Circularly Polarized Antenna Technology

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• Publisher: De Gruyter
• Year: 2020
• eBook ISBN: 9783110561562
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Science General
• Index: Technology & Engineering

The book presents basic and advanced concepts of circularly polarized antennas, including design procedure and recent applications. Cross dipole antennas, microstrip antennas, helical antennas, quadrifilar helix antennas, frequency independent antennas, horn antennas, omnidirectional circularly polarized antennas and radial line arry antennas are discussed. With abundant examples, the book is an essential reference for researchers and engineers.

Chapter 1 Parameters of antennae

An antenna is an energy convertor in the radio equipment that converts bound circuit fields into propagating electromagnetic waves from the transmitter or converts propagating electromagnetic waves into bound circuit fields to the receiver. With the development of wireless technology, antennae find wider use. The performances of many wireless systems are mainly limited by antennae. The antenna requirements of a system are dependent on antenna parameters in practical engineering. This chapter mainly deals with the antenna parameters used in practical engineering.

1.1 Radiation power density and radiation intensity

1.1.1 Radiation power density

Spherical waves radiated by antennas will propagate in the radial direction for a coordinate system centered on the antenna [1]–[3]. These waves can be approximated at large distances by plane waves in a small area at the antenna directional angle.

Both the direction of propagation and the power density of the electromagnetic wave can be described by the Poynting vector. It is the vector cross product of the electric and magnetic fields and is denoted by S and expressed as follows:

(1.1)$\mathbf{S}=\mathbf{E}\times {\mathbf{H}}^{\ast }\left(\mathrm{W}/{\mathrm{m}}^2\right)$

where E is the electric field vector measured in units of volt per meter (V/m). H is the magnetic field vector measured in units of ampere per meter (A/m). ${\mathbf{H}}^{\ast }$is the complex conjugate of the magnetic field vector. The direction of the Poynting vector is orthogonal to both electric and magnetic fields. The directions of E, H and S define a right-handed coordinate system. We can determine the intensity and direction of the energy flow at any point in the space if we know E and H by using eq. (1.1).

The average power density, W, could be expressed as follows：

(1.2)$W(r,\theta ,\varphi )=S_{av}=\frac{1}{2}Re(\mathbf{E}\times {\mathbf{H}}^{\ast })=\frac{{\left|\mathbf{E}\right|}^2}{2\eta }$

where η is the intrinsic impedance of the medium (η = 376.73 Ω in free space).

Power density can be expressed as a spherical energy flow. The total power P of the antenna radiation can be obtained by taking the closed-surface integration of the power density on the enclosed surface of the antenna.

(1.3) $P={\displaystyle ∯W\cdot gds}={\displaystyle {\int }_0^{2\pi }{\displaystyle {\int }_0^{\pi }{W}_r}}(r,\theta ,\varphi )r^2\sin \theta d\theta d\varphi ={\displaystyle {\int }_0^{2\pi }{\displaystyle {\int }_0^{\pi }{W}_r}}(r,\theta ,\varphi )r^{2}d\Omega$

where $d\mathrm{\Omega }=sin\theta d\theta d\varphi$ is the differentiation of the solid angle, shown in Fig. 1.1.

Fig. 1.1: The dΩ shown in polar coo...

Table of contents

• Title Page
• Copyright
• Contents
• Introduction
• Chapter 1 Parameters of antennae
• Chapter 2 Polarization theory
• Chapter 3 Crossed dipole circularly polarized antenna
• Chapter 4 Circularly polarized microstrip antenna
• Chapter 5 Helix antenna
• Chapter 6 Quadrifilar helix antennas
• Chapter 7 Circularly polarized frequency-independent antenna
• Chapter 8 Circularly polarized horn antennas
• Chapter 9 Omnidirectional circularly polarized antenna
• Chapter 10 Circularly polarized radial line array antenna
• Index