KR102454359B1 - Multiple band antenna - Google Patents

Abstract

A multi-band antenna of the present embodiment includes multiple unit antennas. The unit antennas may include: a monopole antenna including a meander pattern; a microstrip patch antenna and a monopole antenna including a U-shaped slot; and a low pass filter connecting the microstrip patch antenna. The monopole antenna operates at a first frequency, and the microstrip patch antenna operates at a second frequency higher than the first frequency.

Description

MULTIPLE BAND ANTENNA

The present technology relates to multi-band antennas.

Modern mobile communication systems require multi-band small antennas due to the limited space of mobile phones. In particular, complex feeding techniques for multiple antennas can cause additional losses in the mm-wave band, which is more susceptible to this problem. Therefore, multi-band antennas are one of the preferred solutions for 5G mobile applications.

Currently, the realization of multi-band antennas in sub-6 GHz and millimeter wave bands has been the focus of research in this field, and in recent years, extensive research has been carried out on mm-wave technology for use in 5G communication systems. This will ultimately meet the demands for high data rates, low time delays, the Internet of Things, miniaturization goals, high capacity and user density for effective communication. To achieve the desired high-speed broadband service, national governments and international organizations have proposed millimeter-wave spectrums (eg 24 GHz, 28 GHz, 37 GHz - 39 GHz and 60 GHz). 5G cellular communication in the millimeter wave spectrum still has challenges and propagation-related shortcomings, which slows network deployment. Currently, these millimeter wave bands are being developed for short-range indoor links and local area networks.

However, frequencies below 6 GHz for 5G wide-area coverage are already in use in several countries. ITU WRC-15 has allocated the main 5G mid-band (3.4 GHz - 3.6 GHz) for future broadband cellular communication systems, which can provide wider coverage and low propagation loss. ) is shown.

For 5G communication, sub-6 GHz mobile handset antennas have been studied by several researchers, and small-sized millimeter wave antennas have also been studied a lot, but most antennas operate in a single frequency band. However, it is difficult to embed multiple single-mode antennas in a limited space of a portable terminal such as a handset. In this regard, the integration of sub-6 GHz and millimeter wave antennas has been the subject of research for 5G cellular communications.

In the past decade, various methods using patch antennas, monopole antennas, dipole antennas, slot antennas and PIFA (Planar Inverted-F antenna), etc. However, few studies have achieved low-profile and broadband characteristics suitable for portable devices.

In addition, all of these preceding studies integrated only the sub-6GHz band and could not realize the millimeter wave 5G band operation. Unlike multi-band operation in the sub-6 GHz band, designing a 5G MIMO antenna array with satisfactory isolation and small size at these low frequencies for modern smartphones is still a *?* difficult task. Therefore, some studies are focusing on the miniaturization of MIMO antenna arrays with advantageous isolation for 5G communication systems.

One of the problems to be solved by this embodiment is to provide an antenna capable of solving the above-described difficulties of the prior art.

The multi-band antenna of this embodiment includes: a plurality of unit antennas, and the unit antenna includes: a monopole antenna including a meander pattern, and a microstrip patch including a U-shaped slot an antenna (microstrip patch antenna) and a monopole antenna, and a low-pass filter connecting the microstrip patch antenna, wherein the monopole antenna operates at a first frequency, and the microstrip patch antenna operates at a second frequency higher than the first frequency do.

According to one aspect of the present embodiment, the multi-band antenna includes a rectangular substrate on which a plurality of unit antennas are positioned, and the plurality of unit antennas are arranged along an edge of the rectangular substrate.

According to one aspect of the present embodiment, in the monopole antenna, line patterns are arranged in a meandering pattern to form a meander pattern.

According to one aspect of the present embodiment, the monopole antenna includes a cut ground pattern.

According to one aspect of the present embodiment, the first frequency is a frequency of a band less than 6 GHz.

According to one aspect of the present embodiment, the microstrip patch antenna includes a U-shaped slot.

According to one aspect of the present embodiment, the microstrip patch antenna includes a U-shaped slot.

According to one aspect of this embodiment, the microstrip patch antenna includes a tank circuit in which an inductor, a capacitor, and a resistor are connected in parallel to each other in an equivalent circuit, and the equivalent circuit of the microstrip patch antenna includes a plurality of tank circuits connected in series do.

According to one aspect of the present embodiment, the second frequency is a frequency of a millimeter wave band.

According to one aspect of the present embodiment, the low-pass filter passes a frequency band lower than the cutoff frequency and passes a frequency band higher than the cutoff frequency, wherein the cutoff frequency is a frequency greater than the first frequency and smaller than the second frequency.

According to one aspect of the present embodiment, the multi-band antenna is a multiple input multiple output (MIMO) antenna.

