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Due to limited antenna space, high communication requirements, and strict regulatory constraints, the design of antennas for modern mobile phones has become an exceedingly challenging task. In recent years, numerous studies have been conducted in this area, leading to significant advancements. This review paper comprehensively summarizes recent progress made in antenna design for modern mobile phones. Firstly, the challenges faced in antenna design for modern mobile phones are described, including bandwidth enhancement, integration and decoupling techniques, mm-wave array antennas, satellite communication antennas, as well as interactions between mobile antennas and the human body. Secondly, the basic antenna types (such as inverted-F, slot, loop, and planar inverted-F antennas) commonly used in modern metal-bezel mobile phones along with their key characteristics are briefly summarized. Thirdly, the commonly exployed methods used in practical applications for designing wideband antennas within compact sizes and achieving decoupling among multiple antennas with wide bandwidths are collected. Fourthly, recent advances in the design of compact, wideband, and wide-angle scanning mm-wave arrays for modern mobile phones are summarized. Fifthly, recent progress made in satellite communication antenna designs for modern mobile phones, including broadside and end-fire radiation patterns, is presented. Sixthly, recent studies on the interaction between mobile antennas and the human body are briefly concluded. Finally, the future challenge of antenna design for mobile phones is briefly discussed. It is our hope that this comprehensive review will provide readers with a systematic understanding of antenna design principles applicable to modern mobile phones.

Health and safety concerns have grown in recent years due to the increasing frequency bands and the demand for wireless communication apparatus. Electromagnetic (EM) radiation breakthrough from Radio frequency (RF) into the human head is an issue that needs to be addressed. Radiation from RF sources can cause serious biological hazards inside the human body. This study measures the average Specific Absorption Rate in a 7-year-old child's head tissues using the ANSYS HFSS software and varying the distance from the source to the antenna in order to address these issues. SAR levels of phones sold should be below certain standard limits. We have used an internal antenna of a mobile phone It's a planar inverted F-antenna (PIFA) with a connected feeding structure.

In this paper, a reconfigurable metal rim antenna with a small clearance and compact structure for 4G/5G smartphones is proposed. It consists of the system ground plane and a metal rim with two slits, in which a U-shaped slot of 1 mm (the smallest) clearance is realized between the system ground and metal rim. The theory of characteristic modes is applied to analyze the eigenmodes of the antenna so as to aid the optimum design. The characteristic modes (CMs) in the band of interest are studied, and an inductive coupling exciter is identified as the best since three CMs can therefore be generated in the lower frequency band (0.69-0.96 GHz), and an SP4T switch can be utilized to increase the bandwidth of the whole lower band. A prototype antenna of the optimized design was fabricated. A good agreement was obtained between the measured and simulated results. The 6-dB frequency bands are the lower band (0.69-0.96 GHz), the middle band (1.7- 2.7 GHz), and the higher 5G band (3.4- 3.6 GHz), respectively, and the total efficiencies are over 50% in all these frequency bands. They indicate that the antenna is a very good candidate for smartphone applications.

A novel antenna design with a low specific absorption rate (SAR) is introduced. The antenna has a very low profile and it is designed to be placed on the back cover of a mobile device at around 2 GHz. The solution is based on nested loops which distribute the field over a large volume so that the maximum SAR value remains relatively low in the user’s tissue. The proposed design also provides relatively good efficiency, considering the extremely low profile, and the close proximity of lossy human tissue and the phone’s main body. The manufactured prototype exhibits almost 50% lower maximum SAR than a patch antenna used as a reference.

In recent years, the screen-to-body ratio of mobile handsets has been increasing. Today, the screen nearly fills up the entire front side. Conventionally, the screen is mainly seen as a metallic object that adversely affects antenna performance. In this paper, the large screen is used for the first time to facilitate an additional uncorrelated MIMO port in a tri-port design, for several LTE bands below 1 GHz. To this end, the screen and the terminal chassis are modeled as two metal plates and their characteristic modes are analyzed. Four modes are then tuned to resonance and selectively excited to yield three uncorrelated MIMO ports. Simulation and measurement results are in good agreement. The measured bandwidths are 23%, 17% and 21%. Within the operating band, the measured isolation is above 13 dB, envelope correlation coefficient below 0.16 and average total efficiency above 72%.

