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Recent Advances in the mm-Wave Array for Mobile Phones

Written By

Yan Wang and Xiaoxue Fan

Submitted: 06 May 2023 Reviewed: 01 June 2023 Published: 24 June 2023

DOI: 10.5772/intechopen.112043

MIMO Communications IntechOpen
MIMO Communications Fundamental Theory, Propagation Channels, and... Edited by Ahmed Kishk

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MIMO Communications - Fundamental Theory, Propagation Channels, and Antenna Systems

Edited by Ahmed A. Kishk and Xiaoming Chen

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Abstract

With the development of communication system to the mm-wave band, the antenna design in the mm-wave band for mobile phones encounters new requirements and challenges. The mm-wave characteristics of short wavelength, high free-space path loss, and easy-to-be-blocking usually require mm-wave antennas with high gain and beam-scanning capability. Also, considering the very limited space occupied by antennas in mobile phones and the massive production of consumer electronics, small size, low cost, multiband, multi-polarization, and wide beam steering becomes the main key point of mm-wave array performance. In addition, as a special situation of the mobile antenna, the analysis of effect of the human tissue on the antenna performance is also important. So, in this chapter, a comprehensive summary on the recent advances in the mm-wave array for mobile phones including single-band, dual-band, and reconfigurable design of broadside array, horizontal polarized, vertical polarized, and dual-polarized design of endfire array, co-design of mm-wave array with lower band antenna, and user influence are summarized.

Keywords

  • mm-wave array
  • mobile phones
  • broadside array
  • endfire array
  • reconfigurable array
  • shared-aperture
  • beam steering
  • user influence

1. Introduction

Mobile communication has been updated greatly from the first-generation (1G) to recent fifth-generation (5G) and future promising sixth-generation (6G) mobile communication systems to meet the requirement of high data rate, large capacity, low latency, et al. for consumers [1]. As one of the key techniques for 5G and 6G communication system, millimeter-wave (mm-wave) frequency band with large bandwidth is adopted [2, 3]. Comparison with the centimeter-wave or decimeter-wave, the frequency band of mm-wave is much higher and thus shorter wavelength. However, due to its high frequency with short wavelength, the free-space loss of mm-wave is higher than that of lower frequency bands, and the mm-wave beam is usually blocked [4]. To mitigate the path loss and beam blockage, a high-gain antenna with wide-angle beam scanning is usually adopted to catch the strongest signal and ensure effective radiation in a 5G mm-wave system [5].

To ensure the wireless connection using mm-wave frequency band, the mm-wave array antenna should be applied in mobile phones. Besides the requirements of frequency bands, maximum output power, additional spectrum emission mask, and spurious emission from the 3GPP [6], four additional key difficulties should be considered for mm-wave array in mobile phones:

  • Array size: Because most of the spaces are reserved for the displays, cameras, battery, printed circuit board (PCB), motor, speaker, and so on [7] for better user experience, the mm-wave array in mobile phones should only occupy a very small space. In addition, most of the antenna space in mobile phones has been occupied by the antennas working at the lower frequency band. The space for mm-wave arrays in mobile phones is extremely limited.

  • Beam coverage: Because the posture of mobile phones is usually arbitrary in realistic scenarios [8], the mm-wave array in mobile phones should cover as wide as possible beam coverage with the required performance to catch the strongest signal for an effective signal connection. In practical applications, 2 or 3 mm-wave arrays are usually deployed in mobile phones to achieve the desired beam coverage.

  • Integration with the mobile phones: Because of the requirements of mobile phones for the full-display, curved-display, metal-bezel, glass back cover, metal back cover [7], the mm-wave array in mobile phones should fit the industry design (ID) of mobile phones. In practical applications, the geometry, layout, thickness, and deployment of the mm-wave array are determined by the ID of the mobile phone.

