12.9.6 Why Are There So Many Different Types of Antennas?
- Why Isn't There One Perfect Antenna?
- What Factors Influence Antenna Selection?
- Why Is the Dipole So Popular?
- When Is a Monopole a Better Choice?
- Why Are Yagi Antennas So Common?
- Why Do Satellite Systems Use Reflector Antennas?
- Why Are Patch Antennas So Popular?
- Why Are Loop Antennas Still Used?
- What Is a Log-Periodic Antenna?
- Why Are Arrays Becoming More Common?
- Can One Antenna Cover Every Frequency?
- Why Is There No Universal Antenna?
- What Should You Remember?
Short Answer
No single antenna can provide the best performance for every application. Different communication systems require different combinations of gain, bandwidth, beamwidth, polarization, efficiency, size, cost, and mechanical strength. As a result, engineers have developed many antenna designs, each optimized for a particular purpose. A simple dipole may be ideal for one application, while a large parabolic reflector, phased array, or microstrip antenna may be far better suited to another. Choosing the right antenna is therefore an exercise in engineering compromise.
Why Isn't There One Perfect Antenna?
If one antenna could provide:
- high gain;
- wide bandwidth;
- omnidirectional coverage;
- compact size;
- low cost;
- high efficiency; and
- simple construction,
there would be little reason to develop alternative designs.
Unfortunately, these desirable characteristics often conflict with one another. For example:
- increasing gain usually narrows the beamwidth;
- increasing bandwidth may reduce efficiency;
- reducing antenna size often decreases performance;
- improving directivity generally increases physical dimensions.
Every antenna therefore represents a compromise between competing requirements.
What Factors Influence Antenna Selection?
When selecting an antenna, engineers consider many factors, including:
- operating frequency;
- required bandwidth;
- communication range;
- antenna gain;
- beamwidth;
- polarization;
- physical size;
- weight;
- environmental conditions;
- installation location;
- mechanical strength; and
- cost.
The importance of each factor depends entirely upon the intended application.
Why Is the Dipole So Popular?
The half-wave dipole is one of the simplest and most widely used antennas.
It offers:
- moderate gain;
- predictable performance;
- relatively wide bandwidth;
- simple construction; and
- a well-understood radiation pattern.
For these reasons it serves as the basis for many other antenna designs. Arrays, Yagi antennas, log-periodic antennas, and numerous modern antennas all evolved from the fundamental dipole concept.
Because of its simplicity, the dipole is often regarded as the reference antenna for practical communication systems.
When Is a Monopole a Better Choice?
A monopole is essentially half of a dipole mounted above a conducting surface called the ground plane.
It provides:
- omnidirectional horizontal coverage;
- compact construction;
- low cost; and
- mechanical simplicity.
Monopoles are widely used for:
- vehicle radios;
- handheld transceivers;
- broadcast transmitters;
- mobile-phone base stations; and
- marine communication.
Whenever communication is required equally in all horizontal directions, the monopole is often an excellent choice.
Why Are Yagi Antennas So Common?
The Yagi–Uda antenna combines a driven element with several passive elements.
This arrangement provides:
- significantly higher gain;
- good front-to-back ratio;
- moderate beamwidth;
- relatively simple construction; and
- modest cost.
Yagi antennas are widely used for:
- television reception;
- amateur radio;
- point-to-point communication; and
- scientific applications.
They provide much greater directivity than a simple dipole without the complexity of larger reflector systems.
Why Do Satellite Systems Use Reflector Antennas?
When extremely high gain is required, reflector antennas become attractive.
A parabolic reflector concentrates radio waves into a very narrow beam. This provides:
- very high gain;
- excellent directivity;
- low sidelobes;
- long communication range; and
- high receiver sensitivity.
Reflector antennas are therefore used extensively for:
- satellite communication;
- radio astronomy;
- radar;
- deep-space communication; and
- terrestrial microwave links.
Their principal disadvantage is the requirement for accurate pointing.
Why Are Patch Antennas So Popular?
Many modern electronic devices require antennas that are:
- small;
- lightweight;
- inexpensive;
- low profile; and
- easy to manufacture.
The microstrip patch antenna satisfies many of these requirements. Patch antennas consist of conductive patterns printed directly onto circuit boards. They are widely used in:
- GPS receivers;
- Wi-Fi equipment;
- smartphones;
- satellite navigation systems;
- aircraft; and
- phased-array antennas.
Although individual patches provide only modest gain, many patches can be combined into large electronically steerable arrays.
Why Are Loop Antennas Still Used?
Loop antennas respond primarily to the magnetic component of the electromagnetic wave.
Depending upon their size, they may provide:
- directional reception;
- reduced sensitivity to electrical noise;
- compact construction; and
- excellent performance at lower frequencies.
Small loop antennas are often used in:
- portable AM receivers;
- navigation equipment;
- RFID systems; and
- direction-finding applications.
Large loop arrays continue to serve specialised military and scientific applications.
What Is a Log-Periodic Antenna?
Many communication systems operate over wide frequency ranges.
A conventional antenna may perform well at one frequency but poorly at another. The log-periodic antenna overcomes this problem by maintaining relatively consistent characteristics across a broad bandwidth. It is commonly used for:
- frequency monitoring;
- spectrum measurements;
- EMC testing;
- surveillance; and
- broadband communication systems.
Its wide operating range makes it invaluable where multiple frequency bands must be covered using a single antenna.
Why Are Arrays Becoming More Common?
Instead of relying on a single radiating element, many modern systems combine hundreds or even thousands of individual antennas.
Such antenna arrays offer:
- higher gain;
- electronically steerable beams;
- adaptive interference suppression;
- multiple simultaneous beams;
- improved reliability; and
- support for MIMO communication.
Arrays have become central to:
- modern radar;
- satellite communication;
- radio astronomy;
- 5G and emerging 6G networks; and
- military communication systems.
As digital signal processing has improved, array technology has become increasingly practical and affordable.
Can One Antenna Cover Every Frequency?
Generally, no.
Although broadband antennas exist, every antenna has practical frequency limits.
As operating frequency moves away from the antenna's design frequency:
- impedance changes;
- matching deteriorates;
- gain may decrease;
- radiation patterns change; and
- efficiency may fall.
For this reason, modern communication equipment often contains several separate antennas, each optimised for a different frequency band.
Many smartphones, for example, incorporate antennas for:
- cellular communication;
- Wi-Fi;
- Bluetooth;
- GPS;
- NFC; and
- ultra-wideband (UWB).
Each serves a different purpose despite sharing the same device.
Why Is There No Universal Antenna?
The enormous variety of antenna designs reflects the equally enormous variety of communication requirements.
A deep-space spacecraft, a submarine, a mobile phone, a weather radar, and a Wi-Fi router all operate under completely different constraints. An antenna that performs exceptionally well in one application may perform poorly in another. Successful antenna design therefore begins by asking: "What is the communication system trying to achieve?"
Only then can the most appropriate antenna be selected.
What Should You Remember?
- No antenna is best for every application.
- Every antenna represents a compromise between gain, bandwidth, size, efficiency, beamwidth, cost, and mechanical complexity.
- Dipoles and monopoles provide simple general-purpose solutions.
- Yagi antennas and reflector antennas offer higher gain for directional communication.
- Patch antennas enable compact modern wireless equipment.
- Log-periodic antennas provide exceptionally wide bandwidth.
- Phased arrays combine many antenna elements to produce electronically steerable beams and have become one of the most important antenna technologies in modern communication systems.
- The wide variety of antenna designs reflects the diverse requirements of modern wireless communication rather than the existence of a single superior antenna.