In this paper, 4 × 4/8 × 8/10 × 10 multiple input multiple output (MIMO) antenna systems composed of co-located self-neutralized antenna pairs are proposed to operate at 4.8-5.0 GHz (part of N77 band) for the fifth-generation (5G) communication applications. The proposed antenna pairs consist of a loop antenna and a monopole antenna, co-locating together with a compact size of 6.7 × 15.5 ×3.08 mm3. Meanwhile, the co-located design can miniaturize 50% of the antenna size, which is quite significant for practical mobile applications with limited space environment. In addition, the adoption of the self-neutralization technique between the co-located loop antenna and the monopole antenna contributes to a satisfactory isolation with better than 25/20/16.5 dB for the 4 × 4/8 × 8/10 × 10 MIMO systems respectively. Analysis of the isolation improvement is also discussed in this study. Moreover, the antenna pairs are able to generate complementary radiation patterns, enabling the envelope correlation coefficients (ECC) between the antennas to be less than 0.1. Also, efficiencies of the MIMO antenna system achieve up to 60% as there is no external decoupling structure deteriorating the radiation performance of the proposed antenna pairs. Finally, a 4 × 4 MIMO antenna system prototype is fabricated and measured to verify its prospect for 5G MIMO applications.

The study results of parameters of main high-frequency range mobile antennas are presented: whip antenna, sloping wire antenna, inverted V symmetrical vibrator (dipole), T-shaped antenna, sloping V antenna, NVIS, traveling wave antenna, λ-shaped antenna. The analysis of the input active and reactive resistances of the antennas, as well as standing wave ratio is performed depending on the frequency. The corresponding graphical dependencies are presented.

This research presents a far-field (FF) antenna with near-field communication (NFC) capability for 3G/4G/LTE mobile devices. The integrated farand near-field communication (FNFC) antenna was fabricated using conductive silver ink on polyethylene terephthalate (PET) flexible substrate. The FF segment of the antenna is operable in the frequency range of 1.8-2.1 GHz, and the NFC antenna is of dual loop and operable at 13.56 MHz. In the antenna realization, simulations were performed and, to validate, an antenna prototype was fabricated. The experimental results revealed that the FF antenna achieved an impedance bandwidth of 37% (1.52-2.21 GHz), given |S11| of less than -6 dB, with the minimum and maximum efficiency of 92.1% and 98%. The experimental gains are 1.76-2.08 dBi across the target operating frequency band, with near-omnidirectional radiation pattern. The simulation and experimental results are in good agreement. Moreover, the FNFC antenna achieves strong magnetic field distributions in Hx, Hy, and Hz orientations and holds promising potential for 3G/4G/LTE applications.

In this paper, we introduce a ground radiation antenna that uses controlled endless metal rim modes. In the proposed technique, the metal rim mode is tuned and excited as a one‐wavelength radiator by a small ground radiation antenna. The proposed antenna occupies a clearance of 1 mm × 4 mm in a 30 mm × 20 mm ground plane. A metal rim with dimensions of 34 mm × 24 mm surrounds the ground plane, and the metal rim is separated from the ground plane by a gap of 2 mm. In addition, a lumped capacitor is inserted between the metal rim and the ground plane to control the characteristic mode of the metal rim such that the resonance of the metal rim is tuned to be equal to the operating frequency. By performing simulations and measurements, we compare the performance of the proposed antenna with that of a reference antenna that does not have an inserted capacitor between the metal rim and the ground plane. The results show that a significant improvement of the radiation performance is obtained by employing the proposed technique.