  • User influence: Because mobile phones are usually held by the human hands [8], the mm-wave array in mobile phones might also be covered by the human band. In practical applications, the effect of the human hands or human fingers on the antenna impedance, bandwidth, gain, and beam coverage should be studied.

Since the first mm-wave array was designed for mobile phones in 2014 [9] and the first commercial mm-wave array module was adopted in Samsung Galaxy S20 in 2020 [10], significant progress has been achieved in addressing the above difficulties in recent years. The desired beam coverage as shown in Figure 1 should be achieved with mm-wave arrays.

Figure 1.

Conceptual diagram of the mm-wave array with desired spherical coverage for mobile phones. (a) Front view. (b) Side view [11].

In this chapter, a comprehensive summary of the recent advances in the mm-wave array for mobile phone, such as broadside mm-wave array, endfire mm-wave array, co-design of the mm-wave array with metal-bezel and lower frequency band antenna, and user influence is conducted. Figure 2 illustrates the block diagram of the mm-wave array for mobile phones. For the broadside mm-wave array, we focus on the single-band, dual-band, and reconfigurable designs. For the endfire mm-wave array, single-polarization and dual-polarization designs are summarized. For the co-design of the mm-wave array, integrating metal-bezel with mobile phone design and shared-aperture with lower band antenna design are summarized.

Figure 2.

Block diagram of the mm-wave array for mobile phones.

This chapter is organized as follows. In Section 2, the common antenna element types of broadside radiation are introduced, and the design challenges of mm-wave broadside arrays are analyzed. Then, the broadside arrays are divided into three parts: single-band design, dual-band design, and reconfigurable design, to be summarized respectively. In Section 3, the challenges of endfire mm-wave array design are first analyzed. Then, the typical horizontal polarized, vertical polarized, and dual-polarized mm-wave endfire arrays are summarized. In Section 4, the co-design of the mm-wave array in the mobile phone with a lower frequency band antenna is introduced, including an integrated design with metal-bezel and shared-aperture design, respectively. In Section 5, the user influence on the mm-wave array in the mobile phone is illustrated. Finally, conclusions are drawn in Section 6.

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2. Broadside mm-wave array for mobile phone

Broadside array antenna is the array with the direction of maximum radiation, which is vertical to the array. As shown in Figure 3, the broadside array is achieved with the array element in the xy-plane and maximum radiation direction along the z-axis. As shown in Figure 4(a), when the array is placed horizontally with the mobile phone, the desired beam directions 5 and 6 in Figure 1 can be achieved. In Figure 4(b), when the array is placed vertically with the mobile phone, the desired beam directions 1, 2, 3, and 4 in Figure 1 can be achieved. Usually, due to the thickness limitation of the mobile phone, beam directions 1, 2, 3, and 4 are mainly achieved by endfire arrays, which will be explained in detail in Section 3. The broadside arrays are mainly used to achieve beam directions 5 and 6.

Figure 3.

Conceptual diagram of the antenna array with broadside radiation pattern.

Figure 4.

Conceptual diagram of the broadside mm-wave array and desired beam directions. (a) Array placed horizontally with the mobile phone. (b) Array placed vertically with the mobile phone.

For broadside array, the typical antenna elements are patch antenna [12], slot antenna [13], printed dipole antenna [14], dielectric resonant antenna [15], substrate integrated waveguide (SIW) cavity antenna [16], and so on. For the above antenna types, dual polarization can be achieved simply by quadrature feeding or by placing a pair of quadrature elements. The main challenge of broadside array design is how to achieve the array with the superior performance of small size, wide bandwidth, multiband, and wide beam coverage. In this section, the broadside arrays are classified into three parts: single-band, dual-band, and reconfigurable to summarize. At the same time, several solutions to the above challenges are also summarized.

