Uploaded February 2025 | Updated September 2026, 1 week ago
Antenna Design playlist. Watch these video to understand more on Antenna Design.
youtube.com/watch?v=RTtCxtSaG8w&list=PLFxhgwM1F4ywAyke2KC22BLBl1V4vV9Jt
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What is an Antenna & How Does it Release Electromagnetic Wave into the Environment?
The IEEE Standard Definitions of Terms for Antennas (IEEE Std 145–1983) defines an antenna or aerial as “a means for radiating or receiving radio waves.” In other words, an antenna is a transitional structure between free space and a guiding device.
The guiding device or transmission line may take the form of a coaxial cable or waveguide and is used to transport electromagnetic energy either from the transmitting source to the antenna or from the antenna to the receiver. In the former case, it functions as a transmitting antenna, and in the latter, as a receiving antenna.
A transmission-line Thevenin equivalent of the antenna system in the transmitting mode where the source is represented by an ideal generator, the transmission line is represented by a line with characteristic impedance Zc, and the antenna is represented by a load ZA = RL + Rr + jXA connected to the transmission line.
Under ideal conditions, energy generated by the source should be totally transferred to the radiation resistance Rr, which is used to represent radiation by the antenna.
However, in a practical system, conduction and dielectric losses occur due to the lossy nature of the transmission line. The antenna, along with reflection (mismatch) losses at the interface between the line and the antenna. Considering the internal impedance of the source and neglecting line and reflection losses, maximum power is delivered to the antenna under conjugate matching.
Complex Conjugate match for Max Pwr Transfer: ZA = RL + Rr - jXA
The reflected waves from the interface, along with the traveling waves from the source toward the antenna, create constructive and destructive interference patterns inside the transmission line. These patterns, known as standing waves, form regions of energy concentration and storage, characteristic of resonant devices. A typical standing wave pattern is shown as a dashed line. If the antenna system is not properly designed, the transmission line could act largely as an energy storage element instead of a wave-guiding and energy-transporting device.
The losses due to the transmission line, antenna, and the standing waves are undesirable. The losses due to the transmission line can be minimized by selecting low-loss transmission lines while those of the antenna can be decreased by reducing the loss resistance represented by RL.
The standing waves can be reduced, and the energy storage capacity of the line minimized, by matching the impedance of the antenna (load) to the characteristic impedance of the line. This is the same as matching loads to transmission lines, where the load here is the antenna
An equivalent circuit is used to represent the antenna system in receiving mode, where the source is replaced by a receiver. All other parts of the transmission-line equivalent remain the same. The radiation resistance Rr represents the transfer of energy from the free-space wave to the antenna in receiving mode.
In addition to receiving or transmitting energy, an antenna in an advanced wireless system is typically required to optimize or enhance radiation in certain directions while suppressing it in others. Thus, the antenna must function not only as a probing device but also as a directional device. To fulfill specific requirements, it can take various forms, such as a conducting wire, an aperture, a patch, an array of elements, a reflector, or a lens, among others.
The propagation of waves is easily observed in the 'water analogy.' While not a perfect match for radio waves, it effectively illustrates the concept.
The figure below illustrates a body of water into which a ball is dropped (Fig. A). Upon impact with the water (Fig. B), the ball displaces water at the point of contact, pushing a leading wave outward. As the ball continues to sink, the wave propagates away from it until the energy dissipates.
The wave produced by a dropped ball is not continuous, but rather is damped (i.e., it will reduce in amplitude on successive crests until the energy is dissipated and the wave ceases to exist)
Although the figures show the action in only one dimension (a side view), the actual waves propagate outward in all directions, forming concentric circles when viewed from above.
Antenna Design playlist. Watch these video to understand more on Antenna Design.
youtube.com/watch?v=RTtCxtSaG8w&list=PLFxhgwM1F4ywAyke2KC22BLBl1V4vV9Jt
For access to this presentation materials, membership is required: I need the Material PPT
Sent me an email to Technologies.Discussion@gmail.com
If you need the whole playlist material, send me email and we discuss.
Give me some time to response. Thanks.
What is an Antenna & How Does it Release Electromagnetic Wave into the Environment?
The IEEE Standard Definitions of Terms for Antennas (IEEE Std 145–1983) defines an antenna or aerial as “a means for radiating or receiving radio waves.” In other words, an antenna is a transitional structure between free space and a guiding device.
The guiding device or transmission line may take the form of a coaxial cable or waveguide and is used to transport electromagnetic energy either from the transmitting source to the antenna or from the antenna to the receiver. In the former case, it functions as a transmitting antenna, and in the latter, as a receiving antenna.
A transmission-line Thevenin equivalent of the antenna system in the transmitting mode where the source is represented by an ideal generator, the transmission line is represented by a line with characteristic impedance Zc, and the antenna is represented by a load ZA = RL + Rr + jXA connected to the transmission line.
Under ideal conditions, energy generated by the source should be totally transferred to the radiation resistance Rr, which is used to represent radiation by the antenna.
However, in a practical system, conduction and dielectric losses occur due to the lossy nature of the transmission line. The antenna, along with reflection (mismatch) losses at the interface between the line and the antenna. Considering the internal impedance of the source and neglecting line and reflection losses, maximum power is delivered to the antenna under conjugate matching.
Complex Conjugate match for Max Pwr Transfer: ZA = RL + Rr - jXA
The reflected waves from the interface, along with the traveling waves from the source toward the antenna, create constructive and destructive interference patterns inside the transmission line. These patterns, known as standing waves, form regions of energy concentration and storage, characteristic of resonant devices. A typical standing wave pattern is shown as a dashed line. If the antenna system is not properly designed, the transmission line could act largely as an energy storage element instead of a wave-guiding and energy-transporting device.
The losses due to the transmission line, antenna, and the standing waves are undesirable. The losses due to the transmission line can be minimized by selecting low-loss transmission lines while those of the antenna can be decreased by reducing the loss resistance represented by RL.
The standing waves can be reduced, and the energy storage capacity of the line minimized, by matching the impedance of the antenna (load) to the characteristic impedance of the line. This is the same as matching loads to transmission lines, where the load here is the antenna
An equivalent circuit is used to represent the antenna system in receiving mode, where the source is replaced by a receiver. All other parts of the transmission-line equivalent remain the same. The radiation resistance Rr represents the transfer of energy from the free-space wave to the antenna in receiving mode.
In addition to receiving or transmitting energy, an antenna in an advanced wireless system is typically required to optimize or enhance radiation in certain directions while suppressing it in others. Thus, the antenna must function not only as a probing device but also as a directional device. To fulfill specific requirements, it can take various forms, such as a conducting wire, an aperture, a patch, an array of elements, a reflector, or a lens, among others.
The propagation of waves is easily observed in the 'water analogy.' While not a perfect match for radio waves, it effectively illustrates the concept.
The figure below illustrates a body of water into which a ball is dropped (Fig. A). Upon impact with the water (Fig. B), the ball displaces water at the point of contact, pushing a leading wave outward. As the ball continues to sink, the wave propagates away from it until the energy dissipates.
The wave produced by a dropped ball is not continuous, but rather is damped (i.e., it will reduce in amplitude on successive crests until the energy is dissipated and the wave ceases to exist)
Although the figures show the action in only one dimension (a side view), the actual waves propagate outward in all directions, forming concentric circles when viewed from above.
