ECE GR4

T / F Antenna gain tells us how much the antenna can focus power.

Ture; The gain of the antenna tells us how much energy goes in various directions relative to the antenna's orientation.

What is Electromagnetic Attack (EA)?

Use of EM energy, directed energy, or antiradiation weapons to degrade, neutralize, or destroy enemy capability

Which form of wireless communications works the best at night? a. Line-of-sight (LOS) b. Ground wave c. Sky wave d. Forward scatter

c. Sky wave

which of the following techniques are used to counter jamming? a. spread spectrum b. frequency hopping c. chirping d. both b and c e. all the above

e. all the above

T/F: communications jamming is less effective the closer it gets tot eh reciever

false

T/F: communications with submerged submarines are done using carrier frequencies in the EHF band

false

T/F: effective DEAD requires the destruction of the enemy's air defenses

false

T/F: metallic waveguides are an economical choice to send information over long distances at high data rates

false

T/F: more bandwidth is available at lower frequency carrier signals, while higher frequencies travel further

false

T/F: the higher the SNR, the less likely the signal was received

false

T / F An antenna can be used to transmit signals more easily than it can be used to receive signals.

false; There is no difference between an antenna's transmit and receive capability

SNR

how loud you are talking / how loud everyone else is talking -signal/noise

Dipole antenna length and gain

length: λ/2 Gain: 1.64 (ideal)

Monopole antenna length and gain

length: λ/4 gain: 3.28 (ideal)

As 𝑹 𝒕𝒐 𝑻𝒙↓, jamming is ______________ effective

less

As 𝑅𝑗𝑡𝑜 𝑅𝑥↓, jamming is _________ effective

more

if your communications jamming is ineffective, how can you increase its effectiveness? a. move closer b. get higher c. get a smaller antenna d. decrease the jamming antenna transmitted power

move closer

what causes a waveguide to act as a HPF a. physical dimensions b. construction materials c. ece magic

physical dimensions

What was the inspiration for RADAR? What are some uses today?

Biology - Bats/Dolphins. Used to detect weather, incoming aircraft, find speeding cars

DEAD =

Destruction of Enemy Air Defenses (non-reversible - the RADAR is blown up)

optical fiber channel cons

Difficult to install Difficult to repair

What factors can limit communication?

Distance, antenna strength, weather, terrain

What is the Radar Cross Section (RCS) and why does it matter?

How much electromagnetic energy is reflected in a certain direction. In this course, we care about the energy reflected back in the direction of the RADAR

Wired channel cons

Internal resistances Limited Frequencies

How does using a pulse fix the problem discussed above?

It allows the antenna to switch from transmit and receive mode.

Chaff creates a false radar target that is brighter than the actual target. (a) True (b) False

True; The whole point of chaff is to get the missile to go after something else.

PT:

The power sent by the transmitting antenna (in Watts)

How does this take advantage of radar functionality?

The return pulses overlap, so the RADAR can't tell when one ends and the next one starts 𝜟𝑹=𝒄(𝝉)/𝟐

λ:

The wavelength of the radio signal (in meters)

What special property do waveguides have?

They act as a HPF governed by: 𝑓𝑐/𝑜= 𝑐2𝑎

Spread Spectrum:

Transmit the message bearing signals using a wider bandwidth than actually needed. The resulting wideband signal appears as a noise signal with greater resistance to intentional and unintentional interference

What are some possible issues with using the same antenna to send and receive?

Can't transmit and receive at the same time

Chirp Signals:

Change the Carrier Frequency by sweeping

Frequency Hopping:

Change the Carrier frequency according to pre-established hopping sequence (Heddy Lamar and the player piano)

T / F Decibels are fundamentally used to depict a voltage ratio.

False; Fundamentally, decibels represent a power ratio.

Both radar jamming and communications jamming become more effective as the jamming platform moves towards the site being jammed. (a) True (b) False

False; Only communications jamming is more effective the closer you get. The closer a RADAR jammer gets to the RADAR, the less effective it becomes.

T / F Increasing the carrier frequency in a communication system increases the size of the necessary antenna.

False; The size of the antenna is inversely proportional to the frequency. As frequency increases, the size of the antenna decreases.

How do we hide the number of aircraft we have?

Fly close together - closer than the RADAR's range resolution

What will be different in the Friis equation for RADAR?