According to the present embodiment, there is an advantage in that a multi-band antenna operating in a plurality of significantly different frequency bands is provided.

FIG. 1 (a) is a diagram showing an outline of an 8 * 8 MIMO antenna according to the present embodiment, and FIG. 1 (b) is an outline of a unit antenna Ant-3 illustrated by a dashed rectangle in FIG. 1 (a). is a diagram showing
FIG. 2 is a diagram schematically illustrating a CMRC LPF illustrated by a broken line circle in FIG. 1( b ).
3 is a diagram illustrating S11 and S21 among the S parameters of the proposed CMRC LPF 130 .
Figure 4 (a) is a diagram showing the current distribution in a band less than 6 GHz (3.5 GHz) in a single antenna element including a radiating patch and a ground plane, Figure 4 (b) is a millimeter wave band (28 GHz) in the single antenna element ), and FIG. 4(c) is a diagram showing the current distribution in the millimeter wave band (38 GHz) in a single antenna element.
5 is a diagram showing a simplified equivalent circuit of the proposed antenna.
6 is a diagram illustrating an equivalent circuit and a reflection coefficient obtained through simulation.
7 is a diagram illustrating simulation results of transmission coefficients in a plurality of frequency bands.

Hereinafter, this embodiment will be described with reference to the accompanying drawings.

A. Suggested 8 * 8 MIMO The structure of the antenna configuration

1 (a) is a diagram showing an outline of an 8 * 8 MIMO antenna 10 according to the present embodiment, and FIG. 1 (b) is a unit antenna (Ant-3) exemplified by a dashed rectangle in FIG. 1 (a). ) is a diagram showing the outline of Referring to FIG. 1( a ), eight identical unit antennas Ant-1 - Ant-8 are arranged along upper and lower periphery, and eight identical unit antennas Ant-1 - Ant-8 are two Forms a MIMO sub-array.

Eight identical unit antennas (Ant-1 - Ant-8) have a double-sided copper-cladding with a relative permittivity (ε _r ) of 2.2, a loss tangent (tanδ) of 0.0009, and a thickness of 0.508 mm. ) was formed on a Rogers RT/duroid 5880 substrate. In the design of this embodiment, a Rogers substrate with low electrical loss, low water absorption, and constant electrical properties at high frequencies was selected. The size of the substrate is 157.7mm * 70mm, which is similar to the size of a typical mobile phone.

The antennas are placed in a vertical position to make the best use of space and to maintain good isolation properties between the nearest unit antenna elements. All eight unit antennas (Ant-1 - Ant-8) are arranged along a short edge, four unit antennas (Ant-5 - Ant-8) are arranged on the upper side, and 4 unit antennas (Ant- 1-Ant-4) is deployed. In order to obtain a minimum isolation of 15dB at a lower frequency and to maintain beamforming characteristics, a 10mm separation distance was formed between the two nearest unit antennas.

In the embodiment illustrated by Fig. 1(a), the upper and lower perimeters are regions suitable for smart phone antenna placement to avoid interference with other components. The design of this example kept the monopole structure inside the substrate for measurement advantage. In another embodiment the MIMO antenna elements can be moved anywhere on the substrate while maintaining a minimum distance of 10 mm between the antenna elements. Initial antenna modeling, simulation and optimization were performed using radio electromagnetic (EM), ANSYS High Frequency Structure Simulator (HFSS) software. However, for further results such as SAR and PD using human head and hand models, a Sim4life Finite-Difference-Time-Domain (FDTD) based simulator was used.

B. Microstrip patch antenna and monopole antenna design

FIG. 1(b) is a view showing the overall shape including the detailed size of the unit antenna element Ant-3 shown by the dashed rectangle in FIG. 1(a). The unit antenna element (Ant-3) is designed by integrating two different antennas. A radiating patch (orange) and a ground plane (light blue) are printed on opposite sides of the substrate. The lower part of the antenna in the diagram of FIG. 1(b) includes a simple microstrip patch antenna 110 with a U-shaped slot. Microstrip patch antenna 110 operates in dual bands in the millimeter wave (28 GHz and 38 GHz) range.

The upper portion of the antenna includes a monopole antenna 120 in the form of a meander for operation below 6 GHz. To achieve a small antenna size for MIMO configuration inside a small smart phone, a low-band radiator is extended in electrical length in a meander linear pattern. A microstrip patch antenna 110 and a meander-type monopole antenna 120 were combined using a microstrip resonant cell (CMRC)-based low-pass filter (LPF) 130 . The CMRC LPF 130 blocks the upper two millimeter wave bands of the 20 GHz or higher frequency so that the meander-type monopole antenna 120 operates at 3.5 GHz.

