Information
-
Patent Grant
-
6611180
-
Patent Number
6,611,180
-
Date Filed
Tuesday, April 16, 200222 years ago
-
Date Issued
Tuesday, August 26, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Cunningham; Terry D.
- Tra; Quan
Agents
- Daly, Crowley & Mofford, LLP
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
Abstract
A planar circulator assembly includes a dielectric substrate having a first surface and an opposing second surface, a plurality of circulator circuits, each circulator circuit having a first ferrite receiving pad disposed on the first surface and a second ferrite receiving pad; disposed on the second surface a first sub-assembly board disposed on the first surface having a plurality of first apertures, a plurality of ferrite-magnet sub-assemblies, each ferrite-magnet sub-assembly disposed in a corresponding first aperture and aligned with a corresponding first ferrite receiving pad and electromagnetically coupled to the corresponding first ferrite receiving pad. The assembly further includes a second sub-assembly board disposed on the second surface having a plurality of second apertures, and a plurality of ferrites, each ferrite disposed in a corresponding second aperture and aligned with a corresponding second ferrite receiving pad and electromagnetically coupled to the corresponding second ferrite receiving pad.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
FIELD OF THE INVENTION
This invention relates generally to communications systems and, more particularly, to planar circulators and methods of fabrication.
BACKGROUND OF THE INVENTION
As is known in the art, a radar or communications system antenna generally includes a feed circuit and at least one conductive member generally referred to as a reflector or radiator. As is also known, an array antenna can include a plurality of radio frequency (RF) circulators disposed in an array in a manner in which RF signals can be received from or transmitted to the same individual radiator. Sharing the radiators for both transmitting and receiving signals allows a reduction in the size of the antenna in applications where simultaneous transmission and reception is not required. The circulators are also referred to as transmit/receive (T/R) elements.
As is also known in the art, the radio frequency (RF) circulator is a three-port device, having a first, a second, and a third port. A conventional circulator provides a directional capability so that an RF signal applied as an input to the first port provides an output signal at only the second port. Similarly, an RF signal applied as an input to the second port provides an output signal at only the third port, and an RF signal applied as an input to the third port provides an output signal at only the first port.
Conventional circulators are typically provided as discrete devices that can be mounted to a circuit board. Since it contains discrete devices, the conventional circulator does not provide an optimal form factor for high density electronics packaging. In commercial applications, it is often desirable to integrate RF circuits into low profile, low cost packages. For example such devices would be desirable for commercial cell phones. In military surface and airborne applications, there is a need for tile arrays having multiple board layers. Further, in these applications there is a need for low profile, low cost arrays which often require a large number of circulators for corresponding radiators. In conventional systems the circulators are often individually packaged in the transmitter/receiver (T/R) modules thereby increasing module cost and increasing the unit cell footprint so as to reduce an array scan volume versus frequency characteristic due to interference from adjacent lobes in the antenna pattern.
One conventional method (referred to as the discrete method) includes steps for fabricating individual circulators having gaussed (i.e. magnetized) magnets and embedding each individual circulator in a dielectric or metal carrier. This method requires precise alignment and ribbon (or wire) bonding to complete the RF circuit. In addition, the gaussed magnets must be individually magnetized and are exposed to high lamination temperatures during fabrication. Consequently, the magnets experience partial de-magnetization causing a non-uniform magnetization adversely affecting circulator performance. This effect is a function of magnet location across the array. Embedding each individual circulator in a dielectric or metal carrier requires precise individual alignment between the circulator transmission line ports and the carrier transmission line ports. Ribbon (or wire) bonding between circulator transmission lines and board transmission lines to complete an RF circuit requires special plating (e.g., gold plating) for soldering or bonding. Consequently, the RF bandwidth is reduced and signal losses are increased due to process variations that add parasitic reactances to the RF transmission line.
It would, therefore, be desirable to eliminate the ribbon or wire bonding steps, and reduce the alignment tolerances and magnetize (gauss) the magnets after lamination and processing. It would be further desirable to reduce the antenna unit cell spacing by reducing the T/R module footprint to provide a larger scan volume. It would be further desirable to seal the circulators from the environment, and to produce planar assemblies with a plurality of circulators and to produce individual circulators in bulk at a low cost.
SUMMARY OF THE INVENTION
In accordance with the present invention, a planar circulator assembly includes a dielectric substrate having a first surface and an opposing second surface, a plurality of circulator circuits each having a first ferrite receiving pad disposed on the first surface and a second ferrite receiving pad disposed on the second surface a first sub-assembly board. The first sub-assembly board is disposed on the first surface, has a plurality of first apertures, a plurality of ferrite-magnet sub-assemblies, each ferrite-magnet sub-assembly disposed in a corresponding first aperture and aligned with a corresponding first ferrite receiving pad and electromagnetically coupled to the corresponding first ferrite receiving pad. The assembly further includes a second sub-assembly board disposed on the second surface having a plurality of second apertures, and a plurality of ferrites each disposed in a corresponding second aperture aligned with a corresponding second ferrite receiving pad and electromagnetically coupled to the corresponding second ferrite receiving pad.
