Small Ground Clearance Research Articles

Effect of Trailing Edge and Span Morphing on the Performance of an Optimised NACA6409 Wing in Ground Effect

Abstract A CFD investigation was carried out on a three-dimensional NACA6409 wing in ground effect at a Reynolds number of 320,000. Using a Multi-Objective-SHERPA algorithm, a root angle of 4 degrees angle of attack, a tip angle of 6 degrees, a forward sweep and a tip chord of 20% of the root chord produced an optimum aerodynamic efficiency across all ground clearances. Optimisation showed a gain in aerodynamic efficiency of 41% at h/c = 0.05 ground clearance and a 31% gain at h/c = 0.2 compared to a rectangular planform wing. Next FishBAC camber morphing was applied to the optimised wing varying the morphing start locations along the chord at both the tip and root. A later start location produced the highest aerodynamic efficiency but increased manufacturing complexity. Extendable span morphing was also tested and was found increasing the span from 1c to 1.5c increased the aerodynamic efficiency of the optimised wing by 27.4% at h/c = 0.1. Varying the span from 0.8c to 1.2c in ground effect had a small effect on the drag for small ground clearances, for large ground clearances the total drag decreased as the span increased. Smaller gains were seen when the span morphing was applied to the rectangular wing. The FishBAC morphing was applied in the spanwise direction to morph the wing tip, sealing the flow beneath the wing. Also, the proportion of the morphing wing tip caused the trailing edge to be closer to the ground further enhancing ground effect.

Wideband Dual-Polarized Endfire Phased Array Antenna With Small Ground Clearance for 5G mmWave Mobile Terminals

A dual-polarized end-fire phased array antenna is presented for 5G mmWave mobile terminal applications. The antenna element combines a pair of top-hat dipoles with an open slot in two substrate layers. The dipole is excited by an open-ended substrate integrated waveguide (SIW) for vertical polarization, and the slot is coupled by a bent stripline for horizontal polarization. Both radiators can provide wide bandwidth, and share a small ground clearance of merely 1.6 mm. A 1 × 4 phased array is designed with an element spacing of 6 mm. Decoupling vias and decoupling slots are added between elements to improve port isolation. The simulated and measured overlapped bandwidth of the two polarizations are 21.4% and 14.6%, respectively. The isolation between any two ports is higher than 18 dB. The measured scanning beams of both polarizations are capable of covering ±42° within 3-dB gain variation.

Аналіз конструктивних особливостей мініобприскувачів для невеликих фермерських господарств

The purpose of the study is to perform an analysis of the design characteristics and efficiency of various types of mini-sprayers in small areas of row crops and to form criteria by which a new self-propelled mini-sprayer with a rod stabilization system should be designed. An analysis of the efficiency of various types of mini-sprayers in small areas used for planting various crops in small farms was carried out. For the outlined areas of treatment of field crops (within 0.2 hectares), it was established that knapsack sprayers require a significant amount of physical labor of the operator: to move the mass of the sprayer with the working fluid, pumping with a manual pump (for the option without an electric pump), frequent refueling. In addition, manual movement of the rod cannot guarantee the uniformity of application of the working preparation over the entire area, especially with continuous application. For wheelbarrow sprayers, it is established that their mass is transferred to the chassis, but the operator must push it to move. If we talk about the inter-row of plants, then a furrow is formed in the loose soil, which greatly complicates the movement of such a sprayer. In addition, small ground clearance and unregulated furrow do not allow movement by inter-rows of row crops. In the option of using a hinged rod, it is difficult to maintain a constant speed of movement if the sprayer is moved manually. When using the mini energy tool, the same issues arise – a small clearance of the energy tool and the inability to adjust the furrow width. There is also no rod stabilization system. Hinged sprayers are more dependent on the parameters of the power supply chassis. Here, mainly, the same problems arise – limited adjustment of furrow width and fixed clearance, which narrows their use in certain phases of plant growth, when the ground clearance of the energy source is insufficient to avoid damaging plants during processing. In addition, the absence of a rod stabilization system can be seen. This leads to its oscillations, which are transmitted from the wheels of the energy store when moving by field irregularities, and this has an effect on the uniformity of the introduction of the operating solution and the resource of work. Regarding trailed mini-sprayers, it is possible to eliminate some of the described drawbacks in their designs, but their functionality is significantly limited by the parameters of the energy tools with which they are aggregated. To increase the efficiency of applying the operating solution to the treated areas, at least the simplest pendulum suspensions should be used to stabilize the rod. In order to improve the quality of application of the operating solution on the treated surfaces, universal use for processing various crops, including work in gardens, reducing the manual labor of the operator, etc., it is necessary to develop a self-propelled small-sized sprayer, analogues of which are not observed on the Ukrainian market. The following requirements are put forward to the developed design: self-moving (using an engine); the ability to change the furrow width using service mechanisms; have sufficient clearance or regulate it; the hinged rod must have a stabilization system and be adjustable in height of the installation; the pressure line must maintain a constant and controlled pressure of the operating solution; the developed model of a self-propelled sprayer should be affordable for the average agricultural producer in the subsistence farming. Taking into account these requirements and the implementation of the sprayer design in practice, we will get a highly efficient and competitive machine in the mini sprayer market.

