# Reconfigurable Antennas: Switching Techniques--A Survey
###### Abstract  
Due to the fast development of wireless communication technology, reconfigurable antennas with multimode and cognitive radio operation in modern wireless applications with a high-data rate have drawn very close attention from researchers. Reconfigurable antennas can provide various functions in operating frequency, beam pattern, polarization, etc. The dynamic tuning can be achieved by manipulating a certain switching mechanism through controlling electronic, mechanical, physical or optical switches. Among them, electronic switches are the most popular in constituting reconfigurable antennas due to their efficiency, reliability and ease of integrating with microwave circuitry. In this paper, we review different implementation techniques for reconfigurable antennas. Different types of effective implementation techniques have been investigated to be used in various wireless communication systems such as satellite, multiple-input multiple-output (MIMO), mobile terminals and cognitive radio communications. Characteristics and fundamental properties of the reconfigurable antennas are investigated.  
active elements; cognitive radio; implementation techniques; reconfigurable antennas; MIMO; modern wireless communications [table]capposition=top  
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,19,20,21,22,23,24,25,26,27,28,29,27,28,29,27,28,29,27,28,29,27,28,29,29,27,28,29,27,2  
Due to these attractive features, reconfigurable antennas have received considerable attention, and a number of works have been demonstrated in past years [14; 15]. Furthermore, several review and survey papers have been published recently [16; 17]. However, these reviews have only focused on electrical reconfiguration with active elements such as positive-intrinsic-negative (PIN) diodes. In [18], various kinds of reconfigurable antennas including radiation pattern reconfigurable antenna, polarization reconfigurable antenna and a combination of radiation and frequency reconfigurable antenna are discussed. In addition, more details of different types of reconfigurable antennas are described in [19]. Unlike the reported reviews, we investigate here different types of effective implementation techniques including not only electronic switching but also other possible switching techniques of reconfigurable antennas. In order to demonstrate the reconfigurable antennas, various effective implementation techniques have been proposed to be used in different wireless systems such as satellite, multiple-input multiple-output (MIMO) and cognitive ratio communications, which are classified as below:  
* Electrical reconfiguration;
* Optical reconfiguration;
* Physical reconfiguration;
* Reconfigurable antennas with smart materials.  
The most common technique is electrical reconfiguration, which uses active elements such as positive-intrinsic-negative (PIN) diodes, varactors and radiofrequency micro-electromechanical system (RFMEMS) switches [20; 21; 22; 23]. Compared to RFMEMS switches, PIN diodes have acceptable performance and a low price. Another technique is called optical reconfiguration, which relies on photoconductive switching elements [24; 25]. The antenna reconfigurable characteristic can also be implemented by altering the structure of the antenna--this is called the mechanical reconfiguration method [26; 27]. Apart from the mentioned techniques, the antenna can be also reconfigured using smart materials in the antenna configuration [28]. In this section, we investigate different types of reconfigurable antenna implementation techniques by providing some detailed examples.