Wideband phased array antenna employing increased packaging density laminate structure containing feed network, balun and power divider circuitry

A `four-square element` phased array antenna structure and associated feed network laminate architecture has a linear physical geometry of multiple trimmed four-square antenna elements disposed on a thin dielectric support layer, which facilitates compactly placing multiple linear arrays in a highly spatially densified side-by-side arrangement. This allows for placement of a greater number of antenna elements in a direction orthogonal to the array than in the longitudinal dimension of the array, so that the frequency of operation of an overall array can be increased relative to that of a conventional four-square architecture, thereby improving bandwidth coverage. For a linearly polarized beam, the trimmed four-square array of the invention enjoys a frequency response that is equal to or better than that of a conventional non-trimmed four-square architecture.

FIELD OF THE INVENTION
 The present invention relates in general to communication systems, and is
 particularly directed to a new and improved, highly compact, phased array
 antenna architecture having a plurality of antenna elements, that are
 integrated in a compact and highly densified laminate structure with, and
 fed by, associated signal distribution networks of a printed circuit power
 divider network that incorporates a balun feeding each pair of power
 dividers.
 BACKGROUND OF THE INVENTION
 Among desired characteristics of multielement antenna systems (e.g., phased
 array antennas) of the type that may be folded, stowed and deployed from a
 mobile platform, such as a satellite launch vehicle, are that the antennas
 be physically compact (low profile) and lightweight, while also being
 sufficiently broadband to meet performance requirements of terrestrial
 communication systems. Although progress has been made in reducing the
 physical size and packaging density of the radiating elements, per se, the
 substantial physical space required to implement and mount their
 associated feed networks and interconnection circuitry have effectively
 limited the size and packaging density of the total system.
 SUMMARY OF THE INVENTION
 Pursuant to the present invention, there is provided a new and improved,
 highly compact, wideband multi-element antenna structure that successfully
 integrates within a relatively thin laminate structure a plurality of
 closely spaced and fed printed circuit antenna elements, together with
 their associated feed, balum and power divider networks, in a support
 architecture that enjoys a significantly reduced size and packaging
 density compared with prior art systems.
 In accordance with a non-limiting example of a multi-element two
 dimensional antenna array, each of its radiating elements may be
 configured as a `trimmed` four-square arrangement, selectively etched or
 plated atop a thin dielectric support layer. By `trimmed` four-square is
 meant that outer edges of two diametrically opposed, non-fed components of
 a set of four, closely spatially arrayed square-shaped components have a
 `shaped` or `trimmed` square geometrical configuration. This outer edge
 trimming of the two non-fed components allows multiple four-squares to be
 arranged side-by-side in a relatively tightly packed array, thereby
 providing a substantially enhanced spatial density.
 In order to conform with the narrow geometry of an individual linear array
 of such `trimmed` four-square antenna elements, the support structure for
 the associated feed, balum and power divider circuitry is configured of a
 laminate design. This laminate design contains a plurality of power
 divider-feed networks that incorporate printed circuit baluns for
 alternate sets of antenna elements linearly distributed on a stripe-shaped
 dielectric feed network support member, that forms part of a multilayer
 architecture containing the antenna array. The feed network support member
 is spaced apart from subarrays of the antenna elements by a layer of
 dielectric, such as lightweight foam.
 A stripline ground plane metalization layer is formed on the bottom surface
 of the feed network support layer. A printed circuit power divider network
 includes a balun and an associated printed circuit branch network for feed
 ports of the driven antenna elements. The balun is coupled through a
 plated aperture in the dielectric support layer to the center conductor of
 a subarray feed port at the bottom surface of the support layer and is
 dielectrically isolated from the ground plane metalization layer on the
 bottom surface of the dielectric support layer.

