The present invention relates to the field of filtering baluns in radio-frequency circuits, and more particularly, to a LTCC wide stopband filtering balun based on discriminating coupling, which can be used in differential antenna feeding and a differential amplifier circuit.
With the rapid development of a modern wireless communication system, trends of miniaturization and multifunction of radio-frequency devices and modules are increasingly obvious. A balun and a bandpass filter are used as two important devices of a radio-frequency circuit, and often need to be used in a cascade way, and the miniaturization of the whole circuit is particularly important. On one hand, a fusion design of a filtering balun integrates functions of the two important devices, so that the module is multifunctional, and on the other hand, performance deterioration caused by cascade mismatch is avoided, and meanwhile, overall volume of the module is reduced. Relevant researches for the filtering baluns based on a dielectric resonator (DR), a substrate integrated waveguide (SIW) and planar printed circuit board (PCB) technology have been conducted, but the filtering baluns are usually large in volume. Therefore, a low-temperature co-fired ceramic (LTCC) technology with advantages of low cost, low insertion loss and high frequency performance is used to design filtering baluns to reduce a device volume. However, most of them only focus on a passband performance, and an out-of-band performance is deteriorated due to the existence of harmonics.
At present, few researches seek to improve a stopband performance of the filtering balun. Relevant methods proposed include using a capacitive load to move a harmonic, and using a cascade balun and a low-pass filter to suppress a harmonic, etc. However, they have problems of large structure volume, narrow suppression stopband, increased in-band insertion loss, deterioration of a balun characteristic output performance, etc.
In order to overcome at least one defect in the prior art, the present invention provides a LTCC wide stopband filtering balun based on discriminating coupling, which can suppress the second harmonic and the third harmonic. A low-temperature co-fired ceramic technology is used in the device, which reduces a volume of the filtering balun. A discriminating coupling technology is used to suppress the second harmonic and the third harmonic, thus realizing a filtering performance of a wide stopband. A symmetrical feeding technology is used to introduce two zeros on both sides of a pass band, thus increasing a selectivity of the passband. Good balun output is realized by using a reverse-phase characteristic of both ends of a half-wavelength resonator.
In order to solve the technical problems above, the technical solutions used in the present invention are as follows.
A LTCC wide stopband filtering balun based on discriminating coupling includes a dielectric, and a resonator, a feeding line and a metal ground which are arranged inside the dielectric, the resonator includes a resonator tail end, a feeding coupling area and a resonator mutual-coupling area which are sequentially arranged from top to bottom along an inside of the dielectric, the resonator tail end is connected to the feeding coupling area through a metal via hole, the feeding coupling area is connected to the resonator mutual-coupling area through the metal via hole, the feeding line is arranged between the resonator tail end and the feeding coupling area, the metal ground includes a first metal ground arranged at a top of the dielectric and a second metal ground arranged at a bottom of the dielectric, a third metal ground arranged between the resonator tail end and the feeding line, and a fourth metal ground arranged between the feeding coupling area and the resonator mutual-coupling area, and the third metal ground and the fourth metal ground are provided with through holes for the metal via io hole to pass through;
a feeding coupling area of a first resonator includes a feeding coupling area I and a feeding coupling area II, the feeding coupling area I and the feeding coupling area II are in left-right mirror symmetry; a feeding coupling area of a second resonator includes a feeding coupling area III and a feeding coupling area IV, and the feeding coupling area III and the feeding coupling area IV are in left-right mirror symmetry;
the resonator includes a first resonator and a second resonator; a sum of a length from a point on the feeding coupling area of the first resonator and perpendicularly corresponding to a center of the feeding line coupled with the feeding coupling area of the first resonator for performing feeding to one end at which the feeding coupling area of the first resonator is connected to a resonator tail end of the first resonator and a length of the resonator tail end of the first resonator is a quarter of an entire length of the first resonator, thus realizing suppression of a second harmonic by discriminating coupling;
a sum of a length from a point on the feeding coupling area of the second resonator and perpendicularly corresponding to a center of the feeding line coupled with the feeding coupling area of the second resonator for performing feeding to one end at which the feeding coupling area of the second resonator is connected to a resonator tail end of the second resonator and a length of the resonator tail end of the second resonator is one-sixth of an entire length of the second resonator, thus realizing suppression of a third harmonic by discriminating coupling.
