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.
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.
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