2.1 Single-band broadside mm-wave array

The patch antenna is one of the most commonly used antenna elements in the broadside mm-wave wave array. The bandwidth of patch antennas is usually narrow, covering only a portion of the commercial mm-wave band. For example, as shown in Figure 5(a), an optically invisible common patch antenna on display only has a bandwidth of 9% (27.1–29.7 GHz) [17]. As shown in Figure 5(b)-(d), in order to improve the bandwidth of the patch antenna element, slotting on the patches [18], using parasitic patches [19], and using parasitic branches [20] are used to obtain more than 20% impedance bandwidth. Although the optimized patch antenna in [19] can cover the mm-wave band from 23 to 30.5 GHz (N257/258) band, it cannot cover the N259/N260 near 40GHz. In contrast, printed dipole antennas have a wider bandwidth. For example, the printed dipole antenna in [21] achieves a 50% (24–40 GHz) impedance bandwidth. In addition, as shown in Figure 5(f) and (g), dual polarization can be easily achieved by placing a pair of antenna elements orthogonally [22] or by quadrature feeding [23].

Figure 5.

Typical design schematics of single-band broadside mm-wave array. (a) Common patch antenna element. (b) Slotting on the patches. (c) Using parasitic patches. (d) Using parasitic branches. (e) Printed dipole antenna, dual-polarized realized by orthogonal placement. (f) Dual-polarized. Realized by quadrature feeding.

The patch antenna is one of the most commonly used antenna elements in the broadside mm-wave wave array. The bandwidth of patch antennas is usually narrow, covering only a portion of the commercial mm-wave band. For example, similar to the common patch antenna element shown in Figure 5(a), an optically invisible common patch antenna on display only has a bandwidth of 9% (27.1–29.7 GHz) [17]. As shown in Figure 5(b)-(d), in order to improve the bandwidth of the patch antenna element, slotting on the patches [18], using parasitic patches [19], and using parasitic branches [20] are used to obtain more than 20% impedance bandwidth. Although the optimized patch antenna in [19] can cover the mm-wave band from 23 to 30.5 GHz (N257/258) band, it cannot cover the N259/N260 near 40GHz. In contrast, printed dipole antennas have a wider bandwidth. For example, the printed dipole antenna in [21] achieves a 50% (24–40 GHz) impedance bandwidth. In addition, as shown in Figure 5(e) and (f), dual polarization can be easily achieved by placing a pair of antenna elements orthogonally [22] or by quadrature feeding [23].

2.2 Dual-band broadside mm-wave array

With several mm-wave bands around 28, 38, 45, and 60 GHz have been assigned for 5G development [24], mm-wave ultra-wideband antennas or multiband antennas are widely investigated to cover two or more frequency bands simultaneously to expand the available spectrum, improve antenna space utilization, save fabricated cost, and achieve high integration. And this part mainly focuses on dual-band broadside mm-wave array.

There are usually two ways to achieve dual-band antennas. One general way to achieve dual-band antennas is to combine two different structures operating at different frequency bands together [15, 25, 26]. For example, a hybrid antenna consisting of three resonators of strip, slot, and dielectric resonant antenna is proposed [15]. The strip and slot modes are used to cover the lower frequency band of 26.41–30.42 GHz, while the TE111 and TE131 modes of the DRA are employed to cover the upper-frequency band of 36.05–40.88 GHz. Two pairs of dipole antennas are proposed in [25]; the low-band radiation is generated by the pair of dipole arms along co-polarized direction, while the high-band radiation is realized by the dipole arms along cross-polarized direction.

Another way to achieve dual-band antennas is to adjust different modes of the same antenna structure to achieve dual resonance [14, 27, 28, 29]. For example, a compact dual-wideband magnetoelectric dipole is proposed in [14], the lower band of 24–29.3 GHz is achieved by 0.5λ mode, and the higher band of 35.5–43.5 GHz is achieved by 1λ mode. Also, the TM10 mode and TM20 mode of the gridded patches antenna are used to achieve dual-band coverage [27] .

