Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-05-04
2003-01-07
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S895000, C029S600000
Reexamination Certificate
active
06504508
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to meander line antennas and, more particularly, to a method for fabricating meander line antennas that require no manual assembly.
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 allowed the antenna to be easily excited 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 the frequency decreased, the antenna dimensions proportionally increased. In order to address the shortcomings of traditional antenna design and functionality, researchers have developed the meander line loaded antenna (MLA).
A typical meander line loaded antenna is disclosed in U.S. Pat. No. 5,790,080, hereby incorporated by reference. An example of a meander line loaded antenna is also known as a variable impedance transmission line (VITL) antenna. The antenna consists of two vertical conductors and a horizontal conductor. The vertical and horizontal conductors are separated by gaps.
Also, part of the antenna comprises meander lines. These meander lines are connected between the vertical and horizontal conductors at the gaps, one or both of which are bridged by meander lines. The meander line is designed to adjust the electrical length of the antenna. In addition, these meander lines provide for a slow wave structure, and make possible switching lengths that can be quickly applied to and removed from the circuit with negligible loss. This switching provides a change in the effective electrical length of the antenna, and is possible because the meander line is constructed with its active switching structure always located in the high impedance sections of the meander line. This keeps the current through the device low, which results in very low dissipation losses. Thus high antenna efficiency is achieved.
The typical antenna can be operated in a loop mode that provides a “figure eight” coverage pattern. A 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 a 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 the 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 frequency using a given mode.
The invention of the meander line loaded antenna allows the physical antenna dimensions to be significantly reduced in size, while maintaining an electrical length that maintains a multiple of a quarter wavelength. Antennas and radiating structures fabricated with this design operate in the region where the limitation on their fundamental performance is governed by the Chu-Harrington relation:
Efficiency=
FV
2
Q
where:
Q=Quality Factor
V
2
=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 a comparable gain.
The existing MLA antennas are individually designed and are built by hand. The high labor costs of manufacturing these antennas make their use prohibitive. Unfortunately, communication applications require devices that can be made cheaply, in order that the manufacturer keeps competitive. This invention reflects the discovery of a way to mass produce VITL antennas for commodity applications, such as cell phones.
DISCUSSION OF RELATED ART
U.S. Pat. No. 5,790,080, entitled MEANDER LINE LOADED ANTENNA, assigned to Lockheed Sanders, Inc. of Nashua, N.H., describes an antenna that includes one or more conductive elements. These elements act as radiating antenna elements, and provide a slow wave meander line that is adapted to couple electrical signals between the conductive elements. The meander line has an effective physical length, which affects the electrical length and the operating characteristics of the antenna. The electrical length and operating mode of the antenna may be readily controlled.
U.S. Pat. No. 6,034,637 entitled DOUBLE RESONANT WIDE BAND PATCH ANTENNA, AND METHOD OF FORMING SAME, assigned to Motorola, Inc., of Schaumburg, Ill., describes a double resonant wide band patch antenna that includes a planar resonator forming a substantially trapezoidal shape having a non-parallel edge that provides a substantially wide bandwidth. A feed line extends parallel to the non-parallel edge for coupling, while a ground plane extends beneath the planar resonator for increasing radiation efficiency.
U.S. Pat. No. 6,008,762, entitled FOLDED QUARTER WAVE PATCH ANTENNA, assigned to QUALCOMM Incorporated of San Diego, Calif., 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 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 comprising a first frequency band, and a second signal comprising a second frequency band.
The main difference between this inventive antenna and that of the related art is the cost saving circuit printing of the antenna meander lines. Previous meander lines were constructed of sheet metal. Printing the circuit assembly lowers costs.
The key advantages of using printed circuit board technology, are:
1) Ease of manufacturing.
2) The use of standard printed wiring board techniques.
3) The ability to manufacture small MLAs for use at microwave frequencies.
4) Increased mechanical stability.
5) Higher vibration and shock resistance.
6) Increased reliability.
7) High reproducibility.
8) No need for tuning during assembly.
9) Lower costs.
A meander line printed circuit board implementation is disclosed in U.S. Pat. No. 6,094,170 assigned to Advanced Application Technology of Taiwan. This patent describes implementing a planar array element as a meander line on the surface of a dielectric plate, according to Printed circuit board techniques that are well known in the art. Meander line generally refers to a transmission line, such as a microstrip line, that meanders or wanders in an indirect path. As described in this prior art patent, this meander line functions as a radiating element of a planar device.
However, in distinction, the geometry and overall functionality of the present invention are different. The present meander line is a different design and implementation. The whole dielectric and printed circuit board are mounted on a ground plane. Elements are on two levels, on the upper surface and on the lower surface of the printed circuit board as well as on the sides and through the plated through holes.
The present invention does not radiate, but rather performs the function of the meander line as described herein and previously implemented as shown in FIG.
2
. The present invention is placed in the gap of the radiating structure of the antenna shown in FIG.
1
. The present device is affixed in the gap either on the horizontal underside surface or on the inner vertical surfaces of an antenna device.
SUMMARY OF THE INVENTION
The antenna structure of this invention features a new meander li
Asmus Scott J.
BAE Systems Information and Electronic Systems Integration INC
Ho Tan
Maine Vernon C.
Maine & Asmus
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