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Circular polarization is indispensable for robust wireless communication between mobile devices that operate at mm-wave frequencies. Additionally, phased-array solutions are required to cope with the associated free space path loss. In view of the size constraints for antennas integrated on (Bi)CMOS chips, an array of linearly polarized dipoles using a sequential rotation scheme is an attractive approach to comply with all mentioned requirements. When steering such an array off broadside, however, the axial ratio will severely degrade. It is the purpose of this communication to demonstrate how the axial ratio can be retained by compensating the amplitudes and phases of the individual antenna elements. Measured results on a 6 GHz test-bed show that the axial ratio with the proposed calibration scheme remains below 3 dB within the 3 dB beamwidth of the scanned beam. Results from a 60 GHz test-bed confirm the effectiveness of the method. [ABSTRACT FROM AUTHOR]

A simple scheme is developed to compute the Green's function of a periodic semiinfinite array in free space. It is based on the spectral representation of the fields radiated by an infinite linear array of dipoles. Results related to successive linear arrays are added in the space domain. This summation can be accelerated tremendously by using an elementary extrapolation technique. The resulting formulation converges everywhere in the plane containing the array, and the number of terms required to achieve a given precision increases slowly away from this plane. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Multiple‐input‐multiple‐output (MIMO) radar imaging systems require a high angular resolution to realize a high detectability level of the target directly related to the aperture size of the virtual array. Since in MIMO radars, the virtual array topology depends on the transmit and receive array topologies, two methods are proposed for the synthesis of sparse virtual arrays by designing the sparse transmit and receive arrays using a two‐step synthesis procedure (TSP) for antenna array sparsity via convex optimization. Both methods are formulated in detail, and it is shown that adjustments in formulations with respect to physical constraints in design specifications are feasible. In the first method, both the sparse transmit and the sparse receive array are synthesized using the TSP independently of each other. In the second method, the sparse receive array is synthesized based on the transmit array topology or vice versa using the method of least squares. With the help of numerical examples, it is shown that a sparse virtual array has better performance in terms of beamwidth and side lobe level compared with the traditional dense virtual array with the same number of transmit and receive array elements. It is also shown that the proposed design methods lead to broadband performance. [ABSTRACT FROM AUTHOR]

Commonly used connection methods for measuring antennas in the mm-wave range, like connectors or probes, influence the intrinsic behavior of the antenna under test (AUT). It is shown that nearby structures supporting the antenna and probe or connector cause strong interference on the measured antenna pattern. A new connection setup is proposed eliminating the interfering signal. This is confirmed by a detailed simulation model and verified with experimental results. Furthermore, the probe radiates significantly due to the discontinuity from the transitions of the probe tip to the microstrip line. This radiation influences the signal-to-noise ratio, i.e., the dynamic range. Measures are proposed to reduce this interference, resulting in an improved signal-to-noise ratio by approximately 15 dB. [ABSTRACT FROM PUBLISHER]

A phased-array fed reflector antenna system is presented which can be used for mm-wave base station applications. The proposed system is designed to support massive-multi-input–multi-output (MIMO) scenarios within a wide coverage ($\pm 30^\circ $) in the azimuth plane and a limited coverage at the elevation plane. A design and characterization methodology has been established to optimize the system for the operation in various line-of-sight conditions by adopting the maximum-ratio-transmission (MRT) and zero-forcing (ZF) MIMO algorithms. A two-user MIMO case study has been considered for the evaluation of the key system performance metrics, i.e., the effective isotropic radiated power, power consumption, signal-to-noise-ratio (SNR), and signal-to-interference-plus-noise-ratio (SINR). This study demonstrates that the phased-array fed reflector concept has a major advantage over traditional direct-radiating phased-array (DRPA) antennas to reduce energy consumption. In the present example, it requires 12–14 dB less transmitted power as compared with the MRT-beamformed DRPAs for the same SNR, and 26–27 dB less transmitted power relatively to ZF-beamformed DRPA systems for the same SINR. A prototype, employing a 55 cm diameter torus reflector and operating at 28 GHz-band, has been manufactured and tested. The measurement results agree well with simulations. [ABSTRACT FROM AUTHOR]

