Rat-race coupler
A rat-race coupler (also known as a hybrid ring coupler) is a type of coupler used in RF and Microwave systems. In its simplest form it is a 3dB coupler and is thus an alternative to a magic tee. Compared to the magic tee, it has the advantage of being easy to realize in planar technologies such as microstrip and stripline, although waveguide rat races are also practical. Unlike magic tees, a rat-race needs no matching structure to achieve correct operation.
The rat-race coupler has four ports, each placed one quarter wavelength away from each other around the top half of the ring. The bottom half of the ring is three quarter wavelengths in length. The ring has a characteristic impedance of factor 
compared to port impedance.
A signal input on port 1, will be split between ports 2 and 4, and port 3 will be isolated. The full scattering matrix for an ideal 3dB rat-race is
Rat-race couplers are used to sum two in-phase combined signals with essentially no loss or to equally split an input signal with no resultant phase difference between its outputs. It is also possible to configure the coupler as a 180 degree phase-shifted output divider or to sum two 180 degree phase-shifted combined signals with almost no loss.
Podcasts:
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by Billy Idol
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by Baha Men
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by Avantasia
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by Bigwig
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by A Broken Silence
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by Specials
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by UK Subs
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by Bob Marley
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by Insyderz
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by Stephen Bishop
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by Bunny Wailer
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by Gift Of Gab
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by The Insyderz
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by Scroobius Pip
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by Rob Rock
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by Impellitteri
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by Greatest Movie Hits Soundtrack
Rat Race
by: Billy IdolWake me from my sleep
A cautionary tale
A walk in infancy
A way to derail
I wanted to be free
And I wanted only you
The walls are falling down
And somebody says
Give a little love, give a little love
But take your time
And somebody sighs
Yes, give a little love, give a little love
But take your time
A private life, c'mon now
I said livin' gets to be
Just like a rat race, rat race
C'mon, I'm a-read between the lines
Fierce stuggle, a natural one
A Tough job gets to be
Just like a rat race, rat race
C'mon, I'm locked up in myself
Check before rising
Check before we work
Childproof the scene
No screams can be heard
The roof is caving in
The space between our hearts
The walls are falling down
It's a rat, it's a rat, it's a rat race
It's a rat, it's a rat race
Aah life, living in a rat race, c'mon
Hmm life, are you living in a rat race?
C'mon, here inside yourself