CN201017976Y - A Broadband Balun Based on Left and Right Handed Composite Transmission Lines - Google Patents

Abstract

The broadband balun based on the left-hand composite transmission line disclosed by the utility model includes a Wilkinson power divider and a phase shifter composed of a right-hand transmission line and a left-hand composite transmission line. The right-hand transmission line is connected to an output end of the Wilkinson power divider. The composite transmission line is connected to the other output end of the Wilkinson power divider. The said left and right hand composite transmission line is formed by series connection of n left and right hand composite transmission line units, and each left and right hand composite transmission line unit is composed of two connected impedance units and connected in A T-shaped circuit formed by the admittance unit at the junction of two impedance units. The utility model has the advantages of simple structure, low cost, small size, wide operating frequency band, low insertion loss, low return loss and high isolation, and is convenient for making and integrating microwave and millimeter wave circuits.

Description

A Broadband Balun Based on Left and Right Handed Composite Transmission Lines

technical field

The utility model relates to a balun, in particular to a broadband balun based on left and right hand composite transmission lines.

Background technique

Balun is a three-port device that can convert unbalanced single-ended signals into balanced differential signals. It is widely used in the feeding system of microwave antennas such as dual-wire antennas and other radio frequency or microwave communications, satellite communications, Wireless communication, cable television.

Balun designs are usually of two types, distributed transmission line and lumped parameter elements. Due to the frequency dependence of the distributed transmission line type balun, its bandwidth is very narrow. If it is to achieve broadband, its structure cannot be compact. The design structure of the lumped parameter element can be made very compact, but it will cause the phase response mismatch of the low-pass and high-pass output lines.

At present, the known baluns are usually Wilkinson structures and T-shaped structures, but due to the linear dispersion relationship of the components used, these baluns have narrow operating frequency bands, low frequencies, complex structures, large sizes, and high manufacturing process requirements. Shortcomings.

Working frequency band, size, mass size, structural complexity, low insertion loss, return loss and high isolation are factors that must be considered in designing a good balun. In order to expand the working frequency band of the balun, reduce the size, and simplify the manufacturing process, many people have proposed some new design methods. For example, a miniaturized Wilkinson structure power divider structure is used, or a differential phase shifter using double left-handed transmission lines, but its bandwidth can only reach 2:1, which has not been greatly improved.

Contents of the invention

The purpose of this utility model is to overcome the shortcomings of existing baluns such as narrow frequency band, complex structure, large size, and high manufacturing process requirements, and provide a wide working frequency band, low insertion loss, high isolation, and at the same time Low cost, small size, easy to fabricate and integrate broadband balun based on left and right hand composite transmission lines.

The broadband balun based on the left and right hand composite transmission line of the present utility model is characterized in that it includes a Wilkinson power divider and a phase shifter composed of a right hand transmission line and a left and right hand composite transmission line, and an output end of the right hand transmission line and the Wilkinson power divider The left and right hand composite transmission lines are connected to the other output terminal of the Wilkinson power divider. The left and right hand composite transmission lines are connected in series by n left and right hand composite transmission line units, n=1, 2, ... positive integer, each left and right hand composite The transmission line unit is a T-shaped circuit composed of two connected impedance units and an admittance unit connected at the junction of the two impedance units. A capacitor is connected in parallel with a left-handed inductor.

The beneficial effect of the utility model is that: a wide working frequency band can be obtained, low insertion loss, low return loss and high isolation; at the same time, because of the use of capacitance and inductance components, the balun structure of the left and right hand composite transmission line is simple, low in cost and small in size , easy to manufacture and integrate microwave and millimeter wave circuits. Experiments have shown that the utility model has good performance in a wide frequency range, and can increase the bandwidth to 4.37:1, so it can be ideally fed to planar devices that require broadband differential signals, such as printed bow tie antennas or series fed dipoles Feed for the subscan array.

Description of drawings

Figure 1 is a schematic diagram of the composition of a broadband balun based on a left-handed composite transmission line;

Figure 2 is a schematic diagram of a left-handed composite transmission line unit;

Fig. 3 is a schematic diagram of the phase response performance of the broadband balun output port of the present invention; in the figure: 1 is a composite transmission line for left and right hands, and 2 is a transmission line for a right hand;

Fig. 4 is the bandwidth schematic diagram of the stable phase difference of the broadband balun output port of the utility model;

Fig. 5 is a schematic diagram of isolation and straight-through characteristics of each output port of the broadband balun of the present invention; Fig. 6 is a schematic diagram of return loss characteristics of each port of the broadband balun of the present invention.

Detailed ways

Further illustrate the utility model below in conjunction with accompanying drawing.