Designing Uncorrelated Multiple Antennas with Round Patterns Using Handset Metal Frames

Multiple antennas with low correlations are highly in demand in the mobile handsets for higher data rate. At the same time, the total pattern provided by the antennas should be as round as possible for reliable links. In this paper, by analysing the characteristic modes of the mobile chassis loaded by ultra-thin metal frames, a four-antenna system with a round total pattern is designed at 2.4 GHz. The gain variations are only 3.4 dB and 3.6 dB on two dominant planes. The isolations between antennas are above 15 dB, and the correlations are below 0.01, with intact ground plane and small ground clearance of 2 mm maintained. Afterwards, an eight-port antenna system is designed by taking advantage of the ground clearance and exciting modes with different phases. Low correlations of below 0.07 are obtained. The antenna system is fabricated, with the measured results agreeing well with the simulated ones.

Ground Effect of a Two-Dimensional Flapping Wing Hovering in Inclined Stroke Plane

Abstract The ground effect aerodynamics and flow physics of a 2D dragonfly wing hovering (the Reynolds number is 157) in an inclined stroke plane are investigated via solving 2D unsteady incompressible laminar flow Navier–Stokes equations. An analysis road map is proposed to explain the influence of the ground on the flow field, pressure distribution on the wing surface, and the aerodynamic force. In the analysis road map, the flow relative to the wing surface induced by the wing motion and vortex is classified into vertical and parallel wing surface flows. The vertical flow impinges on the wing surface to form a positive pressure zone. In contrast, the parallel flow generates the boundary layer and further concentrated vortex and secondary vortex, which induce negative pressure on the wing surface. The ground impacts the flow relative to the wing in three ways: changing the trajectory of the shed vortex by the mirror effect, promoting the deformation and fusion of the vortices, and causing the cushion effect at extremely small ground clearance.

Distinct Wing-in-Ground Effect of Airfoil in Proximity to Water Waves

The present study numerically explores the distinct aerodynamic characteristics of an airfoil flying in proximity to water waves. The water wave is treated by both two-phase-flow wavy water and rigid moving wavy ground, with a specific goal to clarify whether the water wave can be substituted by rigid wavy ground. Results show that for large ground clearance (), the aerodynamic forces and flow structures of the near-field airfoil are basically dominated by the passage shape between airfoil and wave surface where the wavy water can be replaced by means of using wavy ground. However, it is different for small ground clearance that the airfoil-induced airflow has a strong relative speed to the water flow and subsequently creates a strong shear force on the forthcoming wave to eject water spray from wave crest. The spray has a sufficient influence on the flow topology and consequently leads to a distinct aerodynamic behavior. Particularly, the strong upstream shear on the wave resulted from the stagnation region at a positive angle of attack induces upwind spray, which can be elevated to hit onto the airfoil with larger density and momentum than airflow causing extraordinarily high pressure on the lower surface as well as unstable aerodynamic forces.

Designing Hand-Immune Handset Antennas With Adaptive Excitation and Characteristic Modes

This article presents a design process for a hand-immune mobile antenna system. Characteristic modes (CMs) of a mobile phone and hand combination are analyzed to find the desired modes with good radiation properties. The efficient excitation of these modes is implemented by utilizing the antenna cluster technique. The proposed mobile antenna design has a small ground clearance of only 2 mm and can cover the 700-960 MHz low band, 1700-2700 MHz middle-high band (MHB) with two multiple-input-multiple-output (MIMO) antennas, and the 3300-3800 MHz high band with four MIMO antennas. The measurement results confirm that the proposed CM analysis-based design method in a realistic use case leads to a robust antenna design with competitive performance.

