Multiple-input-multiple-output (MIMO) antenna systems are a key enabling technology for modern fourth-generation (4G) wireless systems. The need for higher data rates for multimedia applications within the limited bandwidth and power levels led the way to the use of multiple antennas at the receiver and transmitter ends. Printed MIMO antenna systems, supporting multiple bands, including the lower band of the 4G wireless standard (LTE), pose a challenge in terms of available size. In this work, we start by defi ning the new required metrics to characterize MIMO antenna systems. We then present several recent printed multi-band MIMO antenna systems, along with some isolation-enhancement mechanisms that are used in these closely packed antennas.

Printed Multi-Band MIMO Antenna Systems and Their Performance Metrics

Advances in antenna technologies for cellular hand-held devices have been synchronous with the evolution of mobile phones over nearly 40 years. Having gone through four major wireless evolutions [1], [2], starting with the analog-based first generation to the current fourth-generation (4G) mobile broadband, technologies from manufacturers and their wireless network capacities today are advancing at unprecedented rates to meet our unrelenting service demands. These ever-growing demands, driven by exponential growth in wireless data usage around the globe [3], have gone hand in hand with major technological milestones achieved by the antenna design community. For instance, realizing the theory regarding the physical limitation of antennas [4]-[6] was paramount to the elimination of external antennas for mobile phones in the 1990s. This achievement triggered a variety of revolutionary mobile phone designs and the creation of new wireless services, establishing the current cycle of cellular advances and advances in mobile antenna technologies.

Solving the 5G Mobile Antenna Puzzle: Assessing Future Directions for the 5G Mobile Antenna Paradigm Shift

Phased-array modules at frequencies >20 GHz are expected to play an important role for 5G applications. Antenna-in-package (AiP) is a reliable and cost-effective method to realize these phased arrays. This paper introduces a practical Ka-band AiP structure and discusses the antenna element design and implementation tradeoffs. The AiP design is based on multilayer organic buildup substrates that are suitable for phased-array module integration needs and supports both horizontal and vertical polarizations. Measurement results from the fabricated antenna prototypes show 0.8 GHz return loss bandwidth and 3.8-dBi peak gain at 30.5 GHz. Simulation results agree with the measured ones.

Antenna-in-Package Design Considerations for Ka-Band 5G Communication Applications

Antenna-in-package (AiP) technology, in which there is an antenna (or antennas) with a transceiver die (or dies) in a standard surface-mounted device, represents an important antenna and packaging technology achievement in recent years. AiP technology has been widely adopted by chipmakers for 60-GHz radios and gesture radars. It has also found applications in 77-GHz automotive radars, 94-GHz phased arrays, 122-GHz imaging sensors, and 300-GHz wireless links. It is believed that AiP technology will also provide elegant antenna and packaging solutions to the fifth generation and beyond operating in the lower millimeter-wave (mmWave) bands. Thus, one can conclude that AiP technology has emerged as the mainstream antenna and packaging technology for various mmWave applications. This article will provide an overview of the development of AiP technology. It will consider antennas, packages, and interconnects for AiP technology. It will show that the antenna choice is usually based on those popular antennas that can be easily designed for the application, that the package choice is governed for automatic assembly, and that the materials and processes choices involve tradeoffs among constraints, such as electrical performance, thermal–mechanical reliability, compactness, manufacturability, and cost. This article also shows a probe-based setup to measure mmWave AiP impedance and radiation characteristics. It goes on to give AiP examples implemented, respectively, in a low-temperature co-fired ceramic, an embedded wafer level ball grid array process, and a high-density interconnect processes. Finally, this article will summarize and present some recommendations on research topics to further the state of the art of AiP technology.

An Overview of the Development of Antenna-in-Package Technology for Highly Integrated Wireless Devices

In the last couple of decades, solid-state device technologies, particularly electronic semiconductor devices, have been greatly advanced and investigated for possible adoption in various terahertz (THz) applications, such as imaging, security, and wireless communications. In tandem with these investigations, researchers have been exploring ways to package those THz electronic devices and integrated circuits for practical use. Packages are fundamentally expected to provide a physical housing for devices and integrated circuits (ICs) and reliable signal interconnections from the inside to the outside or vice versa . However, as frequency increases, we face several challenges associated with signal loss, dimensions, and fabrication. This paper provides a broad overview of recent progress in interconnections and packaging technologies dealing with these issues for THz electronics. In particular, emerging concepts based on commercial ceramic technologies, micromachining, and 3-D printing technologies for compact and lightweight packaging in practical applications are highlighted, along with metallic split blocks with rectangular waveguides, which are still considered the most valid and reliable approach.

