Micropower-oriented high-efficiency dual-frequency omnidirectional circularly polarized radio frequency rectification antenna

Abstract

The invention discloses a micropower-oriented high-efficiency dual-frequency omnidirectional circularly polarized radio frequency rectification antenna. The antenna comprises a receiving antenna unit and a dual-frequency rectification circuit unit which are connected with each other. The receiving antenna adopts a dual-frequency omnidirectional circular polarization design; the double-frequency rectification circuit comprises a diode branch and a load branch which are connected in parallel. The diode branch comprises a coupling microstrip line, a pilot frequency impedance conversion network and a dual-frequency harmonic suppression structure which are connected in sequence; the load branch is formed by connecting a straight-through filter with a load in series. The double-frequency harmonic suppression structure forms a band-stop characteristic at the secondary harmonic of the double working frequency points; the pilot frequency impedance conversion network realizes a double-frequency-point same-input impedance characteristic; the coupling microstrip line enhances the voltage amplitude of the diode so as to improve the rectification efficiency of the circuit under the condition of micro input power. The antenna has good omnidirectivity and circular polarization performance, and can collect dual-frequency, multi-direction and multi-polarization electromagnetic waves; and meanwhile, the rectifier has the advantages of high rectification efficiency, small size and compact structure under a micro-input power condition, and better meets the requirement of collecting weak radio frequency energy in an actual scene.

Description

Technical Field

[0001] This invention belongs to the field of wireless power transmission, specifically relating to a high-efficiency dual-band omnidirectional circularly polarized radio frequency rectifier antenna for low power applications. Background Technology

[0002] With the rapid development of IoT technology, wearable devices, and mobile electronic products, powering the widely deployed and numerous sensor devices has become an urgent problem to be solved. Traditional battery power supply methods face significant limitations due to replacement costs and environmental pollution issues, making wireless power transfer (WPT) technology, which features independent remote power supply, a research hotspot. At the same time, the significant increase in the number of radio frequency sources such as 5G base stations and Wi-Fi networks has enhanced the feasibility of implantable and sustainable radio frequency energy harvesting technologies, thus attracting considerable attention.

[0003] As a core component of microwave energy harvesting systems, rectifier antennas are responsible for converting received microwave energy into DC energy output. A rectifier antenna typically consists of a receiving antenna and a rectifier circuit, and its rectification performance determines the transmission efficiency of the entire system. Radio frequency (RF) energy in the environment is characterized by random frequency band distribution, complex polarization, and low power density. Harvesting microwave energy at only a single frequency or polarization often fails to meet the power supply requirements of sensing devices. While current research has focused on multi-polarization, multi-band RF energy harvesting, the receiving antennas are mostly directional antennas, and design optimizations are concentrated in the higher input power range, resulting in low rectification efficiency under low input power conditions. Existing technologies struggle to achieve efficient omnidirectional, multi-polarization, and multi-band harvesting of weak RF energy in real-world environments. Therefore, this paper proposes a high-efficiency dual-band omnidirectional circularly polarized RF rectifier antenna for low-power applications. Summary of the Invention

[0004] The purpose of this invention is to provide a high-efficiency dual-band omnidirectional circularly polarized radio frequency rectifier antenna for low power, which has high rectification efficiency under low input power conditions and can collect electromagnetic waves of various directions and polarizations within the dual-band. It has good omnidirectional and circular polarization performance and can collect weak radio frequency energy in the environment to power sensing devices.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention includes a receiving antenna unit and a dual-frequency rectifier circuit unit that are interconnected; wherein:

[0006] The receiving antenna employs a dual-frequency omnidirectional circular polarization design; the dual-frequency rectifier circuit includes a parallel diode branch and a load branch. The diode branch comprises a coupled microstrip line, an impedance transformation network, and a dual-frequency harmonic suppression structure connected in sequence; the load branch consists of a through-filter connected in series with a load. The dual-frequency harmonic suppression structure creates band-stop characteristics at the second harmonic of both operating frequencies; the impedance transformation network achieves the same input impedance characteristics at both frequencies; the coupled microstrip line enhances the diode voltage amplitude to improve the circuit's rectification efficiency under low input power conditions.