This arrangement eliminates fabrication of individual circulators by embedding each individual circulator in a dielectric or metal carrier. Such an arrangement further eliminates precise alignment and ribbon (or wire) bonding for attaching circulators in fixed orientations to complete the RF circuit by using epoxies and/or solders. With such an arrangement, a plurality of low-profile circulators are embedded in a multi-layer laminate in one bonding step using standard Printed Wiring Board (PWB) and Surface Mount Technology (SMT) processes, for example this arrangement reduces the antenna unit cell spacing by reducing the T/R module footprint in order to provide a larger radar scan volume.
In accordance with a further aspect of the present invention, a planar circulator assembly includes at least one first RF port via disposed in the first sub-assembly board, each first RF port via having a first end coupled to a corresponding one of the first, second and third ports and a second end coupled to a connection disposed on a first outer surface of the circulator assembly. The planar circulator assembly further includes at least one second RF port via disposed in the second sub-assembly board, each second RF via having a first end coupled to one of the first, second and third ports and a second end coupled to a connection disposed on a second outer surface of the circulator assembly disposed opposite the first outer surface. With such an arrangement, the circulators can be bonded to seal the circulators from the environment.
In accordance with a further aspect of the present invention, a method for making an embedded planar circulator assembly includes providing a circulator board having a first surface and an opposing second surface, forming a plurality of circulator circuits disposed on the circulator board, each circuit having a ferrite receiving pad disposed on the first surface and a corresponding ferrite receiving pad on the second surface, providing a plurality of ferrite-magnet sub-assemblies disposed in a first sub-assembly. The method further includes providing a plurality of ferrites disposed in a second sub-assembly, and bonding the circulator board between the first sub-assembly and the second sub-assembly such that the ferrite-magnet sub-assemblies are urged against a corresponding ferrite receiving pad disposed on the first surface of the circulator board and the ferrites are urged against the corresponding ferrite receiving pad on the second surface of the circulator board. With such a technique, the ribbon or wire bonding steps are eliminated, alignment tolerances are reduced and the magnets can be magnetized after the lamination and processing steps.
In accordance with another aspect of the present invention, a method for making an embedded planar circulator assembly further includes separating the plurality of circulator circuits into a corresponding plurality of individual unit cells. With this technique, individual circulators can be produced in bulk in a low profile package and at a low cost.
The relatively high cost of phased arrays has precluded the use of phased arrays in all but the most specialized applications. Assembly and component costs (especially the active transmit/receive module including circulators) are major cost drivers. Phased array costs can be reduced by leveraging batch processing and minimizing touch labor of components and assemblies. In one embodiment, the circulators which are typically discrete components wired into T/R modules, are embedded in Polytetrafluoroethylene (PTFE) dielectric laminates, thus reducing cost and complexity in the T/R modules. In addition, the size of the unit cell of a phased array is reduced by including the array of circulators in a single planar assembly. The embedded planar circulator is fabricated with high temperature bonding adhesives common to the PWB industry and the circulator magnets are conveniently magnetized after bonding. The result is a compact, sealed, low cost and high performance array of circulators in a planar array arrangement. Individual circulators are produced in volume by spacing a plurality of circulators on a single circulator board to facilitate separation into individual unit cells.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing features of this invention, as well as the invention itself, may be more fully understood from the following description of the drawings in which:
FIG. 1
is a block diagram of a radar or communications system including an embedded planar circulator assembly in accordance with the present invention;
FIG. 2
is an exploded perspective view of the embedded planar circulator assembly of
FIG. 1
;
FIG. 3A
is an isometric view of a circulator circuit board unit cell of the embedded planar circulator assembly of
FIG. 2
;
FIG. 3B
is an isometric view of the unit cell of
FIG. 3A
including interconnecting vias;
FIG. 3C
is an isometric view of the unit cell of
FIG. 3A
including mode suppression posts and transmit, receive and antenna RF vias;
FIG. 4
is a cross-sectional view of the embedded planar circulator assembly of FIG.
1
and circulator circuit of
FIG. 3
taken across line
4
—
4
in
FIG. 3
;
FIG. 4A
is a more detailed cross-sectional view of a counter drilled via of
FIG. 4
;
FIG. 5
is an exploded cross-sectional view of the upper encapsulating sub-assembly of the embedded planar circulator assembly of
FIG. 1
;
FIG. 6
is an exploded cross-sectional view of the lower encapsulating sub-assembly of the embedded planar circulator assembly of
FIG. 1
; and
FIG. 7
is a flow diagram illustrating the steps to fabricate the embedded planar circulator of FIG.
1
.
DETAILED DESCRIPTION OF THE INVENTION
Before describing the radar system of the present invention, it should be noted that reference is sometimes made herein to a circulator board having a particular array shape. One of ordinary skill in the art will appreciate of course that the techniques described herein are applicable to various sizes and shapes of circulator boards. It should thus be noted that although the description provided herein below describes the inventive concepts in the context of a rectangular unit cell, those of ordinary skill in the art will appreciate that the concepts equally apply to other sizes and shapes of array antennas having corresponding circulator board arrays arrangements including, but not limited to, rectangular, circular, and other arbitrary lattice geometries such as square, equilateral, isosceles triangle, and spiral geometries. Each embedded circulator occupies a portion of the unit cell area for each antenna element. The inventive embedded planar circulator approach is applicable to linear or circularly polarized phased arrays for military or commercial wireless applications.
