Hello
I am just looking information about microwave engineering. I saw the some useful information on internet but still I am confused on some point.
1. what are microwave ? can someone tell me why we need to use microwave ?
as my understanding , microwave are electromagnetic wave with frequency between 300 MHz to 300 GHz, used in long distance communication
2. which circuits are the microwave circuit ?
I think microwave amplifier , microwave oscillator circuit are the example of microwave, example microwave amplifier amplify the microwaves

 

Microwave is the common name given to electromagnetic waves in the 300 MHz to 300 GHz frequency range you noted.
It was named for its wavelength (speed-of-light / frequency).
They are fundamentally no different than electromagnetic waves at other frequencies.
Microwave circuits are obviously those that operate in that frequency range.
We don't "need" to use microwaves, they are just frequencies used for many common applications such as Bluetooth, WiFi cell-phone networks, and of course the microwave oven.

 

Microwave is the common name given to electromagnetic waves in the 300 MHz to 300 GHz frequency range you noted.
It was named for its wavelength (speed-of-light / frequency).
They are fundamentally no different than electromagnetic waves at other frequencies.
Microwave circuits are obviously those that operate in that frequency range.
We don't "need" to use microwaves, they are just frequencies used for many common applications such as Bluetooth, WiFi cell-phone networks, and of course the microwave oven.

I disagree. We need to use microwave communication for spacecraft, because microwaves pass through the ionosphere.

 

Hello
I am just looking information about microwave engineering. I saw the some useful information on internet but still I am confused on some point.
1. what are microwave ? can someone tell me why we need to use microwave ?
as my understanding , microwave are electromagnetic wave with frequency between 300 MHz to 300 GHz, used in long distance communication
2. which circuits are the microwave circuit ?
I think microwave amplifier , microwave oscillator circuit are the example of microwave, example microwave amplifier amplify the microwaves

You've answered your own questions.

1) What are microwaves? A: Electromagnetic waves with frequencies between 300 MHz to 300 GHz.

2) What is a microwave circuit? A: Circuits that operate at microwave frequencies?

 

I disagree. We need to use microwave communication for spacecraft, because microwaves pass through the ionosphere.

Okay, you got me.

 

Okay, you got me.

Hard to catch you nappin'

 

We need to use microwave communication for spacecraft,

That depends on whether you believe we need space craft.
Personally, I think our satellites have done amazing things for our convenience, but I was raised where we had to go get water with a bucket, and I haven't quite moved into the 21st century.

 

AFAIK, spacecraft includes satellites. The same radio communication rules apply to them as to maned spacecraft.

 

I disagree. We need to use microwave communication for spacecraft, because microwaves pass through the ionosphere.

Agreed, but the window is considerably wider than this - it includes VHF/UHF. One of the main reasons we use microwaves here is because the VHF/UHF spectrum is either too congested on the ground or we need more bandwidth.

This looks about right, from http://www.spaceacademy.net.au/spacelink/radiospace.htm
There are in fact only two main windows of the EM spectrum that are open to space. One is the visible spectrum, as mentioned above, and the other is the radio spectrum. However, not all of the radio spectrum is useable for space communication. The available window spans from about 30 MHz to 30 GHz, although these are not absolute end frequencies.

Below 30 MHz, the ionosphere, at altitudes from around 100 to 500 km, absorbs and reflects signals. Above 30 GHz, the lower atmosphere or troposphere, below 10 km, absorbs radio signals due to oxygen and water vapour. Even between 20 and 30 GHz, there are some absorption bands that must be avoided.

 

Cool diagram, but I didn't immediately grasp that the frequency axis was reversed.

 

Cool diagram, but I didn't immediately grasp that the frequency axis was reversed.

Maybe it's because it makes more sense thinking in terms of wavelength instead of frequency? So in the diagram, the shortest wavelength lies at the left, and the longest at the right. I would've added a second line of labels to the horizontal axis to make the graphic clearer.

 

You've answered your own questions.

1) What are microwaves? A: Electromagnetic waves with frequencies between 300 MHz to 300 GHz.

2) What is a microwave circuit? A: Circuits that operate at microwave frequencies?

sorry for late reply
but still I am confused on some point

1. I saw link https://en.wikipedia.org/wiki/Klystron
but I don't understand what is klystron, Is it component, circuit, amplifier, oscillator or tube ? can someone tell me what is klystron ?

 

sorry for late reply
but still I am confused on some point

1. I saw link https://en.wikipedia.org/wiki/Klystron
but I don't understand what is klystron, Is it component, circuit, amplifier, oscillator or tube ? can someone tell me what is klystron ?

FFS read the first paragraph in that wiki article!

 

FFS read the first paragraph in that wiki article!

that means A klystron is a tube which is used as an amplifier or oscillators depend on power
as we know transmitter is used to transmit signal, receiver is used to receive signal using antenna, waves propagate in free space. i know how transmitter ,oscillator circuit make. but when its time to come in microwave I don't understand how they different from the basic electronics

I am confused because when we see the amplifier or oscillator in electronics term. first things come in mind that it can be circuit that made with electronics component such as transistor, resistor , capacitors .. etc, but when same words amplifier , oscillator use in microwave why its so difficult to understand,

 

The biggest difference is that at microwave frequencies you can no longer treat components as lumped elements or assume that the voltage on a wire is the same everywhere along the wire. The wavelengths are on the order of or shorter than your components and interconnects. So you have to treat everything as distributed. That greatly complicates the math. But it also opens up doors that were previously closed to the designer and no just how you layout a conductor on a printed circuit board becomes a filter or other circuit component. Of course, the reverse is true, conductors on a printed circuit board (or elsewhere) that you only wanted to be a conductor act as unintended filters or other circuit components.

 

We always just called it RF plumbing. Waveguides and resonant cavities. Just a bunch of copper pipe through which we could push a full megawatt of microwave RF.
Feedhorns and reflector dishes, LNA's and (for our OP)
A klystron used as a local oscillator inside a special signal generator which simulated moving target echoes for use in signal injected troubleshooting of the video and doppler portions of the receiver section.

 

satelites have used frequencies lower than microwaves for years. vhf, uhf, and even short waves. a lot of russian satelites used a frequency just above the 10 mhz frquency.