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Packages for Terahertz Electronics

An integrated multilayer antenna-in-package (AiP) targeted for stationary 60-GHz communication is presented. The key differences in design conditions for mass-market-level and prototype-level AiP are discussed and reflected during the design process. Hence, a low-cost and high-reliability package solution is realized. The proposed AiP consists of a 4 × 6 array of 24 stacked circular patch antennas and corresponding antenna feed lines designed for phased array. The finalized LTCC AiP prototype features 20 × 15 × 1.02 mm3 in dimension. Solder bump flip-chip technology is used to attach the AiP to the RFIC for system-level assembly. The assembled package is evaluated using a custom-designed near-field measurement setup. EM simulations and measurements confirm the presented AiP features more than 9 GHz bandwidth, 45° beam-steering ranges in both E- and H-planes, and more than 14.5 dBi gain at boresight.

24-Element Antenna-in-Package for Stationary 60-GHz Communication Scenarios

A key feature of upcoming 4G wireless communication standards is multiple-input-multiple-output (MIMO) technology. To make the best use of MIMO, the antenna correlation between adjacent antennas must be low (&#60; 0.5). In this context, we propose a new correlation reduction technique suitable for closely spaced antennas (distance, d &#60; λ/40). This technique reduces mutual coupling between antennas and concurrently uncorrelates the antennas' radiation characteristic by inducing negative group delay in the target frequency band. The validity of the technique is demonstrated with a USB dongle MIMO antenna designed for LTE 700MHz band. Measurement results show that the antenna correlation is reduced more than 37% using the proposed technique.

Low correlation MIMO antenna for LTE 700MHz band

A key feature of upcoming 4G wireless communication systems is multiple-input-multiple-output (MIMO) technology. To make the best use of MIMO, the antenna correlation between adjacent antennas should be low (< 0:5). In this context, we propose a correlation reduction technique suitable for closely spaced antennas (distance, d < ‚=40). This technique reduces mutual coupling between antennas and concurrently uncorrelates antennas' radiation characteristics by inducing the negative group delay at the target frequency. The validity of the technique is demonstrated with a USB dongle MIMO antenna designed for LTE 700MHz band. Measurement results show that the antenna correlation is reduced more than 40% using the proposed technique.

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Low Correlation MIMO Antennas with Negative Group Delay

A multi-band antenna, which consists of a diversity antenna in the DCS/PCS/UMTS bands and a MIMO antenna in the LTE17/LTE4 bands, is proposed and designed for mobile handset applications. The proposed antenna consists of the meandered PIFAs with branch lines. The radiation efficiency of the proposed antenna is higher than 30% in the LTE17/LTE4 bands and higher than 40% in the DCS/PCS/UMTS bands. The ECC between two identical antennas is less than 0.5 over the entire LTE17/LTE4/DCS/PCS/ UMTS bands.

Diversity and MIMO antenna for multi-band mobile handset applications

The design, fabrication and measurement of a monolithic Circular Stacked Antenna (CSA) array for 60 GHz applications in consumer electronics is presented and proposed. The multilayer CSA is devised using LTCC printing technology for high-volume production scenarios. A detailed study of the antenna element topology and antenna array layout is presented. Simulated and measured results indicate the CSA array features 2∶1 VSWR from 57 GHz to 66 GHz and more than 15.5 dBi gain at boresight angle.

Juhyung Lee

Papers

24-Element Antenna-in-Package for Stationary 60-GHz Communication Scenarios

Low correlation MIMO antenna for LTE 700MHz band

Low Correlation MIMO Antennas with Negative Group Delay

Diversity and MIMO antenna for multi-band mobile handset applications

Monolithic Circular Stacked Antenna array using high-volume LTCC technology for 60 GHz