Antennas for Wireless Communications

The antenna is introduced and treated as a transducer. Emphasis is placed on possible mismatch between the feed line and the antenna, thus creating a reflection coefficient. The Standing Wave Ratio is defined, and the antenna is modeled using simple equivalent circuits based on the transmitting and receiving modes.

In here, we define radiation patterns and their types (directional, omnidirectional), as well as the principal cuts of a pattern, what are sidelobes and beamwidths (HPBW, FNBW), how to calculate them, and the three different regions of an antenna.

In this Lecture, we present the spherical coordinate system first, and then, we define important antenna parameters such as radiated power density, radiated power, radiation intensity, the half-power beamwidth and the first-null beamwidth.

A step-by-step procedure on how to calculate the directivity of an antenna is presented and explained. Approximate formulas widely used in industry for the quick and easy calculation of directivity for directional and omnidirectional patterns are also provided.

In here, we explain with every detail the terms Efficiency, Gain, Beam Efficiency, and Bandwidth. These are very important antenna figures of merit that every antenna engineer must be familiar with. The difference between gain and directivity is also clarified.

The concept of Polarization is explained through examples and pictures. There are three types of antenna polarization: linear, circular and elliptical, as well as two senses of rotation: left hand (LH) and right hand (RH). The antenna polarization loss factor (PLF) is also defined.

We present the equivalent circuit of an antenna in the transmitting mode and explain the input impedance of the antenna including a loss term. The efficiency of the antenna is explained based on the power delivered to the radiation resistance of the antenna. We also define important terms such as equivalent length and equivalent area of the antenna. At last, we present the Friis Transmission equation which is widely used to calculate the received power at the terminals of the receiving antenna knowing the characteristics of both receiving and transmitting antennas, the operating wavelength and the distance between them.

We introduce the vector potentials A and F, and calculate the radiated fields by any type of antenna using the governing electric and magnetic current sources on the surface of the antenna. Simplification of the results is implemented for the far-field region of the antenna. We also discuss reciprocity and duality principles.

We use the auxiliary vector potential and a constant current density along the length of the infinitesimal dipole to calculate the radiated fields in all field regions of the antenna. Important antenna parameters such as the radiation resistance are also calculated.

We use the auxiliary vector potential formulation and a given current density to calculate the radiated fields by a short dipole and a finite-length dipole. Important performance parameters such as radiation patterns, radiation resistance, input impedance, radiated power, and directivity are calculated based on knowledge acquired from earlier lectures.

Here, we explain the use of image theory for an electric/magnetic dipole on top of an infinite electric/magnetic ground plane. We use the auxiliary potential formulation to calculate the radiated fields by an infinitesimal dipole on top of an infinite electric conducting plane. We also calculate the radiated fields by a quarter-wave monopole above a ground. Then, we consider the case of a horizontal dipole above a ground, as well as the case of a lossy ground. Earth ground has a profound effect on the radiation patterns of a dipole antenna. This is Part A.

Here, we explain the use of image theory for an electric/magnetic dipole on top of an infinite electric/magnetic ground plane. We use the auxiliary potential formulation to calculate the radiated fields by an infinitesimal dipole on top of an infinite electric conducting plane. We also calculate the radiated fields by a quarter-wave monopole above a ground. Then, we consider the case of a horizontal dipole above a ground, as well as the case of a lossy ground. Earth ground has a profound effect on the radiation patterns of a dipole antenna. This is Part B.

Introduction of loop antennas and their characteristics and applications. Use of cylindrical coordinates and the auxiliary vector potential formulation for the derivation of the radiated fields by a small circular loop with a constant current density along its length. Derivation of important antenna figures of merit such as radiation efficiency and directivity.

Analysis of large circular loop with uniform current density along its circumference. Derivation of the radiated fields in the far-field region and calculation of radiation resistance, directivity, and maximum effective aperture.

Here, we analyze the radiation properties of a circular loop with nonuniform current along its circumference. We present important antenna parameters and various parametric studies as well as a design method. The design method is illustrated through an example. We also consider polygonal loop antennas and the ferrite loop antenna widely used in portable transistor receivers.

We provide examples and various applications of antenna arrays, as well as their usefulness in the area of wireless communications. This is simply an introduction to arrays and their impact on our lives.

