Dielectric lens antenna

A radio frequency (RF) antenna including a patch antenna element, a microstrip transmission line, a ground plane, a waveguide, and a dielectric lens. The patch antenna element is disposed on a top surface of a first substrate of the RF antenna, and includes a slot aperture through which the patch antenna element is configured to be electromagnetically coupled to the microstrip transmission line. The microstrip transmission line is disposed between the first substrate and a second substrate. The ground plane is disposed on a third substrate. The microstrip transmission line is configured to be electromagnetically coupled to the ground plane. The waveguide includes a proximal aperture attached to the top surface and enclosing the patch antenna element. The waveguide includes a distal aperture opposite the proximal aperture, and the waveguide is configured to be electromagnetically coupled to the patch antenna element. The dielectric lens is disposed in the distal aperture.

FIELD

The field of the disclosure relates generally to radio and microwave frequency systems and, more specifically, to a dielectric lens antenna.

BACKGROUND

Many known radar applications utilize “steerable,” or directed, beams. Such steering is often accomplished with an active electronically steerable antenna (AESA) or, alternatively, with a mechanically scanned antenna, i.e., an antenna array that is physically steered. Such antennas are commonly installed on air, land, and sea vehicles, as well as on fixed land installations. Similar antennas may also be utilized in certain radio frequency (RF) or microwave frequency communication systems. Mechanically-scanned and electronically steerable alternatives are often too large, too expensive, and consume too-much power for certain applications. For many applications, particularly in aircraft, it is desirable to have low-cost, low-power, and low-size and low-weight steerable antenna arrays.

BRIEF DESCRIPTION

One aspect of the present disclosure includes an RF antenna. The RF antenna includes a patch antenna element, a microstrip transmission line, a ground plane, a waveguide, and a dielectric lens. The patch antenna element is disposed on a top surface of a first substrate of the RF antenna, and includes a slot aperture through which the patch antenna element is configured to be electromagnetically coupled to the microstrip transmission line. The microstrip transmission line is disposed between the first substrate and a second substrate. The ground plane is disposed on a third substrate. The microstrip transmission line is configured to be electromagnetically coupled to the ground plane. The waveguide includes a proximal aperture attached to the top surface and enclosing the patch antenna element. The waveguide includes a distal aperture opposite the proximal aperture, and the waveguide is configured to be electromagnetically coupled to the patch antenna element. The dielectric lens is disposed in the distal aperture.

Another aspect of the present disclosure includes a method of fabricating an RF antenna. The method includes disposing a patch antenna element on a first dielectric layer, disposing a microstrip transmission line on a second dielectric layer, and disposing a ground plane on a third dielectric layer. The patch antenna element includes a slot aperture. The method includes laminating at least the first dielectric layer, the second dielectric layer, and the third dielectric layer into a board assembly such that the microstrip transmission line is configured to be electromagnetically coupled to the ground plane and electromagnetically coupled to the patch antenna element through the slot aperture. The method includes attaching a proximal aperture of a waveguide to a top surface of the first dielectric layer and enclosing the patch antenna element. The waveguide is configured to be electromagnetically coupled to the patch antenna element. The method includes disposing a dielectric lens in a distal aperture of the waveguide.

DETAILED DESCRIPTION

Embodiments of the systems described herein include an RF antenna and, more specifically, a dielectric lens antenna. The RF antenna includes an RF printed circuit board (PCB), or board assembly, having a ground plane, a microstrip transmission line, and a patch antenna element. The patch antenna element is disposed on a top surface of the RF antenna and includes a slot aperture through which the patch antenna element is electromagnetically coupled to the microstrip transmission line. The slot aperture decreases the axial ratio of the antenna, resulting in reduced polarization loss. The microstrip transmission line is positioned, or embedded, in a layer between the ground plane and the patch antenna element. The ground plane reduces the effects of conductive environmental surfaces to which the RF antenna may be coupled, connected, or otherwise attached. In certain embodiments, a coupling element, or “tuning element,” is positioned on another layer between the microstrip transmission line and the patch antenna element. The RF antenna includes a waveguide having a proximal aperture attached to the top surface of the RF antenna and encloses the patch antenna element, and a distal aperture opposite the proximal. The RF antenna includes a dielectric lens disposed in the distal aperture of the waveguide. The dielectric lens improves the radiation performance of the antenna. The RF antennas described herein may be fabricated, in certain embodiments, for example, by additive manufacturing methods, such as printing, or by subtractive methods, such as wet etching.

