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In this study, we designed the unit channel of beamforming transceivers for flexible access common spectrum (FACS) applications. The designed unit channel consisted of power amplifier, low noise amplifier, gain amplifier, attenuator, phase shifter, and switches. In particular, in this study, in order to miniaturize the entire system, the 180° phase shift function of the phase shifter was implemented in the power amplifier and the low noise amplifier. At this time, the area of the phase shifter was reduced without increasing the area of the power amplifier and the low noise amplifier with the 180° phase shift function. In addition, the stagger tuning technique was applied to the amplifiers constituting the unit channel to secure bandwidth. The designed unit channel was fabricated using 65-nm RFCMOS process. The operating frequency range was 22.0 GHz to 23.6 GHz. At 23.6 GHz, when the bandwidth of the 64-QAM 5G NR modulated signal was 100 MHz, 200 MHz, and 400 MHz, the output power satisfying 5.62% of EVM was measured as 9.79 dBm, 7.82 dBm, and 4.47 dBm, respectively. The noise figure (NF) in Rx mode was measured to be less than 4.88 dB.

Target source extractionis significant for improving human speech intelligibility and the speech recognition performance of computers. This study describes a method for target source extraction, called the similarity-and-independence-awarebeamformer (SIBF). The SIBF extracts the target source using a rough magnitude spectrogram as the reference signal. The advantage of the SIBF is that it can obtain a more accurate signal than the spectrogram generated by target-enhancing methods such as speech enhancement based on deep neural networks. For the extraction, we extend the framework of deflationary independent component analysis (ICA) by considering the similarities between the reference and extracted target sources, in addition to the mutual independence of all the potential sources. To solve the extraction problem by maximum-likelihood estimation, we introduce three source models that can reflect the similarities. The major contributions of this study are as follows. First, the extraction performance is improved using two methods, namely boost start for faster convergence and iterative casting for generating a more accurate reference. The effectiveness of these methods is verified through experiments using the CHiME3 dataset. Second, a concept of a fixed point pertaining to accuracy is developed. This concept facilitates understanding the relationship between the reference and SIBF output in terms of accuracy. Third, a unified formulation of the SIBF and mask-based beamformer is realized to apply the expertise of conventional BFs to the SIBF. The findings of this study can also improve the performance of the SIBF and promote research on ICA and conventional beamformers.

In this article, the design and implementation of a low-loss bidirectional microelectromechanical system (MEMS)-like passive beamformer for emerging millimeter-wave (mm-Wave) applications are illustrated. A 4 $\times $ 4 phased-array antenna (PAA) is fabricated employing the proposed beamformer for demonstration. The phase shifter (PS) embedded in the beamformer operates based on the principle of loaded-transmission line (TL) PSs. Slow wave mechanism is employed to shrink the size of the PS. The PS measurement results show the average insertion loss (IL) of 1.3 dB in all the tuning states and the IL variation is 0.9 dB. The PS provides 380° of the phase tuning range in a compact footprint area of 2.4 mm $\times $ 3 mm. The antenna array incorporates slot-coupled patch antennas with left-handed circularly polarized (LHCP) radiation. The operating frequency bandwidth of the antenna system ranges from 28 to 30 GHz to provide co-pol/X-pol discrimination of more than 12 dB for all the steering angles. Measurement results show the beam steering angular range of ± 30° in both elevation and azimuth planes. The measurement results also show the peak directivity of 18.48 dBic and the radiation efficiency of 58% at boresight at the frequency of 29 GHz. The efficiency drops 16% when the steering angle reaches the maximum. [ABSTRACT FROM AUTHOR]

Coherent plane-wave compound imaging (CPWCI) is used as alternative for conventional focused imaging (CFI) to increase frame rates linearly with the ratio number of imaging lines to steering angles. In this study, the image quality was compared between CPWCI and CFI, and the effect of steering angles (range and number) and beamforming strategies was evaluated in CPWCI. In automated breast volume scanners (ABVSs), which suffer from reduced volume rates, CPWCI might be an excellent candidate to replace CFI. Therefore, the image quality of CFI currently in ABVS and CPWCI was also compared in an in vivo breast lesion. Images were obtained by a Siemens Sequoia ultrasound system, and two transducers (14L5 and 10L4) in a CIRS multipurpose phantom (040GSE) and a breast lesion. Phantom results showed that contrast sensitivity and resolution, axial resolution, and generalized contrast-to-noise ratio (gCNR; imaging depths <45 mm) were similar for most imaging sequences. CNR (imaging depths ≥45 mm), penetration, and lateral resolution were significantly improved for CPWCI (15 angles) compared to CFI for both transducers. In CPWCI, certain combinations of steering angles and beamforming methods yielded improved gCNR (small angles and delay-and-sum) or lateral resolution (large angles and Lu’s-fk). Image quality seemed similar between CPWCI and CFI (three angles incoherent compounded as in ABVS) by visual inspection of the in vivo breast lesion images. [ABSTRACT FROM AUTHOR]

Three dimensional (3D) resource reuse is an important design requirement for the prospective sixth generation (6 G) wireless communication systems. Hence, we propose a cooperative 3D beamformer for use in 3D space. Explicitly, we harness multiple base station antennas for joint zero forcing transmit pre-coding for beaming the transmit signals in specific 3D directions. The technique advocated is judiciously configured for use in both cell-based and cell-free wireless architectures. We evaluate the performance of the proposed scheme using the metric of Volumetric Spectral Efficiency (VSE). We also characterized the performance of the scheme in terms of its spectral efficiency (SE) and Bit Error Rate (BER) through extensive simulation studies. [ABSTRACT FROM AUTHOR]

