RF Passive Circuits
Module Bank – 2
Faculty name— Dr. P Sambaiah
ECE-III, 2nd semester
1.
a. What is the significance of “90o ” in 90o - hybrid? (L2-2M)
b. Two 90o couplers with C=8.34 dB are connected as shown below. Calculate the resulting
phase and amplitudes at ports 2 and 3 relative to port 1. (L3-4M)
c. Determine the resulting phase and amplitudes at ports 2’ and 3’ relative to port 1 in the
problem given in b. (L4-4M)
2.
a. A three port microwave network cannot be lossless, matched and reciprocal at the same
time. Justify. (L2-2M))
b. A 4 W power source is connected to the input of a directional coupler with C=20 dB, D=35
dB and an insertion loss of 0.5 dB. Compute the output powers (in dBm) at the through,
coupled and isolated ports. Assume all ports to be matched. (L4-4M)
c. A directional coupler has the scattering matrix given below. Evaluate the directivity,
coupling, return loss at the input port when the other ports are terminated in matched loads.
(L4-4M)
3.
a. How a Wilkinson power divider can be used to divide unequal power to the loads? (L2-
2M)
b. Design a Wilkinson power divider with power division ratio of P 3/P2=1/3, and a source
impedance of 50 Ω. (L3-4M)
𝑓0 , and plot the return loss S11 , insertion loss (S21=S31) and isolation (S23=S32) versus
c. Design an equal-split Wilkinson power divider for a 50 Ω system impedance at frequency
frequency from 0.5𝑓0 to 1.5𝑓0 . The operating frequency is 2 GHz. (L3-4M)
4.
a. What is the advantage of coupled line filter over lumped element microwave filters? (L1-
2M)
b. Design a coupled line bandpass filter with N=3 and a 0.5 dB equal-ripple response. The
center frequency is 2 GHz, the bandwidth is 10% and characteristic impedance is 50 Ω and
obtain the attenuation at 1.6 GHz. (L4-4M)
c. Design a stepped-impedance low-pass filter having a maximally flat response and cut off
frequency of 2 GHz. It is necessary to have more than 18dB insertion loss at 3.5 GHz. The
filter impedance is 50 Ω; the highest practical line impedance is 150 Ω and lowest impedance
is 10 Ω. (L4-4M)
5.
a. How to choose the dominant mode of a rectangular cavity resonator in terms of its
dimensions?(L2-2M)
b. A transmission line resonator is made from a length L of a lossless transmission lines of
characteristic impedance 75 Ω. If the line is terminated at both ends as shown, evaluate L/λ
for the first resonance and Q of this resonator. (L3-4M)
c. A dielectric filled (dielectric constant 4), brass plated rectangular waveguide cavity has
dimensions a=4 cm, b=2 cm, d=5cm. Dtermine the resonant frequency and Q of the TE101 and
TE102 modes. (L3-4M)
6.
a) What are the advantages of realizing low pass filters with step impedances? (L1-2M)
b) Design a stepped-impedance low-pass filter with fc = 2.0 GHz and R0 = 50 ohm, using the
exact transmission line equivalent circuit. Assume a maximally flat N = 5 response, and solve
for the necessary line lengths and impedances if Zl= 10 ohm and Zh = 150 ohm. (L4-4M)
c) Lay out the microstrip implementation of the filter on an FR4 substrate having ℇr = 4.2, d
= 0.079 cm, and tan δ = 0.02, and with copper conductors 0.5 mil thick. (L3-4M)
7.
a) Explain the need of transmission line resonators? (L2-2M))
b) Consider a microstrip resonator constructed from a λ/2 length of 50 ohm open-circuited
microstrip line. The substrate is Teflon (ℇr = 2.08, tan δ = 0.0004), with a thickness of 0.159
cm, and the conductors are copper. Compute the required length of the line for resonance at 5
GHz, and the unloaded Q of the resonator. Ignore fringing fields at the end of the line. (L3-
4M)
c) Derive an expression for the unloaded Q of a transmission line resonator consisting of a
short-circuited transmission line 1λ long. (L4-4M)
8.
a) Why the scattering parameters are preferred at microwave frequency? (L2-2M))
b) A two-port network is known to have the following scattering matrix:
Determine if the network is reciprocal and lossless. If port 2 is terminated with a matched
load, what is the return loss seen at port 1? If port 2 is terminated with a short circuit, what is
the return loss seen at port 1? (L3-4M)
c) A certain three-port network is lossless and reciprocal, and has S13 = S23 and S11 = S22. Show
that if port 2 is terminated with a matched load, then port 1 can be matched by placing an
appropriate reactance at port 3. (L4-4M)
