A multi-zero integrated directional coupler

Abstract

The invention discloses an integrated directional coupler with multiple zero points. Two LC rings connected by mutual inductance and capacitance are connected with four LC parallel circuits. The anti-phase branch of the LC ring is used to generate transmission zero points, resonance points and low-pass effects. The mutual inductance and capacitance between the LC rings affect the through poles, through zero points, coupling zero points and isolation zero points. The through poles and transmission zero points of each channel are regulated by the LC parallel circuits to realize the integrated directional coupler with multiple zero points. The integrated directional coupler has the advantages of a large number of transmission zero points, a low rectangular coefficient and a wide stopband width, and can take into account the characteristics of high integration and small size.

Description

Technical Field

[0001] The invention relates to a microwave communication device, in particular to an integrated directional coupler. Background Art

[0002] A directional coupler is a four-port device located at the RF front end, which can realize three channels: through, coupled and isolated. Part of the power of the through channel is coupled to the coupled channel output, while the isolation channel is expected to have no power output. Therefore, directional couplers are mostly used in power monitoring and signal analysis. Integrated directional couplers are conducive to improving the integration of the system and are widely used in RF front ends. Furthermore, an integrated directional coupler with zero points can form an operating frequency band with a lower rectangular coefficient and a wider stop band, resulting in good in-band operation and out-of-band suppression effects. Therefore, multi-zero integrated directional couplers have good engineering value and application value.

[0003] There are three main design methods for existing multi-zero integrated directional couplers. The first is to achieve this by cascading a four-terminal coupled stripline, a diagonal open-circuit coupled stripline, and a half-wavelength stepped impedance stripline. This can generate two high and low transmission zeros in the through and coupled channels, but the relatively small number of transmission zeros results in a high rectangular coefficient. The second is to achieve this by connecting a four-terminal coupled stripline in parallel with four single-ended short-circuited coupled striplines. This can generate four transmission zeros in each of the through and coupled channels, but the transmission zero generated by the single-ended short-circuited coupled stripline is far from the sideband, and there is still a problem of a high rectangular coefficient. At the same time, both of the above methods have a large size and are implemented using a three-layer stripline structure, which is not conducive to integration, increases the difficulty and cost of integration, and the parasitic harmonic response is not easy to eliminate, resulting in a narrow stopband. The third method is to combine a four-terminal coupled microstrip line with a centrally loaded inductor and an open-circuit branch with four stepped impedance short-circuit branches and four three-wire coupled microstrip lines, which can generate two transmission zeros in each of the through and coupled channels. Although this method reduces the number of layers and is conducive to integration, it still has the problem of large size. At the same time, due to the small number of transmission zeros and the resonance point outside the low-frequency band, the rectangular coefficient is high, the stopband is narrow, and the bandwidth difference between the through and coupled channels is large. Therefore, it is necessary to propose a new type of multi-zero integrated directional coupler to achieve high integration, small size, multiple zeros, low rectangular coefficient and wide stopband. Summary of the invention

[0004] Purpose of the invention: In view of the above-mentioned prior art, a multi-zero integrated directional coupler is proposed to increase the number of transmission zeros of each channel of the integrated directional coupler, reduce the rectangular coefficient and widen the stopband bandwidth.

[0005] Technical solution: A multi-zero integrated directional coupler, including ports one to four, a central LC circuit and four LC parallel circuits, and the overall circuit is centrally symmetrical;

[0006] The central LC circuit includes two LC loops, which are connected by coupling mutual inductance and capacitance;

[0007] Each LC parallel circuit has the same structure, including two parallel branches, and there is mutual inductance between the inductors of the two parallel branches;

[0008] Each LC ring of the central LC circuit is connected to two LC parallel circuits respectively, and two branch intersection points of each LC parallel circuit are connected to port one to port four respectively.

[0009] Furthermore, in the central LC circuit, each LC loop includes four inductors connected in series, and a capacitor is connected in parallel between a common point of adjacent inductors and the ground respectively; and two LC loops are connected via mutual inductance and capacitance.

[0010] Furthermore, in the central LC circuit, an inductor is arranged opposite to each other in the LC rings on the left and right sides, and a coupled mutual inductance is formed between the two inductors. Two capacitors are connected in parallel between the two LC rings, one of which is connected in parallel to the same-name ends of the two inductors, and the other capacitor is connected in parallel to the other ends of the two inductors.

