Yicai Ji

A Novel Compact Double Exponentially Tapered Slot Antenna (DETSA) for GPR Applications

A novel compact double exponentially tapered slot antenna (DETSA) for GPR applications is presented. To extend the antennas impedance bandwidth, the antenna arms are rolled back and lengthened, and lumped resistors are used near the ends of the rolled arms. An improved coplanar waveguide (CPW) to coupled stripline (CPS) transition for feeding is also investigated. The measured transmission loss of two back-to-back CPW-to-CPS transitions is less than 2.6 dB in the frequency band of 200 MHz-6 GHz, which agrees well with the simulated result. The measured S11 of the antenna in frequency domain is less than -10 dB in the band of 220 MHz-6 GHz, and it is also verified that the resistors mainly have influence on the antennas S11 below 1 GHz. The measured reflected pulses show that there are only two reflecting points, and the reflection is weak. The simulated and measured antenna gains at boresight show little variations with loading resistors of different values, and this means that the resistive loadings do not affect the gain characteristics of the antenna. The antennas transmission re- sponse in time domain is also tested, and its application in GPR detection of a buried target is validated by experiments.

Data processing and initial results of Chang'e-3 lunar penetrating radar

To improve our understanding of the formation and evolution of the Moon, one of the payloads onboard the Chang’e-3 (CE-3) rover is Lunar Penetrating Radar (LPR). This investigation is the first attempt to explore the lunar subsurface structure by using ground penetrating radar with high resolution. We have probed the subsurface to a depth of several hundred meters using LPR. In-orbit testing, data processing and the preliminary results are presented. These observations have revealed the configuration of regolith where the thickness of regolith varies from about 4 m to 6 m. In addition, one layer of lunar rock, which is about 330 m deep and might have been accumulated during the depositional hiatus of mare basalts, was detected.

Analysis of GPR UWB Half-Ellipse Antennas With Different Heights of Backed Cavity Above Ground

Ultrawideband (UWB) antenna is a critical part of the ground penetrating radar (GPR) system, and the bow-tie antenna is the most popular one in all kinds of UWB antennas. In this letter, an antenna with two half-elliptical-shape arms, which is an improvement of the bow-tie antenna, is presented with the input impedance of around 100 ¿. The voltage standing wave ratio (VSWR) and radiated waveform are analyzed as the antennas with different backed cavity heights and different elevations above ground surface. The influence of the vehicle on which the half-ellipse antenna (HEA) is mounted is also given in the above three aspects.

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.

Performance evaluation of lunar penetrating radar onboard the rover of CE-3 probe based on results from ground experiments

Lunar Penetrating Radar (LPR) onboard the rover that is part of the Chang’e-3 (CE-3) mission was firstly utilized to obtain in situ measurements about geological structure on the lunar surface and the thickness of the lunar regolith, which are key elements for studying the evolutional history of lunar crust. Because penetration depth and resolution of LPR are related to the scientific objectives of this mission, a series of ground-based experiments using LPR was carried out, and results of the experimental data were obtained in a glacial area located in the northwest region of China. The results show that the penetration depth of the first channel antenna used for LPR is over 79 m with a resolution of 2.8 m, and that for the second channel antenna is over 50.8 m with a resolution of 17.1 cm.

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.

Analysis of GPR Antenna System Mounted on a Vehicle

This letter describes a ground penetrating radar (GPR) antenna system mounted on a moving vehicle for the exploration of the subsurface. The antenna system includes two identical half-ellipse antennas: One is used for transmission, and the other is for reception. Each antenna has a pair of half-elliptical-shaped arms, which are loaded by continuous resistive elements. A shallow rectangular conducting backed cavity is attached above the antenna system. The antenna efficiency, VSWR, radiation patterns, and isolation are analyzed. The time-domain waveforms of the antenna system are also given. The results of simulations and measurements are compared together, and good agreements between them are achieved. The results show that the antenna system is suitable for a variety of broadband radar applications under different conditions.

A Novel Ultrawideband Exponentially Tapered Slot Antenna of Combined Electric-Magnetic Type

A novel exponentially tapered slot antenna with ultrawide bandwidth and small late-time ring is presented. A microstrip-to-coplanar-stripline (CPS) transition of Chebyshev multisection type is used as feeding transmission. The exponentially tapered slot, which is considered as electric-type radiator (ER), is combined with a magnetic-type radiator (MR) to achieve ultrawideband performance and small size. The MR is completed by a lumped resistor bridged between the loop arm and the transmission ground. The measured impedance bandwidth (VSWR <; 2) of optimized antenna is 0.65 ~ 5.9 GHz, which agrees well with the simulated results. The measured gain is almost 3 dBi in the whole band, and the front-to-back ratio is about 15 dB.

Four-element planar array antenna for UWB application

A novel low-cost 4-element planar array antenna directly fed by a coaxial cable for Ultrawideband (UWB) application is presented. The proposed antenna consists of 2*2 bowtie elements and a simple 1*4 power divider feeding network. Comparing with the basic bowtie element, the impedance bandwidth of the array antenna has a significant improvement that the low cut-off frequency is extended from 6GHz of the bowtie element to 2GHz. The measured results show that the antenna has a bandwidth of 2GHz to 11GHz for VSWR<;2. The proposed antenna exhibits a bidirectional radiation pattern and a modest gain across the operating band and a peak gain of about 9 dBi at 11 GHz.