A compact beam-steerable antenna array is proposed for 28 GHz mobile terminals. The proposed array consists of one active element and two passive parasitic elements. Two switches are utilized in the design instead of phase shifters. Each parasitic element can be terminated with short-circuited transmission lines of different lengths via one switch. By controlling the two switches, different reactive impedance is loaded on two parasitic elements. The radiation pattern of the active element can be scattered into different directions by two parasitic elements. The switching loss is studied, where two switches with 2.8 dB loss cause less than 1.82 dB loss for the whole array. The small array locations on the chassis are also investigated. The designed array is smaller than 0.81 wavelength, and covers the band of 28–29 GHz with the scan angle ≥±90°. By placing two arrays on each long chassis edge, 360° beam steering can be realized. Surface currents on the chassis are efficiently excited to achieve high gain with the small array. Measurements are carried out and align well with simulations. In practical applications, several small arrays can be implemented on the metal back cover and around a cellphone to combat users’ mobility. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a ground radiation antenna that uses controlled endless metal rim modes. In the proposed technique, the metal rim mode is tuned and excited as a one‐wavelength radiator by a small ground radiation antenna. The proposed antenna occupies a clearance of 1 mm × 4 mm in a 30 mm × 20 mm ground plane. A metal rim with dimensions of 34 mm × 24 mm surrounds the ground plane, and the metal rim is separated from the ground plane by a gap of 2 mm. In addition, a lumped capacitor is inserted between the metal rim and the ground plane to control the characteristic mode of the metal rim such that the resonance of the metal rim is tuned to be equal to the operating frequency. By performing simulations and measurements, we compare the performance of the proposed antenna with that of a reference antenna that does not have an inserted capacitor between the metal rim and the ground plane. The results show that a significant improvement of the radiation performance is obtained by employing the proposed technique. [ABSTRACT FROM AUTHOR]

This communication presents a planar ultra-wideband multi-input multi-output antenna with pattern diversity and isolation improvement based on the theory of characteristic modes. The proposed antenna (for new-generation wireless mobile terminals) consists of two ultra-wideband antenna elements—a compact quarter loop and a circular planar monopole located on the opposite edges of a rectangular ground plane. These two antenna elements are able to excite different modes in the ground plane and thus realize the desired diverse radiation patterns and high isolation without any additional decoupling structures. The experimental results show that both antenna elements are ultra-wideband with impedance bandwidths (return losses more than 6 dB for the quarter-loop antenna and more than 10 dB for the circular planar monopole antenna) of 130% (2–9.5 GHz). The isolation is over 20 dB with a peak value of 50 dB. The realized gains are above 1.5 dBi. The total efficiencies are above 70%. The envelope correlation coefficient is less than 0.03 assuming that the antenna operates in an isotropic channel. [ABSTRACT FROM AUTHOR]

This paper presents a multiple input multiple output (MIMO) antenna for multiband operation based on meander lines with L shaped metallic strip. Meander lines is basically a monopole antenna loaded with multiple sections of short circuited transmission line that acts as inductor and alter the impedance characteristics of antenna. Antenna size miniaturization of 69 % has been achieved by placing double U slots on the ground plane and a line slot DGS (Defective Ground Structure) is used to reduce the mutual coupling between the antenna elements. The values of envelope correlation coefficient (ECC) and Specific Absorption Rate (SAR) lie well below the specified limit. [ABSTRACT FROM AUTHOR]

Measuring multiple-input multiple-output (MIMO) specific absorption rate (SAR) is an important part of mobile handset evaluation, following the introduction of uplink MIMO transmission schemes in long-term evolution advanced systems. However, the measurement of MIMO-SAR is complex and time consuming. In this communication, six unique dual-antenna mobile handsets, including both typical and novel designs, are analyzed to determine the dependence of MIMO-SAR on antenna configuration and correlation. It is found that, for certain antenna configurations, the location of the maximum MIMO-SAR and the corresponding relative phase between the ports can be predicted. This can be applied to drastically reduce measurement time. In addition, dual antennas with low envelope correlation coefficients in the radiation patterns also offer near-orthogonal electric near fields. This leads to smaller MIMO-SAR than stand-alone SAR (S-SAR) over all relative phases, making MIMO-SAR measurement unnecessary. The results also provide guidelines for designing multi-antenna handsets with low SARs. For verification, the S-SAR and MIMO-SAR at a relative phase of 0° were measured for several prototypes. The measured SAR distributions showed good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

