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A wideband feed network for a Vivaldi antenna array is presented. A limitation of current wideband antenna arrays is the bandwidth of either the feed network or the antenna element. The proposed antenna array consists of four wideband Vivaldi antennas fed with an improved wideband feed network to extend the useable bandwidth of the array. The proposed feed network consists of coplanar waveguide-to-slotline-to-microstrip line transitions. The feed network has a single coplanar waveguide input and four microstrip line output ports. The feed network achieved uniform amplitude and phase balance and an impedance bandwidth of 160% from 1 GHz to 9 GHz. The feed network was used in a uniform linear antenna array to feed four Vivaldi antenna elements. The Vivaldi antenna array achieved stable radiation patterns from 1.3 GHz to 8 GHz, resulting in a useable bandwidth of 144%. The antenna array has a minimum gain of 8 dBi and a maximum of 13.8 dBi within the frequency band. Results for a prototype Vivaldi antenna array, measured in a compact antenna test range, are presented and compared to simulated results from CST Studio Suite.

A new technique to implement wideband 90° hybrid coupling profiles on non‐optimal substrate configurations is presented. The technique uses an impedance taper over the whole length of the hybrid to remove the restriction of a substrate defined maximum coupling coefficient at crossover, thus resulting in much more flexibility for the implementation of hybrids on integrated printed circuit boards. The choice of board thicknesses and material type no longer needs to be dominated by the hybrid, but can be optimized for other components or priorities. The flexibility provided by the technique is shown in the implementation of a 2–18 GHz hybrid on a large range of substrate thicknesses as well as on a non‐optimal substrate material, for which acceptable measured performance is still obtained.

Broadband double‐ridged guide horn (DRGH) antennas are extensively used in antenna measurement and electromagnetic compatibility and interference testing, especially the 1–18 GHz DRGH antenna which is widely accepted as a standard for this band. Certain deficiencies in the radiation patterns have been identified and corrected by several authors, but the use was still limited to the 1–18 GHz frequency band. The incorporation of absorber materials and lenses has resulted in horn antennas with wider bandwidths; however, this complicates the manufacturing process and restricts these designs to lower power applications. Simulated and measured results for a new 0.5–18 GHz (36:1) DRGH antenna are presented here. The wider bandwidth is made possible by a new cavity design and optimising the design of the other antenna sections to allow wideband operation without using a lens or absorber. The new design has double the bandwidth ratio and is very compact, with an aperture size of 26.4 cm × 15.2 cm; the aperture sides are less than 12% larger than the sides of the aperture of the conventional 1–18 GHz DRGH antenna (24.2 cm × 13.6 cm).

Scenarios with high levels of diversity lend themselves to be represented or imitated by disaggregate, agent-based models as the individual agents can capture the unique attributes of the constituents of the overall system. This paper describes the methodology to establish a baseline transport simulation model, using MATSim, to represent and imitate vehicle-specific emissions. The study area is the multi-metropolitan megacity (and province) of Gauteng, South Africa.

Agent-based simulation lends itself to study emergent behaviour when agents respond autonomously, based on their unique and individual attributes, to external interventions. In transport, the vehicle-specific attribute of interest is its fuel efficiency and emissions. While research showed that vehicle-specific emissions can be accounted for in terms of pollutant quantities, this paper aims to demonstrate that the chosen model is sensitive to a vehicle’s designated emissions concept. In urban freight or city logistics, such behavioural sensitivity is necessary to evaluate interventions like low emission zones where access is provided to goods vehicles based on their emission category.

Paratransit often emerges in the absence of sufficient formal transit. As governments try to catch up and improve the formal transit service offering, their efforts are often undermined by the quick and dynamic response of the paratransit mode. Recent advances in transport modelling, using agent-based simulation, can provide better decision support. It can allow authorities to evaluate both the intended and unintended consequences of their decisions to introduce or change the formal transit. In this paper, we systematically evaluate paratransit’s response to changes in the formal transit and show that paratransit operators capitalise most on long headways of the formal service.