From the truncated ground structure 122 shown in FIG. 1(b), impedance matching, miniaturization, and wide isolated bandwidth can be obtained below 6 GHz. The size of a single antenna is 22mm * 10mm * 0.508mm. The antenna is fed through 50 matched microstrip feed lines (not shown), 1.5 mm wide and 6 mm long. The feed line was kept longer to maintain the spacing between the millimeter wave connectors, but in actual application, the length of the feeding line can be minimized.

C. CMRC LPF's design

FIG. 2 is a diagram schematically illustrating the CMRC LPF 130 shown by a broken line circle in FIG. 1( b ). Referring to FIG. 2 , the CMRC LPF 130 of this embodiment is designed with two pairs of circular open stubs having different diameters. The two circular patches 132 , 134 are symmetrically connected to both sides of the transmission line 136 . The micro-strip patch antenna 110 structure in which the U-shaped slot is formed and the meander line structure of the monopole antenna 120 are connected and integrated by the CMRC LPF 130, and can operate in two frequency bands that are significantly different. The CMRC LPF 130 is designed to pass only frequencies below 20 GHz. Therefore, when a higher frequency is provided, the current passing through the filter is designed to be cut off, and it acts as an open circuit preventing the current from being supplied to the meander pattern of the monopole antenna 120 . Conversely, at low frequencies, it acts as a short circuit. The input impedance of the CMRC LPF 130 was maintained at 50Ω, and the dispersion model was simulated and optimized using ANSYS HFSS based on FEM (Finite Element-Method). The total area of the proposed CMRC LPF 130 is 10 mm * 10 mm, which is suitable for integration with a small antenna.

3 is a diagram illustrating S11 and S21 among the S parameters of the proposed CMRC LPF 130 . Referring to FIG. 3 , the insertion loss of the CMRC LPF 130 according to the present embodiment is less than 0.5 dB in the frequency range of 1 GHz to 10 GHz in the pass band, whereas the return loss exceeds 20 dB in the entire pass band. The attenuation level is less than -20dB at the stopband frequencies (22GHz - 40GHz). It can be seen from FIG. 3 that the filter according to the present embodiment has an ultra-wide stopband for a higher frequency covering a desired frequency band.

D. Current distribution

Figure 4 (a) is a diagram showing the current distribution in a band less than 6 GHz (3.5 GHz) in a single antenna element including a radiating patch and a ground plane, Figure 4 (b) is a millimeter wave band (28 GHz) in the single antenna element ) is a diagram showing the current distribution, and FIG. 4(c) is a diagram showing the current distribution in the millimeter wave band (38 GHz) in a single antenna element. Referring to FIG. 4( a ), as described above, the CMRC LPF 120 operates as a short circuit below the cutoff frequency and opens circuit in a band above the cutoff frequency (eg, high frequency of 20 GHz or higher). ) works as Accordingly, the surface current passes through the CMRC LPF 120 and is provided as a meander pattern of the monopole antenna 120. A current is supplied to the meander pattern line of the monopole antenna 120 through the C MRC LPF 120 to supply the monopole antenna. It can be seen that (120) has a high current density.

Referring to FIG. 4(b), the surface current of the unit antenna element in the millimeter wave band (28 GHz) is mainly concentrated on the slotted micro-strip antenna 110, while the monopole antenna 120 by the CMRC LPF 130. It can be seen that the current flowing to the meander pattern line is blocked. There may be a small leakage of current, but there is no significant change in the resonant frequency of the antenna.

Referring to FIG. 4( c ), a U-shaped slot was introduced into the microstrip patch portion of the unit antenna in the millimeter wave band (38 GHz), and a second resonance occurred in the millimeter wave band at 38 GHz. As in the case of 28 GHz, no leakage current was observed in the CMRC LPF 130 .

E. Simplified equivalent circuit for the proposed integrated antenna

5 is a diagram showing a simplified equivalent circuit of the proposed antenna. The equivalent circuit was designed and optimized using Keysight Technologies' Advanced Design System (ADS) simulator. The equivalent circuit of the microstrip antenna 110 in which the U-shaped slot is formed is indicated by 110eq, the equivalent circuit of the CMRC LPF 120 is indicated by 130eq, and the equivalent circuit for the monopole antenna 120 is indicated by 120eq.

Referring to FIG. 5 , the equivalent circuit 110eq of the microstrip antenna 110 in which the U-shaped slot is formed includes two RLC tank circuits T1 and T2 connected in parallel. L1 is the inductance of the antenna feeding line. Each of the RLC tank circuits T1 and T2 resonates in the millimeter wave band. The element values of the RLC tank circuits T1 and T2 may be calculated as follows. From the product of LC, the resonant frequency of the patch antenna is determined as in Equation ① of Equation 1 below. The input resistance is considered as R at resonance, and the antenna quality factor is determined as ② in Equation 1.