A wideband planar double-segmented loop antenna that can excite different modes with perpendicular polarized omnidirectional radiation patterns is designed for mobile platforms. The proposed antenna combines these resonant modes with adjacent resonant frequencies for wideband application. One of the modes is induced by the loop element itself and generates horizontally polarized radiation pattern. Meanwhile, the other mode generates vertically polarized radiation pattern when the ground plane is excited by the loop element and operates as a radiator. The measured results confirm that the antenna is capable of achieving wide bandwidth (10-dB return loss) from 2.1 to 2.9 GHz (the corresponding fractional bandwidth is 32%). The average total realized gain of the antenna is 2.75 dBi over the entire operating bandwidth. [ABSTRACT FROM PUBLISHER]

An octa-band WWAN/LTE monopole antenna with a size of 80\,\textmm \times 8\,\textmm \times 5.8\,\textmm for 5.7-inch mobile phones is proposed and studied. The proposed antenna consists of a folded metal plate with a lumped-element high-pass matching circuit. The working mechanism is analyzed based on the S-parameters and the surface current distributions. The 0.25-wavelength, 0.5-wavelength, and 1-wavelength modes of the monopole antenna are excited and used. The attractive merit of the proposed antenna is that the height of the nonground portion is only 8 mm. A prototype is fabricated and measured. Its measured -6\;\textdB impedance bandwidths are 290 MHz (0.69–0.98 GHz) and 1.11 GHz (1.63–2.74 GHz) which cover the LTE700, GSM850, GSM900, GSM1800, GSM1900, UMTS, LTE2300, and LTE2500 bands. Within the two frequency bands, good radiation performances are obtained. [ABSTRACT FROM AUTHOR]

In this communication, a compact frequency reconfigurable antenna for LTE/WWAN mobile handset applications is proposed. The proposed antenna mainly consists of radiating elements and two PIN diodes. In addition, the antenna has a simple structure with a compact size of 36.5 \times 10\;\textmm^2. This antenna operates in six modes, and each mode is given a different resonant pathway by adjusting the bias states of two PIN diodes. When PIN diodes #1 and #2 are in the on and off states, respectively, the proposed antenna can cover the LTE700 (698–787 MHz) band by operating in mode 1. Moreover, the wide bandwidth in a higher band formed by combining modes 2 and 3 can cover the LTE2300 (2305–2400 MHz) and LTE2500 (2500–2690 MHz) bands. When PIN diodes #1 and #2 are in the off and on states, respectively, a resonant frequency in the lower band is formed by integrating modes 4 and 5. This can cover the GSM850 (824–894 MHz) and GSM900 (880–960 MHz) bands. When the two PIN diodes are in the on state, the proposed antenna can cover the GSM1800 (1710–1880 MHz), GSM1900 (1850–1990 MHz), and UMTS (1920–2170 MHz) bands in operating mode 6. [ABSTRACT FROM PUBLISHER]

A worst-case estimate of an envelope correlation coefficient (ECC) is obtained for small multiple-input multiple-output (MIMO) mobile antennas operating below 1 GHz. The worst-case estimate is numerically derived in this paper using spherical and exponential wave functions. The derived result confirms that the worst-case ECC can be easily obtained from the rotation angle between the radiation patterns of two MIMO elements, which are attained directly from the amplitude of 2D electric field patterns without any additional phase and polarization information. As a practical example, MIMO mobile antennas with different antenna element arrangements are compared to verify the validity of the proposed worst-case estimate. Moreover, based on these analyses, we also suggest an effective approach to reduce the ECC of a small MIMO mobile antenna operating below 1 GHz by properly locating the antenna elements to make the radiation patterns perpendicular to each other. [ABSTRACT FROM AUTHOR]

