CST – Computer Simulation Technology

Phasing Characteristics of a Single Layer Microstrip Reflectarray Employing Various Basic Element Shapes
M. E. Bialkowski1 , K. H. Sayidmarie
Antenna International Workshop on Technology: Small Antennas and Novel Metamaterials, 2008. iWAT 2008.
4-6 March 2008
79 - 82
The reflectarray is the type of antenna that includes a feed similar to that used in a conventional curved reflector antenna but its reflector is planar and formed by an array of reflecting elements. These elements use a suitable phasing mechanism to beam an incident wave, as launched by the feed, in a desired direction. Recent years have seen a considerable interest in microstrip reflectarrays [1-4]. This variation of reflectarray is attractive because it brings a promise of a lowcost manufacturing. Single or multi-layer microstrip structures can be used to this purpose. Although the multi-layer structure offers more design flexibilities and thus an increased potential of providing an advanced performance, the most recent research activities have concentrated on the single layer structure. The reason is that this variety incurs a lower manufacturing cost. At the same time, by a proper choice of phasing elements it can offer an enhanced performance comparable to that of the multi-layer reflectarray. Designers of single layer microstrip reflectarrays choose various shape elements in the reflector to obtain the reflected wave phasing. In one approach, the same shape elements with variable size printed on a dielectric substrate are used. These include dipoles [2], square patches [3, 4], circular discs [5], and their combinations [6, 7]. In an alternative approach, the rotation of fixed shape and size elements is adopted [8] to obtain the phasing function. In the two approaches the change of dimensions with respect to the principal polarization electric field vector) of the incident plane wave is responsible for the phasing mechanism. One important issue in the design of microstrip reflectarrays is obtaining a wide phasing range and a slow phase variation (slope) as a function of the phasing element’s variable size. Slower variations or lower slope of the phase response as a function of the elements dimensions result in less tolerance restrictions on manufacturing errors. In turn, a wider phase range gives the designer more flexibility in selecting proper element sizes for a given phase value. It needs to be noted that the limited phasing range has a two-fold adverse effect on the operation of reflectarray. One is that some of the required phase values need to be approximated. Another problem is that the truncation of the actual required phase shift (or signal delay) to the 360° range is responsible for intersymbol interference (ISI) in digitally phase modulated signals [9]. The present paper reports on investigations into the phase change with respect to the element’s size change ( dS d / F ) for a single layer microstrip reflectarray. The investigations are commenced with comparing phase response parameters (range, slope, and working size) for various element shapes that are adopted in a typical single layer microstrip reflectarray. Next, the effect of the substrate characteristics such as its dielectric constant and thickness is considered. The study is carried out by applying full EM simulations of a single unit cell containing a phasing element.

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