Antenna Diversity Research Articles

A Dual Orthogonal Fed Monopole Antenna for Circular Polarization Diversity

A monopole antenna with circular polarization diversity and high isolation is proposed in this paper. The proposed antenna consists of two bent monopole antennas and a partial ground plane. Two monopole antennas are implemented on opposite planes with respect to the ground plane. The ground plane is a right-angled isosceles triangle, and the antenna is located at one end of the ground plane. Circular polarization (CP) characteristics are obtained using this structural asymmetry. In the proposed structure, the resonant frequency at S11 is controlled by the antenna length, and the null frequency at S21 (isolation) is controlled using the bending angle of the monopole and the distance between the two antennas. From the measured results, the CP operating bandwidth of the proposed antenna is 13.8% (1.76–2.02 GHz). The measured isolation is –50 dB at the resonant frequency and –20 dB within the operating bandwidth.

Cooperative wideband spectrum sensing under reporting channel errors: Analysis and algorithm

This paper focuses on the performance analysis and the algorithm development for cooperative wideband spectrum sensing (CWSS) under imperfect reporting channels for cognitive radio (CR). The centralized approach with multiple distributed cooperating secondary users (CSUs) and a fusion center (FC) is considered for CWSS. Nakagami fading is used to model the channel between PUs and the CSUs. The CSUs equipped with multiple diversity antennas are considered to take advantage of both space and antenna diversity. In this work, the reporting channel model under erroneous reporting is proposed. The repetition code-based CWSS (RC-CWSS) algorithm is proposed for performance improvement. First, the modified, improved theoretical analysis of an existing algorithm called partial band Nyquist sampling-based CWSS (PBNS-CWSS) under no reporting errors is given. The theoretical analysis under an imperfect reporting channel is then carried out for the same algorithm. Then, the complete theoretical analysis for the proposed RC-CWSS algorithm is carried out. The theoretical analyses are verified using Monte-Carlo simulations. The analysis shows that the performance of CWSS is greatly affected by the reporting channel errors. Also, the RC-CWSS outperforms recently proposed state-of-the-art algorithms. Finally, the effects of different parameters on the performance of the proposed algorithm are also studied.

Flexible CP diversity antenna for 5G cellular Vehicle-to-Everything applications

A flexible circularly polarized (CP) MIMO antenna is evaluated for Sub-6 GHz 5G and cellular-vehicle-to-everything (C-V2X) applications. The design radiates CP waves with an L-shaped feed line and a modified ground plane embedded in the slot antenna. The MIMO design resonates in the band of frequencies 3.23–6.26 GHz and radiates CP waves in the 2.95 – 6.02 GHz frequency band. This antenna model is suitable for LTE-V2X/ 5G (3.3 to 4.2 GHz), WLAN 5.2 GHz, WiMAX 5.5 GHz, and IEEE 802.11p (5.85–5.925 GHz) vehicular application bands. Here both planar and antenna conformed on foam material and a car wing mirror are investigated. Improved lowest isolation of 18.2 dB is achieved in the entire working band using the orthogonal CP arrangement of elements. The diversity functionality is tested in terms of ECC, MEG, CCL, etc. Further, the antenna radiation characteristics are tested by positioning it on the vehicle roof-top and side mirror using the Ansys savant tool.

A compact planar dual band two‐port MIMO antenna with high isolation and efficiency

A dual-band two-port MIMO antenna with high isolation and efficiency is proposed in this article. Each antenna element is composed of a rotated U-shaped strip and an L-shaped strip. The MIMO antenna is optimized to operate in 2.5–2.7 GHz and 4.8–5 GHz, which can cover the 5G bands of China Mobile. The defected ground structure consists of a slant square loop with a T-shaped slit and a U-shaped slot. A rectangle parasitic strip is placed in the U-shaped slot. The use of defected ground structure and parasitic strip makes the antenna obtain good isolation which is better than −17.96 dB and − 20.1 dB at the lower and higher frequency bands. To evaluate the antenna diversity, envelope correlation coefficient (ECC) is analyzed which is lower than 0.0006 and 0.12 at the lower and higher frequency bands, respectively. The measured gains are 4.35 dBi and 4.6 dBi, while the measured efficiencies are 63.23% and 68.69% at 2.6 GHz and 4.9 GHz, respectively. The prototype of antenna is fabricated to verify the functioning of proposed antenna design.

