Calculating Reflection And VSWR In Antennas

2y ago
42 Views
4 Downloads
396.62 KB
13 Pages
Last View : 15d ago
Last Download : 2m ago
Upload by : Braxton Mach
Transcription

Calculating Reflection and VSWRin AntennasDr. FarahmandUpdated: 10/20/14

Antennao How much RF energy the antennacan radiate or emit?RadiationPradiatedPowerForwardn This is due to its radiation resistance(Rr) (resistive characteristic of theantenna – imaginary part: jX)n The ohmic resistance (Ro)of theantenna acts as physical resistance,converting energy to heat)ZLPowerReflectedZoo Radiate Power Pt: I2xRrZinRF Currentat thefeedline

RememberHow Electromagnetic Waves Worko So if waves travel what happens when they hit anobject?n n RF signal creates disturbances in the mediaSome of the signal reflects when the standing wave hits anobject (some get observed)o Reflected wave (BLUE)o Incident wave (RED)o Resulting Standing wave (BLACK)Between source efl.htm

Voltage Standing Wave Radio(VSWR)o Determines loss of forwarded radiation due to returned powern Note that the loss can be compensated by high power à Damagethe transmittero o VSWR results from mismatched impedanceTo calculate the VSWR, first calculate the reflection coefficient:o VWSR is represented as VWSR:1;n o e.g., 3:1 assuming reflection coefficient is 0.5 – represent howmuch mismatch we have!Based on VWSR we can determine the power lossn alculatorhttp://www.antennex.com/preview/vswr.htm

Voltage Standing Wave Radio(VSWR)o Determines loss of forwarded radiation due to returned power§ Whatis minimum value of COR?o VSWR results from mismatched impedanceCORà -1 by high powero § Short:The loss canbe compensatedn Damage the transmitter§ Open:CORà 1o To calculate the VSWR, first calculate the reflection coefficient:VWSR is represented as VWSR:1; e.g., 3:1 assuming reflectioncoefficientis 0.5 maximum value of VSWR?§ Whatis theo Based on VWSR we can determine the power loss§ n Shortà ZeroVerify these values: eturn.pdf§ Openà Infinityo http://www.antennex.com/preview/vswr.htm

Voltage Standing Wave Radio(VSWR)o Determines loss of forwarded radiation due to returned power§ Whatis minimum value of COR?o VSWR results from mismatched impedanceCORà -1 by high powero § Short:The loss canbe compensatedn Damage the transmitter§ Open:CORà 1o To calculate the VSWR, first calculate the reflection coefficient:We want COR 0à VSWR 1VWSR is represented as VWSR:1; e.g., 3:1 assuming reflectioncoefficientis 0.5 maximum value of VSWR?§ Whatis theo Based on VWSR we can determine the power loss§ n Γ 1à InfinityVerify these values: eturn.pdf§ Γ 0à 1o http://www.antennex.com/preview/vswr.htm

Return Losso The return loss of a load is merely themagnitude of the reflection coefficientexpressed in decibels

Exampleo Consider VSWR of 3:1n Find CORn Find Return Loss (dB)n Find Mismatch Loss swr-calculator

ExamplesBounce DiagramAssume Vg 60V ; Rg 100; Zo 50; L 1 meter; Vp 2C/3t 0;V1Time Response VoltageV(z 0.5,t)V1.ΓL -6.6710ns20-6.67 13.337.5ns11.13 0.74 13.33- 11.872.2 11.1312.5ns17.5ns5 ns7.5ns12.5 ns15 nsV1.ΓL.Γg -6.67/3 2.225ns0.23469V1.ΓL. ΓL.Γg 0.74202.5ns2.5ns20nsStables22.5 nsL/2

Power Reduction Due toReflection

Power Budgeto Read the tm#fresnel

Introduction to Power Budget –A simple Exampleo Assume the following:n n n n n o Transmitter is transmitting 100mW on channel 1, 802.11bA, C, D connectors each have a loss of -3dBTransmitter antenna has an active gain of 12dBThe two antennas are 124 meters away from one anotherIgnore the attenuation of the coax cableAnswer the followingn n The power in Watts as Receiver Y receives.Assuming the sensitivity of the receiver antenna is -5dBm, will Yreceive the transmitted information properly?TransmitterXDo it!ACoaxCableCDdReceiverY

802.11b Frequency Bando In the United States and Canada there are 11 channels available foruse in the 802.11b 2.4GHz WiFi Frequency range. This standard isdefined by the 482.4532.4582.4632.4682.473

Oct 20, 2014 · In the United States and Canada there are 11 channels available for use in the 802.11b 2.4GHz WiFi Frequency range. This standard is defined by the IEEE. 1 2.401 2.412 2.423 2 2.404 2.417 2.428 3 2.411 2.422 2.433 4 2.41

Related Documents:

VSWR at the Input of a Lossy Line Because of the losses in a transmission line,! the measured VSWR at the input of the line is! less than the VSWR measured at the load end of ! the line. VSWR Input a ρ a ρ Example 250 feet of RG-8X @ 30 MHz (ML 2.0 dB x 2.5 5.0 dB) with a VSWR at the load of 6:1 ρ 0.71 a 3.16 VSWR Input 1.58

Reflection Product Name Reflection for IBM Reflection for HP Reflection for UNIX and OpenVMS Reflection for Se cure IT SSH Client Reflection for ReGIS Graphics Reflection X Reflection FTP Client Reflection SFTP Client Reflection NFS Client Reflection for the Multi-Host Enterprise, Professional Edition

Antenna Noise Bridge from Palomar, MFJ, or from plans in the ARRL Handbook Spectrum analyzer with a tracking generator and an external directional coupler or RF bridge . MFJ-269t. MFJ-202Bt. 23. Measuring VSWR. Directional Couplers RF Bridges. 24. Measuring VSWR. VSWR can be measured using a VSWR meter or directional watt

VSWR mobilefish.com In an ideal situation when no power is reflected back, (Z L Z S) the VSWR 1.0 or as commonly expressed as a ratio of 1:1. The higher the impedance mismatch, the higher the VSWR value. If Z S Z L than power is reflected back, for example VSWR 1.4 or 1.4:1. An antenna with a VSWR 1.4 is considered to be an excellent .

to 100 ohm, the VSWR is equal to 2 as shown by simula- tion at . Figure 2(b), and for a load 200 ohm the VSWR goes to 4. This confirms that when the load changes and it differs from the line's characteristic impedance . Z. 0, VSWR also changes because of reflected waves [7,8]. The second scenario, as in . Figure 3, considers a gate-

of your transmit signal going to the antenna and the amount of signal reflected back by the antenna. A VSWR meter measure P out, P reflected and VSWR. How are there related ? The best VSWR is 1:1. This means that 100% of the signal is going to the load (0% reflected) At VSWR 2:1, 11% of the power is reflected

The VSWR can be used to judge the quality of impedance matching for cables and other passive devices. It is also mainly used to determine the efficiency of antennas to radiate power. A perfectly matched antenna/cable system will have a VSWR 1. In reality, VSWR's are typically in the 1.1 to 1.2 range.

VSWR Measurement in 75 Systems Using the R&S FSH3-TV TV Analyzer Application Note The voltage standing wave ratio (VSWR) is one of the parameters in RF systems that measures the impedance mismatch. Under ideal conditions, when the load is perfectly matched to the source, the VSWR will be 1. A mismatch in the system causes reflections that will .