In this article, a circularly polarized dielectric resonator antenna (DRA) array with conformal characteristics and improved specific absorption rate (SAR) has been proposed for X-band applications. The proposed structure has been fed through the corporate feed network which excites a radiating mode inside DRA, i.e., $TE_{1\delta1}$. This mode has been utilized to enhance the impedance bandwidth which is below −10 dB for both the E- and H-plane so as to meet the requirements of next-generation defense communication and low-cost satellite systems. To generate the axial ratio (AR), the extended off-set feed has been employed to provide the required 90$^{\circ}$ phase shift. Further, in order to enhance the gain and reduce the SAR, an electromagnetic band gap structure has been used as a reflector. Furthermore, multiple arrays have been introduced to extend the coverage area through beam-forming. The proposed design has been fabricated for the experimental validation. The measured IBW and ARBW is 34.74% and 12.2%, respectively. The gain is 10.1 dBic throughout the band of operation along with the radiation efficiency above 85% in various bending conditions. The SAR is much below the permissible limit of 1.6 W/kg. Thus, the proposed array is compact, and it clearly achieves a smaller footprint, better IBW, ARBW and a low SAR with potential prospect for X-band purposes.

A work of compact dual-port transparent multiple-input multiple-output antenna optimized for fifth-generation (5G) N77 (3.3–4.2 GHz) and N78 (3.3–3.8 GHz) bandwidth has been simulated, investigated, and optimized for robust performance in high-speed wireless communication. It features an impedance bandwidth of 3–4.3 GHz with a minimum simulated return loss of −28 dB, with 100% 3-dB axial ratio bandwidth and a simulated gain of 3.5 dB. The conducting plane material is indium tin oxide (ITO), chosen for its high optical transparency and sufficient electrical conductivity to seamlessly integrate into visually demanding applications. The substrate is glass, chosen for its lightweight and durable properties, which enhance both the mechanical durability of the antenna and its electromagnetic performance. To validate the ITO-based simulated design, the prototype with the same geometrical specification has been fabricated with the conducting portion replaced with copper and substrate as glass material due to a lack of facilities for transparent antenna fabrication. The comparative investigation study between the proposed ITO-based transparent antenna and with copper-based prototype (simulated/measured) both on a glass substrate, has been discussed, which supports the findings.

This paper describes the application of the differential evolution (DE) method for synthesizing radiation patterns of two 4×4 microstrip planar antenna arrays. The performance of the DE algorithm was evaluated by optimizing beam steering with simultaneous sidelobe level (SLL) control. Additionally, the algorithm optimizes the cross-polarization decoupling (XPD) to improve the polarization purity. In the optimization process, the active element patterns were incorporated into the DE algorithm to account for mutual coupling and truncation of the ground plane and the substrate in the determination of the excitation coefficients of each array element. The results demonstrate that the DE method can be effectively used to optimize radiation patterns particularly in terms of main beam pointing direction, SLL control, and XPD with fast convergence and low computational cost.

This paper elaborates the design and analysis of cross-aperture-coupled twin port ceramic radiator. Stimulation of alumina ceramic using a cross slot helps to produce circular waves within 7.35–7.8 GHz. The polarization diversity concept helps to improve the separation level by above 25 dB. Loading of double negative unit cell made metasurface (MS) improves the antenna gain over 11.5 dBi within the working spectrum. Machine learning (ML) techniques, i.e. Decision Tree and Random Forest are utilized to predict the |S11|/Axial ratio parameters. Experimental verification/ML prediction and optimized simulated consequences confirm that the structured radiator works efficiently between 7.21 and 8.2 GHz with over 25 dB isolation between the ports. Directive pattern and decent values of (MIMO) parameters make the radiator applicable for the 6G communication system.

This article proposes a hexagonal shaped circularly polarized (CP) antenna at ultra-high frequency (UHF) for radio frequency identification (RFID) and X-band applications. Initially, the antenna operates only in X-band and to convert this CP dual-band antenna asymmetric ground plane and four electromagnetic band gap structures are employed. A metasurface consisting of two complementary metamaterial structures is positioned above the patch at a 9 mm distance to enhance the gain and impedance bandwidth in both the bands. The presented antenna whose electrical dimension 0.48 λg × 0.48 λg × 0.02 λg achieves an impedance bandwidth of 796 MHz and of 4.24 GHz in UHF–RFID and X-band spectrum, respectively. The proposed antenna achieves circular polarization and has a bandwidth of 995 MHz and 796 MHz which spans 2.28–3.28 GHz and 10.44–11.24 GHz, respectively, with a 3 dB axial ratio. In addition to these, a stable radiation characteristic with an average gain of 6 dBi at both 2.45 GHz and 11.21 GHz are achieved which makes it suitable for RFID based real time logistic warehousing applications.

