Dipole antennas are used to transmit and receive radio frequency signals.
Feed impedance is one of the characteristics affecting the performance of dipole antennas.
By making the dipole antenna feed impedance equal to the source or load impedance, antenna efficiency is maximized.
Optimizing antenna impedance is important for achieving maximum power transfers in dipole antennas
Due to their excellent directional properties, dipole antennas are regularly used in radio and telecommunication systems as well as systems handling ultra-wideband signals. In a dipole antenna, feed point impedance plays a significant role in establishing good dipole characteristics. Optimizing the antenna impedance is important for achieving maximum power transfers in dipole antennas, and various dipole antenna impedance matching techniques can be used to achieve high-end antenna performance.
What Is a Dipole Antenna?
Dipole antennas are the simplest form of antenna and are extensively used for transmitting and receiving radio frequency signals. As the name suggests, there are two poles in dipole antennas. A conducting metal is broken at the center for making two poles. Usually, copper material is used for the construction of these antennas.
Dipole Antenna Construction
The construction of a dipole antenna is comparatively easy compared to other antenna types. They can be created on printed circuit boards using two traces. This makes them a popular choice for radio and communication applications. Apart from their simple construction, the good amplitude, phase, and polarization characteristics of dipole antennas make them desirable for use in antenna applications.
Types of Dipole Antennas
The size of a dipole antenna is dependent on the wavelength of the signal transmitted or received. The types of dipole antennas available are:
- Quarter-wavelength dipole antennas - The length of the antenna is one-fourth of the wavelength of interest.
- Half-wavelength dipole antennas - The length of the antenna is one-half of the wavelength of the signal to be transmitted or received.
- Dual-dipole antennas - This type of antenna consists of two dipoles.
- Folded-dipole antennas - A folded dipole antenna consists of two or more conductors of half-wavelength connected in parallel.
The Operation of a Dipole Antenna
Dipole antennas receive their signal from a source through a transmission line or feeder circuit. When a half-wavelength dipole antenna is excited from a source, current flows in each side of the dipoles. The current magnitude increases and reaches the maximum value at the center of the dipole antenna. The voltage also increases, but maximum voltage exists at the two ends, not at the center.
There is a charging and discharging cycle in the dipole antenna during each half-cycle of the waveform transmitted. The charging-discharging process creates a rising and falling electric field between the dipoles, which radiates out of the antenna. Similarly, the current in the dipole antenna creates a magnetic field, which is also emitted outwards. Together, the electric and magnetic fields form the radiated electromagnetic field in the dipole antennas.
Dipole Antenna Impedance Matching
Feed impedance is one of the characteristics affecting the performance of a dipole antenna. Feed impedance, otherwise called input impedance, is the ratio of voltage and current at the feed point of a dipole antenna. The feed point can be anywhere in the dipole antenna. The general trend followed in dipole antennas is that the center point of the dipole is kept as the feed point. At this point, the voltage is minimum and the current is maximum, making the feed impedance the lowest.
To ensure maximum power transfer in dipole antennas, dipole antenna impedance matching is essential. Impedance matching means the dipole antenna feed impedance should match the source or load impedance. By making the dipole antenna feed impedance equal to the source or load impedance, antenna efficiency reaches its maximum.
As far as energy transfer is concerned, dipole antenna impedance matching is crucial. The antenna impedance depends on factors such as feed point, length, ambient conditions, etc. Cadence software can help antenna designers develop impedance matching circuits that ensure maximum power delivery in antennas.