Patent Application
20190044234
As is known in the art, a plurality of antenna elements can be disposed to form an array antenna. It is often desirable to utilize antenna elements capable of receiving orthogonally polarized radio frequency (RF) signals. Such antenna elements include, for example, four arm, dual polarized current sheet antenna elements such as tightly coupled dipole array (TCDA), planar ultrawideband modular antenna (PUMA), and other known current loop radiators. These radiator elements rely on polarization aligned coupling to maintain their polarization scan performance over the scan volume, particularly at large scan angles. Patch radiators may also be used and are low cost and easy to integrate, but suffer from poor circularly polarized performance over scan. Deposing such antenna elements on a rectangular array lattice pattern (or more simply a “rectangular lattice”) provides certain advantages since a rectangular lattice is naturally suited to aligning the orthogonally polarized arms of the respective radiating element and can maintain radiator performance over scan, particularly at far scan angles.
In accordance with the concepts, systems, methods and techniques described herein, a tripole current loop antenna element is provided having three conductors (also sometimes referred to herein as “arms”), with each of the three conductors including a ground via to couple a surface of the respective conductor to a ground plane and a signal via to receive radio frequency (RF) signals provided from a single feed circuit. The feed circuit is disposed to provide the RF signals to each of the three conductors having equal amplitudes and distributed with relative phases of 0°/120°/240° respectively (i.e., the RF signal provided to each arm is phase shifted by 120° from an adjacent one of the arms).
With this particular arrangement, RF signals having a circular polarization may be coupled to and/or from the antenna element via the single feed circuit. In an embodiment, the three conductors can be spaced from each other and disposed such that they provide polarization alignment when they are disposed within an array antenna having a triangular lattice spacing.
In an embodiment, the antenna element having three conductors and disposed in an array antenna on the triangular lattice results in the ability to provide an array antenna having more radiating elements per area without resulting in grating lobes as compared with antenna elements disposed on rectangular lattices. Thus, the number of active device channels required to realize a desired level of gain for a particular antenna element or array of antenna elements may be reduced. In some embodiments, the single feed used to realize the right-hand circular polarized (RHCP) antenna element can reduce the number of active devices needed by half compared to a dual feed architecture. Thus, an antenna element having three conductors (or arms) may be used to provide a low profile, circularly polarized, antenna element suitable for use in an array antenna having a triangular lattice shape and configured to generate circular polarization using a single feed and able to maintain circularly polarized performance over a broad scan volume. In an embodiment, a broad scan volume may refer to scan volumes that cover all scan angles out to a 60° scan angle (i.e., 60° scan cone) or greater with respect to a boresight axis of the respective antenna element or array antenna. For example, in some embodiments, such as the embodiments described herein, a circular polarized performance can be maintained up to a 70° scan volume.
For example, the antenna element can be sized such that it is compact and thus may be easier to accommodate within a unit cell of an array antenna with enough room to also accommodate vertical transitions to active devices. In an embodiment, the structure of the antenna element includes ground vias to form a grounded structure where the entire radiator circuit is DC grounded. Thus, improving high frequency performance and inhibiting propagation of surface waves. In an embodiment, high frequency may refer to a frequency in the range of about 2 GHz to about 50 GHZ (e.g., from the S-band range to the Q-band range). In some embodiments, high frequency may refer to frequencies above the Q-band frequency range. It should be appreciated that the antenna elements as described herein can be scaled to a variety of different frequencies with such frequencies selected based upon the needs of a particular application in which the antenna or antenna element is being used as well as upon manufacturing technologies (e.g., printed wiring board (PWB) technology).
