Question

Figure 1.2 Figure 1.2 shows a Wilkinson coupler, with conducting strip shown hatched, implemented in microstrip designed to split power equally between two matched 502 outputs. Briefly explain the following features: 2%) why the electrical length of the two output arms of the coupler is designed to be a quarter wavelength; (i) (ii why the characteristic impedance of each arm is approximately 70.7 2 2%) (iii) what the purpose of the resistor R is, and what value it should have. 2%) (d) In a left-hand circularly polarized Transverse Electromagnetic (TEM) wave the electric field vector in the plane of polarization rotates in an anticlockwise sense when viewed along the direction of propagation (i.e. from the source of the wave). If such a wave is incident perpendicularly on a perfectly conducting plane surface, explain: (i) Why the amplitude of the reflected wave is the same as that of the incident wave. 12% (ii) why the reflected wave must be right-hand circularly polarized. 2%]

Answer 1

The coupled section should be a quarter wave at center frequency because of directivity and quadrature phase. And because of this Bandwidth will be greater. \r\n Characteristic impedance of each arm Z_oc = squareroot 2 times 50 Z_oc = 1.414 times 50 = 70.7Ohm Output impedance Z_0 = 50Ohm \r\n In real coupler, there is a finite phase through the resistor that eill limit the isolation of the output ports.and for a signle input at eitherport, half the power is dissipated in resistor and half is delivered to port. value of R = 2Z_o R = 2 times 50 R = 100 Ohm