Novel Reconfigurable Fractal Antenna Design based Metasurface Layer for Modem Wireless Systems

A novel wideband-pattern reconfigurable metasurface antenna based on H-tree fractal slots is presented in this work. the H-tree fractal slots patch illuminates a metasurface layer of $5\times 5$ unit cells array. Four PIN diodes are embedded in the patch, in the H-tree slots, to switch the radiating slots and control the antenna radiations. The individual unit cell dimensions are $33\times 33m\text{m}^{2}$. The overall antenna size is $173\times 173\times 56.6m\text{m}^{3}$. Switching the antenna by PIN diodes, the antenna main lobe can be steered toward different nine directions. The antenna provides again in the front lobe direction of 8. 99dBi at 1. 268GHz without significant change degradation in the gain during the beam steering process. Nevertheless, the antenna shows a wide operating frequency bandwidth of 55.5% from 0.978-1.73 GHz around the frequency resonance of interest. The proposed design shows a novelty in controlling the main lobe direction by switching four PIN diodes to be steered from −10° to 10°. The diode switching process shows no significant effects on the antenna bandwidth. The proposed antenna is designed with aid of a software package based on the finite integration technique of the CST MWS formulations.

I. Introduction

A huge research impact has been recently applied [1] on the field of reconfigurable antennas designs due to their flexibility of operation to suit different wireless communication applications. reconfigurable antenna designs can generally be categorized into four main types including radiation pattern [1], polarization [2], frequency [3], and any of these combinations [4], [5]. among these kinds, pattern reconfigurable antennas are advisable as their radiation patterns can be changed in several pre-defined directions for monitoring and tracking systems. Recently, different methods were suggested for electronically steering the antenna beam; for example, Butler Matrix [6], Rotman Lens [7], Luneburg lens [8], parasitic controllable elements [9], [10], parallel plate lens [11] and phased array antenna [12], [13]. Although, these methods are effective in offering beam reconfiguration; nevertheless, they suffer from being narrow operating bandwidth, high cost, a bulky structure at low frequencies, and difficult to manufacture. Therefore, the metasurface design was proven as a promising way to achieve beam-switching in microwave antennas [14] –[17]. In such designs, Metasurface can be placed close to the radiation source and leads to a low antenna profile. Such a technique, in general, is performed based on three methods: the first technique is to rotate the metasurface around the antenna [14]. The feature of such a technique is to obtain continuous control on the beam steering process, But the mechanical process is complex and difficult in addition to the errors resulting from it. The second mechanism is the reconfigurable MS antenna as described in [15]; nevertheless, a large number of pin diodes are required. The third technique is proposed to overcome these lacks by shifting the radiation source from the center of the Metasurface [16], [17]. As far as the authors know, the open literature contains a limited number of pattern antennas that can be reconfigured based on MS. A great deal of research was carried out on MS antennas because they have unique electromagnetic properties, including NZRI in addition to low profile, lightweight, low loss, and cost-efficient manufacturing processes. [18], [19]. MS can also be placed in front of the antenna as a lens to collect the electromagnetic field in the required direction into a focused beam [20]. In [21], The antenna beam steering theory was discussed thoroughly in front of a dielectric lens. It was found that a pattern direction of the antenna can be controlled in front of the lens by offsetting the position of the antenna from the center of the lens and vice versa. The beam switching structure is presented in [22], [10] using an acceptable number of PIN diodes to tune the frequency resonance of the MS unit cell. Each cell requires at least one PIN diode and a DC bias [19], [23]; thus, the complexity and manufacturing costs are increased.