CS200840B1 - High-pass filter arranged from coaxial cables sections - Google Patents

Description

The present invention relates to a high-pass filter made up of sections of coaxial cables which are open at both ends or short-circuited at one end, their sheaths being grounded on one ground plate.

Filters for higher frequency bands cannot be assembled from discrete components. Already from frequencies around 100 MHz, these filters are realized by means of components, which behave as circuits with distributed parameters. The construction of such filters is known. For example, simple filters can be constructed from line sections. However, when designing for higher parameters such as high selectivity, both design and implementation are often quite difficult. That is why mixed circuit elements are used in more complex filters - both elements with lumped parameters, such as simple coils and capacitors, as well as line sections that connect appropriately. This brings some disadvantages, such as increased losses and, above all, the complexity of the structure, which also reduces the reliability of the function, since all elements must be well shielded. Disadvantages of such a solution are eliminated by the circuit according to the invention.

The subject of the invention is a high-pass filter composed of coaxial cable sections, characterized in that the coaxial cable sections are open at both ends and short-circuited at one end, the sheaths of these sections being grounded at two points on a single ground plate.

200 840

A filter consisting exclusively of coaxial wiring sections of its cable without any other components was designed and experimentally verified. The filter is a high-pass filter made up of n 5 5 cells, which are realized in longitudinal branches by capacitances and in transverse branches by inductances. The perimeter elements are then replaced by the line sections of the appropriate length for which the following applies:

á * o cotg

2 & A el, with both open ends,

el, at one short-circuited end, where Zp is the impedance at the input, Z _{Q is the} wavelength impedance of the line, λ _{0 the} wavelength and el the length of the segment.

If - ---, then A 8 will be applied to the open segment

Zp = -jZ _Q , which represents the net capacity for frequency f _Q , and short-circuited at one end

OF? - jZ _Q , which is equivalent to the inductance.

Fig. 1 shows a single pass through 3 sections, Fig. 2 shows a pass through 13 sections of a coaxial cable, the construction is shown in Fig. 3a, Fig. 4 shows an amplitude characteristic.

At the same time, the single-pass filter is adapted to loads of impedances equal to the wavelength of the cable impedance. If higher selectivity is required, we build a filter from a cascade of simple ^ O cells. The length of the sections is calculated such that the internal short-circuit sections have half the impedance for a given frequency compared to the external sections whose length is equal to the length of the sections at both ends of the open, equivalent capacities. Since each line is an electrical circuit with distributed parameters and the impedance pattern is periodically repeated at a multiple of the frequency, unlimited bandwidth cannot be achieved in the manner described. The filter is still well adapted at a bandwidth of 0.9 f _& .

To reduce losses due to mismatch, a high-pass calculation was made up of a total of 11, 13 and 15 coaxial cable sections. The optimal length for capacitances and ultimate inductances was λ '/ 6 and for internal sections λ ^ζ / ΐθ, 9; where λ ^ζ is the reduced wavelength, relative to the frequency at the edge of the passband, multiplied by the coaxial cable shortening factor. 50-17 and 75Λ impedance cables were tested. Throughputs in the 200 UHz to 500 MHz band, made up of 11 to 15 sub-bands, showed both good selectivity and low losses.

Fig. 3 shows a base plate Z of double-clad cuprextite. On this plate Z, individual sections terminated by winding 1 or a short-circuit 2 representing inductances are fastened on both sides by fly-through. The free ends of the sections are connected by

200,840 plate of unilaterally clad cuprextite to eliminate the inductance of the joints.

The entire culvert is enclosed in a simple housing with connectors with inlet £ and outlet 2 ·

Fig. 4 shows the amplitude characteristic of the realized filter made up of 15 sections. The filter is very simple in design and the tolerances of the coaxial cable parameters have no noticeable influence on the filter parameters.

Claims (1)

A high-pass filter composed of coaxial cable sections, characterized in that the coaxial cable sections are open at both ends and short-circuited at one end, the sheaths of these sections being grounded at two points on a single ground plate.