Importance

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Abstract

A first spiral-mode microstrip (SMM) antenna has an antenna element situated over and spaced from a parallel ground plane. The antenna element is a frequency-independent planar structure having a plurality of spiraling arms extending outwardly in a plane from a central portion, the arms having respective feed points to excite the spiral modes. Of particular significance, a shorting mechanism connects one or more arms to the ground plane element for influencing the shape of the electromagnetic radiation pattern. A second embodiment of the SMM antenna is constructed as the first, but has a center feed and an off-center feed, and further comprises shorting mechanisms situated well within the periphery of the antenna element. A third embodiment of the SMM antenna is constructed similar to the first, but has a concentric gap situated within the arms so that there is, in effect, a first antenna element having a first plurality of arms and a second concentric antenna element having a second plurality of arms. Capacitors, inductors, and electrical/mechanical switches can be included in the shorting mechanism to facilitate multi-mode, multi-function, and/or broadband operations. By recognizing that the SMM antenna is equivalent to a slot antenna or a magnetic current antenna, a super-thin fourth SMM antenna can be constructed and is a fourth embodiment of the present invention. In this super-thin antenna, the distance between the antenna element and the ground plane is less than or equal to 0.03 of the geometric mean wavelength of the operating band.

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First Claim