Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1999-08-19
2001-01-30
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S797000
Reexamination Certificate
active
06181298
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to antennas and specifically to improved quadrafilar helical antennas.
DISCUSSION OF THE PRIOR ART
Top fed quadrafilar helical antennas are known in the art for their high circular polarization (CP) gain over most of the upper hemisphere. The top-fed type of the quadrafilar helix is one of the few antenna structures known to be capable of producing circular polarization with near uniform gain over the upper hemisphere. Thus, top-fed quadrafilar helical antennas are ideal for satellite communications terminals. Unfortunately, this type of antenna is expensive and difficult to manufacture. Different designs have been suggested for this type of antenna, however, none of these alternatives overcome this basic manufacturing problem.
A quadrafilar helical antenna is presented by Senglee Foo in the article “A Quadrafilar Helical Antenna for Low Elevation GPS Applications” published in
Microwave Journal
January 1998 issue. However, this antenna is bottom fed by a microstrip feed circuit and does not provide near uniform circular polarized gain above the horizon.
Kilgus, in “Resonant Quadrafilar Helix Design”, published in
Microwave Journal
December 1970, shows a top fed quadrafilar helical antenna that has the desired characteristics noted above. Unfortunately, the design shown in the article is not only complicated, but also difficult and expensive to manufacture. Furthermore, the design is also fragile in that the helical conductors are subject to the vagaries of harsh environments.
U.S. Pat. No. 5,170,176 issued to Yasunaga et al, also discloses a top fed quadrafilar helical antenna. This design is illustrated in FIG.
1
. However, this design again suffers from the drawbacks noted above. The skill required to produce the proper winding or the percentage of a revolution per quadrant that a conductor makes around the z-axis is high. There is no guarantee that each and every antenna produced will provide the same characteristics given that the winding will depend on the individual constructing the antenna. Furthermore, the helical conductors do not have any visible means of support and are therefore freely hanging. They can therefore be easily snagged and broken.
A fourth design, disclosed in U.S. Pat. No. 5,349,365 issued to Ow et al and illustrated in
FIG. 2
, is also a top fed quadrafilar design. However, the conductors in the Ow et al design are made from four metal strips radiating from a common center, each strip having been deformed to a helical pattern. While this design does provide a more rigid and therefore less fragile antenna, it is difficult and expensive to manufacture. Specifically, the skill involved in bending the individual strips at specific points to produce the winding required necessitates not only precision in the bend angle but also accuracy in where the bend is placed.
Another conventional design is shown in FIG.
3
. In this design, four wires are wound around a cylindrical dielectric mandrel with an arbitrary small fraction of a turn or multiple turns on each winding, each wire forming a constantly flowing curve without straight sections. The windings start at the top of the mandrel at locations oriented 90 degrees apart on the top of the mandrel. The windings may extend to the bottom of the mandrel or to some distance above the bottom. Horizontal wires join the helical wires to centrally located coaxial cables which run from the bottom of the mandrel to the top. The horizontal wires introduce a zenith component to the field. The bottom ends of the coaxial cables are connected to a feed network which impedance matches to the cables and excites them with relative phases of 0,90,180 and 270 degrees. The skill and time required to insert the coaxial cables and wind the conductors on the cylindrical mandrel render this type of antenna unsuitable for low-cost, mass manufacturing processes.
As can be seen from FIG.
3
and as noted above, it is difficult to feed the coaxial cables within the antenna structure. Also, winding the helical conductors properly is difficult and time consuming.
What is therefore required is a low-cost, easy to assemble, top-fed quadrafilar antenna that provides high circular polarization (CP) gain over most of the upper hemisphere and near uniform circular polarized gain above the horizon.
SUMMARY OF THE INVENTION
The present invention overcomes the deficiencies identified in the prior art by providing a top fed quadrafilar helical antenna comprising a pair of crossed printed circuit boards with two feed lines and two horizontal arms per board and four piecewise linear conductors. Each arm is connected to a feed line and to a conductor that is piecewise linearly attached to the edges of the crossed printed circuit boards.
The invention provides for a top fed quadrafilar helical antenna comprising:
at least two printed circuit boards, each board having:
a first feed network located on a front side of the board and substantially parallel and adjacent to a first side of a longitudinal axis of the board
a second feed network located on a back side of the board and substantially parallel and adjacent to a second side of the longitudinal axis of the board
a first horizontal arm extending from the longitudinal axis to a first outer edge of the board, said first arm being located on the front side of the board
a second horizontal arm extending from the longitudinal axis to a second outer edge, said second arm being located on the back side of the board and
a slot located substantially collinear with the longitudinal axis of the board
and a plurality of linear conductors wherein
each feed network is connected to a proximal or inner end of a horizontal arm
each linear conductor is connected to a distal or outer end of a horizontal arm
each linear conductor is wound around the outer edges of the at least two printed circuit boards in a helical manner
each printed circuit board is crossed with at least one other printed circuit board by interlocking their respective slots.
In another embodiment, the invention provides a top fed quadrafilar helical antenna comprising:
a pair of double-sided printed circuit boards, each board having:
a slot located substantially on a longitudinal axis of the board for interlocking with a mating slot on the other circuit board;
a pair of impedance matching transformers located adjacent and parallel to the longitudinal axis of each board, said transformers being located on opposite sides of the board; and
two horizontal arms of a feed network, said arms having a distal end and a proximal end and each arm being located on opposite sides of the board and outwardly extending from the longitudinal axis of the board to a longitudinal edge of the board and connected at a proximal end to an impedance matching transformer; and
a plurality of piecewise linear conductors, each conductor electrically connected to the distal end of an arm of the feed network wherein
the pair of printed circuit boards are connected to each other in a crosswise fashion by means of the slot on one board interlocking with a slot on the other board
the piecewise linear conductors are helically wound around a perimeter defined by the longitudinal edges of the crossed circuit boards.
Another embodiment of the invention provides a top fed quadrafilar helical antenna comprising:
four identical printed circuit boards, each board having:
a feed network adjacent to and substantially parallel to an inner edge of the board and located on a front side of the board
a horizontal arm located on the front side of the board and extending from the feed network to an outer edge of the board, said arm being substantially parallel and adjacent to a top edge of the board
a ground plane located on a back side of the board
a plurality of positioning means to position and hold captive a conductor, each positioning means being disposed adjacent to the outer edge of the board
attachment means for attaching and fixing the four identical printed circuit boards to each other such that all the inner edges coincide at a connection
EMS Technologies Canada Ltd.
Pascal & Associates
Tran Thuy Vinh
Wong Don
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