TECHNICAL FIELD
[0002] Embodiments of the present invention relate to the field of communications technologies,
and in particular, to a transverse electromagnetic mode dielectric filter, a radio
frequency module, and a base station.
BACKGROUND
[0003] With development of wireless communications technologies, a wireless communications
device increasingly strives for miniaturization and a low insertion loss. Compared
with a conventional metal cavity filter, a dielectric filter has an advantage such
as a small size, a low insertion loss, high bearing power, and low costs. A transverse
electromagnetic mode (TEM, transverse electromagnetic mode) dielectric filter is an
important dielectric filter type, and may be applied to a device such as a wireless
base station, a radio frequency terminal, or a radio frequency or microwave transceiver
component.
[0004] However, a transverse electromagnetic mode dielectric filter provided in the prior
art has poor near-end rejection performance, and therefore, cannot be applied to a
location, such as a radio frequency front-end or a microwave antenna feeder front-end,
that has a relatively high requirement on filter performance. Consequently, an application
scenario is limited.
SUMMARY
[0005] Embodiments of the present invention provide a transverse electromagnetic mode dielectric
filter that has good near-end rejection performance; and the embodiments of the present
invention further provide a radio frequency module and a base station.
[0006] According to a first aspect, an embodiment of the present invention provides a transverse
electromagnetic mode dielectric filter, including: a resonator, a dielectric body,
and a metal housing, where an outer surface of the dielectric body is covered with
a conductive material, the metal housing is fastened above the dielectric body, and
there is a gap between the metal housing and the dielectric body; the resonator includes
a resonant plate and a resonant hole, where the resonant plate is disposed on a top
surface of the dielectric body, the resonant hole is a hollow cylindrical structure
with openings on upper and lower ends, an upper opening of the resonant hole is provided
on the resonant plate, a lower opening of the resonant hole is provided on a lower
surface of the dielectric body, an inner surface of the resonant hole is covered with
a conductive material, and the resonant plate is of a metal materials; and the filter
further includes a near-end rejection structure, where the near-end rejection structure
is inside the dielectric body, and a shape, a location, and a size of the near-end
rejection structure are determined by a frequency of a signal that the filter is to
filter out.
[0007] In a first possible implementation of the first aspect, that a shape, a location,
and a size of the near-end rejection structure are determined by a frequency of a
signal that the filter is to filter out includes:
a height, a length, and a distance away from the resonant hole that are of the near-end
rejection structure are determined according to a coupling coefficient of the filter,
where the coupling coefficient is corresponding to the frequency of the signal that
the filter is to filter out.
[0008] With reference to either of the possible implementations, in a second possible implementation
of the first aspect, the near-end rejection structure has at least two ends in contact
with the lower surface of the dielectric body, and a remaining part of the near-end
rejection structure is within a magnetic field area inside the dielectric body.
[0009] With reference to any one of the possible implementations, in a third possible implementation
of the first aspect, the near-end rejection structure is within an electric field
area inside the dielectric body.
[0010] With reference to any one of the possible implementations, in a fourth possible implementation
of the first aspect, that a shape, a location, and a size of the near-end rejection
structure are determined by a frequency of a signal that the filter is to filter out
includes: a height, a length, and a distance away from the resonant hole that are
of the near-end rejection structure are determined according to an electrical wavelength
corresponding to the frequency of the signal that the filter is to filter out.
[0011] With reference to any one of the possible implementations, in a fifth possible implementation
of the first aspect, the near-end rejection structure is any one of a metalized through
hole, a metalized strip line, a physical metal structure, a metalized conductor, or
a thin metal piece.
[0012] According to a second aspect, an embodiment of the present invention provides a radio
frequency module, including the transverse electromagnetic mode dielectric filter
according to any one of the first aspect or the possible implementations.
[0013] According to a third aspect, an embodiment of the present invention provides a base
station, including the radio frequency module according to the second aspect.
