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An active transmitarray antenna is presented for Ka-band monopulse tracking radar in the 34-36-GHz range. A novel contribution is the application of commercial SiGe-based 5G beamforming chips in a large-scale naval radar array, demonstrating how developments in Ka-band communications can benefit radar technology. Three arrays of 0.77 m diameter each with 24368, 19424, and 7824 radiating elements are presented to compare amplitude-tapered, space-tapered, and hybrid-tapered designs. All designs achieve a sub-1° half-power beamwidth (HPBW), peak sidelobe levels (SLL) below -26 dB, and effective isotropic radiated power (EIRP) of 100 dBm at broadside with a ±60° grating-lobe-free scan range. Furthermore, a small-scale demonstrator is realized and presented that consists of an eight-layer printed circuit board (PCB) with 8× 8 patch antennas on one side and a 4× 4 open-ended waveguide (OEWG) feed-array with beamforming chips and integrated liquid cooling channels on the other side. After over-the-air calibration, the realized array achieves a peak EIRP of 56 dBm, a 12° HPBW, and the ability to scan to ±60° in the H-plane with cos θ scan loss and no grating lobes. E-plane scanning is achieved up to ±45° with θ 1.1 scan loss.

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.

A cost-effective millimeter-wave measurement setup for narrowband path loss and angle-of-arrival measurements is presented in this paper. The setup consists of ubiquitous radio-frequency lab equipment and additional low-cost components. An algorithm is developed, which improves the measurement accuracy and reduces the required measurement time. An uncertainty analysis is performed, including a noise analysis, amplifier linearity, antenna misalignment and general system impairments. A theoretical model of the received signal plus noise is developed, which is used in Monte Carlo simulations to show the impact of snapshot averaging on the uncertainty. The estimated combined uncertainty with a 95.45% confidence level is 1.1 dB at the maximum measurable path loss and 0.3 dB in the case of low path loss, where the uncertainty due to receiver noise is negligible. The measurement setup is used in outdoor specular building reflection measurements at 24.00–24.25 GHz. The measured single-building reflections show a 1–9 dB excess loss compared to the free-space path loss. The measured excess loss is 9–20 dB for double-building reflections. These results indicate that buildings could potentially be used as effective millimeter-wave specular reflectors to extend millimeter-wave coverage.

This article introduces a simple, but novel, concept of a single-layer dual-frequency microstrip patch antenna array for joint communication and sensing operating at 24 and 28 GHz. The frequencies are separated by polarization: the radar sensing function at the 24-24.25 GHz ISM band is vertically polarized, whilst communication at the n261 (27.5-28.35 GHz) band for 5G NR uses horizontal polarization. Based on simulation results, the antenna array is expected to achieve an azimuthal scan range of ±45◦ at the radar band with frequency scanning in elevation limited to only ±1◦. The scan ranges for communication are ±45◦ and ±40◦ in azimuth and elevation, respectively.

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.

This paper presents the design of a Ka-band active transmitarray consisting of radiating waveguide elements, a transition from waveguide to PCB, and commercial phase shifters and high-power amplifiers. A unit cell design is presented, which at a size of (0.7λ)2 allows for beamsteering without grating lobes up to around ±20° from broadside. The modeled performance of a 68-element array is presented, demonstrating the feasibility of a 81.6 dBm EIRP at 35 GHz from a 7 cm wide aperture.

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.

Fixed-beam, high-gain antenna systems can be used for a finer partitioning of the currently used cell-sectoring. This partitioning has the benefit of reducing the number of users seen per antenna beam, which reduces interference. Furthermore, the high antenna gain allows for a high effective isotropic radiated power while keeping the transmit power low. In this paper, we study the performance of such a fixed-beam, high gain antenna system design for millimeter-wave mobile communications. The antenna system is designed to keep the inter-sector interference in a multi-site scenario low. The performance is analyzed for single- and multi-user environments. In single-input single-output mode, the 50th percentile of the signal-to-interference-plus-noise ratio lies between 12.5 dB to 39.7 dB if 3 to 0 interferers are present, respectively. For multiple-input multiple-output transmission using zero-forcing, the signal-to-interference-plus-noise ratio increases and the 50th percentile ranges from 36.1 dB to 43.3 dB if 3 to 0 interferes are present, respectively. By using maximum ratio transmission, the best performance is achieved with no interferers present, while a plunge in performance is observed with interferers. Furthermore, the study revealed that the narrow beam antenna system can also provide a clear signal separation for small spatial separations. In the given example, the signal-to-interference-plus-noise ratio is larger than 32.1 dB with 11 active antenna elements, where 2.8 meters separate the users. Hence, the paper shows that the cell-partitioning antenna systems provide coverage in the desired area while keeping the inter-sector interference low, and the considered transmission techniques can be used for situation optimized mobile communication links.

