Patent Application
20230369780
The present invention relates to an on-chip antenna mounted on a semiconductor chip and a phased array antenna including the same.
A wireless communication device such as a mobile terminal is strongly required to be large in capacity, small in size, and easily carried. In order to achieve those properties, it is important to widen bandwidths (which leads to an increase in data rate) of an antenna and a radio frequency electronic circuit (hereinafter, RF circuit) serving as a radio frequency (RF) front end of a wireless communication device included in a terminal and to reduce sizes of the antenna and the RF circuit. Here, the bandwidth of the RF front end is determined based on an operating bandwidth of high-frequency components including the antenna and analog circuits such as an amplifier and frequency converter serving as components of the RF front end.
Assuming that a ratio of the operating bandwidth of those high-frequency components to a center frequency of the operating band (referred to as a fractional bandwidth) is constant (this assumption is normally established: Non Patent Literature 1), the operating bandwidth can be increased by increasing a carrier frequency because the bandwidth is proportional to the carrier frequency. When the carrier frequency is increased, a wavelength of a radio signal is shortened. Thus, it is also possible to reduce sizes of components including the analog circuits and an impedance element (e.g. quarter-wave line) determined based on a wavelength of the antenna. Therefore, increasing the carrier frequency is effective as a method of meeting needs such as an increase in data rate of the wireless communication device and reduction in size thereof.
In view of this, in recent years, research on high-speed and small wireless communication devices using extremely and tremendously high frequencies such as millimeter waves and terahertz waves has been actively conducted. A problem in using millimeter waves and terahertz waves is a connection portion between a high frequency circuit and an antenna. When a method used in a low frequency band, such as wire bonding or a flip chip, is applied to the connection portion in a tremendously high frequency band exceeding 300 GHz, a large connection loss occurs due to inductance caused by a physical length of the connection portion. Using an on-chip antenna (Non Patent Literature 2) integrated on a semiconductor chip on which a high frequency circuit is formed can eliminate the connection portion between the high frequency circuit and the antenna. Thus, this is effective for reducing a loss in the tremendously high frequency band. Further, the on-chip antenna is manufactured by a semiconductor integration process and is therefore generally small. This also contributes to reduction in size of the wireless communication device.
Typical examples of the on-chip antenna include a patch antenna and slot antenna. An operation principle of those antennas is basically similar to that of a dipole antenna and is such that distributions of standing waves of voltage and current are formed on an antenna conductor pattern to radiate an electric field. The antennas are easily manufactured because of their simple structures, but generally have a narrow band characteristic determined by a Q factor of resonance because the antennas use a resonance phenomenon caused by formation of standing waves. Meanwhile, examples of an antenna having a wide bandwidth and relatively large directivity include a Vivaldi antenna. However, the antenna has a large structure whose size is about a wavelength and thus needs to be multilayered, for example, in order to perform beamforming. Therefore, the antenna is not suitably mounted as one chip.
However, such a conventional structure has poor directivity and has substantially poor radiation efficiency of radiant power from an input to a specific reception direction. This reduces a transmission distance of a wireless transmission system including an antenna, which is problematic. Further, the conventional structure is a resonant system of a single frequency and thus has a peak at the single frequency as a frequency characteristic of radiation. Therefore, it is difficult to increase a bandwidth of the wireless transmission system including the antenna and to increase a transmission speed, which are also problematic.
Even in a case where a wideband on-chip antenna is designed as a solution to the above problems, the antenna needs to include a plurality of resonance structures. Therefore, there is a problem that a size of an element is increased, which makes it difficult to array the antennas. Similarly, there is also a problem that a gain in the band becomes unstable when the wideband on-chip antenna is designed.
The present invention has been made in order to solve the above problems, and an object thereof is to provide an on-chip antenna capable of significantly improving directivity and gain and obtaining a wideband radiation characteristic.
In order to achieve such an object, an on-chip antenna according to the present invention includes: a substrate made from a dielectric; a patch conductor formed on a front surface of the substrate and configured to radiate a fed electromagnetic field; a feed line formed on the front surface of the substrate and configured to feed an input electromagnetic field to the patch conductor; and a pair of stub conductors formed on the front surface of the substrate and provided to symmetrically protrude from the feed line in the vicinity of a connection portion where the feed line is connected to the patch conductor, in which the patch conductor has a hexagonal shape in which both corners of one side of a rectangle are obliquely cut off, and the one side is connected to the feed line at the connection portion.
Further, a phased array antenna according to the present invention includes: a plurality of the on-chip antennas according to the present invention; and a plurality of feed lines configured to individually supply a high frequency signal to the plurality of on-chip antennas, respectively, in which: the plurality of on-chip antennas is periodically arrayed one-dimensionally or two-dimensionally at an interval of about a half wavelength of a radio wave in a target frequency band in a direction different from a feeding direction of the plurality of feed lines; and the plurality of feed lines individually feed each of a plurality of radio frequency signals having a same phase or different phases to a corresponding on-chip antenna of the plurality of on-chip antennas.
