CN106205184A - Parking space detector - Google Patents

Abstract

A parking space detector is used to detect whether a parking space is occupied, and includes a modulation module for providing a sine wave with a modulation frequency; an active antenna module for transmitting a frequency modulated continuous wave signal according to the modulation frequency and receiving the reflected frequency modulated continuous wave signal; a first intermediate frequency filter for extracting a first demodulated signal from the frequency modulated continuous wave signal, the first demodulated signal having a modulation frequency; a second intermediate frequency filter for extracting a second demodulated signal from the first demodulated signal, the frequency of the second demodulated signal being a predetermined multiple of the modulation frequency; an integrator for integrating the second demodulated signal to output an integrated voltage; a trigger circuit for outputting a trigger signal when the integrated voltage is greater than a reference voltage; and a controller for managing the presence of a vehicle in the parking space when receiving the trigger signal.

Description

parking spot detector

technical field

The invention relates to a microwave detector, in particular to a detector that uses frequency-modulated continuous waves to detect parking spaces.

Background technique

At present, the design of indoor parking space detectors mostly uses infrared rays as their sensing devices. For example, as shown in Taiwan Patent Publication No. I333636, it judges whether the parking space has been occupied by using the principle of whether the infrared sending and receiving light is blocked by the reflecting component. Please refer to FIG. 9 . FIG. 9 shows a schematic diagram of detecting parking spaces in the prior art. If the parking space is empty, the infrared rays emitted by the light emitting unit 12 are sent to the reflecting component 14 and then reflected back to the light sensing unit 16 . Conversely, if the parking space is occupied, an object blocks between the light emitting unit 12 and the reflective assembly 14, so the infrared rays are blocked and cannot be emitted by the light emitting unit 12 to the reflective assembly 14, so the light sensing unit 16 cannot detect to any infrared light reflected back.

However, existing sensing devices use infrared sensors for sensing, and the infrared sensors are generally suitable for indoor parking space management systems. Because a fixed distance must be maintained between the light emitting unit 12 and the light sensing unit 16 and the reflection assembly 14, in the indoor parking lot, the light emitting unit 12 and the light sensing unit 16 are usually installed on the steel frame on the ceiling. Or elevated installations such as hydroelectric steel pipes in the basement. Therefore, the current use of infrared sensors as parking space detectors is a limitation of its application due to the requirements of erection and the installation of angles.

Also, to use infrared sensors for outdoor parking spaces, additional overhead installations are required. Moreover, weather factors, such as rain or heavy fog, or environmental factors, such as dust or mud, will affect the sensing effect of infrared rays.

Therefore, how to provide a parking space detector that is not disturbed by weather or environmental factors no matter it is located indoors or outdoors has become a very important issue.

Contents of the invention

The object of the present invention is to provide a microwave detector as a parking space detector. No matter whether the microwave detector is located indoors or outdoors, it is not affected by weather or environmental factors. At the same time, the parking space detector can provide an accurate sensing method for judging whether there is still an empty parking space.

The present invention provides a parking space detector, which is used to detect whether a parking space is occupied. The parking space detector includes: a modulation module, which is used to provide a sine wave with a modulation frequency; an active Antenna module, electrically connected to the modulation module, used to transmit a first FM continuous wave signal according to the modulation frequency, and receive a reflected second FM continuous wave signal; a first intermediate frequency filter, electrically connected to The active antenna module is used to extract a first demodulated signal from the second frequency-modulated continuous wave signal, and the first demodulated signal has the modulated frequency; a second intermediate frequency filter is electrically connected to the first demodulated signal An intermediate frequency filter is used to extract a second demodulated signal from the first demodulated signal, the second demodulated signal has a trigger frequency, and the trigger frequency is a predetermined multiple of the modulation frequency; an integrator, electrically Connected to the second intermediate frequency filter, used to integrate the second demodulated signal to output an integrated voltage; a trigger circuit, electrically connected to the integrator, used to act as the integrated voltage of the second demodulated signal When the voltage is greater than a reference voltage, a trigger signal is output; and a controller, electrically connected to the trigger circuit, is used to perform the operation of vehicles existing in the parking space when receiving the trigger signal.

