Duplexer using λ /4- stubs have a relatively small bandwith caused of the frequency depended length of the stubs. This is very impractical by existing electronic jamming on a particular frequency.
Radar sets working on a wider frequency band, need a duplexer with a wider bandwith e.g. the “Balanced Duplexer”. This duplexer works in accordance with the following principle:
Figure 1: Principle of a “Balanced Duplexer”
- A -3 dB-hybride divides the transmitters power in two parts;
- this part passed the slot of the hybride take a phase-shift of 90°;
- both parts of power cause an arc across both spark gaps
- these arcs short-circuit the waveguide and the power would be reflected;
- the power divides in the -3 dB-hybride once again;
- this part passed the slot of the hybride again take a phase-shift of 90°;
- among the parts in the direction of the transmitter occurs a phase-shift of 180° and these parts of power compensates among each other;
- both parts in the direction of the antenna have the same phase and accumulate to the full power.
During reception the amplitude of the received echo is not sufficient to cause an arc across either spark gap. both parts of the received echo can pass the spark gaps. The echoes recur both hybrides and accumulate their parts in-phase. The loss of this duplexer is about 0.5 to 1.5 dB.