Resistive broadband directional coupler based on transmission line structure

Abstract

The application belongs to the technical field of directional coupler, and is a resistance type wideband directional coupler based on transmission line structure, which comprises two uncoupled uniform transmission lines, the two lines have a common reference ground, and are spatially isolated by a split surface, the split surface is perpendicular to the conductor plane between the connecting lines of the two uncoupled uniform transmission lines; an input port, a straight-through output port, a coupled output port and an isolation port are arranged on the two lines respectively. The two lines are both composed of quarter wavelength transmission line groups of the same order, one is a main transmission line, and the other is a coupled transmission line, and the characteristic impedances of the two lines are the same as the impedance of the external port. There is a coupling resistor across the quarter wavelength coupled transmission line group. The transmission line electric length between adjacent coupling resistors is a quarter wavelength; the application can reduce the requirement for processing error due to the symmetrical and simple structure, and has the characteristics of low reflection coefficient and ultra-wideband operation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of directional coupler, in particular, it is a kind of resistance type broadband directional coupler based on transmission line structure. BACKGROUND

[0002] Directional coupler is a kind of electronic components for directional coupling sampling of electromagnetic wave signal, which has a large number of applications in power synthesis network, antenna transceiver system and microwave measurement system. The key performance evaluation indexes of directional coupler mainly include insertion loss, coupling degree, operating frequency, isolation, reflection coefficient and relative operating bandwidth.

[0003] In the architecture of transmission line type directional coupler, there are generally two independent parallel transmission lines. By adjusting the length, odd-even mode impedance and order of parallel coupled lines, the design goals of operating frequency, coupling degree and bandwidth can be achieved. In the above design, it is necessary to ensure that the parallel coupled lines work in TEM mode to ensure the difference in odd-even mode phase velocity. The above problem is particularly important in broadband directional coupler design, which directly limits the application of microstrip line structure broadband directional coupler and is a problem that needs to be solved in the field of microwave and radio frequency.

[0004] In addition, in order to ensure the accurate realization of odd-even mode impedance, the traditional transmission line type directional coupler has high requirements for the precision of processing technology, which increases the manufacturing cost. SUMMARY

[0005] The present application aims to solve the sensitivity of traditional transmission line type directional coupler to the difference in odd-even mode phase velocity and the high requirement for circuit processing precision.

[0006] In order to achieve the above purpose, the present application discloses a resistance type broadband directional coupler based on transmission line structure, and the specific technical scheme is as follows:

[0007] A resistance type broadband directional coupler based on transmission line structure, characterized in that an input port, a straight-through output port, a coupled output port, an isolation port, a split surface, a quarter wavelength main transmission line group, a quarter wavelength coupled transmission line group and a coupled resistance group are arranged on two uncoupled uniform transmission lines. By reasonably setting the number and resistance value of the coupled resistance, a broadband directional coupler can be realized. The two uncoupled uniform transmission lines have the same characteristic impedance, the first uniform transmission line is provided with an input port and a straight-through output port, and the second uniform transmission line is provided with a coupled output port and an isolation port. The two uniform transmission lines have a common reference ground, and the characteristic impedance of the two uniform transmission lines is the same as the impedance of the corresponding port.

[0008] The further improvement of the present application is that the two uncoupled uniform transmission lines are physically isolated by a split surface, and the electromagnetic coupling between the lines through the split surface is zero or weak to be negligible.

[0009] The further improvement of the present application is that the quarter-wavelength main transmission line group is located above the first uniform transmission line, and the quarter-wavelength coupling transmission line group is located above the second uniform transmission line. The coupling resistance group is composed of multiple cross-over resistances, each of which is connected to the corresponding nodes of the quarter-wavelength main transmission line group and the quarter-wavelength coupling transmission line group through the split surface. The uniform transmission line between adjacent resistances of the coupling resistance group has a uniform transmission line electrical length of a quarter wavelength.

[0010] The further improvement of the present application is that the two uncoupled uniform transmission lines can be coplanar microstrip lines, non-coplanar microstrip lines, strip lines, coaxial lines, coplanar parallel wires, coplanar waveguides, and combinations thereof.

[0011] The present application has the following technical effects: by reasonably setting the number and resistance value of the coupling resistances, the present application can realize a broadband directional coupler; compared with the traditional transmission line directional coupler, the present application has the following technical effects: supporting dispersion transmission lines, low processing precision requirement, ultra-wideband operation, easy debugging, and low cost. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The figure is a structural topology diagram of the present application.

[0013] Figure 2 The figure is a planar structure diagram of a three-order coplanar microstrip line directional coupler embodiment.

[0014] Figure 3 The figure is a three-dimensional structure diagram of a three-order coplanar microstrip line directional coupler embodiment.