[0007] The antenna unit includes a top metal patch and a ring-shaped parasitic patch, an intermediate dielectric substrate, and a bottom metal ground; wherein the circular top metal patch, the bottom metal ground, and the dielectric substrate are based on the same center.

[0008] Preferably, the top patch and the bottom metal ground are connected through four metal vias on the dielectric substrate, and the bottom metal ground is loaded with four bent annular stubs to achieve omnidirectional circular polarization characteristics at low frequencies.

[0009] Preferably, a coupled-fed oscillator structure with bending loading is adopted, and eight parasitic ring oscillator units are evenly distributed around the top layer patch. The ends of the ring oscillators are connected to the bottom metal ground through metal vias, and the patch parameters are adjusted to achieve omnidirectional circular polarization characteristics at high frequency.

[0010] In the dual-frequency rectifier circuit unit, the dual-frequency harmonic suppression structure adopts a composite structure of diode cathode connected in parallel with a low-frequency point one-eighth wavelength open-circuit microstrip line and anode connected in series with a high-frequency point one-eighth wavelength short-circuit microstrip line, which forms band-stop characteristics for the second harmonics at high and low frequencies, thereby achieving dual-frequency second harmonic suppression.

[0011] Preferably, the heterodyne impedance transformation network consists of a set of low-frequency half-wavelength open-circuit microstrip lines and series microstrip lines. By adjusting the width of the two microstrip lines, the input impedances of the circuit at both frequencies are the same, and both are real numbers.

[0012] Preferably, the series-coupled microstrip line enhances the diode voltage amplitude and reduces diode energy loss to improve rectification efficiency; at the same time, by adjusting the odd-even mode impedance of the coupled microstrip line, the circuit input impedance and source impedance are matched.

[0013] Preferably, the intermediate layer dielectric substrate of the antenna unit is made of F4BM-2 material with a dielectric constant of 2.2 and a loss tangent of 0.001; the dielectric substrate of the dual-frequency rectifier circuit unit is Rogers4003C with a dielectric constant of 3.55, a loss tangent of 0.0034, and a thickness of 0.508mm.

[0014] Preferably, the diode in the dual-frequency rectifier circuit unit is an SMS7630.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The receiving antenna has good omnidirectional and circular polarization characteristics, and can receive electromagnetic waves of various directions and polarizations in the dual frequency band, with higher energy receiving efficiency.

[0017] (2) The dual-frequency rectifier circuit omits the impedance matching network, making the structure more compact and more conducive to miniaturization and integration; and under micro-input power conditions, the rectification efficiency is high, which is more in line with the actual application needs. Attached Figure Description

[0018] Figure 1 This is a side view of the antenna element in an embodiment of the present invention;

[0019] Figure 2 This is a top view of the antenna element in an embodiment of the present invention;

[0020] Figure 3 This is a bottom view of the antenna element in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the topology of the dual-frequency rectifier circuit unit in an embodiment of the present invention;

[0022] Figure 5 This is a schematic diagram of the dual-frequency rectifier circuit structure in an embodiment of the present invention;

[0023] Figure 6 This is a graph of the reflection coefficient |S11| of the receiving antenna in an embodiment of the present invention;

[0024] Figure 7 This is a directional gain diagram of the receiving antenna in an embodiment of the present invention;

[0025] Figure 8 A graph showing the axial ratio of the receiving antenna;

[0026] Figure 9 This is a graph showing the reflection coefficient |S11| of the dual-frequency rectifier circuit in this embodiment of the invention.

[0027] Figure 10 This is a curve showing the rectification efficiency of the dual-frequency rectifier circuit as a function of frequency in an embodiment of the present invention.

[0028] Figure 11 This is a curve showing the rectification efficiency as a function of input power. Detailed Implementation

[0029] To make the objectives and technical solutions of the present invention clearer, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0030] like Figures 1-3As shown, the receiving antenna unit consists of three layers: the upper layer includes a circular radiating patch 1 and a ring-shaped coupling parasitic unit 5; the middle layer is a dielectric substrate 2; and the bottom layer is a metal ground plane 3. The upper radiating patch 1 is connected to the ground plane 3 through four metal through holes 8, and the coupling parasitic unit 5 is connected to the ground plane through conductive through holes 6. The top radiating patch 1, the dielectric substrate 2, and the bottom metal ground plane 3 are all based on the same center, and the feeding method adopts a coaxial probe form, with the coaxial probe 7 located at the center of this concentric circle.

