ECER02-Radiowave Propagation / Microwave

This set of vocabulary flashcards covers radio wave propagation principles, optical properties, terrestrial propagation modes, ionospheric characteristics, and microwave link budget parameters based on the provided lecture transcript.

Electromagnetic Wave

Electrical energy that has escaped into free space, traveling in a straight line at approximately the speed of light.

Velocity of Propagation ($V_p$)

The rate of travel of a wave in a medium, calculated as $V_p = \frac{1}{\sqrt{\mu\varepsilon}}$ meters per second, where $\mu$ is permeability and $\varepsilon$ is permittivity.

Characteristic Impedance ($Z$)

For free space, it is the ratio of the magnetic field to the electric field, equal to $120\pi\,\Omega$ or approximately $377\,\Omega$.

Power Density ($P_d$)

The rate at which energy passes through a given surface area in free space, expressed by the formula $P_d = \frac{P_T G_T}{4\pi D^2}$ in $\text{W/m}^2$.

Free Space Path Loss (FSL)

The loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection from nearby objects.

Attenuation

The reduction in power density as distance from the source increases.

Absorption

The reduction in the intensity of radiated energy caused by the conversion of energy into another form, such as when atoms or molecules in the atmosphere absorb radio waves.

Specular Reflection

A mirror-like reflection phenomenon where a wave hits a smooth surface and satisfies the law of reflection where $\theta_{inc} = \theta_{ref}$.

Diffuse Reflection

A phenomenon where a reflected signal is scattered in different directions after hitting a rough surface.

Rayleigh Criterion

A condition used to determine if a semi-rough surface will reflect a wave specularly, defined as $\cos(\theta_{inc}) > \frac{\lambda}{8h}$.

Refraction

The change in direction that occurs when a wave of energy passes from one medium to another with a different density.

Refractive Index ($n$)

The ratio of the velocity of light in free space ($c$) to the velocity of light in a given medium ($V_p$), expressed as $n = \frac{c}{V_p}$.

Diffraction

The bending or spreading out of waves as they pass around the edge of an obstacle or through a narrow aperture.

Huygen’s Principle

States that every point on a given spherical wavefront can be considered as a secondary point source of electromagnetic waves from which secondary wavelets are reradiated.

Ground-Wave Propagation

A method of propagation where the wave travels along the surface of the Earth, following its contours through the process of diffraction.

Sky Wave Propagation

Propagation where electromagnetic waves are beamed toward the upper portion of the Earth's atmosphere.

Skip Distance

The distance from the transmitter to the point where the sky wave is first returned to Earth.

Skip Zone

The zone of silence between the point where the ground wave becomes too weak for reception and the point where the sky wave is first returned to Earth.

D-Layer

The lowest ionospheric region (30 to 55 miles) which has low ionization and refracts low-frequency signals while attenuating high frequencies.

E-Layer (Kennelly-Heaviside Layer)

An ionospheric layer (55 to 90 miles) that can refract signals up to $20\,\text{MHz}$ and almost disappears at night due to rapid ionic recombination.

F-Layer

An ionospheric layer (90 to 240 miles) responsible for high-frequency, long-distance transmission, which separates into F1 and F2 layers during daylight hours.

Sporadic E

Irregular, unpredictable cloud-like patches of unusually high ionization that form near the normal E layer.

Critical Frequency ($f_c$)

The highest frequency that can be propagated directly upward and still be refracted back to Earth by a specific ionospheric layer, calculated as $f_c = 9\sqrt{N_{max}}$.

Maximum Usable Frequency (MUF)

The highest frequency that can be used for sky wave communication between two points, defined as $\text{MUF} = \frac{f_c}{\cos(\theta)}$.

Optimum Working Frequency (OWF/FOT)

The most effective frequency for sky wave transmission, typically taken as $85\%$ of the MUF ($\text{OWF} = 0.85 \times \text{MUF}$).

Microwave

Electromagnetic waves with wavelengths ranging from $1.0\,\text{mm}$ to $30\,\text{cm}$, used in radar, communications, and heating.

Line of Sight (LOS)

A straight path between a transmitting and receiving antenna that is unobstructed by the horizon.

k-factor

A numerical figure that accounts for atmospheric refraction, defined as the ratio of the effective Earth radius ($r_e$) to the true Earth radius ($r_o$).

Standard Condition ($k = 4/3$)

An atmospheric condition where the fictitious Earth radius appears longer than the true Earth radius to microwave beams.

Earth Bulge

The vertical distance an obstacle is raised into the signal path due to the Earth's curvature.

Fresnel Clearance

The additional obstacle clearance required to account for the expanding properties of a wavefront as it travels through space.

Effective Isotropic Radiated Power (EIRP)

The amount of power that would need to be emitted by an isotropic antenna to produce the same peak power density as the actual antenna in its direction of maximum gain.

Received Signal Level (RSL)

The actual power level of the signal at the receiver input, accounting for gains and losses in the link budget.

Fade Margin

The design allowance or difference between the Received Signal Level (RSL) and the Receiver Threshold, intended to accommodate signal variations and outages.

System Gain ($G_s$)

The difference between the nominal transmitter output power and the minimum input power required by the receiver for a given quality objective.