A new kind of double- and single-arm cantilever type DC-contact RF MEMS actuators has been monolithically integrated with an antenna architecture to develop a frequency reconfigurable antenna. The design, microfabrication, and characterization of this ¿reconfigurable antenna (RA) annular slot¿ which was built on a microwave laminate TMM10i ( ¿r = 9.8, tan ¿ = 0.002), are presented in this paper. By activating/deactivating the RF MEMS actuators, which are strategically located within the antenna geometry and microstrip feed line, the operating frequency band is changed. The RA annular slot has two reconfigurable frequencies of operation with center frequencies f _low = 2.4 GHz and f _high = 5.2 GHz, compatible with IEEE 802.11 WLAN standards. The radiation and impedance characteristics of the antenna along with the RF performance of individual actuators are presented and discussed.

The magnitude of the optical sheet conductance of single-layer graphene is universal, and equal to e ²/4ħ (where 2πħ = h (the Planck constant)). As the optical frequency decreases, the conductivity decreases. However, at some frequency in the THz range, the conductivity increases again, eventually reaching the DC value, where the magnitude of the DC sheet conductance generally displays a sample- and doping-dependent value between ∼e ²/h and 100 e ²/h. Thus, the THz range is predicted to be a non-trivial region of the spectrum for electron transport in graphene, and may have interesting technological applications. In this paper, we present the first frequency domain measurements of the absolute value of multilayer graphene (MLG) and single-layer graphene (SLG) sheet conductivity and transparency from DC to 1 THz, and establish a firm foundation for future THz applications of graphene.

The design methodology, analysis, and characterization of a radio frequency microelectromechanical systems (RF MEMS)-based reconfigurable antenna operating in the United States Public Safety bands are presented. It has two modes of operation with central frequencies of 718 and 4960 MHz, providing a high reconfigurable frequency ratio of $\sim {7}$. This antenna is electrically small with lateral dimensions being $\sim \lambda/10 \times \lambda/10$ at 718 MHz. The reconfigurability between the modes is achieved by a single RF MEMS switch, which enables changing the length of the current flow path, thereby the resonance frequency is changed. The measurement results for impedance and radiation characteristics of the fabricated antenna prototype agree well with the simulations. The measured bandwidths of the antenna are 2.6% and 7.6% at 718 and 4960 MHz, respectively.

A reconfigurable antenna (RA) capable of steering its beam into the hemisphere corresponding to θ ∈ {-40°, 0°, 40°}, φ ∈ {0°, 45°, 90°, -45°}, and of changing 3 dB beamwidth, where θ ₃ dB ∈ (40°, 100°), φ ∈ {45°, 90°, -45°} for broadside direction is presented. The RA operating in 5 GHz band consists of a driven patch antenna with a parasitic layer placed above it. The upper surface of the parasitic layer has two pixelated metallic strips, where each strip has four pixels. The pixels connected via p-i-n diode switches enable to change the current distribution on the antenna providing the desired modes of operation. A prototype RA was characterized indicating an average gain of 8 dB. Measured and simulated impedance and radiation patterns agreed well. The proposed RA offers an efficient solution by using less number of switches compared to other RAs. The system level simulations for a 5G orthogonal frequency division multiple access system show that the RA improves capacity/coverage tradeoff significantly, where the RA modes and users are jointly determined to create proper beamwidth and directivity at the access point antennas. For a hotspot scenario, the presented RA provided 29% coverage and 16% capacity gain concurrently.

A small-sized, low-profile, and planar integrated Bluetooth and ultrawideband (UWB) antenna is presented. The antenna exhibits a dual-band operation covering 2400-2484 MHz (Bluetooth) and 3100-10600 MHz (UWB) frequency bands. It is fed by a microstrip line and built on a FR-4 substrate with 42times46 mm² surface area. The impedance, radiation, phase linearity, and impulse response properties of the antenna are studied both theoretically and experimentally. The calculated and measured results agree well. The antenna shows acceptable gain flatness with stable omnidirectional radiation patterns across the integrated Bluetooth and UWB bands. The average group delay is approximately 0.2 ns across UWB frequencies. The impulse response is very good, with some level of ringing observed.

Microwave tomographic imaging technology using a bifocusing operator has been developed in order to detect the internal voids/objects inside concrete structures. The imaging system consists of several cylindrical or planar array antennas for transmitting and receiving signals, and a numerical focusing operator is applied to the external signals both in transmitting and in receiving fields. An imaging algorithm using a numerical focusing operator was developed, which allows the recovery of a two-dimensional object from its scattered field. Numerical simulation demonstrated that a subsurface image can be successfully reconstructed by using the proposed tomographic imaging technology. For experimental verification, a prototype planar antenna array was fabricated and tested on a concrete specimen.