Example exam 3

Universitat Politècnica de Catalunya UPCommons. Portal del coneixement obert de la UPC Escola d'Enginyeria de Telecomunicació i Aeroespacial de CastelldefelsGRAU EN ENGINYERIA D'AERONAVEGACIÓ (Pla 2010) Aquesta obra està protegida pels drets de propietat intel·lectual i industrial corresponents. Llevat que s'hi indiqui el contrari, els seus continguts estan subjectes a la llicència de Creative Commons: http://creativecommons.org/licenses/by-nc-nd/3.0/es/ 2014 Example exam 3 Collado Gómez, Juan Carlos; González Arbesú, José María COMUNICACIONS AERONÀUTIQUES - 300226 Universitat Politècnica de Catalunya http://hdl.handle.net/2117/183185 Descarregat per usuari no autentificat el 08/06/2025 12:51 d'UPCommons, repositori institucional de la Universitat Politècnica de Catalunya Aeronautical Communications QT1314 Name: Examen 14.11.13  La copia en un examen se considera una falta de respeto al trabajo del resto de compañeros y será penalizada con un suspenso en la asignatura. No se permitirá, bajo ninguna circunstancia, tener teléfonos móviles durante el examen. Duración del examen: 90 minutos Potentially useful equations: L L IN S SS S ρ ρ ρ 22 2112 11 1− += G G OUT S SS S ρ ρ ρ 11 2112 22 1− += 2 2 2 22 2 21 1 1 1 IN L L IN L S S P P G ρ ρ ρ − − − == 2 2 2 11 2 21 1 1 1 OUT G G avs avn A S S P P G ρ ρ ρ − − − == ( ) ( ) 2 22 2 22 2 21 1 1 1 1 ING LG L avs L T S S P P G ρρ ρρ ρ − −− − == USS t = * ( ) ( ) ( ) ( ) ( ) ( ) ljZZ ljZZ Z ljZlZ ljZlZ ZZ L L L L IN β β ββ β β tan tan sincos sincos 0 0 0 0 0 0 + + = + + = Aeronautical Communications QT1314 Name: 1. Make a proposal for a matching network that allows matching all the possible loads inside the circumference R/Z 0 =1. The network should be designed using two lumped elements. Graphically explain how to calculate the values of the lumped elements constituting the network. 2. The directional coupler of the figure has the given S parameters matrix. Place the ports numbering (1,2,3 and 4) and the ports name ( input port, isolation port, coupled port, and through port ) on the figure to be in accordance to the S parameters matrix.             − − = 01.033.0007.094.0 33.001.094.0007.0 007.094.001.033.0 94.0007.033.001.0 S 3. Calculate the equation of the voltage phasor V(z) along the transmission line and plot its variation within the line when L=2λ and Z G =Z 0 . 4. In relation with an isolator (input port:1, output port: 2): a. Which is its ideal scattering matrix? b. Given the following brochure for an isolator in the frequency range from 26.5 to 40 GHz, find the scattering matrix (linear scale) from the typical values provided by the manufacturer. Aeronautical Communications QT1314 Name: 5. Given the S parameters matrix of a filter in its passband, what statements are true and what are false. Each incorrect mark cancels a correct one. TRUE FALSE The filter is symmetric . The filter is reciprocal . The filter matching is good (RL > 20 dB) . Insertion losses are small (IL<0.5 dB) . The filter is passive and lossless . 6. Given the filter of the previous exercise find the power gain when the filter is connected to a 100Ω load and to a matched source. The reference impedance is 50Ω. 7. Mark the statements as true or false. Each incorrect mark cancels a correct one. TRUE FALSE A VNA (Vector Network Analyzer) is used to get the magnitude and phase of the scattering parameters of a microwave device. To measure the power delivered by a microwave device we could use a power meter or a spectrum analyzer. S parameters can have magnitudes grea ter than 1. Waveguide technology is mainly used to carry low powers. The circuit of the figure is a hybrid microwave integrated circuit. A spectrum signal analyzer is useful for plotting voltage variations of a signal versus time. When characterizing a microwave device, the calibration of the measurement set-up is never required. A low losses transmission line is considered distortionless. Adding (lossless) elements to a matching network can be useful for providing bandwidth to the network. Voltage v(z,t) and current i(z,t) waves are always in - phase in a transmission line (in other words v(z,t)/i(z,t)=Z 0 ). ( ) ( )             − + = j j S 1 10 1 10 27 10 27 1 10 1 Aeronautical Communications QT1314 Name: 8. By using the Smith Chart: a. Find the smallest length of a 50Ω transmission line that transforms the load impedance of Z L =50-j50 into an impedance of Z L2 =50+j50. b. Which is the smallest length of an open-circuited transmission line (50Ω characteristic impedance) to behave as an impedance of Z L3 =-j50.