Attenuators and loads.

Waveguide matched loads are performed in the form of waveguide sections with wedge-shaped absorbing inserts. The length of the wedge is usually at least two wavelengths in the waveguide . In this case, you can get K bv about 0.95.

In loads designed for low power, absorbing plates can be used (for example, textolite with graphite coating) placed in a maximum of the electric field parallel to the vector E. More often loads are applied with wedges made of absorbing masses such as SKB-90, PM, etc. , designed for units of watts, reinforced absorbing materials are used.

Strip attenuators and loads.

In strip-type (especially printed) attenuators and loads, absorbing tapes with a thickness of 0.1–0.2 mm, having surface resistance of about 100 Ω / cm 2 , as well as tapes of high-resistance alloys (for example, nichrome) are widely used . For nichrome, the attenuation at 9 GHz is 20 dB / m, and for silver-plated conductor, 2 dB / m.

Fig. 5.15. The inclusion of a fixed attenuator and a matched load in the strip line: 1 - the center conductor of the strip line;

2 — fixed attenuator; 3 — matched load

An attenuator or a load in a strip line can be formed by brazing pieces of an absorbing tape of a certain shape to the dielectric plate and to the central conductor of the strip line (Fig. 5.15). By selecting the shape of the absorbing tape, it is possible to get K bv not worse than 0.95 in the 20% frequency range and not worse than 0.83 in the double range. The attenuation value of the attenuator is determined by the value of h. The attenuator is made as shown in Fig. 5.15, can provide attenuation no more than 7 dB. To obtain large attenuation, a small portion of the center conductor is replaced with absorbing material.

If the load is performed in the form of a short-circuited nichrome line, then to reduce the size, this line is folded into a spiral. Attenuation of a nichrome short-circuited line per 1 m is 40 dB.

The center conductor of the main line at the point of load connection is made with bevels in order to eliminate reflections from the junction, and the bevel length is chosen equal to l = (2-3) d (d is the width of the center conductor).

The designs of attenuators and loads on air-filled strip lines do not fundamentally differ from those of similar coaxial elements.