Phased array antenna

Abstract

This phased array antenna is provided with a plurality of antenna elements. Each of the plurality of antenna elements has a common electrode, a bias electrode, a liquid crystal layer, a microstrip line, and an antenna electrode. The common electrode is shared by the plurality of antenna elements and is configured to be supplied with a constant potential. The bias electrode is apart from the common electrode and is present in the same layer as the common electrode. The liquid crystal layer is positioned on the common electrode and the bias electrode. The microstrip line is positioned on the liquid crystal layer while overlapping with the bias electrode and the common electrode, and is configured to be supplied with an alternating current potential. The antenna electrode is positioned on the liquid crystal layer, while being physically connected to the microstrip line and overlapping with the common electrode.

Description

Phased Array Antenna

[0001] One embodiment of the present invention relates to a phased array antenna that utilizes liquid crystals.

[0002] Since liquid crystal molecules have a dielectric anisotropy, the dielectric constant of the liquid crystal layer can be controlled by adjusting the electric field applied to the liquid crystal layer containing the liquid crystal molecules to control the orientation of the liquid crystal molecules. By utilizing this property, a phased array antenna that can transmit directional radio waves in any direction can be realized (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 11-103201

[0004] An object of one embodiment of the present invention is to provide a novel antenna element that utilizes the dielectric anisotropy of liquid crystal, and a phased array antenna having the antenna element. Alternatively, an object of one embodiment of the present invention is to provide an antenna element that includes a liquid crystal layer and exhibits stable antenna characteristics, and a phased array antenna having the antenna element.

[0005] One embodiment of the present invention is a phased array antenna including a plurality of antenna elements. Each of the plurality of antenna elements includes a common electrode, a bias electrode, a liquid crystal layer, a microstrip line, and an antenna electrode. The common electrode is shared by the plurality of antenna elements and configured to be supplied with a constant potential. The bias electrode is spaced apart from the common electrode and is in the same layer as the common electrode. The liquid crystal layer is positioned on the common electrode and the bias electrode. The microstrip line is positioned on the liquid crystal layer, overlaps the bias electrode and the common electrode, and is configured to be supplied with an AC potential. The antenna electrode is positioned on the liquid crystal layer, physically connected to the microstrip line, and overlaps the common electrode.

[0006] One embodiment of the present invention is a phased array antenna including a plurality of antenna elements. Each of the plurality of antenna elements includes a common electrode, a bias electrode, a liquid crystal layer, a microstrip line, and an antenna electrode. The common electrode is shared by the plurality of antenna elements and configured to be supplied with a constant potential. The bias electrode is spaced apart from the common electrode and is in the same layer as the common electrode. The liquid crystal layer is positioned on the common electrode and the bias electrode. The microstrip line is positioned on the liquid crystal layer, overlapping the bias electrode and the common electrode, and configured to be supplied with an AC potential. The antenna electrode is positioned on the microstrip line and overlapping the microstrip line and the common electrode.

[0007] One embodiment of the present invention is a phased array antenna having a plurality of antenna elements. Each of the plurality of antenna elements has a common electrode, a bias electrode, a liquid crystal layer, a microstrip line, and an antenna electrode. The common electrode is shared by the plurality of antenna elements and configured to be supplied with a constant potential. The bias electrode is spaced apart from the common electrode and is in the same layer as the common electrode. The liquid crystal layer is located on the common electrode and the bias electrode. The microstrip line is located on the liquid crystal layer, overlaps the bias electrode and common electrode, and is configured to be supplied with an AC potential. The antenna electrode is located below the electrode and overlaps the common electrode and the microstrip line.

[0008] 1 is a schematic top view of a phased array antenna according to one embodiment of the present invention. 2 is a schematic top view of an antenna element according to one embodiment of the present invention. 3 is a schematic end view of an antenna element according to one embodiment of the present invention. 4 is a schematic end view of an antenna element according to one embodiment of the present invention. 5 is a schematic diagram illustrating operation of a phased array antenna according to one embodiment of the present invention. 6 is a schematic diagram illustrating operation of a phased array antenna according to one embodiment of the present invention. 7 is a schematic top view of an antenna element according to one embodiment of the present invention. 8 is a schematic top view of a portion of an antenna element according to one embodiment of the present invention. 9 is a schematic end view of an antenna element according to one embodiment of the present invention. 10 is a schematic end view of an antenna element according to one embodiment of the present invention. 11 is a schematic end view of an antenna element according to one embodiment of the present invention. 12 is a schematic perspective view of a portion of an antenna element according to one embodiment of the present invention. 13 is a schematic top view of an antenna element according to one embodiment of the present invention. 14 is a schematic end view of an antenna element according to one embodiment of the present invention. 15 is a schematic perspective view of a portion of an antenna element according to one embodiment of the present invention. 1A and 1B are schematic top and end views of an antenna element according to an embodiment of the present invention;

[0009] Hereinafter, various embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the present invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0010] In order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same function as those described in the previous drawings may be assigned the same reference numerals, and duplicate explanations may be omitted. When multiple identical or similar components are collectively referred to, this reference numeral is used, and when these multiple components are individually referred to, a hyphen and a natural number are used after the reference numeral. Furthermore, when referring to a part of one component, a lowercase alphabet is used after the reference numeral.