Gain is the same - but it is squared because the sending and receiving antenna (RADAR) are the same. The range is now to the object and back again so it's raised to the fourth

wave guide channel cons

Heavy Rigid Difficult to repair

Is it better to have a high or low SNR?

Higher SNR is better

wireless channel cons

Hindered by Line of Sight Susceptible to Interference Limited Security

5. Which of these techniques is not used to counter jamming? (a) Chirp signals (b) Chaff and flares (c) Direct-sequence spread spectrum (d) Frequency hopping

(b) Chaff and flares; Chaff and flares are not counter jamming techniques. They act as decoys to missiles.

In order for an attack to be successful, the planners determine a SAM site must be destroyed. What kind of electronic warfare is this? (a) SEAD (b) DEAD (c) Jamming (d) Chaff

(b) DEAD

What is the gain and how can we express it?

- Antenna gain refers to the antenna's ability to focus energy in a specific direction. - Acts like a multiplier - amplifies power - Can plot transmission patterns

T / F A waveguide acts as a high pass filter.

True

T / F Line-of-sight communications are the primary way of communicating with satellites.

True

How will changing each term affect the power received?

- Double power transmitted, double power received - Double the receiver or transmitter gain, double the power received; Double the wavelength (lower the freq), quadruple the power received; Lower frequencies travel farther than higher frequencies; Double the distance between antennas, reduce the power received by 4; Increase power by: Increasing antenna gains, Higher transmitting powers, Going to a lower frequency / longer wave length, Decreasing distance between antennas

How does the dipole antenna function?

- Electric field created by charge differences - Changing the polarity reverses the field causing it to propagate

Forward Scatter:

- Occurs when a signal strikes discontinuities in the troposphere and the signal is scattered in all directions - some is scattered back to earth - Useful in VHF, UHF, and SHF bands - Not used as often due to satellite coms - 30MHz < fc < 30GHz

Skywave:

- Radio waves reflected off the ionosphere and back to earth are called sky wave - Most useful in the HF bands - Medium Frequencies (MF) can be used at night - Larger reflection angle gives better results - Wave "hugs" and curves around the earth's surface - fc < 30MHz

What are the four types of communication channels and an example of each?

- Transmission lines: Ethernet cable, coaxial cable - Fiber optics: fiber optic lines - Waveguides: antenna feeds - Wireless: radio

Surface Wave:

- Wave "hugs" and curves around the earths surface - Only useful at VLF & LF - cuts off at around 3 MHz - Common use is AM broadcast radio - fc < 3MHz

wireless communication channels

-line of sight -surface wave -skywave -skywave and surface wave -forward scatter

What are the three types of basic antennas and their associated lengths and gains?

1. Dipole: Length=2, Gain=1.64 2. Monopole: Length=4, Gain=3.28 3. Dish antenna: Length=r, Gain=see eq sheeet

What three variables might we be able to control?

1. Power transmitted by the jammer 2. Ranger from the jammer to the receiver 3. Gain of the jammer

What five variables might we be able to control?

1. 𝑃t - Jammer 2. 𝐺t - Jammer 3. 𝑅 - (from RADAR) 4. PR - Radar Power (destroy it DEAD) 5. RCS (orientation and acquisition)

What is the Doppler Effect?

A reflected RADAR pulse will have a frequency that is shifted from the original pulse This shift is proportional to the speed of the target

Line of Sight:

All electromagnetic waves can propagate by LOS - Communication distance is limited by earth's curvature - Common Uses: o Earth to satellite communication -- Cell Phones -- Secure military communications

T / F Sky wave propagation requires "blobs" of air in the troposphere to bounce off.

False

T / F The distance that ground waves travel increases as the frequency of the signal increases.

False

Optical Fiber pros

Large BW's Flexible Relatively inexpensive Fairly low attenuation

Skywave and Surface Wave:

Long range comm, but there are places (depending on frequencies, angle of incidence, and ionization level) where signals cannot be received.

Wave Guide channel pros

Low attenuation

What other problem are introduced by using pulses?

Return of a pulse after a second pulse has been sent

______________ involving the use of electromagnetic and directed energy to control the electromagnetic spectrum or to attack the enemy.

