A balanced broadband filter phase shifter

Abstract

This invention discloses a balanced broadband filter phase shifter, comprising a reference line and a main line. The reference line and main line have identical structures, each including first to fourth feed lines, a first half-wavelength microstrip line, a second half-wavelength microstrip line, third to eighth microstrip lines, a coupling microstrip line, and a capacitor. Existing filter phase shifters are mainly single-ended structures, exhibiting weak common-mode interference rejection. Furthermore, existing balanced filter phase shifters suffer from narrow bandwidth or poor frequency selectivity. This invention achieves a balanced broadband filter phase shifter simultaneously possessing broadband differential-mode phase shifting, high frequency selectivity, and broadband common-mode rejection by loading short-circuit stubs between the microstrip line and the coupling line in a capacitor-cascaded microstrip line transmission structure.

Description

Technical Field

[0001] This invention relates to a microwave communication device, and more particularly to a phase shifter. Background Technology

[0002] With the development of wireless technology, higher demands are being placed on the broadband, miniaturization, and integration of wireless communication systems. Filters and phase shifters, as key components of phased arrays, respectively possess frequency selection and phase modulation functions. Wideband filter phase shifters integrate broadband filters and phase shifters in a single design, reducing the overall circuit size, complexity, and losses, while also improving system integration. Compared to single-ended designs, balanced broadband filter phase shifters not only offer broadband filtering and phase shifting capabilities but also possess excellent common-mode signal rejection, effectively addressing environmental noise and electromagnetic crosstalk issues within the system. Therefore, balanced broadband filter phase shifters, with their broadband, high frequency selectivity, and high common-mode rejection, align with the current development trend of wireless communication systems. However, the design of balanced broadband filter phase shifters still faces significant challenges.

[0003] Currently, most reported filter phase shifters are single-ended designs, primarily employing methods such as multi-stub loaded T-type transmission lines, multimode resonators, wide-side coupling, and open-circuit stubs at the coupling line terminals. However, they lack common-mode rejection capability, which is detrimental to mitigating environmental noise and electromagnetic crosstalk in the system. Existing balanced filter phase shifters utilize structures such as multimode T-type resonators and cascaded microstrip lines with three-terminal folded coupling lines. These designs suffer from drawbacks such as narrow operating bandwidth or poor frequency selectivity. Therefore, designing a balanced broadband filter phase shifter to further increase its operating bandwidth while improving frequency selectivity and common-mode rejection capability is crucial. Summary of the Invention

[0004] Purpose of the invention: To address the problems of narrow operating bandwidth and poor frequency selectivity in the existing technology, a balanced broadband filter phase shifter is proposed, which also has good common-mode rejection capability and a simple and easy-to-manufacture structure.

[0005] Technical solution: A balanced broadband filter phase shifter, including a reference line and a main line, the reference line and the main line have the same structure, both including first to fourth feed lines, a first half-wavelength microstrip line, a second half-wavelength microstrip line, a third to eighth microstrip line, a coupling microstrip line and a capacitor;

[0006] Among them, the first feed line and the second feed line correspond to a pair of balanced input ports, and the third feed line and the fourth feed line correspond to a pair of balanced output ports; the two ends of the first half-wavelength microstrip line are respectively connected to the first feed line and the second feed line, and the two ends of the second half-wavelength microstrip line are respectively connected to the third feed line and the fourth feed line.

[0007] The third and seventh microstrip lines are connected in series, one end of the fifth microstrip line is connected to the junction of the third and seventh microstrip lines, and the other end of the fifth microstrip line is grounded; the fourth and eighth microstrip lines are connected in series, one end of the sixth microstrip line is connected to the junction of the fourth and eighth microstrip lines, and the other end of the sixth microstrip line is grounded.

[0008] A capacitor is connected between two ports on one side of the coupled microstrip line, and the two ports are respectively connected to one end of the seventh microstrip line and one end of the eighth microstrip line; the two ports on the other side of the coupled microstrip line are grounded.

[0009] The physical dimensions of the third and fourth microstrip lines in the main structure are different from those of the third and fourth microstrip lines in the reference structure. The resulting phase difference is used as the phase shift reference value of the phase shifter.

[0010] Beneficial effects: Existing filter phase shifters are mainly single-ended structures with weak common-mode interference immunity. Existing balanced filter phase shifters suffer from narrow bandwidth or poor frequency selectivity. This invention achieves a balanced broadband filter phase shifter that simultaneously possesses broadband differential-mode phase shifting, high frequency selectivity, and broadband common-mode rejection by loading short-circuit stubs between the microstrip line and the coupling line in a capacitor-cascaded microstrip line transmission structure.