DETAILED DESCRIPTION
 Referring now to FIGS. 1-14 of the drawings, a first non-limiting example
 of the application of the compact laminate antenna architecture of the
 invention to a four-square wideband phased array antenna array will be
 described. The invention will be initially described for the case of a
 `trimmed` four-square array, shown in FIG. 1 as a linear subarray 10 of
 printed metalization trimmed four-square elements 11-1, 11-2, . . . ,
 11-N. Each four-square element 11 (shown in greater detail in FIG. 2, to
 be described) may comprise one ounce copper metalization patches), that
 are selectively plated or etched in a linear array on the top surface 13
 of a thin, low loss dielectric support layer 15, such as sheet of 28 mils
 thick Duroid 5870. As diagrammatically illustrated in FIG. 3, in a
 multi-element laminate structure, the support layer 15 is mounted to a
 first surface 16 of a relatively lightweight spacing layer 17, such as a
 layer of plastic foam material (such as Rohacell 51HF foam), having a
 ground plane layer 18 formed on opposite surface 19 of foam spacing layer
 17.
 When used with the power distribution feed laminate structure of the
 invention, the thickness of lightweight foam spacing layer 17 is such
 that, when combined with the thicknesses of the dielectric support layer
 15 and those of the laminate structure, the total separation or spacing
 between the four-square antenna patch metalizations 11 and a ground plane
 metalization layer on the bottom surface of the laminate is preferably on
 the order of one-quarter of the wavelength of the highest frequency of
 operation of the array.
 As shown in the enlarged plan view of FIG. 2, each `trimmed` four-square
 element 11-i of the linear subarray 10 of FIG. 1 is configured as four,
 generally square-shaped conductive (metal) components or layers 21, 22, 23
 and 24, that are placed closely adjacent to one another on the top surface
 13 of dielectric support layer 15 in a generally square configuration, and
 are mutually spaced apart by narrow gaps 31, 32, 33 and 34 therebetween.
 The overall diagonal length D of an individual four-square element 11-i
 along longitudinal dimension 12 of linear subarray 10 may be on the order
 of one-half wavelength at the lowest frequency of operation of an antenna
 element.
 Each of the component-to-component gaps 31-34 may have a width W on the
 order of ten mils, leaving an interior diagonal corner-to-corner spacing
 SD on the order of 14.14 mils, as non-limiting example. The input
 impedance of a respective trimmed four-square antenna element 11-i is
 determined partially by the gap width, partially by the dimensions of its
 four-square components 21-24, and by the height or separation of the
 element above the underlying ground plane 18.
 Within a respective trimmed four-square antenna element 11-i, two
 diametrically opposed components 21 and 23 are electrically driven by
 means of a balanced power divider feed network to be described, at feed
 points 21F and 23F immediately their adjacent interior corners 41 and 43.
 This allows the trimmed four-square antenna element to be effectively fed
 at a center region thereof, so as to produce, for example, a broadside
 scanned linearly polarized radiation pattern. The physical separation or
 distance F between feed points 21F and 23F should be as small as possible,
 and is ideally equal to the diagonal gap separation between the diagonally
 opposed interior corners 41 and 43 of the respective driven components 21
 and 23.
 The feed points 21F and 23F may be slightly displaced from the corners of
 driven components 21 and 23, so as to provide sufficient surrounding metal
 for the attachment of center conductors 25 of sections of the coaxial
 cable 26 extending through plated apertures 14 in the support layer 15 and
 apertures 27 in the foam spacing layer 17, as shown diagrammatically in
 the side sectional view of FIG. 3. As a non-limiting example, the
 separation distance F between feed points 21F and 23F may be on the order
 of 86 mils. By appropriate opposite phase ((0.degree./180.degree.) feeding
 of the two opposed driven components 21 and 23 of a respective four-square
 element 11-i, such as porting the coax cable sections 26 to 0.degree. and
 180.degree. ports of a balun 28, linear polarization can be produced,
 thereby enabling the overall array to produce a highly directive linear
 polarization scanning of the beam, by controlling the phase for the driven
 components in a conventional manner.
 As further shown in the enlarged plan view of FIG. 2, the non-driven (or
 parasitic) and diametrically opposed `trimmed` components 22 and 24 of a
 respective trimmed four-square trimmed antenna element 11-i are located
 between the (0.degree./180.degree.) driven components 21 and 23. As noted
 previously, by `trimmed` is meant that outer corner portions of the
 non-fed components 22 and 24 of the set of four, shown in broken lines 52
 and 54, respectively, are effectively shaped as though they have been
 `trimmed` away.