[0031] Furthermore, the antenna unit operates as follows: In the low operating frequency band, the coaxial probe 7 and the metal through-hole 8 generate current in the vertical direction, radiating vertically polarized waves; the annular stubs on the metal ground plate 3 generate annular current on the horizontal plane, producing a horizontally omnidirectional polarized waveform. The two polarized waveforms have a 90-degree phase difference in the far field, forming a horizontally omnidirectional circular polarization characteristic.

[0032] Furthermore, at high operating frequencies, the coupling currents of the top-layer annular parasitic unit 5 are aligned, generating an annular current that radiates a horizontally omnidirectional polarized waveform; a vertical current of the same magnitude is generated in the conductive via 6 connected to the metal ground, radiating a vertically polarized waveform. The two polarized waves are 90 degrees out of phase in the far field, forming a horizontally omnidirectional circularly polarized waveform.

[0033] Based on the above analysis, such as Figure 2 , 3 It can be seen that the radius rt of the radiating patch 1 determines the performance of the antenna in the dual frequency band; the radius r and number of the metal through hole 8, the radius rg of the ground plane 3, the angle qangle and bending angle of the annular stub 4 determine the performance of the antenna in the low operating frequency band; the angle rag, width and end disk diameter rw of the parasitic element 5 have a greater impact on the performance of the antenna in the high operating frequency band.

[0034] Furthermore, the ground plane 4-ring stub reduces the overall size of the antenna while maintaining performance by bending the angle.

[0035] Based on the above analysis, it can be seen that the parameter adjustment of this receiving antenna is independent: adjusting the corresponding parameters of the parasitic element 5 will not significantly affect the low-frequency performance of the antenna; adjusting the radius rg of the ground plane 3 and the relevant angle parameters qangle and angle of the annular stub 4 will not affect the high-frequency performance of the antenna. This antenna has strong flexibility and adjustability.

[0036] like Figure 4 As shown, the dual-frequency rectifier circuit is divided into a parallel diode branch and a load branch. The diode branch consists of a dual-frequency harmonic suppression network 19, a diode 13, a different-frequency impedance transformation network 20, and a coupled microstrip line 14. The load branch includes a filter inductor 15, a filter capacitor 17, and a load 16. Capacitor 18 is a DC blocking capacitor to protect the RF source.

[0037] Furthermore, the dual-frequency harmonic suppression network consists of microstrip line 9 and microstrip line 10. Microstrip line 9 is a λ2 / 8 short-circuit line at the high operating frequency f2, exhibiting open-circuit characteristics at frequency 2f2, thus suppressing the second harmonic of f2; microstrip line 10 is a λ1 / 8 open-circuit line at the low operating frequency f1, exhibiting short-circuit characteristics at frequency 2f1, thus suppressing the second harmonic of f1.

[0038] Furthermore, by calculating the characteristic impedances of microstrip lines 9 and 10, the imaginary part of the impedance of diode 13 at both operating frequencies is compensated while suppressing the second harmonic of the dual-frequency circuit. This ensures that the overall input impedance is real, facilitating impedance matching. The characteristic impedance calculation formula is as follows:

[0039]

[0040] Where X D1 and X D2 Let f1 and f2 represent the imaginary parts of the diode input impedance under frequencies f1 and f2, respectively. The characteristic impedances Z1 and Z2 of microstrip lines 9 and 10 that meet the conditions are calculated using Matlab software.

[0041] Furthermore, the impedance transformation network consists of microstrip line 11 and microstrip line 12 connected in parallel. Microstrip line 11 is an open-circuit line with a λ1 / 2 of the low operating frequency f1, and microstrip line 12 is a series-connected microstrip line with a λ1 / 2 of f1. As mentioned above, the addition of the dual-frequency harmonic suppression network ensures that the input impedance of the diode branch is real under dual-frequency conditions; therefore, by adjusting the characteristic impedances of microstrip lines 11 and 12, the same input impedance characteristic of the diode branch at both frequencies can be achieved. The characteristic impedance calculation formula is as follows:

[0042]

[0043] in, and Let f2 and f1 represent the input impedances of branches respectively, and k = f2 / f1. The calculation satisfies... The characteristic impedances Z3 and Z4 of microstrip lines 11 and 12.