Reference is also sometimes made herein to the array antenna including a radiating element of a particular type, size and shape. For example, one type of radiating element is a so-called patch antenna element having a square shape and a size compatible with operation at a particular frequency (e.g. 10 GHz). Those of ordinary skill in the art will recognize, of course that other shapes and types of antenna elements may also be used and that the size of one or more radiating elements may be selected for operation at any frequency in the RF frequency range (e.g. any frequency in the range of about 1 GHz to about 100 GHz). The types of radiating elements which may be used in the antenna of the present invention include but are not limited to notch elements, dipoles, slots or any other radiating element known to those of ordinary skill in the art which can be coupled to a circulator.
Referring now to
FIG. 1
, an exemplary embodiment of a radar or communications system
100
including an embedded planar circulator assembly
10
in accordance with the present invention for transmitting and receiving signals is shown. The radar or communication system
100
includes an antenna array
16
having a plurality of radiating elements
12
a
-
12
n
(generally referred to as radiating elements
12
). The embedded planar circulator assembly
10
includes a plurality of transmit/receive (T/R) modules
14
a
-
14
n
(generally referred to as T/R modules
14
). The radiating elements
12
are coupled to corresponding T/R modules
14
a
-
14
n
, each of which is coupled to a plurality of amplifiers
24
a
-
24
n
and a plurality of phase shifters
22
a
-
22
n
in the transmit path and a plurality of amplifiers
20
a
-
20
n
, a plurality of attenuators
26
a
-
26
n
and a plurality of phase shifters
28
a
-
28
n
in the receive path, respectively. In a radar system the T/R modules
14
can be shared by the radiating elements of both a sum channel beamformer (not shown) and a difference channel beamformer (not shown), for example.
Now referring to FIG;
2
, an embedded planar circulator assembly
10
includes an upper board sub-assembly
40
disposed on a circulator circuit board
42
, which is disposed on a lower board sub-assembly
44
. The upper board sub-assembly
40
includes a plurality of recessed two-step cavities
46
adapted to receive a plurality of ferrite-magnet sub-assemblies
48
, which includes a magnet
50
disposed on a ferrite
52
.
The upper board sub-assembly
40
further includes a plurality of antenna port vias
62
adapted to connect to a plurality of radiators (not shown). The circulator circuit board
42
comprises a plurality of circulator board unit cells
54
a
-
54
n
(generally referred to as unit cells
54
), which are coupled to the plurality of antenna port vias
62
and to the plurality of ferrite-magnet sub-assemblies. The lower board sub-assembly
44
includes a plurality of recessed cavities
58
adapted to receive a plurality of ferrite-pole piece assemblies
59
. The plurality of ferrite-pole piece assemblies
59
include a plurality of ferrites
56
disposed on a corresponding plurality of pole pieces
57
, here for example steel pole pieces
57
which have approximately the same diameter of the ferrite
56
and are bonded to each of the ferrites
56
. The lower board sub-assembly
44
further includes a plurality of receive port vias
64
and transmit port vias
66
which are adapted to couple receive and transmit feed circuits (not shown) to respective ports on the plurality of circulator board unit cells
54
. It will be appreciated by those of ordinary skill in the art that that the lower ferrite
56
and pole piece
57
forming ferrite-pole piece assemblies
59
can be replaced with a ferrite-pole piece-magnet assembly, and that pole pieces (not shown) can be added to the upper ferrite-magnet sub-assemblies
48
for improved bandwidth and lower loss.
In one particular embodiment, the circulator circuits include etched copper circuits on both sides of a copper clad PTFE (Polytetrafluoroethylene) substrate, for example Rogers 3010 (a high frequency circuit material manufactured by Rogers corporation), and the upper and lower upper board sub-assembly
40
and
44
are fabricated from PTFE. In another embodiment the ferrite
52
material is includes Garnet and the magnet
50
material includes Samarium Cobalt (SmCo). The magnets
50
provide a static (DC) magnetic field to each circulator board unit cell
54
to induce circulator action. Other exemplary materials and properties used in the alternate embodiments of the embedded planar circulator assembly
10
are listed in Table 1:
TABLE 1
|
|
Embedded Planar Circulator Materials
|
Description
Material Property
Exemplary Material
|
|
Thermoplastic
ε
r
= 2.32; tanδ = .0013
Arlon CuClad 6250
|
Adhesive
|
Circuit Carrier
ε
r
= 10.2; tanδ = .0035
Rogers 3010
|
Upper & Lower
ε
r
= 10.2; tanδ = .0035
Rogers 3010
|
Board Substrate
|
(40, 44)
|
Ferrite (52, 56)
ε
r
= 15.8; tanδ = 0.0002;
Garnet Ferrite
|
σ = 0.01 S/m
Material
|
4πMs = 1780; ΔH = 45
|
Oersteds; Lande g = 2
|
Magnet (50)
Hdc = 40 kA/m
Samarium-Cobalt
|
magnet
|
Pole Piece (57)
410 Steel
|
|
Where
ε
6
is the dielectric constant;
tan δ is the loss tangent of the material;
