Abstract
A broadband dual circularly polarized (dual-CP) reflectarray based on 3-D printed dielectric materials is proposed in this article. A novel 3-D dielectric array element that enables the broadband linearly polarization (LP) to CP transformation is proposed. The unit cell consists of two orthogonal dielectric cuboids that adjust the phases of the two orthogonal LP waves independently and then combine them into a CP wave. The innovative unit cell design provides an extra degree of freedom in varying the geometries of the array elements in all three dimensions, which enables us to independently control the phases of the two LP waves. This maintains an equal amplitude and 90° phase difference condition across the entire reflectarray surface, realizing a broadband and high gain LP–CP reflectarray. The placement of the feed is also optimized to achieve the highest aperture efficiency. Finally, an off-set reflectarray was designed and fabricated using lost-cost 3-D printing. The reflectarray is able to provide both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), with just an LP feed. The measurements agree well with simulated results where the maximum realized gain and directivity at 34 GHz are measured as 27.9 and 28.1 dBi, respectively. The measured 3 dB gain bandwidth and aperture efficiency are 30% and up to 38%, respectively. More importantly, a broad 3 dB axial ratio (AR) bandwidth greater than 40% has been achieved for both LHCP and RHCP, covering almost the entire frequency band of interest, ranging from 26 to 40 GHz.
Highlights
A reflectarray antenna consists of a reflecting surface of unit cells and a feeding antenna [1], [2]
The linearly polarization (LP)-left-hand circular polarization (LHCP) and LP-right-hand circular polarization (RHCP) are the two types of reflectarrays which we focus on in this paper
Where ri and rf are the position vectors of the i-th element and the feed, respectively. u0 is the unit vector in the main beam direction, and φ is a constant reference phase added to all the elements. φ introduces an additional degree of freedom for the reflectarray design, which varies from 0 to 360◦
Summary
A reflectarray antenna consists of a reflecting surface of unit cells and a feeding antenna [1], [2]. The unit cells shift the phases of incoming waves such that the reflected waves add constructively in a desired direction. Reflectarray antennas combine the features of both reflector antennas and phased array antennas. They are compact in size, lightweight, have a high gain and are capable of beam-steering using simple and low-cost tunable elements [3]. Current research focuses on either improving the performance in terms of large bandwidth [4], [5], high gain [6], [7] and high efficiency [8], or exploring new functionalities such as dual polarization [9], [10], circular polarization [11], [12], multi-band [13], [14], multi-beam [15], [16] and dynamic beam-steering [3], [17], [18]
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