In this work, we show that high antenna frequency selectivity can make it more challenging to accurately measure antenna efficiency in a reverberation chamber (RC) when using the two-antenna method since electronic noise can affect the measured stirred-energy component of the $S$ -parameters. Recognizing whether the measured antenna-efficiency estimate is significantly affected by electronic noise is not trivial. The measured $S$ -parameters used for calculation may have high signal-to-noise ratios (SNRs), but the antenna-efficiency estimate can still show large systematic errors due to noise. We model noise as a component of the measured stirred energy, showing that the measured reflection is much more susceptible to noise than the measured transmission. We do not focus on the origin of the noise, but rather on the effect it has on the measurement. We show the effect of noise on the overestimation of the stirred energy components of the $S$ -parameters, which affects the two-antenna formulation more significantly than the three-antenna method one. We show that this overestimation can cause efficiency estimates calculated with the two- and three-antenna methods to be significantly over- or under-estimated and we show that uncertainties increase as well. Finally, we provide clear steps to recognize and reduce noise effects in antenna efficiency measurements. [ABSTRACT FROM AUTHOR]

The far-field pattern of a geometrically large and complex antenna used in low-frequency radio astronomy is computationally expensive to simulate on electromagnetic simulators, such as FEKO. For example, one station of the Square Kilometer Array, which consists of 256 log-periodic antenna elements, will take years to simulate using the full CAD model for the full operational frequency band. This paper focuses on reducing the simulation time for a single antenna element by simplifying the simulation model, thus decreasing the number of unknowns that have to be solved in a simulation. An iterative process for optimizing the simplification of such an element is described, while keeping the reflection coefficient within 1 dB absolute mean deviation of the measured data. After four iterations, the amount of unknowns to be solved, which includes the number of triangles and segments, was reduced from 29,307 to 11,991. This decreased the computation time by 86.5%, making array simulations feasible. Using the techniques described in the paper, other antenna constructions can benefit from it and be simulated more efficiently. [ABSTRACT FROM AUTHOR]

A novel technique is presented for the design and optimization of waveguide antenna arrays based on overlapping subarrays for limited field-of-view (FoV) applications. Each subarray consists of one directly fed antenna element and several passive reactive-loaded elements. The proposed overlapping scheme exploits a free-space reactive coupling instead of more conventional schemes based on complex beamforming networks. This results in a drastic reduction in the number of waveguide components required in the feeding network. The optimization of the considered class of array structures using a full-wave electromagnetic (EM) solver is extremely time-consuming even in the presence of subarrays with a reduced number of passive elements. To overcome this limitation, an effective semi-analytical design algorithm has been specifically developed. Using this algorithm, a novel subarray structure with a predefined pulse-shaped radiation pattern was synthesized. The designed subarray is inherently matched and features reduced spurious EM coupling level with adjacent subarray elements. In particular, the analysis of an array consisting of 38 such subarray elements has been carried out with the main goal of illustrating the effect of the subarray pattern on the total array characteristics. To validate the subarray overlapping scheme, an array composed of three contiguous subarrays has been realized and measured experimentally. In this way, a scan range in the FoV [−4°; 4°] with 15 dB grating lobe suppression has been demonstrated. [ABSTRACT FROM AUTHOR]

