In this article, a dual-sense triband circularly polarized modified slot antenna loaded with metamaterial structures such as split-ring resonator and cross strips is proposed. The first resonant frequency is generated using the modified square slot which produces the two degenerative modes required to achieve circular polarization (CP). The corners of slot antenna are extended to obtain the orthogonal modes. The second resonant band is obtained using the single split-ring resonator. Two micro-splits in Split Ring Resonator (SRR) orthogonal to each other produces CP due to electric field generated by the micro-splits. The third resonance band is obtained due to loading of cross strips. The orthogonal phase is adjusted by varying the length of cross strips, so that the CP is achieved. All resonance bands are tuned independently. The measured impedance bandwidth of 31.68%, 4.55%, and 8.6% is obtained in first, second, and third bands respectively. The axial ratio bandwidth of 13.04%, 2.7%, 8.6% and peak gain of 3.8 dBic, 3.9 dBic, 3.7 dBic are obtained respectively. The simulated radiation efficiencies of above 80% is achieved in all bands. The left-hand CP is obtained in first two band as co-polarization and right-hand CP is obtained at the third band as co-polarization with respect to cross-polarization radiation. The cross-polarization of minimum −10 dB is obtained in all three bands. The proposed design is well suitable for the Bluetooth, n78 and n79 5G applications.

With the increasing demand for smarter antenna design in advanced technology applications, well-designed antennas have been an important factor in enhancing system performance. Most traditional antenna design requires multiple iterations and extensive testing to produce a final product. Machine learning (ML) algorithms have been used as an alternative to predict the optimal design parameters, but the outcome depends highly on the ML model efficiency. With recent development in machine learning algorithms and the availability of data for antenna design, we investigated different machine learning algorithms for optimizing the output strength of three basic antennae by analyzing the signal strength of the antenna for various antenna parameters. Different regression-based ML models were used to learn the behaviors and efficiency of three different antennas and to predict the output strength (S11) for different ranges of frequencies. The experiment compared and analyzed these ML regression algorithms for three different antennas: shot antenna, patch antenna, and bowtie antenna. In addition, the paper also provides comparison of ensemble ML models for performance analysis using the best three ML algorithms from the preliminary study. This study optimizes antenna parameters and quicker and smarter antenna design procedure using ML algorithms as compared to traditional design methods.

In this work, a compact size 4 ports multiple input multiple output (MIMO) slot antenna with the connected ground for Ultra-Wide Band (UWB) and X band applications is introduced and discussed. The single antenna is a cross-shaped slot antenna in the ground plane and a 50 Ω microstrip line with a small L-stub is used to feed the antenna on the other side. The suggested MIMO antenna has four identical elements arranged to be orthogonal to each other to enhance the MIMO system performance. The antenna elements are connected with a small strip to compose the proposed connected ground antennas. The suggested MIMO antenna has an overall size of 47 mm × 47 mm. The antenna has tested and simulated bandwidth with S11 < −10 dB extended from 4– 14 GHz and has isolation greater than 20 dB between ports without utilizing the decoupling elements and with good consistency between results. The MIMO antenna has peak gain and efficiency, envelope correlation coefficient, diversity gain, and channel capacity loss of 5.6 dBi and 80%, <5 × 10–3, 10 dB, and <0.4 bit/s/Hz, respectively which prove that our antenna can be suggested for the UWB MIMO applications.

The novel compact size orthogonally fed 2 x 2 Multiple Input and Multiple Output (MIMO) array antenna for mid-band Fifth Generation (5G) wireless application is presented. The antenna configuration consists of diamond-shaped patches employed at the top of substrate. The V-shaped common ground slot structure is employed at the bottom of substrate. A broadband circular polarization is achieved by simply combining two circular polarization modes obtained from ground V slot and top patch feed structure. Mainly, the impedance bandwidth (IBW) and gain are enhanced by protruding slots on ground and cutting edges of patches. The measured result shows that 1.70 – 8.00 GHz (6.30 GHz) of IBW, 8.8 dBic of peak gain, and 3 dB axial ratio bandwidth from 1.81 – 3.87 GHz (2.06 GHz) are obtained. The proposed antenna performances are experimentally validated by fabricating and testing it for measured result analysis without using power divider.

