Accurate Modeling of Advanced Reflectarrays

PhD student Min Zhou
Professor Olav Breinbjerg
Associated professor Oleksiy Kim (supervisor)
Senior engineer Erik Jørgensen (external supervisor)
Senior engineer Peter Meincke (external supervisor)

October 2009 – September 2012

This project is part of the Danish Industrial PhD Programme, and is sponsed by TICRA and the Ministry of Science, Technology, and Innovation.

Reflectarrays were proposed more than 4 decades ago as a promising candidate for realizing low-cost high-gain antennas. Such antennas are needed in many application areas such as telecommunication, earth observation, and satellite antennas. Reflectarrays constitute a successful merge of two commonly used techniques for realizing high-gain antennas: Reflector antennas and array antennas. The reflectarray eliminates the need for the bulky, expensive, and relatively high-loss feeding network required by conventional array antennas. At the same time, the reflectarray is much easier to fabricate than a traditional reflector antenna, which employs a curved surface, e.g. a parabolic surface, for focusing of electromagnetic energy. The reflectarray is similar to a conventional reflector antenna but the focusing effect is achieved by using a planar reflecting surface with a controllable phase delay on different parts of the surface. This controllable phase delay is typically realized by using printed microstrip antenna elements with a single tuneable geometrical parameter. The planar reflecting surface has many advantages such as easy deployment and stowing as well as cheap manufacturing costs. The basic principle described above has been applied to design and manufacture a large number of advanced reflectarrays. The advanced capabilities that have been demonstrated by various researchers include: dual- and tri-band reflectarrays for simultaneous operation in 2 or 3 distinct frequency bands; dual-polarized reflectarrays; contoured-beam and multi-beam reflectarrays; inflatable reflectarrays for deployment of large antennas in space; reconfigurable reflectarrays with in-orbit change of radiation pattern; combination of reflectarrays and solar panels. Despite the advanced capabilities described above, reflectarrays have not yet gained widespread acceptance for space applications due to limited bandwidth, ohmic loss, and cross polarization level etc. Further improvements of the reflectarray performance rely heavily on the development and refinement of analysis and optimization tools. 


Figure 1. Typical geometry of a printed reflectarray antenna 


Accurate analysis of reflectarrays problems is a challenging problem due to the huge electrical size of the problem and the lack of periodicity. These issues have resulted in a relatively poor correlation between simulations and measurements. Even state-of-the-art reflectarray modeling algorithms cannot reach the prediction accuracy of conventional reflector- and array-modeling algorithms. The commonly adopted analysis and synthesis method is based on a spectral domain Method of Moments. Each element in the reflectarray is analyzed by assuming local periodicity, that is, the individual array element is embedded in an infinite array of identical elements. The reflectarray radiation pattern is then evaluated by summing the contributions from each element when it is illuminated by the actual feed

The periodic assumption is not fulfilled in the actual reflectarray problem and this lack of periodicity is presumed to be one of the contributors to the relatively poor correlation between theoretical simulations and measurements. In addition to the lack of periodicity, the reflectarray is also assumed to be of infinite size and the truncation effects at the edges of the array are therefore not accounted for.

The main goal of the PhD project is to identify the sources of error in current modeling techniques and to develop enhanced modeling tools. It is expected that an efficient and accurate simulation tool will improve the performance and usability of reflectarrays, and greatly contribute to solving the associated issues with reflectarray antennas.

measured vs simulated

Figure 2. Comparison of simulated and measured radiation patterns

grasp reflectarray

Figure 3. A reflectarray simulated using the commercially available software GRASP from TICRA


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