Monostatic Antenna Research Articles

Novel Orthogonal Random Phase-Coded Pulsed Radar for Automotive Application

In contrast to remote sensing radar, automotive radar focuses on the detection of short-range targets in the 0–1000 m range. Conventional automotive pulsed radar usually uses a monostatic antenna and it requires high peak power for the transmission of the short duration pulses to reliably detect targets at close range with a high resolution. Unfortunately, it is difficult and expensive to generate high-powered pulses on the nanosecond scale. Meanwhile, the existing automotive radars suffer from bottlenecks, i.e., spatial resolution, sidelobe levels, and Inter-Sensor Interference (ISI). To overcome the above challenges, a bistatic antenna to transmit and receive large time-bandwidth product waveforms is firstly proposed in this paper. Secondly, high spatial resolution is implemented using a Digital Beam Forming (DBF) transmitter and the high range resolution is achieved by using the pulse compression technique. Additionally, the radial velocity of the target is calculated by applying pulse Doppler processing. Finally, to deal with the sidelobe effect of impulse response function of point target and the interference arising from neighboring radars, novel Orthogonal Random Phase-Coded (ORPC) radar signals are presented. Using these ORPC signals, the impulse response function of the radar can achieve a peak sidelobe ratio of –45 dB without any loss in the signal-to-noise ratio. Most importantly, interference can be significantly reduced by using the proposed signals. Extensive simulations demonstrate the effectiveness and advantages of the proposed radar.

Indented Antenna Arrays for High Isolation: The Growing Interest in Simultaneous-Transmit-and-Receive-Based Full-Duplex Communication Systems

In full-duplex communication systems, reflections of transmitted waves as a result of the antenna mismatch may leak into the receiver and create strong on-site interferences. Such reflections cannot be suppressed by conventional frontend isolation techniques even with ideal circulators. Indented antenna arrays are thus proposed to destructively combine the reflection from each antenna element and prevent them from negatively impacting the receiver sensitivity. The essential idea is to break the symmetry between the transmitting and receiving paths by using an antenna aperture that is curved by indenting the antenna elements. Because of this asymmetry, all of the elements contribute to the wave transmission and reception in phase, whereas the reflections from those elements are out of phase and cancel each other out. With indented antenna configurations, broadband isolation between the transmitting and receiving paths can be achieved for both monostatic and bistatic antenna settings. The improvement is obtained without sacrificing antenna radiation patterns or polarizations. Measured results with a four-element indented quasi-Yagi antenna array operating from 3.2 to 3.4 GHz are presented. The results have demonstrated a 13-dB improvement on the antenna return loss of a single array, a 15-dB transmit/receive isolation improvement in a monostatic array, including circulators, and a 20-dB transmit/receive isolation improvement for a bistatic array without using circulators.

Compact Antenna Module With Optimized Tx-to-Rx Isolation for Monostatic RFID

In this letter, a compact monostatic antenna module with Tx-to-Rx isolation optimized by on-board reconfigurable leakage canceller and balanced antenna structure is presented. The self-interference of monostatic structure is managed by a directional coupler with impedance mismatch (Γ) reflector integrated into the antenna module with small area occupation. Also, quadruple inverted-F antenna is adopted to minimize the effect of antenna load variation and reduce the overall module size. The proposed antenna-integrated module was implemented and tested at 917 MHz as a UHF radio-frequency identification application. The measurement with various tag antennas showed the improvements in Tx-to-Rx isolation characteristic more than 20 dB and tag read distances.