This article reviews the current state-of-the-art of active-integrated antennas co-designed with power amplifiers (PAs). Three strategies to improve output power and power-added efficiency are described using examples, namely direct matching between PA and antenna, tuning of harmonic reflections in the antenna, and in antenna power combining from multiple PAs. An outlook is given on the challenges to be faced in the application of these strategies in wide-scanning phased arrays.

This article introduces the FORMAT array, a reconfigurable millimeter-wave antenna array platform based on antenna tiles. FORMAT stands for Flexible Organization and Reconfiguration of Millimeter-wave Antenna Tiles, which is a unique hardware solution aiming to implement and demonstrate a variety of antenna array concepts, as well as different array architectures and configurations from the same basic module, providing even benchmark between different solutions and thus valuable insights into fifth-generation (5G) and beyond-5G antenna systems. The combination of a minimum-sized tile with 3D-printed frame parts enables antenna arrays of a variety of sizes, allows multiple beamforming architectures, and a range of different antenna element positioning in the array. The hardware implementation is thoroughly described, with a few different array assemblies being manufactured and measured, validating their antenna performance with over-the-air measurements. Finally, using FORMAT hardware as both base station and user equipment, a 5-m wireless communication link was set up, achieving 4.8 Gbps downlink speed with QAM64 modulation.

Fifth-generation mobile networks (5G) are the solution for the demanding mobile traffic requirements, providing technologies that fulfill the requisites of different type of services. The utilization of the millimeter-wave (mm-wave) band is the straightforward technique to achieve high bit rates. Moreover, analog radio-over-fiber (ARoF) brings outstanding benefits such as low cost, low power consumption, and high spectral efficiency, among others. Thereby, mm-wave ARoF is a strong candidate to pave the way for common public radio interface (CPRI) in the fronthaul for the future 5G architecture. As orthogonal frequency-division multiplexing (OFDM) is the adopted waveform in the 5G standard, it should be also utilized in mm-wave ARoF systems for 5G. However, phase noise is one of the most degrading factors in mm-wave OFDM ARoF systems. Therefore, in this work, an analysis of the phase noise is carried out through an experimental setup up. The configuration of this setup enables to gradually modify the final phase noise level of the system. Furthermore, an original and novel algorithm to compensate the phase noise in OFDM receivers is proposed. The performance of this algorithm is experimentally evaluated through the setup for different phase noise levels and different subcarrier spacings. The obtained results show the effectiveness of the proposed algorithm under those conditions, highlighting the viability of mm-wave OFDM ARoF for 5G and beyond.

Antenna and low-noise amplifier (LNA) co-design is a promising method for increasing the sensitivity of millimeter-wave (mmWave) receiver systems. Co-design involves several individual steps which usually do not intersect with each other in one design flow, but this method combines all of them together and allows to obtain mutual benefits for all components. This paper gives an overview of several different mmWave engineering tasks like antennas and monolithic microwave integrated circuit (MMIC) design together with RF interconnection solutions like wirebonding, flip-chip and packaging technology. The suggestion of the mmWave receiver co-design for achieving minimum noise figure at low costs is also provided.

A V-band Vivaldi antenna design for beyond-5G base station applications operating within V-band is demonstrated. The device can be used for interfacing with radio-over-fibre links and optoelectronic components through a coplanar waveguide to slotline transition. Simulations show an end-fire radiation with a 3 dB gain bandwidth ranging between 46.9-77.4 GHz combined with the reflection coefficients remaining below-10dB for the same frequency range. A comb structure inspired by optical grating couplers is added providing an increased maximum gain of 12.6 dBi at 68.5 GHz. Measurement results validate the promising characteristics of the planar antenna.

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.

