A reflectarray Antenna is designed to operate at X-band as a Local Multipoint Distribution Service (LMDS) base station antenna. It is a center-fed single layer reflectarray consisting of 23×27 elements. The unit cell of the reflectarray has linear polarization with more than 400° linear phase shift and its geometrical parameters have been optimized to achieve wide bandwidth and low cross polarization (XP) level for the reflectarray. An iterative design procedure, that is valid for obtaining any arbitrary pattern, has been implemented to achieve the specified radiation pattern over a desired frequency range. The method has been successfully applied to a LMDS base station antenna, characterized by a sectorial cosecant squared Beam in the frequency range of 9.3 GHz - 11.5 GHz. The simulation results are in a good agreement with the design requirements. The antenna has cosecant squared pattern over the bandwidth of 21%, XP level better than -30 dB, and SLL less than -20 dB in both elevation and azimuth planes. The total size of the 23×27-element array is 246×289 mm2 , and its 1dB gain bandwidth is wider than 19%. The proposed antenna performs significantly better than similar structures and has all the features and standards required for LMDS base station antenna

In this paper a new strategy is proposed to design a fixed-structure robust controller for a flexible Beam. Robust controller designed by the conventional H¥ loop shaping method is not appropriate for a Beam because of its high order and complicated form. Fixed-structure H¥ loop shaping control in conjunction with particle swarm optimization (PSO) algorithm is used to overcome this drawback. The performance and robust stability conditions of the H¥ loop shaping controller are formulated as the cost function in the optimization problem. PSO is adopted to optimize the parameters and cost function. The proposed control design and H¥ loop shaping method are successfully applied on the flexible Beam, and results of the two approaches are compared. Simulation results show the superiorities of the proposed controller in terms of having a lower order and simple structure; besides the Beam stability and robust performance are retained as well. Also in comparison to the solutions based on genetic algorithms, the use of PSO shows better efficiency in terms of computational time.

In recent years reflectarray antennas have received considerable attention due to their unique capabilities. However, due to their large size, analyzing the performance of these antennas using traditional full wave finite-difference and finite-element techniques requires considerable computational resources. In this paper, we present an efficient method to accurately analyze these class of antennas which considerably reduces the computational burden. First, the radiation properties of the unit cells of the antennas are obtained by applying periodic boundary conditions, which corresponds to an infinite array. Then, a phase-only algorithm is used to obtain required phase shift on the antenna surface. Next, different unit cells are used to achieve the required phase on the antenna surface. Lastly, to confirm the validity of our approach, each designed antenna is simulated by full wave method using method of moment and the full wave simulation results of co and cross polarization levels are compared with those obtained using the proposed formula. There is excellent agreement between the co- and cross polarization levels obtained by proposed approach and those obtained using full wave simulation.

A reflectarray optimized through a Generative Adversarial Network (GAN) is demonstrated. This design focuses on the impact of the top layer on the reflection phase and utilizes the correlation between phase distribution and the direction of the reflected Beam. Six programmable subcells are optimized to accommodate two incident angle waves simultaneously. Silicon substrate is exploited making the design compatible with integrated circuits. The far-field analysis indicates that for incident angles of 19.471° and 41.81°, as well as their vicinity, the reflectarray effectively redirects the incoming waves to reflect towards near-normal direction to its surface. This suggests a near independence of the deflection angle from the incident angle within a specific angular range, making the proposed reflectarray a planar THz Beam collimator. The proposed subcells achieve a reflection phase range of 342°. The return losses for the incident angles of 19.471° and 41.81° are 1.9 dB and 1.4 dB, respectively. For a finite reflectarray measuring 15λ×5λ, the pattern gain and fractional bandwidth are reported as 19.44 dB and 24.8% for the incident angle of 19.471°, and 19.17 dB and 29.9% for the incident angle of 41.81°. This denotes an excellent wideband behavior for the proposed single-layer pixelated reflectarray.

A new study for a boron neutron capture therapy irradiation facility, based on a 2. 5 MeV proton accelerator on a thick Li target as neutron converter, is presented here. The Beam shaping assembly (BSA) modeling has been performed with the use of the MCNP5 Monte Carlo code. The fast (i. e., > 10 keV) neutron component yielded by the 7Li(p, n)7Be reaction is slowed down through TiF3 neutron spectrum shifter, while to obtain a high-quality epithermal neutron Beam at the Beam port exit additional layers for thermal neutrons removal and shielding of gamma rays were used. Moreover, 60Ni and Ti6Al14V were selected to filter out and further remove the residual fast neutron component, while cadmium was chosen as thermal neutrons absorber, and bismuth was selected for gamma rays shielding. The therapeutic effectiveness of the proposed BSA was evaluated by performing a set of dose-equivalent distribution calculations in a standard Snyder head phantom. The simulation results show that the proposed BSA modeling meets all the recommended by IAEA criteria and provides one possible technical choice for an accelerator-based BNCT irradiation facility in a hospital environment.