Separate Sub-arrays Research Articles

Octave-Band Four-Beam Antenna Arrays with Stable Beam Direction Fed by Broadband 4 × 4 Butler Matrix

A novel concept of four-beam antenna arrays operating in a one-octave frequency range that allows stable beam directions and beamwidths to be achieved is proposed. As shown, such radiation patterns can be obtained when radiating elements are appropriately spaced and fed by a broadband 4 × 4 Butler matrix with directional filters connected to its outputs. In this solution, broadband radiating elements are arranged in such a way that, for the lower and upper frequencies, two separate subarrays can be distinguished, each one consisting of identically arranged radiating elements. The subarrays are fed by a broadband Butler matrix at the output to which an appropriate feeding network based on directional filters is connected. These filters ensure smooth signal switching across the operational bandwidth between elements utilized at lower and higher frequency bands. Therefore, as shown, it is possible to control both beamwidths and beam directions of the resulting multi-beam antenna arrays. Moreover, two different concepts of the feeding network connected in between the Butler matrix and radiating elements for lowering the sidelobes are discussed. The theoretical analyses of the proposed antenna arrays are shown and confirmed by measurements of the developed two-antenna arrays consisting of eight and twelve radiating elements, operating in a 2–4 GHz frequency range.

Filtering Antennas: Design Methods and Recent Developments

With wireless communication technologies continually and rapidly developing, RF front-end systems are experiencing a profound evolution toward the goal of highly integrated and miniaturized RF front ends with improved performance. Traditionally, passive components in the RF front end, such as filters, antennas, and duplexers, have been designed individually and cascaded through a 50-Ω interface. This inevitably leads to bulky physical dimensions and complex circuits, high insertion loss, and signal distortion, especially at the band edges. In multiband or multistandard communication systems, multiple operating bands of the base station antenna are normally achieved using several separate subarrays operating at different frequencies, which can cause serious interference among different bands for various services due to the limited space on the antenna platform. Highly integrated multifunctional RF front ends would provide a high-efficiency solution to those advanced and miniaturized wireless systems. As the key components in any RF front-end system, the integration of filters and antennas can significantly improve the frequency selectivity and bandwidth; stability of the in-band gain, out-of-band rejection, and system efficiency. They have therefore received much research interest and opened up a broad avenue for antenna R&D in recent years.

The MeerKAT telescope as a pulsar facility: System verification and early science results from MeerTime

AbstractWe describe system verification tests and early science results from the pulsar processor (PTUSE) developed for the newly commissioned 64-dish SARAO MeerKAT radio telescope in South Africa. MeerKAT is a high-gain (${\sim}2.8\,\mbox{K Jy}^{-1}$) low-system temperature (${\sim}18\,\mbox{K at }20\,\mbox{cm}$) radio array that currently operates at 580–1 670 MHz and can produce tied-array beams suitable for pulsar observations. This paper presents results from the MeerTime Large Survey Project and commissioning tests with PTUSE. Highlights include observations of the double pulsar$\mbox{J}0737{-}3039\mbox{A}$, pulse profiles from 34 millisecond pulsars (MSPs) from a single 2.5-h observation of the Globular cluster Terzan 5, the rotation measure of Ter5O, a 420-sigma giant pulse from the Large Magellanic Cloud pulsar PSR$\mbox{J}0540{-}6919$, and nulling identified in the slow pulsar PSR J0633–2015. One of the key design specifications for MeerKAT was absolute timing errors of less than 5 ns using their novel precise time system. Our timing of two bright MSPs confirm that MeerKAT delivers exceptional timing. PSR$\mbox{J}2241{-}5236$exhibits a jitter limit of$<4\,\mbox{ns h}^{-1}$whilst timing of PSR$\mbox{J}1909{-}3744$over almost 11 months yields an rms residual of 66 ns with only 4 min integrations. Our results confirm that the MeerKAT is an exceptional pulsar telescope. The array can be split into four separate sub-arrays to time over 1 000 pulsars per day and the future deployment of S-band (1 750–3 500 MHz) receivers will further enhance its capabilities.

Joint DOD and DOA Estimation for Bistatic MIMO Radar in Unknown Correlated Noise

In this paper, joint direction-of-departure (DOD) and direction-of-arrival (DOA) estimation for bistatic multiple-input–multi-output (MIMO) radar in an unknown spatially correlated noise environment is investigated. The signal model is based on the assumption that the waveforms are transmitted by two separated subarrays having $M_1$ and $M_2$ sensors and received by two separated subarrays having $N_1$ and $N_2$ sensors, respectively. The received data are pulse-compressed using a matching matrix consisting of $M=M_1+M_2$ orthogonally transmitted waveforms. The joint covariance matrix of unknown correlated noise is analyzed. A novel algorithm is proposed by jointly estimating the DOD and DOA with transmitter and receiver subarrays in unknown noise. The joint estimation algorithm is based on the canonical correlation decomposition (CCD) and exploits the shift-invariance properties in the Kronecker product structure of each column of the various steering matrices. The estimated DOA and DOD can be automatically paired correspondingly. In addition, the formulas of stochastic Cramer–Rao bounds (CRB) for DOD and DOA estimation are derived. Simulations show that our method can effectively improve the performance of estimation in unknown correlated noise environments and is insensitive to having different noise environments in the two subarrays.

