Main Beam Direction Research Articles

Low-Profile ESPAR Antenna for RSS-Based DoA Estimation in IoT Applications

In this paper, we have introduced a low-profile electronically steerable parasitic array radiator (ESPAR) antenna that can successfully be used to estimate the direction-of-arrival (DoA) of incoming signals in wireless sensor network (WSN) applications, in which the height of the complete antenna has to be low. The proposed antenna is over three times lower than high-profile ESPAR antenna designs currently available in the literature for the DoA estimation; it can provide eight unique main beam directions and relies on simplified beam steering, which makes it applicable to simple and inexpensive WSN nodes. Measurements using our fabricated ESPAR antenna prototype indicate that relying solely on the received signal strength values recorded at the antenna output port, it is possible to achieve accurate DoA estimation results with error levels similar to those available for high-profile ESPAR antennas relying on the similar energy-efficient simplified beam steering concept and having 12 unique main beam directions. As a consequence, the overall time required for the DoA estimation using the proposed antenna can be reduced by 33%.

Environmental Monitoring and Evaluation of the X-Ray Field Flaw Inspection Workplace in a Factory Building

The surrounding radiation environment of the field flaw detection workplace has been theoretically calculated and monitored on site when an industrial X-ray flaw detector in a factory building is operated during the field flaw detection. The results show that when 5mA tube current and 250 kV tube voltage penetrate the steel tube at the thickness of 16mm twice, the calculated value of the air kerma rate at the inspection point is basically consistent with the measured value. Additionally, the boundary of the controlled area and the supervised area corresponded to the measured value along the main beam direction belongs to the wall in the east of the workshop. The calculated distances of the leaking beam corresponding to the boundary of the controlled area and the supervised area of the calculated value should be 19m and 58m, respectively. The minimum and maximum distances of the controlled area of the measured value are 13m and 17m, respectively; while the maximum and minimum distances of the supervised area of the measured value are 31m and 36m, respectively, both areas are within the workshop. Meanwhile, annual effective doses that might be accepted by professionals and the public have been estimated.

Electronically beamscannable sinusoidally modulated reactance surface antenna

An electronically beamscannable sinusoidally modulated reactance surface (SMRS) antenna and its design procedure are investigated. The antenna is composed of capacitively modulated reactance surface whose profile is a sinusoidally varying form. This configuration generates a radiating leaky wave and the antenna's radiation pattern including beam angle and beamwidth can be controlled with different parameters of the modulated surface reactance of the SMRS period. A beamscanning characteristic of the capacitively modulated SMRS antenna is shown with the design procedure and the simulated results. Designed antenna was simulated using commercial EM tool and the result was well matched with the calculated main beam direction verifying the validity of design method. About 33° of beamcanning range was obtained with the center radiating angle of 45° at 9 GHz. Designed antenna showed reasonable input matching and efficiencies within beamscanning range of the antenna.

GO aperture and radiated fields of classical omnidirectional axis-displaced dual-reflector antennas

This work presents the vector geometrical optics (GO) aperture field of classical omnidirectional dual-reflector antennas with an arbitrary main-beam direction in the elevation plane. These antennas are composed of two axially symmetric reflectors generated by axis-displaced conic sections and are capable of operating in the microwave and millimeter wave bands. By using the aperture method (ApM), a formulation to obtain the electric far field radiated by all classical configurations is also derived. Some case studies are analyzed by the method-of-moments (MoM) technique in order to validate the proposed GO-ApM analysis procedure.

3-D Printer Based Lens Design Method for Integrated Lens Antennas

We propose a new and straightforward dielectric lens design method to increase the gain of integrated lens antennas (ILAs). Our lens is divided into several cone-shaped radial sections. Each section consists of specific permittivity to provide desired phase delays for the waves passing through the section. Our method does not depend on the operating frequencies and the physical appearance of the lens, because all the radial sections share one common phase center as a starting point. Accordingly, to change the main beam direction, we only need to rearrange the sections. However, the required permittivity is all different in every section, which is extremely difficult to be realized using conventional dielectric materials. To fabricate the required permittivity based on an effective medium theory, we use a cutting-edge three-dimensional printing technology. Consequently, we can obtain all the required permittivity using only one base printing material. Through experiments, we can show that our lens not only can form a desired beam but also can increase gain in the target direction, which proves the validity of our lens design method.

