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--- user:kurser:ham_vt2023_l7 [2023/04/11 08:44] – user
+++ user:kurser:ham_vt2023_l7 [2023/04/22 12:12] – user
@@ Line 25: / Line 25: @@
 ==Antennas==
-Antenna = two port that converts energy from propagating in a transmission line to propagation in free-space.
+//Antenna = two port that converts energy from propagating in a transmission line to propagation in free-space.//
+What is an antenna? An antenna is a device that converts EM waves between a bound medium and a free medium, for instance between a cable and free space.
-Characterized by:
+//Antenna types.//
-  * Input impedance, SWR, Z_in
+There are many different types of antennas, since different antenna designs are optimised for solving different problems. There is no antenna that is perfect for every single operational situation. However, the opposite is true; there are indeed antennas that are quite bad at everything.
-  * Operation frequency, resonance frequency, f_0
-  * Directivity D, antenna gain, dBi, dBd
-  * far field distance = d_f > 2*D^2/lambda, given d_f >> D, d_f >> lambda
-  * Radiation efficiency, eta
-  * radiation pattern, E & H patterns
-  * Polarization and x-pol suppression and so on...
-We can only measure input impedance and operational frequency easily with a VNA/Antena analyzer ... so lets do that at ETA.
+Different antenna types, roughly in order of most common -> least common
-Different types
   * Dipole
   * Monopole
   * Small loop
-  * Yagi
+  * Yagi (Yagi-Uda)
-  * Quad
   * Patch
-  * Bowtie
+  * Quad
   * PCB/PIFA
+  * Waveguide slot
+  * Bowtie
   * Spiral/Helical
+  * Vivaldi
+Antennas may often be combined together for different effects. These group of antennas acting together as one, are denoted //antenna arrays// (gruppantenner). Some antenna arrays are more common than others, for example:
+  * Log-periodic dipole array (LDPA)
+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.
+All antennas can be characterised using //at least// the following parameters:
+  * Input impedance, Z_in
+  * Standing wave ratio, SWR
+  * Operational frequency
+  * Resonance frequency, f_0
+  * Directivity, D
+  * Antenna gain, dBi, dBd
+  * Far-field distance = d_f > 2*D^2/lambda, given d_f >> D, d_f >> lambda
+  * Radiation efficiency, eta
+  * Radiation pattern, E & H patterns
+  * Polarisation and x-pol suppression
+Of these parameters, only input impedance and operational frequency are arguably easy to analyse. This analysis is done with either a vector network analyser, or an antenna analyser. Let's do that at ETA.
-Talk about polarization.
+Talk about antenna polarisation.
 Common mode current on coax = bad!