FIG. 1is a perspective schematic diagram of an example RF antenna100with a circular waveguide102and a dielectric lens104. RF antenna100includes a board assembly106.FIG. 2is a perspective cross-section schematic diagram of RF antenna100shown inFIG. 1.FIG. 3is another perspective schematic diagram of RF antenna100shown inFIG. 1with certain components illustrated as partially transparent to reveal additional components. Likewise,FIG. 4is another perspective cross-section schematic diagram of RF antenna100with those same components illustrated as partially transparent.

RF antenna100and, more specifically, board assembly106includes a microstrip transmission line108, a patch antenna element110, and a ground plane112. Patch antenna element110includes a slot aperture114through which patch antenna element110may be electromagnetically coupled to microstrip transmission line108, which feeds patch antenna element110. A signal radiated by patch antenna element110electromagnetically couples into waveguide102, through which it propagates from a proximal aperture116toward a distal aperture118. Dielectric lens104is disposed in distal aperture118of waveguide102. Dielectric lens104improves the radiation performance from distal aperture118of waveguide102. Additionally, the microstrip-to-waveguide transition formed between microstrip transmission line108and waveguide102is simple and avoids the size, weight, and cost of coaxial adapters. Moreover, in certain embodiments, patch antenna element110may be combined with slot aperture114and a dielectric lens (not shown) disposed on patch antenna element110, which results in good insertion loss and good return loss performance for a given desired operating frequency. In certain embodiments, RF antenna100includes a coupling element120, which improves the electromagnetic coupling of signals from microstrip transmission line108to patch antenna element110. Generally, coupling element120is embedded in a layer of board assembly106between microstrip transmission line108and patch antenna element110, and has dimensions and orientation to enhance electromagnetic coupling from microstrip transmission line108to waveguide102. For example, coupling element120is a linear conductive element oriented orthogonal to microstrip transmission line108and at about a 45 degree angle with respect to slot aperture114. The length and width of coupling element120are selected according to the desired operating frequency and impedance of microstrip transmission line108and patch antenna element110.

Waveguide102has a shape and dimensions that define the range of signals (e.g., frequency and mode) that will propagate through waveguide102. Waveguide102, for example, may include a circular or rectangular waveguide, or any other shape of waveguide. Generally, although the antenna is referred to as an RF antenna, waveguide102is dimensioned for microwave signals, or signals having a frequency between about 300 Megahertz (MHz) and about 300 Gigahertz (GHz). Accordingly, RF antenna100may also be referred to as a dielectric lens antenna or a microwave antenna. For example, in one embodiment, waveguide102is dimensioned for an operating frequency of 20 GHz. Likewise, microstrip transmission line108, patch antenna element110, slot aperture114, and the size and shape of dielectric lens104are designed for efficient signal propagation at the desired operating frequency, and are further designed for impedance matching at, for example, the transition from microstrip transmission line108to dielectric lens104. Further, the size and shape of dielectric lens104are selected to produce a desired radiation pattern, or emission pattern. Generally, slot aperture114has a length and width corresponding to the desired operating frequency, and patch antenna element110has a diameter corresponding to the desired operating frequency. The orientation of slot aperture114is selected for efficient signal propagation for the desired operating frequency. Generally, microstrip transmission line108has a width corresponding to an impedance suitable for the operating frequency and for transitioning to patch antenna element110. Generally, dielectric lens104has a shape corresponding to the shape of waveguide102. For example, dielectric lens104shown inFIG. 1is a spherical body of dielectric material, or spherical in shape, and extends partially into waveguide102up to, for example, within a quarter-wavelength of patch antenna element110at the nadir of dielectric lens104. The distance dielectric lens104extends into waveguide102and, consequently, its range to patch antenna element110, may vary according to the desired operating frequency for RF antenna100and for the purpose of impedance matching, for example. Moreover, the radius of dielectric lens104is selected to impedance-match waveguide102and an operating frequency of waveguide102, and improve a gain of RF antenna100.