Hdc is the static (DC) magnetic field; and
410 Steel is a typical steel material used to provide pole pieces.
Now referring to
FIG. 3A
, a circulator board unit cell
54
includes an upper surface circuit portion
68
u
and a corresponding lower surface circuit portion
681
separated by an insulating dielectric
43
of the circulator board
42
. The upper surface circuit portion
68
u
includes a first port portion
70
u
coupled to an upper circulator junction
76
u
(also referred to as upper ferrite receiving pad) by a stripline circuit
84
u
. The upper circulator junction
76
u
is coupled to a second port portion
72
u
by a stripline circuit
86
u
and to a third port portion
74
u
by a further stripline circuit
82
u
. The first port portion
70
u
includes a connection
91
TX
, the second port portion
72
u
includes a connection
91
RX
, and the third port portion
74
u
includes a connection
91
A
.
The lower surface circuit portion
681
includes a first port portion
701
coupled to a lower circulator junction
761
(also referred to as lower ferrite receiving pad
761
) by a stripline circuit
841
. The lower circulator junction
761
is coupled to a second port portion
721
by a stripline circuit
861
and to a third port portion
741
by a further stripline circuit
821
. The first port portion
701
includes a connection
91
TX
, the second port portion
721
includes a connection
91
RX
, and the third port portion
741
includes a connection
91
A
. The connections
91
RX
,
91
TX
,
91
A
are coupled to plated RF vias
90
RX
,
90
TX
and
90
A
when these vias are fabricated. The upper and lower surface circuits
68
u
,
681
and the upper and lower circulator junctions
761
,
76
u
include a plurality of interconnecting via connections
79
a
-
79
n
(generally referred to as interconnecting via connections
79
).
Now referring to
FIG. 3B
showing different elements of the circulator board unit cell
54
of
FIG. 3A
which are shown separately for clarity, a plurality of plated interconnecting vias
78
a
-
78
n
connect the stripline circuits
82
u
,
84
u
, and
86
u
on the upper surface circuit
68
u
to corresponding circuit elements on the lower surface circuit
681
. For clarity, not all of the plated interconnecting vias
78
a
-
78
n
are shown. The plated interconnecting vias
78
a
-
78
n
are coupled to the plurality of interconnecting via connections
79
. Thus, the upper and lower surface circuits
68
u
,
681
are electrically interconnected with the plated interconnecting vias
78
forming an equivalent “thicker” RF circuit for each of the unit cells
54
. The thicker RF circuits are referred to as transmission lines
82
,
84
and
86
which are connected to the interconnected circulator junction
76
u
and
761
referred to as the circulator junction
76
or the ferrite receiving pad
76
. The plated interconnecting vias
78
a
-
78
n
are formed during fabrication of the circulator board
42
(described below in further detail in conjunction with step
202
of FIG.
7
). The upper and lower surface circuits
68
u
,
681
include a plurality of mode suppression post connections
81
.
Now referring to
FIG. 3C
showing different elements of the circulator board unit cell
54
of
FIG. 3A
which are shown separately for clarity, a plurality of mode suppression posts
80
are disposed between the upper surface circuit portion
68
u
and the lower surface circuit portion
681
. For clarity, not all of the plurality of mode suppression posts
80
are shown. The RF circuit further includes a receive port RF via
90
RX
, an antenna port RF via
90
A
, and a transmit port RF via
90
TX
(the three vias are generally referred to as RF vias
90
) for each unit cell
54
.
FIG. 3C
is shown for clarity without the plurality of plated interconnecting vias
78
a
-
78
n
of FIG.
3
B. Thus the upper and lower surface circuits
68
u
and
681
are electrically interconnected with the plated RF vias
90
RX
,
90
TX
and
90
A
forming an equivalent “thicker” RF circuit for each of the unit cells
54
and, in particular, form a first port
70
, second port
72
and third port
74
connected to the circulator junction
76
(ferrite receiving pad
76
) through transmission lines
82
-
86
. In one embodiment the first port
70
is a transmit port, the second port
72
is a receive port, and the third port
74
is an antenna port. It will be appreciated by those of ordinary skill in the art that an embedded planar isolator can be provided by terminating either the transmit RF port via
90
TX
or the receive RF port via
90
RX
in a resistive load. The RF vias
90
are disposed in the upper board sub-assembly
40
,the circulator circuit board
42
and the lower board sub-assembly
44
. For clarity, the RF vias
90
A
,
90
RX
,
90
TX
are not shown being terminated in connections on the outer surfaces of the upper board sub-assembly
40
,and the lower board sub-assembly
44
respectively.