2.3 Reconfigurable broadside mm-wave array

Considering the massive production of consumer electronics, the cost of each mobile antenna should be as low as possible. The reconfigurable design enables multiple operating modes of the mm-wave array through simple p-i-n diodes control and switching, which is one of the effective ways to save cost.

The reconfigurable design can be divided into two categories: direct control of the pattern reconfiguration, and control of the phased array excitation phase difference reconfiguration. As direct control of the pattern reconfiguration usually requires a large antenna design space and is not applicable for mobile phones [30], this part focuses on the reconfigurable design of the phase shifter. For the mm-wave arrays, the phase shifter is usually designed with the feeding network, and the excitation phase difference between elements is set by switching p-i-n diodes to achieve different directions. As shown in Figure 6, in [31], a low-cost reconfigurable 1-bit patch antenna is designed with moderate performance. What is more, a series-fed beam-steerable 2-bit reconfigurable design is proposed in [32].

Figure 6.

1-bit reconfigurable broadside mm-wave design [31].

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3. Endfire mm-wave array for mobile phone

Endfire array antenna is the array with the direction of maximum radiation, which lies along the line of the array. As shown in Figure 7, the endfire array is achieved with array element along the y-axis and maximum radiation direction in the x-axis. Compared with the broadside array, for the mobile phone with desired beam directions 1, 2, 3, and 4 in Figure 1, endfire array can be directly integrated into the PCB and save the thickness of the mobile phone. So, for mobile phones with a specific geometry of thin thickness, endfire array is preferable. However, due to the thin thickness of the mobile phone and thus the thin thickness of the endfire array, how to achieve the endfire array with the superior performance of thin thickness, small clearance, wide bandwidth, multiple polarization, and wide beam coverage is challenging. This section summarizes the typical design methods of horizontal-polarized endfire mm-wave array first. Then, the typical design methods of vertical-polarized endfire mm-wave array are summarized. Finally, the dual-polarized endfire mm-wave arrays are summarized.

Figure 7.

Conceptual diagram of the antenna array with endfire radiation pattern.

3.1 Horizontal-polarized endfire mm-wave array

To better summarize the horizontal polarization endfire mm-wave array for mobile phones, Figure 8 shows the conceptual diagram of some typical horizontal polarization endfire mm-wave arrays. As shown in Figure 9(b), the simplest method to achieve the endfire radiation is to deploy the mm-wave array vertical to the system ground. As the radiation element is horizontal polarization, horizontal polarization endfire mm-wave array is achieved. A similar idea can be found in [33] where the broadband magnetoelectric dipole antenna is applied as the element where 109.5% relative bandwidth is achieved. However, the critical drawback of this method is that the width of the mm-wave array should be enough to achieve proper performance. Thus, the thickness of the mobile phone is affected by the mm-wave array. A dipole antenna closing to the system ground, as shown in Figure 9(c), has endfire radiation with horizontal polarization. The system ground can redirect the radiation to achieve a high gain. The parallel double line [34] or the slot line with balun [35] can be applied to feed the dipole. To achieve the wide bandwidth, the distance between the dipole antenna ground should be large. In [36], the arm length of the dipole antenna is tuned to different values to widen the bandwidth. Similar to the Yagi antenna, several directors are applied in [37, 38, 39] to further enhance the array gain and bandwidth. The monopole antenna of half-wavelength mode can also be placed near the system ground to achieve the horizontal polarization endfire radiation, as shown in Figure 9(d). This structure has been studied in [40], working at 60 GHz with a bandwidth of 6 GHz. Also, the open-ended slot antenna can radiate the horizontal polarization endfire pattern, as shown in Figure 9(e). This structure has been studied in [41] working at 28 GHz with a bandwidth of 5 GHz. To achieve good performance with wide bandwidth, the space of the monopole antenna and slot antenna in Figure 8 should be large.

Figure 8.

