In this article, a 1 × 2 bandwidth (BW) and frequency-reconfigurable dielectric resonator-based multiple input multiple output (MIMO) antenna array is presented for 5G sub-6 GHz (3.3–6.0 GHz)/Wi-Fi 6E (5.925–6.425 GHz)/Wi-Fi 5G (5.15–5.85 GHz) applications. Additional dual-ring-open loop resonator structures with varied dimensions are introduced within antenna’s feeding network to achieve BW and frequency reconfigurability. RF PIN and varactor diodes (VDs) are integrated with proposed structure to enable switching between various modes and continuous tuning of frequency and BW, respectively. Further, Taguchi neural network (TNN) has been incorporated to predict percentage bandwidth of proposed antenna, getting a maximum deviation of only 0.6% from actual value. The proposed structure operated from 4.98 to 6.5 GHz, achieving wide continuous frequency tuning of 20.36% in passband and 6.1% reconfiguration for notch band. It also demonstrates continuous BW tunability from 16.69% to 34.44% with measured BWs of 19.58%, 34.44%, and 16.69% at 0, 3, and 8 V reverse bias voltages of VDs, respectively. MIMO antenna array structure also shows enhanced gain performance with a peak gain of 11.03 dBi and an overall gain above 7 dBi in the whole operating band.

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.

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 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.

Dielectric resonator antennas (DRAs) are developed antennas that are lightweight, wideband, small-sized and have high radiation efficiency. A DRA is an appropriate candidate for any radio communication including radar applications mainly because of its high efficiency and wideband performance. As the development of DRAs has been a continuous process for more than five decades the plethora of the same has become magnificent in all possible ways. Scientists have walked the technical path for more than centuries and tried to meet the various challenges in the most graceful ways. Reduction of loss, lightweight, and desired radiation patterns are some of the issues which are effectively met by DRAs. This paper presents a brief comprehensive review of the state of art techniques, giving an exhaustive idea of achieving broadband and multi-frequency operations in the areas of DRAs. The paper associates the references of the past and correlates with the current and future trends of research in DRAs that could be of immense help to the young upcoming researchers interested in this field.

This paper describes a multiple-input multiple-output (MIMO) antenna for low millimeter (mm)-wave applications based on dielectric resonators. This is the first time that a filtering response is used in conjunction with an MIMO antenna operating at a low mm-wave frequency. The antenna is simulated using an asymmetrical U-shaped aperture and a microstrip line feed. The suggested filtenna has two distinguishing characteristics: (i) the diversity parameters of the proposed MIMO are increased by including pattern and spatial diversity, and (ii) the proposed feed mechanism of a dielectric resonator provides the filtering response. Between the two ports, a metallic plate tilts the radiation pattern by 45°. The anti-parallel locations of the ports increase the isolation value by >30 dB. To validate the performance of the suggested antenna, the proposed filtenna was built and confirmed. The proposed antenna operates between the frequencies 27.9 and 28.5 GHz. Within the operating frequency range, the observed gain is ~4.5 dBi. On the contrary, the gain suppression level beyond the operational frequency range is ~15 dB. The stable radiation properties and high diversity parameter values of the suggested filtenna make it an effective solution for 5G Internet of Things sensing applications.

A superstrate loaded cylindrical dielectric resonator antenna is developed and demonstrated for dual-band circular polarization. The proposed antenna employs a microstrip-fed rotated cross-shaped slot coupling technique for exciting the dielectric resonator (DR). The design is developed in a straight forward way. Firstly, the DR is coupled with a conventional plus-shaped slot and operates in linear polarization mode at 7.4 and 11.2 GHz. Secondly, the slot is rotated by 10° to enable out-of-phase excitation and ensure circular polarization at the above-mentioned frequencies. In the third step, a square dielectric superstrate is placed above the DR which creates multiple reflection and enhance the gain up to ~8 dBi in both the frequencies without affecting other performances. The development stages are discussed in detail. The proposed design is demonstrated through prototype fabrication and characterization. This antenna can be used for X-band satellite communications.

In this paper, a reduced-size dielectric resonator antenna with switchable diversity patterns is proposed. Ring- and linear-shaped slots are etched in the ground plane of the antenna so as to generate two modes $TE_{\delta 11}^x$ and $TE_{\delta 12}^x$ at a center frequency of 19 GHz. Moreover, two groups of PIN diodes are integrated into these slots to short one group of slots, and let the other group generates the required mode. Thus, the antenna is able to generate two switchable patterns with an envelope correlation coefficient of 0.4. Furthermore, the antenna size is reduced to half of its original size by placing a copper sheet over certain plane of the antenna structure. The antenna achieves wide bandwidths of 17.6–20.9 GHz (17.1$\percnt $) and 18.3–21.6 GHz (13.8$\percnt $) in cases of exciting $TE_{\delta 11}^x$ and $TE_{\delta 12}^x$ modes, respectively. The antenna also attainsa high gain of 7.1 and 3.2 dB at the center frequency.