Unitary dual-resolution ESPRIT for joint DOD and DOA estimation in bistatic MIMO radar

This paper investigates the problem of joint direction of departure (DOD) and direction of arrival (DOA) estimation in bistatic MIMO radar. A new bistatic MIMO array, both the transmit array and the receive array consist of two separated subarrays with dual baselines is proposed, in contrast to the modeling of both the transmit array and the receive array to be uniform linear array in the existing research literature. And a new joint DOD and DOA estimation algorithm, called unitary dual-resolution ESPRIT, is proposed. First, the short baseline rotational invariance within subarray yields non-ambiguous coarse DOD and DOA estimation. Then the long baseline rotational invariance between subarray yields high accuracy but cyclically ambiguous DOD and DOA estimation. Last, the combination of both estimates yield high accuracy and non-ambiguous DOD and DOA estimation. Moreover, we propose to utilize the properties of centro-Hermitian matrices to transform the complex-valued computations into real-valued computations throughout the whole process. The proposed algorithm gives significant improvement in DOD and DOA estimation performance, with automatic pairing and without extra antennas and computational complexity compared with the conventional algorithms. Simulation results verify the effectiveness of the proposed algorithm.

Application of MIMO technology in wideband millimeter range wireless communications systems

A concept of using MIMO technology in millimeter range wireless communications systems with orthogonal frequency division multiplexing is considered. The concept is based on dividing transmitting and receiving multi-element antenna arrays into separate sub-arrays with analogue radiation pattern shaping and on using two most powerful space sub-channels for information transmission. Sequence and structure of transmitted packets between transceivers are suggested that allow for obtaining information on communications channel based on additional training sequences without feedback channel. Modeling results of communications system’s operation in conditions of multipath frequency-selective fading channel are presented.

Deubiquitylase, DeSUMOylase, and DeISGylase Activity Microarrays for Assay of Substrate Preference and Functional Modifiers

Microarray-based proteomics expanded the information potential of DNA arrays to the level of protein translation and interaction, but so far, not much beyond. Although enzymatic activity from immobilized proteins has been reliably studied using surface plasmon resonance, a microarray of catalytically competent enzymes would facilitate high throughput, parallel study of their function. The ability to localize activity from soluble substrates has frustrated development of such an array. Here, we report the novel use of previously developed, highly specific suicide substrates for three families of enzymes: deubiquitylases, deSUMOylases, and deISGylases. We show specificity of each family to its cognate substrate, and demonstrate utility of the array in a secondary screen of small molecule inhibitors.

Cross correlation and energy detection in multiarray processing

Multiple arrays can be modeled as a single array that is composed of separate subarrays. Likelihood ratio testing, maximum likelihood delay-Doppler estimation, and maximum likelihood estimation of signal and noise parameters are applied to such a model in order to determine whether cross correlation should be used alone or in conjunction with other operations. The results indicate that cross correlation alone is usually suboptimum. Detection or combined detection-estimation should use a weighted sum of pairwise cross correlations between subarrays and energy detection at each subarray. Subarray cross correlation alone is only optimum for certain estimation problems and time windows. Cross-correlator and energy detector outputs at different frequencies should be linearly combined using frequency-dependent weighting functions. These functions are obtained for multiarray processing. For the special case of two-array cross correlation, the weighting function is the same as the one obtained by Knapp and Carter.

On the influence of unequal sub-array spacing configurations on source localization and the similarity with multipath ranging

The influence of varied linear array configurations on passive ranging is determined when imperfect measurements of the time delays between the sub-arrays are available. The exact bias and farfield bias and variance relations on the source range estimates are derived as a function on unequal sub-array separation. The results are contrasted with those found in the literature on equally separated sub-arrays to highlight the sensitivity and resulting degradation in performance. It is found, for instance, that the range bias more than doubles when the internal sub-array is moved from the midpoint to the quarter-point from either end sub-arrays and more than quadruples when it is moved from the quarter-point to the one-eighth-point. Since the range variance is related to the true range and to the incurred bias, it degrades much more rapidly. The commonality between array ranging and multipath ranging is also developed for various channels of interests. The optimal placement for the receiving sensor in multipath channels is derived. Though it turns out that the same relations apply to both ranging problems, the existence of a multipath channel will support a longer ranging capability with the baseline now effectively determined by such large parameters as water depth, receiver, and source depths. Such results enable the merger of multisensor data according to their individual merits and the provision for a credence estimate of the source range choice.

Multidimensional maximum-likelihood processing of a large aperture seismic array

The experimental Large Aperture Seismic Array (LASA) represents an attempt to improve the capability to monitor underground nuclear weapons tests and small earthquakes by making a large extrapolation in the existing art of building arrays of spaced and interconnected seismic transducers. The LASA is roughly equivalent to 21 separate subarrays, each consisting of 25 sensors, spread over an aperture of 200 km. The present work considers the problem of designing a linear filter which combines the outputs of the 25 sensors in a subarray so as to suppress the noise without distorting the signal, or event. This filter provides a minimum-variance unbiased estimate of the signal which is the same as the maximum-likelihood estimate of the signal if the noise is a multidimensional Gaussian process. An extensive discussion of the theory of multidimensional maximum-likelihood processing is given. A computer program implementation of the maximum-likelihood filter is presented which employs the cross-correlation matrix of noise measured just prior to the arrival of the event. This time-domain synthesis procedure requires relatively large amounts of computer time to synthesize the filter, and is quite sensitive to the assumption of noise stationarity. The asymptotic theory of maximum-likelihood filtering is also given. An asymptotically optimum frequency-domain synthesis technique is given for two-sided multidimensional filters. This procedure is well suited to machine computation and has the advantage with respect to the time-domain procedure of requiring about 10 times less computation time. A description of a computer program implementation of the frequency-domain synthesis method is given which employs the spectral matrix of the noise estimated just before the arrival of the event. The experimental results obtained by processing several events recorded at the LASA are presented, as well as a comparison of the performance of the frequency-domain method relative to the time-domain synthesis technique. It is found that the signal-to-noise improvement given by the frequency-domain procedure is within 2 dB of the gain obtained with the time-domain procedure, and that the frequency-domain method is relatively insensitive to the assumption of noise stationarity.