According to an embodiment of the present invention, the active antenna module includes: a loop antenna, which includes a transmitting end and a receiving end, the transmitting end is used to transmit the first FM continuous wave signal, and the receiving end is used to transmit the first FM continuous wave signal Two FM continuous wave signals; and a radio frequency transistor with a control port, a first port and a second port, the second port is coupled to the transmitting end, the control port is coupled to the receiving end, and the control port is connected to the receiving end. The second port is inverting.

According to an embodiment of the present invention, the RF transistor is a bipolar junction transistor, the control port is a base, the first port is an emitter, and the second port is a collector.

According to an embodiment of the present invention, the radio frequency transistor is a field effect transistor, and the field effect transistor includes a pseudotype high-speed electron mobility transistor (P-Hemt), the control port is a gate, and the first port is a source, and the second port is a drain.

According to an embodiment of the present invention, the parking space detector further includes a first capacitor, the two ends of the first capacitor are connected across the first port and the second port of the RF transistor, wherein the loop antenna includes: a a first inductor coupled to the second port of the radio frequency transistor; a second inductor coupled to the control port of the radio frequency transistor; a second capacitor coupled to the first inductor and the control port of the radio frequency transistor between the second inductors; and a third capacitor coupled between the second inductor and the third inductor.

According to an embodiment of the present invention, the active antenna module includes a substrate including a first surface and a second surface opposite to each other; a first microstrip antenna metal disposed on the first surface of the substrate; a The second microstrip antenna metal is arranged on the first surface of the substrate; a third microstrip antenna metal is arranged on the first surface of the substrate; a first coupling metal sheet is arranged on the first surface of the substrate On the two surfaces; a second coupling metal sheet, arranged on the second surface; and a third coupling metal sheet, arranged on the second surface; the radio frequency transistor, arranged on the first surface, the The control port of the radio frequency transistor is connected to the third microstrip metal, and the first port and the second port are respectively connected to the first coupling metal sheet and the first microstrip metal. A first part of the first microstrip antenna metal and the first coupling metal sheet constitute a first capacitor, a second part of the first microstrip antenna metal is in phase with the first part of the first microstrip antenna metal A first part of the adjacent second microstrip antenna metal and the second coupling metal sheet form a third capacitance, a second part of the second microstrip antenna metal and the first part of the second microstrip antenna metal The third microstrip antenna metal and the third coupling metal sheet in two adjacent parts form a third capacitor.

According to an embodiment of the present invention, the trigger frequency is 8-10 times the modulation frequency.

According to an embodiment of the present invention, the parking space detector is located on the plane of the parking space, or above the parking space, and maintains a preset distance from the plane of the parking space.

According to an embodiment of the present invention, the parking space detector further includes a switching switch, electrically connected to the modulating module and the controller, and the controller is used to output a switching signal when receiving the trigger signal, and the switching When the switch receives the switching signal, it controls the modulating module to suspend outputting the sine wave.

According to an embodiment of the present invention, the switching switch controls the modulation module to output a DC voltage when receiving the switching signal. According to an embodiment of the present invention, the active antenna module includes a loop antenna and a radio frequency transistor. The loop antenna includes a transmitting end and a receiving end, the transmitting end is used to transmit the first FM continuous wave signal, and the receiving end is used to transmit the second FM continuous wave signal. The radio frequency transistor has a control port, a first port and a second port, the second port is coupled to the transmitting end, the control port is coupled to the receiving end, and the control port and the second port are opposite phases.

