How does the gain of a parabolic dish antenna change when the operating frequency is doubled?

Gain increases 6 dB.

Gain for an antenna refers to the performance in transmission of more power in a specific direction, as compared with the made up (theoretical) antenna that radiates in all directions.

For a specific frequency, the area transmission reaches is directly proportional to the gain. So, if you double the frequency, then the gain logarithmically increases also.

For more information, please see All About Circuits site for the article The RF Engineer’s Guide to the Decibel Chapter 1 - Introduction to RF Principles and Components

See Wikipedia's article for article on Gain (electronics)

See Tutorials Point site for article on Radar Systems - Range Equation

See Radar Tutorial EU for article on The Radar Range Equation

See CS Binghamton Edu site for the short pdf article on Gain of Directional Antennas

To learn to compute gain, please see Phys Hawaii Edu site for the pdf article on ANTENNA INTRODUCTION / BASIC

For online dB calculator, see Everything RF Parabolic Reflector Antenna Gain

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What type of antenna or pickup device is used to extract the RADAR signal from the wave guide?

J-hook.

This simple answer--just memorize it--refers to a number of characteristics of radars to be able to understand it.

In J-hook configuration, the energy is sent and received from the waveguide in a RADAR.

See Wikipedia's article Radar signal characteristics This is what the J-hook deals with.

Also, see the FAA publication Section 5. Surveillance Systems This is about monitoring airplanes.

And, useful information from the Radar Tutorials EU called Basics of waveguide theory

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What happens to the beamwidth of an antenna as the gain is increased? The beamwidth:

Decreases as the gain is increased.

Just like a flashlight, when you tune into a single spot for stronger light, the beam width decreases. For radars, when you focus on a smaller area, you achieve higher gain.

So, the beamwidth and antenna gain are inversely proportional.

For more information, please see A.H. Systems site for the article Understanding Antenna Gain, Beamwidth, And Directivity, and also the article called The Importance of Antenna Beamwidth in RF Testing

And, RF Venue site for the article The Tradeoff: Higher Gain Antenna, Narrower Beam-Width

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A common shipboard RADAR antenna is the:

Slotted array.

The metal box with one side containing many openings transmits radar waves as it turns around. The "slotted array" refers to the long thin openings in some patterns.

The slotted array picks up horizontal radio signals. The back is kind of conical, so that the vertical radio signals are partially eliminated.

For more information, please see Wikipedia's article Slot antenna

Also see the Rantec Microwave Systems, for the article A Brief Guide to Slotted Array Antennas

For more details, please see the Antenna Theory site for the article Slot Antennas. Inserted there is a YouTube video from Pete's Free Info Center channel, called Antenna-Theory.com Presents: Analysis of the Slot Antenna and see the article Slotted Waveguide Antennas

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Conductance takes place in a waveguide:

Through electromagnetic and electrostatic fields in the walls of the waveguide.

Both forms of the wave, electrostatic and magnetic are trapped inside the walls of the waveguide, and are directed toward the opening.

Please see Analog IC Tips site for the article What are RF waveguides? Part 2: implementation and components

For more information please see MIT Lincoln Laboratory pdf presentation called Introduction to Radar Systems Radar Transmitter/Receive

Also, please see Itechopen site for the article Wideband Antennas for Modern Radar Systems

For extensive in-depth knowledge in this area, please see the pdf from the U.S. Department of Commerce, NTIA Report TR-06-444, called the Effects of RF Interference on Radar Receivers

See Radar Tutorial EU site for Basics of waveguide theory

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To couple energy into and out of a waveguide use:

A thin piece of wire as an antenna.

For a radar antenna, the waveguide needs to be able to guide the radar's emissions of waves. This thin piece of wire appears to be a simple solution. The choice of waveguide antenna greatly affects the performance of a radar.

Please see Analog IC Tips site for the article What are RF waveguides? Part 2: implementation and components

For more information please see MIT Lincoln Laboratory pdf presentation called Introduction to Radar Systems Radar Transmitter/Receive

Also, please see Itechopen site for the article Wideband Antennas for Modern Radar Systems

And, from Antenna Theory site, the article Slotted Waveguide Antennas

See Radar Tutorial EU site for Basics of waveguide theory

For extensive in-depth knowledge in this area, please see the pdf from the U.S. Department of Commerce, NTIA Report TR-06-444, called the Effects of RF Interference on Radar Receivers

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