The circulator board
42
includes a plurality of mode suppression posts
80
(
FIG. 3C
) having first ends, for example, disposed in a circular pattern partially surrounding circuit portions
70
u
,
72
u
,
74
u
, and having second ends disposed in a circular pattern partially surrounding circuit portions
701
,
721
,
741
. The mode suppression posts
80
include plated vias coupled to ground planes
98
,
99
(
FIG. 4
) to provide pseudo-coaxial RF transmission lines in combination with the corresponding port vias
90
for each RF port. For clarity, the mode suppression posts
80
are not shown being coupled to ground planes
98
,
99
. The RF vias
90
and mode suppression posts
80
are formed after the sub-assemblies have been bonded (described below in further detail in conjunction with steps
222
-
228
).
In one particular embodiment, the upper surface circuit
68
u
and the corresponding lower surface circuit
681
are etched copper circuits, the circulator board
42
is about 0.005 inches thick, the connections
79
,
81
,
91
RX
,
91
TX
,
91
A
are plated-thru holes, and the ferrite receiving pad
76
has a diameter of about 0.2 inches.
Now referring to
FIG. 4
, in which like reference numbers refer to like elements in
FIG. 3
, a cross section of
FIG. 3A
being taken along line
4
—
4
including the upper board sub-assembly
40
and the lower board sub-assembly
44
(
FIG.2
) is shown. An individual circulator unit cell
54
includes a magnet
50
disposed on a ferrite
52
, which is disposed on a circulator circuit board
42
. The unit cell
54
includes a pseudo-coaxial transmission line formed by antenna port
74
u
and
741
(FIG.
3
C), plated interconnecting vias
78
a
-
78
n
, mode suppression posts
80
and RF via
90
A
which are coupled to the circulator junction
76
(
FIG. 3B
) by the stripline circuit
82
(FIG.
3
C), a receive port
72
RF via
90
RX which is coupled to the circulator junction
76
by the stripline circuit
86
(FIG.
3
A), and a transmit port RF via (not shown). The antenna port RF via
90
A
includes a plated portion
92
A
in the upper board sub-assembly
40
and a counter-drilled portion
94
A
in the lower board sub-assembly
44
. The receive port RF via
90
RX
includes a plated portion
92
RX
in the lower board sub-assembly
44
and a counter-drilled portion
94
RX
in the upper board sub-assembly
40
. The upper board sub-assembly
40
includes a ground plane
98
and the lower board sub-assembly
44
includes a further ground plane
99
. The ground planes
98
,
99
complete the stripline circuit formed by the upper surface circuit portion
68
u and the lower surface circuit portion
681
. The transmit port RF via includes a plated portion (not shown) in the lower board sub-assembly
44
and a counter-drilled portion (not shown) in the upper board sub-assembly
40
.
In operation, received signals are coupled from an antenna radiator (not shown) through the antenna port RF via
90
A
through the stripline circuit
82
to the circulator junction
76
where the signals controlled by known circulator action are directed to the receive port RF via
90
RX
through the stripline circuit
86
. The receive port RF via
90
RX
couples received signals to the receiver circuitry (not shown). Transmitted signals are coupled from the transmitter circuitry (not shown) to the transmit port RF via through the stripline circuit
84
to the circulator junction
76
where the signals controlled by known circulator action are directed through the stripline circuit
82
to the antenna port RF via
90
A
which is coupled to the antenna radiator (not shown).
Now referring to
FIG. 4A
, in which like reference numbers refer to like elements in
FIG. 4
, an RF via
90
(which here represents either the receive or transmit RF via) includes a plated portion
92
substantially disposed in the lower board sub-assembly
44
and a counter-drilled portion
94
. An upper interconnection
96
u
with the upper surface circuit portion
68
u
and a lower interconnection
96
lower with the lower surface stripline circuit
681
is formed when the via
90
is drilled out and plated. In a subsequent operation, the RF via
90
is counter drilled to remove the plating in the counter-drilled portion
94
to eliminate any unwanted RF effects. It will be appreciated that antenna RF via plated portion
92
A
is substantially disposed in the upper board sub-assembly
40
and
FIG. 4A
would be rotated
180
degrees to illustrate RF via plated portion
92
A
.
Now referring to
FIG. 5
, in which like reference numbers refer to like elements in
FIG. 2
, before bonding, an upper board sub-assembly
40
includes the plurality of cavities
46
a
-
46
n
into which the plurality of ferrite-magnet sub-assemblies
48
are press fit. Before the lower board sub-assembly
44
, the upper board sub-assembly
40
and circulator circuit board
42
are bonded together, the ferrite-magnet sub-assemblies
48
stand proud (i.e. are taller than the cavities
46
) of the upper board sub-assembly
40
. After bonding under temperature and pressure, the ferrite-magnet sub-assemblies
48
are urged into contact with the circulator junction
76
.
Now referring to
FIG. 6
in which like reference numbers refer to like elements in
FIG. 2
, before bonding, a lower board sub-assembly
44
includes the plurality of cavities
58
a
-
58
n
into which the plurality of ferrite-pole piece assemblies
59
(
FIG. 2
) are press fit. Before the lower board sub-assembly
44
upper board sub-assembly
40
and circulator circuit board
42
are bonded together, the ferrite-pole piece assemblies
59
stand proud (i.e. are taller than the cavity
58
) of the lower board sub-assembly
44
. After bonding under temperature and pressure, the ferrites
56
are urged into contact with the ferrite receiving pad
76
.