Compared with the prior art, the small microwave detector used in the parking space detector of the present invention is applied to target detection at a very short distance (within 1 meter). Because it integrates the oscillator, mixer and antenna of the radio frequency module, the radio frequency transceiver can be simplified and reduced in size. At the same time, replacing the voltage-controlled oscillator and the mixer with a BJT or FET (for example: P-Hemt) can significantly improve both the volume and the power consumption rate. Therefore, the parking space detector of the present invention is easily integrated with the circuit of the existing outdoor solar lighting device. As a parking space detector for outdoor parking lots and road parking spaces, it can achieve intelligent management and application of urban parking. In addition, the modulation module of the present invention outputs a modulation signal generated by a sine wave. The modulated signal is generated by using the frequency of the sine wave as the modulated frequency, and the Bessel function of the modulated signal contains distributions of odd-order and even-order terms. The saturated and distorted high-order harmonics of the first demodulated signal generated after demodulation at the modulation frequency can demodulate the second demodulated signal. Because the present invention uses the second demodulated signal as the basis for target detection, it is different from the traditional FM continuous wave short-distance detection method. Since the parking space detector is not disturbed by weather or environmental factors no matter it is located indoors or outdoors, and at the same time, the parking space detector can provide accurate sensing methods for the public to conveniently and accurately know the vacancy of the parking lot.

In order to make the above content of the present invention more obvious and understandable, the following preferred embodiments are specifically cited below, and in conjunction with the accompanying drawings, the detailed description is as follows:

Description of drawings

1A and 1B are schematic diagrams of the parking space detector and the vehicle of the present invention.

FIG. 2 is a functional block diagram of the parking space detector of the present invention.

FIG. 3 is an equivalent circuit diagram of the active antenna module in FIG. 2 .

FIG. 4 is a cross-sectional view of the structure of the active antenna module of the present invention.

FIG. 5 is a comparison diagram of the front and back structures of the active antenna module in FIG. 4 .

FIG. 6 is a front view of the structure of the active antenna module in FIG. 4 .

FIGS. 7A and 7B are respectively a waveform diagram of a time domain response and a waveform diagram of a frequency response of the first demodulated signal output by the first IF filter when there is no vehicle in the parking space.

FIGS. 8A and 8B are respectively a waveform diagram of a time domain response and a waveform diagram of a frequency response of the first demodulated signal output by the first IF filter when the parking space is occupied by a vehicle.

FIG. 9 is a schematic diagram of detecting a parking space in the prior art.

detailed description

The following descriptions of the various embodiments refer to the accompanying drawings to illustrate specific embodiments in which the present invention can be practiced. The directional terms mentioned in the present invention, such as "up", "down", "front", "back", "left", "right", "top", "bottom", "horizontal", "vertical" etc. , are for orientation only with reference to the attached drawings. Therefore, the directional terms used are used to illustrate and understand the present invention, but not to limit the present invention.

Please refer to FIG. 1A and FIG. 1B . FIG. 1A and FIG. 1B are schematic diagrams of a parking space detector 100 and a vehicle 20 according to the present invention. The parking space detector 100 uses a small microwave detector to detect whether a parking space is occupied by a vehicle 20 . Whether it is an indoor or outdoor parking space 50 , the parking space detector 100 can be installed on the plane of the parking space 50 , or above the parking space 50 , maintaining a predetermined distance L from the plane of the parking space 50 . Preferably, the preset distance L is within 2 meters. Preferably, the parking space detector 100 can be placed in the center of the parking space 50, and the detection distance of the parking space detector 100 is adjusted to 1 meter, so as to avoid being reflected by the vehicles 20 adjacent to the parking space 50 signal interference.

