Purpose -The purpose of this paper is to describe a modified Hilbert-based fractal antenna for ultra wideband (UWB) wireless applications. Simulation results show excellent multi-band characteristics for UWB wireless applications. Design/methodology/approach -A Hilbert curve-based fractal is optimised for self-replicating, space-filling and self-avoiding properties. In the proposed design, the Hilbert curve is applied to a rectangle as an initial iteration and maintained for the later iterations. Additionally, a Yagi-like strip is removed from the second iteration of the Hilbert patch and a hexagonal portion is removed from the substrate to achieve good optimization. The antenna feed is created through a micro-strip line with a feeding section. Finally, a partial ground plane technique is used for improved impedance matching characteristics. A finite element method (FEM) is used to simulate the modified Hilbert model with commercially available Ansoft HFSS software. Findings -The proposed antenna is miniaturized (39 mm length £ 30 mm width) and has multi-band characteristics. The simulation results show that the antenna has a reflection coefficient characteristic of ,210 dB, a linear phase reflection coefficient, better than 65 percent radiation efficiency, 2.2-4 dBi antenna gain and nearly omni-directional radiation pattern properties over the UWB bandwidth (3.1-10.6 GHz). Originality/value -The antenna shows promising characteristics for the full 7.5 GHz UWB bandwidth. In addition, the performance is achieved by using laceration techniques on the Hilbert patch and substrate, respectively. A partial ground plane ensures impedance matching of 50 over full UWB bandwidth. The simulation analysis of the modified Hilbert fractal antenna design constitutes the main contribution of the paper.

Purpose -A vertically stacked, three layer hybrid Hilbert fractal geometry and serpentine radiatorbased patch antenna is proposed and characterized for medical implant applications at the Industrial, Scientific and Medical band (2.4-2.48 GHz). Antenna parameters are optimised to achieve miniaturized, biocompatible and stable transmission characteristics. The paper aims to discuss these issues. Design/methodology/approach -Human tissue effects on the antenna electrical characteristics were simulated with a three-layer (skin, fat and muscle) human tissue model with the dimensions of 180 × 70 × 60 mm 3 (width × height × thickness mm 3 ). Different stacked substrates are utilized for the satisfactory characteristics. Two identical radiating patches are printed on Roger 3,010 (ε r ¼ 10.2) and Alumina (ε r ¼ 9.4) substrate materials, respectively. In addition, various superstrate materials are considered and simulated to prevent short circuit the antenna while having a direct contact with the metallization, and achieve biocompatibility. Finally, superstrate material of Zirconia (ε r ¼ 29) is used to achieve biocompatibility and long-life. A finite element method is used to simulate the proposed hybrid model with commercially available Ansoft HFSS software. Findings -The antenna is miniaturized, having dimensions of 10 × 8.4 × 2 mm 3 (width × height × thickness mm 3 ). The resonance frequency of the antenna is 2.4 GHz with a bandwidth of 100 MHz at return loss (S11) of better than −10 dB characteristics. Overall, the proposed antenna have 50 Ω impedance matching, −21 dB far field antenna gain, single-plane omni-directional radiation pattern properties and incident power of 5.3 mW to adhere Specific Absorption Rate regulation limit. Originality/value -Vertically stacked three layer hybrid design have miniaturized characteristics, wide bandwidth, biocompatible, and stable characteristics in three layer human tissue model make this antenna suitable for implant biomedical monitor systems. The advanced simulation analysis of the proposed design constitutes the main contribution of the paper.

A new combined fractal geometry based Monopole antenna design for ultra wideband (UWB) applications is presented in this paper. This fractal structure is implemented on square and Minkowski fractal is applied to the lines of a square. Then, a Sierpinski carpet fractal is formed on the first iteration of the Minkowski fractal. The proposed antenna is miniaturized (45 mm x 45 mm) and has multi-band characteristics. Simulation results show that the presented antenna has a reflection coefficient characteristic < -15dB, 80% radiation efficiency, 4-6dBi antenna gain and omnidirectional radiation pattern properties over the UWB bandwidth (3.1 -10.6 GHz). The gain variation is due to increased directivity at higher frequencies.

Özetçe-Bu bildiride, kablosuz sağlık alanında uygulamaları için birleşik, Hilbert fraktal geometri ve serpentine şekli, yapı tabanlı mikroşerit anten tasarımı optimize edilerek sunulmaktadır. Önerilen anten minyatür 5.5 x 5.8 x 1.7 mm 3 (genişlik x uzunluk x kalınlık mm 3 ) özelliklere sahip olarak çift bant Çift bantlı (MICS 402-405 MHz ile ISM 2.4-2.48GHz) haberleşme özelliklerine sahiptir. Anten tasarımının üzerine fazladan Zirconia katmanı (superstrate) yerleştirilmesi sonucunda biyouyumluluk sağlanmış ve implantın insan dokusu ile direk temasını engellenmiştir. Implant anten üç katmanlı doku modeline (deri, yağ ve kas) yerleştirilerek benzetim yolu ile analiz edilmiştir. Benzetim çalışmaları göstermiştir ki tüm MICS bant genişliği için sunulan anten -13dB'den daha iyi geri dönüş kayıp özelliği, tüm yönlü ışınım örüntü özellikleri ve insan vücüdunda kullanıma uygun özgül soğurma oran özellikleri göstermektedir. Anahtar Kelimeler -implant anten; minyatür yapı; çift bantlı; biyouyumlu.Abstract-In this paper, the combination of Hilbert fractal geometry and the serpentine shape based microstrip implant antenna design proposed and optimized for wireless medical applications. The proposed antenna is miniaturized 5.5 x 5.8 x 1.7 (width x height x thickness mm 3 ) and operates for dual band (MICS 402-405 MHz ile ISM 2.4-2.48GHz) operations. Superstrate is applied on top of the antenna to avoid a direct contact with the metallization and achieve biocompatibility. Implant antenna is simulated in three layer tissue (skin, fat and muscle) model. Simulation results show that the presented antenna has a reflection coefficient characteristic better than -10dB, omni-directional radiation pattern and acceptable specific absorption rate values for human body.

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