TWI384684B - Dual - frequency miniaturized antenna and its design method - Google Patents

Description

Dual-frequency miniaturized antenna and design method thereof

The present invention relates to an antenna, and more particularly to a dual frequency antenna and a method of designing same.

In the process of continuous growth of the automotive electronics market, the demand for wireless communication for vehicles is increasing, and the future is bound to move toward the coexistence of multiple communication interfaces. The pace of integration has long been urgent. Although it is not difficult to make the digital circuit compact and exquisite in today's mature integrated circuit processing technology, a variety of communication functions can be easily integrated into one machine. However, the necessary antenna integration of the wireless communication system is not easy, and is subject to Limited to the size of the antenna also makes the product difficult to miniaturize, and the car remote control is an example.

The early car anti-theft remote control function was singular, and the antenna only needed to work at a single frequency. It is not too difficult to design the antenna. However, with the development of automotive electronics technology, many functional controls need to be achieved wirelessly. Users must use different remote controllers to perform remote control of different functions (such as wireless key, wireless anti-theft control), which is very inconvenient. . In line with the needs of users, although some integrated remote controllers have been developed, when designing the antennas of these integrated remote controllers, it is often encountered because of the difference in wavelength of the received signals due to antennas suitable for different frequency ranges. Too large, and the different antenna sizes available make design difficult. Moreover, for an antenna that receives long-wavelength (low-frequency, such as 125 kHz) electromagnetic waves, the current practice mainly uses a high-turn precision winding of an enameled wire, and an inductor made of two orthogonally arranged high-magnetic materials to form a three-dimensional X, Y, Z low-frequency magnetic field sensing area, but low-frequency antenna inductor winding precision, production is not easy and time-consuming (costly and complex process), and the low-frequency antenna physical size is also very large. If a low-frequency antenna of 125 kHz is used in combination with a relatively high-frequency antenna (for example, 433 MHz), the design of the dual-frequency antenna module is difficult, because the applicable wavelength sizes of the two are 3,500 times different.

In order to solve the technical problem that the above-mentioned dual-frequency antenna is integrated, because the size of the low-frequency antenna is large and the wavelength of the high-frequency antenna is far away, which leads to difficulty in integrating design, the present invention uses the slow wave effect to achieve the antenna size miniature. The high-frequency and low-frequency antennas of different frequency bands are integrated on the same circuit board to achieve the integration and simplify the technical effect of the design.

The present invention provides a dual-frequency miniaturized antenna including a circuit board and a conductive pattern formed on the surface of the circuit board and isolated from each other and a ground plane. The figure is a wire segment having a plurality of bends and operates at a first frequency, the conductive pattern includes a feed point disposed at a free end of the conductive pattern, the conductive pattern and the ground plane Connected by a capacitor-inductor circuit, the conductive pattern and the ground plane connected to the capacitor-inductor circuit together provide another resonant frequency different from a frequency band to which the first frequency belongs, wherein the resonant frequency and the capacitive-inductor circuit The equivalent reactance value is inversely proportional.

Wherein, the conductive pattern is a spiral line with an odd number of turns, and the feeding point is disposed at a free end of the outer periphery of the spiral, the grounding surface corresponding to the feeding point, and the grounding surface It is a conductive plate larger than the area of the spiral.

Wherein, the spiral can be wound into a rectangle, a circle, a hexagon or other shapes. The present invention is exemplified by a rectangle having a total outer diameter of 30 mm, a total outer diameter of 10 mm, and a line width of A rectangular conductive plate body having a line width of 1 mm and a line width of 1 mm at the center and a size of 40 mm * 30 mm.

The invention further provides a dual frequency miniaturized antenna design method, the steps comprising:

Designing and arranging the first frequency antenna according to an operating frequency of an antenna, wherein at least one high frequency and one low frequency are included, wherein any one of the high frequency or the low frequency is used as a first frequency to calculate Simulating a layout of a conductive pattern and a ground plane, and obtaining an equivalent capacitance inductance value of the first frequency antenna of the conductive pattern according to an analog or measurement result; calculating a resonance frequency antenna compensation value, and calculating an equivalent according to the first frequency a first frequency capacitor inductance value, and calculating a reactance compensation capacitor inductance value by using the first frequency capacitor inductance value and the resonance frequency antenna equivalent capacitance inductance value, and then having a capacitance inductance circuit having the reactance compensation capacitor inductance value The conductive pattern and the ground plane are connected.

