A brief introduction to antennas

Over the last few weeks, we’ve been talking a lot about communications technology, both terrestrial and satellite-based. For example, take a look at our articles on the history of mobile generations, or on satellite applications.

Terrestrial and satellite technology play different roles in communications, but they both involve radio waves, which means they both require antennas to transmit and receive those radio waves. Your mobile phone contains at least one antenna; it’s likely to contain more.
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Dr Soheyl Soodmand, our senior RF and antenna architect, has written a piece to share his expertise on the subject of antenna technology. Please enjoy the below article on how antennas work, and on some of the different types of antenna relevant to our work at Darwin.

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Webster’s Dictionary defines an antenna as ‘a usually metallic device (as a rod or wire) for radiating or receiving radio waves’. The Institute of Electrical and Electronics Engineers (IEEE) defines the antenna as ‘a means for radiating or receiving radio waves’. The latter is a better definition, as modern antennas make use of different materials and are implemented in diverse shapes.

When we informally refer to antennas, we are most commonly thinking of a set of three distinct elements:

1. the antenna, which transmits and receives the radio waves to/from free space
2. the receiver or transmitter, which transforms these waves into electrical signals
3. the intermediary structure or waveguide or transmission line, which transports the waves between the other two elements

Antennas are designed to work in specific radio frequencies, and the antenna does not transmit or receive radio waves outside this operating frequency range.

For wireless communication systems, the antenna is one of the most critical components. A good antenna design can relax system requirements and improve overall system performance. The antenna serves to a communication system the same purpose that eyes and eyeglasses serve to a human. Some famous antenna types include wire, aperture, microstrip, array, reflector, lens etc.

To describe the performance of an antenna, it is necessary to consider various parameters: radiation pattern, radiation power density, radiation intensity, beamwidth, directivity, efficiency, gain, beam efficiency, bandwidth, polarisation, input impedance, radiation efficiency, vector effective length, temperature etc. For multi-input antennas and array antennas other parameters, such as isolation, need to be considered. A description of these parameters is beyond the scope of this article, but the list should give the reader an idea of the complexity involved in analysing antenna options to identify the optimal solution for a given application.

In the case of Darwin’s work, antennas are mounted in vehicles for communication with mobile base stations and with satellites. To optimise transmission and reception of radio waves, there is a need to focus transmission and reception of waves between the vehicle and the cellular tower or satellite in space; this is achieved through a technique called beamforming. Because there is movement relative to vehicle and satellite or cellular tower coordinates, the radio wave beams need to be constantly realigned; this is achieved through a technique called beamsteering. Finally, to improve aerodynamics and preserve the aesthetics of vehicles, there is a preference for antennas which are either flat or able to conform with the roof surface of the vehicle.

Three main technological options have been identified for low-profile antennas: metamaterial antennas, lens antennas and phased array antennas.

• Metamaterial antennas: A metamaterial is a material that gains its properties from its structure rather than directly from its composition. Metamaterials have unique properties that are not found in natural materials. Curiously, the most common implementation of metamaterials leverages liquid crystal to individually tune thousands of irradiating elements, in a similar way to technology used in LCD televisions.
• Lens antennas: A lens antenna uses the convergence and divergence properties of a lens to transmit and receive signals. These antennas consist of a small feed antenna followed by a lens made of dielectric material, which manipulates electromagnetic waves.
• Phased array antennas: Phased array antennas, as the name suggests, can be termed as an antenna array. What makes them unique is their ability to change the shape and direction of the radiation pattern without physically moving the antennas. This is achieved by transmitting signals of equal frequency from all the individual elements in the array with a certain phase difference/shift between them.

Darwin is following developments in antenna technology very closely to select the most fitting options for our converged satellite and mobile solution.

Dr Soheyl Soodmand, Senior RF and Antenna Architect

Darwin Innovation Group is a UK-based company that provides services related to autonomous vehicles and communications. If you’re interested in working with us, take a look at our careers page. If you’d like to know how we can help your organisation make use of autonomous vehicles, contact us. You can also follow us on LinkedIn or Twitter.