Title: Series feeding system and method for interleaved antennas sharing the same aperture centerline
Abstract: An antenna feed system for an interleaved series fed antennas is provided, wherein the interleaved antennas share the same centerline. The antenna systems are fed in series from parallel feedlines while preserving similar coverage and maintaining similar aperture space.
Patent Number: 6,972,731 Issued on 12/06/2005 to Schadler
| Inventors:
|
Schadler; John (Raymond, ME)
|
| Assignee:
|
SPX Corporation (Charlotte, NC)
|
| Appl. No.:
|
747157 |
| Filed:
|
December 30, 2003 |
| Current U.S. Class: |
343/853; 343/850; 343/890 |
| Intern'l Class: |
H01Q 021/00 |
| Field of Search: |
343/893,895,743,879,890-891,850,853,874
|
References Cited [Referenced By]
U.S. Patent Documents
| 6320555 | Nov., 2001 | Schadler.
| |
| 6650300 | Nov., 2003 | Skalina et al.
| |
| 6914579 | Jul., 2005 | Schadler.
| |
| 2005/0088360 | Apr., 2005 | Schadler.
| |
Primary Examiner: Tran; Thuy Vinh
Attorney, Agent or Firm: Baker & Hostetler LLP
Claims
1. An antenna feed system for series feeding interleaved antennas sharing a common
centerline, comprising:
a feedline tap housing having:
a first and second substantially vertical-facing apertures collinear and substantially
opposite each other at one portion of the housing to enable insertion of a substantially
vertical antenna feedline therein; and
a third substantially horizontal-facing aperture at an opposite portion of the
housing, the third aperture being orientated substantially orthogonal to the first
aperture to enable insertion of a substantially horizontal antenna support centerline.
2. The antenna feed system according to claim 1, further comprising:
a fourth substantially horizontal-facing aperture at the opposite portion of
the housing, being substantially orthogonally to the third aperture to enable access
to an interior of the housing.
3. The antenna feed system according to claim 1, wherein the housing is reversible
about a vertical axis bisecting a center of the third aperture to enable the first
and second apertures of the housing to accommodate an other substantially vertical
antenna feedline therein, when the housing is reversed.
4. The antenna feed system according to claim 1, further comprising:
a plurality of fitting plate mounting holes disposed about the first, second,
and third apertures.
5. The antenna feed system according to claim 4, wherein the mounting holes are threaded.
6. The antenna feed system according to claim 1, further comprising:
a first and second fitting plate that seal the housing to the vertical feedline; and
a third fitting plate that seals the antenna support to the housing.
7. The antenna feed system according to claim 1, further comprising:
an attachment detent at a rear portion of the housing.
8. The antenna feed system according to claim 1, wherein the housing is in the
shape of a tee.
9. The antenna feed system according to claim 1, wherein an inner edge of the
first, second and third apertures are threaded.
10. An antenna feed block for interleaved series fed antennas, sharing a common
centerline, comprising:
an antenna-to-feedline coupling means for series coupling the feedline to the
interleaved antennas, the coupling means comprising:
a first and second substantially vertical-facing apertures collinear and substantially
opposite each other at one portion of the coupling means to enable insertion of
a substantially vertical antenna feedline therein; and
a third substantially horizontal-facing aperture at an opposite portion of the
coupling means, the third aperture being orientated substantially orthogonal to
the first aperture to enable insertion of a substantially horizontal antenna support centerline.
11. The antenna feed block according to claim 10, wherein the coupling means
is reversible about a vertical axis bisecting a center of the third aperture to
enable the first and second apertures of the coupling means to accommodate an other
substantially vertical antenna feedline therein, when the coupling means is reversed.
12. The antenna feed block according to claim 10, further comprising:
a fourth substantially horizontal-facing aperture at the opposite portion of
the coupling means, being substantially orthogonally to the third aperture to enable
access to an interior of the coupling means.
13. The antenna feed block according to claim 10, further comprising:
a plurality of aperture fitting means for fitting the coupling means to the feedline
and the antenna.
