A hybrid fractal shape planar monopole antenna covering multiple wireless communication bands is presented for multiple-input-multiple-output (MIMO) implementation for handheld mobile devices. The proposed structure is the combination of Minkowski island curve and Koch curve fractals. It is placed with edge to edge separation of 0.16λ0 at 1.75 GHz. The T-shape strip is inserted and rectangular slot is etched at top side of ground plane, respectively to improve the impedance matching and isolation between the antennas. A measured impedance matching fractional bandwidths ( S11 ≤ -10 dB) are 14% from 1.65 GHz to 1.9 GHz for the band 1 and 80% from 2.68 GHz to 6.25 GHz for the band 2. Acceptable agreement is obtained between the simulated and measured antenna performance parameters. These characteristics demonstrate that the proposed antenna is an attractive candidate for handheld mobile devices.

Hybrid Fractal Shape Planar Monopole Antenna Covering Multiband Wireless Communications With MIMO Implementation for Handheld Mobile Devices

A printed wide-slot antenna with a parasitic patch for bandwidth enhancement is proposed and experimentally investigated. A simple 50-Ω microstrip line is used to excite the slot. A rotated square slot resonator is considered as reference geometry. The rotated square slot antenna exhibits two resonances (f1 : lower resonant frequency, f2: higher resonant frequency). By embedding a parasitic patch into the center of the rotated square slot, the lower resonant frequency is decreased and the higher resonant frequency is increased. Thus, broadband characteristic of the wide-slot antenna is achieved. The measured results demonstrate that this structure exhibits a wide impedance bandwidth, which is over 80% for |S11| ≤ -10 dB ranging from 2.23 to 5.35 GHz. Also, a stable and omnidirectional radiation pattern is observed within the operating bandwidth. In this design, a smaller ground plane is considered compared to the reference antenna (rotated square slot antenna without the parasitic center patch).

Bandwidth Enhancement of a Microstrip Line-Fed Printed Wide-Slot Antenna With a Parasitic Center Patch

Wireless Sensor Networks (WSNs) can be defined as a self-configured and infrastructureless wireless networks to monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the network to a main location or sink where the data can be observed and analysed. A sink or base station acts like an interface between users and the network. One can retrieve required information from the network by injecting queries and gathering results from the sink. Typically a wireless sensor network contains hundreds of thousands of sensor nodes. The sensor nodes can communicate among themselves using radio signals. A wireless sensor node is equipped with sensing and computing devices, radio transceivers and power components. The individual nodes in a wireless sensor network (WSN) are inherently resource constrained: they have limited processing speed, storage capacity, and communication bandwidth. After the sensor nodes are deployed, they are responsible for self-organizing an appropriate network infrastructure often with multi-hop communication with them. Then the onboard sensors start collecting information of interest. Wireless sensor devices also respond to queries sent from a “control site” to perform specific instructions or provide sensing samples. The working mode of the sensor nodes may be either continuous or event driven. Global Positioning System (GPS) and local positioning algorithms can be used to obtain location and positioning information. Wireless sensor devices can be equipped with actuators to “act” upon certain conditions. These networks are sometimes more specifically referred as Wireless Sensor and Actuator Networks as described in (Akkaya et al., 2005).

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Overview of Wireless Sensor Network

A CPW slot loop fed Minkowski shaped fractal dielectric resonator antenna is proposed. Self similar property of fractal geometry is utilized to bring higher order modes close together to realize a wide impedance bandwidth. A comparative study of the resonant frequency behavior between the well established fractal electrical boundary antennas and fractal magnetic boundary antennas is presented to provide insight into the functionality of the proposed antenna. The comparison highlights the fact that electrical boundary lowers resonance frequency, whereas fractal magnetic boundary increases the resonant frequency. Minkowski fractal is also compared with Koch fractal and Sierpinski curve geometries. It is observed that the Minkowski fractal DRA yields the widest impedance bandwidth along with stable gain amongst the three proposed geometries. The proposed antenna exhibits a fractional bandwidth of 64% (5.52 -10.72 GHz) and a maximum gain of 4.9 dBi.

A Wideband Minkowski Fractal Dielectric Resonator Antenna

A compact triple-band H-shaped slot antenna fed by microstrip coupling is proposed. Four resonant modes are excited, including a monopole mode, a slot mode, and their higher-order modes, to cover GPS (1.575 GHz) and Wi-Fi (2.4-2.485 GHz and 5.15-5.85 GHz), respectively. Sensitivity study of the slot geometry upon the resonant modes have been conducted. The measured gains at these four resonant frequencies are 0.2 dBi, 3.5 dBi, 2.37 dBi, and 3.7 dBi, respectively, and the total efficiencies are -2.5 dB, -1.07 dB, -3.06 dB, and -2.7 dB, respectively. The size of this slot antenna is only 0.24λ0×0.034λ0, where λ0 is the free-space wavelength at 1.575 GHz, hence is suitable to install on notebook PC's and handheld devices.

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Compact Multi-Band H-Shaped Slot Antenna

Microstrip-line-fed printed wide-slot antenna with a fractal-shaped slot for bandwidth enhancement is proposed and experimentally studied. By etching the wide slot as fractal shapes, it is experimentally found that the operating bandwidth can be significantly enhanced, and the relation between the bandwidth and the iteration order (IO) and iteration factor (IF) of the fractal shapes is experimentally studied. Experimental results indicate that the impedance bandwidth, defined by - 10 dB reflection coefficient, of the proposed fractal slot antenna can reach an operating bandwidth of 2.4 GHz at operating frequencies around 4 GHz, which is about 3.5 times that of a conventional microstrip-line-fed printed wide-slot antenna. It also achieved a 2-dB gain bandwidth of at least 1.59 GHz.

Bandwidth Enhancement of a Microstrip-Line-Fed Printed Wide-Slot Antenna With a Fractal-Shaped Slot

A novel technique to reduce the size of microstrip patch antennas is proposed. By etching the patch edges according to Koch curves as inductive loading, and inserting the Sierpinski carpets into the patch as slot loading, it is experimentally found that the resonant frequency of the patch can be greatly lowered, and the higher the iteration order of the fractal shapes, the lower the resonant frequency becomes. And this property can be utilized to reduce the size of the microstrip patch antennas. It is also found that, the radiation patterns of the proposed fractal-shaped antennas maintained because of the self-similarity and centro- symmetry of the fractal shapes. The patches derived from this technique can find applications in integrated low-profile wireless communication systems.

Small-Size Microstrip Patch Antennas Combining Koch and Sierpinski Fractal-Shapes

In this article, we present a technique to miniaturize the cascaded wideband branch-line couplers using fractal-shaped geometry. As an example, four-branch couplers operated at 2.0 GHz employing Koch fractal shapes of different iteration orders have been designed successfully. By meandering the branch lines in accordance with the structures of the Koch curves, the fractal-shaped couplers of first and second iteration orders achieved 50.4% and 72.7% size reduction, respectively, with no major effect to overall performances. The technique was verified by the measurement results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 26–29, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24002

Guang-Ming Wang

Papers

Bandwidth Enhancement of a Microstrip-Line-Fed Printed Wide-Slot Antenna With a Fractal-Shaped Slot

Small-Size Microstrip Patch Antennas Combining Koch and Sierpinski Fractal-Shapes

Miniaturization of wideband branch‐line couplers using fractal‐shaped geometry