Rectenna

Abstract

[Problem] To provide a rectenna which can cope with a plurality of operating frequencies, is small-sized, and has a high rectifying efficiency. [Solution] A rectenna having a first operating frequency f1 and a second operating frequency f2 different from each other, the rectenna being characterized in that a first loop antenna A and a second loop antenna B to which a capacitor is connected in series are connected in parallel to the input terminals of a rectifier.

Description

Rectenna

[0001] The present invention relates to a rectenna having multiple operating frequencies.

[0002] A rectenna is a composite device that combines an antenna and a rectifier and has the function of converting received high-frequency power into DC power. With the recent advancement of the Internet of Things (IoT), rectennas have been considered as a means of powering various electronic devices directly or via a charger using radio waves, with the aim of making these devices battery-less.

[0003] The present inventors have previously proposed a rectenna using a loop antenna as a rectenna that operates with very low power (Non-Patent Document 1). This rectenna combines an inductive loop antenna with a rectifier having capacitive impedance, and operates resonantly. However, the rectenna described in the paper is a single-band rectenna designed for one operating frequency. In the field of Wi-Fi routers, for example, multi-band operation using multiple radio wave bands, such as 2.4 GHz and 5.8 GHz, is becoming more common. Therefore, the present inventors investigated a rectenna that can support multiple operating frequencies, leading to the present invention.

[0004] Shinichiro Tsujita, Naoki Sakai, Kenji Itoh, et.al. “920MHz band high sensitive rectenna with a small loop antenna “ 2019 Asia Pacific Microwave Conference

[0005] An object of the present invention is to provide a rectenna that is small in size, has high rectification efficiency, and is compatible with a plurality of operating frequencies.

[0006] The rectenna according to the present invention has two mutually different first operating frequencies f １ and the second operating frequency f ２The rectenna is characterized in that a first loop antenna A and a second loop antenna B, to which a capacitor is connected in series, are connected in parallel to an input terminal of a rectifier. Here, for example, the first loop antenna A and the rectifier have a parallel resonant frequency f ｒ１ and a second loop antenna B having a series resonant frequency f ｒ２ A series resonant circuit is formed, and the parallel resonant frequency f ｒ１ and the series resonance frequency f ｒ２ and the first operating frequency f １ and the second operating frequency f ２ and

[0007] In this invention, a loop antenna is an antenna in which an element made of a conductor such as a lead wire is formed into a loop, and an induced current is generated along the conductor loop by electromagnetic waves. Therefore, the perimeter of the loop is designed to be compatible with the operating frequency by combining with a resonant capacitor and a rectifier with capacitive impedance.

[0008] In the present invention, there are no particular limitations on the arrangement of the multiple loop antennas, but the first loop antenna A and the second loop antenna B may be arranged concentrically, which makes it possible to obtain a rectenna with a more compact layout.

[0009] In the present invention, the first loop antenna A may have a fine tuning capacitor connected in series.

[0010] In the present invention, the rectifier may be a voltage doubler rectifier or a bridge rectifier.

[0011] The rectenna according to the present invention can accommodate multiple operating frequencies, allowing for a greater amount of DC power to be extracted.

[0012] 1 shows a first embodiment of a rectenna according to the present invention. (a) shows a configuration example, and (b) shows an equivalent circuit diagram. The resonance characteristics (f ｒ２ >f ｒ１ ) shows the resonance characteristics (f ｒ２ <fｒ１ ) is shown. Example 2 of the rectenna is shown. Example 3 of the rectenna is shown. (a) shows a configuration example, and (b) shows an equivalent circuit diagram. Example configurations of a rectifier are shown. (a) shows an example where the voltage doubler circuit is a balanced type, and (b) shows an example where it is a bridge type. A specific configuration example of the rectenna of Example 2 is shown. Calculated values ​​of the rectification efficiency of the rectenna of Example 2 are shown. (a) shows frequency characteristics, and (b) shows input / output characteristics. Resonance characteristics of the rectenna according to Example 2 are shown. Resonance characteristics of the first loop antenna A are shown. Resonance characteristics of the second loop antenna B are shown. Radiation characteristics of the rectenna according to Example 2 are shown.

[0013] An example of the configuration of a rectenna according to the present invention will be described below with reference to the drawings, but the present invention is not limited to this example as long as it is configured with a plurality of loop antennas.

[0014] FIG. 1 shows an example of the configuration of a rectenna according to the first embodiment. (a) is a layout diagram, and (b) is an equivalent circuit diagram. Input terminals 13a and 13b of a rectifier 13 are connected in parallel to a first loop antenna A, 11 having a line width W1 and a radius R1, and a second loop antenna B, 12 having a line width W2 and a radius R2 to which capacitors 12a and 12b are connected in series. The equivalent circuit diagram is shown in FIG. 1(b). The capacitor 12a (2C Ｓ２ ), 12b (2C Ｓ２ ) at the resonance frequency f ｒ２ The input capacitance Cr of the rectifier 13 and the first loop antenna A, 11 form a series resonant circuit having a resonant frequency f ｒ１ The rectenna as a whole resonates in parallel at two frequencies, and the output voltage is V ｒｆ The resonance frequency at this time can be calculated from the equivalent circuit diagram shown in FIG.

