Tech Primer
As a component transmitting and receiving radio signal in wireless communication the antenna takes a critical role regarding the communication quality and coverage range of a communication system. An antenna is essentially a length of wire, in which an alternating current creates an alternating inductive electromagnetic field, or an alternating electromagnetic field an alternating current. A single antenna therefore can either be used for transmitting or receiving signals.
The ability of an antenna, to radiate and receive energy to and from its surroundings is related to it's physical properties, such as length, shape and material.
There are many different types of antenna, and their physical attributes are chosen to provide optimal performance at a given frequency, or over a specified bandwidth, so many of their physical proprties will relate to the wavelength of the signal being received or transmitted. A simple verical antenna for example will usually have a length equal to one quarter or one half of the carriers wavelength. More complex antennas, such as the Yagi-Uda antenna, will incorporate director and reflector elements, which improve the performance of tranmission and reception by making the antenna more focussed and directional. polarisation is also an important consideration for attennas, the orientation of erection determines the polarisation of the antenna, vertically errected antennas will produce a vertically polarised signal and a horizontally errected antennas a horizontally polarized one. If the polarisation or the receiving antenna is orthogonal to the transmitting antenna, there will be very little of the transmitted signal received, This effect is sometimes exploited to allow interfering signals to operaterate in the same spectrum but with a different polarisation. The different types of antenna vary in terms of performance parameters such as operation frequency, bandwidth, gain, impedance, standing wave ratio and physical factors like shape, size, and wind-resistant performance, and all of them should be taken into consideration when selecting or designing an antenna.
Other Resources
- Antenna Basics
- Fundamentals of Antenna Theory
- Basic Antenna Theory
- Antenna Primer Part I
- Antenna Primer Part II
- Antenna Primer Part III
- Antenna Tutorial
- Antenna Theory and Transmitters
- A Discussion of Antenna Theory
- Selecting An Antenna
Glossary:
| dBd | Quantification of the gain for an antenna in comparison with the gain of a dipole. |
| dBi | The dB power relative to an isotropic source. |
| Dipole | An antenna--usually a half wavelength long--split at the exact center for connection to a feed line |
| Directional | An antenna having the property of radiating or receiving electromagnetic waves more effectively in some directions than others. |
| E-Plane/H-Plane | Antenna measurements in general and radiation patterns in particular must be performed with polarization in mind. Since polarization is defined as having the same orientation as an antenna electric field vector, it is common practice to refer to measurements aligned with either the electric vector ( E-plane) or magnetic vector (H-plane). |
| ERP | Effective Radiated Power. |
| Front-To-Back Ratio | The ratio of radiated power off the front to the back of a directive antenna. A dipole would have a ratio of 1, for example. |
| LHCP | Left Hand Circular Polarization |
| Omnidirectional | An antenna providing a 360-degree transmission pattern. This type of antenna is used when coverage in all directions is required. |
| Polarization | The sense of the wave radiated by an antenna. This can be horizontal, vertical, elliptical or circular (left or right hand circularity) depending on the design and application. |
| RHCP | Right Hand Circular Polarization |
| Transmission Line | The connecting link allowing the radio frequency energy generated by the radio to be delivered to the antenna. (Coaxial cable, microstrip or coplanar lines in our industry). |
| VSWR | Voltage Standing Wave Ratio (VSWR).VSWR of the antenna is the ratio of the maximum to minimum values of voltage in the standing wave pattern appearing along a lossless 50 Ohms transmission line with an antenna as the load. |
| Whip | The vertical portion of the antenna assembly acting as the radiator of the radio frequency energy. |
| Yagi(Yagi-Uda) | A directional, gain antenna utilizing one or more parasitic elements. Named after one of the Japanese inventors (Yagi and Uda). |