RU2068589C1 - High-frequency coaxial capacitor device - Google Patents

Abstract

FIELD: pulse technique. SUBSTANCE: high-frequency capacitor device has coaxial line formed by two sections with conical internal and external conductors. Resistors are inserted between internal and external conductors and electrically connected to them. Low-voltage capacitor and small-size capacitors are placed between internal conductors. Supporting member built up of insulating disks is fixed at bases of conductor cones. Expression for determining width of disks by vector radius is given in description of invention. EFFECT: improved design. 3 dwg

Description

 The invention relates to a pulse and oscillographic technique and can be used as a separation device between the power supply circuit of the primary Converter and the signal path of a high-speed oscilloscope. Such a device is necessary, since the primary converter requires, as a rule, a high 1 2 kV supply voltage.

For many types of primary converters, the electrical signals at their output have a wide range of frequencies. In such cases, it has a capacitance C _p ≃ 0.1 μF, characterized by a high operating voltage U _p ≃ 1.5 kV, a boundary frequency f _gr ≃ 10 GHz and a uniform amplitude-frequency characteristic (AFC). These requirements are contradictory, since an increase in the capacitance and operating voltage of a capacitor causes an increase in its overall dimensions, and, as a consequence, a decrease in the cutoff frequency.

 Known coaxial capacitor (1), containing input and output coaxial connectors, conical transitions and gaps along the inner and outer conductor of the coaxial line, each of which has a special, non-inductive capacitor wound on a ceramic cylinder. This achieves a reduction in the size of the capacitor while maintaining the required wave impedance and operating voltage.

The closest technical solution to this proposal is a high-frequency coaxial capacitor device containing a coaxial line formed by two segments with cone-shaped internal and external conductors facing each other with bases, resistors with metal contacts placed between the internal and external conductors and electrically connected to them, a low-frequency capacitor mounted between the inner conductors and a central support element fixed to the base housings niyah [2]
If we consider the double cone transition from the point of view of propagation of the front of a spherical electromagnetic wave in it (Fig. 1), then it is clear that when this front passes from the input cone line to the output one, the longitudinal component E _z is necessary to convert the normal component E _p to E _p . Since the structure is symmetrical with respect to the longitudinal axis, higher types of waves E ₀₁ (electric waves) are possible in it. Component E _z excites a wave of type E ₀₁ at a frequency corresponding to the condition λ _cr 0.57 • D, where D is the diameter of the external cone of the cone line at the point of transition of the wave front to the output cone line. This wave, propagating in the opposite direction, enters the supercritical region and quickly damps, leading to energy losses at frequencies that make up the condition λ _cr 0.57 • D.

 Thus, the disadvantages of VKKU (2) are the frequency response unevenness caused by the appearance of higher-type waves and low mechanical strength associated with insufficient thickness of the support element. The aim of the invention is to improve the uniformity of the frequency response and increase the mechanical strength of VKKU.

где H величина, равная расстоянию от начала обоих отрезков до вертикальной оси, разделяющей эти отрезки;
E относительная диэлектрическая проницаемость материала диэлектрических шайб, образующих центральный опорный элемент;
θ₁ и θ₂ угол, образованный соответственно образующей поверхности внешнего и внутреннего проводника с их осью;
θ текущая угловая координата q₂ < θ < θ₁.
Сущность изобретения заключается в том, что предлагаемая конструкция обеспечивает разделение спектра проходящего сигнала на три полосы и прохождение ее по различным цепям, так что полоса пропускания ВККУ простирается от нижней граничной частоты низкочастотного конденсатора до верхней граничной частоты конденсаторного элемента, образованного емкостью боковой и торцевой части зазора между внутренними проводниками двух отрезков, содержащих диэлектрическое кольцо.The purpose of the invention in VKKU containing a coaxial line formed by two segments with conical internal and external semiconductors facing each other with bases, resistors with metal contacts placed between the internal and external conductors and electrically connected to them, a low-frequency capacitor installed between the internal conductors, and a central supporting element fixed in the bases of the housings (2) is achieved by the fact that in the inner conductor of one of the segments from the side of the base A round sample was made in which the inner conductor of the other segment was placed with a gap, with an inserted dielectric ring installed in the side and end parts of the gap and metal disks located on the bases of the inner conductors, with small capacitors connected in parallel between them, and the central supporting element made in the form two dielectric washers having an XY (θ) profile defined by

