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Fractal Antenna with RF MEMS Switches for Multiple Frequency Applications
D.Anagnortou*', Majid Khodier', J.C. Lyke', and C.G. Christadaulou'

' The Universily ofNew Mexico. USA, 'Air Force Research LaboratoryiVSSE Kinland AFB
Ahstmet- A new, concept Of combining RF MEMS switcheS with Fractal antennas is presented. The idea is to connect several antenna configurations together using RI MEMSswitches to cover several frequency bands. By using a ' m a n camhination' of fractal shaped antennas, wideband and coverage can be achieved for ~atellite wireless communications. Moreover the Same antennas can be used for phased array applications as well. The analysis and design principles are discussed and presented in here. Several examples are shown to demonstrate the proposed concept.Index Ten" - Re-conjiguroble anienne$, widehond,frocrd RF-MEMS, smorl onlennos

The requirements for increased functionaliry, such as direction finding and anti-jamming protection, within a confined volume, place more requirements in today's antenna system. For single frequency operations, sufficient ~ o l u l i o n ~ be achieved using switched beam arrays and adapcan tive arrayantennas [1,2]. For mllitipk frequency operations. a Solution Can be an array of fractal antennas. In this work, RF MEMS arc used in conjunction wiih fractal antenna ~ f m ~ h l r c s the as basis of a new re-canfigurable array antenna approach. The RF MEMS switches permit the connectivity of sections of the antenna's conductive parts, and therefore enhance the coupling between the fractal elementsallowing multiple frequency operation with o m antenna. Also, the RF MEMS switches in conjunction with a neural network can develop a new %e of re-configurahlc and smart antenna altogether, in which selfadaptatiodleaming theory plays a role in antenna optimization and gives the whole system great 8UtOnOmy.

The use of fractal shapes provides the multiband characteristic through the property ofsclfsimilarity at equal Or different physical scales. An array of fractal configurations lhat operate over different frequency bands providing different radiation mnems can be the basis for an ultrawideband re-canfigurahle antenna [3] The electromagnetic performance of the RF MEMS switches is considered ideal, and their placement is accomplished by Small physical c~nnectionsof the antenna's adjacentconducting pans. Several configurations have been shldied and analyzed and some of the results are shown in the section^ to follow herein. The analysis of 811 antenna configurations is accomplished with IE3D".

Most fractal antennas, including the Sierpinski Gasket antenna, have been studied extensively over the lasf few years [4,5]. A modifiedSierpinski Casket antenna shown in Fig.1 is chosen for this paper. The selection was based on the antenna's single element pCrf0r"cC when used as a bow-

Figure 1. The design eharactefirtics ofthe Sierpinti gasket antenna with obtuse angle.

Figure 2(a.b). The radiation charactenstics ofthe antenna with all switches in OFF state tie antenna, or setting all the switches to the 'OFF' state. Theantenna has a flare angle of 130" and provider constant radiation pattem all over its bandwidth. The radiation characteristics for this antenna are shown in Fig 2(a,b,e). The bandwidth is from I.5GHz to 2.lGHz and the radiation pattem is similar to the pnnted dipole antenna, making it ideal for receiveruse.

In general, fractal antennas show weak couplingbetween the different elements of the smcm. We comider the RF MEMS switches to be ideal. The switches have dimensions less than lxlmm and are modeled as small patches that connect/disconnect the adjacent conducting patches changing the antenna's physical dimensions. In this implementation, gaps are created in the fractal antenna pattem, which are bridged by a number ofMEMS micro-relays. The...
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