 Namely, outer edges 62, 64 of the two diametrically opposed, non-fed
 components 22 and 24 are parallel to each other, and form acute angles
 with lines parallel to side edges of the square-shaped opposite
 phase-driven components 21 and 23. This trimmed shape leaves the side
 edges of a respective four-square element parallel to the longitudinal
 dimension 12 of the subarray 10. A typical trim spacing or margin T
 between side edges 62, 64 and parallel side edges 16, 17 of the low loss
 dielectric support layer 15 may be on the order of ten mils, as a
 non-limiting example.
 As pointed out above, such trimmed corner-shaping of the side edges 62 and
 64 of the non-driven components 22 and 24 provides what is effectively a
 linear physical geometry of multiple trimmed four-square antenna elements
 11 atop the narrow, thin dielectric support layer 15, and thereby
 facilitates compactly placing multiple trimmed subarrays in a highly
 spatially densified side-by-side arrangement, such as that shown in FIG.
 4. This allows for placement of more trimmed-square antenna elements 11 in
 a direction orthogonal to a subarray array 10 than in the longitudinal
 dimension of a subarray, so that the frequency of operation of an overall
 array comprised of the trimmed four-square antenna elements of the
 invention can be increased relative to that of a conventional four-square
 architecture, thereby improving bandwidth coverage. For a linearly
 polarized beam, a trimmed four-square array enjoys a frequency response
 that is equal to or better than a conventional non-trimmed four-square
 architecture.
 As shown in the side views of FIGS. 5-8 and the plan views of FIGS. 9-11,
 in order to conform with the desired `narrowness` of the trimmed or linear
 geometry of an individual stripe shaped subarray 10 shown in FIG. 1, the
 compact packaging architecture of the invention distributes a
 stripline-configured power divider-feed network 70 within a laminate
 structure 80, interposed between the bottom surf ace 19 of the foam
 support layer 17 and the ground plane layer 18. The printed circuit power
 divider network 70 is configured for the set of four, spatially
 successive, trimmed four-square antenna elements 11-1, 11-2, 11-3, 11-4
 formed atop the support layer 15.
 In particular, power divider-feed network 70, having the printed circuit
 configuration shown in detail in the plan view of FIG. 10, is formed on
 the bottom surface 81 of a first, generally stripe-shaped dielectric feed
 network support layer 82. Like the dielectric support layer 15, the
 dielectric support layer 82 may comprise a 28 mil thick layer of Duroid
 5870. A top surface 83 of the support layer 82 has a distribution of input
 ports 91, shown in FIG. 9, that are connected by conductive vias 84
 through support layer 82 to various connection points of the printed
 circuit network 70, as shown in the side view FIG. 6.
 An input port 91 provides an attachment location for the center conductor
 25 of a section of coax cable 26, which terminates at or abuts against the
 bottom surface 85 of a second generally stripe-shaped dielectric support
 layer 86 of the laminate structure 80. Dielectric support layer 86 may
 also comprise a 28 mil thick layer of Duroid 5870. A solder connection of
 the terminal end of the center conductor 25 of coax cable 26 to plated
 through hole 84 may be effected by using a metallic toroid or `donut` 89.
 As shown in FIG. 5, using a bonding layer (film) 93, the bottom surface 87
 of the support layer 82 and the power divider-feed network 70 are
 laminated against top surface 88 of the second, generally stripe-shaped
 dielectric support layer 86. A stripline ground plane metalization layer
 100, such as one ounce copper, is ubiquitously formed on bottom surface 85
 of support layer 86. As shown in the side view of FIG. 7, that is
 essentially complementary to the configuration of FIG. 6, the bottom
 surface 85 of the support layer 86 contains a distribution of output ports
 93, distributed as shown in the plan view of FIG. 11.
 The output ports are connected by way of conductive vias 94 through the
 support layer 85 to various connection points of the printed circuit
 network 70. An output port 93 provides an attachment location for the
 center conductor 95 of a section of input coax cable 96, which terminates
 at or abuts against the top surface 85 of the first generally
 stripe-shaped dielectric support layer 82 of the laminate structure 80.
