Circularly Polarized Reflectarray Research Articles

Transmission–Reflection‐Integrated Metasurface with Simultaneous Amplitude and Phase Controls of Circularly Polarized Waves in Full Space

AbstractIn recent years, manipulations of amplitudes and phases of circularly polarized (CP) waves using metasurfaces have attracted significant attention. However, most of the current works are limited to operating in reflection or transmission space, and the amplitude manipulations are mainly achieved through polarization conversion or resistive loss, which will inevitably lead to cross‐polarization pollution and energy waste. Here, a transmission–reflection‐integrated metasurface that can manipulate the amplitudes and phases of the CP waves simultaneously in full space, which can not only realize arbitrary amplitude allocation of transmitted and reflected CP waves but also independently manipulate their phase responses is proposed. As proofs of concept, two integrated metasurfaces are designed and demonstrated, including a CP reflectarray antenna with simultaneously low side‐lobe level and low cross‐polarization level, and a meta‐grating that can arbitrarily control the intensity of transmitted diffraction wave while focusing the reflected wave. Both simulated and measured results agree very well with the theoretical predictions, demonstrating the powerful ability of the proposed metasurface to control the CP waves in full space, which is promising to be applied in future satellite communications, photonic meta‐devices, and so on.

A Low-RCS Circularly Polarized Reflectarray Antenna With a Linearly Polarized Feed

A low-radar cross section (RCS) circularly polarized (CP) reflectarray antenna with a linearly polarized (LP) feed is designed. The out-of-band RCS of the reflectarray for both the TE and TM polarized incident waves is reduced by replacing its ground with an absorptive frequency selective reflector (AFSR). A systematic methodology based on synthesis of the equivalent circuit model (ECM) is presented to expedite the design of the AFSR. The unit phasing element of the reflectarray is designed in such a way that it exhibits minimum coupling between the two orthogonal reflected LP-field components. Moreover, during the reflectarray construction, a novel phase synthesis is used which takes into account possible lowest of the existing mutual coupling while providing quadrature phase difference between the orthogonal LP components with minimum phase error. The proposed design is fabricated using 14×14 phasing elements to experimentally validate the numerically simulated results. The performance of the reflectarray is compared with a conventional reflectarray without the AFSR. It is observed that when the reflectarray is integrated with the AFSR, its gain is reduced only by 1.16 dB. However, its out-of-band RCS is reduced significantly. The 8-dB RCS reduction bandwidth can be observed from 3.55-7.2 GHz (67.9%) and from 11.85-14.21 GHz (18.11%). Moreover, it provides peak co-pol CP gain of 21.62 dBi, aperture efficiency of 41%, and 1-dB gain-bandwidth from 8.68-8.95 GHz, respectively.

Wideband Circularly Polarized Reflectarray Antenna Using Rotational Symmetrical Crossed Dipoles

A wideband circularly polarized (CP) reflectarray (RA) antenna using rotational symmetrical crossed dipoles is presented. This is the first time investigating coupled crossed dipoles as the unit cell for wideband reflection bandwidth in the CP RA design. Equivalent circuit analysis shows that when a CP wave impinges on the designed unit cell, two series resonances and two parallel resonances are simultaneously excited on the crossed dipoles. Owing to these four different resonances, the CP reflection bandwidth is greatly improved and elaborately adjusted by controlling the coupling between the crossed dipoles. The CP reflection bandwidth ratio of the unit cell is enhanced up to 2:1 for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S_x</i> <-15 dB with a thin thickness of 0.12λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Based on this unit cell, a wideband -20° collimated CP RA antenna with a circular aperture of 316 unit cells was designed, fabricated, and measured for final performance verification. The measured results show that a wide CP bandwidth of 7.6-15.9 GHz is achieved with the axial ratio <3 dB. In addition, the measured 3dB gain bandwidth is better than 43.7% with the peak realized gain of 26.3 dBic and the maximum aperture efficiency of 58.3%.

A Single-Layer Circularly Polarized Reflectarray Antenna with High Aperture Efficiency for Microwave Power Transmission

In this article, a single-layer circularly polarized reflectarray antenna (RA) with a linearly polarized feed is proposed for microwave power transmission. The unit cell of the reflectarray is composed of a rectangular patch surrounded by four groups of E-shaped structures, which feature a very low level of cross-polarization. Simulation results demonstrate that the phase of its reflection coefficient can be tuned continuously in a range of 500° by adjusting the lengths of the E-shaped structures. In response to a normally incident plane wave, the phase values of the reflection coefficient associated with two orthogonal linear polarization directions of the reflected wave can be tuned independently, which makes it possible to convert a linearly polarized incident wave to a circularly polarized beam. A reflectarray with 15 × 15 unit cells is fabricated and tested. The measurement results demonstrate a 3-dB axial ratio bandwidth of more than 2 GHz around the center frequency of 5.8 GHz. The measured gain value of the fabricated reflectarray is 25.4 dBi, corresponding to an aperture efficiency of 52.5%.