[0011] In this specification and claims, when expressing an aspect of placing another structure on top of a certain structure, the term "on top" is used, unless otherwise specified, to include both a case where another structure is placed directly on top of a certain structure so as to be in contact with the certain structure, and a case where another structure is placed above a certain structure via yet another structure.

[0012] In this specification and claims, the expression "a structure exposed from another structure" means a state in which a part of a structure is not covered by another structure, and also includes a state in which this part not covered by another structure is covered by yet another structure. Here, the hierarchical relationship between the structure and the other structure does not matter. The state expressed by this expression also includes a state in which the structure is not in contact with the other structure.

[0013] In the present invention, when a single film is processed to form multiple films, these multiple films may have different functions and roles. However, these multiple films originate from films formed as the same layer in the same process, and have substantially the same layer structure, the same material, and the same morphology. Therefore, these multiple films are defined as existing in the same layer.

[0014] First Embodiment An antenna element according to one embodiment of the present invention and a phased array antenna including the antenna element will be described below.

[0015] 1. Overall Structure of the Phased Array Antenna A phased array antenna is a collection of multiple antenna elements arranged in a line, a circle, or a matrix, and is a device that can transmit highly directional radio waves in any direction by adjusting the phase of the AC signal (AC potential) supplied to each antenna element. There are no restrictions on the wavelength of the radio waves that can be transmitted by a phased array antenna according to one embodiment of the present invention, and it can transmit radio waves with wavelengths ranging from 400 MHz to 50 GHz, for example. Typically, this phased array antenna can be used to transmit radio waves in the 400 MHz to 6.0 GHz band, the 2.5 GHz to 4.7 GHz band, or the 24 GHz to 50 GHz band.

[0016] A schematic top view of the phased array antenna 100 is shown in FIG. 1 . As shown in FIG. 1 , the phased array antenna 100 has a substrate 102 and an opposing substrate (not shown in FIG. 1 ), with various patterned insulating films, semiconductor films, conductive films, liquid crystal layers, and the like disposed between them. By appropriately stacking these films, multiple antenna elements 110 including microstrip lines 130 are formed. As shown in FIG. 1 , the phased array antenna 100 may have one or more driving circuits 104 on the substrate 102. The driving circuit 104 may also be composed of various insulating films, semiconductor films, conductive films, and the like formed on the substrate 102, or may be composed of a circuit (such as an integrated circuit) formed on a substrate (e.g., a semiconductor substrate) separate from the substrate 102.

[0017] A plurality of terminals (not shown) are formed on the substrate 102, and various signals are supplied from an external circuit (not shown) via the terminals to the drive circuit 104 and the microstrip line 130. The drive circuit 104 generates signals (scanning signals and control signals) for driving each antenna element 110 based on the supplied signals, and supplies these signals to each antenna element 110 via wiring (not shown). The substrate 102 and the opposing substrate are fixed to each other by a sealing material (not shown), and the plurality of antenna elements 110, the drive circuit 104, the microstrip line 130, etc. are protected by the substrate 102, the opposing substrate, and the sealing material.

[0018] 1, the multiple antenna elements 110 are arranged in a line in one direction, but there are no restrictions on the arrangement of the antenna elements 110. For example, the multiple antenna elements 110 may be arranged on a circumference, or in a matrix shape having multiple rows and multiple columns. Also, various signals may be directly supplied to the multiple antenna elements 110 and the microstrip line 130 from an external circuit via terminals without providing the drive circuit 104.

[0019] FIG. 2 shows a schematic top view of one antenna element 110, and FIG. 3 shows a schematic end view taken along the dashed line A-A' in FIG. 1. FIG. 2 shows one antenna element 110 and portions of two adjacent antenna elements 110. As shown in these figures, the antenna element 110 mainly comprises a common electrode 122, a bias electrode 136, an antenna electrode 132, and a microstrip line 130, with a liquid crystal layer 126 provided between the common electrode 122 and the antenna electrode 132 and between the bias electrode 136 and the microstrip line 130. As will be described later, a phase shifter is formed by laminating the bias electrode 136, the liquid crystal layer 126, and the microstrip line 130. Each component of the phased array antenna 100 will be described below.

