A novel miniaturised frequency selective surface (FSS) unit cell is proposed based on the Hilbert fractal and 2.5‐dimensional (2.5‐D) metallic loop. For the increase of current path, both sides of substrate are used which are connected together by four vias. The dimension of FSS unit cell is obtained as 0.041λ0 × 0.041λ0 at the frequency of 2.47 GHz. The transmission coefficient is insensitive and independent of angle and polarisation of incident wave. A prototype model of the proposed FSS is fabricated and measured for the proof of concept. It is shown that it achieves better miniaturisation relative to the FSS reported in the literature.
The characteristic mode theory gives useful insights into the physical behavior of antennas, which can be used for the design of single-feed circularly polarized antennas. For example, an antenna with any geometrical shape may be systematically modified by the characteristic mode analysis to give circular polarization. In this paper, a procedure based on the characteristic mode theory is used for the design and modification of arbitrarily shaped antennas to produce a circularly polarized radiated field at 2.45 GHz for ISM band application. By using this procedure the axial ratio of a proposed antenna has dropped to 0.05 dB without the need of employing an optimization software.
An optimized irregular planar array antenna layout with uniform excitation of antenna elements is presented for Random-LOS OTA (Random Line-Of-Sight Over-The-Air) characterization setups. A plane wave is synthesized within a cylindrical 3D test zone at 2.7 GHz, which can be scaled to mmWave frequencies. The obtained thinned array achieves a 52% reduction of the number of elements and a 45% aperture size as compared to a uniform fully populated planar array with an inter-element distance of 0.93λ, which is the optimum distance through [λ/2, λ] based on the presented cost function at this paper . The obtained maximum phase deviation and the maximum field amplitude deviation from the average field distribution in the 3D test zone of the proposed optimized chamber array antenna layout are approximately 6.4 • and 3.9 dB, respectively. The numerical computation of the radiation pattern of a 10 × 10 element uniform planar array antenna as AUT (Antenna Under Test) placed within the test zone was performed too. Results show a rather good agreement between the radiation pattern to that obtained assuming far-field conditions.
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