14. A method for feeding interleaved antennas, comprising:
interleaving antennas that share a common centerline;
supplying a first and second vertical feedlines offset from and on opposite sides
of the common centerline to the interleaved antennas;
series feeding antennas of a first interleaved antenna set by tapping at an interleaved
interval the first vertical feedline;
series feeding antennas of a second interleaved antenna set by tapping at an
interleaved interval the second vertical feedline, wherein
the tapping of the first and second feedline is performed using a housing that
is reversibly applicable to either the first or second feedline.
15. The method for feeding interleaved antennas according to claim 14, further comprising:
securing the housing to the first feedline through a connecting flange and securing
the housing to the second feedline through another connecting flange.
16. The method for feeding interleaved antennas according to claim 15, wherein
the feedline-flanges are secured to the housing via bolts.
17. The method for feeding interleaved antennas according to claim 15, wherein
the feedline-flanges are mated to the housing via threads on the housing.
18. The method for feeding interleaved antennas according to claim 14, further comprising:
securing the interleaved antennas to the housing with an antenna-to-housing flange.
19. The method for feeding interleaved antennas according to claim 14, further comprising:
providing a housing access port at a housing side adjoining the centerline.
20. The method for feeding interleaved antennas according to claim 14, further comprising:
securing the housing to a tower supporting the interleaved antennas.
Description
FIELD OF THE INVENTION
The present invention relates generally to an antenna feed system. More particularly,
the present invention relates to series feeding interleaved antennas sharing the
same aperture centerline.
BACKGROUND OF THE INVENTION
FM radio is in wide use in the field of radio broadcast. The term FM includes,
for example, any of the Frequency Modulation methodologies used or developed for
signal broadcasting in a frequency band assigned by the U.S. Federal Communications
Commission (FCC), nominally in the transmission range 88 MHz to 108 MHz, which
is near the middle of the Very-High-Frequency (VHF) television broadcast band.
These Frequency Modulation technologies include both analog FM and digital FM.
The FCC has adopted a standard for analog-digital FM transmission called the
iBiquity IBOC (In-Band-On-Channel) for hybrid analog-digital transmission systems.
According to the IBOC standard, FM stations in the United States must be able to
simultaneously broadcast analog and digital signals within their current allocated
frequency range. One approach for achieving the above simulcast is to use two separate
transmission systems (for example, analog-digital) to feed two separate antennas
(for example, analog-digital). Since the elevation of the antenna on the tower
directly affects the antenna's coverage, it would be desirable to co-locate the
radiated analog and digital signals at the same height above the ground to maintain
the same coverage.
Also, since the azimuthal pattern of an FM antenna is very dependent on the
cross section of the tower structure, it would be desirable to mount both the analog
and digital antennas in the same orientation with respect to the tower. When adding
digital coverage, concerns are that many towers are already full having no additional
aperture space available. Therefore, many FM broadcasters have responded by vertically
interleaving the second digital antenna within the aperture of their existing analog
antenna. One challenge to overcome when antennas are placed in this configuration
is a practical feed system which allows for both systems to occupy the same aperture
space without deleteriously altering the characteristics of either antenna system
or the antenna tower.
Accordingly, it is desirable to provide systems and methods which enable
a plurality of antenna systems sharing a common centerline to be fed in a manner
that does not deter from the performance of the antennas or degrade the structural
integrity of the antenna tower.
SUMMARY OF THE INVENTION
The foregoing needs are met, to a great extent, by the present invention, wherein
systems and methods are provided wherein a plurality of antenna systems, being
interleaved and sharing a common centerline, are independently series fed using
offset feedlines and dividing tees.
For example, in accordance with one embodiment of the present invention, an antenna
feed system for series feeding interleaved antennas sharing a common centerline
is provided, comprising a feedline tap housing having a first and second substantially
vertical-facing apertures collinear and substantially opposite each other at one
portion of the housing to enable insertion of a substantially vertical antenna
feedline therein. Also, a third substantially horizontal-facing aperture at an
opposite portion of the housing is provided, the third aperture being orientated
substantially orthogonal to the first aperture to enable insertion of an substantially
horizontal antenna support centerline.