[0020] 2. Substrate and Counter Substrate The substrate 102 and the counter substrate 106 provide physical strength to the phased array antenna 100 and also provide a surface for arranging the multiple antenna elements 110. The substrate 102 and the counter substrate 106 may contain inorganic insulators such as glass or quartz, semiconductors such as silicon, polymers such as polyimide, polycarbonate, or polyester, or metals such as aluminum, copper, or stainless steel. The substrate 102 and the counter substrate 106 may be transparent or opaque to visible light. The substrate 102 and the counter substrate 106 may also be flexible. When a conductive material such as metal is contained, it is preferable to provide an undercoat 112 and an overcoat 108, which function as protective insulating films, on the surfaces on which the antenna elements 110 are provided, i.e., the surface of the substrate 102 facing the counter substrate 106 and the surface of the counter substrate 106 facing the substrate 102, respectively. The undercoat 112 and the overcoat 108 may each be composed of one or more films containing a silicon-containing inorganic compound such as silicon oxide or silicon nitride.

[0021] 3. Common Electrode and Bias Electrode The common electrode 122 is provided on the substrate 102, and is configured to be supplied with a constant potential (e.g., ground potential) directly from an external circuit or via the drive circuit 104. The common electrode 122 can be arranged as a single conductive film so as to be shared by multiple antenna elements 110. The common electrode 122 may include a metal such as molybdenum, tungsten, titanium, aluminum, or copper, or an alloy containing a metal selected from these, or may include a conductive oxide such as indium-tin oxide (ITO) or indium-zinc oxide (IZO).

[0022] A bias electrode 136 is also provided on the substrate 102. Unlike the common electrode 122, the bias electrode 136 is provided for each antenna element 110 and is disposed in an opening or cutout provided in the common electrode 122, as shown in FIG. 2. The bias electrode 136 is physically and electrically independent from the common electrode 122. Therefore, the bias electrode 136 is separated from the common electrode 122, and a gap 134 is formed between them (FIG. 2). The bias electrode 136 is formed to exist in the same layer as the common electrode 122. Therefore, the bias electrode 136 and the common electrode 122 can have the same composition and the same thickness.

[0023] A constant potential is supplied to the common electrode 122, while a variable DC or AC potential is supplied to the bias electrode 136 in order to arbitrarily control the direction of the emitted radio waves. When an AC potential is applied to drive the liquid crystal layer 126, its frequency is preferably 1 kHz or less. The potential of the current applied to the bias electrode 136 of each of the multiple antenna elements 110 is individually controlled.

[0024] The variable DC potential may be supplied to the bias electrode 136 of each antenna element 110 directly from an external circuit via a terminal (not shown), or via the driver circuit 104 and an element circuit provided in each antenna element 110 and electrically connected to the bias electrode 136. The element circuit is disposed between the substrate 102 and the bias electrode 136. While FIGS. 2 and 3 show a single transistor 140 included in the element circuit, the element circuit may be configured by appropriately combining one or more transistors and one or more capacitive elements. The transistor shown in FIG. 3 is a so-called bottom-gate transistor, and is configured by a gate electrode 142 provided directly on the substrate 102 or via an undercoat 112, a gate insulating film 144 on the gate electrode 142, a semiconductor film 146 on the gate insulating film 144, and a pair of terminals 148 and 150 electrically connected to the semiconductor film 146. The structure of the transistor 140 is not limited to this; the transistor 140 may be a top-gate transistor or a dual-gate transistor having gate electrodes above and below the semiconductor film 146. A planarization film 116 is provided on the element circuit to absorb unevenness caused by the transistor 140 etc. As an optional configuration, a first interlayer insulating film 114 may be disposed between the planarization film 116 and the transistor 140.

[0025] The materials constituting the element circuit can be appropriately selected from known materials, and therefore detailed description thereof will be omitted. Briefly, the gate insulating film 144 and the first interlayer insulating film 114 may be formed of one or more films containing a silicon-containing inorganic compound. The gate insulating film 144 may be configured to contain a so-called high-k material, such as hafnium silicate, nitrogen-containing hafnium silicate, hafnium oxide, nitrogen-doped hafnium aluminate, or yttrium oxide. The planarization film 116 may be configured to contain a polymer, such as polyimide, polyamide, acrylic resin, or silicone resin. The gate electrode 142 and the pair of terminals 148, 150 may be configured to contain a metal, such as titanium, molybdenum, tungsten, copper, or aluminum, or an alloy containing a metal selected from these. The semiconductor film 146 may contain a Group 14 element, such as silicon, or may be formed as a film containing an oxide of a Group 13 element, such as indium or gallium.

[0026] 4. Alignment Film and Liquid Crystal Layer A first alignment film 124 and a second alignment film 128 are provided on the common electrode 122 and the bias electrode 136 to cover them, and a liquid crystal layer 126 is disposed between the first alignment film 124 and the second alignment film 128. The first alignment film 124 and the second alignment film 128 are provided to control the alignment of liquid crystal molecules that make up the liquid crystal layer 126. The first alignment film 124 and the second alignment film 128 can be provided continuously across multiple antenna elements 110. In other words, the first alignment film 124 and the second alignment film 128 can be provided so as to be shared by all of the antenna elements 110 without being divided between adjacent antenna elements 110.

