Table Of Contents

Antenna Basics

If you have ever asked, "how do antennas work?" picture devices that can catch radio waves travelling through the air and convert them into electric signals.

They transfer signals into devices such as a radio, television, or telephone system.

Read on for a complete answer to the above question.

This article will discuss the basics of antenna theory, such as what an antenna is, how they work, and how they look. Other areas considered are how electromagnetic waves travel, the length of the antenna, their properties, and antenna types.

In addition, this article will tell you how radio antennas and digital tv antennas work. To round it up, a look at standard antenna designs, upgrading and installing antennas, diagnosing problems, and who to call for antenna issues.

What Is An Antenna?

An antenna is a metallic frame used to transmit or capture radio or electromagnetic signals. Antennas come in various sizes, shapes, and specialisations. For example, a bowl-shaped parabolic antenna transmits and receives electromagnetic signals that propagate vertically and horizontally.

A transmitting antenna converts electric signals into radio waves. The radio waves then travel long distances around the earth or to and from space. Radio signals from space are converted into electrical signals by a receiving antenna.

A ground wave is a radio wave that reaches the receiving antenna and then transmits directly without any reflection from the ionosphere.

How Do Antennas Work?

Assume you wish to transmit a radio program globally. First, you would use microphones to get the sounds from the participants' voices. As radio waves, the sounds are turned into electrical energy and channelled along a metal antenna. They are boosted to travel long distances.

These radio waves propagate at the speed of light to broadcast your radio program. When a listener turns on their radio, the metal antenna channels the radio waves to the device. There, the electrons begin to wiggle back and forth, generating an electric current. Finally, electronic components in the radio convert the signal back to sound.

In summary, the process is as follows:

  • Electrons vibrate up and down the transmitting antenna as electricity flows through it.
  • This vibration produces radio waves that travel across distances at the speed of light.
  • The waves arrive at the receiving antenna and cause electrons to vibrate within it as well.
  • The resultant electric current is converted into sound and picture.

How Transmitter And Receiver Antennas Look

Transmitters and receivers generally look different. Your TV or radio broadcasting antennas are in the form of huge masts that occasionally extend hundreds of meters/feet upwards. They need their powerful signals to travel long distances.

On the other hand, your TV or radio antenna at home is much smaller and does not have to be placed high up over your roof.

Types Of Antennas

Log-Periodic Antennas

It is also known as a log-periodic array. Essentially, this multi-element antenna is a narrow directional beam that can receive a wide range of frequencies. Log-periodic antennas are pretty helpful in a wide range of applications that need variable bandwidth, directivity, and antenna gain.

Generally, there are two types of antennas under Log Periodic Antennas. They are Bow Tie Antennas and Log-Periodic Dipole array.

Bow Tie Antennas

They are also known as Butterfly or Biconical antennas. Biconical antennas are omni directional antennas whose low-frequency responses are used as high-pass filters. However, the radiation patterns become more distorted with higher limit frequencies away from the design frequency.

Log-Periodic Dipole Array

The Log-Periodic Dipole array is a widespread antenna type used in wireless communication technology. It has several dipole elements. Dipole array antennas have a form that reduces in size from the back to the front end.

Wire Antennas

Wire antennas are categorised as either linear or curved types. They are pretty cheap and straightforward to work with. Their use covers a wide range of applications. Wire antennas are further classified into dipole antennas, short dipole antennas, monopole antennas, and loop antennas.

Dipole Antennas

These are antennas you may find relatively easy to assemble and use. You can use them to design a custom antenna. They comprise two thin metal rods with a unique current and frequency flow. Its metal rods are connected to a receiver. Once an incoming signal hits the framing, electrical fields are generated, which causes electrons in the rods to vibrate.

Consequently, one end has a positive charge while the opposite side is negatively charged. The oscillating field induces currents in the rods, inducing a sinusoidal voltage difference between them. Ultimately, the current and voltage flow results in an electromagnetic wave, causing radiating radio signals.

A balun can come in useful when feeding dipole antennas. It helps in transferring power between a single-ended coaxial cable and dipole antennas.

Short-Dipole Antennas

A short-dipole antenna is quite simple. It has two co-linear conductors at both ends with a bit of gap in between.

Monopole Antennas

Guglielmo Marconi discovered you could dispense with one-half of the dipole antenna by grounding the transmitter. He invented the vertical or monopole antenna. Marconi's form was practical mainly because of the circular polarisation, allowing long-distance communications.

Monopole antennas may need to be positioned entirely on top of a tower for higher frequencies like VHF transmissions for TV and FM radio. Thus, a dipole antenna or its variation is needed in such a situation.