Military action

wireless channel pros

No infrastructure

𝑃𝑛𝑜𝑖𝑠𝑒:

Pnoise = k*Tsys*BW

What is Electromagnetic Protection (EP)?

Protection of personnel, facilities, and equipment from employment of EM sprectrum

What is RADAR and what purpose does it have?

RAdio Detection And Ranging - it can tell how far away an object is, or even if anything is there

Wired channel pros

Reliable Easy to Repair Relatively secure

What is Electromagnetic Support (ES)?

Search, intercept, identify, and locate/localize sources of intentional or unintentional radiated EM energy

SEAD =

Suppression of Enemy Air Defenses (reversible, think jamming)

Tsys:

T is noise temperature of the system

Pulse Repetition Frequency (PRF, Hz):

The number of pulses transmitted per second

PR:

The power collected by the receiving antenna (in Watts)

Pulse Repetition Interval (PRI, s):

The amount of time between pulse transmissions

Pulse width (𝜏,𝑠):

The amount of time that the radar transmits a pulse

R:

The distance between the two antennas (in meters)

GR:

The gain of the receiving antenna (unitless)

GT:

The gain of the transmitting antenna (unitless)

How does the frequency of the signal affect the antenna design?

The higher the frequency, the smaller the antenna

A convoy in Iraq employs a jammer system to prevent the remote detonation of improvised explosive devices (IEDs). As the convoy approaches an IED, according to the Friis equation, is the jammer becoming more or less effective?

The jammer is becoming more effective because the Range between the jammer and the IED decreases, which increases the jammed power received by the IED.

𝑃𝑠𝑖𝑔𝑛𝑎𝑙:

The power of the signal you wish to receive

How would we detect a radar signal?

We use a RADAR Warning Receiver (RWR). To figure out the RWR's range, we use the Friis equation because the RWR is like a RADIO

How do we implement RADAR jamming?

We use a radio signal to drown out the RADAR return signature. We must ensure the power received from the jammer is larger than the required minimum signal from the desired communications device. The farther the jammer is from the RADAR, the more effective the jamming is.

How do we implement comm jamming?

We use another radio signal to drown out the desired communications signal. We must ensure the power received from the jammer is larger than the required minimum signal from the desired communications device. The closer the jammer is to the receiver, the more effective the jamming is.

Which of the following is an advantage of low frequency carrier signals (compared to high frequency carrier signals)? a. They can be transmitted or received using smaller antennas b. They can support signals of greater bandwidth c. They can travel farther

c. They can travel farther; Smaller frequencies are not limited to line-of-sight. They can also travel along the curvature of the earth or bounce off the atmosphere (depending on the actual frequencies).

Which frequency band attenuates rapidly in the atmosphere, but the short wavelengths permit very precise measurements? a. Very low frequencies (VLF) b. High frequencies (HF) ECE 315 Lt Col Breiding Lesson 31 7 c. Ultra high frequencies (UFH) d. Extra high frequencies (EHF)

d. Extra high frequencies (EHF)

if you are flying in a hostile territory, which of the methods below will reduce your likelihood of being detected/tracked by RADAR? a. plan your route to keep you as far as possible from the RADAR systems b. fly low to avoid LOS c. jam the RADAR d. all the above

d. all the above

as frequency increases the size of the transmitting atenna

decreases

T/F: a major advantage to fiber optics is that it can accommodate large bandwidth due to visible light's high frequency

true

T/F: an advantage of a wire transmission lines is its ease of repair

true

T/F: an antenna can be used to either transmit or receive, but not both at the same time

true

T/F: dB shows a power ratio relationship

true

T/F: in general, a parabolic dish antenna will have a larger max gain than a quarter wave monopole antenna

true

T/F: the power received for a RADAR signal is much weaker than the power received for a communications signal at identical distances

true

T/F: use of chaff creates a false RADAR target that is brighter than the actual target

true

LOS is the only wireless channel that works for every frequency range. A. True B. False

true - surface wave, sky wave, and forward scatter are limited to certain frequency bands.

parabolic dish antenna length and gain

use the gain equation

What other countermeasures could we implement?

• Minimize RLOS...fly lower • Fly fast ... get to target before enemy can react • Hide: terrain masking • Screen / Decoy: chaff ... launch dipoles

Radar Distance Equation:

𝑅𝑅𝐴𝐷𝐴𝑅= 𝑐𝑡/2