Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-03-19
2002-03-05
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S368000
Reexamination Certificate
active
06353410
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to an antenna; and more particularly relates to a multibeam antenna.
2. Description of Related Art
FIG. 1A
shows an antenna
20
of U.S. Pat. No. 5,589,843 having a space tapered multi-beam antenna
24
, a Butler-matrix feed network
28
, and a radio receiver and/or transmitter
37
. The antenna
20
is known as a space tapered one hundred twenty degree antennas having four thirty degree beams.
The radio receiver and/or transmitter
37
receives and/or provides radio receiver and/or transmitter signals from or to the 4-way Butler matrix feed network
28
via cabling
41
. The radio receiver/transmitter equipment
37
is generally shown since the specific type of equipment used in an actual installation can vary widely. The Butler matrix feed network
28
is implemented using a planar microstrip design
39
shown in
FIG. 1B
with no crossovers and is fabricated from a printed circuit board having a dielectric substrate made of low loss ceramic material, such as glass epoxy. In general, the Butler-matrix feed network
28
has N antenna ports
29
and N receiver/transmitter equipment ports
31
, where N is equal to the number of co-linear arrays of the associated antenna. As shown, the 4-way Butler matrix feed network
28
has four antenna output ports
29
and four radio receiver/transmitter input ports
31
. The standard phase shift of the 4-way Butler matrix feed network
28
is as follows:
ANT1
ANT2
ANT3
ANT4
BEAM 2L
0
−135
+90
−45
BEAM 1L
0
−45
−90
−135
BEAM 1R
0
+45
+90
+135
BEAM 2R
0
+135
−90
+45
The Butler-matrix feed network
28
is connected to the space-tapered antenna
24
with equally phased cables
35
that provide phase shifting of outgoing signals to electronically steer the radiating pattern of the space-tapered antenna
24
.
In
FIG. 1A
, the space tapered multi-beam antenna
24
has a space-tapered array
26
(ANT1, ANT2, ANT3, ANT4) with rows of radiating elements spaced at about ½ &lgr; (i.e. wavelength), where &lgr; is the wavelength of the electromagnetic energy to be received or transmitted. (In practice, the spacing between adjacent co-linear arrays may actually be approximately 0.47 &lgr;.) The number of radiating elements in outermost rows is less than the number of radiating elements in center rows in order to suppress side-lobes distortion in the antenna signal, which is typically −9 or −10 Db. The space-tapered array
26
includes four co-linear arrays of associated electromagnetic radiating elements
30
. Each antenna output port
29
of the 4-way Butler matrix feed network
28
is respectively connected to a respective antenna ANT1, ANT2, ANT3, ANT4 of the co-linear array
26
by cables
35
and connectors
27
associated with each antenna array. The cables
35
are all the same length (i.e. equal phase cables) so as not to introduce any phase change with respect to the signals carried thereover relative to the other cables
35
. In comparison, the cables
41
need not be equal phase cables since any phase changes introduced by these cables is not relevant to the electronic beam(s) being used.
In
FIG. 1A
, the outermost co-linear antenna arrays ANT1 and ANT4 each comprise two radiating elements
30
, while the innermost antenna arrays ANT2 and ANT3 each comprise four radiating elements
30
. These radiating elements
30
are typically dipole elements, although other types of radiating element can be used. Energy is radiated or received from these dipole elements by means of a feedstrap
43
having a centrally located connector
27
. The dipole elements are spaced from each adjacent dipole element of the same array by a distance approximately equal to &lgr;. The feed strap includes portions
45
extending beyond the lowermost and uppermost dipole element, with the end of these portions connected to the electrically conductive back plate
47
of the antenna. Such a feed strap configuration is known in the art as a Bogner type feed (see U.S. Pat. No. 4,086,598, hereby incorporated by reference).
The phase progression for the antenna beam of the antenna shown in
FIG. 1A
is show in the table below:
BEAM
ANT1
ANT2
ANT3
ANT4
2L
0
−135
+90
−45
1L
0
−45
−90
−135
1R
0
+45
+90
+135
2R
0
+135
−90
+45
The one hundred twenty degree antennas
20
suffer from high side-lobe levels that do not meet desired customer specifications of being below −10 dB from the beam peak. Also, the outer beams suffer from a drop in gain as compared to the inner beams.
FIGS. 1C
,
1
D,
1
E show frequency plots for the antenna
20
in
FIG. 1A
that show these problems, including frequency plots respectively at frequencies of 1.850 giga Hertz (hereinafter “GHz”), 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plot shows various plot characteristics, including four plot overlays (i.e. 1LH, 1RH, 2LH, 2RH), four beam peaks in degrees, four beamwidths in degrees, four front-to-back (hereinafter “f/b”) ratios in decibels (hereinafter “dB”) and four sidelobes in degrees and dBs. In
FIGS. 1C
,
1
D,
1
E, the various “triangles” help to indicate these various plot characteristics.
The technical problem to be solved is to provide an antenna having reduced side-lobe suppression, including a spaced-tapered antenna having outer beam signals that do not have a significant drop in gain as compared to inner beam signals.
SUMMARY OF THE INVENTION
The basic idea of the present invention is to either compress the row spacing of radiating elements in the collinear arrays of the antenna, or use phase progression cables leading from the feed system to the collinear array, or both.
The invention provides a new antenna, including a space-tapered antenna, having a collinear array of radiating elements coupled via a cable feeding system to a Butler matrix feed system. In the antenna, either the collinear array has compressed rows spaced in a range of ⅜ to ¼ of a wavelength, the cable feeding system is a phase progression cable feeding system, or both.
One 120° space-tapered antenna has eight compressed rows spaced at ⅜ wavelength for providing six 20° degree beams with −10 dB side lobe suppression. The six beam antenna is unique in that it provides a way to use an 8-way Butler matrix, because in the prior art there is no 6-way Butler matrix feed system.
Another 120° space-tapered antenna has eight compressed rows spaced at ¼ wavelength for providing four 30° beams with −15 dB side lobe suppression.
A 60° space-tapered antenna has eight compressed rows spaced at ⅜ wavelength in combination with a 22 ½° phase progression cable feeding system for providing three 20° beams with −14 dB side lobe suppression.
A 90° space-tapered antenna has eight compressed rows spaced at ¼ wavelength in combination with a 22 ½° phase progression cable feeding system for providing three 30° beams with −17 dB side lobe suppression.
A 90° space-tapered antenna has four rows spaced at ½ wavelength and a 45° phase progression cabling feeding system for providing three 30° beams with −12 dB side lobe suppression. For this antenna, the phase progression shifts the beams so that a center beam is down the middle, normal to the antenna. This also reduces the number of beams by one such that the radiating pattern of the antenna includes the center beam with an equally balanced number of side beams around the center beam. The phase progression may also be achieved directly in the output of the feed network.
One advantage of the present invention includes improved side-lobe distortion suppression and reduced dropoff in gain of the outer beams as compared to the inner beams. The sidelobe distortion is reduced by about −6 dB which translates into 4× less side lobe distortion in the antenna signal for improved signal transmission.
These embodiments provides improved
Gregory Bernarr E.
Radio Frequency Systems Inc.
Ware Fressola Van Der Sluys & Adolphson LLP
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