Further, a phased array antenna according to the present invention includes: a plurality of the on-chip antennas according to the present invention; and a plurality of feed lines configured to individually supply a high frequency signal to the plurality of on-chip antennas, respectively, in which: a structure in which the plurality of on-chip antennas is periodically arrayed one-dimensionally in a feeding direction of the plurality of feed lines serves as one unit, and the structures are periodically arrayed one-dimensionally or two-dimensionally in a direction different from the feeding direction of the plurality of feed lines; and the plurality of feed lines individually feed each of a plurality of radio frequency signals having a same phase or different phases to a corresponding on-chip antenna of the plurality of on-chip antennas.
According to the present invention, it is possible to significantly improve directivity and gain of an on-chip antenna and obtain a wideband radiation characteristic.
Next, embodiments of the present invention will be described with reference to the drawings.
First, an on-chip antenna 10 according to a first embodiment of the present invention will be described with reference to
The on-chip antenna 10 according to the present invention is an antenna formed on a dielectric substrate B on which a semiconductor chip of an integrated circuit such as a monolithic microwave integrated circuit (hereinafter, referred to as MMIC) is formed by using a general semiconductor process technology. Hereinafter, the on-chip antenna 10 will also be referred to as a circuit integrated antenna.
As illustrated in
The feed line 11 includes a microstrip line as a whole and is a transmission line for feeding a high-frequency electromagnetic field input from the outside to the patch conductor 12. Hereinafter, for ease of description, a direction in which the feed line 11 extends on the front surface P (left and right direction on a surface of paper) will be referred to as a direction Y, and a direction orthogonal to the direction Y (up and down direction on the surface of the paper) will be referred to as a direction X.
The patch conductor 12 is an antenna element (radiating element) that radiates an electromagnetic field fed from the feed line 11. The patch conductor 12 has a hexagonal shape as a whole in a plan view in which both corners 12S of one side 12A of a rectangle 12R are obliquely cut off. A connection portion 12X located at a center of the side 12A is connected to the feed line 11, and a side 12B facing the side 12A serves as an end of the patch conductor 12.
In this way, an inclined portion 12E inclined with respect to the direction X is formed between the side 12A and a side 12C of the patch conductor 12, and an inclined portion 12F inclined with respect to the direction X is formed between the side 12A and a side 12D.
The stub conductors 13 are a pair of stubs provided to symmetrically protrude from the feed line 11 in the direction X in the vicinity of the connection portion 12X where the feed line 11 is connected to the patch conductor 12. A distance in the direction X between both ends of the stub conductors 13 is substantially the same as a distance in the direction X between the facing sides 12C and 12D of the patch conductor 12. Each of the stub conductors 13 has a certain conductor width equal to or less than a line width of the feed line 11. In the stub conductor 13, a side 13A on the feed line 11 side (a port PT side) and a side 13B on the patch conductor 12 side protrude from the feed line 11 in the direction X, i.e., in a direction perpendicular to the feed line.
Hereinafter, an example where the feed line 11 is linearly formed will be described. However, the present invention is not limited thereto, and a bent portion, curved portion, or another stub may be provided in the middle of the feed line. Further, an example where a substrate including a compound semiconductor such as indium phosphide (Inp) is used as the substrate B will be described. However, the present invention is not limited thereto, and a general dielectric substrate used for a high frequency circuit may be used. Furthermore, an example where a thin film of gold (Au) is used as a thin film conductor of the feed line 11, the patch conductor 12, the stub conductors 13, and the like will be described. However, the present invention is not limited thereto, and a general metal thin film conductor used for a high frequency circuit may be used.
Next, an analysis result by simulation will be described as an operation of the on-chip antenna 10 according to the present embodiment with reference to
In the explanatory diagram of
In the explanatory diagram of
Meanwhile, as illustrated in
The feed line 51 includes a microstrip line such as a CPW as a whole and is a transmission line for feeding a high-frequency electromagnetic field input from the outside to the patch conductor 52.
The patch conductor 52 has a substantially square outer shape in a plan view as a whole and is an antenna element (radiating element) that radiates an electromagnetic field fed from the feed line 11. In the patch conductor 52, two slits 54 parallel to each other in the direction Y are formed in the vicinity of a connection portion of the feed line 51 so as to extend toward an inner region of the patch conductor 12. A laminated structure of the patch antenna 50 is similar to that in
In the explanatory diagram of
In the explanatory diagram of
For the analysis, as illustrated in
A stub patch antenna, as well as the patch antenna, is fed from the microstrip line, and a feed point is adjusted by changing a value of Slit_y. A resonance frequency is changed depending on the size Pat_y of the patch in a feeding direction. Generally, a bandwidth of the patch antenna cannot be changed depending on its structure and is unintentionally determined depending on a material of the substrate to be mounted.
The on-chip antenna 10 includes the two symmetrical inclined portions 12E and 12F formed on a feeding side of the patch conductor 12 and the stub conductors 13 near the inclined portions 12E and 12F and is fed from the feed line 11 that is a microstrip line in a similar manner to the patch antenna. The resonance frequency of the on-chip antenna 10 can be matched by changing values of the sizes Slit_y and Stub_Int of the stub conductors 13. The center frequency and bandwidth of the on-chip antenna 10 can be changed by changing other structural parameters, and thus the on-chip antenna is more convenient than the patch antenna.