Frame Integrated Wideband Dual-Polarized Arrays for Mm-Wave/Sub 6-GHz Mobile Handsets and Its User Effects

In this work, wideband dual-polarized dielectric resonator antenna (DRA) arrays are designed for 5G mobile handsets and integrated with the sub-6GHz antenna. The dielectric resonators, surrounded by concentric air holes and metal vias, are excited by two orthogonal slots and fed through microstrip lines, providing a wide bandwidth from 25.3 GHz to 29.8 GHz. A high isolation of above 40 dB is obtained between the ports of the orthogonally polarized antennas. Based on the dual-polarized DRA, two 1 × 4 arrays are built and integrated with the longer metal frames of the handset, without occupying extra space on the chassis. The scanning angle for the proposed array is from 47° to 121° for the gain of above 10 dBi, and the overall handset antennas provide a large coverage efficiency of 80% for a threshold gain of 5 dBi. User effect has also been investigated, manifesting that the horizontally polarized antennas are less influenced by the hands in both the one-hand and the two-hand data modes. Furthermore, a sub-6GHz antenna is designed with a wide operating band from 0.7 GHz to 0.94 GHz simply by making use of the shorter frames and the dual-layered DRAs, with a small ground clearance of 2 mm remained. The performances of the arrays are validated by measuring the representative antennas. The proposed antenna is a good candidate for future handsets due to its high integration with the metal frames and with the LTE antenna, its large bandwidth and large coverage in free space and different user scenarios.

4G/5G antenna with small clearance for metal frame smartphone applications

AbstractAn 4G/5G antenna with small clearance for metal frame smartphone applications is proposed. The proposed antenna consists of metal frame, inverted‐T feeding lines, S‐shaped branch, and the system ground on which U‐shaped slot is etched. The metal frame is broken and there is a 2 mm open slit on the metal frame. There is a 2 mm gap between the metal frame and the substrate. The ground clearance of the proposed antenna is 34.5 × 5.5 mm. Inverted‐T feeding lines are connected to the metal rim. Using the multiple radiation patterns of S‐shaped branches and the coupling ring mode of S‐shaped branch and ground‐extending metal frames, the measured −6 dB impedance bandwidth are 1680 to 2820 MHz and 2870 to 5500 MHz bands, which can fully cover DCS1800, PCS1900, UMTS2100, LTE2400, 2600 (1710 to 2690 MHz), and 5G N77/N78/N79 (3300‐4200 MHz, 4400‐5000 MHz) bands. The measured efficiency is greater than 43% in desired bands. The proposed antenna has the advantages of small ground clearance, wide bandwidth, and no lumped elements.

A Wideband Dual-Polarized Endfire Antenna Array With Overlapped Apertures and Small Clearance for 5G Millimeter-Wave Applications

In this article, an endfire dual-polarized phased antenna array with small ground clearance is proposed for the fifth-generation (5G) millimeter-wave (mmW) applications with a wide bandwidth. In this array, each antenna element consists of a dipole fed by a microstrip line for horizontal polarization and an H-plane horn using substrate-integrated waveguide (SIW) for vertical polarization. To achieve a wide bandwidth for vertical polarization, two metal vias are added at the aperture of the horn antenna. Then, a four-element antenna array is designed by partially overlapping the aperture of each horn element. A prototype has been fabricated using multilayer printed circuit board (PCB) process. The measured results agree well with the simulated ones. The antenna is with an impedance bandwidth of |S11| <; -10 dB from 24.4 to 29.5 GHz for both polarizations. The maximum gains of vertical and horizontal polarizations are 9.16 and 9.27 dBi, with the scanning angle from -34° to 33° for both polarizations with gain deterioration less than 3 dB. The proposed antenna is a promising solution for 5G mmW cellphones or antenna-in-package applications.

Small‐size four‐element antenna system for 2 × 2 LTE LB and 4 × 4 LTE M/HB MIMO operations in5Gmobile terminals

A small-size four-element antenna system for 2 × 2 LTE low band (LB, 698-960 MHz) and 4 × 4 LTE middle/high band (M/HB, 1710-2690 MHz) multiple-input multiple-output (MIMO) operations in 5G (fifth-generation) mobile terminals is presented. The proposed antenna system is formed by two identical tunable loop antennas and two identical coupled-fed IFA (Inverted-F Antenna) antennas. By loading a RF switch with four output states as tunable component, the proposed loop antenna can not only operate in the M/HB, but also achieve improved bandwidth coverage in the LB. Each coupled-fed IFA element operating in the M/HB with compact volume. The four antennas are placed on the both short side-edge of the mobile terminal with small ground clearance of 4.2 mm. The simulated S-parameters show that the proposed MIMO system can cover 698 to 960 MHz and 1710 to 2690 MHz with reflection coefficients less than −6 dB and isolations are all more than 12 dB. Good MIMO performances such as radiation efficiencies, envelope correlation coefficient (less than 0.4 within the entire operation bands) and channel capacity are also obtained. The effects of user's hand(s) on performances for the proposed antenna system are also discussed. This four-element antenna system prototype is fabricated and measured.

