The optimization of the sparse time-modulated optimized frequency offset frequency diverse array (S-TMOFO-FDA) with time-invariant spatial-focusing beampattern is presented. The minimum array with smallest number of element is obtained through iterative optimization. From numerical results, the S-TMOFO-FDA can provide above 70% reduction in the element amount while displaying superior side lobe performance than same aperture full uniform time-modulated logarithmically increasing frequency offset frequency diverse arrays (F-TMLFO-FDA). Furthermore, the scanning performance of the optimized array is also investigated. And the S-TMOFO-FDAs of different array length are optimized.

This study presents a Fabry-Perot resonator antenna (FPRA) with dual-band dual-orthogonal circular polarization. The whole FPRA consists of a linearly polarized microstrip patch antenna and a chiral metamaterial superstrate. The linearly polarized microstrip antenna serves as the feed system, while the chiral metamaterial (CMM) superstrate has the function of polarization transformation. The CMM also works as a partial reflective sheet to form an FPRA. Ray-tracing method in the circular base is introduced to describe the mechanism of this type of FPRA. Furthermore, the procedure of controlling the frequency ratio of two bands is discussed as well. An antenna prototype is fabricated to validate the simulated results. In the frequency band from 7.24 GHz to 7.36 GHz, the proposed FPRA produces right-handed circularly polarized wave. However, left-handed circularly polarized wave is achieved when the frequency ranges from7.96 GHz to 8.14 GHz. The realized gains reach 12.98 dBic at 7.28 GHz and 13.25 dBic at 8 GHz, respectively.

In this paper, a novel 2-dimensional (2-D) beam scanning antenna array is designed and fabricated in metallic 3D-printed technology with high integration and reduced fabrication complexity in millimeter wave. The array is composed of four leaky wave antennas and a butler matrix based on groove gap waveguide technology. One dimension of the beam scanning performance is realized by moving one row of pins along the groove based on gap waveguide concept. Meanwhile, the sidelobe levels of the radiation patterns are reduced to -20 dB by controlling the height and distance of pins along groove. The beam direction of the low sidelobe leaky wave antenna changes from 110° to 140°, while the frequency shift from 25 to 35 GHz. Another dimension of the beam scanning capability is realized with the butler matrix in groove gap waveguide. The design of this butler matrix is based on the coupling between multilayered groove gap waveguide. By this means, the low sidelobe leaky wave antennas are connected directly to the butler matrix with no more transition structures. The main beam direction of the antenna array shifts from -41° to 41°, when the exciting ports change in order. The simulated and measured port isolations are lower than -15 dB over the frequency band of 27 to 35 GHz, and they match well with each other.

The design of a multi-layer coding metamaterial absorber (MCMMA) is a multi-objective problem for maximizing the electromagnetic absorption bandwidth (EAB) and minimizing the total thickness (TT) by selecting the optimum variables such as the configuration parameters and the resistive film distribution of the metamaterial unit cell. Empirical methods and parameter sweeping have local search problems and converge slowly. In this letter, a multi-objective optimization (MOO) method is proposed for a low-profile and broadband MCMMA design. A topological encoding strategy is presented for the resistive film distribution where a 10×10-pixel array is divided into 5 parts with the real-valued representation. The non-dominated sorting genetic algorithm (NSGA-Ⅱ) is employed to globally search for the combination of the resistive film distribution, geometrical, and material parameters. With an EAB of 142.68%, the designed MCMMA realizes microwave absorption bandwidth covering 7.24-43.28 GHz with only 4.05 mm, which is further fabricated and measured. The experimental result agrees well with the simulation result. This letter provides a valuable method for designing a low-profile and broadband MCMMA, thereby paving the way for coding metamaterials.

A cooperation of the advanced time-modulated array (TMA) and the retrodirective (RD) technique is introduced to design a transmitting array for multiuser wireless power transmission (WPT) applications. The conventional rectangular-pulse-based TMA is lack of flexibility in dealing with harmonic beamforming limited by its frequency spectral properties. By preprocessing the rectangular pulses with the sinusoid-based control signal, harmonic beams are independently steerable. The proposed array is enabled with self-phasing capability by taking advantage of the RD technique. Besides, to avoid the unexploited radiation caused by unscannable fundamental beam and specular harmonic beams, the single sideband modulator is utilized to enable the transmitting array with high-efficiency beamforming capacity. Numerical results verify that the presented array performs well in various charging scenarios, which brings a highly potential insight for far-field WPT.

A pulse-Doppler (PD) radar has the advantage of strong anti-interference ability, and it is often used as a solution for maneuvering target tracking. In the application of target monitoring and tracking in PD radars, the interacting multiple model algorithm (IMM) has become the main and preferred choice due to its flexibility and high accuracy. However, the probability transfer matrix in classical IMM algorithms generally depends on constant prior knowledge, and if a PD radar is tracking a strong maneuvering target, it is inevitable to encounter some limitations, such as the possibility of target tracking trajectory deviation, and even a loss of the target. The Markov probability transfer matrix is proposed with an adaptive modification ability in real time to overcome the above problems in this paper. Additionally, for improving the speed of switching between the models, the fuzzy control system for secondary updating of model probability is adopted. By this means, the tracking accuracy of maneuvering targets is enhanced. Compared with the classical IMM algorithm, the corresponding simulation results for the PD radar indicate that the overall tracking accuracy of the proposed adaptive IMM algorithm is improved by 19.6%. In conclusion, the continuity and accuracy of the target trajectory can be effectively improved with the proposed adaptive IMM algorithm in PD radar cases.