This paper presents the design of a bidirectional same-sense circularly polarized (CP) antenna that uses metasurfaces. The antenna consists of two metasurfaces, each comprising an array of 2 × 4 corner truncated patches placed back-to-back on the top and bottom of the antenna. In addition, a ground plane with an etched slot is sandwiched between the substrates at the front and back, and the feed line is a 50 Ω coplanar waveguide. The antenna radiates same-sense right-handed CP waves in both the front and back directions and has overall dimensions of 48 mm × 24 mm × 3.048 mm (0.91λo × 0.45λo × 0.05λo at 5.7 GHz). The measured reflection coefficient for |S11| < -10 dB yields an impedance bandwidth of 5.21–6.26 GHz (18.4%) and an axial ratio (AR) bandwidth of 5.36–6 GHz (11.2%) for both front and back directions. The antenna gain is 3–5.29 dBic for both directions and has a radiation efficiency of >96% within its AR bandwidth.

This paper presents a high-gain wideband circularly polarized antenna composed of an end-fire dipole array antenna integrated with a metasurface. The antenna consists of a two-layer cascaded non-uniform metasurface made up of 4 × 4 circular patches with cross-slots of unequal lengths placed above an end-fire dipole array antenna with an air gap between the structures. The end-fire dipole array antenna comprises four equally spaced dipole elements, and each dipole is connected to a parallel stripline printed on the front and back sides of the substrate. The metasurface, which is made up of a circular patch with 2 × 2 center patches that have a different radius than the outer patches, and the cross-slots of unequal lengths are used for the polarization conversion of a linearly polarized wave to a circularly polarized wave. The measured reflection coefficients for |S11| < -10 dB yielded an impedance bandwidth of 25.6–31.8 GHz (21.5%), a 3-dB axial ratio (AR) bandwidth of 26.1–30.5 GHz (15.5%), a 3-dB gain bandwidth of 26.0–31.1 GHz (17.4%) with a peak gain of 11.0 dBic, and a radiation efficiency of more than 80% in the axial ratio bandwidth.

In this paper, the design of a wideband circularly polarized (CP) bowtie slot antenna that uses metasurfaces is presented. The antenna consists of a single-layer substrate with the metasurface made of $4\times4$ periodic corner-truncated patches printed at the top side of the substrate and a bowtie-shaped slot etched on the ground plane. The metasurface made of corner-truncated patches are utilized to convert the linearly polarized wave into a CP wave. The antenna is fed by a 50- $\Omega $ coplanar waveguide. The antenna, with an overall size of 42 mm $\times42$ mm $\times2.3$ mm ( $0.71\,\,\lambda _{\mathrm {o}} \times 0.71\,\,\lambda _{\mathrm {o}} \times 0.038\,\,\lambda _{\mathrm {o}}$ at 5.1 GHz), was fabricated and measured. The measured reflection coefficient for $\vert \text{S}_{11}\vert < -10$ dB yielded an impedance bandwidth of 3.75–6.67 GHz (55.7%), an axial ratio (AR) bandwidth of 4.38–5.98 GHz (31.37%), a 3-dB gain bandwidth of 3.75–6.0 GHz (46.88%), a peak gain of 7 dBic, and a high radiation efficiency of more than 93% within the AR bandwidth.

This paper presents an ultra-thin, ultra-wideband linear-to-circular (LTC) polarization converter based on the crossed-dipole-shaped metasurface. The unit cell of the crossed-dipole-shaped metasurface is made up of two identical T-shaped dipole arms, which are orthogonal to each other and are connected with a diagonal microstrip line. The LTC polarization converter is placed on the top side of an ultra-thin single-substrate layer with a profile size of 0.035 λ _o , where λ _o is a free space wavelength at the center frequency of the axial ratio bandwidth (20.89 GHz). The proposed design shows nearly equal transmission amplitude and stable phase difference of nearly 90° of the two orthogonal components of transmitted waves in a wide frequency range. The right-hand circularly polarized (RHCP) component of the transmitted wave is much larger than the left-hand circularly polarized, and thus, the transmitted wave is RHCP. Numerical and experimental results showed that the polarizer could realize an ultra-wideband LTC polarization conversion at both x- and y-polarized incidences in the frequency range from 11.66 to 30.12 GHz, which is a fractional bandwidth of 88.4%, and it can maintain a stable polarization conversion performance under large-range incidence angles. In addition, a high total transmittance of the electromagnetic wave was obtained.

In this paper, the design of a series-fed angled dipole array antenna incorporated with a polarization conversion metasurface is presented. The antenna consists of a two-layer cascaded metasurface made of 4×4 circular patches with cross-slots of unequal lengths placed above the series-fed angled dipole array antenna in the end-fire direction with an air gap. The series-fed angled dipole array antenna consists of eight dipole elements with equal spacing, and each dipole was connected to a parallel stripline printed on the front and backsides of the substrate. The metasurface made of a circular patch with cross-slots of unequal lengths is used for polarization conversion of the linearly polarized wave to the circularly polarized wave. The measured reflection coefficient for |S11| < -10 dB results yield an impedance bandwidth of 26.2 to 31.4 GHz (18.0%), a 3-dB axial ratio (AR) bandwidth of 26.5 to 31.2 GHz (16.3%), a 3-dB gain bandwidth of 26.2--30.5 GHz (15.16%) with a peak gain of 10.9 dBic, and radiation efficiency of more than 80% within the AR bandwidth.

This paper presents a single-layer wideband linear-to-circular (LTC) polarization converter implemented with a crossed-dipole-shaped metasurface. The LTC polarization converter is placed on the top side of a single-substrate layer. The proposed design yields a nearly equal transmission amplitude and steady phase difference of nearly 90° between the two orthogonal components of electromagnetic waves transmitted across a wide frequency range. The numerical results demonstrate that the polarizer can accomplish wideband LTC polarization conversion at both x- and y-polarized incident waves within a frequency range of 12.1–30.2 GHz, which represents a fractional bandwidth of 85.6%. Furthermore, the proposed LTC polarization converter achieves a high total transmittance of electromagnetic waves.