CN101447604B - Built-in antenna for digital video broadcast-handheld mobile terminal based on variable-capacitance matching circuit - Google Patents

Abstract

A reconfigurable built-in antenna for a matching network of a digital TV broadcasting mobile terminal belongs to the field of antenna design, and is characterized in that a variable capacitance diode is added to the matching circuit printed on the front side of a printed circuit board, and by continuously changing the variable capacitance diode Capacitance value, and then continuously change the matching state of the antenna to adjust the antenna frequency and cover the required frequency band; add a series inductor to reduce the maximum bias voltage required by the varactor diode. The invention has the advantages of multi-frequency band, wide band, miniaturization, easy integration and flexible control, and is suitable for built-in antennas of various small mobile terminals represented by digital TV broadcasting services.

Description

Built-in Antenna of Digital TV Broadcasting Mobile Terminal Based on Variable Capacitance Matching Circuit

technical field

The invention relates to a reconfigurable antenna system design for a matching circuit of a digital TV broadcasting mobile terminal, belonging to the antenna design field of wireless communication technology. the

Background technique

Digital Video Broadcasting (DVB-H, Digital Video Broadcast-Handheld) is a transmission standard developed in recent years to provide multimedia services to handheld terminals through terrestrial digital broadcasting networks. DVB-H terminals have lower power consumption , Mobile reception has strong anti-interference performance, so this standard is suitable for small portable devices such as mobile phones, GPS receivers, and handheld computers to receive digital TV signals through terrestrial digital TV broadcasting networks without occupying precious frequency band resources in mobile communication networks. In recent years, as small mobile devices have become smaller in size, their functions have become more powerful. How to implement mobile digital TV service on small mobile devices has become a new research focus. the

For the existing technology, it is difficult to package the passive components represented by the antenna in a small volume, because the antenna needs the necessary space to ensure good performance, how to solve this problem depends on whether the mobile terminal can achieve The key to miniaturization is mainly manifested in the following aspects: First, for the working frequency band of DVB-H 470-770MHz, the wavelength of free space needs to be at least 64cm. For traditional antennas, it is necessary to ensure normal working conditions in small devices is impossible. Second, the bandwidth of the traditional antenna is generally about 10%, but for the bandwidth of DVB-H 470-770MHz (48.4%), how to increase the bandwidth of the antenna is a great challenge. In response to these requirements, miniaturization, broadband, easy integration, and low cost are the development directions of digital TV broadcasting mobile terminal antennas. A reconfigurable antenna is one of the ideal solutions. the

The reconfigurable antenna adjusts relevant parameters such as frequency and polarization in real time by changing the physical structure of the antenna itself, such as length, width, position, etc., or changing the electrical characteristics of the antenna itself, such as inductive, capacitive, etc., and maintain or Improve the performance of the original antenna. For DVB-H applications, the traditional built-in antenna has a narrow working bandwidth due to volume limitations. Through reconfiguration, the antenna can achieve good performance in different working states, and then combine these working states to meet the high performance and miniaturization requirements of the antenna. At present, there are many studies on reconfigurable antennas, and a commonly used solution is to realize reconfiguration by switching states. For example, use the switch to control the length of the antenna slot or the arm length of the dipole antenna, control the position of the short-circuit point of the antenna, control the position of the antenna feed point to control the path of the surface current, etc.; another common solution is to use a variable Capacitor diodes are used to achieve reconfiguration, for example, using varactor diodes to change the electrical characteristics of the antenna element loading. The above various schemes have great breakthroughs in reducing the size of the antenna and improving the performance, but for the application of DVB-H services, either the size of the antenna is large, or the bandwidth of the antenna is narrow, which is difficult to meet the requirements of DVB-H. -H terminal built-in antenna requirements. Therefore, if a reconfigurable antenna that is wideband (working frequency band covers at least 470-770MHz), miniaturized, easy to integrate, and applicable to DVB-H terminals can be designed, it will not only meet the needs of the development of digital TV broadcasting services, but also make this This antenna design method is applied to small devices with various frequency band requirements to promote the development of new services in wireless mobile communications in the future.

