Understanding Different Types of Antennas in Wireless Communication

Antennas play a crucial role in enabling effective communication across wireless, mobile communication, and mobile computing systems. They serve as the primary interface for transmitting and receiving electromagnetic signals, ensuring seamless connectivity and data transfer. In this article, we will explore different types of antennas, such as horn antennas, parabolic antennas, dipoles, microstrip patches, YAGI antennas, log-periodic antennas, phased array antennas, and helical antennas, and their specific applications in various wireless communication technologies. Understanding these antennas helps in selecting the right one for enhancing system performance and meeting specific requirements.

Horn Antenna

A horn antenna is essentially a flared waveguide. It can work more efficiently when used with a parabolic reflector, as found in dish antennas. Horn antennas are commonly used in satellite and microwave applications. If a normal waveguide is used for transmission of electromagnetic waves, it will not be tightly coupled with free space impedance, resulting in reflected power and standing waves. These mismatches are avoided by flaring the end of the waveguide, which creates the horn antenna. The more gradual the flare, the better the matching and the lesser the losses. This results in greater gain and directivity.

Depending upon the flaring, there are different horn antenna types, including sectoral horns, pyramidal horns, and conical horns. The gain of a pyramidal horn can be summarized as:

$G = \frac{4 \pi K A}{\lambda^2}$

Where:

• $K$ is approximately 0.5 to 0.6, depending on how the phase/amplitude of electromagnetic fields are displaced across the aperture.
• $A$ is the aperture of the horn in square meters.
• $\lambda$ is the wavelength in meters.

The horizontal beamwidth of the pyramidal horn can be summarized as:

$B = \frac{80}{(w/\lambda)}$

Where:

• $B$ is the beamwidth in degrees.
• $w$ is the width of the horn antenna.
• $\lambda$ is the wavelength.

Parabolic Reflector Antenna

This parabolic reflector antenna is used in conjunction with a horn antenna, as shown in the figure. It is made of metal or screen mesh. As shown in the figure, during transmission, electromagnetic waves fall onto the wide dish and get radiated into the air, while during reception, electromagnetic waves fall onto the dish and get focused onto the horn antenna.

The aperture of the parabola antenna is the area of the outer circle of the parabola. The area $A$ is calculated as:

$A = \pi R^2$

The gain $G$ is:

$G = 6 \left( \frac{D}{\lambda} \right)^2$

Where $D$ is the diameter of the dish antenna and $\lambda$ is the wavelength.

Helical Antenna

As the name suggests, a helical antenna is made of a coil surrounding an insulating support. The diameter of the wire is about 1/3 of the wavelength, and the spacing between turns is about 1/4 of the wavelength. About 6-8 turns are usually used in this type of antenna. A ground plane reflector behind the helix, either circular or square in shape, is used. This antenna is widely used in the VHF/UHF range. The gain and beamwidth of this helical antenna are about 12-20 dB and 12-45 degrees, respectively.

Slot Antenna

A slot antenna is formed by cutting a metal sheet or waveguide about half a wavelength in size. Due to this cutting of the slot, it is known as a slot antenna. Several slots can also be cut to form a slot antenna array. An array antenna usually has better gain and directivity compared to a single slot antenna. Slot antennas are widely used in high-speed aircraft by filling the slot with insulating material to create a smooth surface. Other external antennas would not be convenient to use at such high speeds.

Dielectric Antenna

Dielectric antennas are made of polystyrene, plastic, or other dielectric materials. These lens antennas are used for millimeter-wave frequencies above 40 GHz. In this kind of antenna, a dielectric lens is placed over the end of the horn antenna, which focuses waves into a narrower beam. This results in greater gain and directivity.

Microstrip Patch Antenna

This antenna type is made with a microstrip-based design on a PCB. Hence, it is called a microstrip patch antenna. This antenna is basically a circular or rectangular area of copper separated by a conducting ground plane. Between these, there will be an insulating surface. In the case of a rectangular antenna, the width is approximately 1/2 of the wavelength, while in the case of a circular antenna, the diameter is approximately 0.55 to 0.59 of the wavelength.