[0014] According to technical solutions provided in the embodiments of the present invention,
a near-end rejection structure is disposed inside a transverse electromagnetic mode
dielectric filter. By flexibly designing a shape, a location, and a size of the near-end
rejection structure, a transmission zero or zero cavity function is implemented, and
a radio frequency signal on a high-frequency end or a low-frequency end out of a passband
of the filter is rejected. The transverse electromagnetic mode dielectric filter provided
in the embodiments of the present invention has good near-end rejection performance,
and may be widely applied to a radio frequency module and a base station.
BRIEF DESCRIPTION OF DRAWINGS
[0015] To describe the technical solutions in the embodiments of the present invention more
clearly, the following briefly describes the accompanying drawings required for describing
the embodiments. Apparently, the accompanying drawings in the following description
show merely some embodiments of the present invention, and persons of ordinary skill
in the art may still derive other drawings from these accompanying drawings without
creative efforts.
FIG. 1 is a schematic structural diagram of a transverse electromagnetic mode dielectric
filter according to an embodiment of the present invention;
FIG. 2 is a front view of another transverse electromagnetic mode dielectric filter
according to an embodiment of the present invention;
FIG. 3 is a top view of another transverse electromagnetic mode dielectric filter
according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of another transverse electromagnetic mode
dielectric filter according to an embodiment of the present invention; and
FIG. 5 is a schematic structural diagram of a base station according to an embodiment
of the present invention.
DESCRIPTION OF EMBODIMENTS
[0016] To make the objectives, technical solutions, and advantages of the present invention
clearer, the following further describes implementations of the present invention
in detail with reference to the accompanying drawings.
[0017] A filter is a necessary component in a device such as a base station or a radio frequency
terminal. With an advantage in costs, size, and the like, a dielectric filter may
be applied at a location such as a receive link of the base station, and is configured
to perform filtering on a radio frequency signal. A transverse electromagnetic mode
dielectric filter is a widely-used dielectric filter.
[0018] However, a radio frequency performance indicator of the transverse electromagnetic
mode dielectric filter is relatively poor, and cannot be used at a location, such
as a front-end of a radio frequency module, that is, a location between a transmit
antenna and a power amplifier, that has a relatively high requirement on the performance
of the filter. The radio frequency performance indicator of the filter includes multiple
indicators such as an insertion loss, rejection, and inter-modulation. Therefore,
an application scenario of the transverse electromagnetic mode dielectric filter is
greatly limited.
[0019] A main reason causing the relatively poor radio frequency performance indicator of
the transverse electromagnetic mode dielectric filter is that near-end rejection performance
of this type of filter is poor. Near-end rejection is also referred to as sideband
rejection or near band rejection (near band rejection), and means performing strong
rejection on a signal on a high-frequency end or a low-frequency end near an outside
area of a passband of the filter, so as to ensure a filtering effect. Currently, a
design method for cross-coupling or resonance of the transverse electromagnetic mode
dielectric filter is inflexible, a transmission zero or zero cavity structure cannot
be formed effectively, and therefore, the filter does not have good near-end rejection
performance.
[0020] FIG. 1 is a schematic diagram of a transverse electromagnetic mode dielectric filter
according to an embodiment of the present invention.
[0021] As shown in FIG. 1, a transverse electromagnetic mode dielectric filter 1 ("filter
1" for short below) includes a resonator 11, a dielectric body 12, and a metal housing
13. The metal housing 13 is fastened above the dielectric body 12, and there is a
gap between the metal housing 13 and the dielectric body 12.
[0022] An outer surface of the dielectric body 12 is covered with a conductive material.
Optionally, a metal coating, such as a silver coating, may be used.
[0023] The gap between the metal housing 13 and the dielectric body 12 is filled with air.
[0024] The resonator 11 includes a resonant plate 101 and a resonant hole 102, and the resonant
plate 101 is disposed on a top surface of the dielectric body 12.
[0025] Optionally, the resonant plate 101 may be a thin metal piece disposed on the top
surface of the dielectric body 12, or may be a metal coating printed on the top surface
of the dielectric body 12.
