Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
2001-05-31
2002-03-19
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S797000, C343S795000
Reexamination Certificate
active
06359599
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to meander line loaded antenna and, more particularly, to multi-element antennas and arrays of such antennas, and more specifically to a scanning phased array MLA with circular polarization.
BACKGROUND OF THE INVENTION
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 allow the antenna to be easily excited, and to operate at or near resonance. This limits the energy dissipated in resistive losses, and maximizes the transmitted energy. This type of antenna tends to be large in size at the resonant wavelength. Further, as frequency decreases, antenna dimensions increase in proportion.
In order to address the shortcomings of traditional antenna design and functionality, the meander line loaded antenna (MLA) was developed. One such antenna is disclosed in U.S. Pat. No. 5,790,080, entitled MEANDER LINE LOADED ANTENNA hereby incorporated by reference. One type of MLA described in this prior art patent was for two spaced-apart vertical conductors attached to a ground plane, and a horizontal conductor located across the top of the vertical conductors. The vertical and horizontal conductors are separated by gaps, one or both of which are bridged by meander lines.
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 with negligible loss. This is done 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 resulting in very low dissipation losses in the switch, and high antenna efficiency.
The simple, basic MLA can be operated in a loop mode that provides a “figure eight” coverage pattern. Horizontal polarization loop mode, may be obtained when the antenna is operated at a frequency wherein the electrical length of the entire line, including the meander lines is a multiple of full wavelength. 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 operating frequency. The meander lines can be tuned using electrical or mechanical switches to change the mode of operation at a given frequency, or to switch the frequency in a given mode.
The MLA allows the physical dimensions of antennas to be significantly reduced, while maintaining an electrical length that is still a multiple and radiating structures of a quarter wavelength. Meander line loaded antennas achieve the efficiency limit of the Chu-Harrington relationship although the antenna size is much less than a wavelength at the frequency of operation. Height reductions of 10 to 1 can be achieved with comparable gain over quarter wave monopole antennas. The existing MLA antennas are narrow band antennas. Although the switchable meander line allows the antennas to cover wider frequency bands, the instantaneous bandwidth is narrow.
The meander line loaded antenna, as well as antennas in general, have certain limitations when used in arrays. Currently, array antennas are very expensive because each antenna receives its own, separate signal. These signals, typically, are generated by using an external corporate feed network. These limitations are further magnified in the case of phased array antennas that achieve directional control by varying the phase of the transmission signal between different array elements, thus requiring phase control for each element.
DISCUSSIONS OF THE RELATED ART
The aforementioned U.S. Pat. No. 5,790,080 describes an antenna that includes one or more conductive elements that act as radiating antenna elements and a slow wave meander line that couples 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. 5,943,011 entitled ANTENNA ARRAY USING SIMPLIFIED BEAM FORMING NETWORK discloses an example of an antenna array, or multi-element antenna and the feed network used for steering signals transmitted or received through the array. The signals coupled to and from each antenna element are adjusted in phase by a network of radio frequency (RF) hybrid devices.
U.S. Pat. No. 5,144,319 entitled PLANAR SUBSTRATE FERRITE/DIODE PHASE SHIFTER FOR PHASED ARRAY APPLICATIONS is an example of a phase shifter that can be used for an individual antenna element within an array, and shows the use of this shifter for each antenna element of a phased array.
U.S. Pat. No. 4,010,474 entitled TWO DIMENSIONAL ARRAY ANTENNA discloses a phase control network for the elements of a two dimensional array.
U.S. Pat. No. 5,949,303 entitled MOV ABLE DIELECTRIC BODY FOR CONTROLLING PROPAGATION VELOCITY IN A FEED LINE discloses a single phase shifter for use with multiple array elements. As shown in
FIG. 1
, a feed conductor line includes a source input and multiple antenna element outputs. A moveable dielectric material located between the feed line, or the carrier plate thereof, and a ground plane, controls the propagation velocity of signals coupled through the feed line. In this manner a mechanical adjustment is made which determines the phasing of multiple antenna elements.
The prior art shows the level of complexity that is required for the use of multiple element antenna arrays. There are a number of difficulties relating to individual connections as well as problems relating to phase control. What is needed is a simplified coupling and phase control that enables multi-element antennas that are simple to manufacture and operate without sacrificing performance.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a maneuverable, scanning, phased-array, meander line loaded antenna having circular polarization. Linear arrays or transmission lines of crossed MLA elements each allow the application of two feeds—a first signal feed and a 90° phase shifted signal feed. When properly connected, each linear array, therefore, can radiate a circularly polarized RF signal. A compact, low-cost, scanning phased array may be built by forming a symmetrical superstructure of these linear arrays. For high-frequency applications, the inventive antenna structure may be readily formed using printed circuit manufacturing techniques.
An array antenna is disclosed for an inexpensive, dual-feed, array antenna utilizing a stepped or varied impedance transmission line to provide an active antenna array. The stepped nature of the antenna elements create a varied impedance transmission line as those sections that are further from the ground plane have a greater impedance than those elements closer to the ground plane. The higher impedance sections function as individual active array elements for radiating or receiving. Variation of the spacing among the active elements controls the antenna gain pattern. And, the delay line characteristics of the meander line elements are used to control the phase relationship of the antenna elements.
The present invention simplifies the design and manufacture of a phased-array MLA having circular polarization. The inventive antenna has an easily controlled beam and pointing direction. The invention also reduces the complexity of phased-array control logic and reduces the fabrication cost for phased-array antennas, especially antennas where circular polarization is required.
One of the structural differences between the antenna of the present invention and that of the related art, is that the invention features an array of orthogonal meander lines, and a movable back plate. This creates a slow wave configuration, which provides the necessary phase shift, producing a cir
Asmus Scott M.
BAE Systems Information and Electronic Systems Integration INC
Le Hoang-anh
Maine Vernon C.
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