The waves used by artificial satellites for communication purposes are:
Microwaves
Understanding Waves for Artificial Satellite Communication
Artificial satellites orbiting the Earth require a reliable method for communication with ground stations. This communication involves sending signals up to the satellite (uplink) and receiving signals back down (downlink). The type of electromagnetic wave used is crucial because the signal must travel through the Earth's atmosphere and the ionosphere without being significantly absorbed, scattered, or reflected.
Why Microwaves are Suitable for Satellite Communication
Microwaves are a type of electromagnetic wave with frequencies typically ranging from about 300 MHz (0.3 GHz) to 300 GHz. For satellite communication, frequencies in the GHz range are commonly used.
- Atmospheric Penetration: Waves in the microwave frequency range are able to pass through the Earth's ionosphere and lower atmosphere with relatively little attenuation (weakening). The ionosphere, a layer of charged particles in the upper atmosphere, can reflect or absorb lower frequency radio waves (like AM radio), preventing them from reaching space or returning to Earth reliably. Microwaves, however, are largely unaffected by the ionosphere.
- Bandwidth: Higher frequencies allow for larger bandwidths. Bandwidth is the range of frequencies available for transmission, and a larger bandwidth means more information can be transmitted per unit of time. Satellite communication systems need to transmit large amounts of data, including voice, video, and internet traffic, making the high bandwidth capacity of microwaves essential.
- Antenna Size: For a given gain (signal strength focus), the size of the antenna is inversely proportional to the frequency. Using higher microwave frequencies allows for smaller, more directional antennas on both the satellite and the ground station. This directionality helps in focusing the signal and reducing interference.
Why Other Options are Not Suitable
- Ground waves: These waves travel along the surface of the Earth. They are primarily used for short-range terrestrial communication and cannot reach satellites in orbit.
- A. M. radio waves: Amplitude Modulation (AM) radio waves typically use frequencies in the kilohertz (kHz) to lower megahertz (MHz) range. These frequencies are often reflected by the ionosphere, which is useful for long-distance terrestrial broadcasting but prevents reliable communication with satellites beyond the ionosphere.
- F. M. radio waves: Frequency Modulation (FM) radio waves typically use frequencies in the VHF band (around 88-108 MHz) and sometimes UHF bands. These waves are largely line-of-sight and do not reflect off the ionosphere. While some lower frequency satellite communications exist (like amateur radio satellites), the common FM broadcast frequencies are significantly absorbed or scattered by the atmosphere and ionosphere compared to microwaves, and they offer much lower bandwidth than needed for modern satellite services.
Summary of Wave Types for Satellite Communication
Let's summarize the suitability of different wave types:
| Wave Type | Typical Frequency Range | Suitable for Satellite Communication? | Reason |
|---|---|---|---|
| Ground waves | Lower frequencies (kHz to low MHz) | No | Travel along Earth's surface; cannot reach orbit. |
| A. M. radio waves | Lower frequencies (kHz to low MHz) | No | Reflected by the ionosphere. |
| F. M. radio waves | Higher frequencies (VHF/UHF, MHz) | Limited/Generally No | Higher atmospheric attenuation and lower bandwidth compared to microwaves; not reliable for general high-speed satellite links. |
| Microwaves | High frequencies (GHz) | Yes | Penetrate atmosphere/ionosphere, high bandwidth capacity, enables smaller antennas. |
Based on the properties required for communication with satellites orbiting the Earth, microwaves are the most suitable type of waves due to their ability to penetrate the atmosphere and ionosphere, provide high bandwidth, and allow for practical antenna sizes.
Revision Table: Electromagnetic Waves & Uses
| Wave Type | Frequency Characteristics | Common Applications |
|---|---|---|
| Radio Waves (incl. AM/FM) | Lowest frequencies in EM spectrum | Broadcasting (AM/FM), terrestrial communication, radar, navigation |
| Microwaves | Higher frequencies than radio waves | Satellite communication, Wi-Fi, mobile phones, microwave ovens, radar |
| Infrared | Higher frequencies than microwaves | Remote controls, thermal imaging, fiber optic communication |
| Visible Light | Frequencies we can see | Vision, photography, lighting |
| Ultraviolet | Higher frequencies than visible light | Sterilization, tanning beds, security marking |
| X-rays | Higher frequencies than UV | Medical imaging, security scanning |
| Gamma Rays | Highest frequencies | Cancer treatment, sterilization, astronomy |
Additional Information on Satellite Communication Waves
Satellite communication often uses specific frequency bands within the microwave range, allocated internationally to prevent interference. Some common bands include:
- C-band (4-8 GHz): Historically popular, less susceptible to rain fade than higher frequencies.
- Ku-band (12-18 GHz): Widely used for satellite TV broadcasting and VSAT (Very Small Aperture Terminal) networks. More susceptible to rain fade than C-band.
- Ka-band (26-40 GHz): Offers even larger bandwidth, increasingly used for high-speed internet services. More susceptible to rain fade.
These bands fall within the "atmospheric window," which refers to the range of frequencies in the electromagnetic spectrum that can pass through the Earth's atmosphere with minimal absorption or scattering. Microwaves fall nicely within one of these windows, making them ideal for space-to-Earth and Earth-to-space communication.
Important Questions from Electrostatic Potential and Capacitance
The shape of a wavefront when light emerges out of a convex lens after a parallel beam of light is incident on it:
A dielectric material placed in uniform electric field, which of the following option is NOT CORRECT:
A bulb and a capacitor are connected in series to an a.c. source. A dielectric slab is now introduced between the plates of the capacitor. The intensity of the bulb will be:
Eight identical spherical drops, each having a potential of 9V, are combined together to form a single large drop. The potential of this large drop will be:
A uniformly charged conducting sphere of radius 1.3 m has a surface charge density of 70 μC m-2. What is the total electric flux leaving the surface of the sphere?
