A single-fed miniaturized wide-beamwidth circularly polarized implantable antenna, operating in the Industrial, Scientific, and Medical band (2.40-2.48 GHz), is designed and experimentally verified for subcutaneous real-time glucose monitoring applications. The proposed antenna features a very good miniaturization with the dimensions of 8.5 × 8.5 × 1.27 mm ³ byemploying four C-shaped slots and a complementary split-ring resonator (CSRR). Meanwhile, by adjusting the slits of CSRR, circular polarization is realized. The simulation results in a three-layer phantom demonstrate that the impedance bandwidth is 12.2% (2.32- 2.62 GHz) with a peak gain of -17 dBi, and the 3-dB axial-ratio bandwidth is 2.4% (2.42-2.48 GHz) with a wide beamwidth of around 140°. An in vitro test was carried out in a pork slab, and the measured impedance bandwidth is 13% (2.31-2.63 GHz) with S ₁₁ <; -10 dB, confirming the simulated results. The specific absorption rate distribution has been evaluated for the consideration of health safety, and the calculated link margin shows that the reliable communication can be guaranteed within 10 m in free space.

A compact dual-band and dual-circular polarization (CP) stacked patch antenna is investigated for BeiDou navigation satellite system (BDS). The proposed antenna employs a single coaxial probe to feed two layers of patches simultaneously, realizing dual-band operation. The bottom patch with symmetrical slant corner-cuts and the top one with two rectangular stubs on the diagonal produce a pair of degenerated modes, achieving CP radiation. Furthermore, two L-shaped stubs are loaded on the top patch to widen impedance bandwidth. A prototype operating at the bands of 1.615/2.492 GHz was fabricated and measured. Both the left- and right-handed CP radiations are obtained concurrently in the dual bands. The proposed antenna has a profile of 4.6 mm (0.024 $\lambda_0$ ) and occupies an area of 70 mm × 70 mm (0.38 $\lambda_0$ × 0.38 $\lambda_0$ ). The measured impedance bandwidth with | $S_11$ | < -10 dB is 9.1% and 5.1% for the lower and upper bands, respectively. The measured 3-dB axial ratio (AR) bandwidth is more than 1% for both bands.

A broadband circularly polarized (BCP) all-textile antenna and its wearable conformal antenna array (WCAA) are investigated for body-centric communications. Initially, a circularly polarized (CP) microstrip patch antenna loaded with a piece of the modified metasurface is designed to achieve wide impedance and axial ratio (AR) bandwidths. The characteristic mode analysis is employed to understand the operating mechanism, which provides clear physical insight into each mode at various frequencies. Due to the adoption of textile (i.e., felt) as substrate and nylon conductive fabric as conductor, the proposed antenna is flexible, totally conforming to the curve-shaped human body. The antenna with broadside radiation is suitable for off-body communications. For verification, the prototype operating at 5 GHz (5.15–5.825 GHz) band was fabricated. The measured −10 dB impedance and 3 dB AR bandwidths of 35.1% and 17.5% with a peak gain of 8.5 dBi are achieved. Furthermore, the BCP antenna is used as an element to constitute the WCAA, and the omnidirectional radiation pattern in the azimuth plane is achieved for on- and off-body communications. The considerations about how to achieve omnidirectional radiation and avoid radiation nulls are studied in detail. Finally, the WCAA was fabricated and tested; the measured results guarantee its potential for wearable applications.

A miniaturized four-element multiple-input-multiple-output (MIMO) antenna operating in the band of In-dustrial, Scientific, and Medical (ISM) 2.4-2.48 GHz, is investigated to supply sufficient transmission rate and fight against multipath fading. A single antenna integrates with dual radiators, and each radiator is owned by a pair of sub-antenna units, greatly diminishing the whole dimensions of the implanted MIMO device. A cross-shaped slot etched in the radiator, a branch extending on the conductor ground, and a pair of electromagnetic band gaps (EBGs) are integrated to achieve high isolation. The proposed MIMO antenna has the compact dimensions of 18.5 mm × 18.5 mm × 1.27 mm. The simula-tion in the three-layer phantom indicates that the impedance matching is good with a bandwidth of 18.64% (2.14-2.58 GHz) and a maximum gain of -15.18 dBi and the mutual coupling is reduced to less than -15.99 dB at the ISM band. An ex-vivo test was implemented in a fresh pork slab and the measurement results are well matched with the simulation ones. Health safety considerations and link budget are discussed to validate the antenna's availability in biomedical telemetry, and the envelope correlation coefficient is computed, illustrating the high independence between antenna elements.

A wearable all-textile microstrip patch antenna (MPA) operating in the dual bands of medical body area network (2.36—2.40 GHz) and WiMAX (3.4—3.6 GHz), is proposed for body-centric communications. The omnidirectional radiation pattern with linear polarization for on-body link and unidirectional radiation pattern with circular polarization for off-body link are achieved by introducing reactance loading into MPA. Notably, two pairs of shorting pins are employed to tune the TM10 mode of MPA and generate a new mode of TM00, and by adjusting the spacing and radii of shorting pins, the required dual-band and dual-mode operation is achieved. Moreover, due to the adoption of textile (i.e., wool felt) as substrate and nylon conductive fabric as conductor, the antenna is flexible, totally conforming to the human body. The proposed MPA, with the dimensions of 70 mm × 70 mm × 2 mm (0.560 × 0.560 × 0.0160 at 2.38 GHz), was fabricated and characterized. The measured results show that the reflection coefficient, radiation pattern and gain of the antenna are slightly affected by structural deformation and human body loading. With merit characteristics, the proposed design can be well applied to wearable medical applications.

A dual-circular polarization (CP) textile antenna is investigated for wearable applications at 3.5 GHz WiMAX and 5.8 GHz industrial, scientific, and medical bands. The proposed antenna is composed of a dual-band monopole antenna and a polarization rotation artificial magnetic conductor (PRAMC). Through the PRAMC, the dual-CP radiation is enabled and the backward radiation is alleviated, in which the left-handed CP is generated in the lower band and the right-handed CP is realized in the upper band. Notably, dyadic reflection coefficient analysis is employed to understand the operating mechanism. Both monopole and PRAMC are printed on textile substrate, achieving conformability and comfortability. In addition, numerical results indicate that the performance of the antenna is robust to lossy human body and structural deformations. For verification, the prototype of the antenna was fabricated by two types of manufacturing process (i.e., laser cutting and screen printing), and the advantages and drawbacks of each fabricating approach are discussed for referring. The antenna made by laser cutting was tested on the phantom with the −10 dB impedance bandwidths of 11.7% and 9.1%, the 3 dB axial ratio bandwidths of 2.0% and 8.2%, and the peak gains of 6.6 and 7.2 dBic, in dual bands, respectively.