[0027] Both the first alignment film 124 and the second alignment film 128 contain a polymer such as polyimide or polyester. The first alignment film 124 and the second alignment film 128 are formed using a wet film formation method such as an inkjet method, a spin coating method, a printing method, or a dip coating method, and their surfaces are subjected to a rubbing treatment. Alternatively, the first alignment film 124 and the second alignment film 128 may be formed by a photo-alignment treatment. By using a rubbing treatment or a photo-alignment treatment, the first alignment film 124 and the second alignment film 128 can align the liquid crystal molecules in a uniform direction along the major surfaces of the substrate 102 and the counter substrate 106. Therefore, when no electric field is present in the liquid crystal layer 126, the liquid crystal molecules are homogeneously aligned, with their major axis direction being approximately parallel to the major surface of the substrate 102. The direction (alignment direction) in which the first alignment film 124 and the second alignment film 128 align the liquid crystal molecules can be set arbitrarily. For example, the alignment direction may be parallel to, perpendicular to, or tilted at a certain angle to the extension direction of the microstrip line 130 described in detail below. Furthermore, the alignment directions of the first alignment film 124 and the second alignment film 128 may be the same or different. For example, the alignment directions of the first alignment film 124 and the second alignment film 128 may be perpendicular to each other.

[0028] The structure of the liquid crystal molecules constituting the liquid crystal layer 126 is not limited. Therefore, the liquid crystal molecules may be nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, or chiral smectic liquid crystal. The thickness of the liquid crystal layer 126 is, for example, 20 μm to 100 μm, or 30 μm to 50 μm. Although not shown, spacers may be provided in the liquid crystal layer 126 to maintain this thickness throughout the phased array antenna 100.

[0029] 5. Microstrip Line and Antenna Electrode The microstrip line 130 and the antenna electrode 132 are both provided on the liquid crystal layer 126 via the second alignment film 128. The microstrip line 130 and the antenna electrode 132 are physically and electrically connected to each other. The microstrip line 130 and the antenna electrode 132 can be configured to include a metal such as titanium, molybdenum, tungsten, copper, or aluminum, or an alloy containing a metal selected from these. Furthermore, the microstrip line 130 and the antenna electrode 132 can be formed to exist in the same layer or be formed integrally, and therefore can have the same composition and thickness.

[0030] The microstrip line 130 is an electrode with a large aspect ratio (for example, length / width between 2 and 500), and in the examples shown in FIGS. 1 and 2 , the longitudinal direction of a portion of the microstrip line 130 is arranged perpendicular to the direction in which the multiple antenna elements 110 are arranged. The width of the microstrip line 130 may be set to between 20 μm and 500 μm, for example. A pulsed AC signal is input to the microstrip line 130 directly from an external circuit or via the drive circuit 104.

[0031] The antenna electrode 132 emits radio waves at a frequency corresponding to the AC signal input via the microstrip line 130. For this reason, the antenna electrode 132 is preferably formed in a shape having a plurality of intersecting axes as symmetry axes that are parallel to its main surface, such as a regular polygon including a square. For example, although it depends on the frequency of the radio waves emitted by the phased array antenna 100, the antenna electrode 132 may be arranged so as to have a square shape with one side measuring 2 mm to 30 mm.

[0032] 2 and 3 , the microstrip line 130 overlaps with the bias electrode 136 via the liquid crystal layer 126 when viewed from above the phased array antenna 100 (i.e., in the normal direction of the substrate 102). The microstrip line 130 may partially overlap with the common electrode 122 via the liquid crystal layer 126. On the other hand, the antenna electrode 132 entirely overlaps with the common electrode 122 but does not overlap with the bias electrode 136. Note that, as shown in FIG. 3 , the element circuit may partially overlap with the common electrode 122, or as shown in FIG. 4 , the element circuit may not overlap with the common electrode 122 but may entirely overlap with the bias electrode 136.

[0033] As described above, a phase shifter is formed by the overlapping bias electrode 136, the liquid crystal layer 126, and the microstrip line 130. When the element circuit is driven and a DC or AC potential is applied to the bias electrode 136, a potential difference is generated between the bias electrode 136 and the microstrip line 130, generating a vertical electric field in the liquid crystal layer 126 between them. In the absence of a vertical electric field, the liquid crystal molecules constituting the liquid crystal layer 126 are homogeneously aligned, with their long axis direction approximately parallel to the major surface of the substrate 102. However, when a vertical electric field is generated in the liquid crystal layer 126, the liquid crystal molecules stand upright, resulting in a change in the dielectric constant of the liquid crystal layer 126 due to the dielectric anisotropy of the liquid crystal molecules. The transmission speed of an AC signal supplied to the microstrip line 130 varies depending on the dielectric constant of the liquid crystal layer 126. The greater the change in the dielectric constant of the liquid crystal layer 126, the greater the change in the transmission speed. Furthermore, the change in dielectric constant depends on the strength of the electric field generated in the liquid crystal layer 126. Therefore, by controlling the DC potential applied to the bias electrode 136, it is possible to control the dielectric constant of the liquid crystal layer 126 in the phase shifter formed by the bias electrode 136, the liquid crystal layer 126, and the microstrip line 130, and as a result, it is possible to change the transmission speed of the pulsed AC signal, thereby changing the phase of the pulsed AC signal applied to the antenna electrode 132.

