High gain planar dipole antenna with decade gain-bandwidth

Description (excerpt)

GOVERNMENT INTEREST The invention described herein may be manufactured, used and licensed by or for the U.S. Government without the payment of royalties thereon. BACKGROUND OF THE INVENTION Field Embodiments of the present invention are directed to antennas and in particular to a high gain planar dipole antenna with decade gain bandwidths. Description of Related Art A dipole antenna is a canonical antenna and can be designed to function as a narrowband or a wideband antenna. The most wideband planar dipole today is the bowtie dipole which has a typical impedance bandwidth, defined by its voltage standing wave ratio (VSWR) being less than 2, ratio of 4:1 (e.g., the crossing points for the VSWR versus frequency are frequencies f 1 and f 2 whose ratio f 2 /f 1 is 4:1). Bowties are often used for wideband applications given their omni-directional radiation pattern and backed by a ground plane for directional applications; however, the gain-bandwidth, defined as the bandwidth over which the gain remains continuously greater than some value, falls apart after the first octave leaving the last octave of the 4:1 impedance bandwidth limited in its directional application. Thus, improvements for a high gain planar dipole antenna are desired. BRIEF SUMMARY OF THE INVENTION I provide a novel wideband planar dipole with high gain planar dipole antenna with decade gain bandwidth. This novel antenna has five times the gain bandwidth compared to the standard wideband planar bowtie dipole. According to an embodiment, a high gain planar dipole antenna with decade gain-bandwidth includes a substate having a front surface and a rear surface. The front surface has a dipole that includes two poles connected to one another in a symmetric arrangement about an imaginary line along a plane which lies with a feed point of the antenna. Each pole includes: a terminal section connected to the feed point; a half circular resonator section behind and connected to the terminal section; a choke section having a constant cross-sectional width behind and connected to the half circular section; and an asymmetric oval resonator section behind and connected to the choke section. The rear surface has a cross bar that essentially runs coincident to the imaginary line; and a pair of tuning stubs provided on each side of the cross bar. The substate, in some implementations, may be a printed circuit board formed of conductive front and rear surfaces isolated by a dielectric material. The substate may be 0.031 or 0.062 inches thick as a non-limiting example. The substrate can have one or include one or more mounting holes. The half circular resonator sections may be judiciously configured around a frequency threshold, f h , where, for input frequencies above the frequency threshold, the half circular resonator sections are the dominant resonators of the dipole. The frequency threshold, f h , can be defined as: f h = c 2 ⁢ d s , where d s is the diameter of the half circular resonator section and c is the speed of light in vacuum. The dimensions of the antenna may be such that f h is approximately 7.3 GHz, in a non-limiting embodiment. The asymmetric oval resonator sections may have an oblate oval shape. They are configured to ensure constructive interference of electrical currents in a depth direction thereof, normal to the substrate's front and rear surfaces. For instance, they may be formed of conjoined portions of different sized/shaped portions of two cojoined ellipses which are oriented orthogonal to each other. The choke sections provide an electrically conductive path between the half circular sections and the asymmetric oval resonator sections. They may be configured to balance the impedance response of the antenna and preventing higher order multi-pole modes from being excited over the operational band of the antenna, and to ensure that the half circ