Unlocking wireless communications: The power of antennas

Antennas are the eyes and ears of a communication system. They are devices that help electromagnetic energy travel between electronic devices and the air. Therefore, antennas are like a bridge between electronic circuits and radio waves. Through this connection, devices can send and receive signals. In daily life, antennas are commonly found in many devices, such as mobile phones and Wi-Fi. Different antennas have different uses.

Dipole Antenna

Dipole antennas are commonly used to transmit radio and television signals. They are a type of radio frequency antenna. They have two conductive elements in the form of rods or wires. The length of these conductive elements is approximately half the maximum wavelength of the operating frequency in free space. An insulating material separates the two conductive materials from the center of the antenna. The figure below shows a dipole antenna. This antenna can be placed horizontally or vertically.

Figure 1: Dipole antenna

The RF voltage source is located in the middle of the antenna. Two conductive elements provide voltage and current. These elements create an electromagnetic signal, or radio signal, which is radiated out of the antenna. The voltage is lowest and the current is highest at the center of the antenna. The current is lowest and the voltage is highest at the ends of the dipole antenna. This is how the dipole antenna distributes the current.

Figure 2 shows the radiation pattern of a dipole antenna perpendicular to the antenna axis. The radiation characteristics of an antenna are graphically depicted by the radiation pattern. This pattern describes how the antenna radiates energy into space.

Figure 2: Radiation pattern

Therefore, this antenna converts electrical signals into radio frequency electromagnetic signals. These signals are transmitted at the transmitting end and the radio frequency electromagnetic signals are converted into electrical signals at the receiving end.

Loop Antenna

This type of antenna is made by bending a coil or a uniformly thick wire into a loop. In simple terms, it is a RF current-carrying coil bent into shapes such as circles, squares, rectangles, and ovals.

These antennas are simple, inexpensive and versatile. Their applications are numerous and they are commonly used in AM broadcast and low frequency applications.

Figure 3: Loop antenna

Of all the antenna shapes, loop antennas are the most widely used because they are very simple to construct and analyze.

Loop antennas are also called radiating coils, and the cross-section is single coil or multiple coils. Loop antennas with two or more coils are called frames. The operating frequency range allowed by loop antennas is between 300 MHZ and 3 GHz.

Horn Antenna

A horn antenna is an aperture antenna. It is designed for microwave frequencies (300 MHz – 30 GHz). The end of the antenna is shaped like a horn. This shape makes it more directional, so the transmitted signal can easily travel long distances.

Figure 4: Horn antenna

Parabolic dish antenna

Parabolic antennas collect or project energy, such as electromagnetic waves. They are often found in radar engineering.

Figure 5: Parabolic antenna

Circular parabolic reflectors are made of metal. This structure is usually a frame covered with a metal mesh on the inside. The width of the metal mesh slots must be less than λ/10. This metal covering is the reflector and acts as a mirror that reflects the radar energy.

A circular parabolic dish produces a pencil beam. If the reflector is elliptical, a fan beam is produced. Surveillance radars use two different curvatures in the horizontal and vertical planes to achieve the desired pencil beam in azimuth and the classic cosecant squared fan beam in elevation.

Parabolic dish antennas are highly directional and are commonly used in radio astronomy and satellite communications.

Yagi-Uda Antenna

The Yagi-Uda antenna (also known as the Yagi antenna) is a highly directional antenna with two or more parallel resonant antenna elements as half-wave dipoles. The antenna consists of three parts: reflector, driven element, and director. A single driven element is connected to a transmitter or receiver through a transmission line or other parasitic elements. In most cases, the reflector and some directors (longer elements) are parasitic elements.

Figure 6: Yagi-Uda Antenna

These parasitic elements (shorter elements) act as passive resonators. They work together with the driven element and are electrically disconnected from the transmitter or receiver. Yagi antennas usually operate in the HF and UHF range, providing operating frequencies between 30 MHz and 3 GHz, even at the minimum bandwidth. The unique design of these antennas allows good gain values ​​(over 10 dB).