[0011] Furthermore, each LC parallel circuit includes two inductors and five capacitors; wherein, one end of the inductor L11 serves as the input end of the LC parallel circuit and is connected to one end of the capacitor C9, and the other end of the inductor L11 is connected to one end of the capacitor C10 and one end of the capacitor C11; the other end of the capacitor C11 serves as the output end of the LC parallel circuit and is connected to one end of the capacitor C12 and one end of the inductor L12, the other end of the inductor L12 is connected to one end of the capacitor C13 and the other end of the capacitor C9, and the capacitor C9 is connected in parallel between the like ends of the inductor L11 and the inductor L12; the other end of the capacitor C10, the other end of the capacitor C12, and the other end of the capacitor C13 are all grounded; and there is mutual inductance between the inductor L11 and the inductor L12.

[0012] Furthermore, in the LC parallel circuit 2, the grounded capacitor C12, the series capacitor C11, the grounded capacitor C10 and the series inductor L11 are connected in sequence to form a branch of the LC parallel circuit; the series inductor L12, the grounded capacitor C13 and the series capacitor C9 are connected in sequence to form another branch of the LC parallel circuit; in the central LC circuit, the four ends of the two inductors are respectively connected to the input end of an LC parallel circuit.

[0013] Beneficial effects: The existing multi-zero integrated directional couplers have the problems of large size, few transmission zeros in the through and coupled channels, high rectangular coefficient, and narrow stopband. Some designs also have the problems of high integration difficulty and large difference in bandwidth of the through and coupled channels. The present invention connects two LC rings connected by mutual inductance and capacitance with four LC parallel circuits, utilizes the anti-phase branch of the LC ring to generate transmission zeros, resonance points and low-pass effects, and the influence of mutual inductance and capacitance between LC rings on through poles, through zeros, coupling zeros and isolation zeros, combined with the regulation of through poles and transmission zeros of each channel by LC parallel circuits, to realize a multi-zero integrated directional coupler, which has the advantages of many transmission zeros, low rectangular coefficient and wide stopband bandwidth, and can take into account the characteristics of high integration and small size.

[0014] Specifically, the central LC circuit consists of two LC rings, mutual inductance between the LC rings, and two capacitors, and is located in the center of the entire circuit. The left and right half circuits of the LC rings are inverted in phase, and can provide two transmission zeros and four coupling zeros for the through channel and the coupled channel. The low-pass effect of the LC ring can expand the stopband bandwidth. The self-inductance, mutual inductance, and capacitance between the LC rings provide the two outermost coupling zeros and one in-band isolation zero. At the same time, the two LC rings are combined with the mutual inductance and capacitance in the middle to generate two transmission poles. Therefore, the central LC circuit provides a lower rectangular coefficient and a wide stopband response for the through channel and the coupled channel.

[0015] Each LC parallel circuit is composed of three grounded capacitors, two series capacitors and two series inductors, forming two branches, and there is mutual inductance between the two series inductors. The LC parallel circuit is located outside the central LC circuit, which can assist in adjusting the coupling degree and directivity of the overall circuit, and generate two through-channel transmission zeros outside the working frequency band to widen the stopband bandwidth, introduce two transmission poles to adjust the matching, affect the position of the four inner coupling zeros in the coupling channel to improve the rectangular coefficient and stopband bandwidth, and generate two in-band isolation zeros in the isolation channel to improve the isolation bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a circuit diagram of a multi-zero integrated directional coupler;

[0017] Figure 2 The matching and transmission simulation responses of the multi-zero integrated directional coupler of the embodiment;

[0018] Figure 3 A coupling simulation response of a multi-zero integrated directional coupler of an embodiment;

[0019] Figure 4 The isolation and directivity simulation response of the multi-zero integrated directional coupler of the embodiment;

[0020] Figure 51 is a simulated response of the through and coupled output phase differences of the multi-zero integrated directional coupler of the embodiment. DETAILED DESCRIPTION

[0021] The present invention will be further explained below in conjunction with the accompanying drawings.

[0022] like Figure 1 As shown, a multi-zero integrated directional coupler includes ports one to four, a central LC circuit 1 and four LC parallel circuits 2, and the overall circuit is centrally symmetrical.

