user:kurser:ham_vt2023_l7
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user:kurser:ham_vt2023_l7 [2023/04/22 19:52] – user | user:kurser:ham_vt2023_l7 [2023/04/22 20:26] – user | ||
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... however, in practice there is nothing prohibiting an antenna array from being built using any antenna type. | ... however, in practice there is nothing prohibiting an antenna array from being built using any antenna type. | ||
- | Very often, specific antennas are are combination of other antenna types. For example, the very common Yagi-Uda antenna, is a combination of three (or more) dipole antennas, and one magnetic loop antenna. | + | Very often, specific antennas are are combination of other antenna types. For example, the very common Yagi-Uda antenna, is usually built using a combination of three (or more) dipole antennas, and one magnetic loop antenna. |
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* Polarisation and x-pol suppression | * Polarisation and x-pol suppression | ||
- | Most of these parameters can be analysed using a vector network analyser or an antenna analyser. Let's do that at ETA. | + | Many of these parameters can be analysed using a vector network analyser or an antenna analyser. |
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==Direction== | ==Direction== | ||
- | The most ideal antenna is a single charge floating in free space, radiating as a sphere in all directions. Such a single charge is known academically as an //isotropic radiator//. Practically, | + | The most ideal antenna is a single charge floating in free space, radiating as a sphere |
How small that illuminated segment of the sphere is as opposed to size the entire sphere, is known as the //antenna directivity// | How small that illuminated segment of the sphere is as opposed to size the entire sphere, is known as the //antenna directivity// | ||
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== Antenna impedance matching == | == Antenna impedance matching == | ||
- | TODO | + | Different antenna types have different ideal input impedances. And, the the input impedance is typically frequency dependent. For instance, a given antenna may look like a 50 ohm impedance at 5 MHz, but may look more like an open circuit at 10 MHz. |
+ | Example: the ideal dipole antenna has a 73 ohm input impedance. Feeding this antenna with a coaxial cable of 50 ohm characteristic impedance, leads to a 50 ohm -> 73 ohm impedance interconnect. This impedance difference will result in signal reflections, | ||
+ | Overcoming impedance differences in antennas may for instance be done using matching networks. | ||
+ | Matching an antenna gets harder as the operational band of the antenna grows larger. | ||
user/kurser/ham_vt2023_l7.txt · Last modified: 2024/02/13 18:08 by user