This article introduces a millimeter-wave (mm-wave) multi-band transmit (Tx) phased-array design supp- orting the fifth-generation (5G) new radio frequency range 2 (NR FR2) bands. An eight-element phased-array module is presented employing two wideband 16–52 GHz $4{\times }1$ Tx beamformer chips and tapered slot Vivaldi antenna array. The beamformer chips are designed in a SiGe BiCMOS process and flipped on a printed circuit board (PCB). The SiGe integrated circuit (IC) has four differential radio frequency (RF) beamforming channels each consisting of an active balun, analog adder-based phase shifter (PS), variable gain amplifier (VGA), and a two-stage class-AB power amplifier (PA). The RF input signal is distributed to the four channels using a compact Wilkinson network. The measured peak gain is 28.3 dB with 13.5–14.7 dBm output $P_{1{\mathrm {dB}}}$ and 14–15.4 dBm $P_{{\mathrm {sat}}}$ at 20–50 GHz. Each channel dissipates 250 mW from 2 V and 3-V supplies at $P_{1\,{\mathrm{ dB}}}$. The beamformer chip is tested using 64-QAM waveforms and achieves a data rate of 2.4 Gb/s at 5.2% rms EVM and 9.6-dBm average power. The eight-element phased-array module shows a broadband performance with excellent patterns and ±60° scanning capability and with a peak effective isotropic radiated power (EIRP) of 32–34 dBm at 19.5–51 GHz. At an EIRP of 21–22 dBm, 400-MHz 256-QAM 5G-NR compliant waveforms are transmitted with < 2.98% EVM demonstrating 5G NR FR2 operation. To the author’s knowledge, this work achieves the highest bandwidth phased array with a peak EIRP of 34 dBm enabling the construction of multi-standard/multi-band 5G phased-array systems. [ABSTRACT FROM AUTHOR]

In this paper, a beamforming scheme is proposed to maximize a secrecy multicast rate (SMR) in the multicast wiretap channel, in which the multiple unauthorized users overhear the multicast messages. The SMR is formulated by the ratio of multicast rate and information leakage in the numerator and denominator, respectively. By exploiting the SMR structure, we propose three doubly equalizing beamforming approaches: i) zero-forcing algorithm, ii) bottom-first algorithm, and iii) top-first algorithm. Depending on the algorithms, either the legitimate user channels or the unauthorized user channels are fully equalized, and the other set of channels are then equalized through a least-squares approach. While the zero-forcing algorithm optimizes the strength of legitimate user channels, the bottom-first and the top-first algorithms find the balance between the strengths of legitimate user channels and unauthorized user channels. The top-first algorithm encompasses the bottom-first algorithm, where the bottom-first algorithm encompasses the zero-forcing algorithm. Consequently, the proposed top-first algorithm outperforms the other two algorithms. The proposed top-first algorithm improves SMR by effectively preventing overhearing while sustaining almost maximum multicast rate and provide comparable SMR to the multicast rate obtained without unauthorized users. These results are verified by simulation.

This paper presents a multipath component (MPC) parameter estimator that uses a double-directional (D-D) channel sounding system in WiGig millimeter-wave bands. It employs low-cost commercial-off-the-shelf (COTS) RF transceivers capable of beam steering within an azimuth angle range of ±45°; the transmit power is approximately 31 dBm, equivalent isotropic radiated power (EIRP), including a total antenna gain of approximately 19 dBi. The half-power beam widths in the azimuth and elevation planes are 6° and 45°, respectively. A fast D-D channel acquisition in 360° full azimuth range can be achieved by developing a $4 \times 4$ multiple-input-multiple-output (MIMO) time division-multiplexing (TDM) scheme that enables simultaneous use of four antenna arrays at both sides of the transmitter and receiver. The beam switching for all combinations ( $48 \times 48 = 2304$ ) with 12 beams at each array requires less than 200 ms, excluding optional procedure related to data storage. A high-resolution MPC extraction method was developed from the D-D angular delay power spectra obtained using the sub-grid CLEAN algorithm, which is applicable when phase coherence among multiple snapshots obtained via the beam-switching measurement cannot be guaranteed. Furthermore, the operation of the developed system was validated via a measurement at 58.32 GHz in an office floor of a university laboratory. From the data analysis, the cluster properties and the corresponding scattering processes were identified.

This paper reports on the design and practical validation of monopole antenna arrays with reduced half-power beamwidth (HPBW) variation in a bandwidth (BW) greater than one octave of the RF spectrum. The HPBW variation is reduced by feeding the antenna elements with frequency-dependent feed networks. The feed networks are designed in such a way that the element power is gradually shifted from the outer elements at low frequencies to the inner elements at high frequencies. The operating principles of the proposed concept are explored through simulated examples of four-element arrays made of isotropic elements and then realistic monopole elements. Scalability of the concept to eight-element arrays is also explored using ideal simulations. For practical validation purposes, a four-element monopole antenna array and its corresponding feed network are designed and measured. The prototype resulted in a HPBW variation of 78% in a 2.6:1 BW, which is significantly reduced compared to the uniformly fed array, having a 216% variation.