Please refer to FIG. 2 , which is a functional block diagram of the parking space detector 100 of the present invention. The parking space detector 100 includes an active antenna module 110, a first IF filter 120, a modulation module 130, a second IF filter 140, an integrator 150, a trigger circuit 160, and a controller 170 and a toggle switch 180 . The modulation module 130 is used for providing a sine wave with a modulation frequency f _m . The active antenna module 110 integrates the functions of an antenna and a radio frequency module, and includes a loop antenna 101 and a radio frequency transistor 102 . The loop antenna 101 is used to transmit a first frequency modulation continuous wave (FMCW) signal according to the modulation frequency f _m and receive a second reflected frequency modulation continuous wave (FMCW) signal. The first IF filter 120 is electrically connected to the active antenna module 110 and used for extracting a first demodulated signal from the second FM continuous wave signal, and the first demodulated signal has a modulation frequency f _m . The second intermediate frequency filter 140 is electrically connected to the first intermediate frequency filter 120, and is used to extract a certain harmonic signal from the first demodulated signal as a second demodulated signal, and the frequency of the second demodulated signal is the modulated signal. A predetermined multiple of the variable frequency f _m . The integrator 150 is electrically connected to the second IF filter 140 for integrating the second demodulated signal to output an integrated voltage. The trigger circuit 160 is electrically connected to the integrator 150 for outputting a trigger signal when the integrated voltage of the second demodulated signal is greater than a reference voltage. The controller 170 is electrically connected to the trigger circuit 160 , and is used to perform the operation that there is a vehicle on the parking space 50 when receiving the trigger signal. The structure and operation of each component will be described in detail later.

The modulation module 130 generates a sine wave with a modulation frequency f _m , and the sine wave is a modulation signal. The RF bandwidth Δf of the first FM continuous wave signal will be directly affected by the amplitude of the modulation signal. When the amplitude of the modulation signal is larger, the RF bandwidth Δf is larger. Conversely, the amplitude of the modulation signal is smaller. The smaller the RF bandwidth Δf is. Therefore, when the parking space detector 100 needs to increase the detection range, the radio frequency bandwidth Δf of the first FM continuous wave signal is reduced. Conversely, when the parking space detector 100 needs to reduce the detection range, the first FM continuous wave signal is increased. The RF bandwidth Δf of the wave signal. Preferably, the detection range of the parking space detector 100 is 1 meter.

Please refer to FIG. 3 , which is an equivalent circuit diagram of the active antenna module 110 in FIG. 2 . The active antenna module 110 has its own mixing and demodulation structure, including a loop antenna 101 and a radio frequency transistor 102 . The loop antenna 101 has a transmitting end 101T and a receiving end 101R, the transmitting end 101T is used for transmitting the first FM continuous wave signal, and the receiving end 101R is used for transmitting the second FM continuous wave signal. The loop antenna 101 includes a first inductor L11, a second inductor L12, a third inductor L13, a first capacitor C11, a second capacitor C12, a third capacitor C13 and a varactor diode 103, wherein the first capacitor C11 , the second capacitor C12 and the third capacitor C13 are equivalent coupling capacitors of the metal sheet. The RF transistor 102 has a control port 1023 , a first port 1021 and a second port 1022 . The second port 1022 is coupled to the transmitting end 101T, and the control port 1023 is coupled to the receiving end 101R. The first port 1021 and the second port 1022 are respectively connected to two ends of the first capacitor C11. The first port 1021 is electrically connected to the first IF filter 120 and used as an output end of the IF (baseband) demodulated signal. The varactor diode 103 is connected in parallel with the second capacitor C12.

It is worth noting that in FIG. 3 , the transmitting end 101T and the receiving end 101R must have a phase difference of 180° to form a positive feedback circuit, so that the loop antenna 101 can obtain good oscillation. The RF transistor 102 is represented by a bipolar junction transistor (BJT), but in fact, the RF transistor 102 can also be a field effect transistor (field effect transistor, FET). If it is a field effect transistor (field effect transistor, FET), it may be a pseudotype high-speed electron mobility transistor (P-Hemt). When the RF transistor 102 is a BJT, the control port 1023 is a base, the first port 1021 (that is, the down-frequency port) is an emitter, and the second port 1022 is a collector. And when the radio frequency transistor 102 is a FET, the control port 1023 is a gate, the first port 1021 (that is, the down-frequency port) is a source, and the second port 1022 is a drain.