This paper presents a new technique for the enhancement of axial ratio (AR) bandwidth of a circularly polarized dielectric resonator antenna with a single feeding. To enhance the AR bandwidth, adjacent 3-dB AR passbands are merged by inserting the notches and conductive coating in the dielectric resonator. The dimensions of the notches and conductive coating are selected in such manner that impedance bandwidth remains approximately unchanged. The antenna provides the measured AR and impedance bandwidths of 55.22% and 66.45%, respectively.

In this paper, a single-feed dual-frequency dual-linearly-polarized dielectric resonator antenna is proposed which finds application in two- way internet satellite system and modern radar system. In order to achieve dual linear polarization at distinct frequencies, two rectangular dielectric resonators of same dimensions are excited in ${\rm TE}^{x}_{\delta 11}$ and ${\rm TE}^{y}_{1\delta 1}$ modes by a narrow longitudinal and transverse slot, respectively, etched on the top wall of the substrate integrated waveguide. The −10 dB impedance bandwidth of the proposed antenna is 6.76% for both the frequency bands. The antenna radiates along the broadside direction and the gain of the antenna varies from 5.37 to 6.24 dBi and 5.62–7.96 dBi across 8.14–8.71 GHz and 10.29–11.01 GHz, respectively.

In this paper, a simple conical-shaped dielectric resonator antenna operating in HEM11δ mode is presented for X-band wireless applications. A rectangular slot with a running microstrip line is used for excitation purpose. By placing a FR-4 based superstrate at 7 mm height from the ground FR-4 substrate and incorporating a set of modified ground plane on either side of the feed line, gain is improved by 42.85% and bandwidth by 68.92%, simultaneously. A prototype of designed antenna is fabricated and characterized. The measured results are found to be good in matching with the simulated ones.

A terrestrial microwave power transmission system is considered as an effective method for collecting natural energy. In this system, frequency dependence of the refractive index and multipath propagation due to the ground surface poses problems. In the study, a single-frequency retrodirective system was proposed with a beam pilot signal using dual-mode dielectric resonator antenna elements. The results confirmed that the beam pilot signal radiated from the entire surface of the receiving antenna and accurately used the same propagation space as that of microwave power by beam propagation method simulation. A dual-mode dielectric resonator antenna was proposed as a common array antenna element for the beam pilot signal and microwave power. This involves a cross-shaped hemispherical dielectric resonator structure, and an isolation level exceeding 60 dB was experimentally measured between the orthogonal ports of the fabricated antenna. The dual-mode dielectric resonator antenna with an isolation exceeding 60 dB was successfully developed as an enabling device to realize a single-frequency retrodirective system with a beam pilot signal.

In this paper, a microstrip-fed U-shaped dielectric resonator antenna (DRA) is simulated, designed, and fabricated. This antenna, in its simple configuration, operates from 5.45 to 10.8 GHz. To enhance its impedance bandwidth, the ground plane is first modified, which leads to an extended bandwidth from 4 to 10.8 GHz. Then by inserting a rectangular metallic patch inside the U-shaped DRA, the bandwidth is increased more to achieve an operating band from 2.65 to 10.9 GHz. To validate these results, an experimental antenna prototype is fabricated and measured. The obtained measurement results show that the proposed antenna can provide an ultra-wide bandwidth and a symmetric bidirectional radiation patterns. With these features, the proposed antenna is suitable for ultra-wideband applications.

A new simple compact ultra-wideband (UWB) dielectric resonator antenna is presented. The antenna consists of a modified stepped microstrip-fed monopole printed antenna loaded with a rectangular dielectric resonator, truncated ground plane, and a parasitic strip underneath the dielectric resonator (DR). Using an optimized truncated ground plane and a combination of stepped feed line with DR an ultra-wide impedance bandwidth of 153% for (∣S11∣ ≤ −10 dB), covering the frequency range of (3.7–28 GHz) is achieved. The added parasitic strip can improve the radiation pattern, especially at high frequencies. The proposed antenna covers almost the entire UWB (3.1–10.6 GHz), Ku (12.4–18 GHz), and K (18–26.6 GHz) frequency bands. Also this antenna has an omnidirectional and stable radiation pattern over the whole operating frequency range and a compact size of (15 × 20 × 5.8 mm3) that make it suitable for wideband wireless system applications. This structure is light weight and can be easily fabricated. A prototype is built and measured. The simulated and measured results are in good agreement.

In this paper, we propose a novel integrated ultra-wideband (UWB) monopole antenna with dual-band antenna. The antenna consists of planar rectangular with semi-elliptical base and a rectangular dielectric resonator antenna (DRA) with dual-band operation. Both of them are excited via coplanar waveguide (CPW) lines. The experimental measurements show that the planar monopole provides an impedance bandwidth between 2.44 and 11.9 GHz which largely covers the entire UWB spectrum, and the rectangular DRA operates at two bands; 5.3–6.2 and 8.5–9.4 GHz. Additionally, the proposed structure ensures low mutual coupling between the two ports (with S21 less than −20 dB in the whole operating frequency band). The measured and numerical results show a good agreement.