This paper reports on the design of frequency-dependent feed networks for linear antenna arrays with minimum half-power beamwidth (HPBW) variation in more than one octave of the frequency spectrum. The proposed approach is based on: i) frequency-dependent power dividers that gradually shift the RF power from the outer elements of the array to the inner ones with the increase of frequency and ii) uniformly or non-uniformly-spaced directive antenna elements. The operating principles and design trade-offs of the concept are presented through ideal simulations of four- and six-element antenna arrays shaped by isotropic or directive radiators. It is shown that by employing directive antenna elements and non-uniform spacing, minimum HPBW variation can be obtained in a broad bandwidth (BW, e.g., 3:1). For physical verification purposes, two frequency-dependent feed networks and Vivaldi antenna elements were designed, manufactured, and measured. The first network feeds a uniformly-spaced four-element array of Vivaldi antennas and demonstrates a 58% HPBW variation in a 3:1 of BW. The second network feeds a non-uniformly-spaced six-element Vivaldi array and results in a 67% HPBW variation in a 2.5:1 of BW.

This work presents a 15–57 GHz multiband/ multistandard phased-array architecture for the fifth-generation (5G) new radio (NR) frequency range 2 (FR2) bands. An eight-element phased-array receive module is demonstrated based on two four-channel wideband beamformer chips designed in the SiGe BiCMOS process and flipped on a low-cost printed circuit board. The SiGe Rx chip employs RF beamforming and is designed to interface to a wideband differential Vivaldi antenna array. Each channel consists of a low-noise amplifier (LNA), active phase shifter with 5-bit resolution, variable gain amplifier (VGA), and differential-to-single-ended stage. The four channels are combined using a wideband two-stage on-chip Wilkinson network. The beamformer has a peak electronic gain of 24–25 dB and a 4.7–6.2 dB noise figure (NF) with a −29 to −24 dBm input $P_{\boldsymbol {1\,dB}}$ at 20–40 GHz. The eight-element phased-array module also achieved ultra-wideband frequency response with flat gain and low-system NF. The phased array scans ±55° with $ < -12$ -dB sidelobes demonstrating multiband operation. A 1.2-m over-the-air (OTA) link measurement using the eight-element Rx module supports 400-MHz 256-QAM OFDMA modulation with < 2.76% error vector magnitude (EVM) at multiple 5G NR FR2 bands. To the author’s knowledge, this work achieves the widest bandwidth phased array enabling the construction of multistandard systems. [ABSTRACT FROM AUTHOR]

This article presents a $16\times 16$ dual-polarized $Ku$ -band (10.7–12.7 GHz) satellite communications (SATCOM) phased-array receiver with simultaneous dual-beam reception capability. The array incorporates 64 16-channel beamformer chips and 256 dual-polarized antennas. A dual-channel low noise amplifier (LNA) is employed on every antenna to lower the system noise figure (NF) and increase the antenna gain-to-noise temperature (G/T). The phased-array is built on a low-cost printed circuit board (PCB), with an antenna spacing of $\lambda $ /2 at 12.2 GHz in an equilateral triangular grid to result in ±70° scan volume, and is capable of receiving two concurrent data-streams with a distinct direction of arrival (DOA) since it employs two 64:1 Wilkinson combiner networks. A transmit band (14–14.5 GHz) filter is also implemented between the LNA and the beamformer chip. The 256-element array has a directivity of 28 dB at mid-band with a G/T of 5 dB/K ($T_{\mathrm{ ant}}=20$ K), which results in a G/T of 11 dB/K for a 1024-element array. This array is a feasible solution for make-before-break connections and for multi-satellite reception systems, such as simultaneous television (TV) reception and connectivity. [ABSTRACT FROM AUTHOR]

This paper proposes a new technique for improving a generalized sidelobe canceller (GSC) for dual-microphone speech enhancement to be applied in an auditory device such as a hearing aid. Here, the GSC is implemented on a 32-channel uniform polyphase discrete Fourier transform filter bank, where the overall algorithm processing delay is 8 ms to meet hearing aid requirements. The proposed method can improve the fixed beamformer (FBF) and control the adaptive algorithm in the noise canceller (NC) using the phase difference obtained from dual-microphone signals. For this, spatial cues such as the phase differences are used to estimate the target-to-non-target directional signal ratio (TNR). A target-directional speech enhancing spectral gain-attenuator is calculated based on the estimated TNR, which is then incorporated to improve the FBF in the GSC. Furthermore, the weight update of the adaptive NC in the GSC is formulated using the phase difference-based TNR. The experimental results show that the auditory speech enhancement system that employs the proposed dual-microphone GSC algorithm provides better perceptual quality and intelligibility scores than conventional methods such as a beamformer, phase-error-based filter (PEF), GSC, or PEF-controlled GSC under multiple noise conditions of signal-to-noise ratio range 0-20 dB.

This article presents a low-cost and area-efficient 28-GHz CMOS phased-array beamformer chip for 5G millimeter-wave dual-polarized multiple-in-multiple-out (MIMO) (DP-MIMO) systems. A neutralized bi-directional technique is introduced in this work to reduce the chip area significantly. With the proposed technique, completely the same circuit chain is shared between the transmitter and receiver. To further minimize the area, an active bi-directional vector-summing phase shifter is also introduced. Area-efficient and high-resolution active phase shifting could be realized in both TX and RX modes. In measurement, the achieved saturated output power for the TX-mode beamformer is 15.1 dBm. The RX-mode noise figure is 4.2 dB at 28 GHz. To evaluate the over-the-air performance, 16 H+16 V sub-array modules are implemented in this work. Each of the sub-array modules consists of four 4 H+4 V chips. Two sub-array modules in this work are capable of scanning the beam from −50° to +50°. A saturated EIRP of 45.6 dBm is realized by 32 TX-mode beamformers. Within 1-m distance, a maximum SC-mode data rate of 15 Gb/s and the 5G new radio downlink packets transmission in 256-QAM could be supported by the module. A 2 × 2 DP-MIMO communication is also demonstrated with two 5G new radio 64-QAM uplink streams. Thanks to the proposed area-efficient bi-directional technique, the required core area for a single element-beamformer is only 0.58 mm2. Compact and low-cost 5G millimeter-wave MIMO systems could be realized. [ABSTRACT FROM AUTHOR]