Please refer to FIG. 4 and FIG. 5 , FIG. 4 is a cross-sectional view of the structure of the active antenna module of the present invention, and FIG. 5 is a comparison view of the front and back structures of the active antenna module in FIG. 4 . The active antenna module 110 includes a first microstrip antenna metal 1011, a second microstrip antenna metal 1012, a third microstrip antenna metal 1013, a substrate 106, a radio frequency transistor 102, a first coupling metal sheet 1051, A second coupling metal piece 1052 and a third coupling metal piece 1053 . The first microstrip antenna metal 1011 , the second microstrip antenna metal 1012 and the third microstrip antenna metal 1013 are disposed on the first surface 107 (ie, the front surface) of the substrate 106 . The first coupling metal sheet 1051, the second coupling metal sheet 1052, and the third coupling metal sheet 1053 are arranged on the second surface 108 (ie, the reverse side) of the substrate 106, and the first surface 107 and the second surface 108 refer to the opposite side of the substrate 106. two sides. The first microstrip antenna metal 1011, the second microstrip antenna metal 1012, the third microstrip antenna metal 1013, the substrate 106, the first coupling metal sheet 1051, the second coupling metal sheet 1052 and the third coupling metal sheet 1053 are composed as shown in the figure 3 shows the loop antenna 101 . The material of the first microstrip antenna metal 1011, the second microstrip antenna metal 1012, the third microstrip antenna metal 1013, the first coupling metal sheet 1051, the second coupling metal sheet 1052 and the third coupling metal sheet 1053 can be copper foil . The first port 1021, the second port 1022 and the control port 1023 of the RF transistor 102 are respectively connected to the first coupling metal sheet 1051, the first microstrip antenna metal 1011 and the third microstrip antenna metal 1013, and the first port 1021 is a The down-frequency port is used as the output port of the intermediate frequency (base frequency) demodulation signal. The through hole A, the through hole H, the through hole D, and the through hole E all pass through the substrate 106 and are attached with copper foil to form a conductive path. The through hole A is connected to the first microstrip antenna metal 1011 and is also used as an input terminal of the antenna power signal, that is, an antenna power signal is input through the first microstrip antenna metal 1011 (equivalent to the first inductor L11 in FIG. 3 ). The through hole H is connected to the second microstrip antenna metal 1012, which is also used as the input end of the modulation signal, that is, the through hole H is coupled to the modulation module 130, so that the modulation signal passes through the second microstrip antenna metal 1012 (equivalent to The second inductor (L12) in FIG. 3 is input, and the modulation signal can be a triangle wave or a sine wave. The through hole D is connected to the third microstrip antenna metal 1013, which is also used as the bias voltage input terminal of the RF transistor 102. When the RF transistor 102 is a FET, the through hole D can be connected to a fixed voltage (it can be a ground terminal). The through hole E is connected to the first coupling metal sheet 1051 .

The active antenna module 110 may further include a varactor diode 103 disposed on the first surface 107 . Both ends of the varactor diode 103 are respectively connected to the first microstrip antenna metal 1011 and the second microstrip antenna metal 1012 . The capacitance of the varactor diode 103 changes with the voltage applied across it. When the active antenna module 110 is applied to an FM tuner and an FM modulation module, the varactor diode 103 is used to tune FM signals.

Please refer to FIG. 6 , which is a front view of the structure of the active antenna module in FIG. 4 . A first capacitor C11 is formed where a first portion 10111 of the first microstrip antenna metal 1011 overlaps with the first coupling metal piece 1051 . A second part 10112 of the first microstrip antenna metal 1011, a first part 10121 of the second microstrip antenna metal 1012 adjacent to a second part 10112 of the first microstrip antenna metal 1011, and a second coupling metal piece 1052 The overlapped place constitutes a third capacitor C13. The first microstrip antenna metal 1011 is roughly an arc structure, and its first portion 10111 and second portion 10112 are respectively located at two ends of the arc structure. A second part 10122 of the second microstrip antenna metal 1012, a first part 10131 of the third microstrip antenna metal 1013 adjacent to the second part 10122 of the second microstrip antenna metal 1012 and a third coupling metal sheet 1053 overlap form a second capacitor C12. The second microstrip antenna metal 1012 is approximately an arc structure, and its first part 10121 and second part 10122 are respectively located at two ends of the arc structure. The RF transistor 102 is disposed on the first surface 107 , and the control port 1023 of the RF transistor 102 is connected to the third microstrip antenna metal 1013 .

