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Antennas
Published in Mike Tooley, David Wyatt, Aircraft Communications and Navigation Systems, 2017
The standing wave ratio (SWR) of a feeder or transmission line is an indicator of the effectiveness of the impedance match between the transmission line and the antenna. The SWR is the ratio of the maximum to the minimum current along the length of the transmission line, or the ratio of the maximum to the minimum voltage. When the line is absolutely matched the SWR is unity. In other words, we get unity SWR when there is no variation in voltage or current along the transmission line. The greater the number representing SWR, the larger the mismatch. Also, I2R losses increase with increasing SWR.
Radio wave propagation and the frequency spectrum
Published in Laurie Tetley, David Calcutt, Electronic Navigation Systems, 2007
Antennae and feeders are effectively ‘matched transmission lines’, which, when a radio frequency is applied, exhibit standing waves, the length of which are determined by a number of factors outside the scope of this book. However, the waves are basically produced by a combination of forward and reflected power in the system. A measurement of the ratio between forward and reflected power, called the standing wave ratio (SWR), provides a good indication of the quality of the feeder and the antenna. Measurement of the SWR is made using voltage and becomes voltage standing wave ratio (VSWR).
Antenna systems
Published in L. Tetley, D. Calcutt, Understanding GMDSS, 2012
Antennae and feeders are effectively matched transmission lines which, when a radio frequency is applied, exhibit standing waves, the length of which is determined by a number of factors outside the scope of this book. However, the waves are basically produced by a combination of forward and reflected power in the system. A measurement of the ratio between forward and reflected power, called the standing wave ratio (SWR), provides a good indication of the quality of the feeder and the antenna. Measurement of the SWR is made using voltage and becomes VSWR.
Breast Cancer Detection by Terahertz UWB Microstrip Patch Antenna Loaded with 6X6 SRR Array
Published in IETE Journal of Research, 2023
Kritika Singh, Marshal Dhayal, Smrity Dwivedi
Voltage Standing Wave Ratio (VSWR) is the ratio of the standing wave's maximum amplitude to the standing wave's minimum amplitude along a transmission line or at the input of an antenna [53]. The VSWR characteristics indicate how precisely the impedance of an antenna matches that of its radio or transmission line. A high VSWR indicates a large amount of reflected power and a poor impedance match, which can lead to signal degradation, reduced efficiency, and potential damage to the system. Conversely, a low VSWR indicates a good impedance match and efficient power transfer between the source and load [53]. The VSWR of the antenna is shown in Figure 8. Ideally, the VSWR should be less than 2 throughout the frequency band. The VSWR obtained below 2 is between the frequency range of 0.29 and 1.97 THz.
Stepwise implementation of a low-cost and portable radiofrequency hyperthermia system for in vitro/in vivo cancer studies
Published in Instrumentation Science & Technology, 2021
Fatih Senturk, I. Cengiz Kocum, Goknur Guler Ozturk
All components of the radiofrequency power generator are shown in Figure S12. The radiofrequency power system generates 400 W that was monitored by a standing wave ratio (SWR) meter (Figure S12j). After implementing and testing the RF power generator and matching network, water-cooled coils were constructed with solenoid and pancake geometries. The radiofrequency power generator output was connected to a water-cooled solenoid or pancake coil to generate magnetic fields that were transmitted to the biological samples. The radiofrequency coils were manufactured from round copper tubing rather than copper wire since tubing allows the use of flowing cooling water. The impedance matching between the coil and radiofrequency generator was adjusted by tuning the matching network. While the RF-HT system was in operation, it was monitored by a thermal camera (FLIR E6, Sweden) to avoid large temperature increases (Figure S13b). A thermal image of cell culture medium (Figure S13d) was observed immediately after removing the culture flask maintained at humidified atmosphere at 37 °C and 5% CO2 from the incubator (Heraeus, Germany).
Design of Low Profile Cylindrical Conformed Microstrip Patch Antenna for Wideband Operation
Published in IETE Journal of Research, 2021
Sandeep Kohar, Surinder Singh, Asok De
The bandwidth of an antenna is described as the frequency range over which the input impedance of the patch is well matched with the feed line. The matching is said to be proper if the voltage standing wave ratio, VSWR < 2 or the reflection coefficient i.e. S11 < −10 dB. It gives a measure of how much of the incident power is transferred to the antenna and how much is reflected back to the source. Hence for ample power transfer from the input source to the radiator the S11 value should be within the limits. The MPAs suffer from an inherent drawback of low bandwidth. The bandwidth is seen to increase with substrate thickness and decrease with an increase in dielectric constant of substrate [5]. The substrate thickness tends to increase the surface waves which results in a decrease of antenna efficiency, hence the substrate height cannot be increased beyond a threshold. The bandwidth of the conventional patch antennas of standard geometries like rectangle, square, and circular shapes is of the order of 5–10%. Such low bandwidth is insufficient for the present communication system needs. Hence there is a need to design wideband antennas which are capable of operating across multiple frequency bands.