[0026] Optionally, a shape of the resonant plate 101 is not limited. For example, the shape
may be a regular figure such as a rectangle or a circle, or may be modified on the
basis of the regular figure according to specifications and a performance requirement
of the filter, for example, a specific area is cut off to form an irregular figure.
This is not particularly limited in this embodiment of the present invention.
[0027] The resonant hole 102 is a hollow cylindrical structure with openings on upper and
lower ends, an upper opening of the resonant hole 102 is provided on the resonant
plate 101, a lower opening of the resonant hole 102 is provided on a lower surface
of the dielectric body 12, and an inner surface of the resonant hole 102 is covered
with a conductive material.
[0028] Optionally, the conductive material covering the inner surface of the resonant hole
102 may be a metal coating, such as a silver coating.
[0029] Optionally, the resonant hole 102 and the resonant plate 101 may be integrally formed,
or may be separately made and then formed by means of connection.
[0030] The filter 1 further includes a near-end rejection structure 14. The near-end rejection
structure 14 is inside the dielectric body 12, and a shape, a location, and a size
of the near-end rejection structure 14 are determined by a frequency of a signal that
the filter is to filter out.
[0031] As shown in FIG. 1, two ends of the near-end rejection structure 14 are in contact
with the lower surface of the dielectric body 12, and a remaining part of the near-end
rejection structure 14 is within a magnetic field area inside the dielectric body
12. The magnetic field area refers to an area that is inside the dielectric body and
that has a stronger magnetic field than that of another location.
[0032] A strong magnetic field area inside the dielectric body 12 is an area near the lower
surface of the dielectric body 12.
[0033] Optionally, a height, a length, and a distance away from the resonant hole that are
of the near-end rejection structure 14 may be determined according to a coupling coefficient
(coupling coefficient) of the filter, and the coupling coefficient is corresponding
to the frequency of the signal that the filter is to filter out.
[0034] The coupling coefficient is an important parameter during filter design. When the
coupling coefficient is determined, a physical structure of the filter may be designed
according to the coupling coefficient, and a corresponding performance indicator may
be achieved. Generally, the coupling coefficient may be obtained by solving a coupling
matrix (coupling matrix). The coupling matrix may be used to indicate a coupling energy
relationship between resonant cavities, and the coupling coefficient is included in
the coupling matrix.
[0035] Optionally, the coupling matrix may be obtained by means of calculation by using
filter emulation software, or may be determined according to an experimental or empirical
value. This is not particularly limited in this embodiment of the present invention.
[0036] Optionally, the near-end rejection structure 14 may be any one of a metalized through
hole, a metalized strip line, a physical metal structure, a metalized conductor, or
a thin metal piece.
[0037] Optionally, the near-end rejection structure 14 may be a strip structure with a specific
radian. Specifically, the radian may be determined by means of debugging according
to the performance requirement of the filter. This is not particularly limited in
this embodiment of the present invention.
[0038] Optionally, in another embodiment of the present invention, in addition to the two
ends, any other part of the near-end rejection structure 14 may also be in contact
with the lower surface of the dielectric body 12, to play a grounding role.
[0039] In the embodiment shown in FIG. 1, the near-end rejection structure 14 plays an inductive
transmission zero role, and can improve a rejection capability on a high-frequency
end out of a passband of the filter, that is, can reject a signal on the high-frequency
end out of the passband of the filter. It may be understood that the near-end rejection
structure 14 may be designed for only one specific signal frequency, and when the
filter has strong rejection over a specific frequency, the filter has good rejection
over a frequency band neighboring to the frequency.
[0040] Optionally, the filter 1 may include more than three resonators 11, and the near-end
rejection structure 14 is located between nonadjacent resonant cavities. As shown
in FIG. 1, the filter 1 includes four resonators, successively marked as cavity 1,
cavity 2, cavity 3, and cavity 4 from left to right. The two ends of the near-end
rejection structure 14 are respectively located near the cavity 1 and cavity 3. Optionally,
the near-end rejection structure 14 may be located between the cavity 1 and cavity
4, or between the cavity 2 and cavity 4.
