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\(\bullet\) Two satellites at an altitude of 1200 \(\mathrm{km}\) are separated by 28 \(\mathrm{km} .\) If they broadcast 3.6 \(\mathrm{cm}\) microwaves, what minimum receiving-dish diameter is needed to resolve (by Rayleigh's criterion) the two transmissions?

Short Answer

Expert verified
The minimum dish diameter needed is approximately 1.883 meters.

Step by step solution

01

Identify Key Variables

To solve this problem, we first identify the key variables: wavelength \( \lambda = 3.6 \text{ cm} = 0.036 \text{ m} \), separation between the satellites \( s = 28 \text{ km} = 28000 \text{ m} \), and altitude (distance to the satellites) \( D = 1200 \text{ km} = 1200000 \text{ m} \). The goal is to find the minimum diameter \( d \) of the receiving dish necessary to resolve the two sources according to Rayleigh's criterion.
02

Recall Rayleigh's Criterion Formula

Rayleigh's criterion for resolution states that the angular resolution \( \theta \) is given by \( \theta = 1.22 \frac{\lambda}{d} \), where \( \lambda \) is the wavelength and \( d \) is the diameter of the dish.
03

Calculate Angular Separation

The angular separation \( \theta_{sep} \) between the two satellites as seen by the dish is \( \theta_{sep} = \frac{s}{D} = \frac{28000}{1200000} \approx 0.0233 \text{ radians} \).
04

Apply Rayleigh's Criterion

For the dish to resolve the two satellites, the dish must meet Rayleigh's criterion: \( \theta \leq \theta_{sep} \). Therefore, \( 1.22 \frac{\lambda}{d} \leq 0.0233 \).
05

Solve for Minimum Dish Diameter

Re-arrange the inequality \( 1.22 \frac{0.036}{d} \leq 0.0233 \) to find \( d \):\[ d \geq \frac{1.22 \times 0.036}{0.0233} \approx 1.883 \text{ meters} \].
06

Conclusion

Thus, the minimum diameter of the receiving dish needed to resolve the two transmissions is approximately 1.883 meters.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Angular Resolution
Angular resolution is a term that you might come across often in optics and satellite communications. It refers to the smallest angle between two objects that a system, such as a telescope or a satellite dish, can distinguish as two separate entities rather than a merged one. The ability to clearly "resolve" two objects depends on the system's angular resolution.

In the context of satellite communications, achieving good angular resolution is important for distinguishing signals from different sources. When two satellites are close together, the receiving dish must accurately identify signals from each. Using Rayleigh's criterion, we can calculate the minimum dish size required for such tasks, as seen in our example calculation with a dish diameter of 1.883 meters. This parameter ensures that two closely placed satellites appear as separate in the data received.
Wavelength
Wavelength is a fundamental property in understanding wave behaviors, including those used in satellite communication. It is defined as the distance between successive peaks of a wave. In our exercise, the given wavelength is 3.6 cm, or 0.036 meters.

The wavelength plays a crucial role in determining the resolving power of a receiving dish. Rays with shorter wavelengths will generally provide higher resolution results for a given dish size in accordance with Rayleigh's criterion:\( \theta = 1.22 \frac{\lambda}{d} \). This formula shows that resolution improves as wavelength decreases, making it pivotal in designing efficient systems that require precise distinction at long distances.
Satellite Communication
Satellite communication involves transmitting data from Earth to satellites and then back again, enabling globally connected systems such as the internet or TV broadcasting. It utilizes different electromagnetic waves, such as microwaves, to carry digital or analog signals over vast distances.

A significant challenge is ensuring signals from multiple sources don’t overlap, requiring techniques like careful selection of dish sizes and orientation to maintain clarity. In our example, determining the minimum diameter of a receiving dish helps in effectively receiving distinct signals from satellites 1200 km above Earth. Receiving dishes must meet certain specifications, including those derived from Rayleigh's criterion, to ensure clarity and reliability in data reception.
Microwaves
Microwaves are a type of electromagnetic wave within the frequency range typically from 1 GHz to 300 GHz. They are commonly used in satellite communication due to their suitable properties for transmitting signals over long distances without excessive loss, compared to other frequencies.

Given our scenario, where 3.6 cm microwaves are used for communication between satellites and a receiving dish, we can understand why microwaves are preferred. They have a balance between carrying capacity and penetration ability. When microwaves reach a receiving dish on Earth, their properties, including their wavelength, are key in ensuring data from the sky is accurately captured and decoded. These waves provide a stable medium for high-quality transmission, essential for the angular resolution to correctly interpret outgoing signals.

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