CN105720345B - Highly selective broadband coupler in crossing shape - Google Patents

Abstract

The invention discloses a high-selectivity broadband cross-type coupler, which includes four pairs of completely identical traditional coupled lines connected at the input and output ports, and any transmission line in each pair of coupled lines is connected in turn to form an inner loop , one end of the other four transmission lines is connected to the input and output ports, and the other end is connected in series with the same short-circuit branch line. Slots are made on the ground directly below the four pairs of coupling lines, and metal sheets are built in the slots, so that the coupling coefficient can be improved and effectively The second harmonic is suppressed. Due to the rotational symmetry of the structure, it is convenient to use the second-order odd-even mode analysis method to analyze the circuit and obtain the corresponding parameter values. The bandwidth of this cross-type coupler is above 27.5%, the return loss is greater than 20 dB, the isolation is greater than 13.5 dB, and the in-band insertion loss is less than 1.6 dB. It has a compact structure, simple design, and good electrical performance. Integration of circuits and systems.

Description

Highly Selective Broadband Cross Coupler

technical field

The invention belongs to a microwave and millimeter wave hybrid planar integrated circuit, in particular to a high-selectivity broadband cross coupler.

Background technique

The cross coupler is an important passive device in microwave integrated circuits. It enables the two signals interconnected in the transmission path to be isolated from each other and transmitted without interfering with each other. For an ideal cross coupler, adjacent ports have good isolation and opposite ports transmit losslessly. In the past, the most direct approach was to use three-dimensional structures, such as air bridges, welded lines. However, this method is costly and complicated in structure. Many planar single-frequency/dual-frequency cross couplers have been designed, and the ring structure and branch line loading are the most common, such as literature 1 (“Y.Chen and S.-P.Yeo, Asymmetrical four-port microstrip coupler for crossover application,"IEEETrans.Microw.Theory Tech.,vol.55,no.11,pp.2434–2438,Nov.2007."), Literature 2 ("F.Lin,Q.-X.Chu,and S.W.Wong,Dual-band planar crossover with two-section branch-linestructure,IEEE Trans.Microw.Theory Techn.,vol.61,no.6,pp.2309-2316,Jun.2013."), and literature 3( "He Zhu, Yifan Wang, Amin M. Abbosh, Broadband microwave crossover using parallel-coupled microstrip lines and short-ended stubs, IET Microw. Antennas Propag.,, 2015, vol.9, Iss.1, pp.79-85." ), all introduced cross couplers with different structures in detail. Although the cascaded structure broadens the bandwidth, it also increases the size of the circuit and the insertion loss becomes larger. These problems can be solved by patch resonators of different shapes, double Surface structure or microstrip-slot line/coplanar waveguide transition structure solution, such as document 4 ("W.Liu, Z.Zhang, Z.Feng, M.Iskander, A compact wideband micro-stripcrossover, IEEE Microw.Wirel.Compon .Lett.,2012,22,(5),pp.254-256."), and literature 5 ("B.Henin,A.Abbosh,Design of a compact planar crossover using Sierpinskicarpet micro strip patch,IET Microw.Antennas Propag., 2013, 7, (1), pp.54-60."), all introduced several miniaturized cross-type couplers in detail. In addition, the multifunctional circuit structure has also been studied in depth, such as literature 6 ("X.Y. Zhang, Q.-Y. Guo , K.-X.Wang, B.-J.Hu, and H.L.Zhang, Compact filtering crossover using stub-loaded ring resonator, IEEE Microw.Wireless Compon. Lett., vol.24, no.5, pp.327–329 , May 2014.").

However, some of the above-mentioned structures have narrow bandwidths and some have poor selectivity, which cannot meet the needs of broadband and high selectivity.

Contents of the invention

The object of the present invention is to provide a high selectivity broadband cross coupler.

