difference between 3dB coupler and directional coupler?

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Wilson98

Joined: 01 Apr 2004
Posts: 5

01 Apr 2004 6:10 difference between 3dB coupler and directional coupler?

Please kindly advise the difference between 3dB coupler and directional coupler in function ??

AL0117

Joined: 25 Jul 2003
Posts: 237
Helped: 8
Location: dracu-la-nd

01 Apr 2004 6:43 Re: difference between 3dB coupler and directional coupler?

Hi,

You can read some theoretical articles below:

hxxp://www.ee.bilkent.edu.tr/~microwave/programs/magnetic/dcoupler/theory.htm

replace x with t

Basically 3dB couplers are used in application where you need 2 (quasi )identical outputs (power level) with 90/180 degrees phase difference between them (typical apps: balanced amplifiers, mixers, etc). Important figure of merit for these apps is the phase balance between the outputs of the coupler.
while directional couplers are used in apps where you need the main output with low insertion loss, and the coupled output with a small percentage of the power level. (for example output power level measurement, AGC loop, distributing/summing different signals, etc)

The couplers are also known as quarter wave couplers, and if you want to increase their bandwidth, you have to use multiple sections.

rgds, Al

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lguancho

Joined: 07 Jan 2004
Posts: 266
Helped: 5
Location: Singapore

12 Apr 2004 8:28 Re: difference between 3dB coupler and directional coupler?

I think you are referring to Branchline coupler, if you are talking about equal power split (and 90 deg out of phase).

buta

Joined: 16 Apr 2003
Posts: 105

12 Apr 2004 9:04 difference between 3dB coupler and directional coupler?

directional coupler is a 4 ports network.
Power supplied from port 1 is transmitted to port 2 and a small amount of energy is coupled to port 3.

Power supplied from port 2 is transmitted to port 1 and a small amount of energy is coupled to port 4.