[0023] The central LC circuit 1 is composed of eight inductors and ten capacitors. Among them, the inductors L1~L4 are connected in series in sequence, and the capacitors C1~C4 are connected in parallel between each common point between the inductors L1~L4 and the ground; the inductors L5~L8 are connected in series in sequence, and the capacitors C5~C8 are connected in parallel between each common point between the inductors L5~L8 and the ground. In this circuit, the alternately connected series inductors L1~L4 and the grounded capacitors C1~C4 form LC ring one; the alternately connected series inductors L5~L8 and the grounded capacitors C5~C8 form LC ring two. LC ring one and LC ring two are connected through mutual inductance and capacitors C14 and C15. Specifically, a coupled mutual inductance is formed between the inductor L1 and the inductor L5, the capacitor C14 is connected in parallel to the same-name ends of the inductor L1 and the inductor L5, and the capacitor C15 is connected in parallel to the other end of the inductor L1 and the inductor L5.

[0024] Each LC parallel circuit 2 is composed of two inductors and five capacitors. Among them, one end of the inductor L11 is used as the input end of the LC parallel circuit 2 and is connected to one end of the capacitor C9, and the other end of the inductor L11 is connected to one end of the capacitor C10 and one end of the capacitor C11; the other end of the capacitor C11 is used as the output end of the LC parallel circuit 2 and is connected to one end of the capacitor C12 and one end of the inductor L12, the other end of the inductor L12 is connected to one end of the capacitor C13 and the other end of the capacitor C9, and the capacitor C9 is connected in parallel between the same-name ends of the inductor L11 and the inductor L12; the other end of the capacitor C10, the other end of the capacitor C12, and the other end of the capacitor C13 are all grounded. In this circuit, the grounded capacitor C12, the series capacitor C11, the grounded capacitor C10 and the series inductor L11 are connected in sequence to form a branch of the LC parallel circuit; the series inductor L12, the grounded capacitor C13 and the series capacitor C9 are connected in sequence to form another branch of the LC parallel circuit; there is mutual inductance between the inductor L11 and the inductor L12.

[0025] In the overall circuit, each LC ring of the central LC circuit 1 is connected to two LC parallel circuits 2, and the two branch intersections of the four LC parallel circuits 2 are respectively connected to ports 1 to 4. Specifically, in the central LC circuit 1, the four ends of the inductor L1 and the inductor L5 are respectively connected to the input end of an LC parallel circuit 2, and the output end of each LC parallel circuit 2 is respectively connected to ports 1 to 4.

[0026] The four ports of the present invention are reciprocal, and the signal can obtain exactly the same performance from any port input. When the signal is input from port one, it flows into the central LC circuit 1 after passing through an LC parallel circuit 2, and then outputs from port two to port four after passing through three LC parallel circuits 2, forming an integrated directional coupler under the action of the overall circuit.

[0027] In this process, the central LC circuit 1 provides the basis for the three paths of direct, coupled and isolated for the overall circuit, and can play a major role in regulating the coupling degree and directivity of the overall circuit. For the direct channel, the signal will generate two transmission zeros at high and low frequencies due to the phase inversion of the left and right half circuits of the ring when passing through the LC ring, and the two LC rings and the mutual inductance and capacitance between the rings form an in-band double resonance response, generating two in-band transmission poles; for the coupled channel, the signal will generate four coupling zeros when passing through the two LC rings successively, and the self-inductance, mutual inductance and capacitance between the LC rings provide the two outermost coupling zeros; for the isolated channel, the self-inductance, mutual inductance and capacitance provide an in-band isolation zero. In summary, the central LC circuit 1 provides two transmission zeros, two in-band transmission poles, six coupling zeros and one in-band isolation zero, forming a response with a good rectangular coefficient on the direct channel and the coupled channel.

[0028] The LC parallel circuit 2 can assist in adjusting the coupling degree and directivity of the overall circuit. For the through channel, the LC parallel circuit 2 can provide the two outermost transmission zeros to increase the stopband bandwidth, and can introduce two resonance points, that is, introduce two new in-band transmission poles to adjust the in-band matching; for the coupled channel, the LC parallel circuit 2 will affect the position of the four coupling zeros inside the coupled channel, which is beneficial to improve the rectangular coefficient and stopband bandwidth of the coupled channel; for the isolated channel, the LC parallel circuit 2 can provide two additional in-band isolation zeros to improve the isolation bandwidth. In addition, the LC ring series inductance and grounding capacitance can avoid parasitic harmonic response and achieve wide stopband response.

