Jorge Rodriguez-Cuevas

A Multilayer Circular Polarizer Based on Bisected Split-Ring Frequency Selective Surfaces

This letter presents a circular polarizer using a multilayer frequency selective surface based on split rings bisected by a metal strip. This geometry provides the advantages of both low cross-polarization level and low sensibility with respect to the incidence angle of the ring-based topology. To validate the proposed design, a four-layer prototype to operate in Ka-band has been designed, fabricated, and tested. Experimental results show that axial ratios lower than 3 dB are obtained for angles of incidence as high as 25 ° over the frequency range of 25.5-36.5 GHz.

An Active Ring Slot with RF MEMS Switchable Radial Stubs for Reconfigurable Frequency Selective Surface Applications

An active ring slot resonator loaded by switchable radial stubs is investigated. It is shown that this element can be used as the unit cell of a switchable reconflgurable frequency selective surface (RFSS). Equivalent circuit and full-wave mathematical models are obtained to evaluate the re∞ection characteristics of the RFSS based on this element. The possibility to obtain difierent resonant transmission frequencies is discussed. The mathematical model developed is used to design an X band RFSS capable of obtaining resonant frequencies at 9.65, 10.28, 10.83 and 12.05GHz. Commercially available RF MEMS switches are used to evaluate the efiect of the ofi-state capacitances over the response of the periodic structure. To validate the numerical simulation results, difierent active and passive diaphragms were designed, fabricated, and tested using the waveguide simulator. A good agreement between numerical and measured results was found.

Reconfigurable Reflectarrays Based on Optimized Spiraphase-Type Elements

Reconfigurable spiraphase-type reflectarrays based on ring slot resonators with switchable radial stubs are presented. The mathematical model of the infinite array was used to optimize the spiraphase-type element at 36.5 GHz. The optimization goals were to minimize the dissipative loss in the p-i-n diode switches and to reduce the cross-polarization radiation. The mathematical model of the finite array was then used to simulate the radiation characteristics of a reconfigurable reflectarray with 277 optimized elements for different scanning elevation angles θ_ο. The calculated aperture efficiencies were 0.42, 0.40, 0.36, 0.25, 0.16, and 0.12 for θ_ο equal to 0°, 20°, 30°, 40°, 45°, and 50°, respectively. For validation of the numerical simulations, three 277-element reflectarrays for fixed θ_ο of 0°, 20°, and 30° were designed. Metal strips and open circuits were used instead of the forward and reverse p-i-n diode states, respectively. These reflectarrays were then fabricated and tested, demonstrating aperture efficiencies equal to 0.41, 0.40, and 0.28 for θ_ο equal to 0°, 20°, and 30°, respectively. Measured characteristics agreed satisfactorily with theoretical predictions.

Active Dual-Band Frequency Selective Surfaces with Close Band Spacing Based on Switchable Ring Slots

This letter presents active dual-band frequency selective surfaces (AFSS) with close band spacing based on two switchable ring slots loaded by PIN diode switches. The close band response is achieved by splitting the outer ring slot, and then shifting upward its fundamental resonance beyond the resonance of the inner ring slot. The proposed AFSS can provide four states of operation including lower single-band, upper single-band, dual-band with close band spacing, and reflective mode. Experimental results based on the waveguide simulator show that a frequency ratio of 1.14, with insertion loss lower than 0.82 dB at resonant frequencies, is obtained in the X-band.

Wideband-reconfigurable reflectarrays based on rotating loaded split rings

In this paper, reflective periodic arrays with rotating spiraphase-type elements based on loaded split rings are analyzed. It is proven that these arrays can be reconfigured over a wide frequency band with high reflection elevation angles, low conversion losses, and low axial ratios. A full-wave mathematical model has been developed to calculate their reflection characteristics. This model has been used to design a Ka-band reflectarray. The analysis of the designed reflectarray shows that an incident circularly polarized wave can be redirected at reflection elevation angles as high as 40° with conversion losses less than 1.8 dB and axial ratios less than 2 dB over the frequency band from 26.6 to 46.3 GHz. Additionally, the rotation of the reflectarray elements using minimotors is analyzed and discussed. In order to study the velocity properties of the electromechanical actuation, minimotor-driven antenna elements in the X-band have been designed, fabricated, and tested.