This paper is concerned with using MATSim to investigate off-hour delivery collaboration between a carrier and receivers agents in the City of Cape Town, South Africa. Results indicate that the carrier’s delivery cost reduced by up to 12.1% when more receivers were willing to accept off-hour deliveries. This reduction was facilitated by the ability of the carrier to use more extra-large delivery vehicles and better utilise the capacity of its vehicles during deliveries, decreasing its delivery cost per tonne. In addition, it was found that the majority of grand coalition receivers were willing to accept off-hour deliveries when carrier cost savings were transferred to them.

In the automotive industry, a Body in White (BIW) refers to the first step, the basic structure, in the production of a vehicle. Once a BIW production line has been built, the (maximum) capacity is fixed and throughput is therefore limited by the equipment specified during the design phase. The main metric used to inform the production line design is the Net Ideal Cycle Time (NICT). Unfortunately, the state of practice to estimate the NICT is a basic heuristic that does not account for production variation. In this paper, we challenge the current estimation approach by proposing an alternative that assumes actual production to follow a Weibull distribution. The proposed model is derived and estimated from empirical data. The results suggest that BIW production lines have traditionally been designed with too low a capacity, resulting in planned throughput rarely being achieved. On the other hand, increasing the design capacity implies a higher initial investment. In this paper it is demonstrated that the higher investment required is offset by reduced losses, resulting in more reliable planning and returns.

This communication illustrates the ability to perform bistatic radar cross-section (RCS) measurements at a fixed bistatic angle in a compact range. Literature regarding bistatic RCS measurements in compact ranges is limited. The traditional setup of a compact range was adapted to perform bistatic RCS measurements. These bistatic measurements were conducted on canonical and complex realistic scale airframe models. The targets were illuminated with a plane wave created by an offset parabolic dish reflector. The bistatic scattering of the targets was measured by placing a receive antenna at a fixed bistatic angle and finite distance in the compact range. This communication also investigates the effect of the finite separation between the targets and the receiver on the bistatic scattering measurements of large complex targets. The accuracy of the bistatic RCS measurements is compared to full-wave simulations conducted with FEKO using the multilevel fast multipole method solver. Quantitative comparisons are drawn between the simulations and measurements using the feature selective validation method.

Group work is commonly used in undergraduate engineering curricula as it cultivates attributes that make graduates work-ready. However, freeloading behaviour, frequently observed at university level, spoils learning benefits and can deepen marginalisation and prejudice. Therefore, conversations about how to fairly credit individual contribution in group work are ongoing in literature and practice. Peer assessment is a popular mechanism for distinguishing individual marks, but it is not without its criticisms. This study evaluates students’ perspectives regarding the use of mark-influencing peer assessment in two junior-level Industrial Engineering courses at the University of Pretoria. The findings show that students acknowledge the learning benefits of group work but group work overuse and freeloading mars their experience. They support the use of mark-influencing peer assessment in general, regardless of whether groups are self-selected or allocated. The study’s findings offer practical insights for engineering educators and broader inputs to the development of assessment policies.

White rhinoceros (Ceratotherium simum) is one of the most famous victims of poachers in Africa. One of the methods for dealing with decreasing rhino numbers is rehabilitating wounded and/or orphaned animals to successfully release them back into the wild. The status of rescued animal differs among individuals, but general procedures must be established and constantly improved. This study presents the history of successful release of three orphaned white rhino females, rehabilitated for 15 months in Wildlife Rehabilitation Centre in a private game reserve in South Africa. Female A was three years old, female B was one year old and the youngest female was three months old on arrival. The animals were rehabilitated together despite the differences in their age and size, with particular attention paid to keeping them as wild as possible. After being weaned and becoming old enough to go back to the wild, they were released at a distance from the rehabilitation centre, which required immobilization and translocation. Since the rhinos were released, they have been successfully living in the wild. All procedures used in this study proved to be sufficient for preparing the animals for life in the wild and can be recommended for other centres.