The feed circuit can include a signal port, antenna ports, a feed line and multiple delay lines to provide to each of the three conductors, which connect to the antenna element, RF signals having approximately equal amplitudes and a phase relationship (e.g., ideally distributed at 0°/120°/240° respectively) such that the signal provided to each arm of an antenna element is phase shifted by approximately 120° from an adjacent arm. For example, in some embodiments, the feed circuit design produces a phase shift of approximately 120° between RF signals provided to adjacent ones of antenna element conductors by means adapted from Marchand balun design, but that produces the necessary approximate 120° phase difference (instead of approximately 180° used in a conventional Marchand balun) by creating an asymmetry in the length of the two short circuited stubs that realize the RF chokes in the feed circuit. The feed circuit properties, such as but not limited to, the length, width (i.e., impedance) and/or shape of the feed and delay lines can be selected to provide the appropriate phase shift and amplitude distribution between RF signals provided to adjacent conductors. Thus, the feed circuit as described herein can provide approximately equal RF signals to three conductors by exciting signal vias coupled to each of the conductors with RF signals 120° out of phase relative to an adjacent one of the three conductors. This feed circuit is also compact enough to fit within the radiator unit cell lattice, which is not possible with a feed circuit provided from a traditional three-way reactive divider with delay lines.
In a first aspect a radio frequency (RF) antenna element includes a substrate having first and second opposing surfaces, three conductors disposed on the first surface of said substrate, said three conductors being physically spaced apart from each other and being arranged so as to form an antenna element responsive to RF signals at a desired frequency range and a feed circuit having a signal port, and first, second and third antenna ports. Each of the first, second and third antenna ports coupled to a respective one of the three conductors, said feed circuit configured such that in response to an RF signal provided to the signal port thereof, said feed circuit provides at each of the first, second and third antenna ports, RF signals having approximately equal amplitudes and phases shifted by approximately 120 degrees. Ideally, the RF signals have equal amplitudes and phase shifts of 120 degrees. In practical systems, such ideal values may not be achievable over a particular frequency band due to manufacturing tolerances.
In embodiments, three conductors may be provided having similar geometric shape. The antenna element may include a first signal via coupling the first antenna port to a first conductor of the three conductors, a second signal via coupling the second antenna port to a second conductor of the three conductors and a third signal via coupling the third antenna port to a third conductor of the three conductors.
A first ground via can be formed extending from the first conductor to a first ground plane, a second ground via can be formed extending from the second conductor to the first ground plane and a third ground via can be formed extending from the third conductor to the first ground plane.
A plurality of leakage vias can be disposed having a geometric relationship with respect to each other. Each of the plurality of leakage vias can couple the first ground plane to a second ground plane.
In embodiments, the antenna element comprises two layers such that the three conductors are disposed in a first layer and the plurality of leakage vias are disposed in a second layer.
The feed circuit further may include a feed line (e.g., signal path) coupling the signal port to the second signal via, wherein the feed line provides the RF signals to each of the first, second and third signal vias having equal amplitudes and having an approximately 120 degree phase shift relative to the RF signals provided to an adjacent one of the first, second and third signal vias. The feed circuit may include a first delay line having a first length, a second delay line having a second length and a third delay line having a third length. In an embodiment, the first delay line may couple the first ground via to the first signal via, the second delay line may couple the second ground via to the second signal via and the third delay line may couple the second signal via to the third signal via.
A portion of the feed line can be disposed proximate to a portion of the first delay line to couple the feed line to the first delay line such that the first delay serves as a ground reference to the feed line. The first delay line and second delay line can be spaced a predetermined distance from each other. The predetermined distance can be selected such that it produces the approximately 120 degree phase shift between the RF signals provided to the first and second signal vias.
In embodiments, the predetermined distance can be selected such that a combined power factor of the RF signals provided to the second signal via and third via is two times greater than a power factor of the RF signals provided to the first signal via.
A length of the third delay line can be selected to produce the approximately 120 degree phase shift between the RF signals provided to the second signal via and third signal via.
In another aspect, an array antenna includes a substrate having first and second opposing surfaces and a plurality of antenna elements disposed on the first surface of said substrate.
Each of the plurality of antenna elements includes three conductors physically spaced apart from each other and arranged so as to be responsive to RF signals at a desired frequency range, and a feed circuit having a signal port, and first, second and third antenna ports. Each of the first, second and third antenna ports coupled to a respective one of the three conductors, said feed circuit configured such that in response to an RF signal provided to the signal port thereof, said feed circuit provides at each of the first, second and third antenna ports, RF signals having equal amplitudes and phases shifted by approximately 120 degrees.