[0011] Specifically, the capacitor and the coupled microstrip line are used to control the left and right transmission zeros of the differential-mode transmission response to shift towards the center frequency, giving the design high frequency selectivity. The loaded microstrip lines 9 and 10, as well as the capacitor and the coupled microstrip line, can be used simultaneously to generate differential-mode transmission poles and common-mode transmission zeros, enabling the phase shifter to have broadband differential-mode impedance matching and broadband common-mode rejection performance. Attached Figure Description

[0012] Figure 1 This is a circuit diagram of a balanced broadband filter phase shifter.

[0013] Figure 2 These are the simulation results of the differential-mode S-parameters of the balanced broadband filter phase shifter of this invention;

[0014] Figure 3 The simulation results of the common-mode S-parameters of the balanced broadband filter phase shifter of this invention are shown below.

[0015] Figure 4 The simulation results show the differential-mode phase shifting of the balanced broadband filter phase shifter of this invention. Detailed Implementation

[0016] The invention will now be further explained with reference to the accompanying drawings.

[0017] like Figure 1As shown, a balanced broadband filter phase shifter includes a reference line and a main line. The reference line and the main line have the same structure, each including feed lines 1-4, half-wavelength microstrip lines 5 and 6, microstrip lines 7-12, a coupling microstrip line 13, and a capacitor 14. Feed lines 1 and 2 correspond to a pair of balanced input ports, and feed lines 3 and 4 correspond to a pair of balanced output ports. The two ends of the wavelength microstrip line 5 are connected to feed lines 1 and 2 respectively, and the two ends of the half-wavelength microstrip line 6 are connected to feed lines 3 and 4 respectively. Microstrip lines 7 and 11 are connected in series, and one end of microstrip line 9 is connected to the junction of microstrip lines 7 and 11, while the other end is grounded. Microstrip lines 8 and 12 are connected in series, and one end of microstrip line 10 is connected to the junction of microstrip lines 8 and 12, while the other end is grounded. The two lower ports of the coupling microstrip line 13 are grounded, and the two upper ports are connected to the two ends of the capacitor 14 respectively. The two connection points formed by the coupling microstrip line 13 and the capacitor 14 are connected to microstrip line 11 and microstrip line 12 respectively. That is, the two upper ports of the coupling microstrip line 13 are respectively connected to one end of microstrip line 11 and one end of microstrip line 12. The overall structure of the main line and the reference line is symmetrical along the longitudinal centerline.

[0018] In this invention, the circuit structures of the phase shifter reference line and the main line are the same, both as follows: Figure 1 As shown, the difference lies in the different physical dimensions of the corresponding parts. Microstrip lines 7 and 8 have a phase delay effect; that is, the phase difference generated by microstrip lines 7 and 8 in the main line structure and microstrip lines 7 and 8 in the reference line structure serves as the phase shift reference value for the phase shifter. The capacitance of capacitor 14 and the impedance of microstrip lines 9-13 are used to adjust the phase slope, forming a wideband differential-mode phase shift.

[0019] When the phase shifter is excited by a differential-mode signal, the combined action of capacitor 14 and coupling microstrip line 13 generates one transmission zero on the left side and two transmission zeros on the right side of the differential-mode transmission response of this invention. The left transmission zero is mainly controlled by capacitor 14; when the capacitance value decreases, the transmission zero shifts to a higher frequency. The two right transmission zeros are mainly controlled by the electrical length of coupling microstrip line 13; when the electrical length increases, the transmission zeros shift to a lower frequency. Furthermore, under the action of microstrip lines 9 and 10, a transmission zero can also be generated on the right side of the differential-mode transmission response; when the electrical lengths of microstrip lines 9 and 10 increase, the transmission zero shifts to a lower frequency. The adjustment of the transmission zeros has almost no impact on the 3-dB bandwidth. Therefore, by adjusting the electrical length of coupling microstrip line 13, the capacitance value of capacitor 14, and the electrical lengths of microstrip lines 9 and 10, the transmission zeros on both sides can be brought closer to the center frequency, improving frequency selectivity. Meanwhile, microstrip line 9, microstrip line 10, capacitor 14, and coupled microstrip line 13 can also generate differential-mode transmission poles, and differential-mode impedance matching can be improved by adjusting the impedances of microstrip lines 9-12 and coupled microstrip line 13. Therefore, broadband differential-mode impedance matching is achieved while improving frequency selectivity.

[0020] When the phase shifter is excited by a common-mode signal, the signal entering from feed line 2 at the balanced port undergoes a 180° phase change after passing through half-wavelength transmission line 5, canceling out the signal entering from feed line 1 at the balanced port, thus suppressing the common-mode signal. Furthermore, multiple common-mode transmission zeros can be obtained by coupling microstrip lines 13, 9, and 10 through capacitor 14. The degree of common-mode signal suppression can be further improved by adjusting the impedance of microstrip lines 9-12 and coupling microstrip line 13, achieving broadband common-mode suppression.

