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Human blockage and its dynamics are potential challenges for millimeter-wave (mm-wave) mobile communication. This article presents the results of wideband measurements at 27 GHz with one human blocker close by a dynamic mobile terminal (MT) as well as one or multiple dynamic human blockers further away from an MT. The measured human blockage loss is largest when the direct path (DP) in a line-of-sight (LOS) is blocked, but this loss is limited by other multipath components (MPCs). For nonline-of-sight (NLOS) channels, it is shown that human blockage loss is typically negligible. The presented measurement results show that human blockage loss in multipath channels is much smaller than that reported in diffraction-and measurement-based models, which neglect or minimize the contribution of all MPCs other than the DP. This suggests that the multipath nature of the indoor wireless channel highly limits the impact of human blockage.

Lower efficiencies of power amplifiers and increased path losses at higher frequencies are two reasons why utilizing millimeter-wave frequencies for future wireless communications is challenging. In this article, a high-gain multilens-horn antenna system is presented. The antenna system provides highly effective isotropic radiated power by using only a few high-gain antenna elements, where each element only needs a low transmit power of 26 dBm to reach users at far distances. Moreover, due to channel reciprocity, both down- and uplink benefit from an increased antenna gain. It is shown that a reasonable number of high-gain antennas can provide coverage in a 60° sector with an inter-site distance of 300 m. Based on radio-planning simulations, three horn shapes are identified to provide sufficient coverage. The final optimized dual-polarized multilens-horn design is fabricated and experimentally verified. With a low transmit power at the base station (BS) of 26 dBm, a signal strength of at least -65 dBm is achieved in 98.9% of the sector at 28 GHz under non-line-of-sight conditions for the vertical polarization. For the horizontal polarization, an area of 96.2% is covered.

The Friis equation is often used to determine the gain of antennas but assumes that far-field conditions are met. For limited antenna separations on the order of the Fraunhofer distance, its use requires a precise estimate of the amplitude centers of the antennas. Using a new antenna gain measurement technique, it is shown that the amplitude center can be very well estimated and that the measurement results can be used to confirm that far-field conditions are met. Moreover, reflections caused by scatterers are averaged since multiple measurements are performed. The presented method is particularly useful for anechoic chambers that are limited in size, such as small anechoic chambers for the characterization of, for instance, 5G millimeter-wave phased arrays.

This paper presents the design of an open-ended waveguide (OEWG) array element operating between 34 GHz and 36 GHz. The OEWG is coupled to a quarter-wave patch antenna on a PCB, which connects to a millimeter-wave IC via a grounded co-planar waveguide. The radiating element is co-designed with an integrated liquid cooling solution to remove heat from the amplifier and phase-shifting IC. Furthermore, a 4x4-element is presented to demonstrate the OEWG design, feed and cooling operation. Although PCB manufacturing deviations were observed in the demonstrator, the realized elements are expected to operate over the entire desired frequency range.

Phased array antennas enable beamforming, partly overcoming the increase in path loss associated with the 5G mm-wave band. In this paper, the design and calibration of a 5G mm-wave dual-polarized active phased array is presented. A procedure to shape the array's radiation pattern is shown and is verified by measurement results. Moreover, a phase calibration is performed and an increase in gain on the order of 2 dB was measured.

This article reviews the current state-of-the-art of millimeter-wave (mm-wave) antennas for communication and sensing applications in the D-band between 110 and 170 GHz. The most popular design techniques, including Antenna-on-Board (AoB), slotted waveguides, Antenna-in-Package (AiP) and Antenna-on-Chip (AoC), are described using relevant examples from scientific literature. Potential benefits and limitations of integration technologies, such as specialized packaging, chip post-processing steps and interconnects, are listed as well. The reported performances of all listed designs are compared against each other, taking the antenna size relative to operating frequency into account. This novel comparison indicates that small-scale integrated AiP and AoC designs can achieve competitive performance levels with short and low-loss interconnects.

A system-level study is conducted that evaluates the performance of various sparse array topologies for application in 5G base-stations. The performance metric is the probability a user experiences an outage, when applying a Zero-Forcing precoder in a Line-of-Sight scenario. The outage probability is shown to significantly decrease for sparse irregular arrays as compared to sparse regular and dense regular arrays. A re-configurable sparse array design at 28.5GHz is realized as a demonstrator.

The next generation radio access networks (5G) will make use of active phased array antennas to enable beamforming. Calibration of the array is an essential step to maximize its performance. The calibration procedure of an active phased array can be divided into two different phases: post-manufacturing calibration and online calibration. In this paper, a post-manufacturing calibration procedure using over-the-air measurements is presented. This procedure is applied to an 8x8 active phased array containing low-cost silicon-based ICs. It is shown that with this procedure, it is possible to steer the main lobe of the array as far as ±40°, while maintaining a side lobe level of around -20 dB. The measurements were performed at a frequency of 29.5 GHz.

