Multifunctional active reconfigurable frequency selective surface

In this communication, a novel filtering antenna is proposed by utilizing active frequency selective surface (FSS), which can simultaneously achieve filtering and beam steering function. The FSS unit is composed of a metallic rectangular ring and a patch, with a pair of microwave varactor diodes inserted in between along incident electric field polarization direction. Transmission phase of the emitted wave can be tuned by changing the bias voltage applied to the varactor diodes. Through different configurations of the bias voltages, we can obtain the gradient phase distribution of the emitted wave along E- and H-plane. This active FSS is then fabricated and utilized as a radome above a conventional horn antenna to demonstrate its ability of steering the beam radiated from the horn. The experimental results agree well with the simulated ones, which show that the horn antenna with the active FSS can realize beam steering in both E- and H-plane in a range of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\pm 30^{\circ}$</tex></formula> at 5.3 GHz with a bandwidth of 180 MHz.

In this paper, an octahedron electronically beam-scanning antenna using a novel slot active frequency selective surface (AFSS) is presented. The antenna consists of eight panels of octagonal slot AFSS array and an omnidirectional feed antenna located in the center. The beam-scanning of the antenna is obtained by switching the states of the PIN diodes to reconfigure the AFSS as EM transparent or reflective to the incident electromagnetic waves. By controlling the DC bias voltages to PIN diodes which are grouped by columns, the directive beam of the antenna can be switched to cover the entire azimuth plane. A prototype is fabricated and measured. Simulation and measurement results of the antenna are presented to verify the design concept. It is shown that the designed octahedron electronically beam-scanning antenna can cover a full 360°horizontal angular range. The presented design shows obvious advantages in terms of low power consumption, low cost and easy fabrication.

The application of a novel biasing technique to tune frequency selective surfaces (FSS) made of patch elements is described. The methodology follows a recently developed technique where the biasing circuit of an active FSS is etched at the rear of a double sided substrate. On this occasion, the structure consists of dipole patches on one side of the thin polyester substrate and the biasing circuit at the rear, electromagnetically hidden by the patches. Varactor diodes are employed to modify the capacitance between the patches. The novel active FSS structure is able to tune a bandstop filter response over a wide frequency range, which could suit applications such as the time dependent modification of the EM architecture of buildings.

A tunable polarization-insensitive absorber based on an active frequency-selective surface is proposed for electromagnetic (EM) wave absorption in the L and S bands. The frequency-selective surface consists of a diamond-shaped loop that is interconnected by varactor diodes. The proposed design is significant because of its inclusion of wideband tuning and its ability to easily change from single-band tunable absorption to dual-band absorption. The simulation results demonstrate that the absorption response (> 80%) can vary from 1.62 GHz to 3.66 GHz under the reverse bias voltage, thus creating a tunable range of 125.9%. The absorption region (> 90%) spans from 1.86 GHz to 3.31 GHz and generates a 78% tunable range. The single-band tunable absorber is characterised by an equivalent circuit model to obtain the circuit parameters and predict the absorption frequency. Furthermore, a dual-band absorbing structure is obtained by adding a metasurface directly to the single-layer structure, which can easily be changed from single-band absorption to dual-band absorption by separately controlling the bias voltages of the upper and lower unit cells. The two fabricated prototypes were measured using free-space technology, and the experimental results closely mirror the simulation results. Results show that the proposed structure achieves the dynamic control of EM wave absorption.

A new type of active frequency selective surface (AFSS) is proposed to realise a voltage controlled bi-state (transparent and reflecting) response at the specified frequencies. The bi-state switching is achieved by combining a passive array of interleaved spiral slots in conducting screens and active dipole arrays with integrated pin diodes at the opposite sides of a thin dielectric substrate. Simulation results show that such active surfaces have high isolation between the transparency and reflection states, while retaining the merits of substantially sub-wavelength response of the unit cell and large fractional bandwidths (FBWs) inherent to the original passive interwoven spiral arrays. Potential applications include reconfigurable and controllable electromagnetic architecture of buildings.

A novel symmetric anchor-shaped active frequency selective surface (AFSS) with a wide tuning frequency range is proposed. Varactor diodes are used as the active tuning components at the center of each AFSS unit. The equivalent circuit model of the AFSS unit is extracted. SPICE-based circuit simulation and full-wave simulation are compared to predict the resonant frequency. A wide tunable frequency range from 1.76 to 2.45 GHz with a relative bandwidth of 33% is achieved. A prototype of AFSS is fabricated and tested. The measurement result is consistent with the simulation. The design has low power consumption and is potentially used for selectively shielding or reusing of GSM, TD-SCDMA, or Wi-Fi spectrums.

A dual-function switchable and frequency tunable active frequency selective surface (AFSS) is proposed in this article. The proposed AFSS consists of a dielectric substrate and metal patches on the top and bottom surfaces of the substrate, while varactor diodes and PIN diodes are soldered on the top and bottom layers, respectively. A simple bias network is designed to facilitate the function adjustment of the AFSS. By controlling the OFF and ON states of the PIN diode, the AFSS can switch between filtering and wave absorbing functions. Furthermore, by adjusting the bias voltage of the top varactor diode, the AFSS can achieve continuous frequency tunability. Simulation and experimental results confirm the dual-function switchable and frequency tunable performance of the proposed AFSS.

In order to analyze the effects of changing the value of PIN diodes and variodes on the resonant frequency and the depth of the resonance, we firstly use electromagnetic simulation solver to simulate frequency selective surface (FSS) loaded with PIN diodes and variodes respectively in this paper. Then, the equivalent circuit method (ECM) is used to validate correctness and prove rule of influence. Finally, active FSS loaded with DC bias line is also analyzed as a whole, and the influences of the DC bias line on the active FSS's electromagnetic property are illustrated.