Now referring to
FIG. 7
, a flow diagram illustrates exemplary steps to fabricate the embedded planar circulator assembly
10
of FIG.
1
. The procedure starts at step
200
, then at step
202
interconnecting vias
78
a
-
78
n
(
FIG. 3
) on circulator board
42
are drilled and plated. In one example, the circulator board is a 5-mil PTFE substrate and circuit etch tolerances of ±0.5-mils (typically associated with 0.5-oz. copper plating) are used.
At step
204
, the upper surface circuit portion
68
u
(
FIG. 3
) and lower surface circuit
681
are imaged and etched on the circulator board
42
using known PWB techniques. The two circuit portions
68
u
,
681
are electrically connected by plated interconnecting vias
78
a
-
78
n
that were formed in step
202
.
At step
206
, the ferrite-magnet sub-assemblies
48
are fabricated by bonding the magnets
50
onto ferrites
52
. In one embodiment, the magnets
50
and the ferrites
52
are soldered together using a high temperature solder. The magnets
50
do not have to be magnetized at this step in the process.
At step
208
, the upper board sub-assembly
40
is fabricated using layers of PTFE material with cutouts in at least two layers in order to form the recessed two-step cavities
46
adapted to receive a plurality of ferrite-magnet sub-assemblies
48
. At step
210
, the ferrite-magnet sub-assemblies
48
are press fit into the recessed two-step cavities
46
in order to securely retain the assemblies
48
until the bonding step
220
. In one embodiment, the assemblies
48
are press fit using pick and place assembly techniques. The two-step cavity
46
has a diameter and depth such that the ferrite-magnet sub-assembly fits securely and also stands proud of the cavity
46
in order to assure a reliable contact between the ferrite-magnet sub-assembly
48
and the ferrite receiving pad
76
after the planar circulator assembly
10
is bonded at step
220
.
At step
211
, the pole pieces
57
are bonded to the ferrites
56
to provide the ferrite-pole piece assembly
59
(FIG.
2
), for example, by using a high temperature solder.
At step
212
, the lower board sub-assembly
44
is fabricated using layers of PTFE material with cutouts in at least one layer in order to form the recessed cavities
58
adapted to receive a plurality of ferrite-pole piece assemblies
59
. In one embodiment the lower board sub-assembly is fabricated with recessed two-step cavity for an optional additional magnet.
At step
214
the ferrite-pole piece assemblies
59
are press fit into the recessed cavities
58
in order to securely retain the ferrite-pole piece assemblies
59
until the bonding step
220
. In one embodiment, the ferrite-pole piece assemblies
59
are press fit using pick and place assembly techniques. In an alternate embodiment, an additional magnet (not shown) is bonded to the ferrite-pole piece assembly
59
for improved bandwidth and lower loss for high performance applications. To accommodate the additional magnet, the lower board assembly
44
includes a recessed two-step cavity (not shown).
At step
216
, upper and lower adhesive bonding sheets
41
and
45
having cutouts aligned with ferrite-magnet sub-assemblies
48
and the ferrite-pole piece assemblies
59
respectively are placed on each side of the circulator board
42
. In one embodiment, the adhesive bonding sheets
41
and
45
comprise a thermoplastic material such as fluorinated ethylene propylene (FEP). Other materials widely used in the PWB industry, including but not limited to, thermoset materials such as Speedboard-C™ (manufactured by W. L. Gore & Associates, Inc.) can be used to provide the bonding sheets
41
and
45
. The adhesive bonding sheets
41
and
45
are pre-drilled to allow direct contact between the ferrite disks and the ferrite-magnet sub-assemblies
48
with the circulator junctions in order to reduce RF signal loss.
At step
218
, the two sub-assemblies
40
and
42
are aligned with the circulator board
42
. In one embodiment, alignment pins are used.
At step
220
, the embedded planar circulator assembly
10
is bonded under temperature and pressure. The lamination cycle parameters range in temperature from about 250° F. to about 650° F. and in pressures from about 100 psi to about 300 psi depending on the particular materials used. High temperature thermoplastic adhesives are used in this step in order to provide flexibility in fabricating multi-layer stripline circuit assemblies. Multi-layer Printed Circuit Boards with complex architecture are often fabricated using sequential laminations. This technique requires creating sub-assemblies with multiple laminations, done in sequence, starting with the highest temperature bonding materials. The succeeding laminations are done at progressively lower temperatures to prevent the re-melting of the previously created bond lines. Exemplary materials used for the lamination of one layer to another include a thermoplastic and a thermoset material. Thermoset materials, once they have been cured, will not soften or re-melt, and so they are may be a preferred choice for the first lamination in a sequential lamination process. Thermoplastic materials will soften each time they reach their melt temperature. Therefore, when using thermoplastic materials, that the melt temperature in subsequent fabrication steps should be kept below the melt temperature of the previously applied thermoplastic materials. In one embodiment, for example, 875 circulators are formed and embedded using a 18″×24″ sheet of Rogers 3010 with a triangular lattice arrangement of each unit cell spaced 0.590″ and 0.680″ from adjacent unit cell
54
(for X-Band applications) in a single bonding operation. It will be appreciated by those of ordinary skill in the art that the planar circulator design is practical over a range including the S Band through the Ka-Band. In one embodiment, the three sub-assemblies
40
,
42
and
44
include tooling holes (not shown) located outside the circuit area which are used to hold the assemblies in place in an alignment fixture
At step
222
, after the planar circulator assembly
10
is laminated, RF vias for the receive port RF via
90
RX
, the antenna port RF via
90
A
, and the transmit port RF via
90
TX
are drilled through the circulator assembly
10
.
