A checkered network for implementing arbitrary overlapped feed networks

Existing overlapped subarray techniques for beamforming arrays aim to realize flat-topped subarray radiation patterns, where pattern synthesis is constrained by the hardware configuration. A generalized framework for designing compressive arrays with unconstrained feed network responses has recently been proposed with promising results, but no hardware implementation has been proposed. A planar checkered network of directional couplers and fixed phase shifters is proposed for implementing arbitrary complex-valued feed network responses, including completely overlapped networks. An algorithm is proposed for realizing a desired response while minimizing the range of coupling ratios and phase shifts required. The technique is validated by a comparison to the standard 4 x 4 Butler matrix implementation, and its versatility illustrated by sharing an eight-element aperture between three independently designed nonscanning arrays. A manufactured microstrip 2 x 4 compressive array feed network achieves the desired aperture illuminations to within 0.6 dB and 5.2° at 3.15 GHz, and to within 1.4 dB and 10.3° across the impedance bandwidth of 4.5%.The National Research Foundation of South Africa (NRF) under Grant 85845http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=22hj2020Electrical, Electronic and Computer Engineerin

Design and analysis of a proof-of-concept checkered-network compressive array

Compressive arrays have recently been proposed as a new technique for reducing the number of controls in a beamforming system for a given array aperture, promising improved performance over existing thinned-array and subarray techniques. Checkered networks, feed networks consisting of interconnected couplers and fixed phase shifters, have been suggested for realizing the required overlapped subarrays. Although a checkered network has previously been implemented in microstrip, an integrated compressive array, comprising both the antenna elements and the feed network, is required to demonstrate the practical feasibility of such systems. Results for the first successfully manufactured checkered-network compressive array with integrated antenna elements are presented, thereby showing that compressive arrays are promising for use in a variety of real-world beamforming applications. Analysis of the results shows that steered-beam squint is a greater issue than previously assumed, and design guidelines are presented for minimizing the risk of excessive steered-beam squint in manufactured compressive arrays.This work is based on a chapter in H.E.A. Laue, “Design of Compressive Antenna Arrays,” Ph.D. dissertation, Univ. Pretoria, Pretoria, South Africa, 2020. (http://hdl.handle.net/2263/73316)http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=8hj2023Electrical, Electronic and Computer Engineerin

Combination of searches for Higgs boson pairs in pp collisions at \sqrts = 13 TeV with the ATLAS detector

This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb(-1) of proton-proton collision data at a centre-of-mass energy root s = 13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the b (b) over barb (b) over bar, b (b) over barW(+)W(-), b (b) over bar tau(+)tau(-), W+W-W+W-, b (b) over bar gamma gamma and W+W-gamma gamma final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (kappa(lambda)) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to -5.0 &lt; kappa(lambda) &lt; 12.0 (-5.8 &lt; kappa(lambda) &lt; 12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model. For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2019.135103</p

Searches for lepton-flavour-violating decays of the Higgs boson in s=13\sqrt{s}=13 TeV pp\mathit{pp} collisions with the ATLAS detector

This Letter presents direct searches for lepton flavour violation in Higgs boson decays, H → eτ and H → μτ , performed with the ATLAS detector at the LHC. The searches are based on a data sample of proton–proton collisions at a centre-of-mass energy √s = 13 TeV, corresponding to an integrated luminosity of 36.1 fb−1. No significant excess is observed above the expected background from Standard Model processes. The observed (median expected) 95% confidence-level upper limits on the leptonflavour-violating branching ratios are 0.47% (0.34+0.13−0.10%) and 0.28% (0.37+0.14−0.10%) for H → eτ and H → μτ , respectively.publishedVersio

Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb⁻¹ of pp collisions at \sqrts = 13 TeV with the ATLAS experiment

A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb−1 of proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tqγ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tuγ coupling of 36 fb (78 fb) and on the branching ratio for t→γu of 2.8×10−5 (6.1×10−5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tcγ coupling of 40 fb (33 fb) and on the branching ratio for t→γc of 22×10−5 (18×10−5). © 2019 The Author(s