[0034] Therefore, when the same DC potential is applied to the bias electrodes 136 of all antenna elements 110 in the phased array antenna 100, the phase of the pulsed AC signal applied to the antenna electrodes 132 of all antenna elements 110 is the same. As a result, the phase of the radio waves emitted from each antenna element 110 is also the same (see dotted arrows in FIG. 5 ), and the radio wave emission direction is normal to the substrate 102 (see hollow arrows). On the other hand, when the DC potential of the bias electrodes 136 is changed for each antenna element 110, the phase of the pulsed AC signal applied to the antenna electrodes 132 changes between the antenna elements 110. For example, as shown in FIG. 6 , when the phase of the pulsed AC signal is increased or decreased in the order of the arrangement of the antenna elements 110, the phase of the radio waves emitted from the antenna elements 110 changes stepwise (see dotted arrows). As a result, the wavefront of the radio waves (see straight line) is tilted from the normal to the substrate 102, and the emission direction of the radio waves is tilted (see hollow arrows). Therefore, by changing the DC potential of the bias electrode 136 for each antenna element 110, it becomes possible to transmit highly directional radio waves in any direction.

[0035] On the other hand, while a pulsed AC signal is applied to the microstrip line 130 and the antenna electrode 132, the common electrode 122 is configured to be supplied with a constant potential. Furthermore, the antenna electrode 132 does not overlap with the bias electrode 136, but rather overlaps entirely with the common electrode 122. Therefore, the strength of the longitudinal electric field applied to the liquid crystal layer 126 between the common electrode 122 and the antenna electrode 132 varies depending on the frequency of the pulsed AC signal supplied to the antenna electrode 132 via the microstrip line 130. However, the frequency of the pulsed AC signal is very high (e.g., 400 MHz to 50 GHz) compared to the switching speed (60 Hz to 120 Hz) of the voltage applied to the liquid crystal element disposed in each pixel of the liquid crystal display device. Therefore, in the liquid crystal layer 126 between the common electrode 122 and the antenna electrode 132, the liquid crystal molecules cannot effectively follow the change in longitudinal electric field strength caused by the pulsed AC signal, and the liquid crystal molecules can be considered to be aligned in a fixed direction without rotating. Therefore, in the liquid crystal layer 126 between the common electrode 122 and the antenna electrode 132, changes in dielectric constant due to the rotation of liquid crystal molecules can be virtually ignored, and the dielectric constant can be considered constant. As a result, although the phase of the AC signal applied to the antenna electrode 132 is changed by the phase shifter, the dielectric constant of the liquid crystal layer 126 located below it is virtually unchanged, and the phase controlled by the phase shifter is maintained in the antenna electrode 132. Therefore, when the phased array antenna 100 is driven, changes in dielectric constant occurring in the liquid crystal layer 126 above the bias electrode do not affect the antenna electrode 132, and the potential of the antenna electrode 132 faithfully changes in accordance with the AC signal supplied to the microstrip line 130. In other words, by controlling the DC or AC potential applied to the bias electrode 136, the phase of the AC signal transmitted to the antenna electrode can be precisely controlled. As a result, the phased array antenna 100 exhibits stable antenna characteristics and can accurately transmit radio waves in a predetermined direction.

[0036] 6. Other Configurations In the configuration described above, a gap 134 exists between the common electrode 122 and the bias electrode 136, and the microstrip line 130 is exposed from the common electrode 122 and the bias electrode 136 at the gap 134 (see FIGS. 3 and 4). Meanwhile, as described above, a high-frequency AC signal is applied to the microstrip line 130. Therefore, depending on the size of the gap 134, the behavior of the AC signal transmitted through the microstrip line 130 may change, which may result in changes in the antenna characteristics.

[0037] For this reason, as shown in the schematic top views of FIGS. 7 and 8 and FIG. 9 , which is a schematic end view corresponding to FIG. 3 , the first shield electrode 138 may be arranged to overlap the entire gap 134 in the normal direction of the substrate 102. As can be seen from FIG. 8 , the first shield electrode 138 has an opening 138 a, and the first shield electrode 138 is arranged so that the gap 134 extends along the region between the outer periphery of this opening 138 a and the outer periphery of the first shield electrode 138. In other words, the first shield electrode 138 overlaps the end of the common electrode 122 and the end of the bias electrode 136, and the entire outer periphery of the bias electrode 136 overlaps with the first shield electrode 138. The first shield electrode 138 is electrically floating and is not electrically connected to other components (e.g., terminals 148, 150, the common electrode 122, the bias electrode 136, etc.). By providing the first shield electrode 138, the common electrode 122 can be regarded as a single metal plate without any openings or slits for high-frequency signals, thereby preventing deterioration of transmission characteristics. Meanwhile, because of the presence of the gap 134, the potential for driving the liquid crystal layer 126 is supplied only to the region where the bias electrode 136 is present. As a result, unintended changes in the behavior of AC signals transmitted through the microstrip line 130 can be prevented.

