Here, for the first time, we propose a simple strategy to realize an ultra-wideband metamaterial absorber by using room temperature ionic liquids (ILs) which are a new class of organic salts containing purely anions and cations. At first, the microwave loss characteristics of methylimidazolium ILs were investigated. The results reveal that these ILs have large ionic conductivities and dielectric loss factors which means high conductive loss and dielectric loss of microwaves can both be caused, and the IL with a shorter carbon chain on cation has potential to produce a higher absorption. When the IL [EMIm][N(CN)₂] is properly arranged into periodic cylinders supported by a 3D-printed dielectric bracket, impedance matching can be enhanced in a wide band, and a strong absorption of microwave above 90% can be achieved within the whole frequency range of 8.4–29.0 GHz, which was verified in simulations and experiments. In addition, the IL-based metamaterial absorber can work efficiently at arbitrary polarization angles and wide incident angles from 0° to 45°. Mechanism investigations show that the perfect absorption in ILs-based MMAs is mainly originated from the loss of dielectric polarization and induced ionic currents in ILs. Distinct from metamaterial absorbers based on water or other liquids, such IL-based metamaterial absorber can not only broaden the absorption bandwidth significantly, but also have potential application in a wider temperature range because of the exceedingly high thermal stabilities of ILs.

The design, analysis, implementation and measurement of an integrated V-band receiver front-end based on $0.15~\mu \text{m}$ GaAs pHEMT process are presented in this paper. The front-end chip uses the super-heterodyne topology which consists of a low noise amplifier, an image reject mixer, and a multiply-by-four ( $\times 4$ ) LO chain. In order to minimize the power consumed by LO chain, an active single-ended mixer is designed which requires extremely low LO power of −5 dBm. Meanwhile, the effect of signal coupling in the integrated chip is analyzed and solutions are proposed. By introducing appropriate filters into the circuit and optimizing the overall layout, the imbalance of in-phase and quadrature signals caused by unwanted coupling can be effectively mitigated, thus enhancing the image rejection of the chip. Probe and module tests are applied to the receiver front-end, and the measurement results reveal that the chip achieves −3 ± 0.7 dB conversion gain, 7 dB noise figure and more than 25 dB image rejection ratio in the RF frequency range of 52–56 GHz. Only one supply voltage of 3 V is required for the chip, and total power consumption is 312 mW. Moreover, with a continuously adjustable phase control of 360° and very broadband IF characteristics, the front-end chip is very suitable for passive millimeter-wave imaging application.

Recently, all-metal nanostructures for perfect absorption of light have attracted much attention due to their excellent plasmonic and photonic properties, but only narrow absorption bands were obtained in previous studies. In this paper, a new kind of metallic metasurface with wideband absorption of visible light is designed, which consists only of a gold nanotriangle array on the opaque metal substrate. By combining different resonant modes in the gradual-changed triangular nanostructure, the wide absorption waveband in visible region from 378 to 626 nm is achieved with more than 90% absorptivity. We demonstrate that the absorption property of the nanostructure can be controlled by tuning the cell size and incident angle. In addition, a metallic trapezoidal grating structure is proposed which can also realize wideband light absorption. This research provides a novel strategy in designing wideband metamaterial absorbers for visible light based on all-metal nanostructures which have great potential applications in light energy harvesting and photoelectric conversion.

Six-port technology has been widely used in microwave systems, such as interferometric passive imaging. In this paper, an integrated Ka-band (32–36 GHz) six-port chip based on the 0.15-μm GaAs technology is designed and fabricated to simplify the circuit structure and miniaturize the volume of the imaging system. The designed chip integrates two amplifiers, two phase shifters, and a six-port circuit as part of an analog complex correlator. In this integrated chip, the crosstalk between the two amplifiers cannot be ignored. This paper analyzes the influence of the isolation between two amplifiers on the correlation results to guide the six-port chip design. In addition, considering that the radiometer system receives a broadband noise signal, the phase shifter needs to ensure that the phase shift range of each frequency point is the same under the same control conditions. Therefore, the phase shifter is designed with a high-pass and low-pass structure. The measurement results show that the isolation between the two amplifiers is greater than 20 dB, and the measured phase shift range and phase shift range error of the designed chip are 220° and 10°, respectively, with the control voltage varying from 0 to 1.5 V, which meets the requirements of the system.

In this paper, the design, fabrication, and measurement of a compact broadband (4–8 GHz) analog complex correlator for a passive millimeter-wave imaging system are presented. To achieve high sensitivity and high integration of the imaging system, the wideband and miniaturization of the correlator are required. The correlator achieves wide bandwidth by using the add-and-square method, which is composed of a six-port circuit and a detection circuit. In order to realize the miniaturization of the correlator, the six-port circuit is realized on the chip base on the 0.15-μm gallium arsenide (GaAs) process. The influence of mismatch of the detection circuit that employs zero-bias Schottky diodes on the correlator is also analyzed to guide the design of the correlator. The measurement results of the designed chips and detector are consistent with the simulation result. Finally, a Sweep-frequency test is applied to the designed correlator, and the measurement results show that, within the frequency range of 4–8 GHz, the correlation amplitude fluctuation is less than 1.9 dB and the correlation efficiency is larger than 99%, which reveal that the correlator is suited for interferometric passive millimeter-wave imaging applications.