Tuning patch-form FSS

This paper presents a multi-functional frequency selective surface (FSS)based on varactor diode and PIN diode loading. It can be realized that when the varactor diode is not loaded with voltage and the PIN is in the on state, the frequency selective surface(FSS) exhibits strong transmittance at 4 GHz, and when the PIN is in the off state, the frequency selective surface(FSS) exhibits strong reflectivity at 4 GHz. In addition, when the PIN is turned on, stable transmission of electromagnetic waves in a wide frequency range from 1.37GHZ-5.66GHZ can be achieved by changing the capacitance of the loaded varactor diode.

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.

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.

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 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 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.

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 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.

In this paper, a beam switching antenna with a novel active frequency selective surface (AFSS) is proposed at 5.2 GHz. The antenna is composed of an omnidirectional patch antenna and AFSS. The AFSS is made up of 6 columns, each with 2 unit cells, which are placed vertically around a patch antenna to form a hexagonal wall. To steer beam of the antenna, high frequency pin diodes are precisely inserted into the AFSS to reconfigure electromagnetic (EM) response of surfaces. The reflection and transmission characteristics of the proposed AFSS unit cell are investigated. The simulation results show that the transmission and reflection bands of AFSS unit cell can be changed by setting diodes on and off. This new AFSS can be used to implement a sweeping radiation pattern at all azimuth angles. The antenna can sweep the entire azimuth plane in six steps and effectively operate over a bandwidth of more than 500 MHz.

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 novel active frequency selective surface (AFSS) exhibiting a multifunctional characteristic, switching and frequency tuning, is present in this paper. The proposed structure is made up of periodic metallic patterns printed on the opposite sides of a dielectric substrate. Two different active components (varactors and PIN diodes) are mounted on the top and bottom layers, respectively. The switching characteristics between transmission and absorption modes can be obtained by controlling the biasing condition (OFF/ON state) of the PIN diodes on the bottom layer, where both modes having frequency tuning capability by regulating the voltage of varactor diodes on the top layer. Besides, full-wave simulation has been investigated to study the characteristic of the proposed designed. The structure has been fabricated to verify with the simulation results. In transmission mode, the proposed AFSS realizes tunable bandpass responses from 3.70 to 4.27 GHz with 1.96-4.30 dB insertion loss. In absorption mode, the absorption frequency can be tuned from 4.28 to 5.12 GHz with 78.77-90.78% absorptivity.

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.

Conventional active frequency selective surfaces (AFSS) are designed with a DC biasing circuit to apply DC biasing voltage across active components. An innovative method to design AFSS is proposed in this paper to use an induced voltage across both ends of the surface loading components as the biasing signal to control FSS's transmission properties. The result from simulation proved that, a pass band exists on the AFSS at 3.5GHz when it is exposed to an electric field at a smaller intensity; at the electric field intensity (EFI) over 70 V/m, the insertion loss of the electromagnetic wave (EMW) increases at 3.5 GHz; in the case that the incident microwave's field intensity reaches 5000 V/m, the insertion loss is over 20 dB. This interesting phenomenon make the new AFSS has the ability of HPM protection, which mean that a pass band exists when EFI is weak enough, along with increasing incident field intensity, the pass-band finally turns into a stop-band because of the break though of the diodes.

A novel antenna with both frequency and pattern reconfigurability is presented. The reconfigurability is achieved by integrating an active frequency selective surface (AFSS) with feed antenna. The smart FSS comprises a printed slot array loaded by varactors. A novel dc biasing arrangement is proposed to feed the slots vertically so that the unwanted effects caused by bias lines are minimized. A monopole antenna is designed to illuminate the AFSS. The resulting structure can operate in a frequency tuning range of 30%. By reconfiguring the different sections of active FSS cylinder into a transparent or reflector mode, the omnidirectional pattern of the source antenna can be converted to a directive beam. As an illustration, half of the AFSS cylinder is successively biased, enabling the beam switching to cover the entire horizontal plane over a range of frequencies. An antenna prototype was fabricated and measured. Experimental results demonstrate the capability of providing useful gain levels and good impedance matching from 1.7 to 2.3 GHz. The antenna offers a low-cost, low-power solution for wireless systems that require frequency and beam reconfigurable antennas. The proposed design consumes about 1000 times less dc power than the equivalent narrowband beam-switching antenna design using p-i-n diode-loaded AFSS.

In this letter, a broadband polarization-independent tunable absorber is proposed based on active frequency selective surface (AFSS). The AFSS consists of periodic patterns of four-patch array with four p-i-n diodes loaded among them, and a simple bias network is designed behind the ground plane through metalized via holes, which can effectively reduce the influence on the absorbing performance. By changing the bias voltage applied on the p-i-n diodes, the reflectivity of our absorber can be dynamically adjusted from near-unity reflection to less than -10 dB absorptivity under normal incidence over a wide frequency band ranging from 8.5 to 18.2 GHz. Due to the symmetrical structure of the AFSS, our absorber still has polarization insensitivity. We fabricated this AFSS absorber sample, and its measured results agree well with the simulated ones.