In this paper, a compact stepped slot antenna for ultra-wideband (UWB) applications is proposed. A very small size and UWB bandwidth operation are achieved by integrating a stepped slot in the back side of the antenna. This stepped slot is excited by using a 50 Ω-feed line in the top side of the antenna. The antenna is characterized by an impedance bandwidth between 3.05 GHz and more than 12 GHz. The dimensions of the antenna are 17 mm × 8 mm × 1.27 mm, which leads to the most compact size compared with other works in the literature. The integrated stepped slot is divided into additional elementary slots, where each elementary slot has a matching point. Adding these elementary slots allows to increase further the operating bandwidth. The radiation pattern of the compact stepped slot antenna is omnidirectional in the H-plane and bidirectional in the E-plane. The measurement results agree well with the simulated ones in terms of impedance matching and radiation pattern.

In this paper, a wideband circularly polarized corrugated G-shaped grounded ring slot antenna is presented. The proposed antenna structure is excited using a coplanar waveguide-fed monopole antenna, which is placed inside a corrugated G-shaped grounded ring. Due to the asymmetry in the ground plane, two orthogonal modes, having equal magnitude and out of phase by 90° are excited, resulting in circular polarization (CP). The generation of the CP in the proposed antenna structure is explained using thin dipole current element approximation. A prototype of the proposed antenna is fabricated and tested. The measured results exhibit a 3 dB axial ratio bandwidth of 37.6% (2.22–3.25 GHz), and reflection coefficient bandwidth (|S11| ≤ −10 dB) of 47.91% (2.13–3.47 GHz). Additionally, the design guidelines are also presented for G-shaped grounded ring slot antennas.

A novel tri-beam slot antenna array based on substrate integrated waveguide (SIW) technology is proposed in this paper. The beam forming network is a 3 × 3 Butler matrix consisted of three couplers and four phase shifters. A 1.76 dB coupler is located between two 3 dB couplers, with this arrangement; the input signal can be divided into three parts with the same amplitude and certain phase differences. Two parallel slots are cut off broadside of SIW transmission line, which constitutes the basic unit of the antenna array. A 3 × 2 slot antenna array is connected with this circuit. Three beams with the directions of −30, 0 and 30° are produced when different ports are excited, respectively. The S parameters, radiation patterns, and gains are simulated and measured, which show that it can be a candidate for multi-beam wireless communication systems.

This paper presents a novel design of a low profile circularly polarized (CP) metasurface (MTS) antenna with in-band radar cross-section (RCS) reduction property. The MTS is loaded as a superstrate on slot antenna and it can be viewed as a polarization-dependent MTS (PDMTS). The rectangular patch-based PDMTS is analyzed using characteristic mode analysis to find two orthogonal degenerate modes, which produces CP waves. Linearly polarized slot antenna is used to excite the PDMTS. The performance of PDMTS loaded slot antenna is analyzed numerically using full-wave analysis method. The PDMTS CP antenna is fabricated and its performance is tested experimentally. The proposed antenna has a compact structure and it has an overall size of $0.52{\lambda _0}\times 0.52{\lambda _0} \times 0.078{\lambda _0}$ (where ${\lambda _0}$ is the free space wavelength). The measured results show that the PDMTS antenna achieves $-10\,{\rm dB}$ impedance bandwidth of 29.41$\%$, 3-dB axial ratio bandwidth of 9.05$\%$, broadside gain of 6.34 dB, and monostatic RCS reduction of $-30.2\,{\rm dBsm}$ at the resonant frequency of 5.86 GHz. The simulated results are in well agreement with the measured results and it is well suited for C-band Radar and Satellite communication.

This paper presents a cavity-backed dual-slot antenna in 0.13-μm SiGe BiCMOS technology. The dual-slot structure is excited by a cross-shaped strip line and a cavity which is formed by the topmost metal layer connected to the bottom metal layer through vias in between. By adopting dual-slot and cross-shaped feed line, the bandwidth is significantly enhanced by 196% compared with the single-slot antenna with straight feed line. The reason for bandwidth enhancement has been analyzed. The proposed antenna shows a measured impedance bandwidth of 15.2 GHz from 248.2 to 263.4 GHz for |S11| < −10 dB. The simulated and measured peak gains of the cavity-backed dual-slot antenna are −1.3 and −2.1 dBi, respectively. The simulated radiation efficiency is 31.1%. The total size of the antenna is 0.46 mm × 0.48 mm.