[0015] Figure 4 The figure is a transmission phase diagram of the phase shifter state 1 and state 2 in the embodiment 1 obtained by simulation, in which the solid line is the transmission phase when the state 1, and the dashed line is the transmission phase when the state 2.

[0016] In the figure, 1 - input port, 2 - straight-through output port, 3 - coupled output port, 4 - isolated port, 5a - input transmission line, 5b - first quarter section of input transmission line, 5c - last quarter section of input transmission line, 5d - output transmission line, 6a - isolated output transmission line, 6b - first quarter section of output transmission line, 6c - last quarter section of output transmission line, 6d - coupled output transmission line, 7 - split plane, 7a - first coupling resistor, 7b - second coupling resistor, 7c - second-to-last coupling resistor, 7d - first-to-last coupling resistor, 8 - microstrip input port, 9 - microstrip output port, 10 - microstrip coupled output port, 11 - isolated microstrip port, 12 - main input microstrip line, 13 - coupled microstrip line, 14a - first coupling resistor, 14b - second coupling resistor, 14c - third coupling resistor, 15 - split plane, 16 - dielectric substrate and metal backplane. Embodiment

[0017] In order to deepen the understanding of the present application, the present application will be further described in detail below in conjunction with the accompanying drawings and examples, which are only used to explain the present application and do not constitute a limitation on the protection scope of the present application.

[0018] As Figure 1As shown, a kind of resistance type broadband directional coupler based on transmission line structure includes input port 1, straight-through output port 2, coupled output port 3, isolation port 4, input transmission line 5a, input transmission line first quarter section 5b, input transmission line last quarter section 5c, output transmission line 5d, isolation output transmission line 6a, output transmission line first quarter section 6b, output transmission line last quarter section 6c, coupled output transmission line 6d, split surface 7, first coupling resistance 7a, second coupling resistance 7b, penultimate coupling resistance 7c and the first coupling resistance 7d in reverse order;Input port 1 is connected with input transmission line 5a, input transmission line 5a is connected with input transmission line first quarter section 5b, input transmission line first quarter section 5b is connected with input transmission line last quarter section 5c after repeating several times, input transmission line last quarter section 5c is connected with output transmission line 5d, and output transmission line 5d is connected with straight-through output port 2;Isolation output transmission line 6a is connected with output transmission line first quarter section 6b, output transmission line first quarter section 6b is connected with output transmission line first quarter section 6b, output transmission line first quarter section 6b is connected with output transmission line last quarter section 6c after repeating several times, output transmission line last quarter section 6c is connected with coupled output transmission line 6d, and output transmission line 6d is connected with coupled output port 3;The characteristic impedance of each transmission line unit on input transmission line is identical with each other, and identical with the reference impedance of input port and straight-through output port.I.e.the impedance of input port 1, input transmission line 5a, input transmission line first quarter section 5b, input transmission line last quarter section 5c, output transmission line 5d and straight-through output port 2 is identical.The electrical length of input transmission line first quarter section 5b and input transmission line last quarter section 5c is identical, and the electrical length is 90 ° at the center frequency of design working bandwidth.

[0019] According to the working bandwidth to be designed, several equal-length quarter sections uniform transmission lines can be inserted between input transmission line first quarter section 5b and input transmission line last quarter section 5c, and the characteristic impedance of the above-mentioned inserted transmission lines is identical with the impedance of input port 1, and the electrical length of input transmission line first quarter section 5b is equal;

[0020] The characteristic impedance of each transmission line unit on the output transmission line is the same as each other and the same as the reference impedance of the coupling output port and the isolation port. That is, the impedance of the isolation port 3, the isolation output transmission line 6a, the output transmission line first quarter section 6b, the output transmission line last quarter section 6c, the coupling output transmission line 6d and the coupling output port 3 is the same. The electrical length of the output transmission line first quarter section 6b and the output transmission line last quarter section 6b is the same and is 90° at the center frequency of the designed working bandwidth. According to the designed working bandwidth, a plurality of equal-length quarter sections of uniform transmission line can be inserted between the output transmission line first quarter section 6b and the output transmission line last quarter section 6c, and the characteristic impedance of the above-mentioned inserted transmission line is the same as the impedance of the isolation port 4 and the electrical length of the output transmission line first quarter section 6b. Each unit of the input transmission line, that is, the input transmission line 5a, the input transmission line first quarter section 5b, the input transmission line last quarter section 5c and the output transmission line 5d, corresponds to and is equal in number to each unit of the output transmission line, that is, the isolation output transmission line 6a, the output transmission line first quarter section 6b, the output transmission line last quarter section 6c and the coupling output transmission line 6d, and is isolated by the split surface 7 and has no direct electromagnetic coupling therebetween.

