ANTENNA ARRAY SYSTEM FOR MONITORING VITAL SIGNS OF PEOPLE

Abstract

A patch antenna array system for monitoring vital signs of people in a closed environment, the patch antenna array system including three patches, the farfield pattern of which is shaped in the E-plane by series-feeding and in the H-plane by parallel-feeding to attain a heart-shaped pattern compensating free-space losses due to larger distances.

Claims

1. A radar antenna array system for monitoring vital signs of people in a closed environment, the system comprising at least one of: an array of three-by-one patches configured to shape the farfield pattern in the E-plane by series-feeding or parallel-feeding, an array of one-by-three patches configured to shape the farfield pattern in the H-plane by parallel-feeding or series-feeding, or an array of three-by-three patches configured to shape the farfield pattern in the E- and the H-plane by parallel-feeding and/or series-feeding, the configuration being such that the resulting antenna pattern comprises two or more maxima in order to enhance the radiation into certain areas of said closed environment such as edge areas or the corner areas of said closed environment.

2. The system of claim 1, wherein the parallel fed patches for shaping the farfield pattern in the H-plane are specified as follows: TABLE-US-00010 Patch i Amplitude A.sub.i Phase [degree] x-Position [mm] Patch 1 1 0 −6.213 Patch 2 2 175 0 Patch 3 1 0 6.213 and/or wherein the series fed patches for shaping the farfield pattern in the E-plane are specified as follows: TABLE-US-00011 Patch i Amplitude A.sub.i Phase [degree] y-Position [mm] Patch 1 1 0 12.426 Patch 2 2 165 6.213 Patch 3 1 0 0.

3. The system of claim 2, wherein the arrays for E- and the H-plane shaping of the farfield pattern are combined into a 3×3 array containing 9 microstrip patch antennas, the resulting farfield pattern, the amplitude and phase shift between each of these patches are specified as follows: a) patch amplitudes as a function of position TABLE-US-00012 Y [mm] X [mm] −6.213 0 6.213 12.426 0.2 0.4 0.2 6.213 0.4 0.8 0.4 0 0.2 0.4 0.2 b) patch phases as a function of position TABLE-US-00013 Y [mm] X [mm] −6.213 0 6.213 12.426 165° 340° 165°  6.213  0° 175° 0° 0 −165°   10° −165°.  

4. The system of claim 1, wherein the transmission coefficients of a series fed patch array of three patches adapted to the given amplitudes are specified as follows (S21 of each single patch): TABLE-US-00014 Antenna Radiation Power S21 [db] S21 [lin.] Patch 1 0.166 none none Patch 2 0.666 −7.99 0.447 Patch 3 0.166 −0.79 0.912 wherein the phase shift between the patches is adjusted by delay lines.

5. The system of claim 4, wherein the spacing between the patches is λ/2=6.213 mm, the length of the patches is around L.sub.p=3.167 to 3.4 mm, with different patch lengths, variable spacings appearing between the patches, wherein a space of 2.838 mm exists between patch 2 and patch 3 and of 2.971 mm between patch 1 and patch 2 which space is used for phase adjustment of the patches.

6. The system of claim 5, wherein the space between patch 2 and patch 3 is adjusted in order to reduce the interference of the feeding with the patch reflection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

[0024] FIG. 1 shows a schematic of an assumed room in a retirement home;

[0025] FIG. 2 shows a single-port microstrip patch antenna with reflection S.sub.11;

[0026] FIG. 3 shows an H- and E-plane simulation standard patch antenna;

[0027] FIG. 4 shows a characteristic pattern of serial and parallel fed arrays of the antenna of FIG. 3;

[0028] FIG. 5 shows an H-plane standard patch, farfield array of the antenna array system of an embodiment of the invention;

[0029] FIG. 6 shows an E-plane standard patch, farfield array of the antenna array system of an embodiment of the invention;

[0030] FIG. 7 shows the total antenna 3D farfield, simulation farfield array of the antenna array system of an embodiment of the invention;

[0031] FIG. 8 shows a second and third patch of the antenna array system;

[0032] FIG. 9 shows a shifted reference plane of a lower patch relative to a subsequent patch;

[0033] FIG. 10 shows the second and third patch of the antenna array system with feeding lines;

[0034] FIG. 11 shows a simulation of S.sub.21 for the middle patch (i=2) of the antenna array system;

[0035] FIG. 12 shows a simulation of S.sub.21 for the third patch (i=3) of the antenna array system;

[0036] FIG. 13 shows a simulation of the farfield in the E-plane for completed antenna array system;

[0037] FIG. 14 shows a simulation of S.sub.11 completed antenna array system;

[0038] FIG. 15 shows a simulation of the farfield in the E-plane for completed antenna array system; and

[0039] FIG. 16 shows a simulation of the 3D farfield completed Line Array antenna array system.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] In FIG. 1 the schematic of an assumed room in a retirement home is shown. The average room size in retirement homes is assumed to be 3 meters in height, 6 meters in length and 4 meters in width. In order to monitor the complete floor area in one direction, a triangle with a base of 6 meters and the height of 3 meters is assumed. In the other direction a triangle with a base of 4 meters is assumed for the radiation pattern. As the sensor will be installed in the middle of the ceiling the triangles are symmetric. Thus, an opening angle for one antenna would be ±45° and for the other ±33.7°. The distance from sensor to the floor right below (direction defined as φ=0° and θ=0°) is 3 m, from sensor to the floor-wall corner (φ=0° and θ=±45°) is 4.25 m and to the other floor-wall corner (φ=90° and θ=±33.7°) is 3.6 m.