Contents of the invention

The object of the present invention is to provide a structural design of a built-in antenna for a digital TV broadcasting mobile terminal that realizes multi-band/broadband, miniaturization, easy integration, and flexible design. It overcomes the shortcomings of the existing reconfigurable antenna structure and performance, through continuous adjustment of the capacitance in the antenna matching network, the antenna can match any working state in the required frequency band, and achieve the purpose of greatly expanding the antenna bandwidth; Through the joint design of the antenna unit and the metal ground (as the metal shell of the device) structure, the size of the antenna is minimized, making the antenna easy to integrate in the device; using a simple printed circuit board (PCB, printed circuit board) Design the matching circuit, change the parameters of the lumped components in the circuit according to different sizes and bandwidths, without changing the design of the antenna unit, and improve the flexibility of the design. the

The present invention is characterized in that it contains a metal ground, a feeder, an antenna unit, a printed circuit board and a matching circuit, wherein:

A metal ground is connected to the back of the printed circuit board, and at the same time, the metal ground provides grounding for the matching circuit;

The feeder adopts a coaxial cable with an impedance of 50 ohms, the outer conductor of the feeder is connected to one side of the metal ground, and the inner conductor of the feeder is connected to the printed circuit board;

The antenna unit adopts the structure of a serpentine line and is folded into three planes: upper, middle and lower in space. One wide side of the middle plane is vertically connected with the wide side of the upper plane, and the other wide side is vertically connected with the wide side of the lower plane. , The lower two planes are in a parallel relationship, and the output end of the antenna unit is connected to the input end of the matching circuit;

The matching circuit is printed on the front side of the printed circuit board, and the matching circuit includes: the first series inductance L1 and the varactor diode Cv used to adjust the resonant frequency of the antenna unit in the inductively matching state, and adjust the inductively The second inductance L2 used for the working bandwidth of the antenna in the matching state, the bypass capacitor Cp, the DC blocking capacitor Cb, and the bias resistor R1 of the varactor diode Cv, wherein:

Varactor diode Cv, the cathode of which is connected to the first series inductor L1, and the anode connected to the inner conductor of the feeder line, since the varactor diode Cv works in reverse bias, the cathode of the varactor diode Cv is connected to the bias resistor R1 Connect the bias power supply VCC, by continuously changing the capacitance of the varactor diode Cv as the matching capacitance of the matching circuit, control the operating frequency of the antenna unit in the inductance-capacitance matching state, so that the antenna unit can be at any frequency achieve a match;

The first series inductance L1, one end is connected to the DC blocking capacitor Cb, and one end is connected to the negative pole of the varactor diode Cv, which is used to adjust the operating frequency of the antenna unit in the inductance-capacitance matching state, and reduce the varactor Variation range of diode Cv bias voltage;

The second inductance L2, one end is connected to the inner conductor of the feeder line, and one end is grounded, and is used to change the working bandwidth of the antenna unit in the state of inductance-capacitance matching;

Bypass capacitor Cp, one end is connected to the bias power supply VCC, and one end is grounded to prevent AC signals from entering the bias power supply;

One end of the DC blocking capacitor Cb is connected to the output end of the antenna unit, and the other end is connected to the first series inductor L1 to prevent DC signals from entering the antenna unit. the

The invention has the advantages of multi-band/broadband, miniaturization, easy integration and flexible design, and is suitable for the design of built-in antennas for various new communication technologies represented by digital TV broadcasting services. the

Description of drawings

Fig. 1 is a three-dimensional diagram of a reconfigurable serpentine antenna system based on varactor matching provided by the present invention. the

FIG. 2 is a view along the direction A of FIG. 1 , that is, a longitudinal sectional view. the

Fig. 3 is a view taken along direction B of Fig. 1 . the

Fig. 4 is a dimensional diagram of an implementation example of a part of the structure of the serpentine antenna unit in Fig. 1, and the units are millimeters (mm). the

FIG. 5 is a dimensional diagram of an implementation example of the structure viewed from the direction A of FIG. 1 , and the units are millimeters (mm). the

Fig. 6 is a dimensional drawing of the B-direction view structure and the implementation example of the matching network circuit board in Fig. 1, and the unit is millimeter (mm). the

FIG. 7 is a schematic diagram of elements of a matching network. the

Fig. 8 is a circuit diagram of an implementation example of a matching network. the

Fig. 9 is the return loss (S11) measurement diagram of the voltage-controlled varactor matching antenna of the implementation example of Fig. 4-Fig. 8, 1 is the curve when VCC=0V, Cv=8.86pF, 2 is VCC=3.92V, Cv=0.78 Curve in pF. the

Detailed ways

The present invention provides a built-in antenna of a mobile terminal for broadband digital television broadcasting, and the specific implementation scheme includes:

A printed circuit board;

The matching circuit, printed on the front of the printed circuit board, includes a series branch, a parallel branch and a bias branch. The series branch connects the feed point to the antenna, the parallel branch connects the antenna to the ground, and the bias branch connects Varactor diode to ground. The matching circuit contains components:

The series inductance L1, located in the series branch, adjusts the resonant frequency of the antenna in the matching state and reduces the variation range of the varactor bias voltage;