At step
223
, after the planar circulator assembly
10
is laminated, mode suppression posts for the receive port RF via
90
RX
, the antenna port RF via
90
A
, and the transmit port RF via
90
TX
are drilled through the circulator assembly
10
. At step
224
the RF vias
90
and mode suppression posts, which were drilled out in steps
222
,
223
, are plated using known techniques. In one embodiment the vias
90
are plated with copper.
At step
226
, circuits are imaged and etched on both external surfaces of the assembly the outside surfaces of the circulator assembly
10
assembly. The via stubs
94
are drilled out using a known counter drilling (also referred to as depth drilling) technique to remove the excess plating material so that the un-terminated plated via portions will not a conduct RF signal and act as reactive stubs, at step
228
.
At step
230
, the magnets
50
are individually or batch gaussed (i.e. magnetized) to provide a direct current (DC) magnetic field required to support the circulator action. By gaussing the magnets
50
to saturation after the bonding operation at step
220
, the magnets
50
do not lose any of the required magnetic field strength due to the effects of the bonding temperatures. In one embodiment, the magnets
50
are gaussed by placing the planar circulator assembly
10
in the proper orientation between the poles of an electromagnet.
At step
232
, the fabrication of the embedded planar circulator assembly
10
is complete. As described above, if the unit cells
54
are to be used as individual components, the circulator assembly
10
would be further processed to separate the unit cells (i.e. individual circulators) from the final assembly. To facilitate the production of individual components, the overall board layout would be optimized for ease of separation and to maximize the quantity of individual circulators produced. It will be appreciated by those of ordinary skill in the art that some of the above steps can occur in a different order to facilitate the manufacturing process.
In an alternative embodiment, either the transmit port or the receive port is terminated in a resistive load to provide an embedded planar isolator. In one embodiment, the resistive load is provided by resistors buried in the circulator PTFE board layers, for example, Ohmega-Ply® resistors, as is known in the art. The resistors are embedded in the circulator circuit board
42
, etched and exposed on the circulator circuit
54
(
FIG. 3
) to terminate the receive port
72
or the transmit port
70
. Ohmega-Ply® is a registered trademark of Ohmega Technologies, Inc. Configurations having buried resistors are used for example in applications where a low radar cross section (RCS) is required.
All publications and references cited herein are expressly incorporated herein by reference in their entirety.
Having described the preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments but rather should be limited only by the spirit and scope of the appended claims.
Claims
- 1. A planar circulator assembly comprising:a dielectric substrate having a first surface and an opposing second surface; a plurality of circulator circuits each having a first ferrite receiving pad disposed on the first surface and a second ferrite receiving pad disposed on the second surface; a first sub-assembly board disposed on the first surface of the dielectric substrate having a plurality of first apertures; a plurality of ferrite-magnet sub-assemblies, each ferrite-magnet sub-assembly disposed in a corresponding one of the first apertures and aligned and electromagnetically coupled with a corresponding one of the first ferrite receiving pads; a second sub-assembly board disposed on the second surface of the dielectric substrate having a plurality of second apertures; and a plurality of ferrites, each ferrite disposed in a corresponding one of the second apertures and aligned and electromagnetically coupled with a corresponding one of the second ferrite receiving pads.
- 2. The circulator assembly of claim 1 wherein each of the plurality of ferrites further comprises a pole piece.
- 3. The circulator assembly of claim 2 wherein the pole piece is steel.
- 4. The circulator assembly of claim 1 further comprising:a first ground plane disposed in the first sub-assembly board; and a second ground plane disposed in the second sub-assembly board.
- 5. The circulator assembly of claim 1 wherein each of the plurality of circulator circuits further comprises a first circuit portion disposed on the first surface and a second circuit portion disposed on the second surface.
- 6. The circulator assembly of claim 1 wherein:the first ferrite receiving pad comprises a first plurality of interconnecting via connections; the second ferrite receiving pad comprises a second plurality of interconnecting via connections; and the circulator assembly further comprises a plurality of interconnecting vias each having a first end coupled to a corresponding one of the first plurality of interconnecting via connections and a second end coupled to a corresponding one of the second plurality of interconnecting via connections.
- 7. The circulator assembly of claim 1 wherein each of the plurality of circulator circuits further comprises:a first port coupled to the first and second ferrite receiving pads; a second port coupled to the first and second ferrite receiving pads; and a third port coupled to the first and second ferrite receiving pads.