Wherein, in the dual frequency miniaturized antenna design method, the layout simulation of the conductive pattern is simulated in the form of a spiral segment.

The invention further provides a computer program product for designing a dual-frequency miniaturized antenna. After the computer is loaded into the computer program and executed, the dual-frequency miniaturized antenna design method can be completed. Therefore, the design method and the program of the antenna provided by the present invention can make the antenna design completely consider the design of the operating frequency requirement of the antenna one by one, first complete the antenna design of the first frequency by the shape and length of the spiral winding, and then Calculating the resonant reactance value of another required resonant frequency by the slow wave theory greatly simplifies the integration difficulty of the dual-frequency antenna design and solves the problem of difficulty in integrating the conventional technology.

Please refer to the first figure, which is a preferred embodiment of the dual frequency miniaturized antenna design method of the present invention. The steps include: designing and arranging the first frequency antenna (10), calculating the resonant frequency antenna compensation value (20), and forming a double Frequency antenna (30); in addition, please refer to the frequency range and wavelength comparison diagram of each frequency band of RF shown in FIG. 8, wherein the preferred embodiment is applied to a Keyless antenna system, and the first frequency is preferably 315 MHz. Or 433MHz, and the corresponding resonant frequency is preferably 135KHz or 125KHz, so the frequency band of the first frequency is preferably UHF, and the frequency band of the resonant frequency is preferably LF, but this is only the present invention. The preferred embodiment is not intended to limit the applicable frequency band range of the first frequency and the resonant frequency.

In the design and layout of the first frequency antenna (10) step, the operating frequency of the antenna is determined according to the requirements of the use scope. The preferred embodiment uses an antenna that needs to operate at two or more operating frequencies. Therefore, the operating frequency of the antenna includes at least a high frequency and a low frequency, wherein the high frequency and the low frequency are preferred. Each belongs to a different frequency band. For example, the antenna designed in the preferred embodiment has an operating frequency of 125 kHz and 433 MHz. For example, the two frequencies belong to the frequency range of LF and UHF, and the wavelength difference is extremely large, so it is suitable for 433 MHz. As the first frequency, in this example, the first frequency is a high frequency, but depending on the design requirements of different antennas, there is also the possibility of setting the first frequency to a low frequency. After the operating frequency is determined, the corresponding wavelength (c=f‧λ ₄₃₃ ) is calculated according to the determined first frequency, and the antenna length (λ ₄₃₃ /4) of the first frequency operation can be inferred.

Referring to the second figure, the antenna can be formed on a circuit board (51) by using micro-wire technology to form a conductive pattern (52) and a ground plane (53). The conductive pattern (52) is usually a spiral wire. The graphic may be a circular, hexagonal or other shape spiral or a rectangular rectangular spiral pattern as shown in the second figure, wherein the conductive pattern (52) includes a feed point (522) disposed on the conductive pattern (52) The free end of the periphery. The ground plane (53) is disposed adjacent to the conductive pattern (52) but is isolated from the conductive pattern (52). Since the actual operating frequency of the antenna and its characteristics (radiation field shape of the antenna, etc.) are related to the layout of the graphic, the winding pattern of the conductive pattern (52) can utilize various computer-aided analog design software (HFSS, Maxwell). ...) Perform the design to ensure that the conductive pattern (52) can operate at the desired operating frequency. As shown in the preferred embodiment, the conductive pattern (52) is a rectangular spiral segment having a plurality of bends, and the dimensions are: total outer diameter 30 mm, total outer diameter 10 mm, line width 0.5 mm, line spacing. 1mm, the center line is 1mm wide. The grounding surface (53) is a rectangular conductive plate body having a size of 40 mm * 30 mm. After the layout is completed, the monopole antenna of the conductive pattern (52) may be separately measured prior to the operating frequency of the conductive pattern (52) to identify the completed conductive pattern (52) as the first frequency antenna. Radiation efficiency, first-frequency antenna equivalent capacitance inductance value (L, c), operating frequency and impedance matching characteristics (such as the third figure).