Admission control is an effective solution to managing a wireless network with a large user set. It dynamically rejects users in bad conditions, and thereby guarantees high quality-of-service (QoS) for the others. Unfortunately, a frequently-varying admissible user set requests remarkable power to continually re-establish the transmission link. In this work, we explore the stability of admissible user set, and propose a joint long-term admission control and beamforming problem for a network with one multi-antenna base station (BS) and multiple single-antenna users. We consider the downlink transmission in a time period comprised of multiple time slices. By jointly optimizing the admissible users and the BS transmit beamformers in different time slices, we aim to balance the size of user set and the network total power cost for both QoS guarantee and user status switching. We develop two (offline and online) algorithms to find some efficient suboptimal solutions of this NP-hard problem. The offline algorithm requires all channel state information (CSI), and then solves the admissible users and beamformers in different time slices in one shot, based on successive upper-bound minimization (SUM). To support real-time data transmission, we further design an alternating direction method of multipliers (ADMM)-based online algorithm, which outputs the admissible users and beamformers in different time slices successively, utilizing the previous admissible user set, the actual value of current CSI, and the distribution of future CSI. Simulations validate the performance of the two algorithms, and show that the online algorithm is an efficient practical alternative to the offline algorithm. [ABSTRACT FROM AUTHOR]

In this article, we present a high delay resolution and all-digital transmit-beamforming circuit for use in high-frequency and wearable ultrasound imaging systems. The proposed transmit beamformer comprises an all-digital delay-locked loop (ADDLL), a cycle-based beamforming delay line (CBDL), and a pulse controller. ADDLL can provide specific digital control code for the CBDL to generate stable and suitable delays to excite array transducer elements without variations in process, voltage, and temperature. CBDL not only provides a finer delay resolution for high-frequency ultrasound imaging systems but also requires a few delay cells to maintain the duty cycle of long prorogation signals, thereby significantly reducing hardware costs. The pulse controller can adjust the number and width of output pulses to meet the requirements of different ultrasonic transducers and Doppler ultrasound color imaging. The proposed transmit beamformer uses a 0.18- $\mu \text{m}$ CMOS technology for a 30-MHz high-frequency linear array with 256 elements, and the focusing depth is from 3.5 to 8.1 mm. The measurement results indicate that the proposed transmit-beamforming design can achieve a maximum time delay of 562.6 ns with an average time resolution of 535 ps. The proposed design offers a smaller volume and finer delay resolution, and it is highly suitable for wearable ultrasound imaging systems. [ABSTRACT FROM AUTHOR]

Confocal microwave imaging is a promising medical imaging method in which the quality and the speed of imaging depend on the used beamformer. The delay-multiply-and-sum (DMAS) is a potential alternative to the golden standard method delay-and-sum (DAS). The advantages of DMAS over DAS and some other common beamformers, e.g., finer resolution and higher contrast, have been demonstrated through many papers, and the main disadvantage of this method is its high computational complexity. This letter introduces fast DMAS (FDMAS) method, which offers the same linear computational complexity as DAS while maintaining the output similar to DMAS. FDMAS computes the output of DMAS using the first and the second moments of the observations. This letter mathematically proves the equality between the proposed method and DMAS, and also demonstrates the equality of these methods’ results using real random values and experimental complex data. Moreover, the lower computational load order of the proposed method in comparison to the DMAS is shown. As a conclusion, the FDMAS technique provides the advantages of DMAS without encountering the computational complexity issue. It is noteworthy that the FDMAS is an iterative method and thereby can update the results by adding new observations without carrying out any unnecessary computations. [ABSTRACT FROM AUTHOR]

This second part of two articles’ sequence presents the detailed numerical analysis of electrical and noise parameters of a subarray of the Giant Ukrainian Radio Telescope (GURT) designed for operation in the frequency range of 8–80 MHz. The theoretical model of the subarray and calculation technique of its parameters developed in the first part is used. Frequency behaviors of the absorption area, radiation efficiency, and system noise temperature budget of the subarray are studied. Special attention is paid to the subarray sensitivity given in terms of sky noise dominance (SND) and system-equivalent flux density (SEFD). The calculation results show that strong mutual coupling between subarray elements enables a significant increase in the subarray SND and enhancing overall its performance. The frequency dependences of the system noise temperature for 23 beams of the subarray, obtained by in situ measurements, are presented. A good agreement between the measured and calculated results well enough validates the subarray theoretical model. [ABSTRACT FROM AUTHOR]

The new Giant Ukrainian Radio Telescope (GURT) intended for operation in 8–80 MHz range is now under construction. It employs an active phased array antenna composed of many dipole subarrays, several of which have been implemented and now are used for radio astronomy observations. In this two-part paper, the electrical and noise parameters of the subarray are studied by numerical and experimental ways. In this part, a theoretical model of the subarray based on the wave theory of noisy multiport networks that takes into account the mutual coupling in the dipole array placed over imperfect ground and the correlation between all existing noise sources is proposed. It is assumed that the initial parameters for this model should be obtained using the correct electromagnetic and circuit simulation. A technique for using of this model to calculate the effective area, radiation efficiency, internal and external noise temperatures, as well as sensitivity of the subarray in terms of system equivalent flux density (SEFD) for all possible beam directions in the frequency band of the GURT radio telescope is described. [ABSTRACT FROM AUTHOR]