In accordance with another embodiment of the present invention, an antenna feed
block for interleaved series fed antennas, sharing a common centerline is provided,
comprising an antenna-to-feedline coupling means for series coupling the feedline
to the interleaved antennas, the coupling means comprising a first and second substantially
vertical-facing apertures collinear and substantially opposite each other at one
portion of the coupling means to enable insertion of a substantially vertical antenna
feedline therein. Also, a third substantially horizontal-facing aperture at an
opposite portion of the coupling means is provided, the third aperture being orientated
substantially orthogonal to the first aperture to enable insertion of an substantially
horizontal antenna support centerline.
In accordance with yet another embodiment of the present invention, a method
for
feeding interleaved antennas is provided, comprising interleaving antennas that
share a common centerline and supplying a first and second vertical feedlines offset
from and on opposite sides of the common centerline to the interleaved antennas.
Also, the method provides for the series feeding antennas of a first interleaved
antenna set by tapping at an interleaved interval the first vertical feedline and
a series feeding antennas of a second interleaved antenna set by tapping at an
interleaved interval the second vertical feedline, wherein the tapping of the first
and second feedline is performed using a housing that is reversibly applicable
to either the first or second feedline.
In accordance with yet another embodiment of the present invention, a method
for
feeding two sets of interleaved antennas sharing a common centerline is provided,
the method comprising feeding a first interleaved antenna of a first antenna set
using a series feed, and feeding a second interleaved antenna of a second antenna
set using a separate series feed, wherein the feed is centrally accommodated to
enable the series feed to pass through to feed a next interleaved antenna of the
first antenna set.
There has thus been outlined, rather broadly, certain embodiments of the invention
in order that the detailed description thereof herein may be better understood,
and in order that the present contribution to the art may be better appreciated.
There are, of course, additional embodiments of the invention that will be described
below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in
detail, it is to be understood that the invention is not limited in its application
to the details of construction and to the arrangements of the components set forth
in the following description or illustrated in the drawings. The invention is capable
of embodiments in addition to those described and of being practiced and carried
out in various ways within the preview of one of ordinary skill in the art. Also,
it is to be understood that the phraseology and terminology employed herein, as
well as the abstract, are for the purpose of description and should not be regarded
as limiting.
As such, those skilled in the art will appreciate that the conception upon which
this disclosure is based may readily be utilized as a basis for the designing of
other structures, methods and systems for carrying out the several purposes of
the present invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not depart from the
spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of an interleaved antenna systems with an exemplary
feed according to this invention.
FIG. 2 is a closeup illustration of an exemplary feed of FIG. 1.
FIG. 3 is an perspective illustration of an offset feed block.
DETAILED DESCRIPTION
The invention will now be described with reference to the drawing figures, in
which like reference numerals refer to like parts throughout.
Due to the FCC IBOC requirements several practitioners in the antenna community
have devised methods or systems for interleaving antennas. For example, U.S. patent
application Ser. No. 10/396,818, titled "Apparatus and Method of Isolating In-Channel
FM Antennas Sharing Common Aperture Space" filed Mar. 26, 2003 by the present inventor,
the contents of which are incorporated herein by reference in its entirety describes
the generic possibility of interleaving antennas. U.S. patent application Ser.
No. 10/692,688, titled "Feed System and Method for Interleaving a Branch Feed Antenna
with an Existing Series Feed Antenna Within the Same Aperture Centerline", filed
Oct. 27, 2003, by the present inventor, the contents of which are incorporated
herein by reference in its entirety, describes a branch series feed scheme. In
contrast, series feeding multiple interleaved antennas having a common aperture
centerline is described herein.
FIG. 1, an illustration
10 of an exemplary radiating tower
5 with
interleaved digital left-hand polarized antennas
6 within the same centerline
of analog right-hand polarized antennas
4. By interleaving the digital left
hand-polarized antennas
6 with the analog right-hand polarized antennas
4, coupling between the antennas
4 and
6 is greatly reduced.
Therefore, only a small, low cost circulator is need at the output of the respective
transmitter (not shown) to absorb the small amount of coupled energy to achieve
the necessary isolation between the two antenna
4 and
6. Since both
the digital and analog antennas
6 and
4 have the same approximate
tower geometry adjacent to them, the elevation patterns of both systems will be
virtually the same and will meet FCC pattern requirements. It should be appreciated
that while FIG. 1 only illustrates one left-hand polarized antenna
6 interleaved
between two right-hand polarized antennas
4, an additional one or more left-hand
polarized antennas
6 may be interleaved above or below the right-hand polarized
antenna
4.