Many studies have suggested that a fully polarimetric radar or a bistatic radar can improve the classification and recognition of airborne targets due to enhanced target information. This paper makes use of the information theoretic concept of mutual information (MI) and investigates the comparison of the MI content between polarimetric monostatic and bistatic radar cross section (RCS) measurements of a 1:25 Boeing 707 scale model. It aims to quantify the increases in the MI content, and hence recognition performance, due to the additional reflected signals available in a fully polarimetric radar or in a bistatic scenario.

Grating lobe mitigation was achieved for planar, wideband dual-polarized Vivaldi arrays through the rotation and translation of equilateral pentagonally shaped subarrays that form an approximately circular array. The subarray outlines can be adjusted in order to included fewer elements per subarray, but this will result in less grating lobe reduction. By using dual-polarized elements optimized polarization in the main beam can be achieved. The array patterns were determined with both measured and simulated single element patterns of the dual-polarized Vivaldi element. The mutual coupling between the elements in the array was shown to be negligible.

Accurate travel time predictions are required when evaluating transport infrastructure. Travel times, in turn, are influenced by time of day, vehicle type and the density of vehicles, amongst other characteristics. Advances in multi-agent models have shown to predict travel times more accurately, and allow for rich result sets as each vehicle (or person) is modelled individually. Some of the efficiency seems to come from using primitive heuristics to deal with passing and multimodality. This paper introduces a passing regime that is sensitive to vehicle class and traffic density. In this first part, the fundamental relation of traffic flow is estimated from a large set of empirical observations under both free flow and congestion, and for different vehicle types.

Advances in multi-agent models in the field of vehicular transport are showing much potential for improved decision support. Large scenarios of metropolitan or even national scale can be modelled efficiently and provide rich result sets with more accurate travel time predictions. Some of the efficiency seems to come from using primitive heuristics to deal with passing and multimodality. This paper introduces a passing regime that is sensitive to vehicle class and traffic density. In this second part, we implement the estimated fundamental relation of traffic flow in an agent-based setting. The results are consistent with empirical observations and also support recent advances in analytical models based on multiple phase transitions in traffic congestion. We also investigate the effect of link length in the queue-based model.

A low profile dual-circularly polarized printed ring-slot antenna with a small footprint, which radiates above an open cavity loaded with an artificial magnetic conducting reflector, is presented. The feed network consists of two T-shaped capacitive feed structures connected to a miniaturized hybrid branch-line coupler. Experimental results for a final antenna design (with a size of $0.5\lambda _{\mathrm {\mathbf {0}}} \quad \times 0.5\lambda _{\mathrm {\mathbf {0}}} \quad \times 0.057\lambda _{\mathrm {\mathbf {0}}}$ ) show a 4% isolation bandwidth between the two ports of the dual-circularly polarized antenna and a maximum gain of approximately 6.8 dBic. Good front-to-back ratios and low cross-polarization were achieved. These very compact and low profile antennas are suitable for 2.4 GHz wireless local area network (WLAN) communication systems.

This letter presents a dual-band slot antenna with high gain for wireless local area network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) communication covering the IEEE802.11a/b and IEEE802.16d/e standards. The antenna consists of a microstrip-fed slot with a complimentary stub on a single dielectric medium. A reflecting ground plane is employed to achieve a unidirectional radiation pattern with an average gain of 9.1 dBi. The feed of the antenna is optimized to achieve radiation efficiency above 95% in the WLAN and WiMAX frequency bands. The radiation properties of a prototype antenna were measured in a compact antenna range. Simulated and measured results (impedance bandwidth, gain, and radiation patterns) are presented for the proposed antenna.

Establishing cycling as a prominent utility mode is recognised as central to creating sustainable transport systems in many cities around the world. Strategies of starter cycling cities are often biased to the supply of infrastructure along prominent corridors without acknowledging the nature, quantum or location of potential demand for cycling. Decisions are frequently left to local knowledge and experience of local needs, resulting in a bias with little opportunity for repeatability or reproducibility. This study proposes a data-driven approach to estimate the potential market for cycling geographically. Estimates are based on the number of potential cyclists in close proximity to the destinations they want to access. The paper demonstrates the method using Cape Town, South Africa as a case study. Given the virtual absence of utility cycling in the city, characteristics of cyclists in cities where cycling is popular are used to identify potential cyclists. Destination nodes are stratified in terms of the characteristics of their users, while home locations of persons with these characteristics are identified from a publicly available synthetic population for Cape Town. Analysis provides an order of magnitude indication of the cycling potential of selected nodes. It also shows areas with many potential cyclists that are not in proximity of desired destination. The results enable city authorities to focus detailed investigations and interventions where a critical mass of cycling may be achieved with the least effort and in the shortest time.

