Slotted Waveguide Array Antennas: Theory, analysis and design
Slotted waveguide antenna arrays are used in radar, communication and remote sensing systems for high frequencies. They have linear polarization with low cross-polarization and low losses but can also be designed for dual polarizations and phase steered beams. Slotted Waveguide Array Antennas is the first comprehensive treatment of these antennas from an engineering perspective. It provides readers with a thorough foundation in applicable theories as well as hands-on instruction for practical analysis, design, manufacture and use of important types of waveguide slot arrays. It goes beyond some of the commonly discussed topics and ventures into areas that include higher order mode coupling and edge effects; performance optimisation in terms of bandwidth and pattern performance and manufacturing tolerances. With specific examples of waveguide array designs, accompanied by detailed illustrations and antenna characteristics, the book is a must-have reference for engineers involved in antenna design, development and applications.
Inspec keywords: history; slot antenna arrays; electromagnetic field theory
Other keywords: slotted waveguide array antennas; history; applied electromagnetic theory
Subjects: Antenna arrays; General electrical engineering topics; Electric and magnetic fields
- Book DOI: 10.1049/SBEW517E
- Chapter DOI: 10.1049/SBEW517E
- ISBN: 9781613531891
- e-ISBN: 9781613531907
- Page count: 377
- Format: PDF
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Front Matter
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1 Introduction
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The first successful slotted waveguide array antennas were developed in Canada during the Second World War. The immediate applications were in military ground and airborne radar systems for target detection and tracking. Later applications include remote sensing from aircraft and space vehicles and microwave communication links. Spaceborne synthetic aperture radar (SAR) with slotted waveguide arrays are used for weather forecasting, environmental monitoring, climate change studies, etc. The slotted array antenna is also considered in automobile collision avoidance systems. For the interested reader not too familiar with slotted waveguide array antennas a few simple concepts are introduced in the following text.
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2 Review of electromagnetic theory
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In this chapter, we review the electromagnetic theory and concepts used in later chapters. We will start with Maxwell's equations in time harmonic form, followed by boundary conditions. Expressions for energy and power are derived. We then discuss the reciprocity theorem. Vector and scalar potentials are derived. Image principle and the field equivalence principle are presented. Green's functions are discussed with a presentation of dyadic Green's functions for the magnetic current in a waveguide.
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3 History
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The most important technical advance in the 1930s was, in the opinion of the writer, the invention of the resonant slot. This was a device which was both an aperture radiator and a resonant structure. Its novelty was major. Nothing as important had appeared since Hertz invented the dipole and the loop and Lodge and Bose experimented with open-ended waveguide radiators. The words are from Ramsay [1]. He mentions in particular Alan D. Blumlein at EMI Central Research Laboratories in the UK as the inventor of the resonant slot antenna (patent no. GB 515684, 1938). Blumlein also proposed linear arrays of slots.
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4 The slot antenna
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In this chapter, we will consider the single-slot antenna. We will first discuss an arbitrarily shaped aperture in an infinite conducting ground plane. Then we specialise to a rectangular resonant slot antenna and derive its radiation conductance. We continue with the special but important case of a longitudinal slot in the broad wall of a rectangular waveguide. The normalised modal functions for describing fields in waveguides are introduced. The equivalent slot conductance as seen from the feeding waveguide is then calculated. Mutual coupling to other slots and ground plane edge effects is also discussed.
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5 Slot models
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In this chapter we will discuss theoretical models for characterising slots in waveguides. in Chapter 4 we looked at basic theories for slot apertures and found expressions for the conductance of longitudinal slots in rectangular waveguides. We will now look at ways of finding the slot susceptance, the effect of slot offset on resonance conditions, influence of wall thickness, waveguide dimensions, etc. We will demonstrate how electromagnetic models can tell us about slot behaviour in greater detail. The longitudinal slot and the transverse slot in the broad wall of a rectangular waveguide will be treated in. particular. We will thus establish a basis for an efficient design process of high-performance slotted waveguide arrays.