The application of variable‐frequency directional seismic wave technology under complex geological conditions

ABSTRACTMonofrequency directional seismic wave technology can be used to manipulate the phases of seismic waves, thereby focusing seismic signals into beams and strengthening the energy in the main beam direction. However, it is unknown whether a variable‐frequency signal can form a directional seismic wave, and the applicable conditions for utilizing this technology have not yet been reported. In this paper, we analysed the variable‐frequency directional seismic wave theory and methodology through ray tracing and the seismic wave equation. Based on the variable‐frequency directional seismic wave principle, the effects of directional parameters on the main beam direction and half‐power beamwidth were discussed in detail. In addition, the effectiveness of the variable‐frequency directional seismic wave method in several complicated velocity models was discussed. Numerical tests with the variable‐frequency directional seismic wave technique indicated that the energy intensity in the main beam direction increased by two to six times and the signal‐to‐noise ratio of the targets signal increased by 0.60–0.84 dB. Additionally, we used variable‐frequency directional seismic wave technology to analyse a shallow geological structure with a 9‐vibrator array in an area of Jilin Province. The field experiment results revealed that the near‐surface exploration depth increased from 60 to 240 m. Therefore, under complex geological conditions, the variable‐frequency directional seismic wave technology can improve the target signal at little cost.

Nonlinear Constrained Beamforming Algorithm for Circularly Polarized Phased Arrays

In this letter, a beamforming algorithm based on least-squares problem subjected to nonlinear constraints is proposed. The formulation allows the main beam direction, polarization, sidelobe level, and nulls positioning control. For validating the algorithm, the system composed of a circularly polarized microstrip antenna array and a microwave beamforming circuit was manufactured and characterized.

Substrate Integrated Waveguide-Based Periodic Backward-to-Forward Scanning Leaky-Wave Antenna With Low Cross-Polarization

For many leaky-wave antennas (LWAs), it is challenging to realize beam scanning through broadside. A problem is the presence of an open stopband (OSB), which restricts radiation in the broadside direction. In this paper, a novel substrate integrated waveguide (SIW)-based LWA is described to overcome the OSB problem and provide beam scanning continuously from the backward to the forward direction from a conventional periodic LWA. It is demonstrated that the $n =-1$ spatial harmonic can be excited efficiently from an SIW LWA and enables broadside radiation. However, it was found in our initial design that when the beam scans through the broadside, the cross-polarization level increases significantly compared to the beam close to the backfire direction. A technique is developed to reduce the cross-polarization level. As a result, a new antenna configuration is created. The antenna design has been realized and measured to validate the concept. The measured beam scanning range of the prototype is from -74° to +45° (119° of beam scanning) when the frequency sweeps from 7.625 to 11 GHz, and the measured cross-polarization level is 20.8 dB low at the main beam direction for the broadside beam.

Beam-Oriented Digital Predistortion for 5G Massive MIMO Hybrid Beamforming Transmitters

In this paper, we propose a beam-oriented digital predistortion (BO-DPD) technique for power amplifiers (PAs) in hybrid beamforming massive multiple-input multiple-output (MIMO) transmitters, which can achieve linearization of the transmitted signal in the main beam direction and address the DPD implementation issue in the hybrid beamforming array. In massive MIMO hybrid beamforming transmitters, the conventional DPD to linearize each PA is impractical to implement for that the number of digital chains is less than the number of PAs; however, the BO-DPD can resolve this issue by constructing and linearizing the “virtual” main beam signal rather than single PAs. According to the beamforming weights for array elements, the feedback path combines all PA’s outputs to estimate the main beam signal for DPD processing. In addition, an average estimation method is also presented to broaden the linearized angle range around the main beam direction. A $4 \times 16$ (four subarrays and 16 antennas in each subarray) uniform linear array (ULA) simulation along with a $1 \times 2$ ULA at 2.5 GHz and a $2 \times 2$ ULA at 3.5-GHz experimental tests was performed. The experimental results show that the proposed technique and linearization angle range broadening method achieve up to 15-dB adjacent channel power ratio improvement and 10° linearization angle range in the main beam direction.

A Compact, Low-Profile Log-Periodic Meandered Dipole Array Antenna with an Artificial Magnetic Conductor

A compact and low-profile log-periodic meandered dipole array (LPMDA) antenna with an artificial magnetic conductor (AMC) is proposed. For compactness, a meander line configuration is implemented with dipole elements and optimized using a genetic algorithm (GA) to realize the LPMDA antenna. As a result, a size reduction of approximately 30% is achieved as compared to a conventional log-periodic dipole array antenna. To enhance the gain characteristics, the AMC ground plane configuration is realized with 9 × 9 unit cells for the LPMDA antenna. Two prototypes of the proposed LPMDA antennas with and without an AMC are fabricated and measured to verify its performance. The measured −10 dB reflection ratio bandwidths are 2.56 : 1 (0.85–2.18 GHz) and 2.34 : 1 (0.92–2.16 GHz) for the proposed LPMDA antennas with and without the AMC, respectively. The gain at the main beam direction within the operating frequency bandwidth is significantly improved from 3.94–7.17 dBi to 7.86–10.01 dBi by applying the AMC.