Additively Manufactured Metal-Only Millimeter-Wave Dual Circularly Polarized Reflectarray Antenna With Independent Control of Polarizations

This communication proposes an additively manufactured metal-only millimeter-wave dual circularly polarized (CP) reflectarray with independent control of polarizations. A metal-only right-hand CP (RHCP) antenna is designed and used as the reflectarray’s phase-shifting unit cell (UC). The RHCP UC is immune to the LHCP incidence, and the UC directly reflects the LHCP incidence into free space. Thus, the phase shifting of the LHCP wave solely depends on the rotation angle of the UC. For the RHCP incidence, it is received by the RHCP UC first and induced into the metal waveguide. Then, the energy is reflected by the ground of the metal waveguide and reradiated into free space with RHCP. Thus, the phase shifting of the RHCP wave is determined by the rotation angle of the UC and the length of the metal waveguide. By properly selecting the rotation angle of the UC and the length of the metal waveguide, RHCP and LHCP can be independently manipulated. To demonstrate, two reflectarray antennas with different LHCP and RHCP beam directions are fabricated using additive manufacturing and experimentally verified.

A Circularly Polarized 1 Bit Electronically Reconfigurable Reflectarray Based on Electromagnetic Element Rotation

A circularly polarized (CP) reflectarray with 2-D electronically steerable beam is reported. The reconfigurable CP reflectarray element is realized using a circular-patch-based structure with p-i-n diodes incorporated. A new electronical phase manipulation method is proposed based on the element rotation technique and by additionally exploiting symmetries in the field distribution of the element's fundamental resonant mode. Element rotation can be equivalently achieved by altering the biasing voltage and changing the electromagnetic behavior of the reflective phasing cell. The proposed design approach brings about simplification in element configuration, leading to a reduction in the number of required diodes by a factor of one half. Practical concerns of the element and biasing complexity as well as the insertion loss are, therefore, well-handled. A fully functional 16×16 reconfigurable CP reflectarray is designed, fabricated, and tested to validate the concept. Good beam focusing and 2-D dynamic beam steering capabilities are confirmed through experiments, along with decent polarization purity and comparatively high aperture efficiency. The proposed simple and robust design could be attractive for implementing lightweight, low-cost, and large-scale 2-D reconfigurable CP reflectarrays.

Design of Single-Layer Circularly Polarized Reflectarray With Efficient Beam Scanning

This letter presents the design of wideband, low-cost, single-layer, ultrathin, beam-scanning circularly polarized reflectarray (CP-RA) antenna with high-radiation characteristics. To obtain efficient single and multiple CP beams, a subwavelength unit cell based on Pancharatnam–Berry (PB) geometrical phase was used to increase the beam scanning efficiency. PB unit cell with periodicity of 0.28 λ o and ultrathin thickness of 0.11 λ o is used to achieve the required phase correction across the reflectarray aperture to produce a collimated right-hand circularly polarized (RHCP) beam in the desired direction. The unit cell has three plasmonic resonances and the proposed CP-RA consists of 43 × 43 PB unit cells and occupies an area of 215 × 215 mm2. Both simulation and experimental results show that the proposed CP-RA produces RHCP pencil-beam in the desired direction with a 1 dB gain bandwidth (BW) of 24.5% from 17 to 24.5 GHz, 3 dB gain BW of 46.15% from 15 to 24 GHz, peak aperture efficiency of 49.93%, 3 dB axial ratio (AR) of 46.15%. Furthermore, a beam scanning with 70° (±35°) scanning angle is achieved with gain scanning loss of less than 3 dB and beam squint of less than 1.3° within the whole frequency band and for all scanning angles.

Wide-Band Circularly Polarized ReflectarrayUsing Graphene-Based Pancharatnam-Berry Phase Unit-Cells for Terahertz Communication.

A wide-band and high gain circularly polarized (CP) graphene-based reflectarray operating in the THz regime is proposed and theoretically investigated in this paper. The proposed reflectarray consists of a THz CP source and several graphene-based unit-cells. Taking advantages of the Pancharatnam Berry (PB) phase principle, the graphene-based unit-cell is capable of realizing a tunable phase range of 360° in a wide-band (1.4–1.7 THz) by unit-cell rotating, overcoming the restriction of intrinsic narrow-band resonance in graphene. Therefore, this graphene-based unit-cell exhibits superior bandwidth and phase tunability to its previous counterparts. To demonstrate this, a wide-band (1.4–1.7 THz) focusing metasurface based on the proposed unit-cell that exhibits excellent focusing effect was designed. Then, according to the reversibility of the optical path, a CP reflectarray was realized by placing a wide-band CP THz source at the focal point of the metasurface. Numerical simulation demonstrates that this reflectarray can achieve a stable high gain up to 15 dBic and an axial ratio around 2.1 dB over the 1.4–1.7 THz band. The good radiation performance of the proposed CP reflectarray, as demonstrated, underlines its suitability for the THz communication applications. Moreover, the design principle of this graphene-based reflectarray with a full 360° phase range tunable unit-cells provides a new pathway to design high-performance CP reflectarray in the THz regime.

