# Minkowski Island and Crossbar Fractal Microstrip Antennas for Broadband Applications
## 1 Introduction
The philosophy of fractal structure is that it can be subdivided into parts, with each part being a copy of the entire assembly, but reduced in size. One of the main benefits of the fractal structure is the increased electrical length of the antenna when compared to a conventional microstrip antenna. This property allows for the following advantages: it reduces the overall size of the antenna and produces multiple resonant bands. This benefit can be obtained due to the fractal geometry, as fractals have no characteristic size and could be treated as the composition of many copies of themselves at different scales. [PERSON] [5] pointed out that a fractal-shaped antenna demonstrates resonance compression and multi-band behavior. However, as it is underlined in [7], the fractal antenna with etched multiple slots suffers from the reduced overall gain, as a major part of the conducting strip is etched out. Many types of fractal based microstrip antennas are presented in the literature, and their promising electrical properties were already revealed, but fractal structures were introduced mainly to the upper layers (patches), while the conducting ground planes were kept as monolithic strips. [PERSON] et al. [8] and [PERSON] et al. [9] presented microstrip antennas with periodic structures on the bottom layers. The bottom surface was constructed from periodic structures, based on square patches, which allowed for enhancing bandwidth despite the miniaturization of antennas. Only a few papers discussed the electrical properties of microstrip antenna, where both the upper and the lower layers have periodic structures, as opposed to monolithic structures. [PERSON] et al. presented an antenna having upper and lower layers with periodic gaps designed in the form of isolated micro-triangles, while on the bottom ground plane has simple, periodically distributed cross strip-line gaps [10]. They obtained promising electrical properties--the working frequency bandwidth spanning from 200 MHz to 3 GHz. In our previous work, we presented a microstrip antenna with both layers designed using periodic geometry [11]. The upper and lower layers of the antenna had fractal forms, but each fractal layer had a different shape. The Minkowski and crossbar fractals were taken into consideration. In this work, the investigation of the electrical properties of fractal antennas with the following geometries was presented:  
* an antenna, in which the upper layer has fractal geometry while the lower layer has classical monolithic structure,
* an antenna, in which the upper layer is a monolithic patch but the ground is a fractal,an antenna, in which both layers (upper and lower) have fractal structures, but with the same type of fractal,  
an antenna, in which both layers have fractal structures, each with a different type of fractal. Taking into account the above demands, three kinds of antennas with fractals were investigated, i.e., crossbar fractal antennas, a Minkowski fractal antenna, and a crossbar and Minkowski fractals antenna, to recognize the impact of the type of fractal geometry on antenna properties. This also could be used to illustrate the benefits of fractal structures on the lower or upper layers and shows the level of proportional participation of each layer in the total electric properties of fractal antennas. In all cases, the entire structure of the proposed antennas measures 27.6 \(\times\) 31.8 mm\({}^{2}\). The antennas were designed with the RT/Duroid@5880 (Rogers Corporation, Killingly, CT, USA) low-loss substrate (tan\(\delta\) = 0.0009 at 10 GHz) with dielectric constant of 2.2 and thickness of 0.79 mm.