A novel frequency selective surface (FSS)‐backed subwavelength reflectarray element is proposed in this article. The element consists of an inner square ring and an outer Minkowski ring. The proposed fractal element could achieve smaller interelement spacing and better reflection phase performance due to its space‐filling property and self‐similar geometry. An 11 × 11‐element reflectarray with reduced element spacing of 0.38λ0(λ0‐the free space wavelength at 5.8 GHz) is designed. A FSS is used to replace the perfect electric conductor (PEC) ground. In the working frequency, the electromagnetic waves are reflected and result in a smoother and more linear reflection phase curve. Moreover, the radar cross section (RCS) of the reflectarray antenna is also reduced by using the FSS ground. A prototype antenna is then fabricated and measured. The measured results show that the antenna has a peak gain of 18.6 dBi, and an aperture efficiency of about 31.9%. A measured 1‐dB gain bandwidth of 14.3% is obtained. Meanwhile, the measured cross‐polarization and side‐lobe levels are −20 dB and −13 dB, respectively. The simulated results demonstrate that the monostatic RCS can be significantly reduced with a fractional bandwidth of 32.76% and 44.83% for the lower and upper bands with reduced levels of 5 dB, respectively.
A two-element low-profile closely coupled dual-band MIMO antenna is demonstrated for WiMAX applications. Based on the principle of metasurface (MTS) decoupling, a double-layer MTS consisting of pairs of elliptic patches with two different sizes is proposed. The MTS is loaded above a coupled dual-band MIMO antenna, and the mutual coupling in the lower and upper band is reduced by the larger and smaller elliptic patches, respectively. The edge-to-edge distance of antenna elements is only 0.01λ0 (λ0 is the free-space wavelength at 2.6 GHz). The measured results show that the working bandwidths of the MIMO antenna are 2.5–2.69 and 3.4–3.69 GHz. The −10 dB impedance bandwidths in two bands are 8.83% (2.49–2.72 GHz) and 8.50% (3.38–3.68 GHz), and the isolation between antenna elements is enhanced by 13.5 and 18.4 dB in two bands, respectively. Moreover, broadside radiation performances in two bands are obtained.
A novel Fabry–Perot resonator antenna with a wide impedance- and gain-bandwidth is proposed in this paper. A wideband aperture-coupled microstrip antenna is used as the primary source, and a single-layer frequency selective surface with a positive reflection phase gradient is designed as a partially reflective surface. To validate the proposed approach, a prototype antenna operating in the X-band is designed, fabricated, and measured. Both simulation and measured results indicate that the proposed antenna exhibits wideband characteristics. The measured impedance bandwidth (| S11| < −10 dB) is 64.4%, ranging from 8.68 to 15.12 GHz. The experiments demonstrate that a 3 dB gain bandwidth of 31.9% from 8.61 to 11.80 GHz with a peak gain of 14.0 dBi at 10 GHz is achieved. In addition, the proposed antenna reveals good directional radiation patterns, low side-lobe level, and low cross-polarization over the whole working band.
This paper presents a transmit-receive (T/R) antenna pair with omnidirectional and broadband radiation performance. The proposed antenna combines a patch with mushroom-like electromagnetic band-gap (EBG) structures. The mushroom structures are utilized to enhance the radiation characteristics such as impedance bandwidth, directivity, and gain. Two T/R antennas with 3 Â 3 and 5 Â 5 arrays working in K-band are designed and fabricated, the transmit (TX) and receive (RX) antennas are printed on a single-layer grounded dielectric substrate. Both the TX and RX antennas consist of an array of mushroom-like EBG structures around the monopole microstrip antenna, which is loaded with four stubs and fed by a 50 Ω coaxial probe. The dimensions of the fabricated prototype 3 Â 3 array antenna are 3:58λ 0 Â 1:61λ 0 (λ 0 -the wavelength in free space at 24 GHz). The TX/RX measured impedance bandwidth (j S 11 j < À10 dB) are 9.58% (23.6 ~25.9 GHz), 12.08% (22.8 ~25.7 GHz), respectively. The measured peak gain is 3.45 dBi at 24.8 GHz. For the 5 Â 5 array antenna, the aperture size is 5:58λ 0 Â 2:61λ 0 . The measured impedance bandwidth (j S 11 j < À10 dB) is 9.17% (23.65 ~25.85 GHz) and 12.71% (22.65 ~25.7 GHz) for the TX and RX, respectively. The measured peak gain increases by nearly 2 dB. Measurement results show that both antennas have a TX/RX isolation level better than 20 dB and achieve monopole-like omnidirectional patterns over its operating frequency band.
A broadband and compact micro strip grid array antenna (MGAA) is proposed. The proposed array is based on hourglass‐shaped loop elements, which are designed to reduce the size of the grid area in both horizontal and vertical directions with an area reduction of about 22%. To improve the radiation performance, a petaloid‐shaped artificial magnetic conductor (AMC) surface is adopted to replace the traditional metal ground. An air gap layer is introduced between the grid array layer and the AMC surface to enhance the gain and bandwidth of the antenna. A prototype antenna was fabricated and tested. The measured results show that the designed antenna has a wide impedance bandwidth (S11<−10dB), which is ranging from 4.63 to 6.08 GHz (25.0%). The 3‐dB gain bandwidth is from 5.23 to 6.45 GHz (21.0%) with a peak gain of 16.1 dBi at 5.8 GHz. The proposed MGAA consists of 14 radiating elements and possesses a compact size of 2.690λ0×2.690λ0×0.077λ0(λ0‐the wavelength in free space at 5.8 GHz).
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