The technical solution to realize the object of the present invention is: a high-selectivity broadband cross coupler, including the upper layer microstrip line structure and the lower layer slot line structure, wherein the first network port, the second network port, and the third network port and the fourth network port are respectively connected to the four first microstrip lines, and the four network ports are respectively located on the four sides of the upper layer of the dielectric substrate, and are rotationally symmetrical about the center of the overall structure;

The first network port, the second network port, the third network port and the fourth network port are connected through four pairs of the same first coupling lines, and the first transmission lines in the first coupling lines are connected in sequence to form an inner ring. One end of the second transmission line in the coupling line is connected in series with the corresponding first microstrip line, and the other end is connected in series with the corresponding second microstrip line. Both ends of the second microstrip line are grounded through corresponding metal through holes, and the first transmission line and The width of the second transmission line is equal, the lengths of the first transmission line, the second transmission line and the second microstrip line are all quarter wavelengths, and the first coupling line, the second microstrip line and the metal via are all rotated about the center of the overall structure symmetry;

Four pairs of the same second coupled lines are respectively connected in parallel at the junction of the first microstrip line and the corresponding first transmission line, the third transmission line and the fourth transmission line in the second coupled lines are equal in width and a quarter wavelength in length, Four pairs of second coupling lines are rotationally symmetrical about the center of the overall structure; the connection between the first microstrip line and the first transmission line is connected in parallel with the third microstrip line, the length of the third microstrip line is half a wavelength, and the four third microstrip lines The lines are rotationally symmetrical about the center of the overall structure; the fifth transmission line on the lower layer of the dielectric plate is located in the corresponding slot line, the length of the slot line is a quarter wavelength, and each fifth transmission line and each slot line are about the first coupling line The short-side symmetry line is symmetrical, and the four fifth transmission lines and the slot line are rotationally symmetrical about the center of the overall structure.

Compared with the prior art, the present invention has the remarkable advantages as follows: (1) the coupler of the present invention utilizes the coupled line of loading and the half-wavelength open line to produce four transmission zeros outside the band, which improves the selection on both sides of the passband The upper stop band extends to 2.95f ₀ (f ₀ is the center frequency); (2) A slot-type broadside coupling structure is introduced on the ground plate of the coupling line, that is, there is a slot line directly below the coupling line, and A metal sheet is etched in the line, which not only enhances the coupling coefficient of the corresponding coupled line, but also effectively suppresses the second harmonic; (3) 5 transmission poles are generated in the band, the passband performance is good, and the bandwidth reaches 27.5%. .

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is a schematic diagram of the superstructure of the high-selectivity broadband cross coupler of the present invention.

Fig. 2 is a schematic diagram of the lower layer structure of the high-selectivity broadband cross coupler of the present invention.

Fig. 3 is a structural schematic diagram of the first coupling line (2) of the high-selectivity broadband cross coupler of the present invention.

Fig. 4 is a schematic structural diagram of the second coupling line (4) of the high-selectivity broadband cross coupler of the present invention.

FIG. 5 is a schematic 3D structure diagram of the high-selectivity broadband cross coupler of the present invention.

Fig. 6 is a graph showing the transmission and isolation results of the high-selectivity broadband cross coupler of the present invention.

Detailed ways

The invention discloses a high-selectivity broadband cross coupler, which includes an upper layer microstrip line structure and a lower layer slot line structure, wherein the first network port P1, the second network port P2, the third network port P3 and the fourth network port The network ports P4 are respectively connected to the four first microstrip lines 1, and the four network ports are respectively located on the four sides of the upper layer of the dielectric substrate, and are rotationally symmetrical about the center of the overall structure;

The first network port P1, the second network port P2, the third network port P3 and the fourth network port P4 are connected through four pairs of the same first coupling lines 2, and the first transmission line 2-1 in the first coupling lines 2 Connected in sequence to form an inner loop, one end of the second transmission line 2-2 in the first coupling line 2 is connected in series with the corresponding first microstrip line 1, and the other end is connected in series with the corresponding second microstrip line 3, and the second microstrip line 3 ends are grounded through the corresponding metal via 8, the width of the first transmission line 2-1 and the second transmission line 2-2 are equal, the first transmission line 2-1, the second transmission line 2-2 and the second microstrip line 3 The length of each is a quarter wavelength, and the first coupling line 2, the second microstrip line 3 and the metal through hole 8 are all rotationally symmetrical about the center of the overall structure;

Four pairs of the same second coupled lines 4 are respectively connected in parallel at the connection between the first microstrip line 1 and the corresponding first transmission line 2-1, the third transmission line 4-1 and the fourth transmission line 4-2 in the second coupled lines 4 The width is equal, the length is a quarter wavelength, and the four pairs of second coupled lines 4 are rotationally symmetrical about the center of the overall structure; the connection between the first microstrip line 1 and the first transmission line 2-1 is connected in parallel with the third microstrip line 5 , the length of the third microstrip line 5 is half a wavelength, and the four third microstrip lines 5 are rotationally symmetrical about the center of the overall structure; the fifth transmission line 7 of the lower layer of the dielectric plate is located in the corresponding slot line 6, and the length of the slot line 6 It is a quarter wavelength, and each fifth transmission line 7 and each slot line 6 are symmetrical about the short-side symmetry line of the first coupling line 2, and the four fifth transmission lines 7 and slot lines 6 are rotationally symmetrical about the center of the overall structure.

