A low-profile circularly polarized wearable antenna with flexible performance and reduced specific absorption rate (SAR) based on graphene is presented. The antenna adopts highly conductive graphene film and polydimethylsiloxane substrate, which have good flexibility, mechanical stability, and light weight. The wearable antenna operating at 5.8 GHz with a profile of 0.05 λ is designed and fabricated, which retains a reflection coefficient of less than -10 dB when loaded on the human body. The measured results indicate the axial-ratio (AR) bandwidth for AR<; 3 dB covers 5.75-5.83 GHz with the realized gain varying from 5.0-6.1 dBic. The SAR peak is 1.02 W/kg when the human tissue is 1 g and 0.947 W/kg when the human tissue is 10 g, which meets the international SAR standards.

In this letter, a transparent ultra-wideband (UWB) halved coplanar Vivaldi antenna (HCVA) with metal mesh film (MMF) is proposed. Based on the equivalence principle, the halved type antenna is achieved by replacing a radiation fin with the ground plane. The proposed HCVA has the advantages of ultra-wideband impedance matching, miniaturized aperture size, high directivity, and simple feed structure. By employing MMF with a low sheet resistance of 0.35 Ω/sq and high optical transmittance above 72% in the radiation fin and ground plane, the antenna is entirely transparent. An example transparent HCVA is fabricated and measured. According to the simulated and measured results, most of the reflection coefficient is below -10 dB from 0.78 GHz to 20 GHz. Moreover, the peak realized gain reaches 10.4 dBi with the compact size of 0.32×0.47×0.052λL 3, where λL is the wavelength at the lowest operating frequency.

In this letter, a novel tunable grounded coplanar waveguide (GCPW) attenuator based on graphene nanoplates is proposed. The attenuator consists of a 50- $\Omega $ GCPW transmission line and three pairs of graphene nanoplate pads periodically located in the gap between the signal line and the upper metal ground. The resistance of graphene pad can be tuned from high to low by increasing the bias voltage, thus changing the attenuation level. Particularly, the distance between two pairs of graphene pads can be adjusted to achieve good impedance matching in different working bands. The impedance matching principle is analyzed in theory. Two prototypes are designed, fabricated, and measured, whereas the other two prototypes are verified by simulation. Attenuation amplitude of the attenuators can be tuned from 2.5 to 14 dB with a low reflection below −10 dB as the bias voltage varies from 0 to 6 V, and the working frequency bands ( $\vert S_{11}\vert < -10$ dB) cover from 3.5 to 38 GHz.

In this communication, we propose glide-symmetric double-layer (D-L) spoof surface plasmon polaritons (SSPPs) structures for controlling the field confinement of SSPPs to achieve antenna beam manipulation with a large frequency-scanning angle. By changing the shape of the glide-symmetric D-L SSPPs, we can control the electric field confinement of the SSPPs to emerge symmetric or asymmetric distribution. Hence, the proposed SSPPs structure can produce electromagnetic (EM) leakage on both sides or single side, furtherly achieving dual-beam (D-B) or single-beam (S-B) radiation. Two SSPPs antennas with dual beams and single beam are designed, fabricated, and measured. Both the D-B antenna and S-B antenna operate from 9 to 24 GHz. Within the working band, the D-B antenna accomplishes 134.3° (−90° to +44.3°) beam-scanning angle with the realized gain of 8.03–12.17 dBi, while the S-B antenna achieves 119° (−77.9° to 41.1°) beam-scanning angle with 10.31–14.24 dBi realized gain. The simulated and experimental results verified the beam manipulation and large frequency-scanning angle in antenna design.

A dual wideband antenna with a large beam steering angle through endfire radiation and frequency scanning radiation in each band is proposed for the first time. The antenna utilizes a double-layer (D-L) spoof surface plasmon polaritons (SSPPs) structure which exhibits stronger field confinement and lower cutoff frequency than the single-layer (S-L) SSPPs structure. The modulated D-L SSPPs structure can excite the space harmonic distributing in the fast-wave region and retains transmission in the slow-wave region. By combing the modulated D-L SSPPs waveguide and the Vivaldi radiator, both the slow-wave radiation (endfire mode) and the fast-wave radiation (frequency scanning mode) can be aroused in the two operating bands. An example antenna is designed and fabricated. In the slow-wave range from 3 to 9 GHz, the antenna works in the endfire mode with the beam direction of 90° and the realized gain varying from 3.55 to 8.24 dBi. Within the fast waveband from 13 to 34 GHz, the antenna operates in the frequency-scanning mode, accomplishing beam scanning from −90° to ±42.5° with the realized gain of 9.45–15.67 dBi. Thus, the proposed dual-band antenna can achieve two operating bands and two radiation modes, which offers a 180° beam-changing angle in total.