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Antennas Before we get into Antennas, it is important to have a clear understanding of some of the terms associated with the subject of Antennas. These are-Standing Wave Ratio (SWR) or Voltage SWR, Reflection coefficient and Return Loss. Standing Wave Ratio or Voltage Standing Wave Ratio ( SWR or VSWR): Standing Wave Ratio is a measure of how much energy is reflected back to the source. A low SWR means less energy is reflected back and a high SWR means a lot of energy is reflected back. Reflection occurs due to impedance mismatch. A perfectly matched Antenna system will have an SWR =1 or 1:1 to indicate that it is a Ratio. 1.5:1 is what industry aims for. There are several ways this Ratio is expressed. First, let us define Reflection Co-efficient, = Vr / Vi (1) Where Vr = reflected voltage Vi = incident voltage, and = Reflection Co-efficient It can be shown that is also equal to = ZL – ZO / ZL + ZO (2) Where ZL = Load Impedance and ZO = Characteristic Impedance of the line We can define the VSWR as follows: VSWR = Vmax / Vmin, both expressed in r.m.s Where Vmax = the maximum voltage on the line = Vi + Vr, and Vmin = the Minimum voltage on the line = Vi - Vr (3) Using algebraic manipulations, it can be shown that SWR = 1 + / 1 - (4) Substituting the value of from Equation 2 into (4), we get SWR = ZL /ZO (5) Also from Equation (4) = SWR – 1 / SWR + 1 Power Reflected = Pr = 2 Pi Where Pi = incident power (6) (7) Power absorbed by the load PL = Pi (1 - 2) (8) Power absorbed by the load in terms of SWR is given by the equation PL = { 4SWR / (1 + SWR)2 }Pi (9) Hyder Khoja Page 1 2/16/2016 Return Loss: is a measure of how much energy is returned or reflected back. Less the energy is returned, better it is. Thus, larger the return loss better it is. Refer to the chart and tables on P8.18, 8.19 C.S Now do examples 8.2 and 8.3 P8.17, 8.18, 8.19 C.S and also examples 6.7,6.8 on P 186, 187 B. Now do P87, 88, 89 90, 91 Course Pack and Chapter 5 C.S Photocopy Antenna handouts (Pictures only Prthy) When you want to convert from dBi to dBd, Remember dBd = GdBi – 2.14 And dBi = dBd +2.14 (10) (11) Also EIRP = Pt Gt, and (12) EIRP = ERP + 2.14 (13) In this equation, EIRP is the Effective radiated Power with respect to an ISOTROPIC RADIATOR and the ERP is the Effective Radiated Power of the Antenna at hand Now do Example 8.4 P8.19 C.S Also, Solve example 16-6, P260 E.W and 16-7 P262 E.W Solve Example 8.1 P260 B, and 8.3, 8.4, 8.5, 8.6 P26-266 B, 8.7 P281and 8.10 P292, 8.11 P 301 B Show Antennas on P304m 306, 308 B Hyder Khoja Page 2 2/16/2016