Each pair of first coupled lines 2 includes two first transmission lines 2-1 and second transmission lines 2-2 with equal width and a length of 1/4 wavelength, and four pairs of first coupled lines 2 rotate about the center of the overall structure symmetry.

Each pair of second coupled lines 4 includes two third transmission lines 4-1 and fourth transmission lines 4-2 with the same width and a length of 1/4 wavelength, wherein one end of the third transmission line 4-1 is connected to the first The microstrip line 1 is connected, the other end is open, the fourth transmission line 4-2 is open at one end where the third transmission line 4-1 is connected to the first microstrip line 1, and the other end is connected in series with the sixth transmission line 4-3, the sixth transmission line 4 -3 is grounded through the metal via 9 .

The four first microstrip lines 1 all have the same length and width, and their impedance values are all equal to 50 ohms.

The lengths of the first transmission line 2-1, the second transmission line 2-2, the second microstrip line 3, the third transmission line 4-1, the fourth transmission line 4-2, and the slot line 6 are equal to one quarter wavelength, wherein the width of the first transmission line 2-1 is equal to that of the second transmission line 2-2, and the width of the third transmission line 4-1 is equal to that of the fourth transmission line 4-2.

The dielectric constant of the dielectric substrate is 2-16, and the height of the dielectric substrate is 0.1-3mm.

There is no limit to the bending of the second coupled line 4 , the second microstrip line 3 and the third microstrip line 5 , and it is only necessary to ensure that their lengths are a quarter wavelength, a quarter wavelength and a half wavelength respectively.

A more detailed description follows:

The invention is a high-selectivity wideband cross-type coupler, which uses open circuit/short circuit coupling lines and open circuit stubs on the input and output ends to generate four transmission zero points outside the band, which improves the selectivity at both ends of the passband and improves upper stopband performance. And, under the action of them and short-circuit stubs, 5 transmission poles appear in the band, and the performance in the band is good. A slot-type broadside coupling structure is introduced on the ground plate of the coupling line, that is, there is a slot line directly below the coupling line, and a metal sheet is etched in the slot line, which not only enhances the coupling coefficient of the coupling line, but also effectively suppresses the the second harmonic. Due to the improvement of the coupling coefficient, the bandwidth becomes larger. The bandwidth of this structure reaches more than 27.5%, and the port isolation is greater than 13.5dB. The structure is compact, the design is simple, and the electrical performance is good, so as to provide a more practical planar broadband multi-port balance. network structure.

With reference to Fig. 1 and Fig. 2, the present invention is a kind of high-selectivity broadband cross-type coupler, comprises the upper layer microstrip line structure and the lower layer slot line structure, wherein the first network port, the second network port, the third network port and the fourth network port are respectively connected with four microstrip lines 1, and the four network ports are respectively located on the four sides of the upper layer of the dielectric substrate, and are rotationally symmetrical about the center of the overall structure. The first network port, the second network port, the third network port and the fourth network port are connected through four pairs of the same coupling lines 2, and the first transmission lines in the coupling lines 2 are connected in sequence to form an inner loop. One end of the second transmission line is connected in series with the microstrip line 1, and the other end is connected in series with the quarter-wavelength microstrip line 3. The end of the microstrip line 3 is grounded through the metal via 8, and four pairs of identical coupling lines 4 and half-wavelength The microstrip line 5 is connected in parallel at the connection between the microstrip line 1 and the first transmission line, and the coupled line 2, the microstrip line 3, the metal via 8, the coupled line 4 and the microstrip line 5 are rotationally symmetrical about the center of the overall structure.

Four transmission zeros are generated by loading open/short coupled lines and open stubs, two of which are located at 0.5f ₀ and 1.5f ₀ (f ₀ is the center frequency), and the positions of the other two can be obtained by formula (1):

Equation (1) shows that the positions of these two transmission zeros are determined only by the odd-even mode impedance of the loaded open/short coupled lines, then the zeros at 0.5f ₀ and 1.5f ₀ are produced by half-wavelength open lines.