Yagi-Uda antennas are highly directional. They are commonly used to receive television signals and for radio communications.

Patch Antenna

A patch antenna is an antenna made by etching a patch of conductive material on a dielectric surface. The dielectric material is mounted on a ground plane which supports the entire structure. A feed line connected to the patch excites the antenna. Patch antennas are also called microstrip antennas or printed antennas because this is a printed circuit board manufactured using microstrip technology.

Figure 7: Patch antenna

Patch antennas are commonly used in Wi-Fi and wireless communications.

Helical Antenna

The helical antenna is the simplest antenna and is widely used in UHF applications, usually in the VHF and UHF range. This antenna has a wire in the shape of a helix.

Figure 8: Helical antenna

Helical antennas have unique characteristics such as high bandwidth, high gain and circular polarization. The frequency range of this antenna is between 30MHz-3GHz and is commonly used in space communications, satellite communications and wireless networks.

Whip Antenna

Whip antennas are commonly seen in monopole radio antennas. This means that one antenna is replaced, rather than two antennas running side by side or forming a loop. These antennas are widely used in devices such as cell phones and handheld radios.

The length of the whip determines its potential wavelength. The loading coil can be mounted anywhere within the length of the antenna to shorten the length of the whip. Therefore, the inductance can be increased without increasing the length of the whip. The most common whip antennas are the half-wavelength whip and the quarter-wavelength whip.

The whip antenna is vertically polarized because it is mounted vertically on the bottom carrier. Whip antennas are often called omnidirectional whip antennas because they are able to radiate signals in all directions in the horizontal plane. However, this is not strictly true because all whip antennas have a top cone-shaped dead zone.

Single and dual-band antennas

Antennas can be classified as single-band antennas and dual-band antennas, depending on whether the antenna can operate in a single frequency band or in multiple frequency bands.

Single frequency antennas operate at a specific frequency. This operating range is usually narrow. Applications that only need one frequency band use this type of antenna. Traditional television systems and broadcast audio use single frequency antennas. This type of antenna can be modified for a specific frequency to get the highest efficiency and gain. Whip antennas, monopoles, loop antennas, horn antennas, and helical antennas are all examples of single frequency antennas.

Dual-band antennas, on the other hand, operate at two different frequencies. These antennas have separate elements or feed points for each frequency band. Typically, applications that require multiple frequency bands use dual-band antennas. Mobile communication systems use dual-band antennas. This type of antenna can operate on various frequency bands without the need to separate the antennas. Examples of dual-band antennas include dipole antennas, patch antennas, Yagi antennas, and log-periodic antennas.

The main difference between single-band and dual-band antennas

The difference between single-band antennas and dual-band antennas lies in their design and the number of frequency bands they each operate in.

Here are some of the key differences in the design of these two antennas:

Single-band antennas are designed to vibrate at a specific frequency. The physical size of the antenna determines this vibration. The length of the antenna determines its operating frequency. These antennas have a narrow bandwidth and can only operate at resonance and nearby frequencies.

Dual-band antennas are designed to have two different resonant frequencies. These frequencies are usually used for two different frequency bands. Dual-band antennas are equipped with separate elements or feed points for each band, allowing the antenna to operate at two different frequencies. If the antenna elements for each band are designed with different physical dimensions, performance can be optimized for each frequency range.

Performance characteristics of single-frequency and dual-frequency antennas

In terms of performance, single-band and dual-band antennas have their own advantages and disadvantages. These advantages depend on the application. The performance comparison is shown in the following table:

Applications of single-band and dual-band antennas

Frequency requirements are key when choosing whether to use a single-band or dual-band antenna. The following are common use cases for each antenna:

Single frequency antenna

• Cell phone tower

• GPS System

• Satellite Communications

• Radar System