A novel base station antenna (BSA) configuration is presented to mitigate degrading physical antenna effects in massive multiple-input multiple-output (MIMO) systems, while minimizing implementation complexities. Instead of using a commonly considered single antenna panel comprising of many elements covering a wide field-of-view (FOV) of 120 degrees, $L$ tilted panels are used employing $L$ times fewer elements and $L$ times smaller FOV per panel. The spatial resolution of each panel is enhanced by employing sparse arrays with suppressed (grating-lobe) radiation outside its corresponding FOV. Therefore, more directive antenna elements can be deployed in each panel to compensate for the effective isotropic radiated power (EIRP) reduction. While sectorisation reduces the antenna gain variation in 120 degrees FOV, cooperation among multiple panels in downlink beamforming is seen to be capable of inter-panel interference suppression for sum-rate enhancement. A network model is used as a multi-user (MU) MIMO simulator incorporating both antenna and channel effects. It is shown that when the number of base station antennas is ten times the number of users, the average downlink sum-rate in pure line-of-sight (LOS), rich and poor multipath environments is increased up to 60.2%, 23% and 11.1%, respectively, by multi-panel sparse arrays applying zero-forcing (ZF) precoding. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Gluing an antenna-on-chip (AoC) directly on a ground plane or heat sink in the lead frame is a standard process for commercial applications. To reduce the effect of losses in the silicon substrate and improve the antenna’s radiation efficiency, the wafer thickness is often drastically reduced. However, the close proximity of the antenna and ground plane can cause an impedance mismatch. Metal tiles, which are embedded in silicon dioxide layers, are designed as an artificial magnetic conductor (AMC) to increase the radiation efficiency and tune the antenna impedance. A double-layer AMC is applied instead of a single-layer AMC to reduce the silicon dielectric loss. Additionally, the double-layer AMC has more capacitance to tune the impedance when integrating with a monopole on-chip antenna. The resulting −10 dB impedance bandwidth is increased to 5.8 GHz around the 60 GHz band, the simulated realized gain increases by 3.3 dB, and the simulated antenna radiation efficiency is increased from 11% to 21%. The measured input impedance of the AoC shows good agreement with the simulation results after probe calibration. [ABSTRACT FROM AUTHOR]

A new complex offset double-reflector configuration for a wideband focal plane array (FPA) is presented which is optimized for Ka-band applications with a scan range of ±20° in the azimuth plane. This configuration is obtained by using a mathematical framework based on geometrical optics which allow us to optimize complex double-reflector FPAs with limited computational effort. The proposed reflector configuration maximizes the number of simultaneously active array elements of the phased-array feed and minimizes the required total number of array elements for this wide scan range. To realize an aperture efficiency of at least 80% at 30 GHz, our concept allows half of the antenna elements in the array to be active during scanning for a scan range of ±10° and at least a quarter of the array elements to be active for a scan range of ±20°. This is a major improvement as compared to the scanning capabilities of focal-plane arrays based on conventional single- and double-parabolic reflector configurations. In addition, the FPA configuration has been optimized for wideband optical true-time-delay beamforming which requires a linear phase distribution along the array elements. We obtained a phase linearity with rms error of 2.81° at 30 GHz. The experiments from the realized prototype demonstrate a good agreement between simulation and measurements and fully prove the required scanning performance over a ±20° scan range. The prototype demonstrates a high directivity up to 46 dBi at 30 GHz and 48 dBi at 40 GHz and reflector efficiency up to 83% at 30 GHz and 77% at 40 GHz. [ABSTRACT FROM AUTHOR]

By using the second bandgap in mushroom electromagnetic bandgap (EBG) structures, a high isolation can be achieved between transmitting (TX) and receiving (RX) microstrip array antennas integrated with a millimeter-wave single-chip frequency-modulated continuous-wave (FMCW) radar. These EBG structures are much easier to manufacture at millimeter waves as compared to the first bandgap mushroom EBG structures. In addition to improving isolation, the EBG structures are also used to reduce radiation pattern ripples caused by edge diffractions due to surface waves. Experimental validation is performed on antenna level and on the radar system level. For the system-level validation, the antenna arrays have been integrated with a single-chip mm-wave FMCW radar using the bond-wire interconnect technology. Measurement results in the 57–64 GHz band show the TX–RX isolation of 40 dB, which is 15–20 dB better than the isolation between TX and RX arrays without EBG structures. In addition, the radiation pattern ripple caused by edge diffractions is reduced below 3 dB. [ABSTRACT FROM AUTHOR]

Due to errors in the phase and amplitude of element excitations in an antenna array, the array radiation pattern gets distorted. In order to derive statistical results on this distortion, specifically on determining the probability of exceeding a certain sidelobe level (SLL), it is often assumed that the magnitude of the array amplitude pattern follows a Rician distribution. It is shown that the Rician distribution implies two assumptions, and therefore, a more general Beckmann distribution is proposed to describe the distribution of the magnitude of the array amplitude pattern. Using Monte Carlo simulations, it is shown that the use of a Beckmann distribution outperforms the Rician distribution. Also, the seemingly counterintuitive result that the maximum probability of exceeding a certain SLL, in general, does not have to be at the angle where the highest sidelobe in the error-free case is located, is obtained. Due to this result, the importance of using an angular probability plot is emphasized. Furthermore, a physical explanation for the observed seemingly counterintuitive behavior is given. [ABSTRACT FROM PUBLISHER]