Compact Eight-Element Antenna Array for Triple-Band MIMO Operation in 5G Mobile Terminals

In this paper, we have introduced a compact eight-element antenna array for triple-band MIMO (multi-input multi-output) operation in 5G (fifth generation) mobile terminals, which consists of two symmetric four-element sub-arrays disposed, respectively, along two long side-edges of the system ground plane of the mobile terminal. This antenna element can operate at two dual-wideband of 3250-3820 MHz and 4790-6200 MHz with three resonance frequencies which can fully cover 5G NR (New Radio) BandN78 (3300-3800 MHz), China 5G-Band of 4800-5000 MHz and LTE Band-46 (5150-5925 MHz). The main parameters that characterize the performance of the proposed MIMO antenna system, such as bandwidth, reflection coefficient, isolation (more than 10.5 dB), total radiation efficiency (more than 43%), ECC (envelope correlation coefficient, less than 0.12) and CC (channel capacity, 34.9-37.6 bps/Hz), are analyzed and presented in this paper. Besides, the effects of single-hand and dual-hand on performance of the MIMO antenna system are also discussed. The structure of antenna element is only 15 mm × 3 mm (0.175 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.035 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the frequency of 3.5 GHz) with a very small ground clearance of 13 mm × 2 mm on the main board of the proposed mobile terminal. The antenna system has the possibility to be used in 5G mobile terminals with triple-band operation, narrow frame and large display. The corresponding antennas prototype is fabricated and measured; and a quite good agreement between simulation and measurement is obtained.

Unbroken Metal Rim MIMO Antenna Utilizing Antenna Clusters

This letter presents an antenna system for mobile devices with an unbroken metal rim. By utilizing the characteristic mode analysis for the unbroken metal rim, efficient multiple-input–multiple-output operation can be achieved. The design is based on an antenna cluster technique that uses several coupled elements that are used to efficiently excite the modes of the rim. Nonresonant antenna elements and matching networks are used to couple to the metal rim. The design has small ground clearance of 5 mm and height of only 4 mm, and can operate in wide bandwidths both in 700–960 MHz low band and 1.56–4 GHz high band. Measurement results confirm that competent performance is achieved.

Wideband MIMO antenna with small ground clearance for mobile terminals

In this study, a compact planar multiple-input-multiple-output (MIMO) antenna is presented for mobile terminal applications. Various dual-element configurations are studied using the theory of characteristic modes. The reason of port isolation is explained from the view of modal weighting coefficients. It is found that by arranging the two elements at the top and bottom sides of the board and placing the feed ports at the corners of the board, not only the bandwidth is enhanced but also the port isolation is improved. To further broaden the bandwidth, three branches are well cooperated to provide three λ/4 modes. The optimised no-ground region (i.e. the ground clearance) of each element only occupies an area of 5 × 30 mm2. The measured bandwidth can cover the 1710–2690 MHz band with the criterion of −10 dB reflection coefficient. The measured port isolation achieves 19 dB without using any decoupling structure. The efficiency is >60% in the entire band. In addition, the user effect on MIMO antenna performance is evaluated.

TCM-Based Bezel Antenna Design With Small Ground Clearance for Mobile Terminals

A high efficiency mobile terminal antenna with small ground clearance is presented in this paper. It consists of a chassis ground, an unbroken metal bezel, and two connecting metal strips. The theory of characteristic modes is applied to analyze the eigenmodes of the design in the frequency range of 600–3000 MHz. All the resonant modes are clearly tracked and identified. Each mode of the bezel has the even and odd states and can be illustrated by a two-slot model. The multiple modes of the bezel can be effectively excited by a simple probe. By changing the locations of the connecting strips and feeder and introducing an inductor, two fundamental modes and four higher order modes of the bezel are merged, providing sufficient bandwidth for mobile communication. The measured −6 dB bandwidths are 805–995 and 1340–2870 MHz, and the measured radiation efficiency is above 65% in both bands.