This paper presents application of split ring resonators (SRR) in conventional waveguide slot array antenna to achieve performance improvement and multiband characteristics. Three SRRs have been placed on the transverse plane of a conventional slotted waveguide and has been simulated and measured. The measured results show that the antenna has dual band response with respective 10 dB return loss bandwidth 8.23–9.23 GHz (11.45%) and 9.68–11.01 GHz (12.87%). The measured gain and radiation pattern reveal that the proposed antenna has higher gain and front to back radiation ratio as compared with a conventional slotted waveguide antenna. Equivalent circuit of the proposed antenna also has been presented.

A microstrip transmission line fed fork-shaped planar antenna is proposed for Bluetooth, WLAN, and WiMAX applications. The antenna made of a microstrip feed line, fork-shape patch on one side and defected ground plane on the other side of dielectric substrate. A fork-shape is formed by two side circular arms and a rectangular central arm. The inverted T-shaped ground plane with a rectangular slot in the center arm is used to increase the bandwidth with better impedance matching of the lower band. The antenna is practically fabricated to validate the design. The antenna resonate dual band to cover an entire the WLAN and WiMAX bands. The antenna shows the measured bandwidth of 410 MHz (2.26–2.67) and 3.78 GHz (3.0–6.78 GHz) at lower and upper bands, respectively.

This paper presents a new broad band circularly polarized slot antenna array based on substrate-integrated waveguide (SIW) and aperture feeding techniques. The antenna element's impedance and 3 dB axial-ratio (AR) bandwidths are from 8.8 to 10.4 GHz (16.67%) and 9.5–10.7 GHz (12%), respectively. Employing aperture-coupled feed and combining this method with sequentially rotated network, a 2 × 2 antenna array is achieved. Parametric optimization procedure is used to enhance the antenna specifications. In the presented scheme by reducing mutual coupling caused by the SIW technique and sequentially rotated feed network, all parameters of antenna are improved. Consequently a novel antenna array with impedance bandwidth of 2.8 GHz (8.7–11.5 GHz) and 3 dB AR bandwidth of 2.1 GHz (9–11.05 GHz) are obtained. The average gain of the proposed antenna is about 16.7 dBic. A new method is used to increase the gain of antenna array. The extracted result shows that side lob level, mutual coupling, impedance bandwidth, and performance of antenna simultaneously are controlled.

In this paper, an array antenna with asymmetric antenna fed network is presented. Total size of the proposed array antenna (with 2 × 2 elements) is 90 × 90 mm2 and distance between elements (fed by fed) is λ0/2 (λ0 = wavelength in free space). The proposed antenna is fed by coaxial cable that isolated input impedance from impedance of the array antenna feed network. The measured impedance bandwidth of the coaxial fed circular polarization array (S11 < −10 dB) is 47.9% from 4.6 to 7.5 GHz (1.63:1), and the measured 3-dB axial-ratio bandwidth is 42% from 4.7 to 7.2 GHz. The peak gain of antenna is 9.1 dBic.

A simple and compact printed ultra-wideband antenna with dual-band-notched characteristics is presented. The proposed antenna is composed of a rectangular patch and a modified ground plane. The rectangular patch is etched onto a lossy FR4 substrate. A circular ring strip parasitizes the rectangular patch embedded by a U-shaped slot. Two inverted-L slits and a rectangular slit are embedded onto the ground plane. Some bandwidth enhancement and band-notched techniques are applied in the antenna structure for broadening the bandwidth and generating notches. The simulated and measured results show that the proposed antenna offers a very wider bandwidth ranging from 3.04 to 17.30 GHz, defined by the return loss less than −10 dB, with dual-notched bands of 3.30–4.20 and 5.10–5.85 GHz covering the 3.3/3.7 GHz WiMAX, 3.7/4.2 GHz C-band, and 5.2/5.8 GHz wireless local area network systems. Furthermore, the proposed antenna presents relatively high antenna gain and quasi-omnidirectional radiation patterns.