In this paper, shaped continuous parallel plate waveguide delay lenses are proposed. The previous configurations introduced by the authors displayed a residual side lobe imbalance, showing the limitations of elliptical delay lens profiles, derived from a starting bifocal constrained lens. Polynomial profiles are proposed here as a way to enhance the scanning performance and the pattern shape. Optimized configurations demonstrate a reduction in the phase aberration levels over a large scanning range ([−30°, 30°]). The associated radiation patterns demonstrate lower and more balanced first side lobe levels (SLLs) ($\cong -18$ dB), as compared to the previous elliptical approach ($\cong -13.2$ dB). A validation has been proposed through the manufacturing and test of a prototype over the down-link Ka-band ([27.5–31] GHz). Excellent radiation performance [half-power beamwidth (HPBW), SLL] has been experimentally obtained over a wide angular range ([−31.5°, 31.5°]), including low scanning loss and high radiation stability over the entire frequency range. High radiation efficiencies are demonstrated with this fully metallic design, particularly suitable for space applications. The mechanical simplicity offered by the concept is also quite attractive for low-cost multi-beam platforms. [ABSTRACT FROM AUTHOR]

A simplified beamforming architecture using a wavelength-selective optical true time delay (OTTD) module is proposed for phased array antenna (PAA) systems. Based on diffraction order multiplexing of an arrayed waveguide grating (AWG), the beamformer can realize multiple simultaneous time delays with only one OTTD module. We design, fabricate, and characterize a compact integrated optical beamformer using this structure for an eight-element X-band PAA system. The time delays generated by the fabricated beamformer are measured to be in the range from 0 to 278 ps in 5.7 ps increments of eight diffraction orders. The measured overall variation in the insertion loss of this device is less than 1.85 dB from 1527 to 1607 nm. The experimental results demonstrate that the proposed architecture can offer many advantages, such as multibeam capability, low insertion loss, a small footprint, and high resolution. [ABSTRACT FROM AUTHOR]

A method for designing multi-input, multi-output metamaterial devices is presented. The devices are 2-D anisotropic, inhomogeneous media. The design technique consists of a custom finite-element method solver coupled to a constrained, nonlinear minimization algorithm. The design method has advantages over existing metamaterial design methods such as transformation optics, in that material constraints can be imposed and multi-input, multi-output functionality allowed. Transformation optics devices only achieve multi-input, multi-output functionality through geometrical symmetry. The gradient-based optimization method employed in the metamaterial design process is fast given that an analytic expression for the gradient of the cost function can be written. The proposed technique is demonstrated through the design of two beamforming devices. A commercial full-wave solver is used to validate the design approach. The constitutive parameters of these 2-D designs can be implemented using printed-circuit board metamaterials, such as tensor transmission-line metamaterials. [ABSTRACT FROM AUTHOR]

An analytical model based on geometrical optics is proposed to design and analyze continuous parallel plate waveguide (PPW) lens-like antennas. The proposed design is based on a transversal PPW section working as a lens-like beamformer. By simplifying the propagation inside this transversal section, a bifocal constrained lens model is first defined; it provides a relevant starting point to design the proposed beamformer. A refined model based on ray tracing and with an enhanced performance prediction is achieved by accounting the wave propagation inside the transversal cavity. The numerical analysis of phase aberrations and radiation demonstrate the performance of the proposed beamformer. The results of the ray-tracing model are in a very good agreement with the corresponding full-wave model, while providing a significant reduction in the computational effort, making the proposed model more suitable for advanced optimization processes. [ABSTRACT FROM AUTHOR]

A broadband, seven-port beamformer is designed and fabricated using printed-circuit, tensor transmission-line metamaterials. The beamformer is first modeled as a 2-D medium with an unknown inhomogeneous, anisotropic material distribution: scalar permittivity $\epsilon _{z}(x,y)$ and tensor permeability $\bar {\bar {\mu }}(x,y)$. Then, a recently developed optimization procedure is employed to determine $\epsilon _{z}(x,y)$ and $\bar {\bar {\mu }}(x,y)$ and subsequently realized using tensor transmission-line metamaterials. The beamformer is designed to switch beams in 10° increments from −30° to 30° in azimuth, over a broad range of frequencies. Measurement results exhibit good agreement with the prescribed design goals. The reported beamformer offers several advantages compared with traditional beamformers, including the stipulation of arbitrary output fields, flat input/output interfaces, and a broad bandwidth performance. [ABSTRACT FROM AUTHOR]

Physical layer security has drawn significant attention in recent years because of its advancement in preventing confidential information leakage to eavesdroppers. In this paper, we focus on secure beamformer designs in multiuser multi-input multi-output (MU-MIMO) systems with a multi-antenna eavesdropper attempting to overhear the confidential information of a particular user. Unlike the existing work, we aim to exploit the inherent multi-user interference to disrupt the reception of the eavesdropper and enhance the security of wireless communications. Particularly, utilizing practical signal-to-interference-noise metrics, the objective of the secure beamformer design is to minimize the eavesdropper's SINR, while providing legitimate users with required prespecified SINRs to guarantee the qualify of service. We propose secure beamformer designs for both downlink and uplink transmissions, under the conditions of known and unknown eavesdropper's channels, respectively. With the proposed secure beamformers, the multiuser signal behaves like the artificial noise or distributed friendly jamming, which can further degrade the reception of the eavesdropper. Extensive simulation studies confirm our analytical performance predictions and illustrate the advantages of proposed beamformer designs for secure MU-MIMO transmissions. [ABSTRACT FROM AUTHOR]