Phased Array Antenna

A phased array antenna is developed using multiple antennas on a common PCB or plane. The antennas used here are patch antennas or dipole antennas in an array. This combination of multiple antennas helps improve gain and directivity. Individually, all the antennas of the array are controlled, and hence electromagnetic waves can be radiated in different directions as desired. The same concept is applied in YAGI antennas and parabolic dish antennas used for TV reception. Another application of this type of antenna is radar and satellite-based communication systems.

There are two types of arrangements designed in this type of antenna. In one configuration, all the antennas are fed from a common transmitter or receiver. In the other configuration, a low-power transmitter amplifier or LNA is used with each of the array antennas.

Dipole Antenna

Antennas radiate effectively when the length of the antenna is directly related to the transmitted signal wavelength. Dipole antennas are available in half-wave or quarter-wavelength sizes. A half-wave dipole antenna, called a doublet, will have a length equal to 1/2 of the wavelength of the operating frequency. Usually, RG-59/U is used for 73 Ohm coax lines, and RG-11/U is used for 75 Ohm lines.

The length of this dipole, $L$, can be approximated as:

$L = \frac{468}{\text{Freq (MHz)}}$

The shape of the radiation pattern of the half-wave dipole antenna is like a doughnut.

Directional Antenna

Antennas having an omnidirectional radiation pattern transmit/receive in any direction. In order to send and receive in a particular direction, an antenna with high directivity is required. This type of antenna, having a radiation pattern limited to a narrow horizontal range, is called a directional antenna. In order to design this kind of antenna, two or more antennas are combined to make an array. This increases gain and directivity. There are two array antenna types: parasitic arrays and driven arrays.

Folded Dipole Antenna

This is one of the popular types of antennas due to its 300 Ohm impedance. The folded dipole antenna is made of 300 Ohm twin lead, having a length equal to one-half wavelength. Their ends are soldered. This is a variation of the standard half-wavelength dipole antenna. As shown in the figure, two parallel conductors are connected at the ends, with one side open at the center. This central open part is interfaced with the transmission line.

The spacing between conductors is inversely proportional to frequency. For low-frequency applications, the spacing is about 2 or 3 inches. For high-frequency applications, the spacing is about 1 inch.

Ground Plane Antenna

When vertical polarization and an omnidirectional pattern are needed, a ground plane antenna can also be a replacement for a standard half-wave dipole antenna. This antenna is fed with a coaxial cable. It is formed by a center conductor connected to the vertical radiator and a shield connected to the earth ground. This generates a vertical omnidirectional radiation pattern.

The vertical ground plane antennas are widely used in cars, trucks, boats, and other vehicles. The flat metallic surface of the vehicle acts as a superior ground plane for VHF/UHF antennas. The impedance of this vertical ground plane antenna is about 36.5 Ohm. As no coaxial cable exists at this impedance, a standard 50 Ohm cable is used, which generates a mismatch of about 1.39 SWR.

YAGI Antenna

YAGI antennas were widely used for TV reception, but as they are designed for one frequency only, they are not suited for a wide frequency range. YAGI antennas are made of one driven element, one reflector, and one or more directors. They are made with aluminum tubes and an aluminum cross member.

Log Periodic Antenna

The benefit of this log-periodic antenna is its wide bandwidth application. It is formed by different-length driven elements. The longest and shortest elements are half a wavelength long at the lowest and highest frequencies of interest. The elements of this log-periodic antenna are fed with transmission line segments. The phases of the signals sent to different elements are properly set to achieve high directivity and the best gain.

Conclusion

Choosing the right type of antenna is vital for optimizing signal strength, coverage, and efficiency in wireless and mobile communication systems. Each antenna type has its own characteristics, making it suitable for different use cases and environments. By understanding the features and benefits of each, users and designers can make informed decisions that improve overall network performance, support diverse applications, and ensure reliable connectivity in a variety of communication scenarios.