where H is a value equal to the distance from the beginning of both segments to the vertical axis separating these segments;
E is the relative dielectric constant of the material of the dielectric washers forming a central support member;
θ ₁ and θ _{2 the} angle formed respectively forming a surface of the outer and inner conductor with their axis;
θ is the current angular coordinate q ₂ <θ <θ ₁ .
The essence of the invention lies in the fact that the proposed design provides for the separation of the spectrum of the transmitted signal into three bands and its passage through different circuits, so that the passband of the CCCH extends from the lower boundary frequency of the low-frequency capacitor to the upper boundary frequency of the capacitor element formed by the capacitance of the side and end parts of the gap between the inner conductors of two segments containing a dielectric ring.

The invention also lies in the fact that the proposed design provides the conditions under which the component E _z does not occur, and also that the execution of the support element in the form of two dielectric washers with a profile defined by expression (1) ensures not only the absence of E _z , but also provides them with a sufficient thickness, therefore, the mechanical strength of the structure.

 Specifically conducted studies and calculations (3) show that the inhomogeneity arising from the installation of two dielectric washers does not significantly affect the frequency response of the CKCC in the operating frequency range.

 The proposed coaxial capacitor device is shown in FIG. 2, in Fig. 3, the amplitude-frequency characteristics of the CWCC without dielectric washers and with dielectric washers installed.

 In FIG. 2, the following designations are adopted: the cone-shaped inner conductor 1, the outer conductor 2, the resistors 3, 4, the reference disks 5, the low-frequency capacitor 6, the capacitor 7 formed by two metal disks and small-sized capacitors connected between them, a dielectric ring 8, a side and end gap between the inner conductors of two segments 9, the metal contacts of the resistors 10, the dielectric washers 11, forming a central support element VKKU.

To prevent the emergence and propagation in the opposite direction of waves of the highest type, leading to energy losses, i.e. non-uniformity of frequency response, continuous dielectric washers 11. The profile is described by expression (1). The profile is calculated on the basis of the equality of the electric path length of various sections of the front of the spherical TV wave over all the radius vectors of its propagation. With this approach, the most smooth turn of the wave front occurs (without excitation in the ideal case) of the component E _z . Complete suppression of E _{z is} possible only if the conditions for the rotation of the front of a spherical wave are perfectly observed. However, even in the manufacture of dielectric washers with a profile approximated by a linear function, in the presence of constructive and technological tolerances, there is a significant improvement in the frequency response in the resonance regions, thereby achieving the purpose of the image.

 The following text shows that the introduction of dielectric washers is expressed in the appearance of two additional capacitances C and inductances of the transition sections.

где W_o волновое сопротивление линии, W_o 50 Ом;
E(X) диэлектрическая проницаемость материала шайб;
Δl длина участка конусной линии с шайбами (см. фиг.2);
E_o, M_o абсолютная диэлектрическая и магнитная проницаемость.Capacities C are calculated by the formula

where W _{o the} wave impedance of the line, W _o 50 Ohms;
E (X) dielectric constant of the washer material;
Δl the length of the section of the conical line with washers (see figure 2);
E _o , M _o absolute dielectric and magnetic permeability.

D диаметр внешнего конуса в месте установки шайб;
d диаметр внутреннего конуса в месте установки шайб;
Х текущая координата по профилю (фиг.2).

D the diameter of the outer cone at the place of installation of the washers;
d the diameter of the inner cone at the place of installation of the washers;
X current coordinate along the profile (figure 2).

(3),
где r₁ радиус внутреннего проводника у основания конуса;
r₂ радиус внешнего проводника у основания конуса.The equivalent inductance of the transition sections from the conical line to the coaxial and vice versa according to (4) is determined by the formula

(3)
where r _{1 is the} radius of the inner conductor at the base of the cone;
r _{2 is the} radius of the outer conductor at the base of the cone.