The monopole antenna is similar to the half-wave dipole antenna in that the radiation patterns above the grounded plane are the same. Monopole antennas are half of the simple dipole antennas, and they are placed over a grounded plane.

They provide the necessary ground plane for antennas mounted above ground and are pretty useful as vehicle-mounted antennas.

Their field radiation is restricted to the upper hemisphere region, and the total power radiated is one-half that of a dipole.

Loop Antennas

Loop antennas are easy to construct. The antenna design takes many different shapes. Based on the designer, loop antennas can be rectangular, circular, or triangular. A loop antenna carries radio frequency signals. You can use them as electromagnetic field probes in microwave bands and in communication links.

Here, the circumference of the loop determines if it is electrically small or large. Small loop antennas are great as receiving antennas. However, they are not used as transmitting antennas because of their low efficiency.

Large loop antennas – also called resonant antennas - are used at higher frequencies like VHF and UHF. Their size is conveniently large. Additionally, they are directed by the operation of wavelength.

Travelling Wave Antennas

Travelling wave antennas are differentiated into helical antennas and Yagi-Uda antennas.

Helical Antennas

Their simple structure comprises one, two, or more wires wound individually to form a helix. They have a ground plane-shaped reflector. Standard helical antenna designs have a single wire fed with a coaxial cable.

Yagi-Uda Antennas

The Yagi-Uda is a common type of antenna. It uses passive elements and can be inexpensive. You can make a Yagi antenna using a frame with a single reflector, director, and a folded dipole active element. Then, you mount it in the forward direction for horizontal polarisation.

Other antenna types include the following:

  • Microwave antennas, which work at microwave frequencies
  • Patch antennas or rectangular microstrip antennas that only need space for a feed line placed behind the ground plane
  • Planar inverted-F antennas provide high gain in horizontal and vertical states. They are great for wireless communications
  • Reflector antennas, which include the corner reflector antenna and parabolic reflector antenna
  • The corner reflector antenna has one or more dipole elements in front of its reflector. This increases the antenna's directivity
  • A parabolic reflector antenna changes a diverging spherical wavefront to a parallel wavefront. Thus, it produces a narrow beam
  • Shaped reflector antennas can be used as outdoor base stations in mobile communications

Directional Antennas

A directional antenna, also referred to as a beam antenna, is an antenna that radiates or receives significant power in a specific direction, allowing for an increase in performance and a reduction of interference from unwanted sources.

Phased Array Antennas

The term phased array can sometimes mean an ordinary array antenna. That said, phased array antennas comprise thousands of individual antennas. You can steer beams of radio waves electronically, so they point in any direction without having to move your antenna.

How Modern Radio Antennas Work

Many modern transistor radios come with a minimum of two antennas. The first extends from the case as a long, shiny telescopic rod. It swivels around to pick up FM (frequency modulation) signals. Typically, FM signals have a frequency of about 100 MHz (megahertz).

This makes them vibrate around a hundred times faster than AM signals. The second antenna is within the case. Usually, it is attached to the main circuit board to pick up amplitude modulated signals. These AM radio signals typically have a frequency of 1000 kHz (kilohertz).

The wavelengths of AM signals are roughly a hundred times bigger than FM signals. This is why you need two antennas. One antenna will not be enough to pick up such largely different wavelengths.

Digital TV Antennas

This type of antenna is specially designed to receive digital TV signals. As usual, it is placed outside on the roof. This way, it can get access to the clearest signals. Its cable is run through your TV point and connected to your TV. As a result, you can watch digital channels.

Digital TV signals in Australia are broadcasted on two frequencies:

  • Very high frequency, which is VHF Band III (channels 6-12)
  • Ultra-high frequency, which is UHF Band IV and V (channels 28-51)

The antenna's polarisation needs to be well set up to get a strong signal. There are vertically and horizontally generated signals when it comes to signal polarisation. As such, your digital antenna installation company should know the antenna's polarisation so that it is in line with your local central transmission tower.

The tower in Brisbane, for example, has horizontal polarisation. On the other hand, the tower in Canberra is vertically polarised.

How Digital TV Antennas Work

Analogue signals are usually transmitted and received by a TV antenna. As a result, you may experience grainy images and fuzzy sounds if there are signal issues. Such signals may not be in the right channel frequency. In other words, they may be sent in the VHF rather than the UHF band range.

Digital TV antennas are specially optimised to pick up particular radio frequency bands, including HF, VHF, and UHF. The signal is decoded as it goes through your antenna. A built-in filter cuts down any "noise" or fuzziness. If the signal is poor, the picture will likely freeze up completely, or you may not see a picture at all.