A novel wideband substrate integrated waveguide (SIW) antenna topology, consisting of coupled half-mode and quarter-mode SIW resonant cavities, is proposed for operation in the 60 GHz band. This innovative topology combines a considerable bandwidth enhancement and a low form factor with compatibility with low-cost printed circuit board manufacturing processes, making it excellently suited for the next generation, high data rate wireless applications. Moreover, exploiting SIW technology, a high antenna-platform isolation is obtained, enabling dense integration with active electronics without harmful coupling. The computer-aided design process yields an antenna that covers the entire 57-64 GHz IEEE 802.11ad band with a measured fractional impedance bandwidth of 11.7% (7 GHz). The measured maximum gain and radiation efficiency of the prototype are larger than 5.1 dBi and 65%, respectively, within the entire impedance bandwidth. [ABSTRACT FROM PUBLISHER]

This paper presents a closed-form expression for the Jones matrix of a dual-polarized inverted-vee dipole antenna based on the Lorentz reciprocity theorem and the basic rules of electromagnetic refraction. The expression is used to determine the intrinsic cross-polarization ratio (IXR) as a function of droop angle, position of the source in the sky, antenna height, frequency, and reflection coefficient of the underlying ground. The expression is verified using full-wave simulations with a method-of-moments solver, showing very good agreement. It explains the increase in the IXR when the antenna is placed over a perfect electric ground plane. This result is used to explain the polarization properties of the Square Kilometre Array Log-periodic Antenna. Through the LOw-Frequency ARray Low-Band Antenna (LOFAR-LBA), the importance of the size of the ground plane is explained. Finally, design consideration for high polarization purity antennas is discussed. [ABSTRACT FROM AUTHOR]

A complete functional 60-GHz BiCMOS single-chip millimeter-wave frequency-modulated continuous wave (FMCW) radar with on-chip integrated antennas is designed, realized, and experimentally validated. The chip is configured with one transmitting and two receiving antennas. A high antenna efficiency and isolation between the transmitting and receiving antennas is achieved by using a cavity-backed on-chip monopole and by optimizing the package environment. Surface-wave losses and back radiation are reduced, and a high antenna gain is obtained with small ripples in the antenna pattern by implementing special structures on the PCB of the integrated circuit package. The experimental results from the single-chip radar show that the on-chip antennas provide a gain of 2 dBi with very low back radiation. The realized antennas achieve an impedance bandwidth of more than 50% with a corresponding simulated efficiency of 45%. In addition, the proposed approach suppresses surface waves and meets the specific FMCW radar requirements, such as a more than 25-dB isolation between the transmitting and receiving antennas. [ABSTRACT FROM PUBLISHER]

This paper presents a millimeter-wave tunable hybrid-transformer-based duplexer concept with dual-antenna configuration. By using orthogonal sequentially-rotated linearly-polarized antennas and the hybrid-transformer-based duplexer, the transmitter and receiver duplexes the two antennas with orthogonal circular-polarized signals. An on-chip tuning technique using magnetic coupling is introduced to improve the isolation of the duplexer in case of impedance imbalances. An alternative duplexer with a similar principle using an on-board rat-race coupler is also proposed and designed for comparison. In order to demonstrate the isolation with practical antenna connections, prototypes have been developed to integrate the on-chip duplexer and the rat-race coupler with on-board aperture-coupled microstrip antennas with sequential rotation technique. Measurement results demonstrate the orthogonal circular polarizations for the receiver and transmitter modes on both prototypes. The achieved isolation by the on-chip tunable duplexer is better than 50 dB between 30.2 and 31.2 GHz, while the achieved isolation by the rat-race version is about 20 dB in the same bandwidth. [ABSTRACT FROM AUTHOR]

In the above article , the port and load numbering used in does not correspond properly to the definitions used in the text. The updated version of is given in this correction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]