Monostatic Co-Polarized Full-Duplex Antenna With Left- or Right-Hand Circular Polarization

A monostatic dual-polarized simultaneous transmit and receive (STAR) antenna system with high isolation is introduced. A beamforming network (BFN) producing 0°, ±90°, ±180°, and ±270° phase progression is used to feed TX and RX ports of four dual-polarized antenna elements arranged in a sequential rotation array (SRA). Due to the phase progression and geometrical symmetry of SRA, the coupling from TX to RX ports is canceled at the RX port of the BFN; therefore, infinite system isolation is theoretically obtained. Full-wave simulations are used to verify the theory and study effects of element spacing and BFN imbalances. An additional cancelation layer is designed and used to compensate for the imbalances by the BFN and nearby scatterers. The proposed STAR antenna system is prototyped and tested in the 2.4–2.5 GHz industrial, scientific, and medical band where the measured isolation and return loss are above 47 and 22 dB, respectively. A dual circularly polarized antenna performance with realized gains above 7 dBic, broadside axial ratio <1.6 dB, and symmetric beams is demonstrated. An ability of the proposed monostatic STAR antenna system to achieve wideband operation is also demonstrated with a quad-ridge horn as an element.

Antenna Systems for Simultaneous Transmit and Receive (STAR) Applications

Abstract Several novel wideband co-polarized circulator-less monostatic antenna and array designs for co-channel simultaneous transmit and receive (STAR) applications are presented. The monostatic STAR apertures are demonstrated first by utilizing multi-arm spiral antennas where a set of arms is used for transmitting (TX) and the other set for receiving (RX). Then, square and hexagonal broadside STAR arrays utilizing closely-spaced spiral antennas are introduced. Finally, (quasi) omnidirectional circular STAR arrays based on phase modes orthogonality principles are realized using four wideband monocone antenna elements. The studied configurations are integrated with the proper beamforming networks to excite the desired modes of TX/RX operations leading to theoretically infinite isolation between TX and RX ports. Practically, the achieved isolation is limited by the electrical asymmetries of the used components. Overall, consistent wideband operation, high isolation, and decent far-field performance are achieved for all proposed STAR approaches.

Monostatic ultra-wideband GPR antenna for through wall detection

The aim of this paper is to present a monostatic arc-shaped ultra-wideband (UWB) printed monopole antenna system with 3-16 GHz frequency bandwidth suitable for through-wall detection. Ground penetrating radar (GPR) technique is used for detection with the gain of 6.2 dB achieved for the proposed antenna using defected ground structure (DGS) method. To serve the purpose, a simulation experiment of through-wall detection model is constructed which consists of a monostatic antenna act as transmitter and receiver, concrete wall and human skin model. The time domain reflection of obtained result is then analysed for target detection.

Perfect Isolation: Dealing with Self-Jamming in Passive RFID Systems

Passive RF identification (RFID) readers transmit a continuous wave (CW) powering signal to remotely power up batteryless transponders, while simultaneously receiving a backscattered signal at the same frequency [1]. To separate the transmitter and receiver paths, readers use either a bistatic or monostatic antenna configuration. The first configuration employs two separate antennas, one to transmit and one to receive; in the second, the transmitter and receiver share a common antenna by means of a coupler or circulator. Both cases, however, suffer from poor transmitter-to-receiver isolation: strong CW signals can leak into the receiver, degrading its sensitivity to the weak transponder backscattered signals. Receiver sensitivity degradation occurs due to the leaked local oscillator (LO) phase noise [1] and also to the saturation of the front end caused by strong CW leakage. This requires high-dynamic-range capability in the RF stage [the low-noise amplifier (LNA) and mixer] as well as in the baseband stage [the amplifiers and analog-to-digital converters (ADCs)].

Front-end antenna system design for the ITER low-field-side reflectometer system using GENRAY ray tracing.

A monostatic antenna array arrangement has been designed for the microwave front-end of the ITER low-field-side reflectometer (LFSR) system. This paper presents details of the antenna coupling coefficient analyses performed using GENRAY, a 3-D ray tracing code, to evaluate the plasma height accommodation capability of such an antenna array design. Utilizing modeled data for the plasma equilibrium and profiles for the ITER baseline and half-field scenarios, a design study was performed for measurement locations varying from the plasma edge to inside the top of the pedestal. A front-end antenna configuration is recommended for the ITER LFSR system based on the results of this coupling analysis.

