In this article, a novel concept for mutual coupling reduction between antenna elements is proposed at 2.45 GHz for Wi-Fi applications. A reject band filter (RBF) is used in order to reduce the mutual coupling between two monopoles for multi-input multi-output (MIMO) systems. The proposed RBF inclusions are developed to have zero refractive index response over a specific frequency band. The inclusions considered here are composed of open-loop resonators; each one with the same iteration level of Minkowski-like pre-fractal structures coupled with an open-stub transmission line to increase the band selectivity. The inclusions are inserted between λ/2-spaced monopole elements at 2.45 GHz. A significant mutual coupling reduction is realized by incorporating only two RBF cells. Such effective response is attributed to the electromagnetic wave cloaking at 2.45 GHz using the developed RBF inclusions. An extensive theoretical study using both numerical and analytical methods is invoked to obtain the best performance of the proposed MIMO antenna structure. Finally, the experimental and numerical results are agreed excellently.

In this paper, an Ultra-Wide-Band (UWB) printed monopole antenna based Hard Surface (HS) is proposed for RF energy harvesting to serve the application of the Internet of Things (IoT). The proposed antenna is constructed of a monopole of an open mouth flower patch mounted on an FR4 substrate and followed by an HS array. The antenna is backed with a partial ground plane to enhance the antenna bandwidth. The stability in the antenna radiation pattern over the entire frequency band is achieved by introducing three rows of the proposed HS based on H-Resonators (HS-HR) next to the patch edge. Such arrays provide an Omni directional antenna at several frequency bands that suit the application of RF energy harvesting. The array of the proposed HS-HR provides high electromagnetic impedance within the frequency band of interest toward the patch length. Numerical simulations are accompanied using CST MWS and HFSS software packages to evaluate the antenna performance. Finally, the related measurements to the antenna performance and RF harvesting are conducted at 2.45GHz. It is found that the proposed antenna provides a conversion efficiency of 35% with an acceptable gain-bandwidth product.

Multiband bandpass filters (BPFs) are one of the core elements in the multi-services wireless communication systems. For this purpose, this paper presents a design of a compact multiband microstrip BPF design based on fractal open loop configuration. The proposed filter structure is composed of an array of equal side length open-loop resonators; each with different fractal iteration level. More specifically, the modified Minkowski fractal geometry has been adopted to be applied to the conventional openloop rectangular resonator. The resulting filter configuration has an array of different open-loop structures corresponding to various iteration levels. The simulation of the presented filter is performed using the EM Sonnet software package environment. The proposed filter is printed on a substrate of dielectric constant is 10.8 with thickness 1.27 mm. A filter structure with three resonators having different fractal iteration levels offers a triple band frequency response around 3.05 GHz, 2.05 GHz, and 1.68 GHz. Each of the three resonant bands is attributed by a distinct resonator according to the iteration levels. Additional resonant bands can be realized using extra loops with higher iteration levels.

This paper suggests a novel 1D Reject Band Filter (RBF) array to prevent the radiation leakage from portable devices around 2.45 GHz. The proposed RBF array is constructed from eight-unit cell elements mounted on the same side of an FR-4 substrate of 1.5-mm thickness. Each two adjacent unit cells are separated with 2 mm. The individual unit cell design is based on fractal-based open-loop resonators of a modified first iteration Minkowski configuration. Such configuration is coupled with an open-stub transmission line to increase the selectivity of the filter stopband response at the frequency of interest. The unit cell performance is evaluated numerically and analytically, and then compared against measurements. Next, the optimal RBF array is fabricated and simulated to evaluate the Specific Absorption Rate (SAR) at 2.45 GHz. The SAR effect on the human thigh tissue is studied numerically to show an excellent reduction from 0.912 to 0.352 W/kg. Finally, the field strength before and after introducing the proposed array underneath a laptop computer, just below the Wi-Fi antenna, is measured and found to be reduced from 497.1 to 171.8 mV/m.

In this paper, a combination of the dual-mode technique and the fractal based resonator geometry has been adopted to design a compact band reject filter. The proposed filter structure relies mainly on that of the triangular patch resonators with an embedded slit structure. The Koch fractal geometry has been applied to the uncoupled side lengths of the triangular patch resonator. The filter structure has been modeled, and its performance is evaluated using the commercially available method of moment (MoM) based simulator, Sonnet. Results imply that the resulting dual-mode response seriously affected by the uncoupled side lengths of the triangular patch resonator. The consequences of varying the Koch indentation angle and the slit length on the resulting filter performance have been explored. Simulation results have confirmed the validity of the proposed resonant structure to realize a compact dual-mode stopband microstrip filter. 

 There is a continuing concern over the risks associated with the use of microwave ovens because of the probable effects of the radiation leakage on the health of the individuals. In this paper, a new microstrip bandstop filter BSF is presented, designed and measured as an attempt to reduce the radiation leakage from the domestic microwave ovens operating at 2.45 GHz. The proposed BSF is composed of fractal based open-loop resonators coupled with an open-stub transmission line. The open-loop resonators are in the form of modified Minkowski fractal geometry of the 1st iteration. The open stubs have been adopted to increase the selectivity of the filter stopband response. The suggested filter is designed at 2.45 GHz. Modeling and performance assessments of the proposed filter have been evaluated by means of the computer software technique CST Microwave Studio and the Sonnet EM simulator. Simulation results reveal that the modeled filter offers stopband response with high selectivity. A prototype of the proposed filter is fabricated. The size limitations of the microwave oven opening width have been taken into account. Good agreement has been found between measured and simulated results. Four arrays of such a filter have been implemented to cover the microwave oven door frame taking into consideration the opening dimensions such that it well fit it. Measured radiated electric fields from the oven show that it considerably reduces the leaked radiation. By suitable choice of substrate material and carrying out the required dimension scaling, the proposed design idea is flexible and can be generalized for use with a wide variety of microwave equipment in which microwave leakage represents a serious issue.