A quad-polarization reconfigurable reflectarray (RA) antenna, which can work in horizontal polarization (HP), vertical polarization (VP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP) modes with simultaneous large-angle beam scanning capability, is designed and experimentally verified. Under the traditional view at the element level, at least 2-bit phases are required because a 90° phase shift step is needed for conversion from linear polarization (LP) to circular polarization (CP). In this work, we found that the extra phase shifts (90°/-90°) can be achieved by changing the global reference phase of the 0/1 coding arrangement in the spatially-fed architecture, while 1-bit phase resolution is used in the element level. As verification, a square patch with four slots loaded with two positive-intrinsic-negative (PIN) diodes is exploited as a RA element with 1-bit phase independent control of dual-linear polarization. Then, the RA aperture contains 16 × 16 elements, where 512 PIN diodes are integrated to control each state independently by a field programmable gate array, excited by a linearly-polarized horn is developed and fabricated. Besides, the superposition of the aperture field approach is used to optimize CP radiation performance, especially the axial ratio (AR). The measured results of the prototype demonstrate the simultaneous multi-polarization reconfigurable and the beam steering capability, where scanning beams are up to 60° in horizontal and vertical planes. The proposed low-lost design is believed to be a promising candidate for mobile communication and cognitive radar applications.

In this paper, an ultra-wideband radar scattering cross section (RCS) reduction metasurface is proposed combining with absorption and phase cancellation mechanisms. A two-lossy-layer absorber is designed first, which is responsible for low frequency RCS reduction from 1.3 to 13 GHz (163.6%). The equivalent circuit of the proposed absorber is extracted, proving that the wideband characteristic is due to the occurrence of multiple resonant points. To further improve the RCS reduction bandwidth, the absorber unit cells are arranged with three different heights. The proposed metasurface consists of 3 × 3 lattice and each lattice has 5 × 5 absorber unit cells. The reflection phase cancellation can be achieved owing to the wave path difference by introducing a certain height difference among sub-regions. Resultantly, high frequency RCS reduction from 13 to 40 GHz can be realized since the backward scattering can be cancelled effectively. Finally, an extraordinary ultra-wideband RCS reduction from 1.5 to 40 GHz (185.5%) can be acquired successfully. A prototype with thickness of 0.104 λ_L (the wavelength of the lowest working frequency) is fabricated and measured for demonstration. The measured results prove that the proposed design has numerous advantages including minimization, ultra-wideband RCS reduction, wide angle stability, and polarization insensitivity.

This paper reports a dual-polarized frequency-selective rasorber that has a transmission window with low insertion loss and two absorption bands at both sides of the passband. Equivalent circuit and simple design guidelines for rasorber design are further developed. First, notch structure with high Q is used to make the absorber realize the notch characteristic. Then, a frequency selective surface is utilized to replace the ground of the absorber. Note that the center frequency of the passband is consistent with the notch frequency. Therefore, the incident power is allowed to penetrate the proposed rasorber with a low insertion loss and transmissive behavior of the proposed rasorber is realized by this way. In addition, it is found that the main transmission band and lower absorption bands almost maintain stable performances in the angular range of 0° to 35° while the upper absorption bands get slightly worse as angular range increases for both TE and TM incidences. A rasorber prototype has been fabricated to experimentally validate the principle and design approach. The measurements agree reasonably with the simulated ones. Finally, a broadband and high-selectivity rasorber is achieved simultaneously.

This paper presents a radiation pattern reconfigurable Yagi-Uda antenna based on graphene operating at terahertz frequencies. The antenna can be reconfigured to change the main beam pattern into two or four different radiation directions. The proposed antenna consists of a driven dipole radiation conductor, parasitic strips and embedded graphene. The hybrid graphene-metal implementation enables the antenna to have dynamic surface conductivity, which can be tuned by changing the chemical potentials. Therefore, the main beam direction, the resonance frequency, and the front-to-back ratio of the proposed antenna can be controlled by tuning the chemical potentials of the graphene embedded in different positions. The proposed two-beam reconfigurable Yagi-Uda antenna can achieve excellent unidirectional symmetrical radiation pattern with the front-to-back ratio of 11.9 dB and the10-dB impedance bandwidth of 15%. The different radiation directivity of the two-beam reconfigurable antenna can be achieved by controlling the chemical potentials of the graphene embedded in the parasitic stubs. The achievable peak gain of the proposed two-beam reconfigurable antenna is about 7.8 dB. Furthermore, we propose a four-beam reconfigurable Yagi-Uda antenna, which has stable reflection-coefficient performance although four main beams in reconfigurable cases point to four totally different directions. The corresponding peak gain, front-to-back ratio, and 10-dB impedance bandwidth of the four-beam reconfigurable antenna are about 6.4 dB, 12 dB, and 10%, respectively. Therefore, this novel design method of reconfigurable antennas is extremely promising for beam-scanning in terahertz and mid-infrared plasmonic devices and systems.