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6 The linear slotted waveguide array antenna
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Based on the analysis of the single-slot antenna in the previous chapters we can now approach the problem of designing linear and planar slot arrays. We will first study longitudinal slot arrays and start with the simple case with one row of slots in a rectangular waveguide. For this case mutual coupling appears mainly in the H-plane and can in many cases be neglected. Some examples of computed and measured performance will be presented. Procedures for designing linear arrays of slots, including some examples, will be discussed.
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7 Design of planar slotted waveguide array antennas
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In this chapter, we will present Elliott's design procedure for planar standing wave slot arrays including a detailed design example with computed and measured results. For large planar arrays a modification to Elliott's design procedure using an infinite array model is sometimes preferred. Large standing wave arrays can be broken up into sub-arrays with a parallel feed network to improve bandwidth. Important parameters are the total normalised slot conductance of radiating waveguides and the total normalised resistance of feed waveguides. Additional examples of slot array designs will be presented, including a procedure for designing a travelling wave feed to excite radiating waveguides with either standing wave or travelling wave slot arrays. Other design and analysis methods in the literature will also be reviewed.
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8 Concepts and models for advanced designs
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In this chapter we will discuss a number of concepts and models used in advanced design and optimisation of slot arrays. Models for coupling slots will be presented followed by a discussion of the edge wall slot and the compound radiating slot. Iris-excited longitudinal slot arrays, slot arrays in ridge waveguides and slot arrays covered by a dielectric layer will also be discussed. Higher-order mode coupling between adjacent coupling slots and that between a coupling slot and radiating slots in its immediate vicinity will be presented. A method of incorporating the finite ground plane effects in the design and analysis will be described. The MoM solution to the coupled integral equations for the apertures of all slots in a planar array will be discussed. Some examples employing the moment method solutions of slot arrays for improved designs will be presented.
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9 Antenna systems and special requirements
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So far we have mainly discussed flat slotted waveguide array antennas consisting of rectangular waveguides, typically with slots in the broad wall, radiating a fixed narrow beam. Many other configurations are possible, however, and even more suitable in special cases. In this chapter we will investigate how slotted waveguide arrays are used in system applications where more advanced antenna functions or special configurations are required. As this is a very broad subject we will concentrate on cases where advantages and perhaps difficulties are of particular interest.
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10 Slot arrays in special waveguide technologies
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In this chapter, we discuss slot arrays in two types of parallel plate waveguides propagating the TEM mode. In the first an electromagnetic wave propagates in the radial direction inward or outward in a circular parallel plate waveguide, while slots cut in one of the parallel plates radiate. Such an array is convenient for large apertures requiring high gain and mass production. The second type has a rectangular shape and propagates the TEM mode. Slots cut in one of the plates radiate. We then present slot arrays in substrate integrated waveguides (SIW) which have a great potential for easy integration with planar devices. Finally slot arrays in gap waveguides are discussed.
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11 Manufacturing aspects
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In this chapter, we will take a look at manufacturing aspects that are important for high-quality production of slotted waveguide array antennas. It is a wide subject so we will concentrate on critical parameters such as mechanical tolerances that relate to electrical performance. We will also discuss joining methods for metal materials, for example, dip brazing of aluminium. Applications at high frequencies (millimetre waves) in particular call for very high precision and special methods. An important area is the use of slotted carbon fibre reinforced plastic (CFRP) waveguides that offer light weight and thermal stability, typically required for large antenna systems for space applications. The technology is also used in some military ground and airborne radar systems. Some of the exciting developments in low-cost fabrication using plastic materials and metallisation techniques are discussed. This area is related to the microelectronic area, particularly for high frequencies and highly integrated antenna/microwave assemblies.
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12 Outlook for the future
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In this book we have analysed the design of several types of slotted waveguide array antennas, from theories and optimisation to applications and manufacturing techniques. In this last chapter we will discuss the current status in the field and look at new technologies and new applications recently presented and researched. Still, in this short overview it is not possible to mention all the details of the evolving field; the reader is referred to the respective chapters and the references for more information.
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Standard waveguide frequency bands
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Standard rectangular waveguides are listed with their common designations and useful frequency ranges. The waveguide inner dimensions are given in mm.
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Back Matter
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Supplementary material
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Supplementary Files for Slotted Waveguide Array Antennas
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Please see the errata sheet for 'Slotted Waveguide Array Antennas'
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