[0029] Compared with the prior art, the present invention has the advantages of more transmission zeros in the through and coupled channels, low rectangular coefficient, wide stopband bandwidth, etc., and takes into account the characteristics of high integration and small size. In this embodiment, when port 1 is used as the input port, the matching and transmission simulation response are as follows: Figure 2 As shown, the coupled simulation response is Figure 3 As shown, the isolation and directivity simulation responses are as follows Figure 4 As shown, the phase difference simulation response between the through end and the coupled end is as follows Figure 5 As shown. Figure 2 It can be seen that the center frequency is 0.59 GHz, the frequency range of the 3-dB working bandwidth of the through channel is 0.46-0.71 GHz, that is, the relative bandwidth is 42.7%, the insertion loss at the center frequency is 0.12 dB, and the 20-dB out-of-band suppression frequency range of the through channel can reach 3.39 f 0, the through channel realizes four transmission poles (0.47 GHz, 0.51 GHz, 0.60 GHz, 0.69 GHz) and four transmission zeros (0GHz, 0.44 GHz, 0.72 GHz, 0.84 GHz), and the ratio of -30dB bandwidth to -3dB bandwidth can reach 1.08, with a low rectangular coefficient. Figure 3 It can be seen that the coupling degree of the coupling channel is 16dB, the relative bandwidth corresponding to the 16dB±2dB coupling range is 37.1%, and the 20-dB out-of-band suppression frequency range of the coupling channel can reach 3.39 f 0, the coupling channel realizes six coupling zero points (0GHz, 0.28 GHz, 0.45 GHz, 0.72 GHz, 0.80 GHz, 0.84 GHz), and the ratio of -15dB bandwidth to -3dB bandwidth can reach 1.03, and it also has a low rectangular coefficient. Figure 4 It can be seen that the isolation within the matching frequency band is greater than 30dB, and the isolation channel has three isolation zero points; the directivity within the matching frequency band remains above 14dB. Figure 5 It can be seen that the phase difference between the output signals of the through end and the coupled end is 90°, and the relative bandwidth of the ±1° phase difference fluctuation is 39.3%.

[0030] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A multi-zero integrated directional coupler, characterized in that: It includes ports 1 to 4, a central LC circuit (1) and four LC parallel circuits (2), and the overall circuit is centrally symmetrical; The central LC circuit (1) includes two LC loops, and the two LC loops are connected via coupling mutual inductance and capacitance; Each LC parallel circuit (2) has the same structure, and includes two parallel branches, and there is a mutual inductance between the inductors of the two parallel branches; Each LC ring of the central LC circuit (1) is connected to two corresponding LC parallel circuits (2), and the two branch intersection points of each LC parallel circuit (2) are connected to port one to port four respectively; In the central LC circuit (1), each LC loop includes four inductors connected in series, and a capacitor is connected in parallel between the common point of adjacent inductors and the ground; In the central LC circuit (1), an inductor is arranged in each of the LC loops on the left and right sides, and a coupled mutual inductance is formed between the two inductors. Two capacitors are connected in parallel between the two LC loops, one of which is connected in parallel to the same-name ends of the two inductors, and the other is connected in parallel to the other ends of the two inductors. Each LC parallel circuit (2) comprises two inductors and five capacitors; wherein one end of the inductor L11 serves as the input end of the LC parallel circuit (2) and is connected to one end of the capacitor C9, and the other end of the inductor L11 is connected to one end of the capacitor C10 and one end of the capacitor C11; the other end of the capacitor C11 serves as the output end of the LC parallel circuit (2) and is connected to one end of the capacitor C12 and one end of the inductor L12, the other end of the inductor L12 is connected to one end of the capacitor C13 and the other end of the capacitor C9, and the capacitor C9 is connected in parallel between the same-name ends of the inductor L11 and the inductor L12; the other end of the capacitor C10, the other end of the capacitor C12, and the other end of the capacitor C13 are all grounded; and there is a mutual inductance between the inductor L11 and the inductor L12; In the LC parallel circuit (2), the grounding capacitor C12, the series capacitor C11, the grounding capacitor C10 and the series inductor L11 are connected in sequence to form a branch of the LC parallel circuit; the series inductor L12, the grounding capacitor C13 and the series capacitor C9 are connected in sequence to form another branch of the LC parallel circuit; in the central LC circuit (1), the four ends of the two inductors are respectively connected to the input end of an LC parallel circuit (2).

Images