A new pattern‐reconfigurable antenna with the function of 360° wide‐beam scanning and main beam direction finely‐adjustable

AbstractA new pattern‐reconfigurable antenna with the function of 360° wide‐beam scanning and main beam direction finely‐adjustable is proposed in this letter. The antenna consists of a central feeding disc which surrounded by four snowflake radiators on the top layer of the FR4 substrate. PIN diodes are placed between the disc and each snowflake patch for realizing the wide‐angle beam steering of the antenna. By controlling the four PIN diodes on the top layer, main beam can be switched in four directions with about 90° steps in the H‐plane (17°, 106°, 197°, and 287°).The bottom layer of the substrate includes a ground plane with eight rectangular ring slots. Eight PIN diodes installed on each slot are used to further control the beam direction of the antenna. By controlling the states of the PIN diodes on the bottom layer, the main beam of the proposed antenna is capable to deflect rightward or leftward about 10° on the basis of the original four states. The simulated and measured results show that the antenna operates well at 3.64–3.88 GHz under 12 states and achieves good performance with flexible pattern reconfigurability in 12 directions. The proposed antenna could be applied in 5G wireless communication systems.

Circularly Polarized Beam-Switching Antenna Array Design for Directional Networks

For modern directional communication networks, there is a significant and growing need for advanced antenna array designs that combine the high gain and broadband performance together with the low-cost and lightweight characteristics. In this letter, the beam-switching characteristics of a new 4 × 8 right-hand circularly polarized long slot antenna (LSA) array were analyzed when fed by an 8 × 8 Butler matrix. The radiation characteristics were analyzed in terms of bandwidth, beamwidth, gain, cross polarization (x-pol), and axial ratio. Stable radiation patterns were obtained when the main beam directions were within the ±30° angle. The beam-switching LSA array has measured gain of 13.5 dBic and beamwidth of 15° with x-pol greater than 10 dB and axial ratio less than 6 dB. Comparative results with a 4 × 8 stacked patch antenna array are also included for reference.

Circular Polarization and Mode Reconfigurable Wideband Orbital Angular Momentum Patch Array Antenna

A circular polarization (CP) and mode reconfigurable wideband orbital angular momentum (OAM) patch array antenna is presented. The proposed design is based on a reconfigurable feed network (RFN), a direct current (dc) bias circuit, and a $2 \times 2$ patch array. By changing the dc bias voltages of p-i-n didoes, the operating state of the antenna can be reconfigured between the left-hand CP with a mode $l = +1$ and right-hand CP (RHCP) with a mode $l = -1$ , over the wide impedance bandwidth of 21%. For the two states, the measured peak gains are larger than 5.3 and 5.2 dBi, and the axial ratios in half-power main beam directions are lower than 1.29 and 1.05 dB, respectively. Different from existing OAM antennas, the diversities of polarization, frequency, and mode, as well as the CP with inherently high cross-polarization discrimination are simultaneously integrated in the proposed antenna, which serves as a good basis for improving the capacity and spectral efficiency of radio systems. In addition, the antenna features single-external input port, a simple RFN occupying a small number of diodes, and a compact size of $1.28 \times 1.28 \times 0.07 \lambda _{0}^{3}$ ( $\lambda _{0}$ is the free-space wavelength at center frequency), all of which ease implementation and reduce fabrication cost. Therefore, the proposed antenna is very promising for modern high-speed and large capacity wireless communication systems.

Exposure level from selected base station tower around Kuala Nerus: a preliminary analysis

Health risk due to RF radiation exposure from base station tower (BST) has been debated for years leading to public concerns. Thus, this preliminary study aims to measure, evaluate and analyze the exposure level on three selected BST around Kuala Nerus. The measurement of exposure level in terms of voltage amplitude (dBmV) data were recorded using spectrum analyzer. The trend of exposure level shows that the characteristics of environment around the BST sites contribute to the variation of voltage amplitude for all study sites. Besides, the radiation exposure level of BST depends on several factors such as: the distance from the radiation sources, the height of the tower, tilt and direction of the antennas fixed on the top of the tower, the number of antennas on single tower, the type of radiation pattern, the direction of main beam of radiation, the feeding power and the operating frequency

GO Shaping of Omnidirectional Dual-Reflector Antennas with Arbitrary Main-Beam Direction in Elevation Plane by Connecting Conic Sections

This work discusses an alternative geometrical optics (GO) technique to synthesize omnidirectional dual-reflector antennas with uniform aperture phase distribution together with an arbitrary main-beam direction for the antenna radiation pattern. Sub- and main reflectors are bodies of revolution generated by shaped curves defined by local conic sections consecutively concatenated. The shaping formulation is derived for configurations like ADC (axis-displaced Cassegrain) and ADE (axis-displaced ellipse) omnidirectional antennas. As case studies, two configurations fed by a TEM coaxial horn are designed and analyzed by a hybrid technique based on mode matching and method of moments in order to validate the GO shaping procedure.