[0041] The near-end rejection structure 14 located between nonadjacent resonant cavities
forms a cross-coupling structure, that is, when signals pass through resonant cavities
through different signal paths, phases of different signal paths are canceled, so
as to form a transmission zero. For example, a signal path of cavity 1-cavity 2-cavity
3 may be considered as a positive phase path, and a signal path of cavity 1-cavity
3 is considered as a negative phase path. Phases of the two paths are canceled, and
a transmission zero is formed at the near-end rejection structure 14. The zero is
corresponding to the frequency of the signal that the filter is to filter out.
[0042] According to the transverse electromagnetic mode dielectric filter provided in this
embodiment of the present invention, a near-end rejection structure is disposed inside
the dielectric filter and near a lower surface of the dielectric filter, so as to
implement an inductive transmission zero function, and reject a radio frequency signal
on a high-frequency end out of a passband of the filter, thereby achieving good near-end
rejection performance.
[0043] FIG. 2 and FIG. 3 are a front view and a top view of another transverse electromagnetic
mode dielectric filter according to an embodiment of the present invention.
[0044] As shown in FIG. 2, a transverse electromagnetic mode dielectric filter 2 ("filter
2" for short below) includes a resonator 21, a dielectric body 22, a metal housing
23, and a near-end rejection structure 24. The metal housing 23 is fastened above
the dielectric body 22, and there is a gap between the metal housing 23 and the dielectric
body 22. As shown in FIG. 3, the resonator 21 includes a resonant plate 211 and a
resonant hole 212.
[0045] Overall structures of the filter 2 and the filter 1 provided in the embodiment shown
in FIG. 1 are similar, and what is different from the embodiment shown in FIG. 1 is
that the near-end rejection structure 24 is located at an area near a top surface
of the dielectric body 22. The area is an electric field area inside the dielectric
body 22, and the electric field area refers to an area that is inside the dielectric
body and that has a stronger electric field than that of another location. A specific
shape, location, and size of the near-end rejection structure 24 may be determined
according to a coupling coefficient of the filter. For a specific determining manner,
reference may be made to the description in the embodiment shown in FIG. 1. This is
not described herein.
[0046] In the embodiments shown in FIG. 2 and FIG. 3, the near-end rejection structure 24
plays a capacitive transmission zero role, and can improve a rejection capability
on a low-frequency end out of a passband of the filter, that is, can reject a signal
on the low-frequency end out of the passband of the filter.
[0047] It may be understood that for detailed description of another component in the filter
2, reference may be made to the content in the embodiment shown in FIG. 1. This is
not described herein.
[0048] A transverse electromagnetic mode dielectric filter whose specification is 90
*44
*20 (mm, millimeter) is used as an example. A near-end rejection structure is disposed
inside a dielectric body of the filter to serve as a capacitive zero. The structure
is a metalized through hole whose specific size is as follows: A length is 23 mm,
a width is 1 mm, a distance away from a resonant hole is 3 mm, and a distance away
from a top surface of the dielectric body, that is, a resonant plate, is 3 mm. A passband
of the filter is 1805 MHz to 1865 MHz, that is, a radio frequency signal whose frequency
is beyond this frequency band can be effectively filtered out.
[0049] According to the transverse electromagnetic mode dielectric filter provided in this
embodiment of the present invention, a near-end rejection structure is disposed inside
the dielectric filter and near a top surface of a dielectric body, so as to implement
a capacitive transmission zero function, and reject a radio frequency signal on a
low-frequency end out of a passband of the filter, thereby achieving good near-end
rejection performance.
[0050] FIG. 4 is a schematic diagram of another transverse electromagnetic mode dielectric
filter according to an embodiment of the present invention.
[0051] As shown in FIG. 4, a transverse electromagnetic mode dielectric filter 3 ("filter
3" for short below) includes a resonator 31, a dielectric body 32, a metal housing
33, and a near-end rejection structure 34. The metal housing 33 is fastened above
the dielectric body 32, there is a gap between the metal housing 33 and the dielectric
body 32, and the resonator 31 includes a resonant plate 301 and a resonant hole 302.