Canal structure subsidence investigation using ground penetrating radar and geotechnical techniques

Channel structure settlement along a canal in Lagos, southwestern Nigeria, was investigated using the ground penetrating radar (GPR) and geotechnical techniques with a view to establishing the cause(s) of the structure failure. GPR probing was carried out along eight parallel traverses in the E–W direction using the GSSI SIR-3000 200 MHz monostatic antenna. Geotechnical investigations involving sieve analysis, Atterberg limits, moisture content, organic content and consolidation test were carried out for soil classification and competence test. X-ray diffraction (XRD) studies were conducted to determine clay mineralogy of the peaty soil. The GPR data were processed using Radpro software. Four lithological layers consisting the topsoil (sand), peat, clay and sandy clay were delineated from the processed GPR data. Peat occurred at shallow depth to depths deeper than the foundation depth of the engineering structure investigated. The geotechnical results revealed that the peat has 125–167 % moisture content, high liquid limit and plastic index values of 109–174 % and 60–100 % respectively and organic content of 5.12 %. The sieve analysis showed that the peaty soil is fine grained having up to 98 % passing at 0.004 mm sieve opening exhibiting high compressibility and low consolidation coefficients. This peat was classified as organic clay with peat using the unified soil classification system. The XRD analyses showed the dominance of kaolinite, illite and quartz minerals in the peaty soil. This study revealed that the peaty soil underlying the investigated area has geologic and engineering properties not suitable to sustain the canal construction.

Temporal Monitoring of the Soil Freeze-Thaw Cycles over a Snow-Covered Surface by Using Air-Launched Ground-Penetrating Radar

We tested an off-ground ground-penetrating radar (GPR) system at a fixed location over a bare agricultural field to monitor the soil freeze-thaw cycles over a snow-covered surface. The GPR system consisted of a monostatic horn antenna combined with a vector network analyzer, providing an ultra-wideband stepped-frequency continuous-wave radar. An antenna calibration experiment was performed to filter antenna and back scattered effects from the raw GPR data. Near the GPR setup, sensors were installed in the soil to monitor the dynamics of soil temperature and dielectric permittivity at different depths. The soil permittivity was retrieved via inversion of time domain GPR data focused on the surface reflection. Significant effects of soil dynamics were observed in the time-lapse GPR, temperature and dielectric permittivity measurements. In particular, five freeze and thaw events were clearly detectable, indicating that the GPR signals respond to the contrast between the dielectric permittivity of frozen and thawed soil. The GPR-derived permittivity was in good agreement with sensor observations. Overall, the off-ground nature of the GPR system permits non-invasive time-lapse observation of the soil freeze-thaw dynamics without disturbing the structure of the snow cover. The proposed method shows promise for the real-time mapping and monitoring of the shallow frozen layer at the field scale.

The use of ground penetrating radar for mapping rock stratigraphy and tectonics: Implications for geotechnical engineering

This paper presents results from ground penetrating radar surveys using the SIR-10B GPR instrument (manufactured by Geophysical Survey System Inc., USA), with 400 MHz monostatic antenna (model 5 103). Survey was made over 3 excavation levels along the highway section at the Ras en Naqab escarpment area, Southwest Jordan. A total of 217 m along 4 profiles were covered in the winter of 2012. The objectives of the study are (i) to evaluate the resolution of the GPR technique in the field for detecting and locating anomalies caused by subsurface structures like cavities, fractures and faults, and (ii) to describe stratigraphic nomenclature of the subsurface rocks of the area. 2D interpre- tation of the obtained data and the geological information demonstrate a strong correlation between the GPR anomalies and the subsurface geology. Based upon the lateral and vertical velocity changes with depth, the thickness and orientation of the subsurface layers are outlined. Analysis of the exposed sec- tion shows good agreement between the estimated thicknesses of lithostratigraphic units and the quan- titative assessment of the radar waves velocity inferred from GPR data.

Design of a Doppler reflectometer for KSTAR.

