Fractal geometry has been proven to be useful in several disciplines. In the field of antenna engineering, fractal geometry is useful to design small and multiband antenna and arrays, and high-directive elements. A historic overview of the most significant fractal mathematic pioneers is presented, at the same time showing how the fractal patterns inspired engineers to design antennas.

Fractal antennas: An historical perspective

Quadrature detection coils–a further √2 improvement in sensitivity

In this paper, a pentagon slot inside fractal circular patch microstrip resonator to design compact antenna over partial ground plane is introduced using 3rd iteration of adopted fractal geometry. This antenna is modeled on FR4 substrate with a size of (20 x 18) mm2, thickness of 1.5mm, permittivity of 4.3 and loss tangent of 0.02. The used type of feeding is microstrip line feed. It is designed to operate at wide frequency range of (4.5-9.3) GHz at resonant frequencies of 5.7GHz and 7.9GHz with impedance bandwidth of 4.8 GHz. Both lengths of ground plane Lg and width of feed line Wf are optimized in order to acquire optimum bandwidth. The simulated return loss values are -33 and -41 dB at two resonant frequencies of 5.7 and 7.9 GHz with gain of 3.2 dB. The simulated results offered noteworthy compatibility with measured results. Also, the proposed wideband microstrip antenna has substantial compactness that can be integrated within numerous wireless devices and systems.

https://metaconferences.org/aemjnew/index.php/AEM/article/download/806/389

Miniaturized Wideband Microstrip Antenna for Recent Wireless Applications

This paper presents a social spider optimization (SSO) design of a small-size microstrip antenna. Two antenna miniaturization techniques, based on the use of a Koch fractal contour and a shorting post (connecting the patch to the ground plane), are combined to enable a major size reduction. The antenna is inset fed by a microstrip line. The developed SSO algorithm is used to find out the best radius and position of the shorting post and the length of the inset feed, to achieve the desired resonant frequency with good impedance matching. Antenna prototypes have been fabricated and measured. The good agreement obtained between numerical simulation and experimental results has validated the design procedure. Compared with a conventional rectangular patch, the antenna resonance frequency is reduced from 2.45 GHz to 730 MHz, which corresponds to a remarkable miniaturization of about 70%. The proposed antenna is suitable for applications in the 700-800 MHz frequency range, such as 4G mobile communication systems.

/pdf/miniaturization-of-a-microstrip-patch-antenna-with-a-koch-5dyu7ihndc.pdf

Miniaturization of a Microstrip Patch Antenna with a Koch Fractal Contour Using a Social Spider Algorithm to Optimize Shorting Post Position and Inset Feeding

This letter presents a wideband high performance 45° linearly polarization 8 × 8-slot array antenna. The gap waveguide technology is utilized to realize the proposed antenna, so that the electromagnetic (EM) leakage among the metallic blocks can be cancelled. 2 × 4-slot subarrays are used to construct the array antenna. An additional cavity power divider layer is inserted between the layers of original cavity power dividers and radiation slots to balance the amplitude and phase distributions in wideband frequency band. This suppresses the grating lobes. Triangular blocks are loaded in the new cavity power divider layer to confine the EM field distribution, thereby improving cross-polarization discrimination (XPD). For demonstration, a prototype antenna covering 5G millimeter-wave (mmW) NR bands of 257, 258, and 261 is design, fabricated, and measured. Measured results show that an impedance bandwidth of 23–30 GHz (| S 11|<−10.5 dB) is achieved. Within this frequency band, the peak gain and antenna efficiency are more than 24.6 dBi and 76.3%. In addition, the sidelobe level (SLL) of lower than –25.8 dB and XPD of better than 30.2 dB are also obtained over the same frequency band.