Either passive calibration targets are expensive and complex to manufacture or their bistatic radar cross section (RCS) levels are significantly lower than the monostatic RCS levels of targets such as spheres, dihedral, and trihedral corner reflectors. In this paper the performance of an active calibration target with relative high bistatic RCS values is illustrated as a reference target for bistatic RCS measurements. The reference target is simple to manufacture, operates over a wide frequency range, and can be configured to calibrate all four polarizations (VV, HH, HV, and VH). Bistatic RCS measurements of canonical targets, performed in a controlled environment, are calibrated with the reference target and the results are compared to simulated results using FEKO.

The radar cross section (RCS) of passive calibration targets is relatively low, which leads to a commensurate increase in the uncertainty of the radar's calibration. To address this deficiency, an active radar calibration (ARC) target was developed, which was mounted on a small remote controlled tri-copter and used for radar calibration. Results are presented for this relatively small, light weight and cost effective airborne ARC, which is suitable for the calibration of a ground to air RCS measurement system. The static RCS characteristics of the airborne ARC target were measured in a compact range and compared to outdoor measurements with the ARC target mounted on the tri-copter. The airborne capability of the calibration target was used to reduce the effects of multi-path and clutter. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1041–1044, 2016

Freight vehicle movement can be captured using activity chains, which capture the freight related activities both spatially and temporally. This is an advancement over origin-destination matrices, since freight vehicles are studied at a disaggregate level. Digicore Fleet Management has provided GPS data of over 40,000 freight vehicles travelling in South Africa over a six month period, from which freight activity chains can be extracted. The first contribution of this paper is to generate synthetic freight activity chains using a complex network that captures the connectivity between firms where freight activities take place, and therefore also captures some aspect of the behaviour of the vehicles. The complex network is built with the activity chains of 60% randomly selected freight vehicles, called the training set. 10 synthetic populations are generated using this complex network, each representing a 10% sample of the total freight population in South Africa. As a second contribution, we use the observed activity chains of the remaining 40% of vehicles, called the test set, to compare to the synthesised activity chains. The results indicate that the complex network approach of generating synthetic populations correctly estimates the fraction of activity chains for different chain lengths. The chain start times of the synthetic populations are generally similar to that of the observed activity chains, except for some underestimation during the morning peak hours. Vehicle kilometres travelled are only slightly overestimated in the synthetic activity chains. This complex network approach to generating synthetic freight populations is novel, and the results indicate that the synthetic populations generated are an accurate representation of South Africa's freight population.

Many city logistic initiatives are large in scale and aim to improve the efficiency and overall state of goods movement within our urban areas. Unfortunately the implementation and day-to-day operations of urban goods movement is less than optimal. Commercial vehicles have many activities in their activity chains, from when they start at a terminal depot, until they return. Some vehicles have as many as hundreds of activities in a single chain. Unfortunately many consecutive activities in a vehicle's chain occur at the same facility, suggesting that vehicles have to maneuver and relocate a few times before their true, economically useful function is completed. In this study we consider such duplicate activities and perform temporal and spatial analyses to better understand the nature of these productivity sinks.

A design approach for printed planar slot array antennas is presented. The antenna array consists of half-wavelength slot radiators positioned on a rectangular grid, and a slotline feed network. Three planar slot array antennas for use in IEEE 802.11a applications are designed, a 2 × 2, a 2 × 4, and a 4 × 2 array, all radiating above an electric conductor ground plane placed a quarter-wavelength below the printed slots. These slot arrays have higher aperture efficiencies and occupy less space than typical microstrip patch arrays. The measured impedance bandwidths of the designed unidirectional slot arrays were 19.8, 15.3, and 16.7%, respectively, with peak gains of 11.7, 13.9, and 14.4 dBi. Measured results show very good agreement with the simulated results, which serves as validation of the array design procedure and the accuracy of the simulated results.