When designing the loop antenna 101 of the present invention, analysis and verification must be carried out through experiments, that is, converting the active antenna module 110 of the present invention into a dual-port circuit as shown in FIG. 3 . Please refer to Fig. 6 together, its circumference length of the loop antenna 101 of planar is about 1/2 of radio frequency wavelength (λ/2=2πr), the first microstrip antenna metal 1011 of its front, the second microstrip antenna metal 1012 And the diameter of the outer edge of the third microstrip antenna metal 1013 is 17.1 mm, so its frequency should be greater than 2.79 GHz, but it can be seen from the structure of Figure 6 that the copper foil on the reverse side is actually an equivalent metal coupling capacitor, making the LC resonator ( The equivalent length of LC Tank) is greater than the circumference of 17.1π (mm), so the antenna frequency is reduced below 2.79GHz. In addition, in the phase control of the RF transistor 102, since there are different electrical phase lengths (Phase Delay) in the drain-gate or collector-base of the RF transistor 102 itself, after it is combined with the phase length of the antenna at the operating frequency, When the length of positive feedback (180°) is formed, the best oscillation condition is formed. Therefore, after experimental testing, when the AT41486 transistor is used as the oscillator, the oscillation frequency is 2.3-2.4GHz. If the BFR92 transistor is used as the oscillator, the oscillation frequency is 2.0-2.1GHz. Therefore, it is necessary to cooperate with metal coupling capacitors and different transistors , can make the antenna under the vibration condition of 2.79GHz in the original size be reduced to the vibration of 2.0-2.1GHz, this contribution can make the size of the antenna shrink and miniaturize.

However, it must be noted that the metal coupling capacitor will affect the stability of the loop antenna 101 when making adjustments. Taking the BJT as the RF transistor 102 as an example, it can be seen from the simple small signal model equation of the BJT that if the capacitance value of the metal equivalent coupling capacitor as the first capacitor C11 is smaller, the internal impedance of the RF transistor 102 is smaller, so that the base current I The value of _B increases, and the value of the collector current I _C increases as the value of the base current I _B increases, so the stability of the radio frequency oscillation radiation of the loop antenna 101 increases accordingly. In addition, if the RF transistor 102 is a BJT, the base current I _B , the emitter current I _E and the collector current I _C must be considered, and if the RF transistor 102 is a FET, the gate current I _G must be considered , source voltage V _S and drain current I _D . For example, the emitter current I _E determines the strength of the radiation signal, which will directly affect the detection range, so special attention must be paid to the design. It is understandable that the operating point of the oscillator can be determined by the bias voltage, and the theoretical value is easy to find, but the optimum point must be verified by experiments, and it can be found from the situation where the signal-to-noise ratio (S/N) is greater than the requirement optimal working point.

In this structure, the first microstrip antenna metal 1011, the second microstrip antenna metal 1012 and the third microstrip antenna metal 1013 and the first coupling metal piece 1051, the second coupling metal piece 1052 and the third coupling metal piece 1053 can be Form the desired equivalent inductance value and equivalent capacitance value. As mentioned above, with the design of the length of the metal coupling capacitor, the working frequency of the active antenna module 110 can be adjusted to a low frequency, in other words, the equivalent size of the half-wavelength (λg/2) is lengthened, and the The operating point of the RF transistor 102 is adjusted to compensate for the phase difference. Finally, the first microstrip antenna metal 1011, the second microstrip antenna metal 1012, and the third microstrip antenna metal 1013 can be designed together with the first coupling metal sheet 1051, the second coupling metal sheet 1052, and the third coupling metal sheet 1053 as Resonator when in resonance with RF transistor 102.