[0052] Overall structures of the filter 3 and the transverse electromagnetic mode dielectric
filter provided in the embodiment in FIG. 1 or FIG. 2 and FIG. 3 are similar, and
what is different from the filter shown in FIG. 1 or FIG. 2 is that a shape, a location,
and a size of the near-end rejection structure 34 are determined by an electrical
wavelength corresponding to a frequency of a signal that the filter is to filter out.
The electrical wavelength is an electromagnetic wave wavelength.
[0053] Specifically, the electrical wavelength may be calculated according to a formula:
c=λ,*f, where f is a signal frequency, λ is an electrical wavelength, and c is a constant.
[0054] It can be learned that a wavelength and a frequency of an electromagnetic wave waveform
are in a one-to-one correspondence relationship. A height, a length, and a distance
away from the resonant hole 302 that are of the near-end rejection structure 34 may
be determined according to the electrical wavelength. Specifically, a size of the
near-end rejection structure 34 may be determined by using filter emulation software,
or may be determined according to an experiment or experience. This is not particularly
limited in this embodiment of the present invention.
[0055] Optionally, as shown in FIG. 4, the near-end rejection structure 34 may be a strip
structure with a bending angle, or may be a strip or tube structure with a radian
in another embodiment.
[0056] As shown in FIG. 4, two ends of the near-end rejection structure 34 are contacted
to a lower surface of the dielectric body 32. Optionally, in another embodiment, in
addition to the two ends, any other parts of the near-end rejection structure 34 may
also be contacted to the lower surface of the dielectric body 32.
[0057] In the embodiment shown in FIG. 4, the near-end rejection structure 34 may play a
zero cavity role, and may improve a rejection capability on a high-frequency end or
a low-frequency end out of a passband of the filter, that is, may reject a signal
on the high-frequency end or the low-frequency end out of the passband of the filter.
[0058] Optionally, by changing a structure of the near-end rejection structure 34, such
as changing a length, the electrical wavelength corresponding to the near-end rejection
structure 34 may be changed, so as to control the frequency of the signal that the
filter is to filter out. Specifically, the length of the near-end rejection structure
34 is inversely proportional to the signal frequency. A longer near-end rejection
structure 34 indicates a lower corresponding signal frequency, and the filter 3 may
be configured to filter out a signal on a low-frequency end. A shorter near-end rejection
structure 34 indicates a higher corresponding signal frequency, and the filter 3 may
be configured to filter out a signal on a high-frequency end.
[0059] It may be understood that for detailed description of another component in the filter
3, reference may be made to the content in the embodiment shown in FIG. 1 or FIG.
2 and FIG. 3. This is not described herein.
[0060] This embodiment of the present invention further provides a radio frequency module.
The radio frequency module includes any transverse electromagnetic mode dielectric
filter described in the foregoing embodiments.
[0061] Optionally, the radio frequency module may be a repeater, a remote radio unit (RRU,
remote radio unit), a radio frequency unit (RFU, radio frequency unit), or another
device. This is not particularly limited in this embodiment of the present invention.
[0062] According to the transverse electromagnetic mode dielectric filter or the radio frequency
module provided in this embodiment of the present invention, when a size of the filter
is not increased, a zero cavity function can be implemented by disposing a near-end
rejection structure inside a dielectric body; and by using the structure, a signal
on a high-frequency end or a low-frequency end out of a passband of the filter can
be rejected, and near-end rejection performance of the filter can be improved, thereby
improving a filtering effect.
[0063] FIG. 5 is an example diagram of a base station according to an embodiment of the
present invention. The base station may include a radio frequency module, and the
radio frequency module includes the transverse electromagnetic mode dielectric filter
shown in any embodiment in FIG. 1 to FIG. 4.
[0064] The base station may further include a baseband processing unit (BBU, base band unit)
402, a power module 403, and the like. All modules or units may be connected by using
a communications bus.
[0065] Optionally, the base station may be a small cell (small cell) device, such as an
indoor small cell product.