Each of the antenna elements may include a first signal via coupling the first antenna port to a first conductor of the three conductors, a second signal via coupling the second antenna port to a second conductor of the three conductors and a third signal via coupling the third antenna port to a third conductor of the three conductors. In some embodiments, each of the antenna elements include a first ground via extending from the first conductor to a first ground plane, a second ground via extending from the second conductor to the first ground plane and a third ground via extending from the third conductor to the first ground plane.
Each of the antenna elements may include a plurality of leakage vias disposed having a geometric relationship with respect to each other, each of the plurality of leakage vias coupling the first ground plane to a second ground plane. In embodiments, each of the antenna elements includes two layers such that the three conductors are disposed in a first layer and the plurality of leakage vias are disposed in a second layer.
A feed line coupling the signal port to the second signal via may be included in each of the antenna elements. The feed line can provide the RF signals to each of the first, second and third signal vias having approximately equal amplitudes and having an approximately 120 degree phase shift relative to the RF signals provided to an adjacent one of the first, second and third signal vias.
In embodiments, each of the antenna elements includes a first delay line having a first length, a second delay line having a second length, and a third delay line having a third length. The first delay line may couple the first ground via to the first signal via, the second delay line may couple the second ground via to the second signal via, and the third delay line may couple the second signal via to the third signal via.
A portion of the feed line can be disposed proximate to a portion of the first delay line to couple the feed line to the first delay line such that the first delay serves as a ground reference to the feed line.
The first delay line and the second delay line can be spaced a predetermined distance from each other. The predetermined distance can be selected such that it produces the approximately 120 degree phase shift between the RF signals provided to the first and second signal vias. A length of the third delay line can be selected to produce the approximately 120 degree phase shift between the RF signals provided to the second signal via and third signal via.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.
The foregoing features may be more fully understood from the following description of the drawings in which:
Like reference symbols in the various drawings indicate like elements.
Now referring to
As illustrated in
In the illustrative embodiment of
Conductors 106a-106c may be provided from any electrical conductor (e.g., a metallic material) or any material electrically responsive to RF signals provided thereto. Conductors 106a-106c may be formed having the same or substantially same geometric shape. In other embodiments, one or more of conductors 106a-106c may have different geometric shapes. Conductors 106a-106c may be formed in a variety of different shapes, including but not limited to any regular or irregular geometric shape. In some embodiments, the thickness (or width) of conductors 106a-106c can be varied to modify (e.g., improve) design performance. The shape and/or properties of conductors 106a-106c can be selected based, at least in part, on the dimensions of array antenna 100 and/or a particular application of array antenna 100. For example, the shape of conductors 106a-106c can be modified to change a performance characteristic and/or frequency band within which the respective antenna element 104 or array antenna 100 operates. Such performance characteristics include, but are not limited to, return and insertion loss, gain, and/or axial ratio characteristics the respective antenna element 104 or array antenna 100.
Substrate 102 comprises a dielectric material. In some embodiments, substrate 102 may include multiple layers some of which may be a dielectric material and some of which may be a non-dielectric material, as will be discussed in greater detail below with respect to
Referring now to
Unit cell 200 further includes a ground plan 108 disposed on a second, opposite surface 102b of substrate 102. A second substrate 103 may be disposed over a second surface 108b of ground plane 108. Each of conductors 106a-106c may be coupled to ground 108 through a ground via as will be described in more detailed below with respect to
Thus, array antenna 100 of
Conductors 106a-106c are disposed on first surface 102a of substrate 102 and spaced apart from each other. Thus, a gap 105a-105c exists between each of conductors 106a-106c such that the conductors 106a-106c are not in physical contact.