Dual band high‐gain antenna with beam switching capability

This study presents an antenna with dual-band and high-gain for a wireless local area network and Worldwide Interoperability for Microwave Access applications operating over 3.4–3.6 and 5–6 GHz bands. The proposed antenna is composed of three double-sided bowtie radiators loaded by a 2 × 6 array of double split rectangular (DSR) unit cells, which leads to a considerable gain enhancement. The DSR unit cell acts as an equivalent medium with a high refractive index operating at 3.5 and 5.5 GHz. By loading 2 × 6 arrays of proposed unit cells in the off-axis of the bowtie antenna in the H-plane, the main beam direction is tilted by 17° and 20° at the 3.5 and 5.5 GHz bands, respectively. A prototype of the bowtie antenna loaded with asymmetric unit cells in the H-plane is fabricated and measured. The measured results confirm the deflection of the main beam direction by 17° at 3.5 and 20° at 5.5 GHz with a peak gain of 10 and 10.5 dBi, respectively.

A Fixed-Beam Leaky-Wave Cavity-Backed Slot Antenna Manufactured by Bulk Silicon MEMS Technology

A fixed-beam leaky-wave slot antenna with an air-filled back cavity is proposed in the millimeter-waveband. The antenna is fabricated based on the bulk silicon microelectromechanical systems micromachining technology. This micromachining process can etch silicon wafers and plate them with gold. Because all surfaces of the proposed antenna are plated with gold, electromagnetic waves can transmit in the air medium without any other dielectric. The air-filled structure contributes to achieving a leaky-wave slot antenna with fixed beam as operating frequency varies. A prototype of the proposed antenna is fabricated to verify the design strategy. The measured results show that the impedance bandwidth of the proposed antenna is 55–67 GHz and within the operating frequency band, the main beam direction only varies from 48° to 53°, which confirms the fixed-beam characteristic. The measured peak gain varies from 9.1 to 10.5 dBi in the operating frequency band.

A Wide-Angle Scanning Phased Array With Microstrip Patch Mode Reconfiguration Technique

A method based on the microstrip patch mode and reconfiguration technique is analyzed, studied, and applied to wide-angle scanning phased arrays. First, a summative evaluation of microstrip patch modes available for wide-angle scanning or near endfire has been made. Second, to validate this new method, a multilayer microstrip patch element is established and its resonant modes TM01 and TM20 are excited. Third, a reconfigurable technique is used to reconfigure the above resonant modes and a wide joint 3-dB beam coverage is obtained. Fourth, a prototype of $1\times 4$ uniform linear phased array with the above reconfigurable elements is proposed. The prototype operates at 5.8 GHz and its main-beam direction can scan from −75° to +75° in the elevation plane with a gain fluctuation less than ±1 dB. Finally, in order to reduce the sidelobe levels, a hybrid particle swarm optimization algorithm is used to optimize the excitation amplitudes and phases. The measured results show an excellent wide-angle scanning performance, which validates the effectiveness of the proposed method.

Optimization of a combined high-power ultrawideband antenna

The results of optimization of the geometry of a combined ultrawideband antenna excited by a 1-ns bipolar pulse are presented. Numerical and physical experiments have been performed to optimize the increase in the electric-field strength in the direction of the antenna main beam. It has been shown that the peak field strength can be increased by 6%.

Pattern Reconfigurable Antenna Based on Morphing Bistable Composite Laminates

In this paper, a novel pattern reconfigurable antenna based on morphing bistable composite laminates is presented. The bistable asymmetric glass-fiber reinforced polymer (GFRP) composite laminates have two stable configurations with curvatures of opposite signs. The antenna pattern is reconfigured by transforming the configuration of the bistable GFRP laminate which acts as the substrate of the antenna. The coplanar waveguide transmission lines feeding technique is used for the microstrip quasi-Yagi antenna. A prototype of the proposed antenna is fabricated using a semi-automatic screen printer and an autoclave. The transformation between the two stable states of the proposed antenna using Ni/Ti shape memory alloy springs is investigated experimentally. The out-of-plane displacements, reflection coefficients and radiation patterns for the two stable configurations of the antenna are measured, which agree well with the simulated results. The main beam direction is 89° and 59° for the two stable configurations, respectively. In addition, the influences of various bending radii on the radiation patterns are investigated to gain a thorough understanding of the reconfigurable mechanism of the proposed antenna. Finally, a two-element array of such an antenna is presented and measured. The proposed antenna provides a potential application in multifunctional, conformal, morphing, and integrated structures.