The lower layer of the dielectric plate has a fifth transmission line and a slot line and the fifth transmission line is located in the slot line, wherein the length of the slot line is a quarter wavelength, and each fifth transmission line and each slot line are about the short side of the first coupling line 2 The line of symmetry is symmetrical, and the four fifth transmission lines and the slot line are rotationally symmetrical about the center of the overall structure. Traditional coupled lines suffer from two limitations. One is that the coupling coefficient has an upper limit, because the actual PCB processing technology cannot guarantee too small line width and gap accuracy; the other is the second harmonic caused by the different phase speeds of odd and even modes. The present invention solves both of these problems by creating a slot directly under the coupled line and etching a metal sheet within the slot. For a simple coupled line, the characteristic impedance of the even mode mainly depends on the capacitance of the microstrip line to ground, and the characteristic impedance of the odd mode mainly depends on the capacitance of the coupled line and the microstrip line to ground. It can be seen from the electric field distribution of the improved coupling line that the capacitance of the even mode decreases and the impedance increases; the capacitance of the odd mode increases and the impedance of the odd mode decreases. Therefore, strong coupling is achieved. Adjusting any parameter value in the present invention can make the second harmonic drop to -20dB, but its peak still exists. The improved coupled line eliminates this spike, creating a fifth zero out of band.

The invention is a high-selectivity broadband cross coupler, the microstrip line 1 connecting four network ports has equal length and width, and its impedance value is equal to 50 ohms. The lengths of the first transmission line, the second transmission line, the microstrip line 3, the third transmission line, the fourth transmission line, and the slot line are equal to a quarter wavelength, wherein the width of the first transmission line is equal to that of the second transmission line, and the third transmission line It is equal to the width of the fourth transmission line. The coupled line 2, the microstrip line 3, the coupled line 4, the microstrip line 5, the slot line 6, the fifth transmission line, the metal via 8 and the metal via 9 are all rotationally symmetrical about the center of the overall structure. The dielectric constant of the dielectric substrate is 2-16, and the height of the dielectric substrate is 0.1-3 mm.

There is no limit to the bending of the coupling line 4, the microstrip line 3 and the microstrip line 5, and it is only necessary to ensure that their lengths are a quarter wavelength, a quarter wavelength and a half wavelength respectively.

Below in conjunction with embodiment the present invention is described in further detail:

The invention is a high-selectivity broadband cross coupler, which adopts a ring resonator and a cascaded structure, realizes 5 in-band transmission poles and 4 out-of-band transmission zeros by loading coupling lines and open and short-circuit stubs, Slots are made directly under the coupled lines and metal sheets are etched in the slots to improve the coupling coefficient of the coupled lines, suppress the second harmonic, and generate a zero point at the double frequency. The size of the dielectric substrate is 56mm*56mm*0.508mm, the dielectric constant of the dielectric substrate is 2.65, and the dielectric substrate is divided into upper and lower layers. The selected cross coupler works in the S-band, the working frequency range is 1.94-2.545GHz, the quarter wavelength of the center frequency is 23.2mm, and the width of the 50-ohm microstrip line 1 connected to the six ports is 1.38mm , the length is 16mm, the gap of coupling line 2 is 0.21mm, the width of the first transmission line and the second transmission line is 0.19mm, the length is 24mm, the gap of coupling line 4 is 0.19mm, and the width of the third transmission line is 0.2mm, the length is 23.7mm, the width of the fourth transmission line is 0.2mm, the length is 23.42mm, the width of the microstrip line 3 is 0.91mm, and the length is 23.55mm, the microstrip line 5 connected between the microstrip line 1 and the coupling line 2 The width is 0.21 mm, the length is 46.5 mm, the diameter of the metal via 8 connected to the microstrip line 3 and the metal via 9 connected to the sixth transmission line are both 0.6 mm, the width of the groove line 6 is 0.6 mm, and the length is 23.12mm, the fifth transmission line has a width of 0.2mm and a length of 22.52mm.

It can be seen from Figure 6 that when the two signals are input at port 1(3) and port 2(4), the 5 zeros outside the band can effectively realize the stop band performance and extend to 2.95f ₀ , and the band has good transmission characteristics and Low insertion loss, and bandwidth increased to 27.5%, the isolation of adjacent ports is greater than 13.5dB in the entire frequency band.

