Directional coupler

Directional couplers are widely used in various branches of radio electronics , both as stand-alone devices in cable and waveguide lines, and as elements of electronic equipment. As stand-alone devices, NOs are used to branch the signal from the line (for example, television splitters) and to control the parameters of the signal in the line and coordinate it. As elements of the BUT equipment, they are mainly used in radio measuring instruments - microwave power meters , devices for measuring the SWR , transmission coefficient , installations for checking attenuators and measuring attenuation , as well as in other cases.

• RF directional couplers
  • Waveguide BUT
  • Waveguide-coaxial BUT
  • Wave-Stripe BUT
  • Coaxial BUT
  • Striped BUT
  • Loopback BUT
  • BUT on lumped elements
• Optical ( fiber optic ) directional couplers

Waveguide BUT

In the centimeter and millimeter wave ranges, the waveguide design of the coupler is used. It consists of two segments of the waveguide , which have a common thin wall (wide or narrow) in a certain area. Holes are made in the wall separating the waveguides, which serve as communication elements, through which a small part of the power branches from the primary waveguide to the secondary. The number of holes, their shape and dimensions determine the characteristics of the coupler. Directional propagation in the secondary waveguide is achieved as a result of the interference of waves excited in it, which, when folded, mutually cancel out in one direction and form the resulting branched wave in the other.

Waveguide-coaxial and waveguide-strip BUT

The waveguide-coaxial BUT has a primary waveguide and a coaxial or strip secondary line, which is placed directly in the waveguide parallel to its longitudinal axis. The line is excited by the transverse components of the magnetic field of the wave in the waveguide, like coupled lines with a wave of type T. The coupler is oppositely directed. Compared with the waveguide BUT, the waveguide-coaxial has significantly smaller dimensions.

BUT on connected transmission lines

The most compact and wideband directional couplers in the microwave range are obtained using the effects of mutual communication in multi-wire transmission lines with T-waves, they can be implemented as coaxial or strip BUT. Coaxial BUT is a segment of a circular two-wire waveguide, strip - two segments of closely spaced strip lines with a common screen with conclusions in the form of coaxial connectors .

Loopback BUT

Loopback BUTs are usually implemented in the form of integrated circuits ; they consist of two segments of strip transmission lines interconnected by two or more loops, length and distance between which are equal to a quarter of the wavelength defined in the strip transmission line. With an increase in the number of loops, the directivity and range characteristics of a loop BUT improve. However, with the number of loops more than three, their wave impedances become so large that they can hardly be implemented in print. In this regard, in the microwave ICs the most widespread are two- and three-loop BUTs.

BUT on lumped elements

On meter and longer wavelengths, NO from segments of transmission lines are usually not used because of their bulkiness, couplers on concentrated reactive elements are used instead. In these couplers, line segments are replaced by four-terminal reactive concentrated resistances. Depending on the connection of the elements between themselves, such couplers may be equivalent to a loopback NO or NO on connected lines.

BUT on dielectric waveguides

At millimeter and shorter wavelengths, NPs from segments of metal waveguides are not effective because of the narrow passband; instead, it is convenient to use NSs formed by two segments of dielectric waveguides (DWs), smoothly reduced to a certain distance. The use of flexible dielectrics makes it possible to make such BUTs with an adjustable power division coefficient into the arms (2) and (4) and a phase shift. And also these NOs differ from NOs on MVs with a very high degree of isolation between input (1) and output (3).

  (12)
        \ ____ /
        / ---- \
 (3) --- / \ --- (4)

Main rated characteristics

• Transient attenuation is the ratio of the input power of the main line to the power branched into the working arm of the auxiliary line, expressed in decibels , when absorbing loads are connected to unused shoulders. Transient attenuation takes positive values, from 3 dB or more. In English literature, a similar value of the coupling factor has the same meaning and opposite sign.
• Directivity - the ratio of power at the output of the working and non-working shoulders of the secondary line, expressed in decibels, when the working arm of the main line is excited and absorbing loads are connected to the remaining shoulders.
• Working attenuation ( main line insertion loss ) is the ratio of power at the input and output of the main line, expressed in decibels, when absorbing loads are connected to unused shoulders.
• Isolation (Eng. Isolation ) - the ratio of the power at the input of the primary line to the power in the non-working shoulder of the secondary line, expressed in decibels, when absorbing loads are connected to unused shoulders.
• The coefficient of the standing wave in the primary and secondary lines
• Working frequency band

• Wattmeter
• Waveguide
• Strip line

• Sazonov D.M., Gridin A.M., Mishustin B.A. Microwave devices - M: Higher. school, 1981
• Chernushenko A. M. Design of screens and microwave devices - 1990
• A.E. Aksenov. Directional coupler on lumped inductive and capacitive elements. - Radio engineering, 1976, No. 2
• Feldstein A. L., Yavich L. R. Synthesis of four-terminal and eight-terminal microwave circuits. - M .: Communication, 1971
• Guide to the elements of strip technology / Ed. A. L. Feldstein - M .: Communication, 1978
• Handbook of electronic devices. In 2 t. / Ed. D.P. Linde - M .: Energy, 1978
• Handbook of elements of electronic devices / Ed. V. N. Dulina et al. - M .: Energy, 1978
• Dielectric waveguides / Vyatyshev V.F. - M .: Soviet Radio, 1970
• Microelectronic devices microwave: Textbook. manual for radio engineering specialties of universities / Ed. G.I. Veselova. - M .: Higher. school, 1988

Normative and technical documentation

• OST11-224.007-82 Coaxial directional couplers. General technical requirements
• OST11-P0.224.001-70 Directional waveguide couplers with equal power division
• OST4-397.001-85 Passive optical couplers and splitters. Application Guide
• OST4-397.006-85 Passive optical couplers and splitters. General specifications
• TU 11-HShM0.356.074TU-88 Directional precision couplers

• Coaxial Directional Coupler
• Directional coupler
• Waveguide Coaxial Directional Coupler
• CALCULATION OF FUNCTIONS OF SENSITIVITY AND TOLERANCES FOR DIMENSIONS OF ADJUSTABLE DIRECTED DIVERSION
• Configuring and matching antenna feeder devices