The series varactor diode Cv is located in the series branch; adjust the resonant frequency of the antenna under the matching state;

Parallel inductor L2, located in the parallel branch, adjusts the working bandwidth of the antenna in the matching state;

Bypass capacitor Cb, located in the bias branch, is used to ground the AC signal to prevent it from entering the bias power supply;

The DC blocking capacitor Cb, located in the series branch, is used to prevent the DC signal from entering the antenna unit;

The power supply provides the working bias voltage for the varactor diode;

The bias resistor R1, located between the bias power supply and the varactor diode, provides a bias voltage for the varactor diode;

The antenna unit adopts the structure of serpentine line, which is folded into three sides and supported by foam plastic. The length of the serpentine line determines the working frequency of the unreconstructed antenna;

Metal ground, the back of the printed circuit board is welded on the metal ground, which can be regarded as the metal shell of the device, which is equivalent to one arm of the dipole antenna (the antenna unit is equivalent to the other arm), and provides grounding for the matching circuit at the same time;

The feeder adopts a coaxial cable, the inner conductor is connected to the matching circuit for feeding, the outer conductor is grounded, and the characteristic impedance is 50 ohms. the

As shown in FIGS. 1-3 , the antenna system includes a metal ground 1 , a matching circuit board 2 , a feeder 3 and an antenna unit 4 . The metal ground 1 is connected to the back of the circuit board 2, and the front of the circuit board 2 is a printed matching circuit; the connection mode of the feeder 3, the antenna unit 4 and the circuit board 2 is shown in Figure 3, the feeder 3, the inner conductor is connected to the circuit board, The outer conductor is connected to the metal ground; the structure of the antenna unit 4 is shown in Figure 4, which adopts a serpentine line structure and is folded on three planes as shown in the figure; the connection mode of the antenna unit 4, the feeder 3 and each component in the circuit board 2 As shown in 8, it includes the series branch from the antenna to the feed point, the parallel branch from the feed point to the metal ground 1, and the varactor diode Cv bias circuit. The connection order of the series branch is characterized by: antenna unit -> DC blocking capacitor Cb->series inductance L1->variable diode Cv->feed point; the connection sequence characteristics of the parallel branch are: feed point->parallel inductance L2->metal ground; the bias circuit connection sequence characteristics are: power supply VCC-> Bias resistor R1->bypass capacitor Cp->metal ground; where the power supply VCC can be an external power supply or a battery. the

The technical scheme of the present invention is achieved in that the antenna unit adopts the purpose of the serpentine line to place a longer antenna in a smaller space, adjust the length of the antenna to make it work at a suitable frequency (that is, between 470-770MHz) Yes, the dimensions in Figure 4 operate at 650MHz). The capacitance of the varactor diode Cv changes monotonously with the bias voltage, and a matching circuit (as shown in FIG. 7 ) can be obtained for each capacitance value, so that the antenna unit covers a certain frequency band. By choosing the varactor diode Cv reasonably, the matching state of the antenna unit can be changed continuously and cover the whole frequency band (470-770MHz) through the continuous change of Cv. the

The structure is described in detail as follows:

First, the antenna unit is designed according to the volume allocated to the antenna by the mobile terminal. Since the housing (metal ground) of the device is the main body of antenna radiation, the antenna unit and the housing are jointly designed to make it work within a reconfigurable range. The purpose of the shape line is to reduce the volume of the antenna unit as much as possible; secondly, by changing the capacitance in the matching circuit, the working frequency of the antenna unit can be reconfigured, and the continuous change of the antenna matching state can be realized, covering the frequency band of 470-770MHz. Simulation optimization determines the various components needed; finally, the matching network is designed into a PCB. Due to the influence of certain parasitic parameters on the circuit board, the components used in the implementation may be slightly different from the components of the simulation results. The matching network of the present invention can be manufactured by the most common digital circuit PCB manufacturing process. the

In the implementation process of the circuit board, some factors of bias and DC blocking should be considered, so additional components such as bias resistors, DC blocking capacitors, bypass capacitors, etc. are required. In order to minimize the parasitic parameters of the circuit and meet the requirements of antenna miniaturization, the varactor diode is packaged in 0603, and all other components are packaged in 0402. The wiring is as short as possible, and the circuit board area is minimized, as shown in Figure 8. the

The metal ground 1 is supported by a dielectric substrate with a thickness of 1.6mm, and the relative dielectric constant is 4.4 (the common digital circuit board material is FR4, which is the same as the matching circuit board material); the dimensions of other parts are shown in Figure 4-6, and the unit All are in millimeters (mm). the