A circularly polarized broadband antenna is designed for Wi-Fi 7 applications. The patch antenna is modeled in the shape of G, and the feed position is adjusted to produce the arms with a length difference of λ/4. The G-shaped patch antenna has shown an impedance bandwidth of 5% (6.16−6.48 GHz) and a peak gain of 6.3 dBi. The metasurface is structured with a periodic array of 4 × 4 patches. The metasurface is sandwiched between dielectric substrates beneath the G-shaped patch. The outcome of these combinations has achieved an impedance bandwidth of 41% (4.85−7.37 GHz) and an axial ratio bandwidth of 26% (5.26−6.83 GHz), and the antenna achieved a peak gain of 7.45 dBic.

In this paper, a polarization-reconfigurable antenna fed by a coplanar waveguide (CPW) using a stepped structure is presented. The main parts of the proposed antenna consist of a CPW-fed monopole and four branches. After studying and analyzing the structure and mechanism of the antenna, it was found that different polarizations can be generated by adjusting the antenna’s structure. Based on the mechanism, four PIN diodes are utilized and inserted between the four branches and the monopole for the switching. By controlling the ON/OFF states of the four PIN diodes, the antenna can switch among left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP). The optimized antenna has been fabricated and measured. Measured results indicate that the antenna’s −10-dB impedance bandwidth for LP is 15.93%, covering the frequency range from 2.3 to 2.71 GHz. The overlap bandwidth of −10-dB impedance and 3-dB axial ratio for the LHCP mode is 18.96%, covering frequencies from 2.1 to 2.54 GHz. For the RHCP mode, the overlap bandwidth is 20.5%, covering frequencies from 2 to 2.52 GHz. At all the three polarization modes, the antenna is capable of covering the 2.4-GHz WLAN band (2400–2480 MHz) as well as the LTE TD 2300 band (2300–2400 MHz).

This research proposes a low-complexity, low-profile square-shaped quad-band dual-sense circularly polarized (CP) perturbed slot antenna with stepped microstrip feed for C-band radar and satellite applications. The proposed antenna is characterized by characteristic mode analysis. The proposed design has a square-shaped slot with diagonally opposite symmetric rectangular corner extensions. Multiband resonance is achieved by exciting the split ring resonator (SRR), cross strips and annular ring structure using the stepped microstrip line-fed slot radiator. The slot antenna and a metallic ring resonate at 1.64 and 8.2 GHz, respectively, showing left-hand circular polarization response, whereas the SRR and cross strips resonate at 3.6 and 6.6 GHz, respectively, exhibiting right-hand circular polarization radiation at these resonance bands. Hence, the proposed design shows quad-band performance with dual-sense CP behavior. Furthermore, the proposed antenna allows for independent tuning of polarization sense at resonance frequencies. The proposed design uses a low-cost FR-4 material as a substrate of dimensions 60 × 60 × 1.6 mm3. The experimentally measured results are in close agreement with the simulated performance parameters of the prototype.

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.

This paper presents a systematic design approach for developing a semiflexible multiple-input–multiple-output antenna system operating in the millimeter wave frequency spectrum, specifically designed for body-worn applications in biotechnologies. The designed antenna features dual flower-shaped antenna radiators placed in a spatial diversity configuration. Strategic modifications have been implemented by integrating dual crescent-shaped slots in the ground layer to attain the targeted frequency band of 25.7–30.6 GHz. Later, the upper edge of the ground plane is truncated in order to achieve circularly polarized radiation characteristics at 29.4 GHz with 3 dB ARBW of 0.6 GHz (29.1–29.7 GHz). The realization of circular polarization in the antenna geometry is validated through the analysis of characteristic mode theory. A maximum gain of 5.6 dBi is attained along with a port isolation of >30 dB. The proposed antenna undergoes analysis to assess its performance in the bending conditions and specific absorption rate, besides validation of diversity metrics encompassing envelope correlation coefficient, diversity gain, channel capacity loss, total active reflection coefficient, and mean effective gain has also been conducted. Finally, the proposed antenna structure is fabricated, and its performance is validated and subsequently compared with that of its simulated counterpart.

This communication designs and investigates a twin-port microstrip antenna loaded with a metasurface (MS). The proposed MS works in two ways: (i) artificial ground plane for radiator and (ii) as an ideal absorber of normal incoming waves at the same time. A stair shaped slot is loaded on rectangular patch for creating circularly polarized wave in between 835–894 MHz. Antenna port slots oriented in a mirror manner increase isolation by 25 dB. To act as a validation tool, the suggested antenna was built and its executions in individually operating modes evaluated by statistical and experimental analysis. It is shown that combining the patch and absorber results in a well-matched antenna in between 710–980 MHz with improved gain (more than 3.0 dBi). The proposed antenna design effectively used for UHF (Ultra High Frequency)radio-frequency identification (RFID) applications, which is due to its ability to mitigate multipath reflection issues and incorrectRFID reading.

