Active Artificial Magnetic Conductor Research Articles

A wideband frequency reconfigurable antenna with improved gain

AbstractA wideband frequency reconfigurable antenna based on active artificial magnetic conductor (AAMC) surface is proposed with improved gain. The AAMC element consists of a composite polygon‐rectangle‐ring with five patches and a cross‐strip inside. A reverse‐bias varactor is inserted between the ring and ground plane to make the in‐phase reflection frequency bands adjustable. A dipole is placed above the AAMC surface which is composed of 5 × 5 unit cells. The measured results show that the reconfigurable frequency ranges from 1.64 to 4.16 GHz while maintaining the radiation patterns stable. Moreover, the peak gain reaches 10.65 dBi at 3.5 GHz.

Design and analysis of varactor‐loaded bi‐state switchable active artificial magnetic conductor reflector for wearable antenna integration

A low profile, bi-state switchable, and flexible active AMC (AAMC) reflector metasurface is presented for wearable antenna integration to improve radiation performance with low specific absorption rate (SAR). The unit cell structure contains concentric rectangular rings with 2-varactor diodes. The unit cell is designed on a flexible PDMS substrate with dimensions 20 × 20 × 1 mm3. Controlled DC bias is applied to both varactor diodes. In state-1, that is, on state, the AMC surface resonates at 3.5, 5.8, and 8.1 GHz frequency, and in state-2, that is, off state, it resonates at 3.5, 5.8, and 7.5 GHz frequencies with zero degrees reflection phase. The proposed AAMC reflector performance is analyzed by integrating a 3 × 3 AAMC surface with the quad-band wearable textile antenna designed to resonate at 3.5, 5.8, 7.5, and 8.1 GHz frequencies. By controlling operating voltages of the integrated AAMC, the antenna radiation performance is improved in bi-state by adapting to reflection pattern switching. In On-state, the peak gain (dBi), FBR (dB) of integrated antenna improved to 7.36, 9.05, 8.9, 7.53 and 9.25, 11.9, 19.7, 16.70; In Off-state, the values are improved to 7.8, 8.98, 8.33, 7.92 and 12.24, 11.37, 14.6, 16.85, respectively. The proposed AAMC with antenna integration is fabricated, and its measured results are well satisfying. The low SAR values are obtained under a 2 mm gap (<0.924 W/kg) and direct contact (<1.5 W/kg) as well. The enhanced radiation performance characteristics with the bi-state switchable feature make it preferable for wearable antenna integration to meet current WBAN demands.

Beam Steering Using Active Artificial Magnetic Conductors: A 10-Degree Step Controlled Steering

An Active Artificial Magnetic Conductor (AAMC) is presented to steer the radiation pattern of a printed dipole working at 2 GHz. The elements that generates the phase shift are a set of Varactor Diodes, which are characterized using its spice model in order to obtain a phase shift - capacitance mapping. Overall beam steering of +/40° with a step size of 10° is achieved. A circuit model that describes any multilayer substrate AAMC unit cell, which uses fist form of Foster's theorem along with transmission line theory, is proposed. Our work is suitable to be used as low profile antenna; for example, street furniture antennas, which are located on the facades of houses or buildings, so that they can be visually mixed up with signs or advertisements. Simulations have been validated using a prototype consisting of an array of 22 × 14 AAMC elements; the overall structure measures 1.9λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 1.21λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . This reflector will generate a phase gradient in its columns, which will modify the reflection angle of an incident electromagnetic wave in the H-Plane. Beam switching control has been achieved using suitably amplified LPF PWM signals generated by two Arduino modules. A printed dipole with a Fractional Bandwidth of 17% is designed and manufactured to illuminate the structure at a distance λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /4 above the surface. Far-field radiation patterns and reflection coefficients have been measured in an anechoic chamber using a spherical system. These compare favorably with simulations performed using the Time Domain solver in CST Microwave Studio.