Please refer to the fourth A and B diagrams. When designing the conductive pattern (52), in addition to changing the characteristics of the antenna by line width, size and spacing, the number of turns of the conductive pattern (52) and odd and even winding The number of lines also affects the performance of the antenna. For example, the fourth A picture (with an odd number of windings) is better than the fourth B picture (with an even number of windings). Current direction). When the radiation pattern of the conductive pattern (52) and the measurement of the operating frequency and characteristics are not good, it can be re-simulated or adjusted for the layout of the winding, such as adjusting the pitch and winding shape (changing to a circle, hexagon) ...etc.), repeat the steps of winding layout, measurement, etc. until the antenna performance requirements are met.

In the step of calculating the resonant frequency antenna compensation value (20), after the conductive pattern (52) is designed, fabricated, and measured to determine the effect thereof, the conductive pattern (52) is calculated by using a slow wave effect. The resonant frequency (such as 125 kHz as described above) generates a resonant frequency capacitive inductance value (L', C') required for resonance (resonance), and according to the resonant frequency capacitive inductance value (L', C') and the first Frequency antenna (10) equivalent capacitance inductance value (L, C), calculate a reactance compensation capacitor inductance value (L _s , C _s ), that is, L _s = L'-L and C _s = C'-C.

The so-called slow wave effect means that the phase velocity (V _p ) of the electromagnetic wave can be reduced by increasing the inductance and capacitance of the antenna resonance. The relationship between the phase velocity and the value of the inductance and capacitance is: Where V _p is the phase velocity, L is the inductance value, and C is the capacitance value. The relationship between phase velocity and wavelength V _p = f λ, where f is the resonant frequency and λ is the wavelength of the resonant frequency, so at the same resonant frequency, reducing the phase velocity reduces the resonant wavelength, which means that the antenna size is greatly Zoom out.

In the step of forming the dual-frequency antenna (30), the foregoing steps are calculated to find that the reactance compensation capacitor inductance (L _s , C _s ) is selected as a capacitive inductance circuit composed of a solid capacitor or an inductor component (in parallel or in series). The method is connected between the feeding point (522) of the conductive pattern (52) and the grounding surface (53), and the equivalent circuit after the connection can be as shown in the fifth figure.

Please refer to the sixth figure, which is a dual-frequency antenna design flow for designing a vehicle anti-theft and keyless remote control system with an operating frequency of 125 kHz and 433 MHz. The reflection loss (S11) of the dual-frequency antenna is as follows. As shown in the figure, it can be confirmed that the dual-frequency antenna with good effect can be completed according to the preferred embodiment.

The sixth figure is a preferred design example according to the design flow of the first figure. In this example, the high frequency 433.92 MHz is selected as the first frequency, and the appropriate antenna length is calculated to be about 173 mm, and then the space size is A spiral-shaped first frequency antenna is wound around an area of 30 mm*10 mm, and the equivalent capacitance inductance value of the first frequency antenna is completed by using a Smith Chart measurement function of a network analyzer (NA) (L=a, C=b) After measuring and confirming that the performance of the first frequency antenna meets the demand, the slow wave effect is used to calculate another low frequency resonance frequency of 124.97 KHz, and the best reactance compensation value can be obtained after calculation (Ls=L'-L= 4.9-a, Cs=C'-C=331-b), finally, the compensation reactance and the first frequency antenna are connected to the ground plane according to the selected optimal feed point position, and the design of the dual-frequency miniaturized antenna is completed.

Further, in the step of forming the dual-frequency antenna (30), if the result of the actual measurement is not as expected, the method may be returned to the step (10) to re-simulate or change the conductive pattern (52) and the ground plane (53). Size, positional relationship.

(51). . . Circuit board

(52). . . Conductive pattern

(522). . . Feeding point

(53). . . Ground plane

The first figure is a flow chart of a preferred embodiment of the present invention.

The second figure is a schematic diagram of a conductive pattern and a ground plane in accordance with a preferred embodiment of the present invention.