The above is the design method and specific example design of the high-selectivity broadband cross coupler. The cross coupler uses an open/short coupling line and an open stub to realize 4 out-of-band transmission zeros. Slots and metal sheets etched in the slots improve the coupling coefficient of the coupled line, effectively suppress the second harmonic, and generate the fifth zero point at the double frequency. The relative bandwidth achieved by this structure is 27.5%, and the design is simple , more practical. The result of testing the design example of the present invention shows that: 5 transmission zero points are located at 1.16GHz, 1.78GHz, 2.83GHz, 3.52GHz, 4.68GHz respectively, the 3dB relative bandwidth is extended to 27.7%, the insertion loss in the band is lower than 1.6dB, and the upper resistance The band extends to 2.95f ₀ and is greater than 25dB, and the isolation is greater than 13.5dB in the entire frequency band. The total volume is 56mm*56mm*0.508mm, and the weight is less than 140 grams.

Claims (5)

1. A kind of 1. highly selective broadband coupler in crossing shape, which is characterized in that the slot including upper strata microstrip line construction and lower floor Cable architecture, wherein first network port (P1), second network port (P2), the third network port (P3) and the 4th network port (P4) be connected respectively with four the first microstrip lines (1), four network ports respectively be located at medium substrate upper strata four sides, and about Overall structure center rotational symmetry；

   Between first network port (P1), second network port (P2), the third network port (P3) and the 4th network port (P4) It is connected by four pairs of identical first coupling lines (2), each pair of first coupling line (2) includes first transmission line (2-1), four pairs the The first transmission line (2-1) of one coupling line is sequentially connected to form an inner ring, the second transmission line in each pair of first coupling line (2) (2-2) one end is connected with corresponding first microstrip line (1), and the other end is connected with corresponding second microstrip line (3), the second microstrip line (3) end is grounded by corresponding metal throuth hole (8), the width phase of first transmission line (2-1) and second transmission line (2-2) Deng, the length of first transmission line (2-1), second transmission line (2-2) and the second microstrip line (3) is quarter-wave, and first Coupling line (2), the second microstrip line (3) and metal throuth hole (8) are about overall structure center rotational symmetry；

   Four pairs of identical second coupling lines (4) are connected in parallel on the first microstrip line (1) and are connected with corresponding first transmission line (2-1) respectively Locate, the third transmission line (4-1) and the 4th transmission line (4-2) width in the second coupling line (4) are equal, and length is a quarter Wavelength, four pair of second coupling line (4) is about overall structure center rotational symmetry；First microstrip line (1) and first transmission line (2-1) Junction is third microstrip line (5) in parallel, and the length of third microstrip line (5) is half-wavelength, and four third microstrip lines (5) are closed In overall structure center rotational symmetry；5th transmission line (7) of the lower floor of dielectric-slab is in the corresponding line of rabbet joint (6), the line of rabbet joint (6) Length for quarter-wave, and every the 5th transmission line (7) and every line of rabbet joint (6) are respectively short about the first coupling line (2) Side line of symmetry is symmetrical, and four article of the 5th transmission line (7) is with the line of rabbet joint (6) about overall structure center rotational symmetry.
2. 2. according to the highly selective broadband coupler in crossing shape described in claim 1, which is characterized in that described each pair of first Coupling line (2) is equal including two width, and length is quarter-wave first transmission line (2-1) and second transmission line (2-2), four pair of first coupling line (2) is about overall structure center rotational symmetry.
3. 3. according to the highly selective broadband coupler in crossing shape described in claim 1, which is characterized in that described each pair of second Coupling line (4) is equal including two width, and length is quarter-wave third transmission line (4-1) and the 4th transmission line (4-2), wherein, third transmission line (4-1) one end is connected with the first microstrip line (1), other end open circuit, the 4th transmission line (4-2) It opens a way in one end that third transmission line (4-1) is connected with the first microstrip line (1), the other end is connected with the 6th transmission line (4-3), the Six transmission lines (4-3) are grounded by metal throuth hole (9).
4. 4. the highly selective broadband coupler in crossing shape according to claim 1 or 3, which is characterized in that four first micro- Equal length and width is respectively provided with line (1), impedance value is equal to 50 ohm.
5. 5. highly selective broadband coupler in crossing shape according to claim 1 or 2, which is characterized in that medium substrate Dielectric constant is 2~16, and the height of medium substrate is 0.1~3mm.