A dipole sub-array with reduced mutual coupling for large antenna array applications

The use of large array antennas in multiple-input multiple-output (MIMO) exploits diversity and reduces the overall transmission power making it a key enabling technology for 5G. Despite all the benefits, mutual coupling (MC) between elements in these array antennas is a concerning issue as it affects the antenna terminal impedance, reflection coefficients, etc. In this paper, a four-element printed dipole sub-array with reduced MC for S-band has been proposed. A balanced transmission line structure has been designed with two dipole arms on the opposite side of the substrate. Simulated and measured results are in good agreement making the design suitable for large array applications such as phased array radars. The proposed array exhibits good impedance matching with a reflection coefficient of -45 dB and resonating at the center frequency of 2.8 GHz. Moreover, isolation of -20 dB has been achieved for each element in a 2×2 planar array structure using out of band, parasitic elements, and planar shift by distributing the separation between the elements

Dual Band Integrated Antennas and Arrays For Global Navigation Satellite System.

The evolution of the Global Navigation Satellite System (GNSS) is aiming to provide more benefits in comparison to the existing standalone Global Positioning System (GPS). The biggest advantage for such an evolution will be higher visibility provided by combined number of navigation satellites in the orbit. Although a multi-band GNSS antenna and the receiver can exploit the advantages of the combined navigational systems, one of the biggest factors affecting the accuracy of the position solution is the presence of the multipath interference. These interference signals are generated by the reflection and diffraction of the incoming line of sight signals from different objects present around the antenna. This work presents the design, development and measurement of a novel dual band multipath mitigating antenna for precise orbit determination (POD) applications. The proposed antenna is the combination of a fully integrated dual band step-shorted annular ring antenna and a compact broadband multipath mitigating ground plane. The proposed antenna is compact, low cost and has a very simple easy to manufacture structure. Moreover, the proposed antenna configuration offers uniform performance across both bands. In order to validate the suitability of the proposed multi-path mitigating antenna for small satellite applications, the performance is compared against the existing multipath mitigating ground planes available in the literature. The figures of merit selected for the characterisation of multipath mitigation are front to back ratio (FBR), gain pattern slope, polarization purity, side lobe level suppression and cross polarisation gain at about and below the horizon. The overall antenna size, design complexity and commissioning have also been considered. This work also presents the design and development of a compact low cost dual band circularly polarized switched beam array antenna for remote sensing applications. The array antenna uses a low cost PIN diode and microstrip line based switching mechanism integrated to the antenna. The array provides left hand circular polarization (LHCP) with +-25 coverage and is intended for GNSS reflectometry where the weak navigation signals are picked up by the high gain antenna array after reflection from the surface of the ocean or the earth and different phenomenon such as speed and direction of the winds, and soil moisture can be estimated. Similar to the dual band multipath mitigating antenna, the measurement results of the integrated antenna array show uniform performance across both bandwidths

IMU Aided GPS Based Navigation of Ackermann Steered Rover

GPS signal loss is a major issue when the navigation system of rovers is based solely on GPS for outdoor navigation rendering the rover stuck in the mid of the road in case of signal loss. In this study, a low-cost IMU aided GPS-based navigation system for Ackermann Steered mobile robots is presented and tested to cater to the issue of GPS signal loss along. GPS path is selected and fed using the android application which provides real-time location tracking of the rover on the map embedded into the application. System utilizes Arduino along with the node MCU, compass, IMU, Rotary encoders, and an Ackermann steered rover. Contorller processes the path file, compares its current position with the path coordinates and navigates using inertial sensor aided navigation algorithm, avoiding obstacles to reach its destination. IMU measures the distance traveled from each path point, and in case of signal loss, it makes the rover move for the remaining distance in the direction of destination point. Rover faced a sinusoidal motion due to the steering, so PID was implemented. The system was successfully tested on the IST premises and finds its application in the delivery trolley, institutional delivery carts, and related applications

IMU Aided GPS Based Navigation of Ackermann Steered Rover

GPS signal loss is a major issue when the navigation system of rovers is based solely on GPS for outdoor navigation rendering the rover stuck in the mid of the road in case of signal loss. In this study, a low-cost IMU aided GPS-based navigation system for Ackermann Steered mobile robots is presented and tested to cater to the issue of GPS signal loss along. GPS path is selected and fed using the android application which provides real-time location tracking of the rover on the map embedded into the application. System utilizes Arduino along with the node MCU, compass, IMU, Rotary encoders, and an Ackermann steered rover. Contorller processes the path file, compares its current position with the path coordinates and navigates using inertial sensor aided navigation algorithm, avoiding obstacles to reach its destination. IMU measures the distance traveled from each path point, and in case of signal loss, it makes the rover move for the remaining distance in the direction of destination point. Rover faced a sinusoidal motion due to the steering, so PID was implemented. The system was successfully tested on the IST premises and finds its application in the delivery trolley, institutional delivery carts, and related applications

