Question 1

An apparatus whose theory of operation is based upon motion of electrons under the influence of combined E field and H field is known as a(n):

Accepted Answer

Magnetron oscillators operate based on the motion of electrons influenced by both electric (E) and magnetic (H) fields. This combined field interaction is essential for their operation, which is utilized in applications like radar systems and microwave ovens.

Question 2

The purpose of the low-loss dielectric material (radome) used to cover the dish is:

Accepted Answer

The low-loss dielectric material (radome) is used to protect the dish and maintain internal pressure, ensuring the dish operates effectively in various environmental conditions.

Question 3

Parametric amplifiers that have pump frequencies that are double the signal frequency are operating in the:

Accepted Answer

Parametric amplifiers operating with pump frequencies that are double the signal frequency are said to be in the degenerate mode. This is because the signal and idler frequencies (in this case, the same as the signal frequency) are degenerate, meaning they are equal or very close to each other, which is a specific condition under which these amplifiers operate efficiently.

Question 4

Which of the following is not an application of a ferrite?

Accepted Answer

Ferrites are magnetic materials that are not typically used in oscillators. Oscillators generate and maintain a continuous wave of a specific frequency, and while ferrites are used in various RF and microwave applications due to their magnetic properties, they are not directly used to generate oscillations. Instead, ferrites are commonly used in isolators, attenuators, and for exploiting the Faraday rotation effect, among other applications.

Question 5

Which of the following is similar to an IMPATT diode?

Accepted Answer

Both IMPATT and TRAPATT diodes are used in microwave applications and operate based on the avalanche breakdown phenomenon.

Question 6

Degenerate mode parametric amplifiers operate with pump frequencies:

Accepted Answer

Degenerate mode parametric amplifiers operate with pump frequencies that are exactly twice the signal frequency, which is a characteristic of their operation.

Question 7

Above 5 GHz, which device offers greater performance?

Accepted Answer

GaAs FETs offer greater performance above 5 GHz due to their higher electron mobility compared to silicon-based devices, which allows for faster signal processing and higher frequencies of operation.

Question 8

Calculate the power gain of a microwave dish antenna with a 6 meter mouth diameter when used at 5 GHz.

Accepted Answer

The power gain $G$ of a microwave dish antenna can be calculated using the formula $G = (\pi d / \lambda)^2$, where $d$ is the diameter of the dish and $\lambda$ is the wavelength of the signal. The wavelength $\lambda$ can be found from the frequency $f$ using the relation $\lambda = c / f$, where $c$ is the speed of light ($3 \times 10^8$ m/s). For a frequency of 5 GHz ($5 \times 10^9$ Hz), $\lambda = 3 \times 10^8 / 5 \times 10^9 = 0.06$ meters. Substituting $d = 6$ meters and $\lambda = 0.06$ meters into the gain formula gives $G = (\pi \times 6 / 0.06)^2$. This results in a numerical gain, which when converted to decibels (dB) using $10 \log_{10}(G)$, gives approximately 47.8 dB.

Question 9

Which microwave oscillator is becoming obsolete due to its large size and the complex, costly sources of dc required for its operation?

Accepted Answer

Klystron oscillators are becoming obsolete because they are large in size and require complex and costly DC power sources for operation.

Question 10

Which of the following is also known as a backward-wave oscillator (BWO)?

Accepted Answer

The backward-wave oscillator (BWO) is also known as a traveling-wave tube (TWT) oscillator. It operates on the principle of electron beam interaction with a slow electromagnetic wave, making it distinct from other microwave oscillators.

Question 11

The model of a RF capacitor shows that the capacitor is:

Accepted Answer

The model of an RF (Radio Frequency) capacitor indicates that it exhibits all three characteristics: resistive (due to dielectric losses and lead resistance), inductive (due to the physical construction and leads), and capacitive (its primary function). At high frequencies, all these effects become significant.

Question 12

What material is most useful in the design of masers for low-noise microwave amplification?

Accepted Answer

Ruby is a material that is commonly used in the design of masers for low-noise microwave amplification.

Question 13

Which of the following is not a vacuum tube?

Accepted Answer

The Gunn oscillator is not a vacuum tube; it is a solid-state device that generates microwave frequencies, unlike the other options which are types of vacuum tubes used in various applications to amplify or generate radio frequency signals.

Question 14

A transphasor is:

Accepted Answer

The answer of A transphasor is:
...

Question 15

A microwave semiconductor that is typically used as T/R switches in RF transceivers operating above 100 MHz is the:

Accepted Answer

P-I-N diodes are commonly used as T/R (transmit/receive) switches in RF transceivers operating above 100 MHz due to their ability to handle high power levels and provide fast switching speeds.

Question 16

Which microwave oscillator is widely used in microwave ovens?

Accepted Answer

Magnetron oscillators are widely used in microwave ovens due to their ability to efficiently generate microwave radiation, which is used for heating and cooking food.

Question 17

Why are microwave antennas characterized by high gain and high directivity?

Accepted Answer

Microwave antennas are characterized by high gain and high directivity for several reasons: A) Microwave links are typically point-to-point, eliminating the need for omnidirectional antennas. B) Microwave transmitters often have limited output power, so high gain is necessary to ensure signal strength over long distances. C) Device noise increases at microwave frequencies, requiring receivers to have larger input signals for clear communication. D) The short wavelengths of microwaves allow for the physical design of antennas with high gain and directivity that would not be practical at lower frequencies.

Question 18

Special ferrites that are typically used as RF chokes are called:

Accepted Answer

Ferrite beads are commonly used as RF chokes to suppress high-frequency noise in electronic circuits.

Quiz 16: Microwaves and Lasers

An apparatus whose theory of operation is based upon motion of electrons under the influence of combined E field and H field is known as a(n) :