The test results of the return loss of the antenna made with the dimensions shown in Figure 4-Figure 6 are shown in Figure 9. Figure 9 includes a continuously changing matching state. The role of the important components in the circuit on the antenna matching is as follows:

1. The role of varactor diode Cv

Adjusting the resonant frequency of the antenna in the inductive capacitance matching state, by increasing the capacitance value of Cv, the resonant frequency of the antenna unit can be reduced; reducing the capacitance value of Cv can increase the resonant frequency of the antenna unit;

2. The role of series inductor L1

Adjust the resonant frequency of the antenna in the inductance-capacitance matching state, by increasing the inductance value of L1, the resonant frequency of the antenna unit can be reduced; the resonant frequency of the antenna unit can be increased by reducing the inductance value of L1; Bias voltage range, reducing the required maximum bias voltage;

3. The role of parallel inductor L2

Adjusting the working bandwidth of the antenna in the inductance-capacitance matching state, the correlation between the value of L2 and the working bandwidth is non-monotonic, and there is an optimum point. After the component values deviate from the optimum, the matching condition will deteriorate. the

By optimization, the element values that are suitable for the antenna matching of the implementation example size of the present invention are: L1=15 nanohenry (nH), L2=22 nanohenry (nH), Cv=0.78～8.86 picofarads (pF), DC blocking capacitance Cb is 47 picofarads (pF), bypass capacitor Cp is 100 picofarads (pF), and bias resistor R1 is 2.2 kohms. As shown in Figure 9, the return loss ≤ -10dB can cover the entire 470-770MHz digital TV broadcast frequency band. the

The matching circuit of the present invention can not only be applied in small mobile terminals for digital TV broadcasting, but also can be used for reconstruction of built-in antennas of mobile terminals for other services. The circuit is not limited by the size of the equipment, and can match antennas in different frequency bands , and then toggle with the switch. Therefore, the present invention is very suitable for the broadband and miniaturization design of the built-in internal line of the mobile terminal. the

Claims (1)

1. be used for the reconfigurable built-in aerial of matching network of digital television broadcast mobile terminal, it is characterized in that: contain metal ground, feeder line, antenna element, printed circuit board (PCB) and match circuit, wherein:

Metal ground is connected with the back side of said printed circuit board (PCB), and simultaneously, this metal ground provides ground connection for said match circuit;

Feeder line, the employing impedance is 50 ohm a coaxial cable, and what link to each other with said metal ground one side is the outer conductor of said feeder line, and what link to each other with said printed circuit board (PCB) is the inner wire of said feeder line;

Antenna element; Adopt the structure of serpentine; Spatially be folded into three planes, upper, middle and lower, midplane one broadside and last plane vertical connection of broadside, another broadside is connected with the lower plane broadside is vertical; Upper and lower two planes are parallel relation, and the output of this antenna element links to each other with the input of said match circuit;

Match circuit; Be printed on the front of said printed circuit board (PCB), this match circuit contains: regulate said antenna element resonance frequency is used under the LC property matching status the 1st series inductance (L1) and variable capacitance diode (Cv), regulate the 2nd inductance (L2) that said antenna element bandwidth of operation is used under the said LC property matching status; Shunt capacitance (Cp); Capacitance (Cb), the biasing resistor (R1) of said variable capacitance diode (Cv), wherein:

Variable capacitance diode (Cv); Negative pole links to each other with said the 1st series inductance (L1); The anodal inner wire that connects said feeder line; Because variable capacitance diode (Cv) is operated in reverse bias, said variable capacitance diode (Cv) negative pole connects bias supply (VCC) after connecting biasing resistor (R1), through continuously changing the electric capacity as the variable capacitance diode (Cv) of the matching capacitance of said match circuit; Control the operating frequency of said antenna element under the LC matching status, make said antenna element reach coupling at any frequency place;

The 1st series inductance (L1); One end links to each other with said capacitance (Cb); One end links to each other with said variable capacitance diode (Cv) negative pole, is used to regulate the operating frequency of said antenna element under the LC matching status, dwindles the constant interval of said variable capacitance diode (Cv) bias voltage;

The 2nd inductance (L2), an end links to each other with the inner wire of said feeder line, and an end ground connection is used to change the bandwidth of operation of said antenna element under the LC matching status;

Shunt capacitance (Cp), an end links to each other with said bias supply (VCC), and an end ground connection is used to prevent that AC signal from getting into bias supply;

Capacitance (Cb), an end links to each other with said antenna element output, and an end links to each other with said the 1st series inductance (L1), is used to prevent that direct current signal from getting into antenna element.

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