[0044] Furthermore, the series-coupled microstrip line 14 can increase the voltage amplitude across the diode, thereby reducing energy loss caused by the diode not conducting under low input power conditions and improving rectification efficiency.

[0045] This invention designs the diode branch and the load branch in parallel, and the load branch includes a filter capacitor 17 and a filter inductor 15, ensuring that this branch maintains a high impedance state for any non-DC frequency. Therefore, the rectifier circuit in this invention only needs to achieve impedance matching between the diode branch and the source impedance. This greatly reduces the complexity and difficulty of impedance matching.

[0046] As analyzed above, the diode branch, after being transformed by the harmonic suppression network 19 and the impedance transformation network 20, exhibits the same real impedance characteristics at both operating frequencies. By adjusting the odd-mode and even-mode impedance values ​​of the coupled microstrip line 14, it is possible to increase the diode voltage amplitude while matching it with the source impedance.

[0047] The ABCD matrix of the coupled microstrip line is:

[0048]

[0049] Among them, Z e0 Z o0 Let represent the even-mode impedance and the odd-mode impedance, respectively, and θ be the electrical length of the microstrip line. To achieve impedance matching, the input impedance of the series-coupled microstrip line 14 circuit must satisfy the following:

[0050]

[0051] Where Z1 is the branch input impedance value of the microstrip line 14 without series coupling. By combining the above formulas, the even-mode impedance Z that satisfies the impedance matching condition can be obtained. e0 and odd-mode impedance Z o0 .

[0052] In an embodiment of the present invention, the antenna dielectric substrate is selected from F4BM-2 material with a dielectric constant of 2.2. The radiating patch 1 has a radius rt = 23 mm, a metal through-hole radius r = 0.5 mm, a ground plane radius rg = 30 mm, an annular stub 4 has an angle qangle = 84 degrees, and a turning angle angle = 22.5 degrees. The parasitic patch 5 has an angle rag = 31.4 degrees, a width width = 2.5 mm, and an end disk diameter rw = 4 mm.

[0053] The rectifier circuit substrate is Rogers4003C, with a dielectric constant of 3.55, a loss tangent of 0.0034, and a thickness of 0.508mm; the diodes are SMS7630-079LF; capacitors 17 and 18 are both 10pF; and inductor 15 is 10nH; microstrip line 9 has a length of 16.94mm and a width of 2.42mm; microstrip line 10 has a length of 0.2mm and a width of 9.22mm; microstrip line 11 has a length of 0.2mm and a width of 21.84mm; microstrip line 12 has a length of 19.67mm and a width of 2.17mm; and the coupling microstrip line has an odd-mode width of 1.41mm, an even-mode width of 0.2mm, and a length of 19.73mm.

[0054] like Figure 6As shown, the receiving antenna reflection coefficient |S11| is less than -10dB in the 2.44–2.47 GHz and 3.49–3.51 GHz frequency bands, and exhibits good impedance matching characteristics at both operating frequencies of 2.45 GHz and 3.5 GHz.

[0055] like Figure 7 As shown, at the two operating frequencies of 2.45 GHz and 3.5 GHz, the H-plane radiation pattern of the receiving antenna is circular, and the E-plane radiation pattern is figure-eight shaped, exhibiting good horizontal omnidirectional radiation characteristics. Meanwhile, as... Figure 8 As shown, the antenna axial ratio is less than 3dB at both 2.45GHz and 3.5GHz, meeting the requirements for circular polarization radiation. Therefore, this receiving antenna is a dual-frequency horizontal omnidirectional circularly polarized antenna, capable of receiving dual-frequency electromagnetic waves in all directions and with various polarizations.

[0056] like Figure 9 As shown, the reflection coefficient |S11| of the dual-frequency rectifier circuit is much less than -10dB at both the 2.45GHz and 3.5GHz operating frequencies, and the circuit exhibits good dual-frequency impedance matching characteristics.

