The invention pertains to meander line loaded antennas and, more particularly, to a crossed element antenna utilizing bow-tie meander line loaded elements.
In the past, efficient antennas have typically required structures with minimum dimensions on the order of a quarter wavelength of the radiating frequency. These dimensions allowed the antenna to be excited easily and to be operated at or near a resonance, limiting the energy dissipated in resistive losses and maximizing the transmitted energy. These antennas tended to be large in size at the resonant wavelength.
Further, as frequency decreased, the antenna dimensions increased in proportion. In order to address the shortcomings of traditional antenna design and functionality, researchers developed the meander line loaded antenna (MLA). One such MLA is disclosed in U.S. Pat. No. 5,790,080 for MEANDER LINE LOADED ANTENNA, which is hereby incorporated herein by reference. An example of an MLA, also known as a varied impedance transmission line antenna, is shown in FIG. 1. The antenna consists of two vertical conductors, 102, and a horizontal conductor, 104 wherein the horizontal conductors are separated from the vertical conductors by gaps, 106.
Meander lines, shown in FIG. 2, are connected between the vertical and horizontal conductors at the gaps. The meander lines are designed to adjust the electrical length of the antenna. In addition, the design of the meander slow wave structure permits lengths of the meander line to be switched in or out of the circuit quickly and with negligible loss, in order to change the effective electrical length of the antenna. This switching is possible because the active switching devices are always located in the high impedance sections of the meander line. This keeps the current through the switching devices low and results in very low dissipation losses in the switch, thereby maintaining high antenna efficiency.
The basic antenna of FIG. 1 can be operated in a loop mode that provides a xe2x80x9cfigure eightxe2x80x9d coverage pattern. Horizontal polarization, loop mode, is obtained when the antenna is operated at a frequency such that the electrical length of the entire line, including the meander lines, is a multiple of full wavelength as shown in FIG. 3C. The antenna can also be operated in a vertically polarized, monopole mode, by adjusting the electrical length to an odd multiple of a half wavelength at the operating frequency, as shown in FIGS. 3B and 3D. The meander lines can be tuned using electrical or mechanical switches to change the mode of operation at a given frequency or to switch frequency using a given mode.
The meander line loaded antenna allows the physical antenna dimensions to be reduced significantly while maintaining an electrical length that is still a multiple of a quarter wavelength of the operating frequency. Antennas and radiating structures built using this design operate in the region where the limitation on their fundamental performance is governed by the Chu-Harrington relation:
Efficiency=FV2Q
where:
Q=Quality Factor
V2=Volume of the structure in cubic wavelengths
F=Geometric Form Factor (F=64 for a cube or a sphere)
Meander line loaded antennas achieve the efficiency limit of the Chu-Harrington relation while allowing the antenna size to be much less than a wavelength at the frequency of operation. Height reductions of 10 to 1 can be achieved over quarter wave monopole antennas, while achieving comparable gain.
Discussion of the Related Art
The aforementioned U.S. Pat. No. 5,790,080 describes an antenna that includes one or more conductive elements for acting as radiating antenna elements, and a slow wave meander line adapted to couple electrical signals between the conductive elements. The meander line has an effective electrical length that affects the electrical length and operating characteristics of the antenna. The electrical length and operating mode of the antenna is readily controlled.
U.S. Pat. No. 6,034,637 for DOUBLE RESONANT WIDEBAND PATCH ANTENNA AND METHOD OF FORMING SAME, describes a double resonant wideband patch antenna that includes a planar resonator forming a substantially trapezoidal shape having a nonparallel edge for providing a wide bandwidth. A feed line extends parallel to the nonparallel edge for coupling, while a ground plane extends beneath the planar resonator for increasing radiation efficiency.
U.S. Pat. No. 6,008,762 for FOLDED QUARTER WAVE PATCH ANTENNA, describes a folded quarter-wave patch antenna which includes a conductor plate having first and second spaced apart arms. A ground plane is separated from the conductor plate by a dielectric substrate and is approximately parallel to the conductor plate. The ground plane is electrically connected to the first arm at one end. A signal unit is also electrically coupled to the first arm. The signal unit transmits and/or receives signals having a selected frequency band. The folded quarter-wave patch antenna can also act as a dual frequency band antenna. In dual frequency band operation, the signal unit provides the antenna with a first signal of a first frequency band and a second signal of a second frequency band.
Existing crossed element meander line antennas have some degree of shadowing and cross-coupling, especially antennas that cross-over another radiating surface. What is needed is an efficient antenna design that addresses the problems and limitations addressed herein. The improved antenna should have a symmetric radiation pattern and be able to operate in circular polarization.
In accordance with the present invention there is provided a crossed, circularly polarized, meander line loaded antenna (MLA), which utilizes pairs of bow-tie MLA elements to reduce pattern distortion caused by crossed MLA elements in prior art antennas.
It is, therefore, an object of the invention to provide a crossed MLA having a symmetric radiation pattern.
It is another object of the invention to provide a crossed MLA that can operate in a circular polarization mode.
It is an additional object of the invention to provide a crossed MLA having an improved axial ratio performance.
An object of the invention is a crossed-element, meander line loaded antenna comprising a ground plane, a dual bow-tie configuration with four triangular sections. Each of the sections has a side member substantially perpendicular from the ground plane and a triangle-shaped top member with a based end and a vertex end. The top member is disposed substantially parallel to the ground plane with the base end abutting the side member, being separated by a side gap. Each vertex end is arranged in close proximity to one another separated by a vertex gap, and there is a first connector operatively connecting a first pair of the triangular sections each at the vertex end. And, there is a second connector operatively connecting a second pair of the triangular sections each at the vertex end, wherein the first and second pair are orthogonal to each other.
A further object is a crossed-element, meander line loaded antenna, further comprising two or more capacitive flaps positioned at the side gaps. And, the crossed-element, meander line loaded antenna further comprising two or more meander line elements positioned at the side gaps.
An additional object is the crossed-element, meander line loaded antenna, wherein the top member is secured to a dielectric material. Furthermore, the crossed-element, meander line loaded antenna, wherein the side member is secured to a dielectric material.
Another object is for the crossed-element, meander line loaded antenna wherein the first and second connector are meander lines elements.
An object of the invention includes a crossed-element, circularly polarized meander line loaded antenna, comprising a ground plane and a dual bow-tie configuration with four triangular sections. Each section having a having a side member substantially perpendicular from the ground plane and a triangle-shaped top member with a base end and a vertex end. The top member is disposed substantially parallel to the ground plane with the base end abutting the side member, being separated by a side gap. Each vertex end is arranged in close proximity to one another separated by a vertex gap. There is a first connector operatively connecting an opposing first pair of the triangular sections each at the vertex end, and a second connector operatively connecting an opposing second pair of the triangular sections each at the vertex end. And, there is a first signal feed connecting to the first pair and a second signal feed connecting to the second pair, wherein the second signal feed is 90 degrees out-of-phase.