[0038] 9, the first shield electrode 138 can be provided on the planarization film 116. In this case, in order to insulate the first shield electrode 138 from the common electrode 122 and the bias electrode 136, a second interlayer insulating film 118 may be provided between the first shield electrode 138 and the common electrode 122 and between the first shield electrode 138 and the bias electrode 136. The second interlayer insulating film 118 may also be composed of one or more films containing a silicon-containing inorganic compound.

[0039] 10, the first shield electrode 138 may be disposed under the planarization film 116. In this case, the first shield electrode 138 is disposed between the first interlayer insulating film 114 and the planarization film 116 to prevent contact with the terminals 148 and 150.

[0040] As described above, in each antenna element 110 of the phased array antenna 100 according to one embodiment of the present invention, a longitudinal electric field is generated in the liquid crystal layer 126 using the bias electrode 136 that is physically and electrically independent from the common electrode 122 facing the antenna electrode 132, in order to control the phase of the AC signal. Furthermore, changes in the dielectric constant of the liquid crystal layer 126 that overlaps with the antenna electrode 132 can be ignored. This makes it possible to precisely control the phase of the AC signal applied to the antenna electrode 132. Therefore, by applying one of the embodiments of the present invention, it is possible to provide a phased array antenna that exhibits stable antenna characteristics and is capable of precisely transmitting radio waves in any direction.

[0041] Second Embodiment In this embodiment, a modified example of the phased array antenna 100 described in the first embodiment will be described. Configurations that are the same as or similar to the configuration described in the first embodiment may be omitted.

[0042] 1. Modification 1 In the antenna element 110 of the phased array antenna 100 according to this modification 1, the antenna electrode 132 is physically separated from the microstrip line 130 and is disposed so as to overlap with the microstrip line 130 in the normal direction of the substrate 102. Specifically, as shown in FIG. 11 and the schematic diagram of the end surface along the dashed line B-B' in FIG. 12, the antenna electrode 132 is disposed above the microstrip line 130 (on the opposite side to the substrate 102) with the opposing substrate 106 interposed therebetween. A capacitive element including the opposing substrate 106 as a dielectric is formed between the microstrip line 130 and the antenna electrode 132, and an AC signal applied to the microstrip line 130 is transmitted to the antenna electrode 132 by capacitive coupling.

[0043] In this arrangement, the distance between the antenna electrode 132 and the liquid crystal layer 126 increases, further reducing the effect of changes in the dielectric constant of the liquid crystal layer 126 on the antenna electrode 132. In addition, by appropriately selecting the thickness and material of the opposing substrate 106, it is also possible to form stronger capacitive coupling between the antenna electrode 132 and the microstrip line 130. This allows AC signals to be transmitted efficiently from the microstrip line 130 to the antenna electrode 132.

[0044] In this first modification, to further reduce the influence of noise and other factors caused by wiring for driving the element circuit, a second shield electrode 160 overlapping the microstrip line 130 and the antenna electrode 132 may be provided between them, as shown in FIG. 13 . In this case, for example, an auxiliary substrate 162 having the antenna electrode 132 and the second shield electrode 160 provided on its upper and lower surfaces, respectively, may be disposed on the opposing substrate 106. The auxiliary substrate 162 may be fixed to the opposing substrate 106 using, for example, an adhesive layer 164. Alternatively, although not shown, the second shield electrode 160 may be provided on the opposing substrate 106 without using the auxiliary substrate 162, and the antenna electrode 132 may be fixed thereon via an adhesive layer. The second shield electrode 160 is also formed to contain a metal or alloy that can be used for the common electrode 122 and the bias electrode 136. The second shield electrode 160 may be electrically floating, or may be configured to be supplied with a constant potential that is the same as or different from the potential applied to the common electrode 122.

[0045] 14 and 15 , the second shield electrode 160 has an opening 160a that overlaps with the microstrip line 130 and the antenna electrode 132. The opening 160a is formed so that its entirety overlaps with the antenna electrode 132. The microstrip line 130 is arranged so as to cross the entire or at least a part of the opening 160a. Therefore, even when the second shield electrode 160 is arranged, capacitive coupling is formed between the microstrip line 130 and the antenna electrode 132 via the opening 160a, and an AC signal can be transmitted from the microstrip line 130 to the antenna electrode 132.