Compact Wideband Pattern Reconfigurable Antennas Inspired by End-Fire Structure for 5G Vehicular Communication

Aiming for 5G-NR vehicular applications, this paper proposes two miniaturized wideband pattern reconfigurable antennas with different pattern steering capabilities. They are inspired by an end-fire structure that could be easily mounted on cars. This newly proposed planar pattern reconfigurable end-fire structure is firstly presented and studied by current distribution and equivalent circuit analysis. By turning the ON / OFF state of the PIN diodes on the passive dipole, a planar reconfigurable antenna with one omnidirectional and two end-fire beams is implemented. Additionally, a low-profile pattern diversity antenna with a compact size of 0.311 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.244 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.106 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is implemented by loading a reactive metasurface, its main lobe can be steered in the broadside direction (35°, 0°, and −35°). Both antennas achieve a wideband response over 3.30 to 4.20 GHz (24.0%) range and good radiation efficiency of 84.0%. They feature the advantages of a miniaturized size (low-profile), structurally simple and fabrication friendly design, wideband, good radiation efficiency (low-loss), and flexible multi-beam switching capability, which are well suited for the coming sub 6 GHz vehicular applications in different scenarios.

Compact dual-band MIMO cubical antenna for automotive applications

ABSTRACT There is a strong demand for compact and multiband antennas as wireless technologies become more integrated into automobiles. These antennas must be able to serve multiple services without compromising the size and installation space. In addition, the antenna incorporated should not affect the aesthetic appearance of the vehicle. This paper presents a compact multiple-input-multiple-output (MIMO) antenna working at 2.45 GHz (Wi-Fi/Bluetooth/RFID) and ultra-wideband (UWB) frequencies. A basic rectangular monopole with a self-complementary structure is used to design the antenna element. The size of the antenna element is 20 × 22 mm2. The proposed MIMO cube is developed with four antenna elements in cubical orientation to achieve compactness and better isolation. The overall dimension of the MIMO antenna is 35 × 22 mm2. The diversity antenna shows impedance bandwidth of 2.4–11.5 GHz and isolation of more than 20 dB. The envelope correlation coefficient (ECC) of the MIMO antenna is less than 0.2, diversity gain (DG) is greater than 9 dB, and total active reflection coefficient (TARC) and channel capacity loss (CCL) are less than −10 dB and 0.4 bits/s/Hz, respectively. The gain and efficiency are found to be greater than 1 dBi and 72%, respectively.

2-D Printed 8-element compact UWB diversity antenna for multi-service-multi-mode applications

A 2-D compact 8-element UWB diversity antenna of dimension 28 mm × 28 mm each, is proposed to operate from (4.1–24) GHz with 141.63% IBW for multi-service-multi-mode (MS2M) applications. With self-similar antennas, the antenna design embodiment is constructed by asserting cross-coupled inter-connect bridge substrates to accomodate eight radiating elements in a compact footprint. This configuration results in good isolation between non overlapped antenna clusters, the ortho-centric antenna arrangement asserts pattern diversity and avoids the dependancy of additional decoupling network. The performance metrics consists of isolation coefficient of >20 dB at all ports, realized gain varies from (4.5–8.1) dBi and ECC from far-field magnitude < 0.08, which makes it suitable for UWB diversity applications. To validate the multi-port antenna performance, a full-wave simulation PTFE shield enclousure with volume of 40 mm × 40 mm × 40 mm has been demonstrated, which shows good results in correlation to EM-simulation. With good performance attributes in the shield enclousure, the multi-port antenna can be exported to a fully fledged plastic jacketed cage for real-time environment. Finally, a prototype antenna is fabricated and measured with good agreements to validate the overall RF performances.