Further, the dielectric includes a first dielectric layer, a second dielectric layer, a third dielectric layer, a fourth dielectric layer, a fifth dielectric layer, a sixth dielectric layer, a seventh dielectric layer and an eighth dielectric layer which are sequentially arranged from top to bottom, the resonator tail end of the first resonator and the resonator tail end of the second resonator are both arranged between the first dielectric layer and the second dielectric layer, the resonator tail end of the first resonator is arranged in front of the resonator tail end of the second resonator, the feeding coupling area of the first resonator and the feeding coupling area of the second resonator are both arranged between the fourth dielectric layer and the fifth dielectric layer, the feeding coupling area of the first resonator is arranged in front of the feeding coupling area of the second resonator, a resonator mutual-coupling area of the first resonator is arranged between the seventh dielectric layer and the eighth dielectric layer, and a resonator mutual-coupling area of the second resonator is arranged between the sixth dielectric layer and the seventh dielectric layer.
Further, the first resonator and the second resonator are both half-wavelength resonators, and good balun output is realized by using an equal-amplitude reverse-phase characteristic of a standing wave of the half-wavelength resonator.
Further, the third metal ground is arranged between the second dielectric layer and the third dielectric layer, and the fourth metal ground is arranged between the fifth dielectric layer and the sixth dielectric layer.
Further, the feeding line is arranged between the third dielectric layer and the fourth dielectric layer, the feeding line includes a first feeding line, a second feeding line and a third feeding line, the first feeding line, the second feeding line and the third feeding line have a same shape and a same length, the first feeding line and the second feeding line are in front-back mirror symmetry, thus generating zeros on both sides of a passband, and the second feeding line and the third feeding line are in left-right mirror symmetry.
Further, the first feeding line, the second feeding line and the third feeding line are each provided with a feeding port at a middle part thereof; and the first feeding line is coupled with the feeding coupling area of the first resonator in an broadside coupling feeding, and the second feeding line and the third feeding are coupled with the feeding coupling area of the second resonator in an broadside coupling feeding. Further, the resonator tail end of the first resonator includes the resonator tail end A and a resonator tail end B, the resonator tail end A and the resonator tail end B are in left-right mirror symmetry, and the resonator tail end of the second resonator includes a resonator tail end C and the resonator tail end D, the resonator tail end C and the resonator tail end D are in left-right mirror symmetry; and the feeding coupling area of the first resonator includes the feeding coupling area I and the feeding coupling area II, the feeding coupling area I and the feeding coupling area II are in left-right mirror symmetry, the first feeding line is coupled with the feeding coupling area I in an broadside coupling feeding, the feeding coupling area of the second resonator includes the feeding coupling area III and the feeding coupling area IV, the feeding coupling area III and the feeding coupling area IV are in left-right mirror symmetry, the second feeding line is coupled with the feeding coupling area III in an broadside coupling feeding, and the third feeding line is coupled with the feeding coupling area IV in an broadside coupling feeding.
Further, the resonator tail end A is connected to one end of the feeding coupling area I through the metal via hole, the other end of the feeding coupling area I is connected to one end of the resonator mutual-coupling area of the first resonator through the metal via hole, the other end of the resonator mutual-coupling area of the first resonator is connected to one end of the feeding coupling area II through the metal via hole, and the other end of the feeding coupling area II is connected to the resonator tail end B through the metal via hole to form the first resonator; and the resonator tail end C is connected to one end of the feeding coupling area III through the metal via hole, the other end of the feeding coupling area III is connected to one end of the resonator mutual-coupling area of the second resonator through the metal via hole, the other end of the resonator mutual-coupling area of the second resonator is connected to one end of the feeding coupling area IV through the metal via hole, and the other end of the feeding coupling area IV is connected to the resonator tail end D through the metal via hole to form the second resonator.