Multi-antenna design in compact mobile handsets at frequency bands below 1 GHz is very challenging, since severe mutual coupling is commonly induced by simultaneous excitation of the chassis' fundamental dipole mode by more than one antenna element. To address this problem, a novel multi-antenna design approach is proposed herein to obtain efficient and uncorrelated antennas. By manipulating the chassis structure, more than one characteristic mode is enabled to resonate at frequencies below 1 GHz. With proper excitations for different characteristic modes, which are orthogonal to each other, well matched multi-antennas with low coupling and correlation are achieved. A chassis loaded with two T-shaped metal strips above its longer edges is taken as an example modification to illustrate the effectiveness of the proposed design approach at 900 MHz. This modification creates a new characteristic mode which resonates near 900 MHz. Afterward, two antenna feeds were designed to efficiently excite the chassis' fundamental dipole mode and the T-strip mode with very low correlation. The T-strip antenna covers LTE Band 8 (880–960 MHz), and the dipole mode antenna covers both LTE Band 5 (824–894 MHz) and LTE Band 8. The proposed dual-antenna design was found to outperform a reference design significantly, both with and without user interactions (i.e., one-hand and two-hand data grips). Practical aspects of mobile handset antennas are also investigated. The prototype was also fabricated and measured, and the measured results show reasonable agreements with the simulated results. [ABSTRACT FROM PUBLISHER]

A compact multiband antenna for handset and tablet applications is presented, covering most LTE Bands (698–960 and 1710–2690 MHz). This study utilizes a new ceramic material suitable for the internal antenna design which gives a shorter guided wavelength and wider bandwidth for each resonant mode to achieve antenna size reduction, sufficient space utilization, and very low correlation coefficient as MIMO antennas. The occupied volume of the antenna radiator is only 35\,\times\,11\,\times\,5 mm^3, equal to 0.082\lambdam\times 0.026\lambdam\times 0.012\lambdam (\lambdam is the wavelength at 700 MHz) whose radiation aperture is only \lambdam/11 so the antenna is a good candidate as an internal antenna. [ABSTRACT FROM PUBLISHER]

A fold monopole/dipole/loop antenna offers unique advantages over a conventional Planar Inverted-F Antenna (PIFA) and monopole antenna for a mobile cellular device. Perhaps the most significant benefit is the fact that up to three resonant modes could be generated in a single continuous loop structure. In this paper, a novel hexa-band internal folded monopole/dipole/loop antenna has been proposed. The proposed antenna has four resonances in which three of them are 0.5\lambda, 1\lambda and 1.5\lambda modes. The distinctive feature of the antenna is an extra 2\lambda folded dipole mode, which has not been reported so far, is excited and utilized. All these four modes can be employed to cover the Low LTE700/GSM850/900 Band (LB: 698–960 MHz) and the High GSM1850/1900/UMTS2100 Band (HB: 1710–2170 MHz). The proposed loop antenna has been simulated, prototyped and tested. It is shown that the numerically simulated results are in close agreement with the experimental prototype results and proved that the antenna operates as proposed. [ABSTRACT FROM PUBLISHER]

In this paper, the triband mobile antenna system for broadband multimedia service in the Ka/K band and direct-broadcast-satellite service in the Ku band is proposed. The proposed antenna has a modified hybrid antenna (HA) structure with a Cassegrain reflector system with feeder for the K/Ka band, and a microstrip array for Ku-band service is composed of four linear subarrays and stacked on the subreflector of the HA. The main purpose of the proposed HA is to realize a high-gain mobile satellite antenna system with rapid 2-D beam scanning ability at low cost. Therefore, we proposed a novel beam-steering method through a subreflector that is rotational and flat. The feeder is composed of 20 dual-band and dual polarized horn elements in a hexagonal structure with an oval-shaped rim to maximize the efficiency of the HA. For system size reduction, small-sized active channel blocks composed of four channels were developed for signal amplification and main beam control, and the active channels for the transmitter and the receiver are connected with the horn elements of the feeder, respectively. In addition, the triplexers were very helpful for structurally simplifying the HA. A fabricated HA was successfully tested in a Korean satellite communications environment with motion simulator that can replace motor vehicles, and all radiation patterns in a beam-steering angle meet the international regulation of the International Telecommunication Union Radiocommunication Sector S.465-5. [ABSTRACT FROM PUBLISHER]