Speckle free efficient light engine for high power laser projectors and automobile headlamps

Laser speckles and spurious fringes are the major obstacles in the development of emerging technologies relating to laser-based projection imaging and illumination. It becomes more challenging when such systems employ high-power lasers, such as laser-based cinema projectors or laser-based automobile headlamps. Addressing such challenges, we report a compact design and step-by-step development scheme of a laser speckle reduction system in this article. The method comprises a metallic ball-mirror connected with the mechanically dynamic and thermally conductive heat sink. The ball-mirror was highly reflecting and coated with a transparent thick film of ZnO nanoparticle embedded epoxy adhesive that provides volume scattering of a highly directional laser beam. Epoxy layer were further diffused by sandblasting to achieve surface scattering of the laser light. The combined effect of volume and surface scattering were utilized to produce spatial diversity, while the temporal diversity was achieved by the rotation of ball-mirror diffuser system. Spatial and temporal diversities are the fundamental speckle reduction techniques that become more efficient when they are employed with a tiny pyramidal reflective cavity. TracePro simulations demonstrate the efficiency enhancement in the system due to the involvement of a pyramidal reflector for three primary wavelengths (RGB). Qualitative results of the light-scattering for red, green, and blue lasers and the quantitative results of speckle contrast are reported. Speckle contrast reduction was experimentally achieved by 0.0248 for red, 0.0298 for green, and 0.0213 for blue laser diodes.

Rayleigh Fading Channel Capacity for Coherent Signaling With Asymmetric Constellations

This paper investigates the channel capacity of coherent reception with antenna diversity in Rayleigh fading using asymmetric constellations, such as nonbinary two-sided amplitude-shift keying (ASK) and quadrature amplitude modulation (QAM) with &#x2265; 8 levels. Due to the asymmetries, the capacity achieving input or a priori probability distributions deviate from uniformity. To perform the investigation, an analytical expression for the mutual information, in terms of an integral over a single variable, between the input (transmitted symbol) and the output (received signal vector comprising signals at receive antennas), is derived. For two-sided ASK, 8-QAM with cross constellation, and 16-QAM, analytical closed form expressions for the high and low signal-to-noise (SNR) approximations, respectively, of the capacity achieving input probability distribution, the capacity, and the relative gain in mutual information (between using the uniform and the capacity achieving input probability distributions) are obtained. Numerical results show that at low SNRs, the use of the capacity achieving nonuniform input probability distribution offers significant advantage over the use of the uniform input probability distribution, while at high SNRs, this advantage is significant only for configurations with one receive antenna. Furthermore, the high and low SNR approximations are shown to be reasonably accurate.

Performance of UAV-Assisted Multiuser Terrestrial-Satellite Communication System Over Mixed FSO/RF Channels

In this letter, performance of a multiantenna multiuser unmanned aerial vehicle (UAV)-assisted terrestrial-satellite communication system over mixed free space optics (FSO)/radiofrequency (RF) channels is analyzed. Downlink transmission from the satellite to the UAV is completed through FSO link which follows gamma&#x2013;gamma distribution with pointing error impairments. Both the heterodyne detection and intensity modulation direct detection techniques are considered at the FSO receiver. To avail the antenna diversity, multiple transmit antennas are considered at the UAV. Selective decode-and-forward scheme is assumed at the UAV and opportunistic user scheduling is performed while considering the practical constraints of outdated channel state information (CSI) during the user selection and transmission phase. The RF links are assumed to follow Nakagami-m distribution due to its versatile nature. In this context, for the performance analysis, analytical expressions of outage probability, asymptotic outage probability, ergodic capacity, effective capacity, and generalized average symbol-error-rate expressions of various quadrature amplitude modulation (QAM) schemes such as hexagonal-QAM, cross-QAM, and rectangular QAM are derived. A comparison of various modulation schemes is presented. Further, the impact of pointing error, number of antennas, delay constraint, fading severity, and imperfect CSI are highlighted on the system performance. Finally, all the analytical results are verified through the Monte&#x2013;Carlo simulations.

