Course Number: 361-2-5931 Lecturer: Professor Arnon Shlomi
Article Summary Assignment
"Reconfigurable Antennas for Wireless and Space Applications" By Christos G. Christodoulou, Fellow IEEE, Youssef Tawk, Steven A. Lane, and Scott R. Erwin, Senior Member IEEE Proceedings of the IEEE 100, no. 7 (2012): 2250-2261
1. Introduction A reconfigurable antenna (RCA) is an antenna that is able to be formed, or bent. From this definition one can deduce the significance of such antenna to wireless communication. RCA will allow adaptation, additional functionality and more versatility. Therefore, RCAs, with the ability to radiate more than one pattern at different frequencies and polarizations, are necessary in modern telecommunication systems. The article discusses the different reconfigurable components that can be used in an antenna to modify its structure and function. These reconfiguration techniques are either based on the integration of radio-frequency micro-electromechanical systems (RF-MEMS), PIN diodes, varactors, photoconductive elements, or on the physical alteration of the antenna radiating structure, or on the use of smart materials such as ferrites and liquid crystals. All of the above techniques redistribute the antenna currents and thus alter the electromagnetic fields of the antenna’s effective aperture. Therefore, enabling the antenna to enhance its bandwidth, change it operating frequency, polarization, and radiation pattern. 2. Reconfiguring Techniques Six major types of reconfiguration techniques are used to implement reconfigurable antennas, as indicated in Fig.1. Here I shell focus on two, electrical and optical RCAs. RCAs can be classified into four different categories. (a) frequency RCA; (b) radiation pattern RCA, for this category, the antenna radiation pattern changes in terms of shape, direction, or gain; (c) polarization RCA; and (d) combination of the previous categories. There are several advantages in using reconfigurable antennas. (a) Ability to support more than one wireless standard. Hence, it minimizes cost and volume requirements, simplifies integration and offers good isolation between different wireless standards; (b) lower front-end processing. Therefore, there is no need for front-end filtering and there is a good out-of-band rejection; (c) best candidate for software-defined radio. Thus, has the capability to adapt and learn and can be automated via a microcontroller or a field programmable gate array (FPGA); and (d) multifunctional capabilities. Consequently, can change functionality as the mission changes, can act as a single element or as an array and can provide narrow- or wide-band operation. However, there are disadvantages for adding tunability to the antenna behavior. (a) the design of the biasing network for activation/deactivation of the switching elements which add complexity to the antenna structure; (b) increase in the required power consumption due to the incorporation of active components which augments the system cost; (c) generation of harmonics and inter modulation products; and (d) need for fast tuning in the antenna radiation characteristics to assure a correct functioning of the system.
Figure 1: Techniques to achieve RCAs
2.1. Electrically RCAs The ease of integration of such switching elements into the antenna structure has attracted antenna researchers to this type of RCAs despite the numerous issues surrounding such reconfiguration techniques. These issues include the nonlinearity effects of switches, and the interference, losses, and negative effect of the biasing lines used to control the state of the switching components on the antenna radiation pattern. RF-MEMS: The antenna shown in Fig. 2 is a reconfigurable rectangular spiral antenna with a set of RF-MEMs switches, which are monolithically integrated and packaged onto the same substrate. The antenna is printed on a PCB substrate and fed...