[0041] An analysis of the radar equation

[00001]$\begin{array}{cc}{P}_r=P_t.Math.\frac{G_{TX}.Math.G_{RX}.Math.{\lambda }^2.Math.\sigma }{{\left(4\pi \right)}^3.Math.R^4}& \left(1\right)\end{array}$

shows that for targets with constant radar target cross section a the received power at a radar with isotropic radiation (G.sub.TX=G.sub.RX=1∀θ,φ) is factor ¼ lower when located in the 45° corner instead of to be located directly below the sensor. For an angle of 33.7° corner the radiation is about ½ lower. Normally patch antennas radiate their maximum power into broadside direction (φ=0° and θ=0°) thus the receive power of targets below the sensor is much higher compared to targets in the corner.

[0042] The free-space loss due to higher distance at θ=±33.7° is 4 dB, the power reduction of a standard patch antenna under θ=±33.7° for the transmit antenna is approx. 3-4 dB. Thus this antenna needs to have a 8 dB higher gain into φ=90°, θ=±33.7° compared to broadside direction.

P.sub.r(φ=90°,θ=33.7°)=P.sub.r(φ=0°,θ=0°)+8 dB   (2)

[0043] The second antenna needs to realize a 10 dB higher gain into φ=0°, θ=±45°:

P.sub.r(φ=0°,θ=45°)=P.sub.r(φ=0°,θ=0°)+10 dB   (3)

[0044] The modeling of the proposed antenna and network are simulated with CST MICROWAVE STUDIO (S. Müller, R. Thull, M. Huber and A. R. Diewald, “Analysis on microstrip transmission line surface coatings”, 2016 Loughborough Antennas & Propagation Conference (LAPC), Loughborough, 2016, pp. 1-4) in the K-band in the frequency domain of 24 GHz to 24.25 GHz. The antenna design is done for a permittivity of 3.66 which is given in the datasheet of ROGERS and for a permittivity of 3.72 which could be taken from a measurement graph in the datasheet.

[0045] Standard Patch Antenna

[0046] To achieve the radiation pattern in both directions, the radiation power and phase shift of each patch antenna need to be determined. In use of a standard microstrip patch antenna and the CST MICROWAVE tool Farfield Array the desired radiation pattern can be simulated. That happens by interfering the farfield of the standard patch three times with a space shifting of λ/2. For all three patches radiation power and phase shifts can be individually adjusted.

[0047] The standard patch and the return loss is shown in the FIG. 2.

[0048] The return loss values in the whole frequency domain are never more than −10 dB. The farfield is split in E- and H-Plane which results from the view of angle. Thus, the H-Plane describes the front view across the feeding (φ=0°,θ=±π°) and the E-Plane describes the side view (φ=90°,θ=±π°). Both are shown in FIG. 3.

[0049] The H-Plane shows a symmetrical radiation. Based on this radiation the desired farfield pattern resulting from the equation (3) is achieved. The E-Plane is unsymmetrical, which is based on the one-sided patch feeding, though the main lobe angle can, by use of the radiation power and phase shift, be partly compensated.

[0050] In the later build line array this patch will be used as patch Y.sub.1, see FIG. 4. Thus the second and third patch need to be created. Also, this patch will be used as transmitting patch in all three patches of the parallel fed array. The characteristic pattern of both, series and parallel fed arrays are shown below.

[0051] H-Plane Shaping

[0052] Due to the symmetrical radiation of the standard patch H-Plane, a cardioid radiation pattern results according to the equation 3. In use of the farfield tool with adjusting the amplitude and phase shift of three patches, the farfield pattern of FIG. 5 shows promising results with a gain difference of 12 dB.

[0053] The specifications for the parallel fed patches are shown in the table 3.1.

TABLE-US-00005 TABLE 3.1 Specifications H-Plane Patch i Amplitude A.sub.i Phase [degree] x-Position [mm] Patch 1 1 0 −6.213 Patch 2 2 175 0 Patch 3 1 0 6.213

[0054] E-Plane Shaping

[0055] In the E-Plane, these specifications can be transferred. Here a gain difference of 8 dB need to be accomplished. Slightly adjusted, the radiation pattern results in FIG. 6, which shows a gain difference of 10 dB in the direction of (φ=90°,θ=33.7°) and a difference of 9 dB in (φ=90°,θ=−33.7°).

