When a signal enters the "a" or "b" arm of the magic t waveguide junction, then a signal appears at the E
and H plane ports but not at the other "b" or "a" arm as shown.
One of the disadvantages of the Magic-T waveguide junction are that reflections arise from the
impedance mismatches that naturally occur within it. These reflections not only give rise to power loss,
but at the voltage peak points they can give rise to arcing when sued with high power transmitters. The
reflections can be reduced by using matching techniques. Normally posts or screws are used within the
E-plane and H-plane ports. While these solutions improve the impedance matches and hence the
reflections, they still reduce the power handling capacity.
Hybrid ring waveguide junction
This form of waveguide junction overcomes the power limitation of the magic-T waveguide junction.
A hybrid ring waveguide junction is a further development of the magic T. It is constructed from a
circular ring of rectangular waveguide - a bit like an annulus. The ports are then joined to the annulus at
the required points. Again, if signal enters one port, it does not appear at allt he others.
The hybrid ring is used primarily in high-power radar and communications systems where it acts as a
duplexer - allowing the same antenna to be used for transmit and receive functions.
During the transmit period, the hybrid ring waveguide junction couples microwave energy from the
transmitter to the antenna while blocking energy from the receiver input. Then as the receive cycle
starts, the hybrid ring waveguide junction couples energy from the antenna to the receiver. During this
period it prevents energy from reaching the transmitter. Waveguide junctions are an essential element
within waveguide technology. Enabling signals to be combined and split, they find applications in many
areas as discussed in the text. The waveguide T junctions are the simplest, and possibly the most widely
used, although the magic-T and hybrid ring versions of the waveguide junction are used in particular
applications where their attributes are required.
1.0.IMPEDANCE MATCHING AND TUNING
Reflections in a waveguide system cause impedance mismatches. When this happens, the cure is
identical to the one that would be employed for transmission lines. That is, a lumped impedance of
required value is placed at a precalculated point in the wave guide to overcome the mismatch,
cancelling the effects of the reflections. Whereas lumped impedance or stubs are employed in
transmission lines, obstacles of various shapes are often used with waveguide
In order to ensure the optimum waveguide impedance matching is obtained, small devices are placed
into the waveguide close to the point where the matching is needed to change its characteristics.
There are a number of ways in which waveguide impedance matching can be achieved:
Use of gradual changes in dimensions of waveguide.
Use of a waveguide iris
Use of a waveguide post or screw
Each method has its own advantages and disadvantages and can be used in different circumstances.
The use of elements including a waveguide iris or a waveguide post or screw has an effect which is
manifest at some distance from the obstacle in the guide since the fields in the vicinity of the waveguide
iris or screw are disturned.
and H plane ports but not at the other "b" or "a" arm as shown.
One of the disadvantages of the Magic-T waveguide junction are that reflections arise from the
impedance mismatches that naturally occur within it. These reflections not only give rise to power loss,
but at the voltage peak points they can give rise to arcing when sued with high power transmitters. The
reflections can be reduced by using matching techniques. Normally posts or screws are used within the
E-plane and H-plane ports. While these solutions improve the impedance matches and hence the
reflections, they still reduce the power handling capacity.
Hybrid ring waveguide junction
This form of waveguide junction overcomes the power limitation of the magic-T waveguide junction.
A hybrid ring waveguide junction is a further development of the magic T. It is constructed from a
circular ring of rectangular waveguide - a bit like an annulus. The ports are then joined to the annulus at
the required points. Again, if signal enters one port, it does not appear at allt he others.
The hybrid ring is used primarily in high-power radar and communications systems where it acts as a
duplexer - allowing the same antenna to be used for transmit and receive functions.
During the transmit period, the hybrid ring waveguide junction couples microwave energy from the
transmitter to the antenna while blocking energy from the receiver input. Then as the receive cycle
starts, the hybrid ring waveguide junction couples energy from the antenna to the receiver. During this
period it prevents energy from reaching the transmitter. Waveguide junctions are an essential element
within waveguide technology. Enabling signals to be combined and split, they find applications in many
areas as discussed in the text. The waveguide T junctions are the simplest, and possibly the most widely
used, although the magic-T and hybrid ring versions of the waveguide junction are used in particular
applications where their attributes are required.
1.0.IMPEDANCE MATCHING AND TUNING
Reflections in a waveguide system cause impedance mismatches. When this happens, the cure is
identical to the one that would be employed for transmission lines. That is, a lumped impedance of
required value is placed at a precalculated point in the wave guide to overcome the mismatch,
cancelling the effects of the reflections. Whereas lumped impedance or stubs are employed in
transmission lines, obstacles of various shapes are often used with waveguide
In order to ensure the optimum waveguide impedance matching is obtained, small devices are placed
into the waveguide close to the point where the matching is needed to change its characteristics.
There are a number of ways in which waveguide impedance matching can be achieved:
Use of gradual changes in dimensions of waveguide.
Use of a waveguide iris
Use of a waveguide post or screw
Each method has its own advantages and disadvantages and can be used in different circumstances.
The use of elements including a waveguide iris or a waveguide post or screw has an effect which is
manifest at some distance from the obstacle in the guide since the fields in the vicinity of the waveguide
iris or screw are disturned.