[0057] like Figure 10 As shown, this dual-frequency rectifier circuit achieves rectification efficiencies of 52.2% and 49.5% at 2.45GHz and 3.5GHz respectively, with an input power of only -10dBm, demonstrating excellent low-input, high-efficiency characteristics; Figure 11 It can be seen that the circuit does not require an additional impedance compression network structure, and can still maintain a rectification efficiency of over 50% in the 10dB dynamic input power range at both frequency points, demonstrating good wide input power adaptability.

[0058] This invention presents a high-efficiency dual-band omnidirectional circularly polarized radio frequency rectifier antenna designed for low-power applications. The receiving antenna exhibits excellent omnidirectional and circular polarization characteristics. The dual-band rectifier circuit achieves high rectification efficiency under low input power conditions and eliminates the need for an impedance matching network, resulting in a simpler and more compact structure. The overall size of the rectifier antenna is small, meeting the requirements for miniaturization and integration, and is more suitable for collecting weak radio frequency signals in practical scenarios.

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited thereto. Any changes, modifications, combinations, simplifications, etc., made without departing from the spirit and principle of the present invention are equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power applications, characterized in that, It includes interconnected receiving antenna units and dual-frequency rectifier circuit units. Among them: The receiving antenna employs a dual-frequency omnidirectional circular polarization design; the dual-frequency rectifier circuit includes a parallel diode branch and a load branch. The diode branch comprises a coupled microstrip line, an impedance transformation network, and a dual-frequency harmonic suppression structure connected in sequence; the load branch consists of a through-filter connected in series with a load. The dual-frequency harmonic suppression structure creates band-stop characteristics at the second harmonic of both operating frequencies; the impedance transformation network achieves the same input impedance characteristics at both frequencies; the coupled microstrip line enhances the diode voltage amplitude to improve the circuit's rectification efficiency under low input power conditions.

2. The high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 1, characterized in that, The antenna unit includes a top metal patch and a ring-shaped parasitic patch, an intermediate dielectric substrate, and a bottom metal ground. The circular top layer patch, bottom metal ground, and dielectric substrate are all based on the same center point.

3. The high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 2, characterized in that, The top patch of the antenna unit is connected to the bottom metal ground through four metal vias on the dielectric substrate, and the bottom metal ground is loaded with four bent annular stubs to achieve omnidirectional circular polarization characteristics at low frequencies.

4. A high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 2, characterized in that, The antenna unit adopts a coupled feed oscillator structure with bending loading. Eight parasitic ring oscillator units are evenly distributed around the top layer patch. The ends of the ring oscillators are connected to the bottom metal ground through metal vias. The patch parameters are adjusted to achieve omnidirectional circular polarization characteristics at high frequencies.

5. A high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 1, characterized in that, In the dual-frequency rectifier circuit unit, the dual-frequency harmonic suppression structure adopts a composite structure of diode cathode connected in parallel with a low-frequency point one-eighth wavelength open-circuit microstrip line and anode connected in series with a high-frequency point one-eighth wavelength short-circuit microstrip line, which forms band-stop characteristics for the second harmonics at high and low frequencies, thereby achieving dual-frequency second harmonic suppression.

6. A high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 1, characterized in that, In the dual-frequency rectifier circuit unit, the heterodyne impedance transformation network consists of a set of low-frequency half-wavelength open-circuit microstrip lines and series microstrip lines. By adjusting the width of the two microstrip lines, the input impedances of the circuit at both frequencies are the same, and both are real numbers.

7. A high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 1, characterized in that, In the dual-frequency rectifier circuit unit, the series-coupled microstrip line enhances the diode voltage amplitude and reduces diode energy loss to improve rectification efficiency; at the same time, by adjusting the odd-even mode impedance of the coupled microstrip line, the circuit input impedance and source impedance are matched.

8. A high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 1, characterized in that, The intermediate layer dielectric substrate of the antenna unit is made of F4BM-2 material with a dielectric constant of 2.2 and a loss tangent of 0.001; the dielectric substrate of the dual-frequency rectifier circuit unit is Rogers4003C with a dielectric constant of 3.55, a loss tangent of 0.0034, and a thickness of 0.508mm.

9. A high-efficiency dual-band omnidirectional circularly polarized radio frequency rectified antenna for low power as described in claim 1, characterized in that, The diode in the dual-frequency rectifier circuit unit is SMS7630.

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