TMAS MIDTERM OBJECTIVES.pdf

## The Medium - Sender and receiver - basic model - A diagram shows a sender with a satellite dish, sending a message through a channel to a receiver with a satellite dish. - The receiver sends feedback back to the sender. - Unguided Medium - This refers to transmission media that does...

## The Medium - Sender and receiver - basic model - A diagram shows a sender with a satellite dish, sending a message through a channel to a receiver with a satellite dish. - The receiver sends feedback back to the sender. - Unguided Medium - This refers to transmission media that does not use physical media to facilitate communication. - Guided Medium - This refers to transmission media that requires physical media to facilitate communication. ## Transmission Lines - Transmission line is a metallic conductor system that is used to transfer electrical energy from one point to another. - Three examples of transmission lines are shown: - A coaxial cable - Two parallel wires - A microstrip line. ## Length of Transmission Line - **Physical Length:** This refers to the actual length of the transmission line, typically measured in m/km/ft/miles. - **Electrical Length:** This refers to the length of the transmission line based on the fraction of its wavelength. ## Types of Transmission Line - **Balanced or differential** - This is a transmission line consisting of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground. - A diagram shows a transmitter (TX) connected to a receiver (RX) via two conductors. - The voltage on each line is equal but 180 degrees out of phase and referenced to ground. - **Unbalanced or Single Ended** - This is a transmission line whose conductors have unequal impedances with respect to ground. - It usually consists of a conductor that is considered the signal line and another conductor that is grounded, or is ground itself. - A diagram shows a transmitter (TX) connected to a receiver (RX) via a coaxial line or twisted pair. - The shield is grounded and the center conductor is the signal line. - **Balun** - This refers to a circuit device used to connect a balanced transmission line to an unbalanced load. - A diagram shows two antennas connected to a balun, which then connects to a transmitter (TX). - **Parallel - Wire Transmission Line** - A parallel wire transmission line is composed of two conducting wires separated by a dielectric. - A diagram shows two parallel wires with insulating spacers. - A schematic diagram shows a cross-sectional view of the parallel wires. - **Coaxial Cable** - This is composed of two concentric conductors and is used extensively for high-frequency applications to reduce losses and to isolate transmission paths. - It provides excellent shielding against external interference. - A diagram shows the internal components of a coaxial cable. - A schematic diagram shows a cross-sectional view of a coaxial cable. ## Transmission Line Equivalent Circuit - Physical properties like diameter and conductor spacing and electrical properties such as conductivity and relative permittivity (otherwise known as a dielectric constant) determine what we call the **primary line constants**. - A schematic diagram shows a section of transmission line with primary line constants: - Resistance: R - Inductance: L - Conductance: G - Capacitance: C ## Secondary Line Constants - Secondary line constants determine the transmission characteristics of the transmission line. These can be calculated using the primary line constants. - **Characteristic Impedance:** This refers to the impedance looking at the input of an infinitely long transmission line. - For maximum power transfer from the source to the load, a transmission line must be terminated in a purely resistive load equal to the characteristic impedance of the line. - It is also known as **surge impedance**. - A diagram shows the source of a transmission line connected to a load through a transmission line, with impedances labeled. - **Propagation Constant:** This is used to express the **attenuation** and the **phase shift** per unit length of a transmission line. - It is represented by: $γ=√(R+jωL)(G+jωC)$, where γ = α + jβ. - An equation shows how to calculate α and β. ## Transverse Electromagnetic Wave - Transverse electromagnetic (TEM) wave refers to a form of radiant energy which is essentially an oscillatory disturbance in free space that is composed of two components: **electric field (E)** and **magnetic field (H)**, which are perpendicular to each other and to the direction of propagation. - A diagram shows a wave with electric and magnetic fields, labeled. ## Velocity of Propagation - This refers to the speed of the TEM wave propagating in a transmission line. - This is always less than the speed of the wave in free space. ## Velocity Factor - The ratio of the actual velocity of propagation through a given medium to the velocity of propagation through free space. ## Reflections - In the event that the transmission line is not terminated with a load impedance equal to the characteristic impedance, **reflections** will occur. - **Incident Waves (E+)**: TEM waves that travel along a transmission line from the source towards the load. - **Reflected Waves (E-)**: TEM waves that travel from the load back towards the source. - A diagram shows a source connected to a load through a transmission line. ## Reflection Coefficient - This refers to a vector quantity that represents the ratio of the reflected voltage to incident voltage. - It is represented by: $Γ= E⁻/E⁺$, and $Γ= Z_L-Z_o/Z_L+Z_o$. ## Standing Waves - The two traveling waves (incident and reflected) setup an interference pattern known as **standing waves**. - A diagram shows incident and reflected waves creating a standing wave pattern. ## SWR - **Standing Wave Ratio (SWR):** This is defined as the ratio of the maximum voltage to the minimum voltage. - It also refers to the measure of mismatch of the characteristic impedance to the load impedance. - The formula is: $VSWR = V_{max}/V_{min}$. ## Impedance of a Section of Tx Line - A diagram shows a transmission line with different impedance sections: - **Z = Z₀(Z_L+jZ₀tan(βl))/Z₀+jZ_Ltan(βl)** - **Z = jZ₀tan(βl)**: Shorted transmission line. - **Z = -jZ₀cot(βl)**: Open transmission line. - **Impedance Inversion:** The impedance at a point in a transmission line inverts every quarter-wave section. ## Transmission Line Instruments - **Stub Chart:** A short section of a transmission line open or shorted. It is used to **remove the reactive component** of a load with complex impedance and match it to the line. - A diagram shows a parallel and a series stub. - **Quarter-Wave Transformer:** Uses a quarter-wave section of a transmission line to match a purely resistive load to a transmission line. - A diagram shows adjusting the spacing of a transmission line to vary the impedance. - **Smith Chart:** This refers to a special circular graph transmission line calculator named after Philip Smith. - A diagram shows a Smith chart. - **Optical Time Domain Reflectometer (OTDR):** This refers to a device used to perform time-domain reflectometry. - The TDR is a technique that can be used to locate an impairment in a metallic cable. - A diagram shows an OTDR with a screen showing a reading of the reflection for an open end and a short circuit fault. - **Slotted Line:** A short section of air-dielectric coaxial line with a slot in outer conductor through which a capacitively-coupled probe is inserted. It measures the wavelength and SWR of the line. - A diagram shows a slotted line.