We propose an analog delay line (ADL) that adopts a current-splitting method (CSM) to reduce power consumption. The proposed ADL employs a pipelined sample-and-hold architecture and includes a buffer in the analog memory cell to prevent a charge sharing problem. The CSM reduces power consumption without distorting the sampled data by dividing the current source of the buffer into a holding current source and a buffering current source, which are, respectively, located inside and outside of the analog memory cell. The simulated power consumption of the proposed ADL without and with the CSM is 1080 and $90~{\mu }\text{W}$ , respectively, indicating that the CSM reduces power consumption by 91.7%. The proposed ADL was fabricated using a 0.18- ${\mu }\text{m}$ CMOS process with a 1.8-V supply voltage and occupies an active area of $120 \times 140~{ \mu }\text{m}^{ 2}$. The sampling capacitor in the analog memory cell was implemented with MOS capacitors instead of metal-insulator-metal capacitors, resulting in an area per unit delay of the proposed ADL of only $600~{ \mu }\text{m}^{ 2}$ , which is much smaller than that in prior works. The measurement results show that the delay of the proposed ADL is accurately controlled from 25 to 475 ns with a unit delay step of 25 ns at a sampling frequency of 40 MHz. [ABSTRACT FROM AUTHOR]

We propose a beamforming method that minimizes the $\ell _1$ norm of a beamformer output vector under the same distortionless constraint as that of the conventional minimum power distortionless response (MPDR) beamformer. Using the $\ell _1$ norm makes the beamformer output sparse. This leads to reducing the residual elements of the interference signal. In addition, the sensitivity of the proposed beamformer can be controlled by adding a norm constraint as in the MPDR beamformer. The proposed method improved the signal-to-interference-noise ratio by 7 dB from that of the MPDR beamformer for reverberation time $T_{60}$ = 300 ms in a simulation. [ABSTRACT FROM AUTHOR]

This paper presents a low-complexity, cost-effective digital beamformer architecture for a high-frequency ultrasound imaging system. The proposed beamformer uses a lookup table and linear interpolation methods for computing the dynamic receive focusing delays and a postfiltering technique to minimize hardware complexity. In the postfiltering technique, channel radio-frequency data having the same fractional delay (i.e., 16f0 resolution) are aggregated prior to interpolation. Thus, only four polyphase structure filters are required in the developed beamformer. In addition, a quadrature bandpass filter that generates an analytic signal is utilized as an interpolation filter; this allows decimation during beam formation and a reduction in computational complexity. The proposed method was evaluated through a 20- \mu \textm wire phantom experiment, and the −6-dB lateral and axial resolutions obtained therein were measured and compared with those obtained using a conventional method. The same lateral (165 \mu \textm ) and axial (80 \mu \textm ) resolutions at a depth of 5.6 mm were obtained using both the methods, and the proposed method could reduce the beamforming points (i.e., computational complexity) by a factor of the decimation factor (≥4). Images from an excised bovine eye were captured; they showed that the proposed beamformer identified fine anatomical structures such as cornea or iris without compromising the spatial resolution and reduced the computational complexity. [ABSTRACT FROM AUTHOR]

A nasogastric tube is commonly used to pour nutrients into the stomachs of patients who have difficulty swallowing in order to provide them with the required nutrition. However, it is possible to inadvertently insert the tube into the lungs. Thus, a method of obtaining the tip position of the tube is desired. In this paper, we use predata of magnetoimpedance (MI) sensors to estimate the position of the magnet attached to the tube tip using a minimum variance beamformer. Experimental results show that the position estimation error is <10 mm even when the distance from the MI sensors is 150 mm using the predata, whereas the error exceeds 10 mm when the predata is not used. These results suggest that the proposed method is a promising method for hospital applications. [ABSTRACT FROM AUTHOR]

This letter proposes a new algorithm for solving the optimal zero-forcing beamforming problem that maximizes the user achievable rate with restriction on the per-antenna element power constraints. An accelerated gradient method with step size search is proposed for solving the problem. For each iteration of the gradient approach, a quick one dimensional search is employed to obtain the step size. The advantage of the step-size search is that it is relatively fast and requires only a few calculations of the objective function. Design examples show that the proposed algorithm converges faster than the gradient approach and the accelerated gradient approach with a constant step size while achieving a low computational complexity. [ABSTRACT FROM AUTHOR]

A dual-circular polarized dielectric lens-loaded cavity-backed four-arm sinuous antenna operating in the frequency range from 600 MHz to 2.5 GHz is proposed. The antenna is built without lossy absorber with several design aspects discussed, including substrate/lens loadings, effects of backing, and impedance match to 50 \Omega. Fabricated prototype is integrated with a dual-CP beamformer network. The complete configuration is unidirectional, flush-mountable, has input \VSWR < \1.5, isolation> 7 dB, boresight realized gain> 3.9 dBic, boresight axial ratio< 2.3 dB, and Wobble of Wave (WoW) at the 3-dB elevation cut< 2 dB. Through a high power test, the antenna is shown to be capable of transmitting 200 W of CW power with a maximum temperature rise of 60~^\circ\!C without any external cooling in the operating frequency range. Average overall efficiency of 70% is demonstrated. Two other high-power capable ferrite-tile-backed sinuous antennas are also fabricated to fully showcase unique benefits of the proposed antenna. Presented results should pave the way for the use of sinuous as a transmit antenna in many nontraditional applications requiring higher radiated powers and efficient high-quality dual-polarized patterns over wide frequency ranges. [ABSTRACT FROM PUBLISHER]