/pdf/wideband-45-linearly-polarized-slot-array-antenna-based-on-paa7qg0d5x.pdf

Wideband 45° Linearly Polarized Slot Array Antenna Based on Gap Waveguide Technology for 5G Millimeter-Wave Applications

In this paper, we investigate a new printed antenna based on the 2D image of a fractal tree-leaf geometry by studying the effect of the irregular boundary of the proposed antenna on its radiation characteristics. Both the impedance matching properties and the radiation patterns of the antenna are studied over the frequency band 1–6 GHz. Four configurations are designed by increasing the complexity of the structure, which ranges from iteration 0 to iteration 3. The fractal properties of the proposed tree-leaf antenna are then compared to those of a conventional fractal antenna with smooth edges. Following this, the proposed antennas are fabricated and characterized experimentally. Finally, results are analyzed and discussed, and a practical application for this new type of antennas is proposed.

/pdf/investigation-of-a-random-fractal-antenna-based-on-a-natural-2jicvhm2sb.pdf

Investigation of a Random-Fractal Antenna Based on a Natural Tree-Leaf Geometry

This paper presents a design of a low-profile high gain aperture array antenna for 5G-Network communication applications (Ka-band). The antenna is comprised of a slotted waveguide array with an integrated wideband feed, and its low-profile makes it a good candidate as a replacement of a reflector, a flat lens or a reflectarray. The array is designed by using a waveguide antenna with 10 slots and a single feed. The waveguide antenna is proposed as a unit element of the aperture array. The prototype of a 4 10 waveguide array antenna has been simulated by using the EM solver "HFSS". The array is excited by using a wideband 4:1 power divider. The aperture array achieves an impedance bandwidth of 70.75% by using matching networks, a low side lobe level and a high gain at an operating frequency of 30 GHz, which is further enhanced by using a dielectric superstrate layer.

Wideband Low-Profile Aperture Antenna for 5G-applications Comprising of a Slotted Waveguide Array and an Integrated Corporate Feed

In this work, a printed antenna based on 2D-images of a fractal liquid jet has been designed and analyzed numerically in order to study the effect of the irregular-fractal boundary of the patch on the antenna performances. It had been carried out to compare the fractal antenna properties to those of a rectangular one with straight edges. Hence, the return loss and gain evolutions have been presented over the frequency band 1-20 GHz. A similar analysis has been carried out for radiation patterns and surface current densities at resonance frequencies.

Numerical Analysis of Radiation Properties of 2D-Irregular Fractal-jet Printed Antenna

Novel low-cost phase shifter that hybridize stepwise and continuously variable phase shifting mechanisms are presented in this work. A combination of straight and curved waveguides is used to realize the step-wise phase shifts, while the variable phase shifts are achieved by inserting one or more layers of metallic vias in the waveguide to achieve a differential phase up to 90°. An alternative scheme, which achieves the phase shift in the entire 0° to 360° range by mechanically changing the length of a telescopic guide, is also described.

Novel Low-cost Phase Shifters for Millimeter Wave Applications

Integral-equation approaches are among the solvers that can be used to analyse RF fields in MRI scanners, in particular when the human body is divided into a collection of homogeneous objects. This solver can be relatively intensive in terms of computation time and memory if the full solution is rerun everytime minor changes are considered in the MRI antennas. In this work, an efficient solving tool based on a nesting approach is proposed. The idea consists of avoiding recomputation of all the equivalent currents inside the body. A validation is provided for a simple structure with a commercial solver (CST); then by using a developed in-house code, the magnetic field inside the brain is shown when a birdcage antenna is used around the human head.

Donia Oueslati

Papers

Investigation of a Random-Fractal Antenna Based on a Natural Tree-Leaf Geometry

Wideband Low-Profile Aperture Antenna for 5G-applications Comprising of a Slotted Waveguide Array and an Integrated Corporate Feed

Numerical Analysis of Radiation Properties of 2D-Irregular Fractal-jet Printed Antenna

Novel Low-cost Phase Shifters for Millimeter Wave Applications

A nesting approach for the numerical analysis of MRI birdcage antennas in the presence of the human head