate the antenna performance, one prototype is fabricated and measured. The results demonstrate that the impedance bandwidth of the tapered slot antenna can span 0.64-6 GHz with the VSWR below 2, which agrees well with the simulated result. The radiation characteristics of the proposed antenna are measured, and its application for moving target tracking is also validated in a GPR system.

Application of Equivalent-Time Sampling Combined with Real-Time Sampling in UWB Through-Wall Imaging Radar

Experiments show that ultra-wideband (UWB) through-wall imaging radar enables good penetration capabilities operating in the frequency range 0.3GHz to 3GHz. According to Shannon sampling theorem, signal acquisition unit only be able to acquire a signal with at least 6GS/s sampling frequency utilizing real-time sampling electronics. It is difficult to find such A/D converter chip in practice. Taking it into account that ultra-wideband through-wall imaging radar transmits signal repeatedly, this paper proposes a method of applying equivalent-time sampling combined with real-time sampling in UWB radar to acquire the echo signal. An ultra-wideband through-wall imaging radar which embeds a PC104 as its main control unit and a FPGA as its timing controller is developed based on this method. The application shows that the ultra-wideband signal can be sampled and recovered with the use of this method.

Semicircular Slot-Tuned Planar Half-Ellipse Antenna With a Shallow Vee-Cavity in Vital Sign Detection

Ultrawideband (UWB) antenna is one critical part of the impulse radar system. In this paper, a shallow Vee-cavity shielded planar dipole antenna working at the center frequency of 400 MHz for UWB vital sign detection radar is investigated numerically and experimentally. It consists of two half-ellipse-shape arms tuned with four semicircular slots and a shallow Vee-cavity. The voltage standing wave ratio (VSWR), input impedance, and radiation waveforms are all analyzed. The resistive and slot loading techniques for improving impulse radiation and reducing late-time ringing are adopted. Several important parameters of the designed antenna have been studied. The influence of a shallow rectangular cavity and the proposed Vee-cavity on the antenna characteristics is also under consideration. Finally, one prototype antenna is fabricated and applied to UWB vital sign detection radar system. The experimental results indicate that the proposed half-ellipse antenna with a Vee-cavity works satisfactorily in the radar system.

Study on a Novel UWB Linear Array Human Respiration Model and Detection Method

A novel ultra-wideband (UWB) linear array human respiration model and detection method is proposed to obtain vital sign feature (VSF) including azimuth, range, and respiration frequency. As the azimuth of the human being cannot be estimated by a single receiving channel, the new method generates new B-scans for different scanning angles. When the azimuth angle is determined by the azimuth estimation method, the corresponding new B-scans can be processed to obtain the range and respiration frequency. The new method not only estimates the azimuth angle of the human being, but also detects multiple respiration motions from the new B-scans instead of the traditional B-scans. Meanwhile, the implementation steps of the new method are fully illustrated both in free-space and rubble situation. Four free-space simulations are performed and prove the necessity of the new method using the UWB linear array. The results verify its capability for the azimuth estimation and the multiple VSFs detection. In addition, the scene with one person trapped in rubble is simulated to validate the new method for the rubble case with unknown permittivity. Furthermore, a practical experimental validation is performed in an artificial ruin to show the effectiveness of the proposed method.

Design of modulated m-sequence ultrawideband radar for life detection

In life detection with ultrawideband (UWB) radar, the high signal-to-noise ratio (SNR) is very important for good performance. In this paper, the m-sequence with a carrier is applied to life detection, and SNR can be improved by pulse compression and linear average. The hybrid sampling technique is used to improve the sampling resolution and reduce the cost. The peak-to-sidelobel ratio after pulse compression would be degraded when the delay resolution of the delay line drifts in different temperature, thus the actual delay resolution of the delay line should be measured before hybrid sampling. Experiments show that the proposed modulated m-sequence UWB radar has good detection performance.

Through-Wall Shape Estimation Based on UWB-SP Radar

This letter presents a new method for localizing and identifying a target through walls with known wall parameters. A time-delay difference curve (TDDC) is utilized in this method for target localization and identification. The characteristic of the TDDC can be applied to estimate the incident angle and offset the influences in propagation path and propagation time delay brought from the wall. This letter analyzes the method and gives out the theoretical TDDC. Extensive simulations and experiments show the effectiveness of the proposed method.

A novel handheld pseudo random coded UWB radar for human sensing applications

A novel handheld pseudo random coded ultra-wideband (UWB) radar for human sensing applications is presented in this paper. In order to reduce the size of the radar and obtain good penetrability, the center frequency of the m-sequence is assigned to about 1.1GHz. The peak voltage of the m-sequence is 4.5Vpp, while the length of the m-sequence can be chosen to obtain different signal-to-noise ratio (SNR). The digital transmitter, the dual-channel receiver and the clock synchronization are discussed in detail. The experimental results show that the proposed handheld pseudo random UWB radar has good detection performance for human sensing applications in complex environment.

Human Respiration Localization Method Using UWB Linear Antenna Array

Human respiration is the basic vital sign in remote monitoring. There has been remarkable progress in this area, but some challenges still remain to obtain the angle-of-arrival (AOA) and distinguish the individual signals. This paper presents a 2D noncontact human respiration localization method using Ultra-Wideband (UWB) 1D linear antenna array. The imaging reconstruction based on beamforming is used to estimate the AOA of the human chest. The distance-slow time 2D matrix at the estimated AOA is processed to obtain the distance and respiration frequency of the vital sign. The proposed method can be used to isolate signals from individual targets when more than one human object is located in the surveillance space. The feasibility of the proposed method is demonstrated via the simulation and experiment results.

Data acquisition system of ultra-wide band life detection radar based on PC104 and FPGA

A data acquisition system to acquire and record the output signal of a pulse generator is described. The system was built around Xilinx FPGA interfaced to an embedded computer via the PC104 bus. The system dynamically adjusts parameters (such as time window, sampling interval, pulse repetition frequency, etc.) to satisfy performance requirements of ultra-wide band life detection radar. The system can provide a minimum sampling interval of 5ps.