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This paper proposes a compact design of dual-sense circularly polarized (CP) antenna for simultaneous transmit (Tx) and receive (Rx) communication systems. The primary radiating aperture of the proposed antenna is a 2 × 2 unit-cell metasurface (MS). The MS is excited by the asymmetric patch in the center, which acts as the CP source of the whole antenna structure. By properly tuning the feeding positions, dual-sense CP with high isolation can be achieved. For verification, an antenna prototype with compact dimensions of 0.36λ × 0.36λ × 0.02λ (λ is the free-space wavelength at the center operating frequency) is fabricated and measured. The measured operating bandwidth is 1.6% (2.45–2.49 GHz), in which the reflection and transmission coefficients are less than—10 dB and the axial ratio is lower than 3 dB. Within this band, the maximum isolation value is 39 dB, and the peak gain is 5.7 dBi. [ABSTRACT FROM AUTHOR]

This paper presents a multiple-input-multiple-output (MIMO) antenna array with low-profile and flexible characteristics. Multiple microstrip patches are arranged in the E-plane configuration and decoupled by shorted quarter-wavelength stubs. The antenna has a small element spacing of 0.032 λ, where λ is a free-space wavelength at the center frequency. To demonstrate the feasibility of the proposed concept, a 1 × 4 MIMO array prototype is fabricated. The measured results on the fabricated prototype demonstrate that the MIMO antenna has good operation features at 4.8 GHz with a reflection coefficient of less than –10 dB and an isolation of better than 20 dB. Besides, good radiation patterns and broadside gain of around 4.5 dBi are also attained. The antenna also works in the bending mode and has the capability of extending to large-scale MIMO arrays. Such attractive features prove the utility of the proposed antenna in various modern electronic devices. [ABSTRACT FROM AUTHOR]

This paper presents an ultrawideband (UWB) circularly polarized (CP) two-arm Archimedean spiral antenna with unidirectional radiation patterns. The antenna is directly fed by a 50-Ω coaxial cable and reflected by a circular cavity. The proposed design is able to exhibit high gain, high radiation efficiency as well as UWB CP operation by properly choosing the reflector's dimensions and the spiral's growth rate. This overcomes the critical drawback of the other reported UWB CP spiral antennas in literature, which always suffer from poor performance in the lower operating frequencies. The measured reflection coefficient and axial-ratio show a good performance over a frequency band 6–16 GHz. Furthermore, the values for gain and radiation efficiency of the proposed design are always better than 5.2 dBic and 85%, respectively. [ABSTRACT FROM AUTHOR]

This article presents a broadband circularly polarized two‐arm Archimedean spiral antenna with a novel simple feeding method. Contrary to the conventional spiral antenna excited by a vertically or horizontally balun, the presented design is directly fed by a coxial cable with a planar feeding section optimized to provide a broadband input impedance matching. An antenna prototype has been fabricated and measured to validate the concept. Measured results of reflection coefficient and axial ratio show a good performance over a frequency range from 1.0 to 3.5 GHz, equivalent to ~111.1%. Within this band, the antenna prototype exhibits bidirectional radiation with broadside gain values of better than 3.6 dBic. [ABSTRACT FROM AUTHOR]

This paper presents a wideband reconfigurable circularly polarized (CP) antenna with omnidirectional radiation pattern. The antenna is based on a shorted monopolar patch surrounded by multiple curved branches and it is proximity‐fed by a disk‐loaded coaxial cable. The polarization reconfigurability is realized by introducing PIN diodes on junctions between the patch and the branches to alter the current direction flowing on the branches. By properly controlling the ON/OFF states of the diodes, the antenna's polarization can be switched between right‐hand circular polarization (RHCP) and left‐hand circular polarization (LHCP). A reconfigurable prototype has been fabricated and measured. The experiments show that the prototype has wide overlapped bandwidth from 2.3 to 3.1 GHz, in which the reflection coefficient and the axial ratio (AR) are less than −10 dB and 3 dB for both polarization states. Besides, the antenna radiates dipole‐like patterns with the realized gain of around 0.6 dBic across this operating band. [ABSTRACT FROM AUTHOR]

This article presents a method to design broadband circularly polarized (CP) Fabry‐Perot Resonator (FPR) antenna. The proposed antenna is based on multi‐layer thin dielectric slabs arranged in close proximity as a partially reflecting surface (PRS) and an Archimedean spiral as a CP radiating source. Experimental results show a broadband operation from 6 to 13 GHz, in which the reflection coefficient is less than −10 dB and the axial ratio (AR) is lower than 3 dB. In addition, good radiation patterns and high broadside gain of better than 10.8 dBic are achieved over the operating bandwidth. The proposed antenna can be used for C‐ and X‐band satellite communications. [ABSTRACT FROM AUTHOR]