Antenna
6 is shown in FIG. 1 as being fed from a tee feed or feed
input block
8 which is attached to a feedline
12 attached to the
tower
5. A secondary interleaved antenna
6 (not shown) is separated
from the visible antenna
6 by approximately 1λ to provide in-phase
constructive interference. The counter polarized antennas
4 are interleaved
with respect to each other at 1λ intervals within neighboring antennas
6
and are fed by feedline
16 that is fed into the feed input bay
14.
Feedlines
12 and
16 are illustrated as being positioned on
"opposite" sides of the centerline
18 of the antennas
4 and
6.
Feedline
12 is shown with a smaller diameter than feedline
16 to
infer that feedline
12 and the attendant antenna(s)
6 require a lower
power than supplied by feedline
16. It should be apparent that the interleaving
of antennas
6 and
4, respectively, over a common centerline of a
face of the tower
5 results in all of antennas
6 and
4 to
be separately fed by feedlines
12 and
16, respectively. Therefore,
while FIG. 1 illustrates the "bottom-most" antenna
4 as being fed by feedline
16, the design could be alternated to where the "bottom-most" antenna is
antenna
6. In this event, the "top-most" antenna would be another antenna
6.
It should be appreciated by one of ordinary skill in the art that while the above
discussion phrases the various elements of the exemplary embodiment of FIG. 1 in
terms of bottom-most and top-most, or primary and secondary, or analog and digital,
these terms are relative and may be exchanged depending on the design and preferences
implemented. Also, while 1λ spacing is used between antennas of the same
polarization, other spacings as deemed efficient maybe used. Furthermore, it should
be appreciated that while FIG. 1 illustrates the feedline
16 as feeding
antennas
4 from the right side of the tower
5, alternative positioning
of the feedline
16 may be accomplished. That is, the feedline
16
may be placed on the left side of the tower
5 face and, additionally, the
feed
12 may be placed on the right side of the tower
5 face. Further,
two or more faces of the tower
5 may have antenna systems located therein.
Similarly, rather than positioning the antenna system solely on a face, the antenna
system may be positioned on "corners" or at other suitable locations of the tower.
Additionally, while the tower
5 is shown to have three faces, the tower
5 can have more or less faces as desired.
In FIG. 1, each antenna
4 and
6 of the sets of antenna shown is
composed of circularly polarized helically wound antennas. The antenna elements
of the respective analog-digital systems are oppositely polarized between the digital
and analog antennas to achieve a high level of isolation, being co-located in the
same aperture window. As is apparent to one of ordinary skill, numerous types of
non-helical antenna elements are available that can radiate circularly polarized
signals and are thus suitable for simulcasting an analog and digital signal in
a single aperture window. While some antenna types do not intrinsically radiate
circularly polarized signals, they can be forced to create such a signal when driven
by properly configured antenna elements and/or phasing. For example, two sets of
crossed linear dipoles may be properly phased to generate opposing circular polarizations.
Therefore, while the above exemplary embodiments illustrate one style of antenna
elements, other forms of antennas, either by physical or by signal manipulation,
may generate orthogonal signals to achieve reduced cross-coupling.
Due to the exemplary interleaving and feed approach provided in FIG. 1, a very
low cost solution to FCC requirements is provided. Specifically, the cost of the
secondary (digital) antenna
6, second run of low power (digital) transmission
line and low power circulator is substantially less than the system cost of a 10
dB coupler and a transmitter large enough to compensate for additional system losses.
Also, the exemplary system
10 also provides a lower risk as each of
the analog and digital arrays are separate from each other and, therefore, can
be operated independently. Because of the reduced mutual coupling, re-tuning requirements
of the analog antenna after installing the digital bays can be minimized. Additionally,
two interleaved antennas
4 and
6 provide a level of redundancy since
both arrays are capable of supporting either the analog or digital signal based
on the input signal.
While FIG. 1 only illustrates three input feed blocks
8 and
14
situated on the tower
5, less or more input feed blocks may be facilitated,
based on power, antenna patterns, etc.
