Radiation and Propagation of Waves Flashcards

Comprehensive flashcards covering definition of terms, fundamental laws, formulas, and layers of the ionosphere based on Dr. Russ Allen B. Napud's lecture on Radiation and Propagation of Waves.

How is the Propagation of Waves defined?

The travel of electromagnetic waves or sound waves through a medium, or the travel of a sudden electric disturbance along a transmission line.

What is free-space attenuation and what is its relationship with distance?

The reduction in signal strength due to spreading of the waves at a distance from the transmitter; it is proportional to the square of the distance traveled.

Define Circular polarized waves.

Waves where the electric field component of the radiated wave rotates $360^{\circ}$ with respect to the direction of propagation; the field is constantly rotating rather than fixed.

What is Critical frequency ($f_c$)?

The highest frequency that a wave will no longer return to earth when beamed vertically upward.

Describe the D layer of the ionosphere.

The lowest layer with a height of approximately $70\,km$ above the earth's surface and an average thickness of $10\,km$.

What is Dielectric strength?

The magnitude of the electric field required to cause breakdown and arcing in a dielectric.

What is the function of a Diplexer?

A circuit or device that permits two different transmitters to operate with a single antenna.

How does a Duplexer differ from a Diplexer?

A duplexer allows a transmitter and receiver, operating at different frequencies, to be connected to the same antenna and operate simultaneously.

What is Diversity in signal reception?

The process of transmitting/receiving a number of signals and either adding them together at the receiver or selecting the best one at any given instant.

Define Ducting.

A means of propagation where waves are confined within a refractive region of the troposphere or between such a region and the ground.

What are the units for Electric Field intensity ($\xi$) and Magnetic field intensity ($H$)?

Electric Field intensity is measured in volts per meter ($V/m$), and Magnetic field intensity is measured in amperes per meter ($A/m$).

What are the common names for the gradual shift in polarization as waves travel through the ionosphere?

Faraday effect or Faraday rotation.

What does the Inverse Square Law state regarding power density?

Power density is inversely proportional to the square of the distance from the source ($PD \propto \frac{1}{d^2}$).

What is an Isotropic radiator?

A hypothetical antenna having zero physical size and no loss, radiating equally in all directions.

What is the frequency range for Microwaves?

Radio waves with frequencies in the range above $1\,GHz$.

Define Multipath distortion and its visual effect.

Changes to the baseband signal caused by a signal arriving at a receiving antenna via two or more paths, resulting in a ghosting effect (double image distortion).

What are the components of an Electromagnetic wave?

Electric field, Magnetic field, and the Direction of propagation.

What does the term Transverse-Electromagnetic (TEM) wave mean?

The electric field, magnetic field, and the direction of propagation are all mutually perpendicular.

What is the approximate velocity ($V_C$) of an electromagnetic wave in free space?

$3 \times 10^8\,m/s$ (or more exactly $299,729,500 \pm 300\,m/s$).

Which conductors reflect electromagnetic waves as mentioned in the text?

Copper and Aluminum.

What formula defines propagation velocity ($V$) in a medium with relative permittivity ($\epsilon_r$)?

$$V = \frac{C}{\sqrt{\epsilon_r}}$$

Categorize radio waves by propagation mode based on frequency.

Ground wave: $f < 3\,MHz$, Sky wave: $3\,MHz$ to $30\,MHz$, Space wave: $f > 30\,MHz$.

What is the E layer also known as?

Kennelly-Heaviside Layer.

What 3 factors determine if the ionosphere will reflect a signal?

Operating frequency, Ion density, and the Angle by which the Skywave strikes the ionosphere.

What happens to the ionospheric layers (D, E, F1, F2) at night?

The D and E regions disappear, and the F1 and F2 layers combine into a single F layer.

Define Maximum Usable Frequency (MUF) and its relationship with the Secant Law.

The highest frequency returned by the ionosphere at a specific angle other than the normal, calculated as $MUF = f_c \sec(\theta_1)$, where $f_c$ is critical frequency.

How is the Optimum Working Frequency (OWF) usually determined?

$OWF$ is chosen to be about $15\%$ lower than the $MUF$ ($OWF = 0.85 \times MUF$).

What is Virtual height?

The apparent height of an ionized layer, which is always greater than the actual height; calculated using $h_t = \frac{cT}{2}$ for vertical waves.

What formula determines the line-of-sight distance ($d$) for space wave propagation given antenna heights in meters?

$d = \sqrt{17h_t} + \sqrt{17h_r}$ (where $d$ is in $km$).

What are the three properties of radio waves that occur during propagation?

Reflection (bouncing), Refraction (bending), and Diffraction (scattering).

State Snell's Law for refraction.

$$n_1 \sin(\theta_1) = n_2 \sin(\theta_2)$$

What are the common remedies for Fading?

Diversity operations, including Space, Field Component, Polarization, Time, Frequency, and Angle Diversity.

What is the characteristic impedance ($Z_0$) of free-space?

$120\pi$ or approximately $377\,\Omega$.

What cycle period is associated with Sunspots and their effect on ionization?

An $11$ year cycle.

How is Power Density ($PD$) calculated for a halfwave dipole antenna?

$$PD = \frac{1.64 P_T}{4\pi d^2}$$