As shown inFIGS. 3 and 4, patch antenna element110includes a circular patch, waveguide102includes a circular waveguide, and dielectric lens104includes a spherical dielectric lens. The circular patch results in current densities having circular rotation that further produces circular polarization that is suitable for transmission into a circular waveguide. Alternatively, in certain embodiments, patch antenna element110may be a rectangular patch, waveguide102may be a rectangular waveguide, and dielectric lens104may have a pyramid shape. The corresponding shapes and dimensions of patch antenna element110, waveguide102, and dielectric lens104results in current densities suitable for propagating through a rectangular waveguide.

FIG. 5is a cross-section schematic diagram of board assembly106for RF antenna100shown inFIGS. 1-4.FIG. 6is a cross-section schematic diagram of RF antenna100shown inFIG. 5.FIG. 5includes various layers of board assembly106, including dielectric layers, or substrates, conductors, and adhesive films for laminating board assembly106. Each layer may be fabricated using subtractive methods, such as laser etching, milling, or wet etching, additive methods, such as printing or film deposition, or a combination of both. Board assembly106includes a first substrate602, a second substrate604, a third substrate606, and a fourth substrate608. Patch antenna element110is disposed on a top surface610of first substrate602. Coupling element120is disposed on second substrate604. Microstrip transmission line108is disposed on third substrate606. Ground plane112is disposed on fourth substrate608.

First, second, third, and fourth substrates602,604,606, and608are laminated, or bonded, together using, for example, adhesive films612disposed between each layer. Microstrip transmission line108is embedded in board assembly106between ground plane112and patch antenna element110, and more specifically, between third substrate606and second substrate604. Similarly, coupling element120is embedded in board assembly106between microstrip transmission line108and patch antenna element110, and more specifically, between first substrate602and second substrate604. In certain embodiments, RF antenna100may may omit coupling element120and may include no other conductive layers between microstrip transmission line108and patch antenna element110(i.e., between first substrate602and second substrate604). Accordingly, in such embodiments, first substrate602and second substrate604may be referred to as a single combined substrate having multiple dielectric layers. In alternative embodiments, second substrate604and coupling element120are both omitted, and first substrate602is bonded directly to third substrate606using adhesive film612.

RF antenna100includes waveguide102having a proximal aperture116and a distal aperture118. Proximal aperture116of waveguide102is attached to top surface610and encloses patch antenna element110, such that a signal radiating from patch antenna element110electromagnetically couples into waveguide102and propagates through waveguide102toward distal aperture118. As illustrated inFIG. 6, dielectric lens104is disposed in distal aperture118of waveguide102. Dielectric lens104, like the dielectric layers and conductive layers of board assembly106, may be deposited using additive methods, such as, for example, using a printing process, such that it would extend both into distal aperture118of waveguide102toward top surface610and out from distal aperture118. Dielectric lens104improves the radiation performance of RF antenna100.