A reconfigurable active frequency selective surface (AFSS) with ultra-wideband (UWB) characteristics is presented in this article. The proposed AFSS is a periodic array structure which consists of three metal layers and two dielectric layers. PIN diodes are arranged on the top and bottom metal layers which can rebuild the function of AFSS. The transmission bandwidth of the OFF-state AFSS is 8-12.5 GHz with a fractional bandwidth of 44%, and the transmission coefficient of the ON-state AFSS is lower than -10 dB from 2 to 18 GHz. Additionally, the AFSS has dual polarization characteristics, and it is angular stable and polarization-insensitive for two polarizations. The simulation results show the proposed AFSS is a valuable candidate for radome applications.

A new conception for a reconfigurable antenna based on an active Frequency Selective Surface (FSS) is presented. The antenna system consists of a 3D cylindrical and a dipole antenna. This design can be achieved reconfigurable beams along the entire azimuth plane. The FSS unit-cell is designed in order to control the transmission characteristics of EM waves by controlling switching devices. Thus, to explain the design concept, the reflection and transmission coefficients of the 3D FSS are provided. Reconfigurable feature of the antenna is studied and demonstrated at 1.8 GHz. This smart antenna can be for wireless communication applications.

A polarization-selective and reconfigurable Fresnel zone plate consisting of frequency selective surfaces (FSS) loaded with varactor diodes is devised for compact vehicular wireless communication devices. The unit cell constituting the impedance zone exhibits rapid impedance transitions from 0 ohm (electrically-opaque) to 377 ohm (electrically-transparent). An I-shape configuration is employed for the resonant unit cell structure, featuring high compatibility with DC bias voltage network. In addition, double-sided FSS is employed on the top and bottom faces for polarization-selective beamforming. The FSS comprise of a dielectric with near zero thickness ( λ /250 of 2.40 GHz) resulting in intentionally high mutual coupling between the layers. The devised unit cell is designed using an equivalent circuit model analysis and optimized using finite element solver, achieving over 30 dB impedance switching. The proposed unit cell is experimentally confirmed in both vertical and horizontal polarizations. By configuring the DC voltage bias lines, the unit cells of the FSS are transformed into electrically-driven impedance zones formulating alternating and repetitive gratings. The width and the interval of the grating manipulate the constructive and destructive interference resulting in beam scanning range of 30° in both vertical and horizontal polarizations. The proposed approach can provide concise and compact beamforming solutions for future vehicular communications.

In this paper a new means for accurate characterisation of active varactor loaded frequency selective surfaces (FSS) is demonstrated. The varactor loaded active doubly periodic wire FSS acts as a variable impedance surface, in which its surface reflectivity and transmitivity can be modified by adjusting by d.c. bias voltage control. The properties of the active FSS are characterised using a specially designed parallel plate waveguide (PPW) simulator. This permits normal incidence excitation of the FSS under test over the frequency range of 2.6 GHz to 3.95 GHz. In addition we present a novel hybrid de-embedding technique to remove the influence the PPW simulator and reveal the true property of active FSS. Typical results are presented and validated against a new 3D EM modelling led de-embedding method for the composite FSS and PPW structure.

The miniaturized frequency selective surface (FSS) obtained by connecting a number of limbs with two flexible adjustable transmission zeros is proposed in this paper. The proposed FSS has two transmission zeros on both sides of the passband. The effects of the geometrical parameters on the bandwidth of transmission zeros and pole are analyzed. Adjusting the numbers of the limbs in the FSS can make a great difference to the ratio of the frequencies of the two working transmission zeros, and the coupling between the adjacent FSS unit cells is used to adjust the ratio of the frequencies of the two working transmission zeros slightly. The simulated results show that the ratio of the frequencies of the two working transmission zeros has wide adjustable range. The effects of the ways to connect the limbs on the ratio of the frequencies of the two working transmission zeros are analyzed. The prototype of the FSS with two limbs is fabricated and tested to verify the feasibility of the proposed method. The measured results show that the FSS designed by the proposed method has good polarization and angel stabilities, and this proves the proposed way is effective. This FSS is a good candidate to isolate the communication systems with two working bands.

in this paper, a novel Frequency Selective Surface (FSS) with polarization staggered bands is proposed. The beams in orthogonal polarization of different frequency bands are divided into a group and transmitted the FSS. The rest are divided into another group and are reflected by the FSS. The FSS with polarization staggered bands is good at separation the bands with narrow transition zone, which realizes transmission and reflection of the incident waves in four different physical mechanisms. What is more, a new frequency separation scheme in quasi-optical feed system is discussed. The FSS with polarization staggered bands, which separate two bands near 90GHz and 108GHz, is fabricated and tested. The reflection coefficient of TM polarization is about 1dB, and the transmission and reflection coefficients in the other band or polarization are less than 0.6dB.

Resonant frequency tunable range is an important character for active frequency selective surfaces (AFSSs), especially when building electronically steerable antennas based on AFSS. In this communication, a broadband tunable bandpass AFSS is presented. The tunable ability is achieved by the varactors mounted on the surface. The proposed design has zigzag resonant current flows through multiple unit cells. Thus, the magnetic field coupling between unit cells is enhanced and the resonant frequency tunable range is extended. The measured resonant frequency tunable range is from 935 MHz to 2.405 GHz. Another advantage of this design is that no additional bias grid is required. Furthermore, this design has stable response under different angles of incidence because it has subwavelength dimensions.