The electromagnetic field was actually analyzed on the basis of the analysis condition and the antenna size described above, and frequency characteristics of a return loss (S11) shown in
In the on-chip antenna 10, as described above, because the inclined portions 12E and 12F are inclined with respect to the direction X by the angle Angle_Patch, capacitances formed between the inclined portions 12E and 12F of the patch conductor 12 and the stub conductors 13 gradually change depending on positions thereof. It can be seen from the results of
An effect of gradually changing and widening the resonance frequency can be similarly obtained in a case where the value of Angle_Patch is increased to make the angles of the inclined portions 12E and 12F steeper or in a case where the value of Pat_x is increased to expand the inclined portions 12E and 12F. In a case where the angles of the inclined portions 12E and 12F are made steeper, an amount of increase in bandwidth is larger, but the center frequency also shifts to a higher frequency. Meanwhile, in a case where the inclined portions 12E and 12F are expanded, the amount of increase in bandwidth is smaller, but a change in the center frequency is also smaller and is stable.
In
It can be seen from
Next, an on-chip antenna 10A according to a second embodiment of the present invention will be described with reference to
As illustrated in
Using such a structure can increase a degree of freedom in design and further improve convenience. In a case of the on-chip antenna 10, the center frequency tends to change when the bandwidth is expanded. Thus, the center frequency may not be matched when the bandwidth is widened in a desired frequency band, or the size of the on-chip antenna may be increased due to the expansion of the bandwidth. Meanwhile, using the on-chip antenna 10A makes it possible to widen the bandwidth while easily reducing an increase in the center frequency, without changing an area of the antenna.
Next, an analysis result by simulation will be described as an operation of the on-chip antenna 10 according to the present embodiment with reference to
In
In
For the analysis, as illustrated in
The electromagnetic field was actually analyzed on the basis of the analysis condition and the antenna size described above, and characteristics shown in
In
In
Next, a phased array antenna 10B according to the present embodiment will be described with reference to
s illustrated in
Individual ports PT1 to PT4 are provided for the antenna elements ANT1 to ANT4, respectively. A plurality of high frequency signals having the same phase or different phases, which is input as a combination from the ports PT1 to PT4, is fed to each of the antenna elements ANT1 to ANT4 via individual feed lines. Because the antenna size is small, the pitches between the antenna elements ANT1 to ANT4 can be about a half wavelength of a radio wave in a target frequency band.
The antenna elements ANT1 to ANT4 can be periodically arrayed one-dimensionally or two-dimensionally in a direction different from the feeding direction (direction Y) of each feed line. Further, a structure in which the antenna elements ANT1 to ANT4 are periodically arrayed one-dimensionally in the feeding direction (direction Y) of each feed line is set as one unit, and the above structures can also be periodically arrayed one-dimensionally or two-dimensionally in a direction different from the feeding direction of each feed line.
The on-chip antennas 10A were arrayed to form the phased array antenna 10B in this way, and an electromagnetic field was analyzed.
According to
In the phased array antenna 10B, radiation characteristics obtained when power was simultaneously supplied to the antenna elements ANT1 to ANT4 from the ports PT1 to PT4 were confirmed.
Among the above drawings,
As described above, the present invention can improve the directivity and gain of the on-chip antenna. This makes it possible to perform wireless communication over a longer distance. Because a wideband radiation characteristic can be obtained, an increase in capacity of wireless communication in the millimeter wave band/terahertz band throughout the entire system can be expected by increasing an amount of transmittable information. From the viewpoint of chip design, it is possible to tune the center frequency and the bandwidth without substantially changing the size of the antenna. Therefore, the chip antenna is highly convenient from the viewpoint of system design. It is possible to reduce the size and improve the gain and radiation efficiency in a wide band.
Both the on-chip antennas 10 and 10A according to the present invention have a small size, and thus it is also possible to easily achieve both improvement in the above characteristics and array as in the phased array antenna 10B, for example. At that time, the element size can be designed to be a ¼ wavelength or less, and thus it is possible to reduce a problem such as electromagnetic field coupling between the elements and double a gain improvement effect of a single element according to the number of elements. Further, because the antennas are arrayed, it is possible to obtain a gain equal to or higher than that of a conventional wideband antenna designed to have a wavelength size, such as a Vivaldi antenna, and automatically control a radiation direction by beamforming. For example, assuming ultra-high speed wireless communication in the 300 GHz band, a slight deviation of a transmission/reception position greatly affects the SN ratio, and thus, when the SN ratio is constantly optimized by finely adjusting a beam angle, it is possible to perform high bit rate wireless transmission at a high modulation level.
The present invention has been described by referring to the embodiments, but is not limited to the above embodiments. Various changes understandable by those skilled in the art can be made for the configurations and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/036852 | 9/29/2020 | WO |