A Doppler reflectometer has been designed to measure the poloidal propagation velocity on the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak. It has the operating frequency range of V-band (50-75 GHz) and the monostatic antenna configuration with extraordinary mode (X-mode). The single sideband modulation with an intermediate frequency of 50 MHz is used for the heterodyne measurement with the 200 MHz in-phase and quadrature (I/Q) phase detector. The corrugated conical horn antenna is used to approximate the Gaussian beam propagation and it is installed together with the oversized rectangular waveguides in the vacuum vessel. The first commissioning test of the Doppler reflectometer system on the KSTAR tokamak is planned in the 2014 KSTAR experimental campaign.

Performance and data analysis aspects of the new DIII-D monostatic profile reflectometer system.

A new frequency-modulated profile reflectometer system, featuring a monostatic antenna geometry (using one microwave antenna for both launch and receive), has been installed on the DIII-D tokamak, providing a first experimental test of this measurement approach for profile reflectometry. Significant features of the new system are briefly described in this paper, including the new monostatic arrangement, use of overmoded, broadband transmission waveguide, and dual-polarization combination/demultiplexing. Updated data processing and analysis, and in-service performance aspects of the new monostatic profile reflectometer system are also presented. By using a raytracing code (GENRAY) to determine the approximate trajectory of the probe beam, the electron density (ne) profile can be successfully reconstructed with L-mode plasmas vertically shifted by more than 10 cm off the vessel midplane. Specifically, it is demonstrated that the new system has a capability to measure ne profiles with plasma vertical offsets of up to ±17 cm. Examples are also presented of accurate, high time and spatial resolution density profile measurements made over a wide range of DIII-D conditions, e.g., the measured temporal evolution of the density profile across a L-H transition.

Peat stratigraphy mapping using ground penetrating radar and geotechnical engineering implications

Ground Penetrating Radar (GPR) surveys was carried out in southwestern part of Lagos, Nigeria with a view of delineating the subsurface peat stratigraphy that would aid geotechnical engineering design of the appropriate soil stability processes . The GPR study was conducted along seven (7) parallel traverses trending E-W using the GSSI SIR-3000 200MHz monostatic shielded antenna. The mineralogy, micro-fabrics and morphology of the delineated stratigraphy was determined using the scanning electron microscope (SEM) and X-Ray diffraction (XRD) methods. The results obtained revealed the presence of five subsurface geological layers, distinct geomorphological features, and high, moderate and low amplitudes, to continuous and discontinuous planar radar facies structures. Borehole information confirms the occurrence of shallow peat and plastic clay layers beneath the area. SEM and XRD analyses of the field samples obtained showed the dominance of kaolinite, illite and quartz minerals in the clay/peat mapped. The derived engineering parameters suggest that the peats found in the area are fibrous peat with low strength and medium to low bedding stress. It is observed that the peat generally depict high compressibility value and low shear modulus. Our findings confirm the efficacy and relevance of GPR technique for pre-construction engineering investigations. Keywords : Compressibility, GPR, Mineralogy, Peat Stratigraphy, Soil Stability.

Ultrawideband Time-Reversal Imaging With Frequency Domain Sampling

A new ultrawideband (UWB) time-reversal imaging method based on the unconventional utilization of UWB frequency data is introduced. First, a set of monostatic antennas is used to acquire the scattering data for a given scenario. Then, a corresponding multistatic data matrix is formed by casting the fine and coarse frequency samples of the scattering information into matrix form. The resulting frequency-frequency monostatic matrix is later fed into the adapted DORT (French acronym for decomposition of the time-reversal operator) and MUSIC (Multiple-Signal Classification) algorithms. The performance of the proposed method is investigated numerically by applying it to discrete scatterers embedded in homogeneous and continuously random inhomogeneous media. The effect of frequency bandwidth on image resolution is studied. It is observed that wider frequency bandwidths yield to better focusing resolutions.