Referring to Fig. 1, the wideband balun based on left-hand composite transmission line of the present utility model includes Wilkinson power divider 1 and a phase shifter composed of right-hand transmission line 2 and left-hand composite transmission line 3, right-hand transmission line 2 and Wilkinson power divider One output end of device 1 is connected, left and right hand composite transmission line 3 is connected with the other output end of Wilkinson power splitter 1, said left and right hand composite transmission line 3 is formed by series connection of n left and right hand composite transmission line units, n=1,2 , ...a positive integer, as shown in Figure 2, each left-handed composite transmission line unit is a T-shaped circuit composed of two connected impedance units Z and an admittance unit Y connected at the junction of the two impedance units, wherein the impedance unit Z is composed of a right-handed inductor _LR and a left-handed capacitor _CL connected in series, and an admittance unit Y is composed of a right-handed capacitor _CR paralleled with a left-handed inductor _LL .

When working, the signal enters from the input end of the Wilkinson power divider and outputs from the two output ends of the phase shifter.

The initial values of capacitances C _R , C _L , inductances L _R , L _L corresponding to the left-handed composite transmission line unit can be obtained by the following formula:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{\mathrm{<span\; class="notranslate">\; \&phi;PRH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;CRLH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}$

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&phi;PRH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;CRLH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}$

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&phi;PRH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&phi;CRLH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}$

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&phi;PRH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&phi;CRLH</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}$

Among them, φ _{PRH, S} , φ _{CRLH, S} are the phase shifts of the right-handed transmission line and the left-handed composite transmission line at the central operating frequency ω _s , N is the number of cascaded units of the left-handed composite transmission line, Z ₀ is the characteristic impedance of the transmission line. The final parameters can be obtained by optimizing the initial parameter values of the components after simulation by using the Agilent design system, and a balun with a fixed port phase difference in a wide frequency band can be designed.

Design example of broadband balun based on left-handed composite transmission line: Design a broadband balun with a center frequency of 1.5GHz and a stable phase difference (180°±10°) in the frequency band from 0.63GHz to 2.75GHz. The absolute bandwidth of the balun It is 2.12GHz, and the frequency ratio bandwidth is 4.37:1. The structure shown in Fig. 1 is used to implement, wherein the number of left and right hand composite transmission cascade units is selected as N=10, the central operating frequency is ω _S =2π*1.5GHz, and the characteristic impedance of the transmission line is Z ₀ =50Ω. Calculate the initial value of the components according to the above-mentioned set of formulas and use the Agilent design system to simulate and optimize the final results: C _R ＝1.82pF, _LR ＝2.28nH, _LL ＝54.49nH, C _L ＝43.60pF, φ _{PRH, S} = 3.51π. The phase response performance of the broadband balun output port designed with the above parameters is shown in Figure 3 and Figure 4.

Figure 5 shows the isolation and straight-through characteristics of the output port. In the figure: S21 is the transmission coefficient between the input terminal of the Wilkinson power divider and the output terminal of the right-hand transmission line, and S31 is the input terminal of the Wilkinson power divider and the output terminal of the right-hand transmission line. The transmission coefficient between the output terminals of the left-hand composite transmission line, S23 is the isolation between the output terminal of the left-hand composite transmission line and the output terminal of the right-hand transmission line.

Figure 6 shows the amplitude response of the return loss of the three ports. In the figure: S11 is the reflection coefficient at the input end of the Wilkinson power splitter, S22 is the reflection coefficient at the output end of the right-hand transmission line, and S33 is the reflection at the output end of the left-hand composite transmission line coefficient. It can be seen from Figures 4 to 6 that the balun of this structure achieves a stable phase difference at the output port within a wide bandwidth range, and also has the advantages of low insertion loss, low return loss and high isolation.

Claims (1)

1. A broadband balun based on a left-right-hand composite transmission line is characterized by comprising a Wilkinson power divider (1) and a phase shifter consisting of a right-hand transmission line (2) and a left-right-hand composite transmission line (3), wherein the right-hand transmission line (2) is connected with one output end of the Wilkinson power divider (1), the left-right-hand composite transmission line (3) is connected with the other output end of the Wilkinson power divider (1), the left-right-hand composite transmission line (3) is formed by connecting n left-right-hand composite transmission line units in series, n =1,2, … positive integers, each left-right-hand composite transmission line unit is a T-shaped circuit consisting of two connected impedance units (Z) and an admittance unit (Y) connected at the joint of the two impedance units, and the impedance unit (Z) consists of a right chiral inductor (L) _R ) And a left-handed capacitor (C) _L ) Formed in series, the admittance unit (Y) is composed of a right-handed capacitor (C) _R ) Parallel left hand inductor (L) _L ) And (4) forming.

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