Typical design schematics of dual-polarized endfire mm-wave array. (a) Vertical deployment of dual-polarized element. (b) Horizontal-polarized dipole with vertical-polarized dipole. (c) Horizontal-polarized dipole with vertical-polarized horn. (d) Horizontal-polarized slot with vertical-polarized horn. (e) Two SIW horns with a polarizer. (f) Dual-polarized slot antennas.

Figure 9.

Conceptual diagram of the typical horizontal polarization endfire mm-wave array. (a) Mm-wave array on the mobile phone. (b) Vertical deployment for endfire radiation. (c) Dipole element for endfire radiation. (d) Monopole element for endfire radiation. (e) Open slot element for endfire radiation.

3.2 Vertical-polarized endfire mm-wave array

To better summary the vertical polarization endfire mm-wave array for mobile phone, Figure 10 shows the conceptual diagram of some typical vertical polarization endfire mm-wave arrays. As shown in Figure 10(b), the simplest method to achieve the endfire radiation is to deploy the mm-wave array vertically to the system ground. As the radiation element is vertical polarization, vertical polarization endfire mm-wave array is achieved. A similar idea can be found in [42, 43] where the slot, dielectric, and cavity resonators are applied simultaneously to achieve a wideband width of 47.1% [42] and 94.1 [43]. However, the critical drawback of this method is also that the width of the mm-wave array should be enough to achieve proper performance. Thus, the thickness of the mobile phone is affected by the mm-wave array. As shown in Figure 10(c), the cavity slot element can be applied to radiate the vertical polarization pattern. Although the cavity slot element can achieve a low profile, the key technical difficulty is to achieve wide bandwidth. In [44], a substrate-integrated waveguide (SIW) endfire antenna array with zero clearance is designed. Three arbitrary pad-loading metallic vias are investigated to match the impedance within a relative bandwidth of 60%. Also, the slot on the SIW [45], taper slot [46], and the metasurface structure [47] can be applied to achieve a wide bandwidth of the SIW slot antenna. For the dipole element in Figure 10(d) and the monopole element in Figure 10(e), vertical polarization with endfire radiation can be achieved. In [30], the monopole element with the parasitic element is applied to achieve the endfire radiation with steering beams. In [48], the compact vertically polarized endfire monopole-based Yagi antenna-in-package is proposed with a relative bandwidth of 16%. For the dipole or monopole element, the height should be large for a large bandwidth. By combing the cavity slot element and dipole/monopole element, the endfire magnetoelectric antenna with stable performance within a wide bandwidth can be achieved. For example, the SIW cavity slot antenna and dipole antenna in [49, 50] and the SIW cavity slot antenna and monopole antenna in [51] are combined to achieve the wideband endfire magnetoelectric antenna. Also, to achieve good performance with wide bandwidth, the profile of the dipole element or the monopole element in Figure 11 should be large.

Figure 10.

Conceptual diagram of the typical vertical-polarized endfire mm-wave array. (a) mm-wave array on the mobile phone. (b) Vertical deployment for endfire radiation. (c) Cavity slot element for endfire radiation. (d) Dipole element for endfire radiation. (e) Monopole element for endfire radiation.

Figure 11.

Typical design schematics of integrating the mm-wave array in the mobile phone. (a) Using a window to reduce the blockage from metal-bezel. (b) Using the metal-bezel to design the mm-wave array antenna.