We provide the analysis and operation of a simple two element array illustrating the effect of the array factor (due to the topology) on the overall radiation pattern of the antenna. The impact of certain parameters, such as the excitation phase shift and the spacing between the two elements, is explained and demonstrated through examples and pictures.

In this lecture, we explain how to obtain the array factor of an N-element linear array and how to obtain important antenna performance parameters such as half-power beamwidth, sidelobe maxima, sidelobe level, and the position of the pattern nulls and maxima. We also consider different orientations of the array; i.e., along the x-axis, y-axis, or z-axis.

Here, we present three important types of linear arrays namely the Broadside array, the Ordinary End-fire array, and the Phased or Scanning array. Important expressions for the characterization of these arrays, as well as the corresponding radiation patterns are presented and discussed.

The description of a special type of end-fire array, namely the Hansen-Woodyard end-fire array, is provided. This type of array provides improved directivity values compared to the ordinary end-fire array. The design conditions required for such an array are provided and explained.

The directivity of an N-element linear array is calculated using knowledge acquired from earlier lectures. We also present an approach for the design of an array based on a set of constraints. The design approach is illustrated through an example. We also explain how to obtain the total radiated field for different orientations of the linear array.

Introduction of nonuniform arrays. Application of nonuniform arrays starts with the binomial type. Important performance characteristics of the binomial design are discussed and pointed out.

Important characteristics of the non-uniform Dolph-Chebyshev array and calculation of important figures of merit (e.g. Directivity). We also present and illustrate through an example a procedure on how to design a Dolph-Chebyshev array based on certain constraints (e.g., sidelobe level).

We introduce planar arrays and explain how to derive the array factor using the knowledge acquired from linear arrays. We also explain how phased planar arrays work by correlating the radiation pattern to the progressive phase shift along the x- and y-directions.

We present the axial and normal modes of a helical antenna as well as a design procedure through examples. Circular polarization is also emphasized including matching of the antenna to a feeding transmission line.

Here, we discuss major characteristics and potential applications of this type of antenna. The performance of this antenna is illustrated through a number of parametric studies by altering geometrical parameters. A design procedure is explained in detailed and illustrated through an example.

We present important characteristics of patch antennas including applications, advantages and disadvantages. We also introduce the transmission-line model which is widely used for the design and analysis of microstrip patch antennas printed on low-loss substrates.

A design procedure is introduced for the rectangular patch antenna. The design is illustrated through an example. The input impedance and power radiated by the patch are calculated based on the slot self and mutual conductance derived using the transmission-line model.

The cavity model is used for the analysis of the rectangular patch antenna. Based on this model, the magnetic current densities are obtained on the surrounding walls, which are used to calculate the radiated fields based on the auxiliary vector potential formulation presented in earlier lectures.

The directivity and beamwidth of a rectangular patch antenna are computed based on the radiated fields obtained using the cavity model. Simple expressions are provided for the directivity and beamwidth.

Introduction of the circular patch antenna and use of the cavity model in cylindrical coordinates for the calculation of the radiated fields and important figures of merit; e.g., directivity. A design procedure is demonstrated through an example.

Discussion of important figures of merit of circular patch antennas such as input impedance, quality factor, bandwidth and efficiency. We also discuss coupling between patch antennas printed on the same substrate with a given separation.

In this lecture, we present techniques commonly used in the design of circularly polarized patch antennas. We also present popular feed networks for an array of patch antennas. Matching of the feed network to the input impedance of the patch elements is highly important. Scanning arrays of patch elements and blind spots due to strong reflections are also discussed.

Use of the Equivalence Principle, the Image Theory and the Auxiliary Vector Potential formulation for the derivation of the radiated fields of a rectangular aperture in an infinite conducting screen. The aperture may be placed in the xy-plane, the xz-plane or the yz-plane.

The radiated fields by a rectangular aperture obtained in the previous lecture are used in order to calculate important antenna figures of merit such as directivity, beamwidth, sidelobe level, and aperture efficiency.

In here, we use cylindrical coordinate system to derive the radiated fields by a circular aperture in an infinite conducting ground plane. The principal E- and H-plane patterns are explicitly given. Important figures of merit, such as directivity, HPBW, FNBW, sidelobe level, are provided. The Babinet's principle is also illustrated through an example.