Diplexer

In principle, a diplexer, a multiplexer, which switches two inputs to an output. In radar systems, this module is the link between two transmitters or receivers and the antenna. Mainly these diplexers are used in pseudo-coherent radars.

The diplexer here is a crossover and has the task of two channels of different frequency (ie, two transmitters and two receivers ) to decouple so that they can be operated at an antenna. The transmitting power of each transmitter to be directed to the antenna and the respective echo signals are distributed to the corresponding receiver. The signals in the passage to be attenuated as little as possible, and the isolation between the two channels should be as large as possible, that is, the signal should be passed only in the desired direction and the other directions should have a very high attenuation.

In radar technology diplexer are usually made ​​of waveguide sections. Particular advantages of a diplexer of waveguide sections are again the high performance strength and on the other hand, a simple change of frequency by changing the lengths of the phasing lines is possible.

Operation

The diplexer in a waveguide system basically consists of two consecutive power dividers ( directional couplers ). After the first power divider power both halves through different path lengths and thus obtain a different phase. The second power divider works as a summation when both halves performance despite different path lengths of the same phase angle (constructive interference). If this phase but different, then there is a slowdown, is the phase angle contradictory, then the power dies out in this way even each other out (destructive interference).

Thus, the diplexer must now be dimensioned in the line length, that on the output power in a frequency summation takes place in the second frequency an erasure. A diplexer then works most effectively when the tunable bypass line meets the following conditions simultaneously:

• The phase shift for the A- rate is 0 °.
• The phase shift for the frequency - B is 180 °.

The frequency separation between the two transmission frequencies is predetermined by the design diplexer. In practice, this detour lines are dimensioned with a multiple of the wavelength, since then multiply smaller phase differences and the diplexer thereby obtains a narrower passband. So that the transmission frequencies are mathematically predetermined by the same waveguide length for which a frequency of an even integer multiple and the second frequency must have an odd number multiple of half the wavelength.

This diplexer is permeable but also for several other frequencies if they can occur in the spectrum of the transmitting tube, then have to be suppressed by an additional filter. Another reason for the use of a multiple wavelength is that characterized by the installed frequency spacing between the two transmitter frequencies is reduced.

Swell

• Merrill Ivan Skolnik, " Radar Handbook ", ISBN 0070579083
• Merrill Ivan Skolnik "Introduction to Radar Systems ", ISBN 0072881380
• Dipl. -Ing. Albrecht Ludloff, " Practical Knowledge radar and radar signal processing ", ISBN 352826568X
• Otto Zinke, Heinrich Brunswig, High Frequency Engineering 1, radio frequency filters, cables, antennas, Springer Verlag