3.3 Dual-polarized endfire mm-wave array

With the horizontal-polarized endfire mm-wave array and vertical-polarized endfire mm-wave array, the dual-polarized endfire mm-wave array can be easily achieved. For example, if the mm-wave array vertical to the system ground in Figure 9(b) and Figure 10(b) can radiate dual-polarized patterns, dual-polarized endfire mm-wave array can be easily achieved. This idea can be found in [52], where a dual-polarized slot antenna is vertically deployed on a mobile phone, as shown in Figure 8(a). Thus, a dual-polarized endfire mm-wave array with a − 10 dB impedance bandwidth from 23.2 to 29.7 GHz is achieved in [52]. This method also has the drawback of being high profile. Also, if the horizontal dipole element in Figure 8(c) and vertical dipole element in Figure 10(d) can be designed in the near space, dual-polarized mm-wave dipole array can also be achieved. In [40, 53], the dual-polarized endfire mm-wave dipole array is achieved by combing the vertical dipole and horizontal dipole as shown in Figure 8(b). The dual-polarized endfire mm-wave array antenna should have a large profile to achieve the good performance. To reduce the profile, the horizontal-polarized dipole element in Figure 9(c) and the vertical-polarized horn element in Figure 10(c) can be combined to achieve the low-profile dual-polarized endfire mm-wave array. In [54], the low-profile dual-polarized endfire mm-wave array is realized by co-designing a horizontal-polarized yagi-uda antenna and a vertical-polarized SIW horn antenna, as shown in Figure 8(c). Also, the horizontal-polarized dipole antenna with balun feeding can replace the yagi-uda antenna to achieve a wide bandwidth [55]. In addition, the clearance of the combination of horizontal-polarized dipole element and vertically polarized horn element can be further reduced by using the transition plates [56, 57] or the overlapped apertures [58]. The dual-polarized endfire mm-wave array antenna with horizontal-polarized dipole element and vertically polarized horn element usually has a large clearance to achieve a good performance. To reduce the clearance, the horizontal-polarized open slot element in Figure 9(e) and vertical-polarized horn element in Figure 10(c) can be applied. In [59], the dual-polarized endfire mm-wave array with a small clearance is realized by co-designing a horizontal-polarized open slot antenna and a vertical-polarized horn element, as shown in Figure 8(d). The horizontal-polarized open slot antenna consists of two metal blocks with a slot, and the vertical-polarized horn element is a SIW horn antenna. In [60, 61], the horizontal-polarized open slot antenna is realized by using two SIW structures. In [41, 62], the horizontal-polarized open slot antenna and the vertical-polarized horn are integrated into a single SIW structure. Besides, two SIW horns with a polarizer can be applied to achieve the dual linearly polarized endfire antenna [63, 64] or 45° dual linearly polarized endfire antenna [65], as shown in Figure 8(e). Also, in [66], the orthogonal slot can be excited simultaneously to achieve the dual-polarized mm-wave endfire chain-slot antenna, as shown in Figure 8(f).

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4. Co-design of the mm-wave array in the mobile phone with lower frequency band antenna

The broadside mm-wave arrays in Section 2 and the endfire mm-wave arrays in Section 3 have achieved superior performance which can cover the desired beam directions 1–6 in Figure 1. The commercial mm-wave array module has been adopted in Samsung Galaxy S20 in 2020 [10]. However, because the full-display, curved-display, metal-bezel, glass back cover, metal back cover requirement of the mobile phone, the mm-wave array in mobile phone should fit the ID of mobile phones. Also, because most of the spaces are reserved for the displays, cameras, battery, PCB, motor, speaker, and so on for better user experience, the antenna in mobile phones should only occupy a very small space. So, the co-design of the mm-wave array in the mobile phone with a lower frequency band antenna is also widely studied. In this section, we first analyze the design of integrating the mm-wave array with metal-bezel in mobile phones. Then, the shared-aperture design of the mm-wave array with the lower frequency band antenna is summarized.