This work focuses on the relationship between real and synthetic aperture radiometers giving a general and common mathematical framework for both of them. It will be demonstrated that a real aperture radiometer array can be understood as a synthetic aperture one, with a high level of redundancy. Therefore, all the recent results from synthetic aperture radiometry can be translated to real aperture radiometer arrays. This fact can be used to create beamforming arrays in a new way. To do this, the beamforming array equation will be written in terms of cross-correlations between all pair of antenna signals (visibility samples). By properly combining the visibility samples, a new type of digital beamforming radiometer can be implemented, which will benefit from the high calibration accuracy achieved in synthetic aperture radiometers (e.g., The Y-shaped MIRAS radiometer used in the Soil Moisture and Ocean Salinity mission of the European Space Agency) and the flexibility to electronically steer the beam. [ABSTRACT FROM AUTHOR]

This paper shows that among frequency independent (FI) conformal antennas, the modulated arm width (MAW) spiral has the simplest architecture for measuring both polarization and angle-of-arrival (AOA) instantaneously if frequency is known. The theory, design and performance of equiangular four-arm MAW spiral antennas when utilizing both sum modes (\pm 1) and difference mode (+2) for direction-finding applications are discussed. It is shown that simultaneous dual-polarization and multi-mode capability is not achievable in more commonly-used four-arm spiral and sinuous antennas. While the co-polarized modes 1, 2 and 3 are well-researched with single-polarized four-arm equiangular spirals, they have not been utilized or controlled on a four-arm MAW spiral. Effects of modulation period on cross-polarization, pattern symmetry, gain, and impedance for all three pattern modes are investigated. The studies are carried out using full-wave modeling and a prototype MAW geometry is built and evaluated with a beamformer to demonstrate its wideband, dual-polarized, multi-mode capability. [ABSTRACT FROM PUBLISHER]

A Ku-, K-, and Ka-band phase shifter for beamforming applications is presented in this paper. An analysis showing the effect of loading conditions on quadrature phase accuracy in a simple poly-phase filter is carried out. Based on the analysis, a novel quadrature phase shifter (QPS) with inductive load is proposed. Sign-selection and vector addition is performed in two stages to lower supply voltage. The proposed phase shifter is fabricated in a 0.18-\mu\ m SiGe BiCMOS process and occupies an area of \520\ \mu\ m\times \370\ \mu\ m. The proposed QPS has a maximum phase error of 6.38^\circ over 15–35 GHz while maintaining an amplitude imbalance less than 2 dB. When combined into a 4-bit phase shifter, the root mean square (rms) gain error is less than 2.2 dB and the rms phase error is less than 13^\circ over 15–35 GHz. The phase shifter thus achieves a full 360^\circ phase-shift range with 22.5^\circ phase resolution. The total power consumption is 14 mA from a 1.8-V power supply. The phase shifter achieves an input P1dB of -6.25 dBm. The measured phase-shifting fractional bandwidth of 87% is the highest reported thus far in the literature for SiGe BiCMOS implementation. [ABSTRACT FROM PUBLISHER]

For over two decades, speech control mechanisms have been widely applied in manufacturing systems such as factory automation, warehouse automation, and industrial robotic control for over two decades. To implement speech controls, a commercial speech recognizer is used as the interface between users and the automation system. However, users' commands are often contaminated by environmental noise which degrades the performance of speech recognition for controlling automation systems. This paper presents a multichannel signal enhancement methodology to improve the performance of commercial speech recognizers. The proposed methodology aims to optimize speech recognition accuracy of a commercial speech recognizer in a noisy environment based on a beamformer, which is developed by an intelligent particle swarm optimization. It overcomes the limitation of the existing signal enhancement approaches whereby the parameters inside commercial speech recognizers are required to be tuned, which is impossible in a real-world situation. Also, it overcomes the limitation of the existing optimization algorithm including gradient descent methods, genetic algorithms and classical particle swarm optimization that are unlikely to develop optimal beamformers for maximizing speech recognition accuracy. The performance of the proposed methodology was evaluated by developing beamformers for a commercial speech recognizer, which was implemented on warehouse automation. Results indicate a significant improvement regarding speech recognition accuracy. [ABSTRACT FROM PUBLISHER]

In beamformer design, the microphone array configuration is often prescribed and the filter coefficients are varied in order to improve on the noise reduction performance. However, the positions of the microphone elements play an important role in the overall performance and should be optimized at the same time. This problem is addressed in this paper. In order to understand the performance improvement through location movements, we first look at the design with an infinite filter length, which gives the performance limit for finite filter length designs. When the filter length is finite, both the filter coefficients and the placement of the microphone array are decision variables. In both situations, the problems can be formulated as constrained optimization problems. As the filter length increases, we show that the performance converges quickly to the limit. For illustration, two numerical examples are solved. Comparing with several popular configurations, we show that the performance of the optimized configuration improves significantly. [ABSTRACT FROM PUBLISHER]

In this paper, the design of near-field broadband beamformer is considered. The idea is to design the beamformer filter coefficients such that the error between the actual response and the desired response is minimized. This problem can be formulated as a minimax optimization problem and can be transformed into a linear semi-definite programming problem. Interior point algorithm can then be applied after discretization. However, if the dimension of the problem is high, the number of discrete points of the specified region and consequently the dimension of the resultant constraint matrix is high. This high dimension provides a difficulty when directly employing interior point algorithm. Since it results in a large size problem, this problem is considered in this paper. To reduce the computational complexity and memory usage, a two-stage method has been proposed. In the first stage, by using an infinite length filter formulation, an infinite length limit for the original problem is obtained. Then, based on that limit, a reduced problem with a finite filter length is found. The computational complexity of this method is derived. It provides a significant reduction compared to a direct solution of the original problem. It is shown that as the filter length increases, the approximative problem comes close to the optimal infinite solution. Furthermore, we demonstrate with examples the close correspondence between proposed design and optimal design. Also the superiority of the suggested method is illustrated in a three-dimensional beamformer design, where the direct method can only design broadband beamformer of very short filter lengths. [ABSTRACT FROM PUBLISHER]