Please refer to Fig. 3 again, the operating frequency of the active antenna module 110 of the present invention is determined by the inductance value L (related to the lengths of the first microstrip antenna metal 1011, the second microstrip antenna metal 1012 and the third microstrip antenna metal 1013) and The capacitance value C of the first, second and third capacitors C11, C12 and C13 (related to the length of the first capacitor C11 and the second and third capacitors C12 and C13) determines that when the LC value is larger, the radio frequency oscillation The lower the frequency; on the contrary, when the LC value is smaller, the higher the radio frequency oscillation frequency. But it is worth noting that the radio frequency stability is closely related to the selection of coupling capacitors and bypass capacitors. When the RF transistor 102 is a BJT, it can be seen from the simple small signal model equation I _C = _βIB that if the capacitance value of the bypass capacitor C2 is smaller, the internal impedance of the RF transistor 102 is smaller, so that the β value increases, that is, the collection The value of the electrode current _IC increases, so the radio frequency stability of the loop antenna 101 increases accordingly. And when the RF transistor 102 is a FET, its simple small-signal model equation is as follows:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; DSS</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; GS</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Among them, V _P is the clamping voltage, V _GS is the gate voltage, and I _DSS is the drain-source saturation current. If the capacitance value of the bypass capacitor C2 is smaller, the internal impedance r _DS of the radio frequency transistor 102 is smaller, since V _DS =r _DS × _ID , so when a constant voltage is input (the drain-source voltage V _DS is a constant value ), the _ID value increases relatively.

To sum up, in this circuit design, if the capacitance value of the first capacitor C11 used as a bypass capacitor is smaller, the radio frequency oscillation will be more stable, and when reflected on the spectrum distribution diagram, the energy of the harmonics will decrease, And the energy of the main wave increases. Conversely, if the capacitance of the first capacitor C11 is larger, the radio frequency oscillation is more unstable, and when reflected on the spectrum distribution diagram, the energy of each harmonic increases while the energy of the main wave decreases. As for the effects of the second and third capacitors C12 and C13, they are just opposite to the first capacitor C11. The larger the capacitance values of the second and third capacitors C12 and C13, the more stable the system is, and when reflected on the spectrum distribution diagram, The energy of each harmonic decreases while the energy of the main wave increases. Conversely, if the capacitance values of the second and third capacitors C12 and C13 are smaller, the system is more unstable, and when reflected on the spectrum distribution diagram, the energy of each harmonic increases while the energy of the main wave decreases.

If the equivalent model architecture in Figure 3 is compared with the standard radar architecture, when it is equivalent to the standard radar antenna, the metal (or copper foil) on the surface and the metal (or copper foil) on the back are equivalent to a loop antenna In addition, when used as a voltage-controlled oscillator (VCO), the loop antenna and the metal stripes on the back are equivalent to the equivalent inductance (L) and equivalent capacitance (C) respectively, and together constitute the resonant cavity of the transistor. In the active antenna module 100 of the present invention, the base and emitter (or gate and drain) of the radio frequency transistor 102 are equivalent to reverse diodes, which can be used as a simple mixer. The RF transistor 102 also functions as a voltage controlled oscillator and a mixer. Through design, the first microstrip antenna metal 1011, the second microstrip antenna metal 1012 and the third microstrip antenna metal 1013 and the first coupling metal piece 1051, the second coupling metal piece 1052 and the third coupling metal piece can be obtained 1053 acts as a resonator when resonating with the RF transistor 102. When used as a mixer, the base bias voltage is used to drive the RF transistor 102 to work in a near-saturation region, so that the intermediate frequency signal can be detected at the emitter terminal.