Spiraphase-Type Reflectarray for Large Reflection Elevation Angles

This paper presents a spiraphase-type reflectarray based on reactively loaded ring slot resonators. The infinite array approach was used to optimize the unit cell geometry to obtain high aperture efficiencies and low cross-polarization levels at large reflection elevation angles θ_o. The results of the optimization were used to design four 367-element reflectarrays for θ_o of 0°, 20°, 40°, and 60° operating at 36.5 GHz. The designed reflectarrays were then fabricated and tested. The experimental investigation of the fabricated reflectarrays revealed that aperture efficiencies of 0.60, 0.51, 0.42, and 0.21 along with cross-polarization levels of -25.8, -24.0, -17.8, and -10.9 dB were obtained for the reflectarrays with reflection elevation angles of 0°, 20°, 40°, and 60°, respectively, at 36.5 GHz. Additionally, it was experimentally demonstrated that for certain planes of scanning the cross-polarization level can be reduced to -19 dB even for reflection elevation angles θ_o as high as 60°.

Analysis of a Spiraphase-Type Reflectarray: Comparison Between Finite and Infinite Models

Abstract A full-wave mathematical model was developed to analyze the radiation characteristics of a spiraphase-type finite reflectarray based on ring slot resonators with stubs controlled by p-i-n diodes. The scanning characteristics of the finite 289-element reflectarray with optimized elements were calculated. According to the simulated characteristics, the optimized reflectarray provides electronic scanning in the XOZ-plane for elevation angles up to 30° with a total aperture efficiency better than 0.22. The characteristics obtained with the developed mathematical model were compared with the simulated characteristics obtained with the mathematical model of the infinite array.

Spiraphase-type leaky-wave structure

Abstract A leaky-wave structure (LWS) based on two stacked spiraphase-type reflectarrays (RAs) is analysed in this paper. Each RA contains capacitively loaded ring slot elements arranged at the nodes of a square periodic grid. The proposed LWS performs frequency scanning of a conical beam by changing the cone aperture angle 2θ0. Furthermore, the reconfiguration of the radiation pattern can be achieved by rotating the RA elements. Four Ka-band LWSs with different angular positions of the capacitive loads at the top RA were designed, fabricated and tested to demonstrate the pattern reconfiguration capability. A full-wave mathematical model was used to optimize the reflectarray elements and a simplified mathematical model was developed to predict the radiation characteristics of the whole structure. It was experimentally proven that frequency sweep from 36.37 to 39.9 GHz leads to the change of the angle θ0 from 0° to 38°. The increment of θ0 from 0° to 23° at 36.4 GHz was observed, when the reactive loads of the ring-slot elements at the top RA were rotated on the angle 18°. Good agreement between theoretical predictions and measurements was observed.

Switchable ring slot frequency selective surfaces with low-disruptive bias circuits

Active frequency selective surfaces based on PIN diode switchable ring slots with low-disruptive bias circuits are investigated. An active diaphragm was measured through the waveguide simulator in X-band. The proposed surface can provide two states of operation and can be used for the effective control of the electromagnetic wave transmission.

Frequency-scanning arrays based on spiraphase-type elements

Spiraphase-type frequency-scanning arrays based on loaded split rings are presented in this paper. The wide operating bandwidth along with the low conversion loss of the spiraphase-type element ensure an array performance with large beam scanning angle over a wide frequency-scanning bandwidth. Simulated results show conversion coefficients better than -1 dB and axial ratios lower than 1.2 dB in the frequency band from 27.1 to 44.2 GHz. Reflection elevation angles of 36.1° and 21.2° can be observed for the lower and higher frequencies, respectively. An array prototype at Ka band was designed, fabricated and tested to validate the computed results.