To incorporate two different communication standards in a single device, a compact triple-band antenna is proposed in this paper. The proposed antenna is formed by etching an inverted L-shaped slot on the patch with defected ground structure. The antenna is targeted to excite three separate bands first from 2.39–2.51, second from 3.15–3.91, and third from 4.91–6.08 GHz that covers entire Wireless Local Area Network (WLAN) (2.4/5.2/5.8 GHz) and Worldwide Interoperability for Microwave Access (WiMAX) (2.5/3.5/5.5) bands. Thus, the proposed antenna provides feasibility to integrate WLAN and WiMAX communication standards in a single device with good radiation pattern quality. Furthermore, a prototype of the proposed antenna fabricated and measured to validate the design, shows a good agreement between simulated and measured results. The simulation and measurement results show that the designed antenna is capable of operating over the 2.39–2.51 GHz, 3.15–3.91 GHz, and 4.91–6.08 GHz frequency bands while rejecting frequency ranges between these three bands. The proposed antenna offers a compact size of 20 × 30 mm2 as compared with earlier reported papers.

An ultra-wideband (UWB) slot antenna for diversity applications is introduced. The overall structure of the antenna consists of two similar coplanar waveguide (CPW)-fed stepped rectangular slots placed in an orthogonal position. The slots are asymmetric with respect to their placement in the ground plane. The CPW feeds are double stepped and terminated on hexagonal patches for better impedance matching. A wide impedance bandwidth (measured) from 3 to 12 GHz with an isolation better than 15 dB is obtained with this antenna. To improve the isolation, the design is modified and an I-shaped slot strip is introduced between the two slot antennas. With this, the isolation is brought about 25 dB of most of the band, while the impedance bandwidth remains the same (2.8–12 GHz for port 1, measured and 2.9–12 GHz for port 2, measured). The far-field radiation patterns are also measured and a peak gain of about 5 dBi is obtained. Finally, the diversity parameters such as envelope correlation coefficient and capacity loss are calculated and found to have low values. The antenna is expected to be useful for UWB diversity applications with good isolation.

In this paper, a microstrip fed, L-shape slot antenna for dual polarization is proposed. The two arms of the slot generate electric fields of orthogonal polarizations. By properly sectioning the slot and the feed line, ultra wideband (UWB) behavior is obtained. The measured impedance bandwidth (S11< −10 dB) is more than 8.6 GHz (112%) and 8.2 GHz (104%) for Port 1 and Port 2, respectively. The measured isolation is better than 25 dB over most of the band. The aperture field distribution justifies the dual polarized nature. A modified version which implements a band-notch over 5.1–5.85 GHz wireless local area network (WLAN) band is also presented. With a compact, single substrate design, the antenna can be useful in MIMO transmission systems, polarimetric UWB radar, high performance microwave imaging, and other future wireless communications devices.

A compact CPW-fed printed monopole slot antenna is presented for ultra-wideband (UWB) applications. The antenna comprises of a dome-shaped radiating element in which embedded is an open-loop inverted triangular-shaped slot (TSS). The antenna is fed through a coplanar waveguide to provide an ultra-wide impedance bandwidth of 8.95 GHz (2.58–11.53 GHz) which corresponds to a bandwidth ratio of 1:4.46 for VSWR <2. The antenna possesses a notch band functionality to filter out interfering C-band signals like wireless local-area network (WLAN). The notch band frequency is determined by physical parameters defining the TSS that allows fine control of the notch's location. The proposed antenna also possesses a flat gain response expect at the notched band and occupies a relatively small volume of 25 × 25 × 0.8 mm3 for ease of system integration.

In this paper, the design, simulation, and fabrication of a novel printed rectangular slot antenna with a band-notched function suitable for 2.4 GHz wireless local area network (WLAN) and ultra-wideband (UWB) applications is presented and investigated. Two pairs of slits are introduced into the ground plane to realize band-notched function, by tuning the position, length, and width of which a suitable rejected frequency band can be obtained. To improve the impedance matching, a rectangular cut is also made in the ground plane so that the antenna can cover 2–12 GHz frequency range. According to the measured results, the proposed antenna has a large bandwidth totally satisfying the requirement of 2.4 GHz WLAN and UWB systems, while providing the required band-notch function from 5.1 to 5.9 GHz. The study of transfer function and time-domain characteristics also indicates the band-notched function of the antenna. The radiation patterns display nearly omni-directional performance and the antenna gain is stable except in the rejected frequency band (5.1–5.9 GHz). Moreover, group delays are within 1.5 ns except for the notch band. These features make it a promising candidate for UWB wireless applications. Details of this antenna are described, and the experimental results of the constructed prototype are given.