Using a high-efficiency tunable antenna to cover a large bandwidth with low return loss is an interesting topic, especially in the case when the physical sizes of the mobile phone and antenna are too small to allow for the coverage of the full band. The limitations of tunable antennas are their losses and the nonlinearity introduced by the tuning devices. A design procedure for the tunable mobile antennas is presented, which accounts for the nonlinearity suppression. Following this procedure, a low-loss tunable Digital Video Broadcasting-Handheld (DVB-H) antenna has been designed and fabricated to cover the DVB-H band (470-702 MHz) with a return loss below 7 dB. This antenna exhibits a small volume of only 6 cm³. Despite the high-power signal from the Extended Global System for Mobile communication transmitter on the same printed circuit board and the nonlinear tuning devices, this antenna is highly linear. [ABSTRACT FROM AUTHOR]

A novel type of short monopole antenna is proposed. Its structure consists of a periodically slotted coaxial line radiating in linear polarization (LP). The structure can be easily modified by the addition of a thin layer of dipoles in order to generate circular polarization (CP). The number of slots along the structure, their periodicity and the tuning of the terminating load allow control of the antenna main beam' angle and width. One advantage of the proposed design over conventional monopoles is that the antenna does not require a ground plane. Both left-hand and right-hand CP are possible with the same design, simply by inverting the symmetry of the printed dipoles. Design details for the annular slotted coaxial line and for the LP and CP mast antennas are given. Prototypes in both LP and CP were fabricated and their characteristics were measured. Simulations and measurement are in good agreement. The proposed CP mast antenna is compliant with the requirements of the XM digital satellite radio system, with a frequency bandwidth of more than 1.7% in which VSWR < 2, and an AR < 4 dB in the elevation range of ±30° < θ < ± ± 70°. [ABSTRACT FROM AUTHOR]

This paper introduces a folded planar monopole antenna, which has a very low profile of about one twentieth of the wavelength of the lowest operating frequency. The effect is achieved by using a bends rectangular radiating patch and an inverted L-shape ground plane. The proposed antenna can be used in multiband operation, with omnidirectional radiation patterns for all operating bands. Its impedance bandwidth, determined by 10 dB return loss, covers almost all present wireless communication systems: Global System for Mobile Communication (GSM), Digital Communication System (DCS), Personal Communication System (PCS), Universal Mobile Communication System (UMTS), and Industrial Science Medical (ISM) band. This paper presents the design and experimental results of the proposed antenna. Moreover, the study also investigates the tuning effects of the geometry parameters on impedance matching. [ABSTRACT FROM AUTHOR]

A multilayer thin film antenna for mobile devices is proposed. The proposed antenna consists of a (indium–zinc–tin oxide) IZTO/Ag/IZTO multilayer film, which is fabricated on a polyimide substrate (εr = 3.5) and a copper layer. The centre frequency of the antenna is 1260 MHz. The geometry of the antenna is made up of a coupled loop and two branches. The proposed antenna was fabricated using the DC pulse sputter instrument. The measured and simulated results of the antenna are given. The measured peak gain of the proposed antenna is 1.66 dBi. The transparency of the IZTO/Ag/IZTO thin film on the polyimide substrate is 86%. The advantages of the proposed antenna are high transparency, low resistivity and flexibility. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a multiple input multiple output (MIMO) antenna for multiband operation based on meander lines with L shaped metallic strip. Meander lines is basically a monopole antenna loaded with multiple sections of short circuited transmission line that acts as inductor and alter the impedance characteristics of antenna. Antenna size miniaturization of 69 % has been achieved by placing double U slots on the ground plane and a line slot DGS (Defective Ground Structure) is used to reduce the mutual coupling between the antenna elements. The values of envelope correlation coefficient (ECC) and Specific Absorption Rate (SAR) lie well below the specified limit.