# Minkowski Island and Crossbar Fractal Microstrip Antennas for Broadband Applications
## 4 The Minkowski Island Fractal Geometry  
Minkowski gasket is one of the earliest structures introduced into the antenna technique and is the most promising structure. [PERSON] et al. presented Minkowski fractals based microstrip antenna allowing for covering five different wireless standards [7]. Geometrical structure of presented antenna was loaded with a nearly square shaped dielectric resonator allowing for obtaining constant gain at all discrete frequencies. [PERSON] et al. [15] presented fractal antenna structure, based on Minkowski squares, operated at four resonant frequencies for WiMAX systems while [PERSON] et al. [16] described Minkowski fractal structure at three frequencies for WiMAX, WLAN and HiperLAN applications. [PERSON] et al. showed that fractals are able to enlarge the frequency antenna operation if their structures are self-similar having the same basic appearance at every scale [17]. [PERSON] et al. showed the geometry of Minkowski fractal allowing for obtaining the wide bandwidth [3].  
The iterative-generation of Minkowski fractals was discussed in [5; 18; 19]. [PERSON] [20] and [PERSON] [21] noted that resonant frequencies can be modified by adjusting the level of fractal iteration. In this investigation, the geometry of unit cell with the first iteration of Minkowski island, as depicted in Figure 4a, will be considered. It should be emphasized that the antenna behavior with increasing fractal iterations yields to worse electrical properties, resulting in decreasing broadbandedness of the antenna.  
The Minkowski fractal based antenna was analyzed only for one configuration--the patch is a solid strip while the ground layer is composed of 7 \(\times\) 6 square unit cells with Minkowski fractals, separated by slot gaps and placed in a periodic arrangement. This configuration of an antenna has been presented in Figure 4b.  
In this work, the configuration when the upper layer is based on Minkowski fractal was not analyzed because of the problem with feeding. With the dimensions of Minkowski fractal (Figure 4a), the feeding line for the upper layer would have not the impedance of 50 \(\Omega\). [PERSON] et al. [10] adapted the feeding technique to Minkowski fractal on the upper layer, but, in their solution, Minkowski fractal has modified geometry. Such modification results in different antenna geometry than that analyzed in this paper.  
The reflection coefficients (S11 [dB]) for the above-mentioned configuration of antenna with Minkowski island fractal was depicted in Figure 5.  
Figure 4: **(a)** The Minkowski island fractal based elementary unit cell of the antenna (dimensions are in mm); **(b)** geometry of the antenna with Minkowski fractal on the lower layer.  
As shown in Figure 5, the plot of S11 demonstrates good reflection properties of the antenna in the frequencies from 4 to 13.5 GHz and above 15.7 GHz. However, the band from 13.5 to 15.7 GHz in unacceptable due reflection properties being too high. This disadvantage will be reduced or mitigated in the final version of the antenna, with the patch based on a crossbar fractal.