Conductors 106a-106c can, for example, be spaced apart from each other and arranged along first surface 102a so as to be responsive to radio frequency (RF) signals at a desired frequency range. In some embodiments, the spacing between conductors 106a-106c can be selected based at least in part on performance requirements and/or frequency band requirements of a particular application in which a respective antenna element 104 and/or array antenna 100 is used. For example, changing the spacing (e.g., changing the gap) between conductors 106a-106c can change the return loss and insertion loss performance, gain, and/or axial ratio characteristics of a respective antenna element 104 and/or array antenna 100. In some embodiments, antenna element 104 and conductors 106a-106c can be configured to be responsive to RF signals in the Q band frequency range (e.g., 33-50 GHZ). However, it should be appreciated that antenna element 104 and conductors 106a-106c can be configured to be responsive to RF signals in a variety of different frequency ranges, based at least in part upon the needs of a particular application in which antenna element 104 is used.
As illustrated in
The use of three conductors 106a-106c (instead of four as in traditional quad pole designs) reduces the footprint required by conductors 106a-106 within unit cell 100 and facilitates inclusion of additional circuitry within unit cell 200. Additionally, the use of the triangular lattice instead of a rectangular lattice provides a large unit cell area that is substantially grating lobe free, which also provides more space for feed circuitry and vertical vias. This additional area for circuitry can become very important at higher frequencies where a particular application of an antenna element or array antenna is required by grating lobe physics to be on a smaller lattice to maintain scan performance. For example, conductors 106a-106c can be sized and provided within unit cell 200 with enough spacing to accommodate vertical transitions to active devices (not shown). The shape and triangular relationship between the three spaced conductors or arms 106a-106c which form the antenna element allows the antenna element to be used in an array having a triangular lattice. This, in turn, allows for fewer antenna elements 104a-104p to be used within an array antenna of a given size (area) as compared to a similarly sized array having a rectangular lattice structure. Such a decrease in the number of antenna elements maintains antenna gain while reducing overall array cost (because fewer active devices and components are required to support fewer channels, simplifying packaging of components on the array and reducing component cost).
Referring now to
Feed circuit 130 includes a signal path 132 coupled to first, second and third antenna ports 121a-121c through signal paths 134, 136, 138 and signal vias 120a-120c with paths 134, 136, 138 corresponding to delay lines. Signal path 132 is coupled to port 131 (e.g., signal port interface) where a vertical RF via transition couples feed circuit 130 to various circuit portions of which the respective antenna element is a part. For example, in one embodiment, port 131 couples feed circuit 130 to active devices mounted on a printed wiring board (PWB). In some embodiments, signal path 132 may be referred to herein as a feed line.
A first end of first signal via 120a is coupled to first conductor 106a and a second end of signal via is coupled to feed circuit 130. In this way, RF signals may be coupled between the antenna element and port 131. Similarly, second signal via 120b has a first end coupled to second conductor 106b and a second end coupled feed circuit 130 and third signal via 120c has a first end coupled to third conductor 106c and a second end coupled to feed circuit 130. Thus, feed circuit 130 can provide RF signals to each of first, second and third conductors 106a-106c.
The feed circuit 130 can be formed and configured to provide RF signals having equal amplitudes and phases shifted by 120° to conductors 106a-106c. For example, signal path 132 and each of delay lines 134, 136, 138 can be positioned, spaced and/or sized such that feed circuit 130 provides RF signals to first, second and third conductors 106a-106c respectively that are phase shifted 120° from RF signals provided to an adjacent (or neighboring) one of first, second and third conductors 106a-106c. Thus, each of the arms may be excited from signals provided through the three signal vias 120a-120c.
In this illustrative embodiment, feed circuit 130 is provided from a pair of conductor signal layers (i.e. as a two-layer feed) which provides 0, 120 and 240 degree phase shifted equal amplitude signals to antenna element arms 106a-106c.
Signal path 132 includes a coupling region 133 in which path 134 serves as a ground to signal path 132. Coupling region 133 directs one-third of the power fed from a first end of signal path 132 (i.e. a port 131) to conductor 106b and two-thirds of the power propagates along path portion 132b toward conductors 106a, 106b. At signal via 120c, the remaining power is split equally such that one-third of the total power provided at input port 131 is provided to conductor (or arm) 106c and one-third of the power is provided to conductor (or arm) 106a via signal path 138. It should be appreciated that paths 134, 136, 138 may be provided having a width selected such that the signal path acts as an RF choke. Thus, each of the arms 106a-106c receive signals having an equal amount of signal power with relative phase shifts of 0°/120°/240° for right hand circuit polarization (RHCP).