FIG. 7is an example graph700of antenna gain versus elevation angle for RF antenna100shown inFIG. 1. Graph700includes antenna gain plots702, a vertical axis704for antenna gain expressed in decibels-isotropic (dBi), and a horizontal axis706for elevation angle expressed in degrees. Generally, antenna gain, or simply “gain,” is a measure of the directivity and electrical efficiency of an antenna, such as RF antenna100. Antenna gain plot702is illustrated versus elevation angle and, thus, further represents a radiation pattern of RF antenna100. For the spherically shaped dielectric lens104, an elevation (theta) of zero degrees represents the direction through waveguide102and orthogonal to the plane defined by patch antenna element110. The elevation angle then increases in value (e.g., positive or negative) as the direction of radiation deviates from zero degrees elevation. Antenna gain plots702includes individual plots for various different dimensioned (i.e., different radius) dielectric lenses, including a control plot708illustrating antenna gain without dielectric lens104, antenna gain710for a 6 millimeter (mm) radius dielectric lens, antenna gain712for an 8 mm radius dielectric lens, antenna gain714for a 10 mm radius dielectric lens, and antenna gain716for a 12 mm radius dielectric lens. As illustrated by plots702, each instance of dielectric lens104improved the radiation performance of RF antenna100with respect to antenna gain. Notably, for example, antenna gain716illustrates a 12 mm radius dielectric lens yields the largest improvement in radiation performance over a like-antenna having no dielectric lens, i.e., where dielectric lens104is omitted.

FIG. 8is an example graph800of return loss versus frequency for RF antenna100shown inFIG. 1. Graph800includes return loss, RL, plots802, a vertical axis804for return loss expressed in decibels (dB), and a horizontal axis806for frequency expressed in GHz. Generally, return loss, RL, is a performance measure of the power reflected in a device, such as, e.g., a waveguide. Here, return loss is a measure of reflections occurring at the transition from waveguide102to dielectric lens104of RF antenna100, and may, in certain embodiments, be expressed in dB and generally defined as 10 log10Pref/Pi, where Prefis reflected power and Piis incident power. More specifically, incident power is power transmitted over the feeding microstrip transmission line108to patch antenna element110and into waveguide102, and reflected power is power reflected by any discontinuity created by dielectric lens104at distal aperture118of waveguide102back toward patch antenna element110and microstrip transmission line108. Generally, when reflections are low, which is preferred, return loss is large and negative. As in graph700, return loss plots802includes individual plots for the various different dimensioned (i.e., different radius) dielectric lenses, including a control plot808illustrating return loss without dielectric lens104, return loss810for a 6 millimeter (mm) radius dielectric lens, return loss812for an 8 mm radius dielectric lens, return loss814for a 10 mm radius dielectric lens, and return loss816for a 12 mm radius dielectric lens.

Control plot808illustrates performance of RF antenna100with respect to return loss is about −24 dB around an operating frequency of about 19.95 GHz without dielectric lens104. When dielectric lens104is introduced, some amount of return loss is also introduced and, consequently, the frequency at which peak return loss performance occurs shifts. Notably among return loss plots802, return loss816for a 12 mm radius dielectric lens yields a peak return loss of about −12 dB, although the same dielectric lens produces the greatest improvement (among the various dielectric lenses tested) in antenna gain, as illustrated in graph700. Further, return loss810for the 6 mm radius dielectric lens and return loss812for the 8 mm radius dielectric lens yield the best performance in return loss at about −14 dB.

FIG. 9is a flow diagram of an embodiment of an example method of fabricating an RF antenna, such as RF antenna100shown inFIGS. 1 and 6. Method900includes disposing910patch antenna element110on top surface610of a first dielectric layer, such as first substrate602. The formation of patch antenna element110includes forming slot aperture114in the conductive material. Microstrip transmission line108likewise is disposed920on a second dielectric layer, such as third substrate606, and ground plane112is disposed930on a third dielectric layer, such as fourth substrate608. Each of the conductive layers, i.e., ground plane112, microstrip transmission line108, and patch antenna element110, may be formed by subtractive methods, such as laser etching, milling, or wet etching, additive methods, such as printing or film deposition, or a combination of both. For example, disposing920microstrip transmission line108may include depositing a layer of conductive material onto the second dielectric layer, or third substrate606, and etching the conductive material to form microstrip transmission line108to a width corresponding to a desired impedance value.

