A novel technique for acquiring high aperture efficiency in dual reflectarray antennas (DRA) is presented. This technique is performed by using a shaped Beam sub-reflectarray which gives optimum illumination on the main reflectarray aperture. Applying this technique resolves the inherent deficiency of reflectarrays; which is the impossibility of controlling elements amplitude. In this regard, it has been shown that using this feature, the aperture efficiency of a classic dual reflectarray antenna can be enhanced significantly by optimally shaping the sub-reflectarray radiation pattern. Theoretical analysis demonstrates an improvement of about 12% in antenna aperture efficiency comparing with a conventional dual reflectarray antenna.

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

n this paper, a X-band Beam steerable non-uniform reflectarray antenna is proposed. The-10dB power Beamwidth and side lobe level of the proposed antenna are respectively 17° and-18dB which show significant improvement proportional to previous works. The Beam steering is carried out with a small movement of a large element, i. e. the ground plane of the antenna. It is shown that the ground plane movement has negligible effect on the reflectarray phase characteristic, as a consequence of the proportionality between reflectarray phase distribution and element phase variation. This ensures that the distortion of far-field pattern is avoided. About ± 10° tilt of antenna Beam from the broadside is achieved with ± 0. 05λ ground movement. In the proposed structure Beam steering capability is provided using passive elements which eliminates the problems of using active circuits such as bias difficulties, component losses and low power handling. After describing design procedure completely, the proposed antenna is simulated with an electromagnetic full-wave software and the results are validated.

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.

A popular method for creating required phase shifts for patches in a microstrip reflectarray uses open ended stubs attached to the patches. Uniform stubs are narrowband and hence limit the bandwidth of the array. In this paper, two novel methods for designing broadband reactive phase shifters are proposed based on the method of least squares. A structure consisting of transmission line sections, open-ended stubs, and resistors is considered for the phase shifter. Another one consists of transmission lines and open-ended. A least square error function is constructed for the required phase shift and the characteristic impedances, electrical lengths of transmission lines and resistances are obtained by its minimization. Then, the circuit is realized by microstrip lines to be attached to the microstrip patch. It is shown that the novel phase shifters create the required phase shifts in a broader bandwidth than those of uniform stub phase shifters. The frequency response of proposed microstrip line phase shifters are validated by the results obtained using AWR's Microwave Office software.

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.

In this paper, a high-gain low-cost reflectarray antenna is proposed. This antenna does not need radome. The exploited dielectric is the FR4 epoxy which is both low-cost and mechanically robust. Reflector of the proposed antenna consists of a layer of FR4, suspended above the ground plane by spacer, with its re-radiating elements on its interior side. Superiority of the suggested antenna over the similar previously reported design is shown. For the proposed design, sensitivity of the phase-delay characteristic, number of elements and gain to the FR4 thickness is studied. In addition, effect of design tolerance for the dielectric and the air gap on the antenna gain is investigated.

This paper proposes a new method for the design of a broadband dual-Beam reflectarray antenna with a single feed. This method is based on the producing a null in the antenna radiation pattern and the appearance of two Beams. The reflection phase distribution on the aperture of the antenna has been studied to achieve this null. A single layer subwavelength element with multi-resonances is used as the phase shifting unit cell due to its wide linear phase range. A comprehensive theoretical analysis and full-wave simulation are accomplished and the results are in good agreement. Two dual Beam reflectarray antennas operating at X band are designed using the proposed method and the geometrical method. The improvement in the gain bandwidth and the Beam squint of the designed reflectarray using our proposed method is observed compared to the other one. The simulation results show the improvement of 1. 1% in 1-dB gain bandwidth and in the Beam squint for the proposed design method compared with the other one.

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.