Novel dual-band antenna with simultaneous linear and circular polarizations

A multi-function microstrip antenna for simultaneous operation at two different frequency bands (centered at 1.575 GHz and 2.4 GHz) is presented. In contrast to the traditional dual-band antennas, the presented antenna design is unique as it can achieve two different polarizations simultaneously. Such a configuration makes the proposed antenna suitable for receiving signals from entirely different systems using a single antenna. In order to achieve the dual-band operation, a stacked configuration of microstrip antennas has been used where the top patch is designed to operate at 2.4 GHz with linear (vertical) polarization while the bottom patch is designed to operate at 1.575 GHz with right hand circular polarization. Although the proposed antenna is a typical dual-band stacked configuration, it is the antenna feed that makes it a novel design. The antenna feed consists of a broadband branch-line coupler but its connection to the antenna is non-symmetric thereby forcing the two different patches to produce different polarizations. Antenna simulation results show that the dual-band antenna achieves greater than 5 dBi gain at both frequency bands whereas the axial ratio remains less than 3 dB at the GNSS band (1.575 GHz). The axial ratio at the ISM band (2.4 GHz) is shown to be greater than 35 dB demonstrating a linearly polarized operation. The antenna has a compact size and low cost, suitable for portable terminal antennas receiving signals at both GNSS and ISM frequency bands

Comparative Analysis on the Structure and Properties of Iron-Based Amorphous Coating Sprayed with the Thermal Spraying Techniques

Iron-based amorphous coatings are getting attention owing to their attractive mechanical, chemical, and thermal properties. In this study, the comparative analysis between high-velocity oxy-fuel (HVOF) and atmospheric plasma (APS) spraying processes has been done. The detailed structural analysis of deposited coatings were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Mechanical and electrochemical properties were investigated by using micro-Vickers hardness testing, pin-on-disc tribometry and potentiodynamic analysis. The microstructure comparison revealed that HVOF-coated samples had better density than that of APS. The porosity in APS-coated samples was 2 times higher than that of HVOF-coated samples. The comparison of tribological properties showed that HVOF-coated samples had 3.9% better hardness than that of coatings obtained via APS. The wear test showed that HVOF-coated samples had better wear resistance in comparison to APS coatings. Furthermore, the potentiodynamic polarization and electrochemical impedance spectroscopy showed that the HVOF-coated samples had better corrosion resistance in comparison to APS-coated samples

Design and Development of a Near Isotropic Printed Arc Antenna for Direction of Arrival (DoA) Applications

This research presents an easy to fabricate isotropic printed arc antenna element to be used for direction of arrival (DoA) arrays. The proposed antenna exhibits a total gain variation of 0.5 dB over the entire sphere for 40 MHz impedance bandwidth at 1 GHz, which is the best design isotropy reported in literature so far. In addition, the isotropic bandwidth of the antenna for total gain variation of ≤3 dB is 225 MHz with 86% efficiency. The isotropic wire antenna is first designed and simulated in Numerical Electromagnetic code (NEC). An equivalent printed antenna is then simulated in CST, where single (short circuited) stub is integrated with the antenna for input matching and the results of NEC simulations are verified. The planar antenna is then manufactured using FR4 substrate for measurements. Good agreement between the measured and simulated results is observed, however the total gain variation is increased to 2 dB for the fabricated antenna. This is because of the unavoidable field scattering from the antenna substrate, the feed cables, and the antenna testing platform

Hyperspectral anomaly detection: a performance comparison of existing techniques

Anomaly detection in Hyperspectral Imagery (HSI) has received considerable attention because of its potential application in several areas. Numerous anomaly detection algorithms for HSI have been proposed in the literature; however, due to the use of different datasets in previous studies, an extensive performance comparison of these algorithms is missing. In this paper, an overview of the current state of research in hyperspectral anomaly detection is presented by broadly dividing all the previously proposed algorithms into eight different categories. In addition, this paper presents the most comprehensive comparative analysis to-date in hyperspectral anomaly detection by evaluating 22 algorithms on 17 different publicly available datasets. Results indicate that attribute and edge-preserving filtering-based detection (AED), local summation anomaly detection based on collaborative representation and inverse distance weight (LSAD-CR-IDW) and local summation unsupervised nearest regularized subspace with an outlier removal anomaly detector (LSUNRSORAD) perform better as indicated by the mean and median values of area under the receiver operating characteristic (ROC) curves. Finally, this paper studies the effect of various dimensionality reduction techniques on anomaly detection. Results indicate that reducing the number of components to around 20 improves the performance; however, any further decrease deteriorates the performance