[0015] First operating frequency f １ , second operating frequency f ２ Then, the relationship is f １ <f ２ and f １ >f ２2 and 3 show the first operating frequency f １ , second operating frequency f ２ and the parallel resonant frequency f of the parallel resonant circuit ｒ１ , the series resonant frequency f of the series resonant circuit ｒ２ The relationship between R ０ indicates the normalized impedance (several kΩ). ｒ２ >f ｒ１ 3 shows the case of f ｒ２ <f ｒ１ The rectenna as a whole operates at the first operating frequency f １ and the second operating frequency f ２ Parallel resonance occurs at

[0016] Example 2 is shown in Figure 4. Example 2 is similar to Example 1, except that the first loop antenna A, 11 and the second loop antenna B, 12 are arranged concentrically. Arranging the two loop antennas concentrically in this way results in a compact layout. In this case, too, the radii (perimeters) and line widths of the two loop antennas are designed to correspond to the two operating frequencies.

[0017] FIG. 5 shows a third embodiment. In the third embodiment, the first loop antenna A, 11 has a resonant frequency f ｒ１ A fine adjustment capacitor 11a (2C Ｓ１ ), 11b (2C Ｓ１ ) is inserted.

[0018] 6 shows an example of the configuration of the rectifier 13 used in this embodiment. (a) shows an example of a balanced voltage doubler circuit, and (b) shows an example of a bridge type. Alternatively, a cross-connect differential pair using CMOS elements as shown in Non-Patent Document 1 may be used.

[0019] Next, a specific design example will be described using the configuration of the rectenna of Example 2. Figure 7 shows this configuration example. For example, a first loop antenna A is formed with a copper pattern on the front surface of a dielectric substrate, and a second loop antenna B is formed with a copper pattern on the back surface. The input terminal of the rectifier is connected to the first loop antenna A on the front surface side, and a capacitor C is formed by the substrate between the first loop antenna A on the front surface side and the second loop antenna B on the back surface side. Ｓ２ The calculated values ​​of the rectification efficiency of the rectenna of Example 2 are shown in FIG. 8. (a) shows the frequency characteristics of the rectification efficiency, and １ ga f １ = Around 2.3 GHz, frequency f ２ ga f ２ It can be seen that the rectification efficiency is high around frequency f = 5.55 GHz. １ =2.3GHz, frequency f ２ 1 shows the input / output characteristics of the rectification characteristics at 5.55 GHz.

[0020] 9 to 11 show the resonance characteristics. FIG. 9 shows the resonance characteristics of the rectenna as a whole, and the frequency f １ =2.3GHz, frequency f ２ = 5.55 GHz, the first resonant frequency f ｒ１ =2.71GHz, second resonance frequency f ｒ２ It can be seen that a frequency of 4.95 GHz appears. The normalized impedance is 2.5 kΩ (frequency range: 2.26 GHz to 6 GHz). Figure 10 shows the resonance characteristics of the first loop antenna A, and Figure 11 shows the resonance characteristics of the second loop antenna B with a capacitor connected in series.

[0021] FIG. 12 shows the radiation characteristics of the antenna in the rectenna of Example 2. １ At frequency f ２ The radiation efficiency is 97%. The radiation gain is about 0 dBi in the Y direction at both frequencies.

[0022] As a rectenna that can support multiple operating frequencies, it can be used in a variety of fields.

[0023] 11 First loop antenna A 12 Second loop antenna B 12a Capacitor 13 Rectifier

Claims

1. First operating frequencies f １ and the second operating frequency f ２ A rectenna having a first loop antenna A and a second loop antenna B having a capacitor connected in series thereto, the rectenna being connected in parallel to an input terminal of a rectifier.

2. The parallel resonance frequency f of the first loop antenna A and the rectifier ｒ１ and a second loop antenna B having a series resonant frequency f ｒ２ A series resonant circuit is formed, and the parallel resonant frequency f ｒ１ and the series resonance frequency f ｒ２ and the first operating frequency f １ and the second operating frequency f ２ 2. The rectenna according to claim 1, further comprising:

3. A rectenna according to claim 2, wherein the first loop antenna A and the second loop antenna B are arranged concentrically.

4. A rectenna according to claim 2, wherein said first loop antenna A has a fine tuning capacitance connected in series.

5. A rectenna according to any one of claims 1 to 4, wherein the rectifier is a voltage doubler rectifier or a bridge rectifier.

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