Maximization of 5G millimeter-wave base station coverage and range is important to reduce the number of required base stations. Buildings could be used as reflectors to provide coverage in NLOS areas due to their high reflectivity at millimeter-waves. This paper presents the results of a measurement campaign investigating specular reflections from buildings at 24.00-24.25 GHz. The angle of minimum path loss for single-building reflections agrees well with the direction of the specular path. This agreement is less accurate in case of a double-building reflection, possibly due to obstructions in the specular path or multipath fading. In case of a single-building reflection, 1-9 dB excess loss compared to free-space path loss is measured. The excess loss is in the range of 9-20 dB for a double-building reflection. Although more research on this topic is required, these results are promising and indicate that buildings can be used as effective millimeter-wave reflectors.

It is not a straightforward task to determine the antenna characteristics of an integrated antenna. In order to measure its input impedance, a contactless characterization method (CCM) can be used. In this paper, the sensitivity of a CCM is assessed. It is shown that small offsets in the position of the antenna-under-test in between measurements can lead to severe errors in the determined input impedance. Moreover, accurate knowledge of the used terminations is essential to acquire accurate results. Furthermore, it is shown that the use of an anechoic environment is not a necessity for this CCM, making this method attractive to be used in many application domains. Finally, the CCM is used to determine the input impedance of an arbitrary antenna. A good match between the measured input impedance via a directly contacted measurement and via the CCM is achieved.

This article reports on a W-Band (75–110 GHz) Schottky diode based balanced envelope detector in microstrip technology, featuring a transition from WR-10 to microstrip. The manufactured detector provides 20 GHz of input RF bandwidth within the W-band. A video bandwidth between 4 GHz and 6 GHz is achieved for input RF frequencies between 75 GHz and 88 GHz, allowing error free transmission of signals up to 12 Gbit/s.

A wide-scan and broadband focal-plane array (FPA) concept is introduced that provides high antenna gain and effective isotropic radiated power (EIRP) with electronic beam-steering within a relative large field-of-view (FoV) up to +/-200. The antenna uses a bi-focal double-reflector concept that optimizes the illumination of the focal-plane region. In this way, we have reduced the required size of the feed array and have maximized the number of simultaneously active array elements. By using a photonics beamformer, a broadband system for the 20-40 GHz band can be created with a fiber-based interface to a central processing unit. This hybrid antenna system proves to be a very interesting concept for future 5G and beyond-5G millimeter-wave base-stations, two-way satellite communication systems and point-to-point wireless backhaul systems. A silicon BiCMOS low-noise amplifier and a photonic integrated circuit for the optical beamformer have been developed and integrated in the overall system. A system-level demonstrator was developed and experimentally validated in receive mode. Our concept provides an antenna gain of more than 40 dBi over a FoV of +/-15 degrees at 28.5 GHz., A wide-scan and broadband focal-plane array (FPA) concept is introduced in this article, which provides high antenna gain and effective isotropic radiated power (EIRP) with electronic beamsteering within a relatively large field of view (FoV), up to +/-20°. The antenna uses a bifocal double-reflector concept that optimizes the illumination of the focal-plane region. In this way, we have reduced the required size of the feed array and have maximized the number of simultaneously active array elements. By using a photonics beamformer, a broadband system for the 20-40-GHz band can be created with a fiber-based interface to a central processing unit. This hybrid antenna system is a very interesting concept for future 5G and beyond [5G millimeter-wave (mm-wave) base stations, two-way satellite communication systems, and point-to-point wireless backhaul systems]. A silicon BiCMOS low-noise amplifier (LNA) and a photonic integrated circuit (PIC) for the optical beamformer have been developed and integrated into the overall system. A system-level demonstrator was developed and experimentally validated in receive mode. Our concept provides an antenna gain of more than 40 dBi over an FoV of +/-15° at 28.5 GHz.

5G mm-wave communications requires a highly densified network of radio access stations to ensure sufficient coverage. Low-complexity nodes based on C-RAN and ARoF fronthaul combined with advanced antenna concepts offer a suitable and potentially low cost technology for single and multi-beam 5G applications.

This manuscript introduces a 5G radio access network architecture concept based on ultra-dense wavelength division multiplexing (UDWDM) and incorporating an optical fronthaul network that uses a novel wireless antenna system for radio frequency transmission and reception. A ring topology is proposed where optical signals travel within the 5G UDWDM passive optical networks and millimeter waves are generated in the optical line terminals by optical heterodyning. The wireless transmission of the millimeter waves is conducted by an innovative phased array fed reflector antenna approach for mobile communications that grants high antenna gain due to highly focused radiation characteristics, as well as multiplexing gain by multiple beam generation. Furthermore, beam steering is provided by a radio frequency analog beamformer network. Finally, implementation options synthesizing the total system are discussed.