The characterization of integrated antennas is challenging as they usually do not provide a suitable direct interface for the measurement equipment. Adding a connector or using on-wafer probes to interconnect to the measurement system often results in a change in antenna characteristics and requires a separate prototype resulting in additional complexity and associated costs. In order to measure the input impedance and realized gain of an integrated antenna, a contactless characterization method (CCM) can be used. In this article, the CCM is applied to an open-ended waveguide (OEWG). The OEWG operates in the $K_{a}$ -band and has a gain similar to typical integrated antennas. A good match between the reference measurements and the CCM is achieved, making this method potentially useful for the characterization of integrated mm-wave antennas.

A system-level study was conducted that evaluated the system performance of various dense and sparse antenna array configurations for application in millimeter-wave multi-user multiple-input multiple-output base stations. The performance was evaluated by investigating the probability that a user experiences an outage when a zero-forcing pre-coder is used in a random line of sight scenario. This paper shows that the outage probability significantly decreased when irregular sparse arrays were used rather than regular sparse or regular dense arrays. A re-configurable linear array was designed and realized as a demonstrator. It used 3D-printed aluminum box horn antenna elements that had wide scanning range in the azimuthal plane and a small scanning range in the elevation plane. For the demonstrator, it was shown that the outage probability was reduced from 3.85% to 0.64% by moving from a sparse regularly spaced array to a sparse randomly spaced array. This amounted to an improvement of a factor of six. The sparse topology allowed for the usage of large antenna elements that had an increased gain and still achieved wide-angle scanning, while reducing mutual coupling to a minimum.

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.

A real-time millimeter wave radio-over-fiber link is experimentally demonstrated transmitting up to 1.4 Gbit/s 5G OFDM signals through a multi-core fiber to an 8 × 4 antenna array employing analog beamforming to radially track a moving receiver.

One of the current trends in the integrated circuit (IC) development is the integration of antennas on-chip or in the package of the IC. This poses challenges in the production testing process of the packaged IC, as the antenna functionality has to be included and at least one of the signal ports cannot be accessed at a conducted manner. In order to measure the reflection coefficient of an integrated antenna, a contactless characterization method (CCM) can be used. In this paper, the practicality of a CCM is assessed, having the application of a cost-effective high-volume testing procedure for integrated antennas in mind. It is shown that the CCM yields accurate results for different imperfections in the measurement setup. Moreover, measurement results around 33 GHz using a connectorized patch antenna are shown, which experimentally verify the validity of using the CCM under near-field conditions.

This paper presents a review of various outphasing methods. Key performance indicators are formulated focusing on reliability, energy consumption and bandwidth and are used to compare state-of-the-art outphasing methods. Outphasing methods which show potential for beyond-5G base station applications are described and relevant advantages, disadvantages and literature gaps are pointed out. Specifically, the recent developments on using antenna elements to be co-designed with an outphasing system will be considered as a promising efficient solution. Findings in this paper show that a co-designed amplifier-antenna outphasing system achieves one of the highest peak power-added efficiencies at millimeter-wave frequencies compared to other PA topologies.

In the near future, lightweight racing bicycles will be equipped with a wireless camera. Such a wireless camera will communicate with the control vehicle via an aircraft flying at an altitude of up to seven kilometers. With the current antenna, a monopole, it is not possible to bridge the distance between the wireles camera and the airplane with sufficient signal strength. The new antenna design must achieve more gain over a specific opening angle, which places demands on the half-power beamwidth. Furthermore, the antenna must be dual-polarized, small and lightweight. It is shown that a quasi-Yagi antenna is a particularly suitable antenna. The final antenna design exhibits a half-power beamwidth of 77° in the E-plane and the H-plane and a gain of 7.5 dBi. The realized antenna weighs 33 grams.

Sea mines are one of the most cost-effective weapons of naval warfare. Underwater mine-disposal vehicles are used to identify and neutralise this threat. In order to localise the position of the vehicle in a shallow water scenario, it needs to surface and update its internal navigation system using a global navigation satellite system. This paper presents the design and prototype of an antenna that can be integrated in the mine-disposal vehicle SeaFox. Simulation and measurement results suggest that the antenna design can cover all major GNSS bands. However, the radiation pattern strongly depends on the water level.

A design concept for a phased-array-fed reflector antenna system intended for millimeter-wave base stations is presented. This concept is motivated by the need for efficient beamforming antenna systems with reduced power consumption as compared to the presently considered fully-populated large-scale MIMO arrays. The main idea is to use a high-gain reflector antenna to maximize the effective isotropic radiated power. That in turn, allows minimizing the number of active antenna elements of the phased-array feed, and hence limit the total supplied power. The proposed reflector antenna system is based on a torus reflector which is illuminated by an offset phased-array feed. We show how to determine the antenna design parameters to achieve the desired cell coverage.

