Antenna Basic Terms
- Antenna Theory - Poynting Vector
- Antenna Theory - Reciprocity
- Antenna Theory - Beam Width
- Antenna - Beam & Polarization
- Isotropic Radiation
- Antenna Theory - Radiation Pattern
- Antenna Theory - Near & Far Fields
- Antenna Theory - Parameters
- Antenna Theory - Basic Parameters
- Antenna Theory - Fundamentals
Types of Antennas
- Parabolic Reflector
- Antenna Theory - Lens
- Antenna Theory - Micro Strip
- Antenna Theory - Slot
- Antenna Theory - Horn
- Antenna Theory - Aperture
- Antenna Theory - Helical
- Antenna Theory - Loop
- Antenna Theory - Rhombic
- Inverted V-Antenna
- Antenna Theory - V-Antennas
- Antenna Theory - Long Wire
- Antenna Theory - Short Dipole
- Antenna - Full-Wave Dipole
- Antenna - Half-Wave Folded Dipole
- Antenna - Half-Wave Dipole
- Antenna Theory - Wire
- Antenna Theory - Types of Antennas
Antenna Arrays
- Turnstile Antenna Theory
- Log-periodic Antenna Theory
- Yagi-Uda Antenna Theory
- Antenna Theory - Parasitic Array
- Antenna Theory - End-fire Array
- Antenna Theory - Broad-side Array
- Antenna Theory - Collinear Array
- Antenna Theory - Antenna Arrays
Wave Propagation
- Terms in Wave Propagation
- Antenna - Lonosphere & its Layers
- Antenna - Types of Propagation
- Antenna - Spectrum & Transmission
Antenna Theory Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
Antenna Theory - Aperture
An Antenna with an aperture at the end can be termed as an Aperture antenna. Waveguide is an example of aperture antenna. The edge of a transmission pne when terminated with an opening, radiates energy. This opening which is an aperture, makes it an Aperture antenna.
The main types of aperture antennas are −
Wave guide antenna
Horn antenna
Slot antenna
Let us now have a look at these types of aperture antennas.
Waveguide Antenna
A Waveguide is capable of radiating energy when excited at one end and opened at the other end. The radiation in wave guide is greater than a two-wire transmission pne.
Frequency Range
The operational frequency range of a wave guide is around 300MHz to 300GHz. This antenna works in UHF and EHF frequency ranges. The following image shows a waveguide.
![Frequency Range](/antenna_theory/images/frequency_range.jpg)
This waveguide with terminated end, acts as an antenna. But only a small portion of the energy is radiated while a large portion of it gets reflected back in the open circuit. It means VSWR (voltage standing wave ratio, discussed in basic parameters chapter) value increases. The diffraction around the waveguide provides poor radiation and non-directive radiation pattern.
Radiation Pattern
The radiation of waveguide antenna is poor and the pattern is non-directive, which means omni-directional. An omni-directional pattern is the one which has no certain directivity but radiates in all directions, hence it is called as non-directive radiation pattern.
![Non Directive Radiation Pattern](/antenna_theory/images/non_directive_radiation_pattern.jpg)
The above figure shows a top section view of an omni-directional pattern, which is also called as non-directional pattern. The two-dimensional view is a figure-of-eight pattern, as we already know.
Advantages
The following are the advantages of Aperture antenna −
Radiation is greater than two-wire transmission pne
Radiation is Omni-directional
Disadvantages
The following are the disadvantages of Aperture antenna −
VSWR increases
Poor radiation
Apppcations
The following are the apppcations of Aperture antenna −
Micro wave apppcations
Surface search radar apppcations
The waveguide antenna has to be further modified to achieve better performance, which results in the formation of Horn antenna.
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