Wearable antennas are the vital components for Body Centric Communication (BCC). These antennas have recently gained the attention of researchers and have received a great deal of popularity due to their attractive characteristics and opportunities. They are fundamental in the Wireless Body Area Networks (WBANs) for health care, military, sports, and identification purposes. Compared to traditional antennas, these antennas work in close proximity to the human body, so their performance in terms of return loss, gain, directivity, bandwidth, radiation pattern, efficiency, and Specific Absorption Rate (SAR) is influenced by the coupling and absorption of the human body tissues. Additionally, in the design of these antennas, size, power consumption, and speed can also play a paramount role. In most cases, these antennas are integrated into the clothes, or in some cases, they may be fixed over the skin of the users. When these characteristics are considered, the design of wearable antennas becomes challenging, particularly when textile materials are examined, high conductivity materials are used during the manufacturing process, and various deformation scenarios have an impact on the design’s performance. To enhance the overall performance of the wearable antennas and to reduce the backward radiation towards the human body, metamaterial surfaces are introduced that provide a high degree of isolation from the human body and significantly reduce the SAR. This paper discusses the state-of-the-art wearable/textile/flexible antennas integrated with metamaterial structures composed of wearable/flexible substrate materials, with a focus on single and dual band antenna designs. The paper also reviews the critical design issues, various fabrication techniques, and other factors that need to be considered in the design of wearable/textile/flexible antennas. All the designs presented in this work are of the recent developments in wearable technology.

In this letter, a circularly polarized Spidron fractal dielectric resonator antenna is presented. A wide 3-dB axial ratio (AR) bandwidth is realized by merging a Spidron fractal dielectric resonator and a C-shaped slot that can produce circular polarization. The proposed antenna is excited through the coupling between a C-shaped slot in the ground plane and a 50-Ω microstrip feeding line. A prototype of the antenna is fabricated and tested. Reasonable agreement is achieved between the measurement and simulation. The experimental results show that the proposed antenna has a -10- dB reflection bandwidth of 37.29% (4.32-6.30 GHz) and a 3-dB AR bandwidth of 11.57% (5.13-5.76 GHz). The measured gain of the antenna ranges 2.20 dBic to 3.16 dBic within the AR bandwidth.

In this letter, a wideband substrate integrated waveguide (SIW) based slot antenna is designed for D -band applications. A wideband response is attributed to the merging of closely lying six resonance frequencies. Two of them at frequencies of 114.25 GHz and 134.75 GHz signifies the excitation of TE $_{310}$ and TE $_{120}$ modes, respectively. The modes at 124 GHz and 144 GHz are identified as hybrid modes that are formed from the combination of TE $_{310}$ –TE $_{120}$ and TE $_{120}$ –TE $_{220}$ modes, respectively. The upper two resonances at the frequencies of 154 GHz and 160 GHz occur due to TE $_{220}$ –TE $_{320}$ based hybrid modes. A two-step wideband WR6-SIW transition is also designed and integrated with the antenna for measurement purpose. In the first step, the three-section Chebyshev transition is developed to match the impedance of standard WR6 with a rectangular waveguide (RWG) of the same height as that of the PCB. In the second step, the RWG is matched with SIW using a dielectric extension. The final antenna with transition is simulated and measured. A wide $-$ 10 dB impedance bandwidth for $|S_{11}| \leq -$ 10 dB of 42.86% (110–170 GHz) is obtained. The gain and radiation measurements were also performed after constructing an in-house measurement system.

In this paper, a new technique for circular polarization in a slot coupled dielectric resonator antenna is proposed. The circular polarization is generated by inserting the two annular vias into dielectric resonator slightly off the diagonal position. In addition to the circular polarization, the proposed technique increases the total realized gain by 1.62 dB as compared to the via-less case on the account of increased directivity while maintaining the same aspect ratio of the DR. To validate the design, a prototype is fabricated and measured. The measured results show that the proposed circularly polarized dielectric resonator antenna has a −10 dB reflection bandwidth of 7.29% (3.3–3.55 GHz) and a 3 dB axial ratio bandwidth of 5.5% (3.28–3.465 GHz) with a measured RHCP gain of 6–7.1 dBic. The measured curves of the S ₁₁ , axial ratio, and the RHCP gain results are in good agreement with the simulated results.

In this study, the mutual coupling in multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) is reduced by employing closed metallic loops. The loops are wrapped around the adjacent edges of the dielectric resonators (DR) where magnetic coupling is significant. The proposed method employs only the conductive metallic strips for mutual coupling reduction and this makes the entire design very simple and compact. The impedance bandwidth varies from 4.73 to 5.1 GHz, covering the Sub–6 GHz 5G band. The realized MIMO DRA has an isolation of 28 dB at the resonant frequency with a measured peak gain at each port of 3.5 dBi and a peak radiation efficiency of 93%. The obtained measured results yield a low correlation coefficient (< 0.05) mostly at the entire band that contribute to diversity gain ( $ > 9.8$ dB) to increase the capacity of communication system, is reported in this paper. The proposed antenna was fabricated and the closed loop strip is wrapped around using in house facility. Furthermore, some issues related to the fabrications tolerance have been investigated to justify the difference between some simulated and measured results.

In this letter, a tilted-D-shaped monopole antenna with wide dual-band dual-sense circular polarization is proposed. The tilted-D-shaped radiator is designed by combining inverted-C-shaped (ICS) and tilted-I-shaped (TIS) structures. The proposed radiator is attached to a 50-Ω line through an impedance transformer. The proposed design is compared with two of its variants, which concludes that the wide 3 dB axial ratio bandwidth (ARBW) in both bands is achieved due to the contributions from the ICS and TIS structures. Besides, the lower and upper bands radiate left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP), respectively. A prototype of the proposed antenna is fabricated, and its performance is experimentally verified. The measurement results show that the proposed antenna exhibits a wide impedance bandwidth for |S11|< -10 dB of 104.54% (3.47-1.07 GHz) entirely covering both CP bands with 3 dB ARBWs of 31.16% (4.28-5.86 GHz) in the lower and 22.62% (7.49-9.4 GHz) in the upper band. In broadside direction, the measured gain varies between (1.26-3.58 dBic) and (3.85-6 dBic) in the lower and upper bands, respectively.