[0046] 2. Modification 2 Alternatively, as shown in FIG. 16 , which is a schematic end view corresponding to FIG. 13 , the antenna electrode 132 may be disposed below the common electrode 122 (i.e., on the opposite side of the microstrip line 130 with respect to the common electrode 122). In this case, the antenna electrode 132 may be provided below the substrate 102, or, although not shown, may be provided between the substrate 102 and the undercoat 112, between the undercoat 112 and the gate insulating film 144, or between the gate insulating film 144 and the first interlayer insulating film 114. When the antenna electrode 132 is provided between the undercoat 112 and the gate insulating film 144, the antenna electrode 132 and the gate electrode 142 may be present in the same layer. When the antenna electrode 132 is provided between the gate insulating film 144 and the first interlayer insulating film 114, the antenna electrode 132 may be present in the same layer as the terminals 148 and 150.

[0047] In Modification 2, as shown in FIGS. 16 to 18 , an opening 122a is formed in the common electrode 122, overlapping the antenna electrode 132 and the microstrip line 130. The opening 122a is formed so that its entirety overlaps the common electrode 122. The microstrip line 130 is arranged to cross the entire or at least a portion of the opening 122a. Therefore, a capacitive element is formed between the microstrip line 130 and the antenna electrode 132 through the opening 122a, with the liquid crystal layer 126, the planarization film 116, the substrate 102, etc., as dielectrics, and AC signals can be transmitted from the microstrip line 130 to the antenna electrode 132 by capacitive coupling. Furthermore, by appropriately selecting the thickness and material of the substrate 102, it is possible to form stronger capacitive coupling between the antenna electrode 132 and the microstrip line 130. As described above, the DC potential applied to the bias electrode 136 does not affect the liquid crystal layer 126 on the antenna electrode 132. Therefore, the capacitance of the capacitive element formed between the microstrip line 130 and the antenna electrode 132 does not change, and stable antenna characteristics can be achieved.

[0048] As in the first modification, in order to further reduce the influence of noise and the like due to wiring for driving the element circuit, a second shield electrode 160 overlapping the antenna electrode 132 and the microstrip line 130 may be provided between the common electrode 122 and the antenna electrode 132, as shown in Figures 19 and 20. In this case, for example, an auxiliary substrate 166 having the second shield electrode 160 and the antenna electrode 132 provided on its upper and lower surfaces, respectively, may be fixed below the substrate 102 using an adhesive layer 168. Alternatively, although not shown, the antenna electrode 132 may be provided below the substrate 102, and the second shield electrode 160 may be provided between the substrate 102 and the undercoat 112, between the undercoat 112 and the gate insulating film 144, between the gate insulating film 144 and the first interlayer insulating film 114, or between the first interlayer insulating film 114 and the planarizing film 116. When the second shield electrode 160 is disposed between the undercoat 112 and the gate insulating film 144, the second shield electrode 160 may be present in the same layer as the gate electrode 142. When the second shield electrode 160 is disposed between the gate insulating film 144 and the first interlayer insulating film 114, the second shield electrode 160 may be present in the same layer as the terminals 148 and 150. The second shield electrode 160 may be electrically floating, or may be configured to be supplied with a constant potential that is the same as or different from the potential applied to the common electrode 122.

[0049] 20 , an opening 160a is formed in the second shield electrode 160, which overlaps with the opening 122a provided in the common electrode 122. The opening 160a is formed so that its entirety overlaps with the antenna electrode 132. The microstrip line 130 is also arranged so as to cross the entire opening 160a. Therefore, the microstrip line 130 and the antenna electrode 132 overlap each other via the openings 122a and 160a, forming a capacitance element between them and allowing AC signals to be transmitted from the microstrip line 130 to the antenna electrode 132.

[0050] In the above-described first and second modifications, in the region where the liquid crystal layer 126 overlaps with the antenna electrode 132 in the normal direction of the substrate 102, the liquid crystal layer 126 is not affected by the DC potential applied to the bias electrode 136, and the dielectric constant can be considered to be substantially constant. Therefore, by applying the first or second modification, a phased array antenna exhibiting stable antenna characteristics can be provided.

[0051] The above-described embodiments of the present invention can be combined as appropriate as long as they are not mutually inconsistent. Furthermore, antenna elements and phased array antennas of the respective embodiments may be combined as appropriate by a person skilled in the art to add or remove components or modify designs, or to add or omit processes or modify conditions, and these combinations are also included within the scope of the present invention as long as they include the gist of the present invention.