Compact ultra-wideband pattern diversity antenna for body-centric communications

AbstractThis paper presents a pattern diversity UWB antenna for Wireless Body Area Network (WBAN) communications. Pattern diversity antenna comprises two antenna elements with directional and omnidirectional patterns suitable for off-body and on-body communications respectively. Several broad-banding techniques such as Co-Planar waveguide, parasitic patches, and cavity resonant techniques are incorporated in microstrip antenna to achieve an ultra-wideband of 7.5 GHz (3.1 to 10.6 GHz) with a directional pattern. Monopole radiator topology is utilized to achieve a UWB frequency range of 2.6–10.6 GHz with an omnidirectional pattern. Pattern diversity is achieved using an orthogonal arrangement of the antenna elements in a compact size of 40 mm × 34 mm, maintaining the isolation &gt;20 dB between the antennas. Gain varies from 2.2 to 4.6 dBi and 2.5 to 7.5 dBi for omnidirectional and directional antenna respectively. The simulated radiation efficiency for the directional antenna and the omnidirectional antenna are 74–86% and 52–66.5% respectively. The proposed design provides a good diversity performance in the entire UWB bandwidth with ECC&lt;0.1 and a diversity gain of approximately 10 dB. SAR impact evaluated under various conditions is found to be &lt;1.6 W/Kg for 1 gram of tissue.

Heatable Vehicle Glazing with Antennas

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;In this paper, we propose a vehicle antenna system on a conductive heat reflecting window. A slot antenna in a heatable vehicle glazing established between the heating bus bar, bus bar extension and the peripheral edge of an electrically conductive IR reflective coating. The antenna slot may be fed directly by a voltage source, a current source, or a coupled coplanar line at a position to excite both fundamental and higher order modes for multiband antenna applications. The slot antenna can be also established between split heating bus bars or heating bus bar extension to reduces heat loss and improve antenna efficiency. Multiple antennas can be integrated into the heatable glazing for multiband applications and/or diversity antenna systems. Results from simulation on the vehicle are compared with measurements.&lt;/div&gt;&lt;/div&gt;

Optimized Super-Wideband MIMO Antenna with High Isolation for IoT Applications.

A compact, low profile, multiple-input–multiple-output (MIMO) diversity antenna with super-wideband (SWB) characteristics has been proposed. The proposed antenna comprises four symmetric monopole-radiating elements printed on low-cost FR4 substrate with the slotted ground plane. The single antenna of a monopole structure and a quad-port MIMO antenna, with the dimensions of 30 × 20 mm2 and 60 × 55 mm2, respectively, are ideal for IoT and high-speed data applications. The proposed MIMO antenna has a high diversity gain and low envelope correlation coefficient (ECC) within the frequency range. Simulated results demonstrate the performance of the MIMO-SWB antenna, which operates from 2.3 to 23 GHz, with a high isolation level over 20 dB in the achieved frequency band. Moreover, the proposed MIMO antenna has been investigated with mirror fashion and orthogonal structure. Both structures provide similar results except for mutual coupling performance. The orthogonal adjustment for high isolation achieves better results with the proposed model. Further, the prototype of the proposed antenna is fabricated and measured effectively. Simulated and measured results show good agreement for super-wideband applications.