 Again, a solder connection of the terminal end of the center conductor 95
 of coax cable 96 to plated through hole 94 may be readily effected by
 using a metallic toroid or `donut` 97. The input coax cable sections 96
 may be ported to external drive circuitry by way of an SMA type connector,
 as a non-limiting example.
 As shown in FIG. 10, pursuant to the laminate-based architecture of the
 invention, the printed circuit power divider network 70 is configured to
 include a balun 71 and an associated printed circuit branch network for
 the (0.degree./180.degree.) feed ports of the fed components of the
 trimmed four-square elements of the subarray 10. A first branch 72 of
 balun 71 extends via a first printed circuit link 73 to a first pair of
 spaced apart, trimmed four-square subarray feed ports 21F-1, 23F-2 for the
 first driven components 21 of respective first and second trimmed
 four-square antenna elements 11-1, 11-2 atop support layer 15.
 In a similar fashion, a second printed circuit link 74 extends from the
 balun 71 to a second pair of spaced apart feed ports for 21F-3, 21F-4 of
 driven components 21 of respective third and fourth second trimmed
 four-square elements 11-3, 11-4. Also, extending from a second branch 75
 of balun 71 is a third printed circuit link 76 to a third pair of spaced
 apart, the trimmed component feed ports 23F-1, 23F-2 for the driven
 components 23 of the first and second trimmed four-square elements 11-1,
 11-2. A fourth printed circuit link 77 extends from the balun to a fourth
 pair of spaced apart feed ports 23F-3, 23F-4 for the driven components 23
 of the third and fourth trimmed four-square elements 11-3, 11-4.
 FIGS. 12 and 13 depict, in solid lines, respective E- and H-plane
 co-polarized antenna patterns of a trimmed four-square element in
 accordance with the invention. Shown in broken lines are associated E- and
 H- plane patterns approximated using a Cos.sup.q (.theta.) pattern (for
 0.degree. less than or equal to .theta., and .theta. less than or equal to
 90.degree.. The value for q is equal to the ratio:
 log(F(.theta.))/log(cos.theta.), where .theta. is taken at -10 dB points.
 The cos.sup.q (.theta.) assumes no backplane radiation. In the
 co-polarized E-plane radiation pattern of FIG. 12, q=2.37, at a frequency
 of 8.5 GHz; in the co-polarized H-plane radiation pattern of FIG. 13,
 q=1.07, at a frequency of 8.5 GHz. FIG. 14, which is a plot of impedance
 vs frequency of a trimmed four-square antenna element, shows that its
 impedance characteristics are equal to or better than those of a
 conventional non-trimmed four-square element.
 Although the laminate configured phased array antenna architecture of the
 present invention has been described for the case of a `trimmed
 four-square`-based phased array antenna, it should be observed that the
 invention may be used with other types of radiating elements, whose
 spatial configurations readily lend themselves to being ported to the
 laminate-integrated power divider, balun and feed networks therefor. As
 non-limiting examples, FIG. 15 shows a linear array of relatively `narrow`
 printed dipole antenna elements 150, whose feed ports 151, 152 are
 spatially positioned in effectively the same geometry as the feed ports 23
 of the trimmed four-square arrangement of FIGS. 1-14, and may be readily
 mated with the underlying feed network laminate structure of the trimmed
 four-square embodiment.
 In like manner, FIG. 16 shows a linear array of relatively `wide` printed
 dipole antenna elements 160 having similarly spatially located feed ports
 161, 162. FIG. 17 shows a linear array of printed folded dipole antenna
 elements 170 having adjacent pairs of feed ports 171, 172, while FIG. 18
 shows a linear array of printed fan dipole antenna elements 180 with pairs
 of feed ports 181, 182. FIG. 19 shows a linear array of printed bowtie
 dipole antenna elements 190 having closely spaced feed ports 191, 192, and
 FIG. 20 shows a linear array of printed open sleeve dipole antenna
 elements 200 with adjacent feed ports 201, 202.
 While we have shown and described several embodiments in accordance with
 the present invention, it is to be understood that the same is not limited
 thereto but is susceptible to numerous changes and modifications as are
 known to a person skilled in the art, and we therefore do not wish to be
 limited to the details shown and described herein, but intend to cover all
 such changes and modifications as are obvious to one of ordinary skill in
 the art.