As illustrated in
Feed circuit 130 includes a first delay line 134 coupling second signal via 120b to a second ground via 124b. A second delay line 136 couples third signal via 120c to a third ground via 124c, and a third delay line 138 couples third signal via 120c to first signal via 120a.
Feed line 132 couples to third signal via 120c with third signal via 120c coupled to first signal via 120a through third delay line 138. Thus, feed line 132 can be configured to provide RF signals having a greater power factor to third signal via 120c as compared to the RF signal provided to second signal via 120b, as third signal via 120c is coupled to first signal via 120a and shares (e.g., splits) the RF signals with first signal via 120a. In one embodiment, a combined power factor of RF signals provided to third and first signal vias 120c, 120a can be two times greater than a power factor of RF signals provided to second signal via 120b.
First delay line 134 and second delay line 136 can be spaced apart from each other a predetermined distance such that the predetermined distance produces a 120° phase shift between the RF signals provided to second signal via 120b and third signal via 120c. It should be appreciated that the predetermined distance between first delay line 134 and second delay line 136 can be selected to achieve a variety of different phase shifts.
Third delay line 136 can be formed such that it splits RF signals between third signal via 120c and first signal via 120a. For example, a length, width (e.g., impedance) and/or shape (here an upside down L shape) of third delay line 138 can be selected such that it produces an approximately 120° phase shift between the RF signals provided to third signal via 120c and first signal via 120a. Thus, each of first, second and third signal vias 120a-120c can be excited with RF signals approximately 120° out of phase relative to an adjacent signal via.
In some embodiments, first, second, and third delay lines 134, 136, 138 can be formed having different lengths, different impedances (e.g., different widths) and/or different shapes. For example, first, second, and third delay lines 134, 136, 138 can be configured to act as an RF choke. The width of first, second and third delay lines 134, 136, 138 can be selected to achieve an appropriate impedance. In some embodiments, first, second, and third delay lines 134, 136, 138 can be selected such that they appear as an open circuit. In the illustrative embodiment of
It should be appreciated that shapes, impedances, lengths and/or spacing between first, second and third delay lines 134, 136, 138 can vary and can be selected and formed to produce a required phase shift (here approximately 120°) between RF signals provided to different signal vias for a particular application of an antenna element.
Each of conductors 106a-106c can be coupled to ground plane (e.g., ground plane 108 of
A plurality of leakage vias 122a-122k can be formed in antenna element 104 to prevent RF leakage through a feed layer, such as the feed layer between feed circuit 130 and conductors 106a-106c. For example, and as will be described in greater detail with respect to
Referring now to
In the illustrative embodiment of
As illustrated in
For example, and referring now to
In the illustrative embodiment of
Ground vias 124a-124c extend from a surface of conductors 106a-106c to ground plane 108.
Referring now to
Manifold 600 may include circuitry operable to couple or otherwise convey an electrical signal (e.g., RF signal) to antenna element 604 or an array antenna having a plurality of antenna elements 604.
In the illustrative embodiment of
Ground plane 608 is generally disposed between first dielectric region 640 and a second layer dielectric region 642 of antenna element 604. Feed circuit 630 may include a feed line, one or more delay lines, a signal port and antenna ports to provide RF signals to conductors 660. Feed circuit 630 be formed within second layer 642. One or more leakage vias 622 can be formed such that they extend from first ground plane 608 to a second ground plane 610. In some embodiments, second ground plane 610 may be a component of manifold 602. In other embodiments, second ground plane 610 may be formed as a component of antenna element 620.
Having described preferred embodiments, which serve to illustrate various concepts, structures and techniques, which are the subject of this patent, it will now become apparent that other embodiments incorporating these concepts, structures and techniques may be used. Accordingly, it is submitted that the scope of the patent should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the following claims.
