He is also grateful for the research collaboration opportunities he has had with Prof. Satish K. Sharma from San Diego State University (SDSU), as well as his mentorship and friendship over the years. He is thankful to his family for their love and support, and who have allowed him to complete this work including his wife Kristine, and his two daughters Joanna and Audrey. Lastly, he is grateful to his parents (Dr. Shih‐Huang Chieh and Mrs. Dolly Chieh), who taught him the importance of learning and to never stop.
Professor Satish K. Sharma, PhDJia‐Chi S. Chieh, PhD
1 February 2021
San Diego, CA, USA
1 Introduction
Satish K. Sharma and Jia‐Chi S. Chieh
1.1 Introduction
In this chapter, we provide basic discussion about an antenna and its importance, type of antennas, and introductory information about the reconfigurable antenna, frequency agile antenna, multifunctional antenna, and antenna measurements.
1.2 Antenna: an Integral Component of Wireless Communications
An antenna is described as a device that radiates or receives transverse electromagnetic waves (TEM) from its surface, or structure. It is an integral component of all the wireless communication systems. As shown in Figure 1.1, the transmitter block which usually consists of the signal generator, modulator, and power amplifiers is terminated with an antenna to radiate the power in free space. A poor choice and design of antenna will result in the power being reflected to the source and cause waste of power, which is undesirable. Efficient power utilization becomes critical in applications such as onboard circuits in satellite communications. To emphasize the importance of antennas for the receiver circuitry, maximum power should be obtained from the incident wave to relax the burden on the succeeding blocks such as low noise amplifiers to maintain the required signal‐to‐noise‐ratio (SNR) for satisfactory wireless links. Different communication application demands different minimum required SNR for a satisfactory link and efficient antenna design plays a big role in achieving this goal.
Figure 1.1 The importance of antenna in a wireless communication system.
1.3 Antenna Performance Parameters
Antenna performance parameters can be categorized into two groups: circuit parameters and radiation parameters. Circuit parameters refer to the impedance matching properties such as reflection coefficient magnitudes (|Sii|) and isolation (|Sij|) between the antenna ports. Antenna radiation parameters refer to radiation patterns, gain, directivity, antenna efficiency, polarization, effective length and effective aperture, antenna temperature, etc. Readers should refer to the well‐known text book by C. A. Balanis, Antenna Theory: Analysis and Design (Fourth Revised edition), Wiley publications [1] for detailed discussion and learning about these antenna performance parameters.
1.4 Antenna Types
Various antennas that find use in wireless communication systems can be classified in many ways. Antenna geometry of four selected antennas is shown in Figure 1.2. Figure 1.2a shows a well‐known bow‐tie planar antenna that is known for wideband operation with omnidirectional radiation pattern performance. A planar inverted F‐antenna (PIFA) is shown in Figure 1.2b which has been known to provide single and multi‐band operation based on suitable dimension of the radiating structures and feeding mechanism. It also offers omnidirectional radiation patterns. Figure 1.2c shows a quasi‐Yagi planar antenna which offers end‐fire directional radiation patterns. Similarly, Figure 1.2d shows a stepped Vivaldi planar antenna which is known for its extremely wideband antenna performance.
The antenna performance can be characterized using impedance matching and radiation patterns. One example is shown in Figure 1.3. Figure 1.3a shows reflection coefficient magnitude versus frequency and Figure 1.3b shows 3D gain radiation patterns of an antenna. There are numerous full‐wave analysis tools, also called Maxwell Solvers, which provide accurate simulation and analysis results for an antenna. One such tool is Ansys high‐frequency structure simulator (HFSS) which has been used to generate these impedance matching and radiation pattern.
Figure 1.2 Some antenna types generated through Antenna Design Kit in Ansys Electronic Package.
1.5 Multifunctional Antennas
Multifunctional antennas can have features of frequency reconfiguration, polarization reconfiguration, beam steering, flexible radiation patterns, and radiation pattern reconfiguration in a single antenna structure. Combination of a couple of these features makes these antennas “multifunctional.” These antennas can meet multiple wireless communication standards and hence can provide multiple communication applications. Such antennas can also be multiband in nature and can have multiple‐input‐multiple‐output (MIMO) implementations. Also, multiple communication antennas on a common small size host platform, such as cellular phone size ground plane, can be categorized as “multifunctional” antenna.
Figure 1.3 Antenna performance shown using (a) reflection coefficient magnitude (S11, dB) and (b) 3D gain radiation pattern.
The full‐polarization reconfigurable antenna can switch between the vertical and horizontal linear polarizations, right‐hand circular polarization (RHCP), and left‐hand circular polarization (LHCP) depending on the communication system requirements. These antennas offer advantages of reduced antenna hardware, low weight, and low cost. Such antennas are very attractive to emerging wireless communications such as 5G communication systems. One such antenna is shown in Figure 1.4, which offers both frequency tunability and polarization reconfiguration [2].