[0021] The input transmission line and the output transmission line are coupled by using a coupling resistor group, and the coupling resistor group is connected to the input transmission line and the output transmission line. Figure 1 In the coupling resistor group, the first coupling resistor 7a, the second coupling resistor 7b, the penultimate coupling resistor 7c and the last coupling resistor 7d are arranged in sequence. The number of the coupling resistors is one less than the number of the input transmission line units. By reasonably setting the resistance distribution of the coupling resistors, a wideband directional coupler can be realized.

[0022] As shown in FIG. 1, the input transmission line and the output transmission line are coupled by using a coupling resistor group. Figure 2 and Figure 3As shown, the coplanar microstrip line set is adopted in the embodiment 1, in which the microstrip input port 8 and the microstrip output port 9 are connected on the main input microstrip line 12 with uniform characteristic impedance, and the microstrip coupling output port 10 and the isolation microstrip port 11 are connected on the coupling microstrip line 13 with uniform characteristic impedance; the main input microstrip line 12 and the coupling microstrip line 13 are connected by three coupling resistors, i.e. the first coupling resistor 14a, the second coupling resistor 14b and the third coupling resistor 14c; the transmission line electrical lengths between the coupling resistors are equal; the main input microstrip line 12 and the coupling microstrip line 13 are divided by the division surface 15 and are jointly manufactured on the dielectric substrate and the metal bottom plate 16. When the direct coupling between the main input microstrip line 12 and the coupling microstrip line 13 is small enough to be ignored, the division surface 15 can be regarded as not existing; when the direct coupling between the main input microstrip line 12 and the coupling microstrip line 13 is strong, the division surface 15 can be realized by a good conductor plane and is electrically connected with the metal bottom plate 16, at this time the coupling resistors need to be connected by holes; the input microstrip line 12 and the coupling microstrip line 13 can be designed in a curved shape to reduce the length.

[0023] In the embodiment 1, all the ports, i.e. the microstrip input port 8, the microstrip output port 9, the microstrip coupling output port 10 and the isolation microstrip port 11, are valued as 50 Ohm; the characteristic impedance of the main input microstrip line 12 and the coupling microstrip line 13 is valued as 50 Ohm, and the electrical length is 90° at 1 GHz; the first coupling resistor 14a, the second coupling resistor 14b and the third coupling resistor 14c are respectively valued as 804 Ohm, 493 Ohm and 804 Ohm.

[0024] The above circuit schematic diagram is simulated by using the ADS simulation software. The S parameter curve obtained by simulation is shown in Figure 4 The dashed line in the figure is S11 and S41, i.e. the reflection coefficient and the isolation, the solid line S31 is the coupling coefficient, and the dotted line S21 is the straight-through transmission coefficient. As can be seen from Figure 2 , the curve S21 presents a low-loss characteristic, the coupling coefficient is 20 dB, the working bandwidth is 0.1-1.9 GHz, the in-band reflection coefficient is better than -20 dB, and the matching is good; the isolation S41 coincides with S11, and is better than 40 dB within 0.7-1.3 GHz, which means that the directivity is 20 dB. By increasing the order and the number of isolation resistors and reasonably adjusting the resistance values, a wider bandwidth and more flexible coupling degree and directivity design can be realized.

[0025] The technical features of the above-described embodiments can be combined arbitrarily, and in order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

Claims

1. A resistive broadband directional coupler based on a transmission line structure, characterized in that, An input port, a through output port, a coupled output port, an isolation port, a split plane, a quarter-wavelength main transmission line group, a quarter-wavelength coupled transmission line group, and a coupling resistor group are disposed on two uncoupled uniform transmission lines. The two uncoupled uniform transmission lines have the same characteristic impedance. The first uniform transmission line is provided with the input port and the through output port, while the second uniform transmission line is provided with the coupled output port and the isolation port. The two uniform transmission lines share a common reference ground, and their characteristic impedances are the same as the impedances of their corresponding connected ports. The two uncoupled uniform transmission lines are physically isolated by a split plane, which is a conductor plane perpendicular to the connection between the two uncoupled uniform transmission lines. The quarter-wavelength main transmission line group is located on the first uniform transmission line, and the quarter-wavelength coupled transmission line group is located on the second uniform transmission line. The coupling resistor group consists of multiple bridging resistors, each of which passes through the split plane and is connected to the corresponding nodes of the quarter-wavelength main transmission line group and the quarter-wavelength coupled transmission line group. The electrical length of the uniform transmission line between adjacent resistors in the coupling resistor group is one-quarter wavelength.

2. The resistive broadband directional coupler based on a transmission line structure according to claim 1, characterized in that, The two uncoupled uniform transmission lines are one or more combinations of coplanar microstrip lines, non-coplanar microstrip lines, striplines, coaxial lines, coplanar parallel conductors, and coplanar waveguides.

Images