Many studies have suggested that bistatic radar can improve the classification and recognition of airborne targets due to enhanced target information. This paper makes use of the information theoretic concept of mutual information (MI) and investigates the comparison of the MI content between monostatic and bistatic radar cross section measurements of a 1:25 Boeing 707 scale model. It aims to quantify the increases in the MI content, and hence recognition performance, due to the additional reflected signals available in a bistatic scenario.

The traditional Double Ridged Guide Horn (DRGH) Antenna consists of three sections: coaxial-to-ridged waveguide transition, cavity and a ridged waveguide flared section. Different variations of the coaxial-to-ridged waveguide and cavity sections of DGRH antennas are available to improve the VSWR to a 2:1 performance. In this paper three different profiles, exponential, Bezier and elliptical, are investigated for the ridges in the flared section, to obtain improved gain and radiation pattern performance for DRGH antennas. The DRGH antenna with an elliptical profile has a mark able increase in gain values, at the lower frequencies of the band.

We present the design of a dual-band slot antenna with high gain for wireless local area network (WLAN) covering the IEEE802.11a/b and IEEE802.116d/e standards. The antenna consists of a feed line with a complementary strip-slot pair and a parasitic slot-element and has a size of $57\times 40\ mm^{2}$ . The antenna is combined with a single-band artificial magnetic conductor (AMC) surface to achieve a unidirectional radiation pattern with an average gain of 9.6 dBi. The size of the antenna with the AMC reflector is $68\times 53\ mm^{2}$ . The proposed antenna was designed and simulated. The simulation results show that the antenna operates from 2.39 – 2.50 GHz and 4.90 – 5.97 GHz, which covers the 2.4, 5.2 and 5.8 GHz WLAN bands. It has a directional radiation pattern with peak gains of 7.5, 10.3 and 10.9 dBi at 2.4, 5.2 and 5.8 GHz, respectively.

Conventional rectangular waveguides are commonly used for high power and other microwave and millimeter-wave applications. Their use at lower frequencies has been limited by their bulky nature. A new type of compact waveguide called a partial $H$ -plane waveguide has previously been proposed that has only one quarter of the cross-sectional area of a conventional waveguide. However, only limited information relating to the feeding of such waveguides is available. This paper presents two types of transitions to partial $H$ -plane waveguides from the coaxial and microstrip transmission mediums. Additionally, in the coaxial case, the transition is end-launched to offer collinear properties. The development of both transitions is discussed and optimized designs presented with simulated and measured results over $H$ -band (3.95–5.85 GHz).

An approach where polar curves are used to miniaturize hybrid couplers is presented. The design of such couplers can be done with the optimization of a few parameters using full-wave analysis software. The results show similar or better electrical performance for a rat-race and branch-line coupler with, respectively, a 75 and 50% size reduction. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2637–2640, 2015

We rarely associate social networks with the movement of freight vehicles. Yet, taking a network perspective on supply chains has seen a strong interest in recent literature. It allows for a variety of system-level analysis that is not possible when taking a single focal firm view as is often the case in more classical supply chain approaches. Creating the network of connectivity on which the analyses are based can be quite a daunting and computationally challenging task. In this paper we create a large-scale network from the movement of commercial vehicles in a metropolitan area in South Africa, using the direct trip between consecutive facilities as a proxy for a tie, or dyad, in the network. We analyse how density-based clustering parameters influence the completeness of the network—that is the number of nodes included—as well as the computational burden of extracting the network. The results of the multi-objective analysis confirm the sensitivity of the resulting network, and suggest much smaller search radii and fewer points per cluster. We also report on a number of node- and network-level properties of the complex network using the proposed clustering configuration on the Nelson Mandela Bay Metropole network in South Africa.

Ultra-wideband (UWB) communications technology increasingly plays an important role in modern communications systems. The complex antenna transfer function (CATF) of a UWB antenna provides valuable information that can be used for better UWB channel and communication system designs. Currently, only the two-antenna and three-antenna measurement techniques are used to measure the transfer functions and impulse responses of UWB antennas. In this paper, a modified version of the gain-transfer method is presented to enable the characterization of UWB antennas using a compact antenna test range facility (CATR). A double-ridged guide horn (DRGH) antenna was used as a UWB transfer-standard, and the complex antenna transfer function of the transfer-standard was determined a priori using full-wave simulations. The gain-transfer method to measure the complex antenna transfer function of UWB antennas in a compact antenna test range was illustrated with two test cases. In the first test case, the measured complex antenna transfer function of an ETS-Lindgren double-ridged guide horn antenna was verified with numerical data from a FEKO model of the antenna. The second case compared the complex antenna transfer function of a UWB circular disc monopole antenna measured in a compact antenna test range to measured data using two identical antennas in a two-antenna measurement setup.

This paper describes the modeling of the complex reflection coefficient S 11 of a meta-material antenna comprised of an etched microstrip dipole antenna radiating in the presence of a back reflector that is an artifical magnetic conductor (AMC). Both the real and imaginary components of the S parameter exhibit significant changes in rate of variation as a function of position along the frequency dimension of the input space. We show that Gaussian process regression — using a specially constructed composite covariance function that allows for a variable length-scale parameter along the frequency dimension — can succesfully model the components of S 11 . The latter model outperforms a GP model using a well-known standard covariance function from the (stationary) Matern family.

This paper illustrates the feasibility to perform bistatic RCS measurements in a conventional monostatic compact range that has been reconfigured to perform bistatic measurements at relatively large bistatic angles. The bistatic RCS measurements are conducted by illuminating the target with an incident plane wave generated by an offset parabolic reflector. The bistatic scattering of the target is measured with a wideband double-ridged horn receive antenna that is positioned at the side of the chamber at various fixed bistatic angles. In this study bistatic RCS measurements were conducted on canonical structures as well as a realistic complex scale aircraft model. The bistatic RCS measurements are compared to the full-wave multi-level fast multipole method (MLFMM) in FEKO.

The accuracy with which various full-wave and asymptotic CEM techniques can calculate the RCS of lossy dielectric objects is investigated. This is conducted through comparison to measured RCS data. The investigated methods include MLFMM, FEM, PO and RL-GO. Different lossy dielectric materials are used to construct canonical targets. The RCS of these targets are measured in a compact range at the University of Pretoria, South Africa. The material properties of these lossy dielectrics are accurately characterised using a waveguide technique. Accurate CAD models of the dielectric objects are constructed and used for simulations. The calculated RCS results are compared to the measurements to determine the accuracy of the various methods. The performance and computational efficiency of these methods are also investigated.

The wideband gain and voltage standing wave ratio (VSWR) performance of quad-ridged horn antennas in general are restricted due to the excitation of higher order modes in the coaxial to quad-ridged waveguide transition. This results in large gain variations vs. frequency and break-up of the radiation patterns at higher frequencies. In this paper, a quad-ridged horn antenna is presented with optimized radiation characteristics and VSWR performance. The performance of the antenna was optimized by separating the antenna into two subsections, viz. a coaxial to quad-ridged waveguide transition section and a flared quad-ridged horn section. The performance of each section was optimized individually using a numerical solver – CST Microwave Studio. Three possible configuration of the coaxial to quad-ridged waveguide transition section were considered and optimized. Four configurations for the flared quad-ridged horn section were also investigated. The best performing configuration from each one of the two section...

We present a quad-ridge horn antenna as a feed for a reflector antenna for use in radio astronomy applications. The antenna uses elliptically shaped sidewalls to limit the variation of beamwidth over a wide frequency range and to obtain greater radiation pattern rotational symmetry. The antenna is dual-polarized and matched over more than a 4:1 bandwidth. A design procedure is presented and a prototype designed according to this procedure is shown. Measured and simulated results of the prototype agree with each other well. The antenna is analyzed with a prime focus reflector to determine the range of efficiencies that can be expected.