A thin shared radiator based ACS‐fed orthogonal pattern diversity antenna with physical tilt for mmWave 5G access points

A low profile and compact two-port antenna is proposed for mmWave 5G access point applications. Since the overall space inside a typical mmWave 5G access point is limited, a small form factor based antenna module is proposed. The two-port antenna shares a common radiator that miniaturizes the overall antenna module. The proposed antenna comprises of single-layered asymmetric coplanar strip (ACS)-fed shared radiator with wide operating bandwidth ranging from 25 to 31 GHz that accounts for fractional bandwidth of 21.4%. The two-port antenna elements are oriented at right angles to each other for obtaining orthogonal pattern diversity (OPD) thereby obtaining wide angular coverage in the E-plane. Vertical linear corrugations with varying lengths are incorporated for decreasing mutual coupling between these two antenna elements and producing a uniform high gain end-fire radiation pattern. Isolation of around 4 dB is enhanced by insertion of these vertical corrugations. The proposed antenna attains peak gain of 7.2 dBi with high pattern integrity over the entire operational frequency band. The presented OPD antenna occupies overall area of 74.75 mm2 which is minimal. Moreover, implementation of the proposed antenna inside a typical mmWave 5G access point is also demonstrated. Simulation and measured results are presented with adequate technical explanation.

Dual-Band Folded Monopole MIMO Antennas with Enhanced Isolation

In this paper, a compact dual-band multiple-input multiple-output (MIMO) diversity antenna is proposed. Each of the two MIMO antennas consists of two folded strips working as radiating elements that are fed by a microstrip line. The antennas operate in three WLAN bands: ISM 2.45 GHz, 5.25 GHz, and ISM 5.775 GHz. To improve the isolation at WLAN (2.4–2.48 GHz), two L-shaped slots are etched in the ground plane while a U-shaped slot is cut in the ground plane to enhance isolation at WLAN (5.15–5.35 GHz and 5.725–5.825 GHz). Three slots on the substrate between radiating patches are also employed for an extra reduction in the mutual coupling at 2.45 GHz. The antenna performance was examined by simulation employing CST Microwave Studio Software. The proposed antenna offers minimum isolation of more than 19.5 dB, a low envelope correlation coefficient (ECC) of less than 0.0016, and good radiation efficiency (∼∼80%) through the operating frequency bands. The antenna is compact, thin, and suitable for portable devices.

Agricultural Land-Use Increases Floral Species Richness in Tropical Dry Forest and Savannah Ecosystems in West Africa

The diversity and structure of plant communities are valuable indicators for assessing landscape quality. Land-use change is one of the main factors considered to affect and have the strongest impacts on biodiversity. In this study, we assessed the effects of the conversion of tropical dry forests and savannahs into agricultural lands on the floral diversity and the structure of the vegetation. For this purpose, we carried out vegetation surveys in 198 plots of 50 m × 50 m. Within each plot, we documented all herbaceous, shrubby, and tree species present. We calculated total, spatial, and local floral diversities by land-use types and characterized the structure of the plant communities. Our results show that the overall floral diversity of the study area remains quite high (483 species of vascular plants from 298 genera and 71 families) and was not strongly impacted by agricultural land use (Pareto inequality index is 23–77). Croplands had the highest spatial (9.4) and local diversities. There was no significant difference between the land-use types in terms of the native species richness while croplands harbored significantly the most alien species. Agricultural land use significantly affected the structure of the plant communities. Trees are very rare in croplands and are frequent in forests and savannahs. The clearing of Guinean dry forests and savannahs for cropping did not automatically lead to a loss of some aspects of ordinary floral diversity. For a better understanding of the effects of land-use change on biodiversity, it would then be more suitable to specify in the studies whether the species concerned are native, alien, generalist, or specialist.

A micro-scaled graphene-based tree-shaped wideband printed MIMO antenna for terahertz applications