This research article proposes a dual-sense dual-port wideband circularly polarized (CP) multi-input multi-output (MIMO) antenna designed for Wi-Fi 6E applications. The main novelty lies in achieving CP for both ports using a truncated rectangular-shaped aperture. By incorporating design and spatial diversity and defective ground structure between the two radiators, the design improves isolation and enables the antenna to generate Left-Hand Circular Polarization (LHCP)depending on the selected feed port. The proposed MIMO rectangular dielectric resonator antenna demonstrates an impressive impedance-matching bandwidth (IBW)from 5.5 to 8.0 GHz (37.10%) as well as an axial ratio bandwidth (ARBW) covering from 6.0 to 6.55 GHz (12.20%). Additionally, the dual-port wideband CP MIMO antenna exhibits satisfactory diversity performance parameters. To validate the simulated results, a physical prototype is fabricated and subjected to experimental testing. The measured outcomes of the fabricated model align closely with the simulated results, confirming the accuracy of the design. With both MIMO and CP capabilities and improved isolation, this proposed model proves beneficial in reducing latency and minimizing the impact of multipath fading. Therefore, it stands as an excellent choice for future devices utilizing the Wi-Fi 6E band due to its broad IBW and overlappingAR.

This paper introduces a tri-band stacked elliptical patch antenna featuring a right-handed circular polarized, designed to operate at the L2, L5, and L1 Global Navigation Satellite System bands. Initially, an elliptic patch is constructed and fed by a probe feed to generate TM110 and TM210 modes at resonance frequencies calculated using Mathieu functions. The probe position is precisely adjusted to excite the quasi-orthogonal mode of TM110 to generate circularly polarized (CP) waves at the L2 and L5 bands. Subsequently, an eye-shaped aperture is engraved into the elliptical patch to enhance the axial ratio (AR) beamwidth in the L2 and L5 bands and stimulate the orthogonal mode of TM210 to produce CP waves at the L1 band. Lastly, a stacked partially elliptical parasitic element is placed beneath the upper slotted elliptical patch to enhance the orthogonality of TM210 surface current versions and thus improve the AR beamwidth at the L1 band. The proposed antenna shows low reflection coefficient values at 1.12–1.33 (L2/L5), and 1.5–1.66 GHz (L1). The AR beamwidths are 133/213∘, 167/163∘, and 36/103∘ at two orthogonal cutplanes at L5, L2, and L1 bands, respectively. The antenna also has decent gains of 6–6.9 dBic across the three bands.

This article presents an innovative design for a low-profile, high-gain circularly polarized (CP) antenna using a single-layer metasurface (MTS). The proposed design incorporates an MTS layer, comprising a 4 × 4 array of hexagonal-shaped patches, printed on the top layer of the substrate. The bottom layer features a coplanar waveguide-fed slotted ground. Circular polarization and broadside radiation are achieved through the application of characteristic mode analysis (CMA). CMA is employed to simultaneously excite desired modes, aiming for wideband circular polarization and gain enhancement. Experimental results validate the effectiveness of the design, with compact dimensions of 0.67λ0 × 0.67λ0 × 0.04λ0. The measurements demonstrate an impressive impedance bandwidth of 84.3% within the 3.7–9.1 GHz. Additionally, a 3-dB axial ratio bandwidth of 18.6% is observed between 4.96 and 5.98 GHz and 3.74% between 8.38 and 8.7 GHz. The antenna exhibits excellent radiation pattern characteristics, featuring a maximum gain of 10.08 dBi at 7.1 GHz. The radiation pattern is symmetrical with broadside directionality, making the antenna well-suited for sensing applications.

In this paper, the design of a circularly polarized (CP) multiple-input–multiple-output (MIMO) antenna system is presented, utilizing a dielectric resonator (DR). This presented antenna system is subsequently integrated with a multifunctional filter, all meticulously structured on a single substrate. The multifunctional filter operates in three modes: reconfigurable band-pass and band-reject filter as well as all-pass filter. The overall structure works as a tunable filtenna. The designed filtenna is expanded into a two-port MIMO system on a unified substrate, providing strong port isolation below −28.5 dB. The overall dimension of proposed radiator is 180 × 180 × 1.6 mm3. The value of peak gain is 5.19 dBic. By switching the states of PIN diodes, the designed filtenna operates as a sensing and communicating antenna for interweave and underlay cognitive radios (CRs). The proposed antenna supports the CP waves within the working band, i.e., 3.6–4.5 GHz. The simulated results are validated by comparing them with the measured results showing less variation among them. MIMO parameters, including the envelope correlation coefficient and diversity gain, have been calculated for the proposed filtenna, representing its suitability for 5G-CR applications.

