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A compact broadband ambient RF energy harvester operating from 1800 MHz up to 2.5 GHz is proposed in this paper. This work is motivated by the huge amount of free and continuously available RF energy in the surroundings that can be utilized into useable energy. Harvest performance is investigated using two antennas in this work, a circular polarized and an array antenna. Due to low ambient power densities, a multistage rectifier is utilized to improve the output dc voltage of the proposed system. Measurements indicate the system is capable of harvesting up to 1.8 Vdc output from nondedicated ambient RF energy sources in an urban area, which is significant in the absence of other energy sources.

A novel of wideband circular polarization (CP) antenna with high gain that is suitable to harvest energy is proposed. In this article, our objective is to design an antenna that is capable of fully harvesting ambient RF energy. A survey on the feasibility of scavenging for RF energy was conducted through power density measurement in an urban area. Using the results, a CP antenna was designed to cover the frequency band from the largest RF contributors, ranging from 1.73 to 2.61 GHz in GSM1800, UMTS, WiMAX and the unlicensed industrial, scientific, and medical (ISM) bands. Hence, a simple single feed electromagnetic (EM) coupled circularly polarized antenna with high gain is presented. The wideband CP is achieved by implementing EM coupled feed with a defected ground plane structure. Experimental results showed the antenna achieved an axial ratio bandwidth of 25% with respect to 2.08 GHz center frequency. Furthermore, the antenna exhibits broad impedance bandwidth of 32.77% with the measured peak gain is 8.7 dBic at 2.05 GHz. The proposed antenna structure is simple and low cost with a size of 0.462 λo and wide 22.1% axial ratio bandwidth.

Abstract-This work presents the design and investigation of the monopole and Koch fractal antenna. The fractal concept and geometry has been used in antenna design to obtain multi-band behavior and miniaturized size, as both of these characteristics are important requirements in current antenna design trends. The aim of this paper is to evaluate the antenna performance between monopole antenna and third iteration Koch fractal antenna. Antenna properties such as reflection coefficient (S 11 ), bandwidth, gain and radiation pattern are analyzed and discussed in this paper. The result shows that both antennas can operate well at respective designed resonances. However, the third iteration Koch fractal antenna is also proven to be advantageous over the planar monopole -more number of resonant frequencies, larger bandwidth and smaller size.

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