The third figure is an impedance matching characteristic diagram of a conductive pattern according to a preferred embodiment of the present invention.

4A and B are schematic diagrams of currents of a conductive pattern in accordance with a preferred embodiment of the present invention.

Figure 5 is an equivalent circuit diagram of a dual band antenna according to a preferred embodiment of the present invention.

The sixth figure is an example of the design flow of the dual-frequency antenna according to the preferred embodiment of the present invention.

FIG. 7 is a schematic diagram of measurement of reflection loss of a dual-frequency antenna according to a preferred embodiment of the present invention.

The eighth figure shows the frequency range and wavelength correspondence chart included in each RF band.

Claims (14)

A dual-frequency miniaturized antenna includes a circuit board and a conductive pattern formed on the surface of the circuit board and isolated from each other, and a ground plane. The conductive pattern is a wire segment having a plurality of bends and operates at a first a frequency, the conductive pattern includes a feed point, the feed point is disposed at one of the free ends of the conductive pattern, and the conductive pattern and the ground plane are connected by a capacitor-inductive circuit, and the conductive after the capacitor-inductor circuit is connected The pattern and the ground plane jointly calculate another resonant frequency different from the first frequency by a slow wave effect, wherein the resonant frequency is inversely proportional to the equivalent reactance value of the capacitive inductive circuit. The dual-frequency miniaturized antenna according to claim 1, wherein the conductive pattern is a helical one of an odd number of turns, and the feeding point is disposed at a free end of the spiral, and the grounding surface is located. Corresponding to the feeding point, and the grounding surface is a conductive plate larger than the spiral area. The dual-frequency miniaturized antenna of claim 1, wherein the spiral can be wound into any one of a rectangle, a circle, or a hexagon. The dual frequency miniaturized antenna of claim 1, wherein the first frequency is different from a frequency band to which the resonant frequency belongs. The dual-frequency miniaturized antenna according to claim 4, wherein the frequency band to which the first frequency belongs is UHF, and the frequency band to which the resonant frequency belongs is LF. The dual frequency miniaturized antenna of claim 5, wherein the first frequency is 315 MHz or 433 MHz, and the corresponding resonant frequency is 135 KHz or 125 KHz. The dual-frequency miniaturized antenna according to claim 2, wherein the rectangular spiral has a total outer diameter of 30 mm, a total outer diameter of 10 mm, a line width of 0.5 mm, a line spacing of 1 mm, and a central line segment. The line width is 1 mm, and the size of the ground plane is a rectangular conductive plate body of 40 mm * 30 mm. A dual-frequency miniaturized antenna design method, the method comprising: designing and arranging a first frequency antenna, calculating a conductive pattern and a ground plane layout simulation according to a first frequency required by an antenna, and according to the simulation or measurement result Obtaining an equivalent capacitance inductance value of the first frequency antenna of the conductive pattern; calculating a resonance frequency antenna compensation value according to a resonance frequency required by the antenna, and calculating a corresponding resonance frequency capacitance inductance value by a slow wave effect And calculating, by the resonant frequency capacitor inductance value and the first frequency antenna equivalent capacitance inductance value, a reactance compensation capacitor inductance value, wherein the inductance and capacitance circuit having the reactance compensation capacitor inductance value is connected to the conductive pattern and the ground plane. For example, in the dual-frequency miniaturized antenna design method described in claim 8, the layout simulation of the conductive pattern is simulated in the form of a spiral segment. The dual-frequency miniaturized antenna design method according to claim 9, wherein the conductive pattern is wound into any one of a rectangle, a circle or a hexagon. The dual frequency miniaturized antenna design method according to claim 8, wherein the first frequency is different from the frequency band to which the resonant frequency belongs. The method for designing a dual-frequency miniaturized antenna according to claim 11, wherein the frequency band to which the first frequency belongs is UHF, and the frequency band to which the resonant frequency belongs is LF. The dual frequency miniaturized antenna design method according to claim 12, wherein the first frequency system is 315 MHz or 433 MHz, and the corresponding resonant frequency is 135 KHz or 125 KHz. A computer program product for designing a dual-band miniaturized antenna. When the computer is loaded into the computer program and executed, the method of claim 8 can be completed.