Dual Circularly Polarized Reflectarray With Independent Control of Polarizations

A reflectarray with independent dual-circular polarizations is proposed for the first time. The reflector panel operates in X-band and contains 97 unit-cells. It is made with a lego-type configuration allowing change manually the phase aperture distribution and demonstrating experimentally the independence of both polarizations in the same frequency band. To this end, various beam pointing directions are selected in right-hand and left-hand polarizations. The achieved bandwidth is 790 MHz (9.4% at the center frequency 8.37 GHz) for an axial ratio lower than 3.5 dB with 1.5 dB gain variations.

Design and Implementation of a Single Layer Circularly Polarized Reflectarray Antenna with Linearly Polarized Feed

A novel microstrip unit cell element with a simple structure is presented for designing circularly polarized reflectarray that converts a linearly polarized incident field into a radiated circularly polarized field. The unit cell element consists of a circular patch with two orthogonal slots etched in it. A parametric study was carried out using CST Microwave Studio (Computer Simulation Technology, worldwide) on the unit cell element to evaluate the effect of the unit cell’s salient parameters. This unit cell element was used to design and implement a prime focus array, which had 3-dB gain bandwidth and 3-dB axial-ratio bandwidth equal to 7.6 and 8.6%, respectively.

Design and Characterization of a CPSS-Based Unit-Cell for Circularly Polarized Reflectarray Applications

A CPSS-based unit-cell is proposed as a building block of future reconfigurable dual-CP reflectarrays illuminated by a dual CP primary feed. It is based on an enhanced version of the original Pierrot's cell with multiple wires bent in a crank-like shape. It provides a 2-bit phase resolution in reflection for the left hand circular polarization (LHCP) and is nearly transparent in right hand circular polarization (RHCP). The main design steps and measurement procedure of the optimized cell are described in detail. The simulated and measured characteristics are in good agreement. The experimental results demonstrate a 6.4% bandwidth for a phase resolution better than 1.9 bits and an insertion loss of 0.5 dB at resonance.

Design, Manufacturing, and Testing of a 20/30-GHz Dual-Band Circularly Polarized Reflectarray Antenna

This letter documents the design, manufacturing, and testing of a single-layer dual-band circularly polarized reflectarray antenna for 19.7-20.2 and 29.5-30.0 GHz. The reflectarray is designed using the concentric dual split-loop element and the variable rotation technique that enables full 360 ° phase adjustment simultaneously in two separate frequency bands. The elements have been optimized to suppress cross-polar reflection. Thereafter, the element data is included in a design tool that computes the reflectarray layout and the associated radiation patterns. The reflectarray is composed of 80 × 80 elements printed on a 40 × 40-cm2 Rogers 5880 substrate. The antenna has been manufactured and measured at the DTU-ESA Spherical Near-Field Antenna Test Facility. The peak gain is 35.8 and 40.0 dBi at 20.0 and 29.8 GHz, respectively, and the aperture illumination efficiency is in the range of 53%-63% over the two frequency bands.

Proof of Concept of a Dual-Band Circularly-Polarized RF MEMS Beam-Switching Reflectarray

In this communication we propose the concept of a circularly polarized reflectarray (RA) antenna capable of independent beam-switching in both K and Ka bands. The RA unit cell comprises one microstrip ring per each operation frequency. Each ring is integrated with six equally spaced series RF micro electro-mechanical systems (RF MEMS) switches, which allows implementing the sequential rotation principle formerly used in circularly-polarized RA for single-frequency operation. A detailed design is proposed, considering the best relative arrangement of the rings corresponding to each frequency, the accurate modeling of the RF MEMS switches, and the full-wave simulation of the full array. The designed RA is implemented on a 4-inch quartz wafer and comprises 109 K-band and 124 Ka-band split-rings. Two prototypes representing two frozen states of the reconfigurable antenna are fabricated and measured. The designed RA can provide ${\pm}{120}^{\circ}$ progressive phase difference in both operation bands exhibiting beam switching to ${\pm}{35}^{\circ}$ and ${\pm}{24}^{\circ}$ off the broad-side in K and Ka bands respectively. The performance of the designed antenna is verified by the agreement of the measured and simulated radiation patterns.