[0056] These gain differences according to equation 2 are up to 3 dB higher which results by reason of the squinting in equation 3. However this is still a sufficient good result, since the main point of a higher gain in certain directions is achieved. The table 3.2 shows the resulting parameters for the series fed patch array.

TABLE-US-00006 TABLE 3.2 Specifications E-Plane Patch i Amplitude A.sub.i Phase [degree] y-Position [mm] Patch 1 1 0 12.426 Patch 2 2 165 6.213 Patch 3 1 0 0

[0057] Complete Array

[0058] If these arrays for E- and H-Plane are combined, a 3×3 array results which contains 9 microstrip patch antennas. To show the resulting farfield pattern, the amplitude and phase shift between each of these patches need to be determined. The tables 3.3 and 3.4 are showing these.

TABLE-US-00007 TABLE 3.3 Patch Amplitudes according to Position Y [mm] X [mm] −6.213 0 6.213 12.426 0.2 0.4 0.2 6.213 0.4 0.8 0.4 0 0.2 0.4 0.2

TABLE-US-00008 TABLE 3.4 Patch Phases according to Position Y [mm] X [mm] −6.213 0 6.213 12.426 165° 340° 165° 6.213  0° 175°  0° 0 −165°   10° −165° 

[0059] These values inserted in the Farfield Array result in a 3D pattern with a higher radiation in the corners as shown in FIG. 7.

[0060] Series Fed Line Array, H-Plane

[0061] To achieve the radiation pattern according to equation 2, a series fed patch array of three microstrip patch antennas is used. Each single patch is designed for low reflection with Γ≈0 at the feeding port (port 1). In the following the balance between radiated power and transmitted power to port 2 is adjusted. The last patch (i=1) with power absorption of 100% is already finished. The amplitude of the middle patch (i=2) is twice the amplitude of the last patch which yields a four times higher power. Thus, the second patch needs to accept the power which is radiated by itself and the power which is transmitted to the last antenna. The following table 4.1 shows the transmission coefficients adapted to the given amplitudes. The phase shift between the patches will be adjusted later by conventional delay lines.

TABLE-US-00009 TABLE 4.1 S21 of Each Single Patch Antenna Radiation Power S21 [db] S21 [lin.] Patch 1 0.166 none none Patch 2 0.666 −7.99 0.447 Patch 3 0.166 −0.79 0.912

[0062] Patch Design, Transmission Adjustment

[0063] The adjustment of the recess length l.sub.1, at the input port has the most effect on the input reflection. The patch width l.sub.p but also the recess width l.sub.2 and recess width w.sub.2 at the output port are influencing the transmission coefficient S.sub.21. Thus, the reflection and the transmission can mostly be controlled independently. First the single patches are created as shown in FIG. 8.

[0064] Feeding Design, Phase Adjustment

[0065] The spacing between the patches is λ/2 which equals 6.213 mm. The length of the patches is around L.sub.p=3.167 up to 3.4 mm. Due to the different patch lengths variable spacings appears between the patches. There is a space of 2.838 mm between patch 2 to patch 3 and of 2.971 mm between patch 1 to patch 2. This space is used for phase adjustment of the several patches. The phase difference corresponding to the specification in table 3.2 is defined from the reference plane of the lower patch which is the patch edge at the ending of the recess to the comparable reference planes of the subsequent patches, shown in FIG. 9. The feeding microstrip lines are designed as short as possible in order to reduce the losses.

[0066] The design of the resulting feeding lines is shown in FIG. 10. Compared to FIG. 8 the recess of the third patch is further adjusted. This occurs by reason of the feeding which interferes with the patch reflection.

[0067] As shown in FIG. 11 the transmissions of both patches depart less than 3% from the specifications of table 4.1. This is a good result, since the transmission loss of the signal lines were not considered in the farfield array tool.

[0068] As shown in FIG. 12 in the third patch a transmission of S21=0.89 and the middle patch of S21=0.46 are achieved which are close to the specifications of 4.1.

[0069] Simulation Line Array

[0070] In FIG. 13 the completed one-dimensional antenna Line Array (LA) is shown which results from the connection of FIG. 2 and FIG. 10.

[0071] The total antenna length is l=15.694 mm and the maximum width is w=6.339 mm. In FIG. 14 the antenna reflection coefficient is shown by simulation. A reflection of less than −15 dB is obtained in the 24 GHz ISM band and the minimal reflection of −24.85 dB is reached at the center frequency of 24.125 GHz.

[0072] The farfield in the E-plane yields a satisfying pattern with a gain difference of more than 8 dB at θ=0° compared to θ=33.7° which is shown in FIG. 15. Due to the microstrip feeding between the single patches and the antenna feeding from the right, the radiation pattern is squinted. Thus, a symmetric farfield of the Line Array is not achieved.

[0073] The total 3D antenna farfield pattern is shown in FIG. 16.