Mapping subvertical discontinuities in rock cuts using a 400-MHz ground penetrating radar antenna

Hidden subvertical discontinuities oriented parallel to subparallel to the exposed faces of outcropping sandstone were effectively mapped at three different study sites in central Missouri using a ground-penetrating radar system (GPR) equipped with a 400-MHz monostatic antenna and a survey wheel. At each site, a suite of 2-D ground-penetrating radar profiles were acquired along multiple closely spaced traverses on relatively smooth exposed rock surfaces. Time-zero correction was applied to the raw GPR data which were then processed using band-pass filtering, range and display gain, color transformation, and deconvolution techniques. Pseudo 3D images of each identified discontinuity at each site were constructed based on the interpretation of the nonmigrated ground-penetrating radar profiles. These pseudo 3D images were hand-migrated and transformed into true 3D images which depict variable depths at “perpendicular horizontal distance” to each discontinuity relative to the exposed rock face. The results demonstrate that GPR can be used to detect and map hidden discontinuities. This information can then be used for rock slope stability analysis and rock engineering purposes.

Image-radargram analysis based on generalized Hough transform: experimental cases

This paper presents an algorithm based on the generalized Hough transform (GHT) to enhance geological structures in a 2D profile image constructed from ground-penetrating radar data. The proposed algorithm is applied over an edge representation image of the radargram; its local application (in Windows) allows us to identify structures and to obtain a global image delimiting the subsurface structures of interest. To show and validate the program, it was applied to two experimental cases: the first one is a profile of volcanic stratigraphic structures, and the second one consists of three buried pipes. The GHT algorithm enhances the main geological structures for both examples. Due to the use of a monostatic antenna in the case of buried pipes, a proper velocity analysis could not be done. As a consequence, the radargram remained under-migrated leaving some traces of diffraction hyperbola tails. These traces were detected by the GHT; therefore, a robust algorithm was designed to adjust a circle over these hyperbola traces. This secondary algorithm is called ‘circular structure determination’.

Ground penetrating radar and palaeontology: The detection of sirenian fossil bones under a sunflower field in Tuscany (Italy)

The application of Ground Penetrating Radar (GPR) in vertebrate palaeontology is very rare. We describe the discovery of an Early Pliocene sirenian skeleton detected by GPR in a locality near Grosseto (Tuscany, Italy). The specimen represents one of the most complete skeletons of Metaxytherium subapenninum (Mammalia: Sirenia) ever found in the Mediterranean area. Using a monostatic antenna of 200MHz, this non-invasive technique allowed us to detect most of the bones of the skeleton (skull, mandible, vertebrae and ribs) revealed in a distinct zone reflecting the electromagnetic waves. Other bones were found in correspondence with some smaller reflective zones of high back-scattered energy. Each bone was located in a grid system to compare its position with the spatial distribution of reflective zones. We are confident that the positive outcomes experienced in this work will encourage the use of GPR for future field research in vertebrate palaeontology.

Novel mono-static arrangement of the ASDEX Upgrade high field side reflectometers compatible with electron cyclotron resonance heating stray radiation

The ASDEX Upgrade frequency modulated continuous wave broadband reflectometer system uses a mono-static antenna configuration with in-vessel hog-horns and 3 dB directional couplers. The operation of the new electron cyclotron resonance heating (ECRH) launcher and the start of collective Thomson scattering experiments caused several events where the fragile dummy loads inside the high field side directional couplers were damaged, due to excessive power resulting from the ECRH stray fields. In this paper, we present a non-conventional application of the existing three-port directional coupler that hardens the system to the ECRH stray fields and at the same time generates the necessary reference signal. Electromagnetic simulations and laboratory tests were performed to validate the proposed solution and are compared with the in-vessel calibration tests.

Wideband Characterization of Backscatter Channels: Derivations and Theoretical Background

The wireless channel of backscatter radio systems is a two-way pinhole channel, created by the concatenation of two standard wireless channels. We present a method to calculate wideband channel parameters of backscatter channels based on the parameters of the constituent one-way channels. The focus is on characteristics that are vital for narrowband and wideband ranging, such as the K-factor w.r.t. the direct (line-of-sight) path and the RMS delay spread. The presented analyses include uncorrelated as well as correlated channel pairs and are thus valid for bistatic and monostatic antenna setups. We also show that the uncorrelated scattering (US) assumption holds for the backscatter channel provided that the constituent channels are US.