[0066] The radio frequency module or the base station provided in this embodiment of the
present invention uses a transverse electromagnetic mode dielectric filter with good
near-end rejection performance, and therefore has low costs and a small size.
[0067] An embodiment of the present invention further provides a method for producing any
transverse electromagnetic mode dielectric filter ("filter" for short below) according
to FIG. 1 to FIG. 4.
[0068] The method includes: preparing two layers or multiple layers of dielectric blank
raw materials; after a through hole or a blind hole is provided on the two layers
or multiple layers of dielectric raw materials, separately sintering each layer of
dielectric raw material; preparing a metalized structure and a punching on each layer
of sintered dielectric; then forming a filter entirety by means of bonding; and forming
the transverse electromagnetic mode dielectric filter provided in this embodiment
of the present invention after metallization of a printed pattern of the filter is
completed.
[0069] In another embodiment of the present invention, the method may be: preparing two
layers or multiple layers of dielectric blank raw materials; obtaining a required
metal structure, that is, a transmission zero or zero cavity structure in the present
invention, by means of opening a hole, printing a circuit, and the like on each layer
of dielectric raw material; then stacking prepared layers of dielectric raw materials
together for sintering; and finally forming the transverse electromagnetic mode dielectric
filter provided in this embodiment of the present invention after metallization of
a printed pattern of the dielectric filter is completed.
[0070] Finally, it should be noted that the foregoing embodiments are merely intended for
describing the technical solutions of the present invention, but not for limiting
the present invention. Although the present invention is described in detail with
reference to the foregoing embodiments, persons of ordinary skill in the art should
understand that they may still make modifications to the technical solutions described
in the foregoing embodiments or make equivalent replacements to some or all technical
features thereof, without departing from the scope of the technical solutions of the
embodiments of the present invention.
1. A transverse electromagnetic mode dielectric filter, comprising:
a resonator, a dielectric body, and a metal housing, wherein an outer surface of the
dielectric body is covered with a conductive material, the metal housing is fastened
above the dielectric body, and there is a gap between the metal housing and the dielectric
body;
the resonator comprises a resonant plate and a resonant hole, wherein the resonant
plate is disposed on a top surface of the dielectric body, the resonant hole is a
hollow cylindrical structure with openings on upper and lower ends, an upper opening
of the resonant hole is provided on the resonant plate, a lower opening of the resonant
hole is provided on a lower surface of the dielectric body, an inner surface of the
resonant hole is covered with a conductive material, and the resonant plate is of
a metal material; and
the filter further comprises a near-end rejection structure, wherein the near-end
rejection structure is inside the dielectric body, and a shape, a location, and a
size of the near-end rejection structure are determined by a frequency of a signal
that the filter is to filter out.
2. The filter according to claim 1, wherein that a shape, a location, and a size of the
near-end rejection structure are determined by a frequency of a signal that the filter
is to filter out comprises:
a height, a length, and a distance away from the resonant hole that are of the near-end
rejection structure are determined according to a coupling coefficient of the filter,
wherein the coupling coefficient is corresponding to the frequency of the signal that
the filter is to filter out.
3. The filter according to claim 2, wherein the near-end rejection structure has at least
two ends in contact with the lower surface of the dielectric body, and a remaining
part of the near-end rejection structure is within a magnetic field area inside the
dielectric body.
4. The filter according to claim 2, wherein the near-end rejection structure is within
an electric field area inside the dielectric body.
5. The filter according to claim 1, wherein that a shape, a location, and a size of the
near-end rejection structure are determined by a frequency of a signal that the filter
is to filter out comprises:
a height, a length, and a distance away from the resonant hole that are of the near-end
rejection structure are determined according to an electrical wavelength corresponding
to the frequency of the signal that the filter is to filter out.
6. The filter according to any one of claims 1 to 5, wherein the near-end rejection structure
is any one of a metalized through hole, a metalized strip line, a physical metal structure,
a metalized conductor, or a thin metal piece.
7. A radio frequency module, comprising the transverse electromagnetic mode dielectric
filter according to any one of claims 1 to 6.
8. Abase station, comprising the radio frequency module according to claim 7.