A multi-band circularly polarized antenna is proposed for WLAN (2.4/5.3/5.8 GHz) and WiMAX (3.5 GHz) applications. The proposed antenna is constructed of a radiation patch and a reflecting metal ground. Characteristic mode theory is utilized to analyze the modes of the patch and based on these results the antenna is optimized. The −10 dB impedance bandwidths of the proposed antenna are 53.53% (2.4–4.15 GHz) and 47.28% (5.25–8.5 GHz), respectively. The antenna radiates left-handed circular polarization in the lower band and right-handed circular polarization in the upper band. A maximum gain of 10 dBic is achieved for the proposed antenna.

A two-port ceramic-based antenna loaded with partially reflecting surface (PRS) is structured and explored. Fan-shaped slot is utilized to create circularly polarized wave in both frequency ranges. Dual frequency ranges are due to hybrid mode creation inside the ceramic material, i.e. HEM11δ and HEM12δ modes. PRS is used to change the phase gradient, which in turn tilts the radiation beam (±35°) obtained from different port in opposite direction. This concept is useful to reduce the envelop correlation coefficient using far-field. Experimental verification confirms that the designed antenna works from 26.1 to 27.5 GHz and 31.7 to 33.6 GHz along with less than 3-dB axial ratio from 26.5 to 27.1 GHz and 31.9 to 33.1 GHz respectively. Orthogonal placement of ports introduces the concept of polarization diversity and decreases the coupling between ports by an amount of −25 dB. Good gain value (up to 7.0 dBi) and better value of diversity performance make the designed radiator applicable for 5 G millimeter-wave uses.

Two metasurface-inspired antennas embedded in a metallic cavity are introduced here. They are expected to be integrated on fast moving platforms enduring harsh accelerations and shocks. The metasurface allows enlarging the antenna bandwidth that is intrinsically reduced for small antennas embedded in sub-wavelength metallic cavities. The first one is only 60 × 60 × 20 mm3 (0.23λ1 × 0.23λ1 × 0.08λ1 at the frequency of 1164 MHz) and presents a dual-band behavior, covering both the lower and upper global navigation satellite systems (GNSS) bands (all GNSS bands are covered). It is fed by four probes and a dedicated circuit, ensuring the phase quadrature between adjacent feeds to achieve circular polarization over these two bands. For the second proposed antenna, circular polarization is achieved using two feed points connected to the radiating aperture of size 50 × 50 × 20 mm3 (0.26λ0 × 0.26λ0 × 0.10λ0 at the frequency of 1559 MHz). It covers the E1, L1, B1, and G1 GNSS bands. The numerical results are successfully validated by measurements.

In this paper, a truncated patch antenna based on the electromagnetic band gap (EBG) structure has been proposed. The fabricated antenna has five operating frequencies at 10.4, 15.68, 19.68, 27.2, and 35.04 GHz. The fabricated prototype of the antenna constitutes a truncated rectangular patch etched with the shape of a symmetrical slot (on top) and an EBG loaded on the ground plane of the dielectric substrate. The optimized volume of the antenna is 20 × 15 × 1.57 mm3. The proposed antenna gives a good radiation pattern for the E-H field in all covered bandwidth and also achieved better performances related to the reference papers. A multiband antenna also covered the 5 G bandwidth, which resonates at 27.2 GHz from 24.2 GHz to 27.84 GHz bandwidth and at 35.04 GHz from 33.84 GHz to 36.2 GHz bandwidth, which can be used in the Internet of Medical Things. On the other hand, X/Ku/K frequency bands have been committed for wireless communication where the multiband antenna can be used to help in monitoring, especially in the case of data transmission from radio frequency sensors to health-care system in real-time applications.

This article explores the possibilities of incorporating a defected ground structure (DGS) for widening the 3 dB axial ratio beamwidth (ARBW) of a simple low-profile planar circularly polarized (CP) antenna. Two pairs of DGSs are etched symmetrically along the diagonals of the ground plane to overcome the limited 3 dB ARBW performance of a crossed-slotted circular-shaped planar CP antenna. Here, one pair of DGSs is orthogonal to another pair of DGSs. The distance between the pairs of DGSs plays a key role in enhancing the 3 dB ARBW by 40.62%. A gap of 0.18λ0 is considered between the DGSs to maintain the symmetrical electric field distribution in the substrate. It also helps to reduce orthogonal current components and provides uniformly distributed patch surface currents. These phenomena collectively help the proposed CP antenna to exhibit right-handed circular polarization radiation with the 3 dB ARBW of 186° and 188° in the E-plane and H-plane, respectively. The measured results yield impedance bandwidth (S11 ≤ −10 dB) of 2.6% (2.283–2.342 GHz), CP bandwidth of 0.9% (2.294–2.315 GHz), gain higher than 4.8 dBic, and total antenna efficiency more than 64% across the entire CP band.