Abstract
We demonstrate a concept for a large enhancement of the directivity and gain of readily available cm- and mm-wave antennas, i.e., without altering any property of the antenna design. Our concept exploits the high reflectivity of a Bragg reflector composed of three bilayers made of transparent materials. The cavity has a triangular aperture in order to resemble the idea of a horn-like, highly directive antenna. Importantly, we report gain enhancements of more than 400% in relation to the gain of the antenna without the Bragg structure, accompanied by a highly directive radiation pattern. The proposed structure is cost-effective and easy to fabricate with 3D-printing. Our results are presented for frequencies within the conventional WiFi frequencies, based on IEEE 802.11 standards, thus, enabling easily implementation by non-experts and needing only to be placed around the antenna to improve the directivity and gain of the signal.
Highlights
Centimeter- and millimeter-wave antennas have attracted extensive research attention during recent decades due to their vast amount of indoor and outdoor applications
We show that quasi-cylindrical Bragg reflector structures can be placed around a dipole antenna to produce directional radiation patterns
Our concept can be scaled to tune the working wavelength according to the requirements, we focused our attention here on a system working at the Unlicensed National Information Infrastructure (U-NII) frequency band, from 5.15 to 5.825 GHz, defined by the IEEE 802.11 standard [22]
Summary
Centimeter (cm)- and millimeter (mm)-wave antennas have attracted extensive research attention during recent decades due to their vast amount of indoor and outdoor applications. Important are the quarter-wavelength Bragg mirrors, commonly called quarter-wave-stacks (QWSs), consisting of alternating layers with thicknesses (for each material) of one-quarter of the working wavelength [19,20], which completely reflect the incident electromagnetic waves These reflectors can be implemented to develop cavity enhanced antennagain [21], less attention has been paid to the use of Bragg mirrors to enhance the directivity and gain of readily available antennas. For βd − φ = mπ, with m as a positive integer number, we have maximum (minimum) values for the reflection (transmission) coefficient, which indicate constructive (destructive) interference for the reflected (transmitted) fields along the structure These results show how to tune and tailor the thicknesses based on the optical properties of the elementary components of our design, as will be shown below.
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