Switch-Reconfigurable Metal Rim MIMO Handset Antenna With Distributed Feeding

A new antenna design method together with a novel metal rim antenna is presented in this paper. The design method transforms an electromagnetic synthesis problem into a circuit problem, which can be solved in a straightforward manner. The new metal rim antenna is based on switches and the antenna cluster concept. The antenna cluster concept uses several, differently fed radiating elements together as one antenna. The proposed method is used to design a handset antenna with small ground clearance of 5 mm capable of 2×2 MIMO operation in the 698-960 MHz low band with 30-40 % efficiency and 4×4 MIMO in the 1.7-2.7 GHz middle-high band with better than 50% efficiency, and the 3-4 GHz high band with efficiency up to 75 %. The proposed optimization method leads to a novel way of distributing the antennas over the entire available volume.

High-Efficiency Crossed-Loop 4G LTE Antenna for All Display Metal-Rimmed Smartphones

A symmetrically crossed-loop antenna featuring very high radiation efficiency across the entire LTE frequency bands for metal-rimmed smartphones with only 2 mm ground clearance is proposed, analyzed, and verified. The employment of even and odd modes is utilized to achieve wide bandwidth across 698–960 MHz (low-frequency spectrum), 1710–2170 MHz (middle-frequency spectrum), and 2300–2690 MHz (high-frequency spectrum). Empirical analysis confirms the crossed-loop topology results in a 180° phase shift of the electric current distribution on the ground plane, resulting in enhancement of the radiation resistance. As a result, the devised LTE antenna exhibits more than 48% to 75% total system efficiency across the entire band of interest, which is the highest efficiency reported in literature for metal-rimmed smartphones with extremely small ground clearance.

Self‐decoupled compact metal‐frame LTE MIMO antennas for the smartphone

AbstractTwo self‐decoupled, closely‐spaced, metal‐frame LTE MIMO antennas with compact frame lengths to fit in the short edge of the metal‐framed smartphone are presented. The 2 MIMO antennas include a first antenna covering the LTE low band (LB) in 824–960 MHz and LTE middle/high band (M/HB) in 1710–2690 MHz and a second antenna covering the LTE M/HB in 1710–2690 MHz. With a small ground clearance of 5 mm, the first antenna uses a radiating metal frame (frame 1) of length 47 mm to cover the LTE L/M/HB, while the second antenna uses a radiating metal frame (frame 2) of 23.4 mm for the LTE M/HB coverage. In addition, frames 1 and 2 are closely spaced with a gap of 2 mm only. Wideband decoupling between the 2 antennas for the 2 × 2 MIMO operation in the LTE M/HB is obtained with frame 2 serving as an inherent decoupling structure. That is, frame 2 not only functions as a radiator of the second antenna but also serves as a decoupling structure to attract the surface currents on the system ground plane which causes the coupling of the 2 antennas. Applications of applying another 2 MIMO antennas at the opposite short edge of the smartphone for the 4 × 4 LTE M/HB and 2 × 2 LTE LB MIMO operations are also addressed.

Small‐size reconfigurable antenna for WWAN/LTE/GNSS smartphone applications

A small-size reconfigurable smartphone antenna using a PIN diode for WWAN/LTE and global navigation satellite system (GNSS) smartphone application is presented. When the diode is in `OFF' state, a T-shaped feeding strip and an encircled T-shaped parasitic shorted strip formed a coupled-fed antenna, which achieves a low-wideband covering GSM850/900 bands and a high-wideband covering GSM1800/1900/UMTS2100/LTE2300/2500 bands. When the diode is in `ON' state, a loop antenna working at 1/2 wavelengths is formed to cover the bands of GNSS, which includes four positioning systems (COMPASS, GALILEO, GPS and GLONASS). In addition, the proposed antenna is easily printed on a small ground clearance of 375 mm 2 without loading any lumped element. Also, the proposed simple and compact antenna is convenient to be optimised for desired bands. Finally, the good agreement of simulated and experimental results proves that the proposed antenna is suitable for practical mobile terminal equipment.

Numerical study on aerodynamics of banked wing in ground effect

Unlike conventional airplane, a WIG craft experiences righting moment and adverse yaw moment in banked turning in ground effect. Numerical simulations are carried out to study the aerodynamics of banked wing in ground effect. Configurations of rectangular wing and delta wing are considered, and performance of endplates and ailerons during banking are also studied. The study shows that righting moment increase nonlinearly with heeling angle, and endplates enhance the righting. The asymmetric aerodynamic distribution along span of wing with heeling angle introduces adverse yaw moment. Heeling in ground effect with small ground clearance increases the vertical aerodynamic force and makes WIG craft climb. Deflections of ailerons introduce lift decrease and a light pitching motion. Delta wing shows advantage in banked turning for smaller righting moment and adverse yaw moment during banking.