4.1 Integrating the mm-wave array with metal-bezel in the mobile phone

As the mm-wave array is deployed in the mobile phone, the modules of the mobile phone might have a significant effect on the performance of the mm-wave array. In [67], the effect of different kinds of mobile phone housing on the performance of four canonical types of mm-wave antennas is studied. The effective beam-scanning efficiency is proposed to evaluate the coverage performance. In [68], the effect of the metal-bezel of the mobile phone on the radiation pattern of the mm-wave array is studied. The blockage of the metal-bezel to the horizontal-polarized antenna is more severe than for the vertical-polarized antenna. And the coupling metal strips [68, 69] can be applied to reduce the blockage from metal-bezel. Also, the slots on the metal-bezel [70, 71] can be also used to reduce the blockage from the metal-bezel. In [72], a rectangle window in the metal-bezel was used to install the mm-wave array so that the mm-wave array could radiate the power through the rectangle window directly as shown in Figure 11(a). This practical solution has been adopted in some commercial 5G mobile terminals such as Apple iPhone 12 with a wee mm-wave window [73]. Apart from reducing the effect from the metal-bezel, in [74], the metal-bezel can be applied to design the mm-wave leaky-wave array as shown in Figure 11(b). In addition, the mm-wave array antenna could be directly implemented via the slot on the metallic bezel of the mobile terminals [75, 76]. Thus, the blockage effect from the metal-bezel is solved.

4.2 Shared-aperture design of the mm-wave array with the lower frequency band antenna

To integrate the mm-wave array with the lower frequency band antenna, a low pass (or high pass) filter can be applied [77, 78]. As shown in Figure 12(a), a 3.5 GHz lower band antenna is directly connected to a 28 GHz mm-wave antenna with a low-pass and high-stop (3.5 GHz pass and 28 GHz stop) filter [77]. Thus, the mm-wave antenna and the lower frequency band can be designed in a near space with a single feeding port. To reduce the occupied space of the mm-wave array and lower frequency band antenna, the mm-wave array can be integrated into the lower frequency band antenna [11, 79, 80, 81, 82, 83]. As shown in Figure 12(b), the mm-wave slot array antenna is integrated into the clearance of the lower frequency band inverted-F antenna [79]. In addition, a notch on the lower frequency band can be applied to integrate the mm-wave array antenna [81, 82]. Also, the mm-wave array antenna can be deployed on the lower frequency band antenna [83]. To further reduce the occupied space of the mm-wave array and the lower frequency band antenna, the metal pattern of the lower frequency band antenna can be applied to design SIW structure for the mm-wave array antenna [84, 85, 86, 87]. As shown in Figure 12(c) [84], the lower frequency band antenna is a simple patch antenna. To integrate the mm-wave array on the patch antenna, the patch of the lower frequency band antenna is designed as a SIW slot array. Thus, the mm-wave array antenna and the lower frequency band antenna is designed in the same aperture. In addition, the mm-wave SIW slot array can be integrated into the monopole antenna [85] or inverted-F antenna [86, 87] of the lower frequency band. Besides using the SIW structure, the higher order mode of the lower frequency band antenna can also be directly applied to design the mm-wave array [88, 89, 90, 91]. Also in [88], the half-wavelength slot mode of the lower frequency band antenna has the higher order mode of the slot. And multiple feedings are applied to excite the higher-order mode of the slot, which is the connected slot array. Thus, a single slot is designed to work at the mm-wave frequency band and lower frequency band simultaneously. In [89], a single microstrip grid array is designed to cover the mm-wave frequency band and lower frequency band simultaneously. In [90], a surface is the integration of a metasurface at the lower frequency band and a partially reflective surface (PRS) at the higher frequency band. In [91], a single slot is designed to function as a decoupling slot at the lower frequency band and the taper slot antenna at the mm-wave frequency band.

Figure 12.

Typical design schematics of co-design of mm-wave array with lower frequency band antenna. (a) Using the filter to integrate the mm-wave and lower frequency band antennas. (b) Using the clearance of the lower frequency band antenna to deploy the mm-wave array. (c) Using the SIW structure to integrate the mm-wave and lower frequency band antennas.

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5. User influence

As a special situation for the mobile antenna, the effect of the human tissue on the antenna performance should be considered when designing the mobile antenna. Also, the electromagnetic field (EMF) exposure to the mobile antenna for the human tissue should also be studied for safety considerations. This is because the mobile antenna is usually close to the human head, body, or hands, as is used in practical situations. In this section, the mutual effect of the mm-wave array and the human tissue in the open literature is summarized.