[Equation 1]

The CMRC LPF 130 is represented by L and C lumping elements to resonate a specific frequency range, while doubling the LC circuit widens the stopband, and the filter is analyzed separately before being integrated with the antenna circuit. The meander line pattern of the monopole antenna 120 was modeled using an inductor, while the spacing between the line patterns was indicated using a capacitor as shown in 120eq of FIG. 5 .

6 and 7 respectively show the simulated reflection coefficients (S22) and transmission coefficients (S23, S24 and S26) of the proposed 8*8 MIMO antenna over the desired frequency band. In Fig. 6, a dotted line shows a reflection coefficient of an equivalent circuit, and a solid line shows an antenna simulation result. Referring to FIG. 6 , it can be seen that the equivalent circuit and the simulation result have similarities in all frequency bands. The optimized values for the components extracted from the ADS circuit are exemplified in Table 1 below.

Referring to FIG. 6 , similar reflection coefficients were observed by symmetrically disposing the same unit antenna elements (Ant-1 - Ant-8) on a substrate, so that only S22 (reflection coefficient) of Ant-2 is indicated in FIG. 6 . It can be seen that the proposed antenna has a -10dB bandwidth of 450MHz at 3.5GHz (3.30Ghz - 3.75GHz), a -10dB bandwidth of 1620MHz at 28GHz (27.15GHz - 28.77GHz) and a -10dB bandwidth of 900MHz (37.59Ghz - 38.49GHz) at 38GHz. can The bandwidth obtained in all three frequency bands meets the high traffic and high-speed data requirements.

Referring to FIG. 7 , it was possible to obtain 15 dB or more of isolation between the closest antenna elements (Ant-2 and Ant-3) in a band below 6 GHz, and 35 dB or more between Ant-2 and Ant-4, Ant- Between 2 and Ant-6, more than 120dB of isolation was achieved.

However, the isolation is improved for millimeter waves with shorter wavelengths. It can be seen that the isolation between the closest MIMO antenna elements at 28 GHz and 38 GHz is more than 25 dB. The mutual coupling characteristic of the proposed antenna without using an external structure is better than that of several 5G antennas in sub-6 GHz and millimeter wave bands and smartphone applications.

Although it has been described with reference to the embodiment shown in the drawings in order to help the understanding of the present invention, this is an embodiment for implementation, it is merely an example, and various modifications and equivalents from those of ordinary skill in the art It will be appreciated that other embodiments are possible. Accordingly, the true technical protection scope of the present invention should be defined by the appended claims.

10: MIMO antenna 110: microstrip patch antenna
110eq: equivalent circuit of microstrip patch antenna
120: monopole antenna having a meander pattern
120eq: equivalent circuit of monopole antenna with meander pattern
122: cut ground structure 130: CMRC LPF
130eq: equivalent circuit of CMRC LPF 132: circular patch
134: circular patch 136: transmission line
T1, T2: tank circuit
Ant-1, Ant-2, ..., Ant-8: unit antenna

Claims (11)

A multi-band antenna, the antenna comprising:
It includes a plurality of unit antennas,
The unit antenna is:
a monopole antenna comprising a meander pattern;
A microstrip patch antenna including a U-shaped slot, and
and a low-pass filter connecting the monopole antenna and the microstrip patch antenna.
The monopole antenna operates at a first frequency, and the microstrip patch antenna operates at a second frequency higher than the first frequency. According to claim 1,
The multi-band antenna,
a rectangular substrate on which the plurality of unit antennas are located;
The plurality of unit antennas is a multi-band antenna arranged along an edge of the rectangular substrate. According to claim 1,
The monopole antenna is
A multi-band antenna in which line patterns are arranged in a meander pattern to form the meander pattern. According to claim 1,
The monopole antenna is
A multi-band antenna with a truncated ground pattern. According to claim 1,
The first frequency is
Multi-band antennas with frequencies below 6 GHz. According to claim 1,
The microstrip patch antenna comprises:
A multi-band antenna with a U-shaped slot. According to claim 1,
The microstrip patch antenna comprises:
Multi-band antenna with U-shaped slot. According to claim 1,
The microstrip patch antenna comprises:
An equivalent circuit comprising a tank circuit in which an inductor, a capacitor and a resistor are connected in parallel to each other,
The equivalent circuit of the microstrip patch antenna is
A multi-band antenna comprising a plurality of the tank circuits connected in series. According to claim 1,
wherein the second frequency is a millimeter wave band frequency. According to claim 1,
The low-pass filter is
Passing a frequency band lower than the cutoff frequency and passing a frequency band higher than the cutoff frequency,
wherein the cutoff frequency is greater than the first frequency and less than the second frequency. According to claim 1,
The multi-band antenna is a multiple input multiple output (MIMO) antenna.

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