[0052] Even if there are other effects and advantages different from those brought about by the aspects of each of the above-mentioned embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

[0053] 100: phased array antenna, 102: substrate, 104: driver circuit, 106: opposing substrate, 108: overcoat, 110: antenna element, 112: undercoat, 114: first interlayer insulating film, 116: planarization film, 118: second interlayer insulating film, 122: common electrode, 122a: opening, 124: first alignment film, 126: liquid crystal layer, 128: second alignment film, 130: microstrip line, 132: antenna electrode, 136: bias electrode, 138: first shield electrode, 138a: opening, 140: transistor, 142: gate electrode, 144: gate insulating film, 146: semiconductor film, 148: terminal, 150: terminal, 160: second shield electrode, 160a: opening, 162: auxiliary substrate, 164: adhesive layer, 166: auxiliary substrate, 168: adhesive layer

Claims

1. A phased array antenna having a plurality of antenna elements, each of the plurality of antenna elements having: a common electrode shared by the plurality of antenna elements and configured to be supplied with a constant potential; a bias electrode spaced apart from the common electrode and present in the same layer as the common electrode; a liquid crystal layer on the common electrode and the bias electrode; a microstrip line located on the liquid crystal layer, overlapping the bias electrode and the common electrode, and configured to be supplied with an AC potential; and an antenna electrode located on the liquid crystal layer, physically connected to the microstrip line, and overlapping the common electrode.

2. A phased array antenna having a plurality of antenna elements, each of the plurality of antenna elements having: a common electrode shared by the plurality of antenna elements and configured to be supplied with a constant potential; a bias electrode spaced apart from the common electrode and present in the same layer as the common electrode; a liquid crystal layer on the common electrode and the bias electrode; a microstrip line positioned on the liquid crystal layer, overlapping the bias electrode and the common electrode, and configured to be supplied with an AC potential; and an antenna electrode positioned on the microstrip line and overlapping the microstrip line and the common electrode.

3. A phased array antenna having a plurality of antenna elements, each of the plurality of antenna elements having: a common electrode shared by the plurality of antenna elements and configured to be supplied with a constant potential; a bias electrode spaced apart from the common electrode and present in the same layer as the common electrode; a liquid crystal layer on the common electrode and the bias electrode; a microstrip line positioned on the liquid crystal layer, overlapping with the bias electrode, and configured to be supplied with an AC potential; and an antenna electrode positioned below the common electrode and overlapping with the common electrode and the microstrip line.

4. A phased array antenna according to any one of claims 1 to 3, wherein the antenna electrode does not overlap the bias electrode.

5. A phased array antenna according to any one of claims 1 to 3, wherein in each of the plurality of antenna elements, the common electrode has an opening or a notch, and the bias electrode is disposed within the opening or the notch.

6. A phased array antenna according to any one of claims 1 to 3, wherein each of the plurality of antenna elements further comprises a first alignment film between the common electrode and the liquid crystal layer and between the bias electrode and the liquid crystal layer, and a second alignment film between the liquid crystal layer and the microstrip line.

7. A phased array antenna as described in any one of claims 1 to 3, wherein each of the plurality of antenna elements further comprises a first shield electrode below the common electrode and the bias electrode, overlapping the common electrode and the bias electrode, and electrically insulated from the common electrode and the bias electrode.

8. The phased array antenna of claim 7, wherein the first shield electrode is electrically floating.

9. The phased array antenna according to claim 7, wherein in each of said plurality of antenna elements, the entire gap between said common electrode and said bias electrode overlaps with said first shield electrode.

10. The phased array antenna according to claim 7, wherein, in each of the plurality of antenna elements, the first shield electrode has an opening, and the entire opening overlaps with the bias electrode.

11. The phased array antenna according to claim 7, wherein each of the plurality of antenna elements further comprises a planarization film below the bias electrode, a transistor located below the planarization film and electrically connected to the bias electrode, and an interlayer insulating film between the planarization film and the bias electrode, and wherein in each of the plurality of antenna elements, the first shield electrode is disposed between the planarization film and the interlayer insulating film.

12. The phased array antenna according to claim 2, wherein each of the plurality of antenna elements further comprises a second shield electrode having an opening between the microstrip line and the antenna electrode, and the microstrip line and the antenna electrode overlap each other via the opening.

13. The phased array antenna according to claim 12, wherein the second shield electrode is configured to be supplied with a constant potential.

14. The phased array antenna according to claim 12, wherein the common electrode and the second shield electrode are configured to be supplied with the same potential.

15. The phased array antenna of claim 12, wherein the second shield electrode overlaps the microstrip line.

16. The phased array antenna according to claim 3, wherein, in each of the plurality of antenna elements, the common electrode has an opening, and the microstrip line and the antenna electrode overlap each other via the opening.

17. The phased array antenna according to claim 3, wherein each of the plurality of antenna elements further comprises a second shield electrode having an opening between the common electrode and the antenna electrode, and the microstrip line and the antenna electrode overlap each other via the opening.

18. The phased array antenna of claim 17, wherein the second shield electrode is configured to be supplied with a constant potential.

19. The phased array antenna according to claim 17, wherein the common electrode and the second shield electrode are configured to be supplied with the same potential.

20. The phased array antenna of claim 17, wherein the second shield electrode overlaps the microstrip line.

Images