The calculation according to formulas (2, 3) gave the following approximate values of the equivalent capacitance and inductance:
C ₁ = C ₁ = C ₂ = 0.2 pF;
L ₁ = L ₁ = L ₂ = 0.1 nH.

 These values do not significantly affect the operating (<10 GHz) frequency range.

 The proposed VKKU works as follows.

The signal under investigation is fed to the input connector, distributed along a cone line, and, at the installation site of the capacitors 6, 7 and branch 9, it is divided into 3 parts. Part of the spectrum of the signal lying in the frequency range 30 kHz to 10 MHz passes through condenser 6 low frequency, mid-frequency part of the spectrum 300 MHz signal 30 passes through the mid-capacitor 7, the high frequency part of the spectrum of 300 MHz-f _{in the} container passes through the side and end of the gap 9.

The signals of all spectral components passing in a conical line form a spherical electromagnetic field. This means that, unlike the structure of the TEM wave in the coaxial line, the wave front is not a plane, but a portion of the sphere located between the inner and outer conductor of the cone line. The front of a spherical wave during the transition from one conical line to the output is distorted in such a way that a longitudinal component of the electric field arises (E see FIG. 1), which at certain frequencies is a source of electric waves of higher types E ₀₁ .

When installing dielectric washers 11, the XY profile of which is described by expression (1), the wave front turns smoothly, so that at first the front smoothly transforms to the front of the TEM wave, and then to the front of the spherical wave in the output cone line. In such a transition, the component E _z has a minimum value due to the imperfect turn-around process of the electric wave, and, consequently, the energy loss on the wave of higher types is significantly less. When considering the equivalent circuit without taking into account the effect of waves of higher types, the capacitances introduced by the washers, together with the inductances of the transition sections, form a 2-link U-shaped low-pass filter with a frequency f _cf > 10 GHz, which corresponds to the required frequency range.

Prototypes of VKKU were made, the amplitude-frequency characteristics of which are presented in FIG. 3, without dielectric washers (a) and with dielectric washers (b). As can be seen, from a comparison of the frequency characteristics (a) and (b), the resonant emissions in case (b) became less deep and wide and do not exceed the level of 3 dB. The dimensions XY of the continuous dielectric washers 11 are determined in accordance with expression (1) and are:
a) on the final section of the inner conductor ≃ 5 mm;
b) in the final section of the outer conductor ≃ 1.2 mm.
The proposed device has two washers located between the end sections of the cones of the inner and outer conductors. The size of XY exceeds the size of the central thrust washer of the prototype, which increases its mechanical strength.

 Thus, the proposed device is characterized by a satisfactory upper frequency (9 10 GHz), a uniform amplitude-frequency characteristic and high mechanical strength.

Information sources
1. Coaxial capacitor. Japanese Application N 55-34572, 1980. Applicant NIPPIUN DEN KOSN.

 2. High-speed oscilloscope C7-15. Technical description and instruction manual. Vilnius, 1976.

 3. V.V. Borisov, V. M. Shuvalov. Calculation and study of microwave nodes of the signal path of analog-to-digital recorders. NIIIT, "O" -634, 1988.

 4. G.V. Glebovich, I.P. Kovalev. Broadband transmission lines of pulse signals. M. Sov. Radio, 1972.

Claims (1)

A high-frequency coaxial capacitor device containing a coaxial line formed by two segments with cone-shaped internal and external conductors facing each other with bases, resistors with metal contacts placed between the internal and external conductors and electrically connected to them, a low-frequency capacitor installed between the internal conductors, and a central supporting element fixed in the bases of the cones, characterized in that in the inner conductor of one of of cuts from the base side, a round sample is made in which the inner conductor of the other segment is placed with a gap, the inserted dielectric ring is installed in the side and end parts of the gap, and metal disks with small-sized capacitors connected in parallel between them are located on the bases of the inner conductors, and the central supporting element is made in the form of two dielectric washers having an XY profile (θ) defined by the expression:

where H is a value equal to the distance from the beginning of both segments to the vertical axis separating these segments;
ε is the relative dielectric constant of the material of the dielectric washers forming a central support element;
q ₁ and θ ₂ angle formed respectively forming a surface of the outer and inner conductor with their axis;
θ current angular coordinate
q ₂ <θ <θ ₁ .

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