FIG. 2 is an illustration showing a closeup view of an exemplary input feed
block
28. The input feed block
28 is shown coupled to the feedline
22 and to the antenna
24. The input feed block
28 is secured
to the face of the antenna tower
27 via a mounting plate
25 that
is attached to the face of the antenna tower
27 via mounting clamps (not
shown). Of course, it should be appreciated that other forms of attachment to the
tower
27 may be accomplished with, for example, bolt, welds, screws, etc.
The exemplary input feed block
28 is positioned on the mounting plate
25
to afford the coupled antenna
24 a centerline location. The exemplary input
feed block
28 is shown as only coupling to the feedline
22 and, therefore,
is disassociated from the neighboring feedline
26.
The exemplary feed block
28 is of a sufficient size to border the centerline
of the tower
27 and accommodate the antenna
24 at the centerline,
and also extend to an adjacent feedline
22, for example. The design of the
exemplary feed block
28 permits the easy reversal of the exemplary feed
block
28 to enable coupling to an "opposite" feedline, for example, feedline
26 as shown in FIG. 2, if desired. Thus, by using the exemplary feed block
28 design, series coupling of the interleaved antennas to feedlines
22
and
26 that run up the tower
27 can be accomplished by using one
type of feed block
28, rather than different types for the different feedlines.
As is obvious from FIG. 2 the feedline
22 is of a smaller diameter than
the feedline
26. To accommodate the ability to have a one size fits all
approach, the interface between the feedline
22 and the opening of the exemplary
input feed block
28 is fitted with a sizing ring
21 to enable a secure
fit of the feedline
22 to the exemplary input feed bay
28. In other
words, the exemplary input feed block
28 may be designed with a feedline
interface opening that can accommodate the larger diameter (or less) of the feedline
26.
FIG. 3 is a perspective view of an exemplary input feed block
30. The
illustrated exemplary input feed block
30 is shown as having the general
shape of a tee with openings
32 and
34 positioned on adjoining faces
of the right portion of the exemplary input feed block
30. The opening
32
is positioned on an outward face of the exemplary input feed block
30, and
accommodates the placement of an antenna boom (not shown) for coupling to an antenna
(see FIGS. 1 and 2). Opening
34 is provided to enable easy access to the
interior of the exemplary input feed block
30, as well as to accommodate
extensions or bridges, if necessary. Opening
36 is shown as being positioned
on a top face of the exemplary input feed block
30 and is provided for securing
the respective tapped feedline. A recessed surface
37 is shown in FIG. 3
at a "rear" portion of the exemplary input feed block
30. The recessed surface
37 is provided for convenient mating to the mounting plate as discussed
in FIG. 2. Each of the openings
32,
34 and
36 are flanked
by holes
31 to facilitate the mating of connecting flange. In the event
that bridge or extensions not needed, the sizing plate for opening
34 can
be a solid plate to seal the opening
34 or, alternatively, the feed block
30 may be fabricated without the opening
34 or the attendant holes
31.
It should be appreciated that while the exemplary embodiments of the input feed
block, discussed above, are illustrated in the Figures as having a predominant
"tee" shape, other shapes or forms may be suitable for accomplishing the desired
result. Additionally, terms as right, left, front, back, outward, etc. are understood
to be relative terms and may be interchanged depending on the orientation chosen.
Furthermore, additional openings may be placed in the input feed block for draining,
inspection, etc. Also, the input feed block may be fabricated from several pieces
and joined to form a single assembly upon completion or mounting to the tower.
It should be appreciated that though the above exemplary embodiments are described
in the context of IBOC applications, non-IBOC applications may be contemplated.
For example, any antenna system requiring "sharing" of a centerline can utilize
the features of the present invention to provide a convenient series fed arrangement.
Accordingly, many features and advantages of the invention are apparent
from the detailed specification, and thus, it is intended by the appended claims
to cover all such features and advantages of the invention which fall within the
true spirit and scope of the invention. Further, since numerous modifications and
variations will readily occur to those skilled in the art, it is not desired to
limit the invention to the exact construction and operation illustrated and described,
and accordingly, all suitable modifications and equivalents may be resorted to,
falling within the scope of the invention.
*