The human body is electronically large at the mm-wave frequency band. To evaluate the mutual effect of the human tissue and the mm-wave array effectively and accurately, [92] developed the numerical and physical phantoms of a human body for evaluation of mobile antennas at 28 GHz. Thus, the ability to design antennas under practical operational conditions involving body effects is achieved. As for the EMF exposure to the mm-wave array, [93] compares the power density of a single antenna element, a four-element linear array, and an eight-element linear array at the near field region and the far field region. Zhao et al. [93] finds that, at the near field region, the power density is extremely high and it can be reduced as the number of array elements increases. At the far field region, the power density increases as the array elements increase.

As for the effect of the human on the mm-wave array, [76] shows that, for an eight-element mm-wave array located alongside the side edge of the mobile phone, the human hand results in a gain reduction of about 7.5 dB. However, for a four-element mm-wave array, if the human hand covers the mm-wave array, the loss from hand blockage on the antenna gains can be up to 20 to 25 dB [94]. To reduce the effect from the human hand, the mm-wave array should be deployed away from the human hand. Ojaroudiparchin et al. [95] illustrates that, if the mm-wave array is not close to the human hand, the gain loss from the human hand can be reduced to about 1.5 dB. Therefore, to achieve a good performance, multiple mm-wave arrays should be deployed in the mobile phone at different positions. In [96], it is concluded that, in the talk mode, the mm-wave array should be placed at the top of the mobile phone (close to the index finger). Also, it the talk mode, the user hand shadowing can be significantly reduced by placing the mm-wave array at the bottom of the chassis (close to the palm). In the data mode, the mm-wave array achieves less gain loss when deployed at the top of the mobile phone.

For the human body shadowing, [97] illustrates that the shadowing by the user’s body might decrease the gain about 20–30 dB if the mm-wave array is close to the user. Zhao et al. [98] also observes a strong shadowing effect from the human body in the mm-wave band, which is around 20–25 dB at 15 GHz. Zhao et al. [99] finds that the equivalent isotropic radiated power (EIRP) values at cumulative distribution function (CDF) of 50% drop about 5–10 dB compared to the case that without the user body. To reduce the shadowing from the human body, the effect of the displacement of the mm-wave array on the shadowing from the human body is studied [100]. Syrytsin et al. [100] finds that the corner positions of the mobile phone achieve the best performance in terms of spatial coverage. Syrytsin et al. [101] compares the coverage efficiency and user shadowing from the mm-wave phased array and mm-wave switch diversity array and finds that the mm-wave phased array has superior performance. Also, in [102], it is found that, for the difference between the user and free-space cases, the circularly polarized array coverage efficiency is relatively less sensitive to user effects.

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6. Conclusions

In this chapter, we summary recently mm-wave arrays for mobile phones. For broadside mm-wave array, the state-of-the-art single-band, dual-band, and reconfigurable designs are proposed in small size, low cost, and have moderate performance. For endfire array, the typical designs of horizontal-polarized, vertical-polarized, and dual-polarized arrays are analyzed, providing good reference solutions for endfire array design. For co-design of mm-wave array in the mobile phone, several ingenious solutions and practical solutions adopted in some commercial terminals are introduced that will contribute to the integrated design of mm-wave antennas with lower band antenna. In addition, the human body model evaluation, the effect of the human body on the mm-wave array, and the human body shadowing are also illustrated. Various designs are being used to solve the mm-wave array challenge in mobile phones, with promising applications.

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Acknowledgments

This work was supported in part by the National Natural Science Foundation of China under Grant 62101133, in part by the Natural Science Foundation of Shanghai under Grant 21ZR1406800, and in part by Shanghai Rising Star Program under Grant 22QC1400100.

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Written By

Yan Wang and Xiaoxue Fan

Submitted: 06 May 2023 Reviewed: 01 June 2023 Published: 24 June 2023

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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