Abstract-This paper critically reviews the electromagnetic advantages of altering the dielectric substrate section of the antenna as opposed to the conducting elements. Changing the dielectric has been used to improve the bandwidth, efficiency and gain of antennas. Heterogeneous substrates have also been employed to lower the effective permittivity, suppress surface waves for high indexed substrate materials and reduce mutual coupling. In the second half of this paper, 3-D printing has been used to create substrates with reduced material consumption for a lightweight flexible wearable antenna.
The polarisation transforming properties of a compact frequency selective surface (FSS) are reported. Although known designs made with meander lines employ several cascaded surfaces with many interconnects, the design methodology presented uses a single planar surface of very closely arrayed metallic meander lines impedance loaded with rectangular metal patches. A simulated axial ratio of ≤ −3 dB was obtained over a 40% bandwidth, from 2.10 to 3.2 GHz and optimised for 2.75 GHz. Simulation of normal and oblique incidence in both planes of polarisation shows a ± 30°wide range of angles of incidence for polariser performance. A unit cell of the FSS circular polariser is λ o /12 in size at the optimised operating frequency. The FSS circular polariser was manufactured and attached to a horn antenna aperture and measurement confirmed axial ratio performance.
Figure 4 Measured return loss against frequency for antenna 2; h s 3.2 mm. Other parameters are the same as in Figure 2 annular-ring microstrip antenna with a regular ground plane Ž excited at the TM mode only about 8% obtained from 21
Recei¨ed 2 March 2001ABSTRACT: Theory and measurements are presented to show that careful shaping of antenna metalization can be used to design TEM horn antennas for ultra-wideband applications in¨ol¨ing high-fidelity impul-si¨e electromagnetic fields. The effect on the radiated pulse, spectral bandwidth, and transfer function is discussed. A numerical time-domain formulation is described to compute the impulsi¨e radiated far-field wa¨eform, and some experimental results are included to indicate the usefulness of the technique. The ringing action of the antenna is recognized as the crucial parameter constraining the usefulness of the design.
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