Design of a Low-Profile, Frequency- Reconfigurable, and High Gain Antenna Using a Varactor-Loaded AMC Ground

In this paper, a novel planar active artificial magnetic conductor (AAMC) frequency-reconfigurable antenna printed on an FR4 substrate is proposed. Its AAMC metal pattern in a unit cell consists of a compound-five-ring nesting (CFRN) structure. It is loaded with only one varactor diode connected to the ground plane by a metallic via. In comparison to the conventional single-circle-ring AMC, the dimension of the CFRN-AMC has been reduced by about 44% along with a lower reflection loss. The frequency-reconfigurable antenna is constructed by placing a triangle-shaped dipole antenna operating at 1.8 GHz over the proposed active CFRN-AMC ground plane consisted with 5×5 periodic unit cells. The prototype of the CFRN-AMC-backed antenna was fabricated and measured. The measured results agree well with the simulated data. It is found that by tuning the capacitance applied on the CFRN-AMC from 2.2 to 0.5 pF, the frequency band of the AMC-based antenna has been varied in the range of 1.51 through 2.12 GHz along with the highest radiation gain of 5.37 dBi at 1.74 GHz. This gain is about 3.16 dB higher than that of the antenna without using the AMC. In addition, the presented CFRN-AMC-based antenna remains a very low profile, since the separation distance between the antenna and the AMC plane is only 2 mm or 0.012λ, where the λ denotes the wavelength at 1.8 GHz in free space.

Polarization-Reconfigurable and Frequency-Tunable Dipole Antenna Using Active AMC Structures

A polarization-reconfigurable and frequency-tunable mechanism based on an active artificial magnetic conductor (AMC) structure is proposed. The active AMC unit cell consists of a four-corner-cut inner patch and four triangles loaded with four varactors, and it can realize polarization-reconfigurable and frequency-tunable reflection characteristics by adjusting the capacitance of the varactors. By employing it as a ground plane of a pair of linearly-polarized dipole antennas, a multi-functional antenna can be well designed with polarization reconfigurability and frequency-tuning capability. By controlling the DC bias of the varactors accordingly, the three polarization states of right-/left-handed circular polarization (R/LHCP) and linear polarization (LP) can be switched, respectively, while the operating frequency of each polarization can be flexibly tuned. The measured tuning frequency ratio for the LP state (|S 11 | <; -10dB) can reach 1.56:1, while the ratio for either the LHCP or RHCP state (axial ratio<; 3dB) is about 1.28:1. Moreover, a large bandwidth for each polarization state can be obtained, where the bandwidths are up to 17.1% and 8.7%, respectively, for the LP and CP states. Besides, it is more flexible for the CP states since the bandwidth can be adjusted. For a demonstration, one prototype of the proposed antenna is fabricated and measured. The agreement between the theoretical and measured results indicates good performances of the proposed antenna.

Dual‐polarised and ultra‐thin broadband AAMCs for both P and L bands applications

Conventional artificial magnetic conductor (AMC) suffers from the thick profile and narrow bandwidth in the low-frequency band. Incorporating varactors into a passive AMC can adjust the working frequency dynamically and broaden the operating band range. This study investigates the different incorporation methods of varactors into AMC using the equivalent circuit analysis method. By establishing the equivalent circuit of the whole configuration, the frequency-domain working characteristics of passive AMC and active AMC (AAMC) are theoretically analysed. It reveals that a parallel incorporation of varactors allows lowering the frequency and increase the working bandwidth more efficiently when compared with a series integration. Following this principle, two dual-polarised AAMCs are proposed. Simulations and measurements indicate that both AAMCs elements have an ultra-low profile (0.0035 λ ) and compact size (0.04 λ ). Moreover, the in-phase-reflection frequency bands of both AAMCs cover P and L bands, proving the effectiveness of the proposed design method.

An Active High-Impedance Surface for Low-Profile Tunable and Steerable Antennas

In this letter, an approach for designing a tunable and steerable antenna is presented. The antenna model is based on a wideband bow-tie radiating element mounted above an active Artificial Magnetic Conductor (AMC). The AMC geometry consists of a Frequency Selective Surface (FSS) printed on a thin grounded dielectric slab in which some chip-set varactor diodes are placed between the metallic elements and the backing plane through vias. The resulting antenna can be tuned over the S-Band by simply changing all varactor capacitances through an appropriate biasing voltage. Moreover, this structure can operate a beam scanning over each working frequency by applying an appropriate biasing voltage to the active elements of the AMC surface in accordance to leaky radiation principles. The low profile active antenna is characterized by an overall thickness of 5.32 mm, which corresponds to approximately lambda/24 at the centre of the operating band.