Further, a sum of a length from a point on the feeding coupling area I and perpendicularly corresponding to a center of the first feeding line to one end at which the feeding coupling area I is connected to the resonator tail end A and the length of the resonator tail end A is a quarter of the entire length of the first resonator.
Further, a sum of a length from a point on the feeding coupling area III and perpendicularly corresponding to a center of the second feeding line to one end at which the feeding coupling area III is connected to the resonator tail end C and the length of the resonator tail end C is one-sixth of the entire length of the second resonator, and a sum of a length from the point on the feeding coupling area IV and perpendicularly corresponding to a center of the third feeding line to one end at which the feeding coupling area IV is connected to the resonator tail end D and the length of the resonator tail end D is one-sixth of the entire length of the second resonator.
Compared with the prior art, the present invention has the following advantages and beneficial effects.
1. Filtering and balun functions are integrated in the same device, thus reducing an overall insertion loss of a circuit module.
2. Good balun output is realized by using the reverse-phase characteristic of the standing wave of the half-wavelength resonator.
3. The second harmonic and the third harmonic are suppressed based on the discriminating coupling, thus expanding a stopband range without additional components.
4. Symmetrical arrangement of the feeding lines generates two transmission zeros on both sides of the passband, thus improving a selectivity of the passband.
5. A LTCC multi-layer technology is used, thus effectively reducing a size of the filtering balun.
The accompanying drawings are for the illustrative purpose only and cannot be construed as limiting the present invention. To better describe the embodiments, some parts can be omitted, enlarged or shrunk in the accompanying drawings, which does not represent the size of the actual product. It is understandable for those skilled in the art that some well-known structures in the accompanying drawings and the descriptions thereof may be omitted. The positional relationship illustrated in the accompanying drawings is for illustrative purpose only and cannot be construed as limiting the present invention.
As shown in
The resonator includes a first resonator and a second resonator; and a sum of a length from a point on the feeding coupling area of the first resonator and perpendicularly corresponding to a center of the feeding line coupled with the feeding coupling area of the first resonator for performing feeding to one end at which the feeding coupling area of the first resonator is connected to a resonator tail end of the first resonator and a length of the resonator tail end of the first resonator is a quarter of an entire length of the first resonator, thus realizing suppression of a second harmonic by discriminating coupling;
A sum of a length from a point on the feeding coupling area of the second resonator io that perpendicularly corresponds to a center of the feeding line coupled with the feeding coupling area of the second resonator for performing feeding to one end of the feeding coupling area of the second resonator connected to a resonator tail end of the second resonator, and a length of the resonator tail end of the second resonator is one-sixth of an entire length of the second resonator, thus realizing suppression of a third harmonic by discriminating coupling.
As shown in
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The resonator tail end of the first resonator is arranged to the left of the resonator tail end of the second resonator, wherein the resonator tail end of the first resonator includes a resonator tail end A19 and a resonator tail end B20, the resonator tail end A19 and the resonator tail end B20 are in mirror symmetry, the resonator tail end of the second resonator includes a resonator tail end C21 and a resonator tail end D22, and the resonator tail end C21 and the resonator tail end D22 are in mirror symmetry.
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Various parameters of the embodiment are described as follows: As shown in
Measured results of an S parameter response are shown in
Measured results of a balun characteristic response are shown in
In summary, the present invention provides the LTCC wide stopband filtering balun using a discriminating coupling structure between the feeding lines and the resonators to suppress the second harmonic and the third harmonic; and the circuit has advantages of small volume, low insertion loss and wide stopband, can be processed into a patch element, is easy to integrate with other circuit module, and can be widely applied in a radio-frequency front end of a wireless communication system.
Obviously, the above embodiments of the present invention are only examples for clearly describing the present invention, and do not limit the embodiments of the present invention. For those having ordinary skills in the art, other different forms of changes or variations can also be made on the basis of the description above. All implementations need not and cannot be exhaustive here. All modifications, equivalents, and improvements made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.
Number | Date | Country | Kind |
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201810605066.1 | Jun 2018 | CN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CN2018/112816 | 10/30/2018 | WO | 00 |