[0021] Compared to existing balanced filter phase shifters, this invention improves frequency selectivity while achieving broadband differential mode operating bandwidth, and also has advantages such as broadband common mode rejection and simple and easy-to-manufacture structure.

[0022] The following are design examples of the present invention at 45° and 90°, and their circuit structure diagrams are as follows: Figure 1 As shown. This balanced broadband filter phase shifter example uses an RO4003C substrate with a dielectric constant of 3.38, a loss angle of 0.0027, a thickness of 0.813 mm, and a center frequency of 1 GHz. The differential-mode S-parameters, common-mode S-parameters, and differential-mode phase-shift response are as follows: Figures 2 to 4 As shown. From Figure 2 and Figure 3 We can obtain the following results: For the reference line, the 10-dB differential-mode impedance matching relative bandwidth is 77%, the 3-dB relative bandwidth is 73%, the minimum insertion loss is 0.56dB, and the 13-dB common-mode rejection relative bandwidth is 210%; for the 45° phase shifter mainline, the 10-dB differential-mode impedance matching relative bandwidth is 78%, the 3-dB relative bandwidth is 74%, the minimum insertion loss is 0.68dB, and the 13-dB common-mode rejection relative bandwidth is 220%; for the 90° phase shifter mainline, the 10-dB differential-mode impedance matching relative bandwidth is 80%, the 3-dB relative bandwidth is 75%, the minimum insertion loss is 0.64dB, and the 13-dB common-mode rejection relative bandwidth is 180%. Figure 4 It can be seen that the differential mode phase shift bandwidth achieving 45°±3° (90°±5°) is 73% (74%). Therefore, the operating bandwidths for the 45° and 90° phase shifters are 73% and 72%, respectively. It can be seen that the common-mode rejection bandwidth of this invention can fully cover the differential mode operating passband.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A balanced broadband filter phase shifter, characterized in that, It includes a reference line and a main line. The reference line and the main line have the same structure, both including the first to fourth feed lines (1~4), the first half-wavelength microstrip line (5), the second half-wavelength microstrip line (6), the third to eighth microstrip lines (7~12), the coupling microstrip line (13), and the capacitor (14). Among them, the first feed line (1) and the second feed line (2) correspond to a pair of balanced input ports, and the third feed line (3) and the fourth feed line (4) correspond to a pair of balanced output ports; one end of the first half-wavelength microstrip line (5) is connected to the first feed line (1), and the other end is connected to the second feed line (2); one end of the second half-wavelength microstrip line (6) is connected to the third feed line (3), and the other end is connected to the fourth feed line (4). The third microstrip line (7) and the seventh microstrip line (11) are connected in series. One end of the fifth microstrip line (9) is connected to the junction of the third microstrip line (7) and the seventh microstrip line (11), and the other end of the fifth microstrip line (9) is grounded. The fourth microstrip line (8) and the eighth microstrip line (12) are connected in series. One end of the sixth microstrip line (10) is connected to the junction of the fourth microstrip line (8) and the eighth microstrip line (12), and the other end of the sixth microstrip line (10) is grounded. A capacitor (14) is connected between two ports on one side of the coupling microstrip line (13), one of which is connected to one end of the seventh microstrip line (11) and the other is connected to one end of the eighth microstrip line (12); the two ports on the other side of the coupling microstrip line (13) are grounded. The physical dimensions of the third and fourth microstrip lines in the main structure are different from those of the third and fourth microstrip lines in the reference structure. The resulting phase difference is used as the phase shift reference value of the phase shifter.

2. The balanced broadband filter phase shifter according to claim 1, characterized in that, The overall structure of both the main line and the reference line is symmetrical along the longitudinal centerline.

3. The balanced broadband filter phase shifter according to claim 1, characterized in that, When the phase shifter is excited by the differential signal, a transmission zero is generated on the left side of the differential transmission response and two transmission zeros are generated on the right side under the combined action of the capacitor (14) and the coupled microstrip line (13). The transmission zero on the left is controlled by capacitor (14). When the capacitance decreases, the transmission zero moves to a higher frequency. The two transmission zeros on the right are controlled by the electrical length of the coupled microstrip line (13). When the electrical length increases, the transmission zero moves to a lower frequency. Under the action of the fifth microstrip line (9) and the sixth microstrip line (10), another transmission zero is generated on the right side of the differential mode transmission response. When the electrical length of the fifth microstrip line (9) and the sixth microstrip line (10) increases, the transmission zero moves to a lower frequency.

4. The balanced broadband filter phase shifter according to claim 1, characterized in that, The fifth microstrip line (9) and the sixth microstrip line (10), the capacitor (14) and the coupling microstrip line (13) are used to generate differential mode transmission poles and common mode transmission zeros, so that the phase shifter has broadband differential mode impedance matching and broadband common mode rejection performance.

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