In this paper three different multi stub antenna arrays at 27–29.5 GHz are designed. The proposed antenna arrays consist of eight single elements. The structure of feeding parts is the same but the radiation elements are different. The feeding network for array is an eight way Wilkinson power divider (WPD). To guarantee the simulation results, one of the proposed structures is fabricated and measured (namely the characteristics of S11, E-, and H-plane patterns) which shows acceptable consistency with measurement results. The simulation results by CST and HFSS show reasonable agreement for reflection coefficient and radiation patterns in the E- and H- planes. The overall size of the proposed antenna in maximum case is 29.5 mm × 52 mm ×  0.38 mm  (2.8 $${{\varvec{\lambda}}}_{0}$$ λ 0 × 4.86$${{\varvec{\lambda}}}_{0}$$ λ 0 × 0.036$${{\varvec{\lambda}}}_{0}$$ λ 0 ). Moreover, for Specific Absorption Rate (SAR) estimation, a three-layer spherical human head model (skin, skull, and the brain) is placed next to the arrays as the exposure source. The simulation results show that the performance of proposed antennas as low-SAR sources makes them ideal candidates for the safe usage and lack of impact of millimeter waves (mmW) on the human health. In all three cases of SAR simulations the value of SAR1g and SAR10g are below the standard limitations.

In this study, a new plasmonic biosensor is proposed, which is highly sensitive with a compact structure, based on numerical methods for glucose concentration monitoring in different samples. The biosensor is based on a metal-insulator-metal waveguide and a ring resonator, and the calculated results are analyzed. The glucose biosensor operation is based on the refractive index of the glucose solution in the structure. In this study, to improve the sensitivity of the biosensor, the effect of the inner radius size parameter on spectral sensing has been fully analyzed. This biosensor in resonance wavelengths has a linear relationship with the refractive index of the glucose solution. In this structure, the maximum linear sensitivity is in glucose concentration. In addition, compared to other similar sensors, this biosensor has a label-free detection basis and has a very simple and ultra-compact structure: its size is . Considering the special features of this sensor, it could be used as optical on-chip biosensors for glucose concentration monitoring.

In this study, an all-optical plasmonic filter is introduced based on metal-insulator-metal waveguides coupled with a square nanocavity filled with a nonlinear Kerr material. This structure is numerically investigated using the finite element method. The structure is then analyzed under linear and nonlinear regimes. The nonlinear material inside the square nanocavity includes gold nanocomposite, and its effective parameters are measured using the Maxwell-Garnett theory. The simulation results show that the resonance peak of the filter structure can be adjusted by changing the physical properties of the gold nanoparticles. Furthermore, we can tune the resonant wavelength within the transmission spectrum by considering the Kerr effect of the gold nanocomposite, and by adjusting the incident light signal without changing the dimensions and physical characteristics of the proposed filter structure. Due to the compact size and the simplicity of fabrication, the proposed plasmonic nanofilter is an ideal option for designing the integrated optical circuits.

Three configurations of compact planar multistub antennas are proposed in the frequency range of 27–29.5 GHz as candidates for the 5G standard frequency band. Each antenna consists of the same feeding part configuration but different structures for the dipole, director, and reflector parts. The feeding part is based on the substrate integrated waveguide (SIW) technology which results in compact size. The TE10 dominant mode is considered in the design procedure by HFSS software simulations. The proposed antennas have been simulated, fabricated, and measured (for S11, E, and H pattern). The simulation and measurement results show reasonable agreement for S11 and radiation patterns of E- and H-planes and impedance bandwidths. Moreover, for specific absorption rate (SAR) estimation, a three-layer human head model (skin, skull, and brain) is placed next to the antennas as the exposure source. The simulation results show the performance of the proposed antennas for low-SAR, which make them good candidates for safe usage concerning the negative impact of millimeter waves (mmWs) on human health. Finally, a comparison table is presented which verifies the compact size of our proposed antennas.

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