We examine a rectangular cavity resonator method to accurately characterize the complex permittivity of dielectric materials over a wide frequency range of 1–5 GHz by exploiting the fundamental mode and higher-order TE<sub>(1,0,<i>l</i>)</sub> modes. For this purpose, a rectangular waveguide is coupled with a cavity resonator through a large inductive aperture. The permittivity characterization at both even and odd TE<sub>(1,0,<i>l</i>)</sub> modes enables continuous determination of the permittivity over operating frequencies. The characterization of the permittivity for even TE<sub>(1,0,<i>l</i>)</sub> modes suffers from potential errors due to the displacement of materials. This paper also proposes a method to compensate for these errors and improve the accuracy in the even modes. The experimental results of the fabricated cavity are presented using different materials (frequency-independent and frequency-dependent). The measured complex permittivity results show a good agreement with the reported results over a wide bandwidth available in the literature.
This paper presents a design study of a shark-fin antenna for future railway communications. Three specific bands are considered here as LTE-R (700 MHz), LTE (2100 MHz), and Lower 5G band (3500 MHz). A 3-D metallic structure using the 3D printing technique has been designed and fabricated for the consideration of the required bands. The volume size of the antenna element is 163 × 61.9 × 10 mm 3. The multi-physical simulations in terms of the smooth air flow and lower drag coefficient are performed for analyzing the need of shark-fin radome cover. More than 70 MHz bandwidth was observed for the LTE-R band and also a wide band response from 1.4 GHz to 4.2 GHz was observed that cover the required bands well, i.e., the LTE, and Lower 5G band. The proposed shark-fin antenna results in the expected omnidirectional radiation pattern in the horizontal plane, with the radiation efficiency of 71.7%, 92.6%, and 96.4% in the railway environment for the LTE-R, LTE, and Lower 5G band frequency, respectively.
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