Conductive layers are generally formed from an electrically conductive material, such as copper or any other electrically conductive material suitable for use in RF circuit boards. In certain embodiments, disposing920microstrip transmission line includes depositing a conductive material onto the second dielectric layer, using a printing process, such that microstrip transmission line108has a width corresponding to a desired impedance value. Likewise, in certain embodiments, disposing910patch antenna element110includes depositing a conductive material onto the first dielectric layer, using a printing process, such that slot aperture114includes a length, a width, and an angular orientation corresponding to an operating frequency of RF antenna100and, for example, waveguide102, and such that the patch antenna element has a geometry corresponding to a geometry of the aperture of waveguide102.

In alternative embodiments, disposing920microstrip transmission line108includes depositing a layer of a conductive material onto the second dielectric layer, e.g., on third substrate606. The conductive material is then etched to form microstrip transmission line108having a width corresponding to a desired impedance value.

In certain embodiments, coupling element120, or a tuning element, is disposed on fourth dielectric layer disposed between the first and second dielectric layers, e.g., between first substrates602and third substrate606. Substrates602,604,606, and608are formed from a dielectric material such as silicon, gallium arsenide, indium phosphide, polytetrafluoroethylene (PTFE) or other polymer, or any other suitable dielectric material. Generally, selections of a dielectric material and its thickness are made based on a desired impedance of transmission lines disposed on the substrate.

The first, second, and third dielectric layers are then laminated940to form board assembly106such that microstrip transmission line108is configured to be electromagnetically coupled to ground plane112and electromagnetically coupled to patch antenna element110through slot aperture114. In certain embodiments, laminating940includes applying first adhesive film612between the first dielectric layer and the second dielectric layer, and applying a second adhesive film612between the second dielectric layer and the third dielectric layer. The dielectric layers are then aligned and pressed together. In embodiments having coupling element120, adhesive film612is applied between the first and fourth dielectric layers, or first substrates602and second substrate604. The four dielectric layers, including substrates602,604,606, and608, are laminated940to form board assembly106, such that coupling element120is embedded in a layer between patch antenna element110and microstrip transmission line108, and such that coupling element120is electromagnetically coupled between microstrip transmission line108and patch antenna element110.

Method900includes attaching950proximal aperture116of waveguide102to top surface610of the first dielectric layer and enclosing patch antenna element110. Waveguide102is configured to be electromagnetically coupled to patch antenna element110. Dielectric lens104is then disposed960in distal aperture118. Dielectric lens104may be deposited using additive methods, such as, for example, a printing process. In certain embodiments, disposing960dielectric lens104includes depositing a dielectric material, using a printing process, in a geometry corresponding to a geometry of distal aperture118of waveguide102. For example, in alternative embodiments, waveguide102is a rectangular waveguide, and disposing dielectric lens104includes depositing the dielectric material in a pyramid shape. Further, in certain embodiments, where the geometry of the aperture of waveguide102includes a rectangular geometry, patch antenna element110includes a linear geometry corresponding to the rectangular geometry of waveguide102. Similarly, where the geometry of the aperture of waveguide102includes a circular geometry, patch antenna element110includes a circular geometry corresponding to the circular geometry of waveguide102. Dielectric lens104may be formed from any suitable dielectric material and, again, is selected along with its size and shape based on a desired impedance and corresponding to an operating frequency of RF antenna100and, for example, waveguide102. The dielectric material is then deposited, for example, using a printing process, in a size and shape corresponding to the operating frequency of RF antenna100, waveguide102, and an emission pattern for RF antenna100.

In certain embodiments, method900further includes disposing a second dielectric lens on patch antenna element110and extending into proximal aperture116of waveguide102. Inclusion of the second dielectric lens improves the electromagnetic coupling of, for example, a microwave signal emitted from patch antenna element110into waveguide102, and improves performance of the microstrip-to-waveguide transition with respect to return loss and insertion loss.

The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein.