A low profile radiating element with nearly hemispheric coverage for satellite communications on-the-move hybrid array antenna

A novel design solution of a dual-linearly polarised Ku-band low-profile radiating element for low elevation angle coverage (down to 10° above horizon) is presented. Such an element is suitable for full-duplex Satellite Communications On-The-Move (SCOTM) hybrid scanned phased array antenna applications. Standard designed radiating elements for array applications with low profile physical structure suffer poor low elevation angle coverage as the element pattern reduces by sine of the elevation angle. The element design demonstrated in this paper features unique louvered array element geometry incorporating a spatial “ray bending” lens facilitates the shaping of the element pattern to increase gain at low elevation angles. Preliminary modelling results using ray tracing analysis shows that the desired low angle coverage can be achieved. Currently in progress full 3D electromagnetic simulations which include the interaction between the basic radiator and the spatial lens indicates that using an ideal tilted element with novel louvered reflector in addition with proposed lens, low angular coverage can potentially be realised in a low profile structure

A new low profile antenna with improved performance for satellite on-the-move communications

A novel design solution for a low-profile fullduplex Satellite-On-The-Move Communications hybrid scanned phased array antenna for low elevation angle coverage (down to 10°) is described. The antenna is operated at Ku-Band. The unique louvered array element geometry in combination with a spatial filter/ “ray bending” lens facilitates the shaping of the element pattern to increase gain at low elevation angles. Preliminary modelling results using simple ray-tracing and 3D E simulation indicate that the desired low angle coverage can be achieved

Dual-polarized broad-band microstrip antennas fed by proximity coupling

A novel antenna structure for dual polarisation is proposed. Advantages over previous structures include simplicity, broad bandwidth, high isolation between ports and low cross-polarization. The antenna design is readily suited to use as an array element and therefore has potential for use in a variety of practical applications. The work was supported in part by EPSRC grant GR/S42538/01

Optimum design of a probe fed dual frequency patch antenna using genetic algorithm

Abstract: Recent research has concentrated on different designs in order to increase the bandwidth of patch antennas and thus improve functionality of wireless communication systems. An alternative approach as shown in this paper is to design a matched probe fed rectangular patch antenna which can operate at both dual frequency (1.9 GHz and 2.4 GHz) and dual polarisation. In this design there are four variables, the two dimensions of the rectangular patch, ‘a ’ and ‘b ’ and position of the probe feed ‘Xp ’ and ‘YP’. As there is not a unique solution Genetic Algorithm (GA) was applied using two objective functions for the return loss at each frequency. The antenna was then modelled using AWR software and the predicted and practical results are shown to be in good agreement. Key Words: Genetic algorithm (GA), dual frequency, dual polarisation, probe fed patch antenn

Effect of losses in an active device and harmonic network on the efficiency of Class F and inverse Class F power amplifiers

High frequency class F and inverse class F power amplifiers obtain high efficiency of dc to ac power conversion, by reducing the overlap of voltage and current waveforms at the output of the active device, to ensure that the power dissipated in the resistance Ron of the active device is minimised. In this paper the active device is modelled as a switch in series with resistance Ron 0 to 5Ω. For ideal switch voltage / current waveforms and equal dc input power for both amplifiers the efficiency of power conversion is compared. To confirm the predicted results ideal lossless load harmonic networks using lumped elements were designed to meet all frequency conditions of the two amplifiers. These networks were done used in Advanced Design System (ADS) software for Ron=0, 2 and 4 Ω. The predicted efficiency for 2Ω and 4 Ω were 80% and 60% and the obtained simulation efficiency were 83.2% and 65.5% for class F amplifier. For the inverse class F amplifier the predicted efficiency was 87.3% and 74.5% and for the simulation results it was 87.26% and 74.4%. Above predicted and simulated results show that the resistance Ron has less effect on the efficiency of inverse class F than for class F amplifier. As lumped elements can not be used at high frequencies they were replaced initially with lossless transmission lines and then by microstrip lines to also investigate also how copper and dielectric losses affect the efficiency of power conversion

Low-cost dual-polarized printed array with broad bandwidth

This work presents a novel design of low-cost broad-band dual-polarized microstrip arrays. The antenna uses the slot-coupled feed for one polarization, while the microstrip line feed with slotted ground plane is used for the other polarization. It can make good use of the space on both sides of the ground plane, as the feed circuits for two orthogonal polarizations are placed on each side of the ground plane, respectively. The prototype four-element array designed at C band yields a bandwidth of more than 14% at both ports, and isolation below -30 dB. Good broadside radiation patterns are observed, and the cross-polar levels are below -20 dB at both E- and H-planes

The application of the segmentation method in the design of compact single-feed circularly and linearly polarised microstrip patch antennas

This thesis presents the application of coplanar circuit analysis in the design of compact single-feed circularly polarised (CP) and linearly polarised (LP) microstrip patch antennas. A CP nearly square patch antenna and a CP truncated corners square patch antenna are designed. Also a LP U-slot rectangular patch antenna is designed. In order to obtain a faster computational run-time, coplanar circuit analysis and segmentation method are applied for the impedance calculations. The coupling and self impedance formulas for both rectangular and right-angled isosceles triangular segments are given. Explicit formulas for the coupling impedance between a perimeter port and a probe port, and also the probe self impedance on both of these segments are new and are derived in detail. A CP nearly square patch antenna is designed using both the cavity and equivalent circuit models. New and simple design equations are derived to determine the dimensions of the patch with a feed in any given position. For a microstrip feed offset from a corner of the patch, the area of perturbation segment is increased which reduces the effect of manufacturing errors. A simple matching network consisting of a short length of microstrip line is designed to achieve a more compact form of the matched antenna. The results obtained from both models are good agreement. A CP truncated corners square patch antenna with a microstrip feed offset from the centre is presented. In previous work the design is a feed along the centre line and the areas of the deleted segments are very small so the performance of the antenna is very sensitive to manufacturing errors. Hence an offset feed is proposed in order to increase the perturbation area and so reduce the effect of the manufacturing errors. The segmentation method is used for which a new explicit matrix input impedance formula is derived. The impedance formula requires a computer run time less than half that required by simulation (full-wave software, Ansoft Ensemble). The change in area of the perturbed segment and input impedance with the microstrip offset feed position is examined. A compromise offset feed position was chosen so as to maximise the area of the perturbation segment and achieve good impedance matching for a compact antenna structure. A LP probe feed U-slot rectangular patch is designed and the input impedance is determined. A set of initial design equation is used to produce a first-pass design. In applying segmentation method a new explicit input impedance formula for the antenna is derived. The basic system of eleven coplanar circuit equations is reduced to seven equivalent circuit equations from which the explicit impedance formula is derived. The dimensions of the patch are adjusted to give good impedance matching. In respect of computational efficiency, the run time of the new matrix input impedance formula is at least 10 times faster than is required by simulation. A thicker substrate is also used in order to improve the bandwidth. The predicted, simulated and measured results of the above three compact patch antennas are in good agreement. Mathcad programming is used to implement the design calculations of the compact patch antennas.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An investigation of reduced size planar fed microstrip patch antennas

The primary goal of this research work is to investigate the use of slot loading in reduced size planar fed microstrip patch antennas and develop new antenna structures based on this technique. At present, little theoretical investigation or design methodology exists to support the design of compact structures and research in this field is largely empirical. Moreover, little work exists on the use of planar fed designs. This necessitates a primary requirement to firstly address this knowledge gap. To facilitate this, a mathematical modelling technique that can be applied to such structures is developed. This is based upon the segmentation and Green's function approach. Using this model, the performance of slot loaded structures in terms of circuit characteristics including resonant frequency, input impedance, and Q factor is determined. Using this knowledge, a design procedure is established and subsequently used to provide a framework for the design of novel slot loaded antennas for specific applications. Several new slot loaded patch antenna configurations are designed that produce size reduction whilst allowing the use of a planar feed. The validity of the designs are confirmed through the use of commercial full-wave modelling software package Ensemble. Three linear polarised antennas are presented which are shown to achieve size reduction of 12, 40 and 55% respectively. Several compact circular polarised antenna structures are successfully implemented producing size reduction of up to 43%. A novel design for a reduced size antenna with a dual frequency response is also presented with a tuneable frequency ratio of between 1.03 — 2.0. Prototypes of the aforementioned antennas are fabricated and tested, and practical results are shown.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Developing autonomy via assessment for learning

This chapter focuses on two case studies in which lecturers employed an holistic model of assessment for learning to redesign their assessment practices across a whole module as part of a ground-breaking effort to embed assessment for learning across an institution. In each instance, self and peer reviewing of formative tasks, accompanied by extensive student–teacher dialogue about corresponding teacher reviews, were embedded as pedagogical techniques to help students learn to evaluate their own work partway through the module. Analysis of the student viewpoint on these reviewing activities highlights some of the issues that surround the use of assessment to develop autonomy as an outcome, especially in the context of increasing diversity