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RF and Microwave Engineering - Two Port RF Networks - Circuit Representation - Important Questions and Answers: Two Port RF Networks - Circuit Representation

**TWO PORT RF NETWORKS –CIRCUIT REPRESENTATION**

**1.Define
Microwave?**

Microwaves are electromagnetic waves with
wavelengths ranging from 1 mm to 1 m, or frequencies between 300 MHz and 300
GHz.

**2.Define
Scattering matrix?**

Scattering matrix is a squre matrix which gives
all the combination of power relationship between the

various input and output ports.

**3.Mention
the limitation in measuring Z,Y and ABCD parameters at microwave frequencies**

ü Non availability of terminal voltage and
current measuring equipment

ü Short circuit and open circuit are nit easily
achieved for a wide range of frequencies

ü Presence of active devices makes the circuit
unstable for short or open circuit

**4.****A 5dB attenuator is specified as having VSWR of
1.2 assuming that the device is reciprocal find S parameters**.

Attenuation dB for any devices is = -20log
[s12]

Log
s12 = -5/20 = -0.25

(or)
[s12] = 10 -0.25 = 0.56

Thus Г =
s11 =VSWR -1/VSWR+1

= 1.2
– 1/1.2+1 = 0.2/2.22 = 0.091

**4. ****Name the
properties of S – Parameters?**

It possess symmetric property sij =sji

It possess unitary property [s][s]*=[i]

**6.Draw
the equivalent circuit for practical capacitor **

**7.Define
reciprocal and symmetrical networks?**

The reciprocal device has a same transmission
characteristics in either direction of a pair of ports and is characterized by
a symmetric scattering matrix

S_{ij} = S_{ji} ; i
!=j

Which results [s]_{t} = [s]

**8.Express
power input and power output under matched conditions for a two port network in
terms of wave components **

P_{in} = ½ [a_{n}]^{2}

P_{rn} = ½ [b_{n}]^{2}

**9. Draw
the equivalent circuit for a inductor at radio frequency**

**10.List
any four reasons for wide use of RF?**

ü Because of high operating frequency microwave
system can carry large quantities of information

ü High frequency mean short wavelength , which
require relatively small antennas

ü Microwave signals are more easily propagated
around physical obstacles , such as water and high mountains

ü Fewer repeaters are necessary for amplification

ü Increased bandwidth availability

ü Minimal cross talk

**11.Give
the relationship between [s] and [z] matrix**

**13. Draw
the high frequency equivalent circuit for resistor and inductor **

__Resistor__

**14. Why
the s-parameters are used in microwaves?**

The H, Y, Z and ABCD parameters are difficult
at microwave frequencies due to the following reasons. (i)Equipment is not
readily available to measure total voltage and total current at the ports of
the network.

(ii)
Short
circuit and open circuit are difficult to achieve over a wide range of
frequencies.

(iii)
Presence
of active devices makes the circuit unstable for short or open circuit.

(iv)
Therefore
microwave circuits are analyzed using scattering or S parameters which linearly
relate the reflected wave amplitude with those of incident waves.

**15 .What
is the Scattering matrix for N port device?**

[S]= S11
S12 S13…… S1n S21 S22 …………S2n

S31 S32 ………….S3n

. .

. .

Sm1 Sm2 ………...Smm

**16.
****Give the application of microwave**

ü Satellite communication

ü Telemetry

ü Microwave oven

ü Transmission of video signals

ü Microwave diathermy

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