JPS5938761B2 - coaxial resonator - Google Patents

Description

[Detailed description of the invention] The present invention relates to a coaxial resonator.

Conventionally, filters used in the VHF band or UHF' band include those using an LC resonator and those using a coaxial resonator.

However, the former method does not provide sufficient selectivity characteristics, and the latter method has the disadvantage of being large in size.

In recent years, in the communication equipment field, there has been a strong desire to make systems smaller and lighter.While other components are being made smaller and lighter, filters are still being used in large numbers due to their importance. However, it has been difficult to make the system smaller and lighter, which has delayed efforts to make the system smaller and lighter.

Therefore, reducing the size and weight of filters has been a top priority for engineers in this field.

Therefore, the present inventors developed a coaxial TEM resonator filled with a dielectric material.

In that case, a half-wavelength resonator with both ends open is often used because of its high Q, but it has the disadvantage that second harmonic resonance occurs as spurious.

This invention was made to eliminate this drawback, and the dielectric constant near the center of a half-wavelength coaxial TEM resonator with both ends open is made smaller than other parts. By doing so, we try to improve the spurious characteristics.

Embodiments of the present invention will be described above with reference to the drawings.

In Figure 1, 1 is an open-ended 1/2 wavelength coaxial TEM.
In the resonator, there are dielectrics 4 and 5 between the inner conductor 2 and the outer conductor 3.
and 6 are filled.

The dielectrics 4 and 6 are made of, for example, titanium oxide ceramic, and the dielectric 5 is made of forsterite, which has a lower dielectric constant than the dielectrics 4 and 6, for example.

For example, dielectrics 4, 5, and 6 each having a center hole are bonded together, silver is baked on the inner surface of the hole to form an inner conductor, and the center hole is filled with a ceramic material.

This increases the strength.

Silver is baked onto the outer surface of each dielectric to form an outer conductor.

The dielectric 5 is preferably made of a ceramic material.

This is because if each conductor is made of silver in order to reduce loss, the firing temperature of silver is 600 to 900°C, so the material must be able to withstand this temperature.

Of course, if each conductor is not formed by baking silver, the dielectric 5
may be a different material or may not be used.

With such a structure, the electric field of the fundamental wave is 0 or close to 0 at or near the center of the resonator, that is, inside the dielectric 5, so even if the dielectric constant of the dielectric 5 is low, it has no effect on the resonant frequency. However, the electric field of the second harmonic has a maximum value or is close to the maximum value at or near the center of the resonator, so the effective dielectric constant decreases significantly and the influence on the resonant frequency becomes large.

In other words, resonance of the second harmonic, which has been a problem as spurious, occurs in a high frequency range.

The resonant frequency of a resonator with such a structure is (where β1 is the electrical length of the dielectrics 4 and 6, β2 is the electrical length of the dielectric 5, β1 is the wavelength constant of the dielectrics 4 and 6, and β2 is the dielectric 5 is the wavelength constant, 11 is the geometric length of the dielectric 4°6, 1
2 is the geometric length of the dielectric 5, ε1 is the dielectric constant of the dielectrics 4 and 6, and ε2 is the dielectric constant of the dielectric 5.

) Now, FIG. 2 shows a curve where i2/';z(i1+lJ is plotted on the horizontal axis and frequency is plotted on the vertical axis according to the above equation.

As is clear from the figure, as the length of the dielectric 5 increases, the frequency of the second harmonic increases rapidly, but the fundamental resonance frequency hardly increases.

As a result of the experiment, the Q of the resonator in this case did not change at all compared to the case where the dielectric constant was constant over the entire length.

As is clear from the above embodiments, the coaxial resonator of the present invention has a dielectric constant near the center of a half-wavelength coaxial TEM resonator with open ends and a dielectric between the inner and outer conductors. Since it is made smaller than other parts, the frequency of the second harmonic resonance moves to a high range where there is no problem in practical use, and the spurious characteristics are improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a fundamental resonance same wave number and a second harmonic resonance when the length of the dielectric material 5 in the resonator length is changed in the embodiment. This is a curve showing changes in each frequency. Reference numeral 1 is a half-wavelength coaxial TEM resonator with both ends open, 2 is an inner conductor, 3 is an outer conductor, and 4, 5, and 6 are dielectric materials.

Claims (1)

[Claims] 1 Open-ended type with a dielectric between the inner and outer conductors 17
A coaxial resonator in which the dielectric constant near the center of the two-wavelength coaxial TEM resonator is smaller than that in other parts.