- 8. The circulator assembly of claim 7 wherein each of the first, second and third ports comprises:a first portion disposed on the first surface of the dielectric substrate having a first RF port via connection; a second portion disposed on the second surface of the dielectric substrate having a second RF port via connection; and an RF port via having a first end coupled to the first RF port via connection and a second end coupled to the second RF port via connection.
- 9. The circulator assembly of claim 8 wherein the RF port via extends to an outer surface of one of the first sub-assembly board and the second sub-assembly board.
- 10. The circulator assembly of claim 8 further comprising:a first ground plane disposed in the first sub-assembly board; a second ground plane disposed in the second sub-assembly board; a first plurality mode suppression post connections disposed adjacent each a plurality of mode suppression posts disposed adjacent to each of the first, second and third ports and coupled to the first and second ground planes.
- 11. The circulator assembly of claim 8 wherein each of the plurality of circulator circuits further comprises a plurality of stripline transmission lines coupling each of the first, second and third ports to the first and second ferrite receiving pads.
- 12. The circulator assembly of claim 11 wherein each of the stripline transmission lines comprises:a first stripline circuit portion disposed on the first surface having a first plurality of interconnecting via connections; a second stripline circuit portion disposed on the second surface having a second plurality of interconnecting via connections; and a plurality of interconnecting vias each having a first end coupled to a corresponding one of the first plurality of interconnecting via connections and a second end coupled to a corresponding one of the second plurality of interconnecting via connections.
- 13. The circulator assembly of claim 7 wherein the first, second and third ports comprise an antenna port, a transmit port and a receive port respectively.
- 14. The circulator assembly of claim 7 wherein the first, second and third ports comprise an antenna port, an isolator port, and at least one of:a transmit port; and a receive port.
- 15. The circulator assembly of claim 7 further comprising:a first outer surface; a second outer surface disposed opposite the first outer surface; at least one first RF port via disposed in the first sub-assembly board, having a first end coupled to at least one of the first, second and third ports and a second end coupled to a connection disposed on the first outer surface of the circulator assembly; and at least one second RF port via disposed in the second sub-assembly board, having a first end coupled to at least one different one of the first, second and third ports and a second end coupled to a connection disposed on the second outer surface of the circulator assembly disposed opposite the first outer surface.
- 16. The circulator assembly of claim 15 wherein the at least one first RF port via and the at least one second RF port comprise copper plated vias.
- 17. The circulator assembly of claim 1 further comprising a plurality of interconnecting vias disposed between each of the first ferrite receiving pads and each of a corresponding second ferrite receiving pad, the interconnecting vias electromagnetically coupling each first ferrite receiving pad to the corresponding second ferrite receiving pad.
- 18. A method for fabricating an embedded planar circulator assembly comprising:providing a circulator board having a first surface and an opposing second surface; forming a plurality of circulator circuits on the circulator board, each circulator circuit having a ferrite receiving pad disposed on the first surface and a corresponding ferrite receiving pad on the second surface; providing a plurality of ferrite-magnet sub-assemblies disposed in a first sub-assembly; providing a plurality of ferrites disposed in a second sub-assembly; and bonding the circulator board between the first sub-assembly and the second sub-assembly such that the ferrite-magnet sub-assemblies are urged against a corresponding ferrite receiving pad disposed on the first surface of the circulator board and the ferrites are urged against the corresponding ferrite receiving pad on the second surface of the circulator board.
- 19. The method of claim 18 wherein forming a plurality of circulator circuits comprises:forming circulator circuit portions on the first surface and the second surface, each of the circulator circuits portions comprising: a first, second and third port portions, each port portion coupled to a corresponding ferrite receiving pad by a stripline circuit.
- 20. The method of claim 19 wherein forming a plurality of circulator circuits further comprises:forming a first, second and third port by connecting the circulator circuit port portions on the first surface and the second surface using interconnecting vias; and connecting the stripline circuits on the first surface and the second surface by using interconnecting vias.
- 21. The method of claim 20 further comprising:forming at least one first RF port vias disposed in the first sub-assembly board, each first RF via having a first end coupled to one of the first, second and third ports and a second end coupled to a connection disposed on a first outer surface of the circulator assembly; and forming at least one second RF vias disposed in the second sub-assembly board, each second RF via having a first end coupled to one of the first, second and third ports and a second end coupled to a connection disposed on a second outer surface of the circulator assembly disposed opposite the first outer surface.
- 22. The method of claim 21 further comprising plating the RF vias with copper.
- 23. The method of claim 22 counter drilling the RF vias to remove excess copper plating.
- 24. The method of claim 18 wherein bonding comprises adhesively bonding the circulator board between the first sub-assembly and the second sub-assembly using thermoplastic materials.
- 25. The method of claim 18 further comprising separating the plurality of circulator circuits into a corresponding plurality of individual unit cells.
US Referenced Citations (7)
Foreign Referenced Citations (1)
Number |
Date |
Country |
09289403 |
Nov 1997 |
JP |