Many tomographic source localization algorithms used in biomagnetic imaging assume, explicitly or sometimes implicitly, that the source activity at different brain locations are either independent or that the correlation structure between sources is known. Among these algorithms is a class of adaptive spatial filters known as beamformers, which have superior spatiotemporal resolution abilities. The performance of beamformers is robust to weakly coherent sources. However, these algorithms are extremely sensitive to the presence of strongly coherent sources. A frequent mode of failure in beamformers occurs with reconstruction of auditory evoked fields (AEFs), in which bilateral auditory cortices are highly coherent in their activation. Here, we present a novel beamformer that suppresses activation from regions with interfering coherent sources. First, a volume containing the interfering sources is defined. The lead field matrix for this volume is computed and reduced into a few significant columns using singular value decomposition (SVD). A vector beamformer is then constructed by rejecting the contribution of sources in the suppression region while allowing for source reconstruction at other specified regions. Performance of this algorithm was first validated with simulated data. Subsequent tests of this modified beamformer were performed on bilateral AEF data. An unmodified vector beamformer using whole head coverage misplaces the source medially. After defining a suppression region containing the temporal cortex on one side, the described method consistently results in clear focal activations at expected regions of the contralateral superior temporal plane. [ABSTRACT FROM AUTHOR]

Below a specific threshold signal-to-noise ratio (SNR), the mean-squared error (MSE) performance of signal parameter estimates derived from the Capon algorithm degrades swiftly. Prediction of this threshold SNR point is of practical significance for robust system design and analysis. The exact pairwise error probabilities for the Capon (and Bartlett) algorithm, derived herein, are given by simple finite sums involving no numerical integration, include finite sample effects, and hold for an arbitrary colored data covariance. Via an adaptation of an interval error based method, these error probabilities, along with the local error MSE predictions of Vaidyanathan and Buckley, facilitate accurate prediction of the Capon threshold region MSE performance for an arbitrary number of well separated sources, circumventing the need for numerous Monte Carlo simulations. A large sample closed-form approximation for the Capon threshold SNR is provided for uniform linear arrays. A new, exact, two-point measure of the probability of resolution for the Capon algorithm, that includes the deleterious effects of signal model mismatch, is a serendipitous byproduct of this analysis that predicts the SNRs required for closely spaced sources to be mutually resolvable by the Capon algorithm. Last, a general strategy is provided for obtaining accurate MSE predictions that account for signal model mismatch. [ABSTRACT FROM AUTHOR]

In this paper, architecture and circuit design of a beamforming baseband receiver lC for uplink W-CDMA communication systems is presented. In the proposed receiver, a four-antenna-element beamformer and a four-finger RAKE combiner are adopted to exploit both spatial diversity and path diversity receiving. To minimize the size and power consumption of the receiver, a latch-based 1024-tap complex delay line is custom designed for the matched filter in the channel estimation circuit. The receiver chip was fabricated in a 0.35-µm n-well CMOS single-poly quadruple-metal technology. The minimum supply voltage with the chip running at the nominal 15.36-MHz clock rate is measured at 2.15 V. The chip has an area of 6 mm by 6.3 mm and a power consumption of about 123 mW.

In Digital TV Broadcasting, the Scheme of Single Frequency Network (SFN) has nontrivial advantages. By forming a SFN, a broadcasting system is able to serve an arbitrary large area with the same program within the same frequency block. At the mean time, the SFN structure provides the receiver with a potential of yielding the space diversity gain, while the power in every single transmitter is not increased. However, there are heavy artificial multipath propagation in the area covered by the SFN broadcasting. Traditionally, a transversal equalizer is used at the receiver to remove the SFN interference. The equalizer always cannot converge properly due to the over-long time delay and the over-large magnitude of the different paths from each transmitter of the SFN. To solve the problem, a new model based on the MIMO structure of the SFN is proposed in this paper, where the signal's space information is exploited. With the model in mind, a new receiving scheme is derived. By using a beamformer, signals with different incident angles are separated, so the problem caused by the over-long delay and the over-large magnitude is avoided. A bank of parallel sub-filters are used to remove the residual multipath spread. The space diversity gain is obtained at the output of a combiner. [ABSTRACT FROM AUTHOR]

We report a first demonstration of a fiber-optic beamformer for independent two-dimensional (2-D) true time-delay steering of a transmitter array. The fiber-optic beamformer is based on a simple dispersive prism optical delay approach, with separate azimuth and elevation control stages. The azimuth dispersive prism stage includes an amount of dispersion in each link proportional to the corresponding column position in the array. The microwave signals, properly time-delayed for azimuth steering, are amplified and serve as inputs to identical dispersive prisms feeding the elements in each column. The elevation dispersive prism stages include an amount of dispersion in each link proportional to the corresponding row position in the array. Each time-delayed microwave signal feeds a single flared-notch element in a 4/spl times/4 array. The 2-D array pattern measurements in an anechoic chamber clearly demonstrate independent /spl plusmn/30/spl deg/ azimuth and /spl plusmn/30/spl deg/ elevation steering. There is no observed squint over the microwave-component determined bandwidth of 6-18 GHz. [ABSTRACT FROM AUTHOR]