Lower efficiencies of power amplifiers and increased path loss at higher frequencies are two reasons why utilizing millimeter-wave frequencies for future wireless communications systems is challenging. In this paper, two distinct antenna systems are presented which address this challenge by using high antenna gain. This allows lower transmit power levels, compared to conventional phased array antennas, while still providing high effective isotropic radiated power.

This paper presents the design, manufacturing, and measurement of a novel miniaturized 3D printed conical waveguide filtenna concept for use in the 5G New Radio n257 band. Field tests, for the band 26.5 to 27.5 GHz, motivates the desire to add a filtering functionality to the wideband horn antenna. Miniaturization is achieved by adding a lens to the antenna and exploiting the symmetrical resonance properties of a cylindrical resonator for dual-mode operation. Therefore, the manufactured concept filtenna consists of a miniaturized lens-fitted conical horn antenna with an integrated 4th order 3D printed dual-mode cylindrical waveguide filter. Tuning screws in the filter enable mechanical control over the filtenna centre frequency and bandwidth. The manufactured filtenna achieves a 10 dB return loss bandwidth of 2 % about a centre frequency of 27 GHz, and a gain of 14.8 dBi.

In this paper we propose to combine the concepts of outphasing and analog-radio over fiber. The analog outphasing signals are generated centrally and transported to the remote antenna system over fiber. There, high-performance and highly non-linear power amplifiers can be used. This approach creates an energy efficient communications infrastructure based on a centralized radio network. A first demonstrator is built at Ka-band using discrete components, experimentally showing the feasibly of this concept at millimeter-wave. Preliminary results show a measured error-vector magnitude of 4.18% over a wireless channel.

Partitioning of mobile communication cells using high gain antennas, e.g. lens-horn antennas, has the potential to improve mobile communication links. Depending on the environment, the radiation pattern has to be shaped to achieve optimal coverage. In the case of dual-polarized elliptical-shaped horn antennas, the differences in radiation characteristics for each polarization state has to be considered. In this paper, the design of a compact elliptical lens-horn antenna fed by a circular waveguide is shown. The simulated radiation patterns of the two orthogonal radiation patterns show mainly an influence in the cut along the short axis. In this cut, the beam broadens by 3.8?. Due to the broader beamwidth, the antenna gain reduces by 1.9 dB, which has to be taken into account during the radio planning phase of the cell partitioning.

When measuring at higher frequencies, as the wavelength becomes shorter, antenna phase measurements are very sensitive to positioning and alignment errors. The results of a radiation pattern measurement of a WR-28 rectangular open-ended waveguide (OEWG) are shown, and the lack of symmetry in the measured phase indicates a misalignment of the OEWG. A two-parameter misalignment model is used to explain this asymmetry. The measurement data are used to determine the two parameters of the model, and the parameters are subsequently used to correct the phase of the measured radiation pattern, restoring the expected symmetry.

Fifth-generation (5G) mobile networks consist of a range of novel technologies to fulfill different and exigent requirements and serve a wide range of services. To reach this, analog radio over fiber (ARoF) fronthaul with millimeter-wave (mm-wave) cells is a firm candidate to be part of the 5G architecture. Nonetheless, combined mm-wave and ARoF systems present new challenges such as high free-space path loss (FSPL), phase noise, chromatic dispersion, and other impairments. Therefore, the selection of the modulation format is crucial to reduce these effects and their impact. This work compares and analyzes different modulation formats in this type of system in order to choose the best waveform candidate for mm-wave 5G and beyond with ARoF fronthaul. An experimental comparison of OFDM, SC-FDM, UFMC, GFDM, and multi-CAP, shows that the standard OFDM may not be the best choice for mm-wave 5G.

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.

Reflector antennas are utilized in a lot of applications that require a high gain antenna system. Conventionally, the reflector antenna is fed by a single radiating element, making the direction of the beam fixed. Using a focal plane array (FPA) as feeding mechanism, the magnitude and direction of the resulting beam can be controlled electronically. Using an in-house developed tool, the amplitude and phase settings for a 28 GHz active phased array antenna are determined in order to mimic the ideal feeding pattern for a certain reflector. The far-field of the FPA in combination with the reflector antenna is determined for a scan angle of 0° and 3°.