A tree-shaped graphene-based microstrip multiple-input and multiple-output (MIMO) antenna for terahertz applications is proposed. The proposed MIMO antenna is designed on a 600 × 300 μm2 polyimide substrate. The designed MIMO antenna provides a wide impedance bandwidth of 88.14% (0.276–0.711 THz) due to the suggested modifications in the antenna configuration. The MIMO design parameters like total active reflection coefficient (TARC), mean effective gain (MEG), envelope correlation coefficient (ECC) and diversity gain (DG), channel capacity loss (CCL) are evaluated, and their values are found within acceptable limits. The proposed MIMO structure offers MEG ≤ − 3.0 dB, TARC ≤ − 10.0 dB, DG ≈ 10 dB, CCL < 0.5 bps/Hz/s and ECC < 0.01 at the resonant frequency. At the resonant frequency, the isolation between the radiating elements of the proposed MIMO antenna is recorded as − 52 dB. The variations in operating frequency and S-parameters are also analyzed as a function of the chemical potential (μc) of the graphene material. The parametric analysis, structural design evolution steps, surface current distribution, antenna characteristics parameters and diversity parameters are discussed in detail in this paper. The designed MIMO antenna is suitable for high-speed short-distance communication, video-rate imaging, biomedical imaging, sensing and security scanning in the THz frequency band.

3-D twelve-port multi-service diversity antenna for automotive communications

This paper presents a twelve-port ultra-wideband multiple-input-multiple-output (MIMO)/diversity antenna integrated with GSM and Bluetooth bands. The twelve-port antenna is constructed by arranging four elements in the horizontal plane and eight elements in the vertical plane. The antenna element, which is created using a simple rectangular monopole, exhibits a frequency range of 3.1 to 12 GHz. The additional Bluetooth and GSM bands are achieved by introducing stubs into the ground plane. The size of the MIMO antenna is 100 × 100 mm2. The antenna offers polarization diversity, with vertical and horizontal polarization in each plane. The diversity antenna has a bandwidth of 1.7–1.9 GHz, 2.35–2.55 GHz, and 3–12 GHz, the radiation efficiency of 90%, and peak gain of 2.19 dBi. The proposed antenna offers an envelope correlation coefficient of < 0.12, apparent diversity gain of > 9.9 dB, effective diversity gain of > 8.9 dB, mean effective gain of < 1 dB, and channel capacity loss of < 0.35 bits/s/Hz. Also, the MIMO antenna is tested for housing effects in order to determine its suitability for automotive applications.

Fourier-Based Near-Field Three-Dimensional Image Reconstruction in a Multistatic Imaging Structure Using Dynamic Metasurface Antennas

Due to physical layer compression, and consequently, the failure to produce uniform radiation patterns, it is not possible to develop fast Fourier-based image reconstruction algorithms using the raw measurements collected from metasurface antennas. An effective solution in the literature is a sub-wavelength sampling of the aperture. However, this solution is currently limited to a panel-to-probe model which requires a mechanical raster scan. On the other hand, existing works are based on time-division multiplexing. This means that only a single transmit/receive channel is active in each time slot. In this paper, we introduce a panel-to-panel model in a multistatic structure. Based on this model, two pre-processing (for two different individually measured signal and combined measured signal (CMS) scenarios) are derived to convert the raw measurements into the space-frequency domain. Then, by using the output data from the pre-processing stage and according to the configuration of the introduced imaging system, the range migration algorithm is adapted. The importance of the proposed solution for the CMS scenario is that, for the first time, it demonstrates the capability of using dynamic metasurface antennas diversity to achieve simultaneous data acquisition. The performance of the proposed approach is compared with state-of-art works in terms of reconstructed image quality and computational complexity using numerical simulations and analytical discussions.

Data-driven Diversity Antenna Selection for MIMO Communication using Machine Learning

&lt;p&gt;With the popularity of wireless application environments, smart antenna technology has completely changed the communication system. In order to improve the quality of wireless transmission, smart antennas have been widely used in wireless devices. Wireless signal modeling and prediction machine learning gradually replaced the traditional smart antenna selection method in the antenna selection solution. This article utilizes mobile devices to adjust the diversity antenna pattern for test verification in a MIMO wireless communication environment. The proposed method manipulates signal parameters through error vector magnitude (EVM) and adds data-driven training data. The results show that the SVM and NN methods proposed in this paper are 10.5% and 14% higher than the traditional EVM calculation methods, respectively. Thereby, realize precise antenna adjustment of mobile devices and improving wireless transmission quality.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;