A novel Koch-like fractal curve is proposed to transform ultra-wideband (UWB) bow-tie into so called Koch-like sided fractal bow-tie dipole. A small isosceles triangle is cut off from center of each side of the initial isosceles triangle, then the procedure iterates along the sides like Koch curve does, forming the Koch-like fractal bow-tie geometry. The fractal bow-tie of each iterative is investigated without feedline in free space for fractal trait unveiling first, followed by detailed expansion upon the four-iterated pragmatic fractal bow-tie dipole fed by 50-coaxial SMA connector through coplanar stripline (CPS) and comparison with Sierpinski gasket. The fractal bow-tie dipole can operate in multiband with moderate gain (3.5-7 dBi) and high efficiency (60%-80%), which is corresponding to certain shape parameters, such as notch ratio , notch angle , and base angles of the isosceles triangle. Compared with conventional bow-tie dipole and Sierpinski gasket with the same size, this fractal-like antenna has almost the same operating properties in low frequency and better radiation pattern in high frequency in multi-band operation, which makes it a better candidate for applications of PCS, WLAN, WiFi, WiMAX, and other communication systems.

Abstract-Koch-like fractal curve and Sierpinski Gasket are syncretized in minor-main way, forming so called Koch-like sided Sierpinski Gasket multifractal dipole (KSSG). Some iterative combinatorial cases of the two monofractals K i S j KSSG have been investigated in free space without feedline for revealing the assumed multifractal property. Then a pragmatical coplanar stripline (CPS) fed K 4 S 1 KSSG multifractal bow-tie dipole with dimension of 61.1 mm × 34.75 mm was designed, fabricated and measured. Six matched bands (S 11 < −10 dB) with moderate gain (2 dBi-6 dBi) and high efficiency (80%-95%) are obtained within band 1.5 GHz-14 GHz, of which f 1 = 2.137 GHz (1.978-2.287 GHz, 309 MHz, 14.46%, PCS1900 + IMT2000 + UMTS), f 2 = 4.103 GHz (3.916-4.2 GHz, 374 MHz, 9.12%, WiMAX), f 3 = 5.596 GHz (5.499-5.679 GHz, 180 MHz, 3.22%, WLAN + WiMAX) are commonly used. Gain patterns of these bands are all almost omnidirectional in Hplane (Phi = 0 • , XOZ) and doughnut-shaped in E-plane (Phi = 90 • , Y OZ), which suggests that K 4 S 1 KSSG operates as a half-wavelength dipole. It behaviors like the main fractal in low frequency and resembles the minor one in high frequency. The consistent results of simulation and measurement have evinced the multifractal antennas' peculiar properties and superiority over its monofractals in impedance uniformity, gain pattern, efficiency and dimension. So it is attractive to PCS, UMTS, WLAN, WiFi, WiMAX and other communication systems.

A Koch-like sided Sierpinski hexagonal carpet multifractal monopole antenna fed by coplanar waveguide with a Koch-like edged fractal ground is designed, fabricated and measured, which covers WLAN, WPAN, WiFi and WiMAX bands simultaneously. The multifractal monopole has ideal dipole-like gain patterns, which are omnidirectional in the H-plane (Phi = 0°, XOZ) and doughnut-shaped in the E-plane (Phi = 90°, YOZ) with considerable gain (2.0-5.11 dBi) and high efficiency (90-97%), of which f 1 = 2.5 GHz (|S 11 | = − 11.6 dB, WLAN + WiMAX), f 2 = 3.5 GHz (|S 11 | = − 15.5 dB, WiMAX), f 3 = 5.5 GHz (|S 11 | = − 15.5 dB; WLAN + WiMAX) are generally useful. The multifractal monopole is superior compared to other designs in bandwidth, directivity, efficiency, polarisation and dimension. It is a very attractive candidate for applications mentioned above and other fixed or mobile wireless multiband communication systems.

Abstract-Koch-like fractal curve and Sierpinski Gasket are syncretized into a novel Sierpinskized Koch-like sided bow-tie (SKLB) multifractal in superior-inferior way. A K 4 S 4 SKLB multifractal dipole fed by a linearly tapered microstrip Balun is designed, simulated, fabricated and measured. The well consistent results from measurement and experiment corroborate validity of design and the multifractal antenna's superiority and advantages over its monofractal counterparts in impedance, bandwidth, directivity, efficiency, and dimension. Six good matched bands (S 11 ≤ −10 dB) with moderate gain (2.12 dBi-9.55 dBi) and high efficiency (87%-97%) are obtained within band 1.5 GHz-14.5 GHz, of which f 1 = 1.92 GHz, f 2 = 3.94 GHz, and f 3 = 5.09 GHz are generally useful. The multibands are all almost omnidirectional or quasi-omnidirectional in H-plane (P hi = 0 • , XOZ) and doughnut-shaped or dented doughnut-shaped in E-plane (P hi = 90 • , Y OZ). So it is an attractive candidate for applications like PCS, IMT2000, UMTS, WLAN, WiFi, WiMAX and other fixed or mobile wireless multiband communication systems.

Abstract-Circularly arced Koch fractal curve (CAKC) is originally proposed. Then, a novel wire dipole is formed with K i -iterated CAKC. The dipole is experimentally studied for fractal electrical characteristics revealing. It manifests many unique properties, such as multiband resonance at odd times of half-wavelength. In particular, it unprecedentedly presents normal mode (0.5 · λ) and axial mode (1.5 · λ) simultaneously. Thus, K 2 CAKC wire is configured into folded monopole with circular disc ground for omni-directional and directive radiation. Five matched bands (|S 11 | ≤ −10 dB) are obtained within 1 GHz-10 GHz, of which f 1 = 1.31 GHz, f 2 = 3.14 GHz, f 3 = 3.63 GHz, f 4 = 4.65 GHz, and f 5 = 7.71 GHz. Compared with straight wire monopole (0.25 · λ), this fractal monopole shows 31% height reduction. It has dipole-like patterns at f 1 and f 2 , endfire patterns at f 3 and f 4 with high gain (10 dBi), and off-endfire patterns at f 5 . Moreover, the fractal antenna possesses compactness, lightweight, simplicity, and low cost. So, it is an attractive candidate for multiband and multifunction antennas, such as satellite antennas, of which omnidirectional normal mode and directive axial mode are needed for beaconing and communication respectively.