Television signals come in the form of electromagnetic waves that induce tiny electric currents. Your TV amplifies the signal and then picks the information-carrying image and sound.

The metal plates at the end of array antennas reflect signals through their length. The parallel rod-like structures along the length of the antenna help optimise signal strength.

Digital TV Antennas Types

There are four types of digital TV antennas:

Indoor Antennas

They appear somewhat like rabbit ears and are placed on top of your TV or nearby. Indoor antennas may be sufficient in areas with outstanding signal strength. You can pick up several local channels. However, they are easily affected by interference compared to an outdoor antenna.

Omnidirectional Antennas

Omnidirectional antennas are small and can receive UHF or VHF frequencies that carry TV signals. Indoor TV antennas tend to perform very poorly for the following reasons.

  • Omnidirectional antennas do not 'point' towards the direction of TV transmission towers. This creates poor signal quality
  • Their single and short element provides low antenna gain – inferior signal power level
  • Unwanted signals are not filtered out, causing interference and TV tuner overload. In turn, this can result in the absence of pictures, audio, or pixelation
  • Their omnidirectional nature causes a low front-to-back ratio. As such, unwanted signals are received, which causes 'noise' and a low-quality signal

Outdoor Antennas

Outdoor antennas provide better signals with minimal interference.

Loft TV Antennas

Loft TV antennas can be installed in roof spaces. This makes installation more straightforward than that of an outdoor antenna. However, it may result in a weaker signal. Still, the signal is better than that of the indoor antenna.

Common Antenna Designs

Australia's most commonly used antenna design is a "Yagi" or Yagi-Uda antenna. The Yagi-Uda antenna gets a stronger signal with a lower frequency range. This frequency range only spans VHF or UHF.

Another typical design you will find in Australia is the Log-periodic antenna. It is pretty compact and has a similar design to the Yagi's. Log-periodic antennas usually receive weaker signals. It spans a broader range of frequencies.

Australia's most commonly used antenna design is a "Yagi" or Yagi-Uda antenna. The Yagi-Uda antenna gets a stronger signal with a lower frequency range. This frequency range only spans VHF or UHF.

Another typical design you will find in Australia is the Log-periodic antenna. It is pretty compact and has a similar design to the Yagi's. Log-periodic antennas usually receive weaker signals. It spans a broader range of frequencies.

Upgrading To Digital TV Antennas

A digital aerial is needed to receive free-to-air broadcast signals. Older antennas were designed for analogue TV signals, but you may be able to receive digital TV wave transmissions on them.

There are merits to getting a newer TV antenna. They are specially designed for digital TV signal reception. If your older antenna has frequency or other signal issues, upgrade to a digital antenna.

Considerations For TV Antenna Installations

  • Use a TV antenna mount/mast and alignment that maximises antenna height
  • A TV antenna booster can provide increased signal power gain
  • You can screw wall plates onto the wall. This makes for an easy plugin of a fly lead or a short patch antenna
  • Use a coaxial cable to get power to TV boosters
  • Find out if there are existing reception, signal coverage, or field strength problems
  • The received signals should not come from multiple antennas with few broadcasting sites. It causes poor signals.

How To Diagnose Digital Antenna Problems

Your antenna may have lost reception or signal strength. How do you find out the issue? Here are some steps to take:

  • Check that the antenna is securely attached and no parts are missing without climbing on your roof.
  • Confirm that it is still pointed towards the direction of transmission towers
  • Check that there is a proper connection between devices and cables
  • Confirm that the TV is on the right source input, such as antenna, video, or HDMI. Use the TV's remote menu
  • Restart or retune your TV and reconnect it to the TV point
  • Check for other issues like internal cabling, TV amplifier, or power supply
  • Rather than go for strictly vertical antennas, you can opt for one-for-all antennas as they can be set to vertical or horizontal polarisation
  • Metallic materials can block both TV and radio signals, so keep the antenna 6 feet or more away from metal objects

Seek The Services Of A Professional Technician

You no longer have the need to ask: 'how do antennas work?' at this point because we have discussed it all above. You now have a sound understanding of how they work. You know their designs, properties, types, and steps to diagnose problems.

When something goes wrong with your antenna systems, you will be able to identify the problem. However, if you are stumped or it is a severe issue, you should invite a professional technician to assess and rectify the issue.

They can make recommendations based on your region's specific antenna requirements. Moreover, they are familiar with antennas, radio technology, wireless communication, and wireless systems. For instance, they can quickly locate the far-field electric and magnetic fields generated by a short dipole.

In other words, you do not really need to intimately understand antenna theory or electric field lines as long as there's a professional around.