Artificial magnetic conductors (AMCs) received a lot of attention for Antenna-on-Chip applications. Typically, these structures suffer from severe dielectric losses. These losses can be separated in two mechanisms; losses due to the propagation through a lossy medium, and losses due to the fringe fields coupling into the silicon. It is shown that a theoretical minimum dielectric loss can be defined, and using intuitive measures, an AMC can be constructed which approaches this theoretical limit.

The next generation of wireless communications has to deal with the demand for higher data rates and the increase of subscribers. A feasible approach to cope with these challenges is to utilize millimeter waves (mmWaves). To provide at these high frequencies a sufficient high signal to noise ratio (SNR) narrow beam antenna systems can be used. These systems require knowledge about the direction of arrival (DoA) to steer their beams towards the optimal direction. The determination of the DoA can become time consuming for large areas where a single narrow beam can cover only a small spot. Dealing with this challenge, the single shot DoA enables to find the optimal direction within an instant of time for multiple users. This paper introduces the single shot DoA method and shows its functionality based on conducted simulations.

Antenna integration is a relative new concept for the miniaturization of Radio Frequency (RF) transceivers where a key problem is to achieve a small size at low cost. Traditional solutions, using ceramic materials, are too costly. Additionally, the current trend in RFID applications is the development of smaller and cheaper tags. In this paper, we present an elegant and low-cost Antenna-in-Package (AiP) solution for RFID tag applications. A printed dipole antenna that integrates the balun function with improved filtering characteristics is designed on a low-cost dielectric material. Simulation and measurement results verify the performance of the proposed antenna.

This paper presents a contactless measurement method for the characterization of highly integrated antennas. It is based on the backscattering method but omits the need to pre-determine the radar-cross-section of the antenna. The input reflection coefficient can even be obtained with an uncalibrated measurement system. Here, results for an X-band antenna are presented and compared with HFSS simulation results.

Artificial magnetic conductors (AMCs) are the focus of a lot of studies, mainly due to their in-phase reflection property. In most cases, the AMC is designed for normal incident plane waves only. In a lot of applications, however, the AMC will also be excited by oblique incident plane waves. In general, the resonance frequency of the AMC changes for different angles of incidence and different polarizations. In this work, a design procedure for an AMC having a stable resonance frequency as function of angle of TM plane waves is presented. It is shown that the AMC is stable for TM plane waves up to angles of grazing incidence.

Confidential wireless transmission of a 150 Mb/s chaotic encoded signal with an artificial signal to noise ratio of 0 dB is experimentally demonstrated at 28 GHz. The chaos is generated by a digitally implemented Duffing oscillator system.

In this paper, an experimental analysis of the phase noise in an OFDM ARoF setup at 25 GHz for beyond 5G is presented. The configuration of the setup allows to gradually scale the final phase noise level of the system. Moreover, an OFDM phase noise mitigation method with low complexity and delay is proposed and explained. The proposed method is an advanced version of the LI-CPE algorithm. The advanced LI-CPE version avoids the one OFDM symbol delay of its antecedent. In addition, the yields of using both methods are shown under different phase noise levels and with different subcarrier spacings. Finally, it is experimentally proven that the proposed method performs better than its previous version.

In this paper, an ultra-wideband millimeter-wave channel sounder is introduced. The channel sounder, consisting of a Vector Network Analyzer and 1 km of fiber, can perform high resolution channel sounding over long distances. A wired response calibration is compared to an over-the-air calibration. It is shown that the over-the-air calibration of the channel sounder increases the dynamic range in the power-delay-profile by 14 dB compared to the wired response calibration.

Wire-bond technology is cost-effective and widely available. This paper presents a mm-wave front-end module concept that exploits this technology for antenna implementation. A straightforward and computationally efficient modeling approach for the design of such antennas is presented that can be used in combination with standard IC design tools. The model was successfully verified with a commercial FDTD solver as well as measurements.

In this paper, we investigate how directional and highly-directional antenna systems using fixed beams can be beneficial in terms of aggregated channel and antenna gains, channel correlation and the massive multiple-input multiple-output (MIMO) capacity in both line-of-sight (LOS) and non-LOS (NLOS) scenarios for single user MIMO (SU-MIMO). It is shown that narrower beams have stronger aggregated channel and antenna gain. However, narrow beamwidth triggers a higher channel correlation as fewer scatterers are seen. A possible solution to reduce the correlation among the beams is to properly decorrelate the beams in advance. To this end, we partition the area of interest and devote one specific partition to each beam to minimize the possible overlaps among the beams. Simulation results show that fixed beam SU-MIMO systems using such highly-directional beams can provide higher MIMO capacity in comparison to isotropic and directional antenna systems.

We experimentally analyze the ARoF based on OPLL mm-Wave generation performance for 5G fronthaul. Remarkable performance improvements are achieved for all 5G NR numerologies and different OPLL configurations despite their inherently high phase noise level.