Since the RF transistor 102 of the active antenna module 110 has the function of a mixer, the RF transistor 102 and the first intermediate frequency filter 120 can be used as a demodulator for the first frequency-modulated continuous wave signal and the second frequency-modulated continuous wave signal. The continuous wave signal is demodulated to detect the carrier signal and obtain a first demodulated signal. That is to say, the first demodulated signal output by the first IF filter 120 is a signal of the modulation frequency f _m directly taken out and amplified. The amplitude of the first demodulated signal is close to the boundary of the DC bias voltage.

See Figures 7A and 7B. FIG. 7A and FIG. 7B respectively show the waveform diagram of the time domain response and the waveform diagram of the frequency response of the first demodulated signal output by the first IF filter 120 when there is no vehicle in the parking space. When there is no vehicle above the parking space 50 , the first demodulation signal is a sine wave, and its frequency is the modulation frequency f _m .

See Figures 8A and 8B. FIGS. 8A and 8B are respectively a waveform diagram of a time domain response and a waveform diagram of a frequency response of the first demodulated signal output by the first IF filter 120 when the parking space is occupied by a vehicle. When there is a vehicle above the parking space 50 , because the near field signal is reflected by the vehicle, the upper edge of the sine wave of the first demodulated signal is cut and distorted. After the distorted sine wave undergoes fast Fourier transform, many harmonics are generated in the frequency domain.

It can be observed from FIG. 7B and FIG. 8B that when the parking space 50 is occupied by vehicles, many harmonics appear in the frequency domain of the first demodulated signal. Therefore, the second intermediate frequency filter 140 is used to extract a second demodulated signal from the first demodulated signal, and the trigger frequency of the second demodulated signal is a predetermined multiple of the modulation frequency f _m . Preferably, the trigger frequency is 8-10 times of the modulation frequency, that is, the frequency of the second demodulation signal extracted by the second IF filter 140 is 8-10 times of the modulation frequency f _m . Because the energy of high-order harmonics is low, the magnification can be increased to a higher magnification, which can increase the signal-to-noise ratio (SNR) of this frequency point to other frequencies.

Next, the integrator 150 integrates the second demodulated signal to output an integrated voltage. The trigger circuit 160 electrically connected to the integrator 150 is used for outputting a trigger signal when the integrated voltage of the second demodulated signal is greater than a reference voltage. When the parking space 50 is not occupied by a vehicle, the extracted second demodulated signal has almost no harmonics at a frequency of 8×f _m -10×f _m . In contrast, when the parking space 50 is occupied by a vehicle, the extracted second demodulated signal contains harmonics with a frequency of 8×f _m -10×f _m . Therefore, when the parking space 50 is occupied by a vehicle, the integral voltage obtained by integrating the second demodulated signal by the integrator 150 will be greater than the reference voltage, causing the trigger circuit 160 to output the trigger signal to the controller 170 .

See Figure 2. When the controller 170 receives the trigger signal, it will control the operation of the back-end circuit 190 , such as controlling the LED to emit light or the alarm to sound an alarm, so as to realize the operation that the parking space 50 is occupied. In addition, the controller 170 outputs a switch signal to the switch 180 when receiving the trigger signal. When the switch 180 electrically connected to the modulation module 130 and the controller 170 receives the switching signal, it controls the modulation module 130 to suspend outputting the sine wave within a default time. Preferably, when the switch 180 receives the switching signal, it controls the modulation module 130 to output a DC voltage within the default time. At this time, the active antenna module 110 will output a single continuous wave signal (continuous wave) instead of a frequency modulated continuous wave (FMCW) signal. This is to avoid the transmission band of the wireless communication module (such as Bluetooth, Zigbee and WiFi, etc.), so that the wireless communication module can successfully complete the communication with the back-end system or cloud host without being affected by the radiation signal of the detector 100 interference and influence. The length of the preset time can be set by the manufacturer, for example, 10 seconds.

The small microwave detector adopted by the parking space detector of the present invention is applied to target detection in a very short distance (within 1 meter). Because it integrates the oscillator, mixer and antenna of the radio frequency module, the radio frequency transceiver can be simplified and reduced in size. At the same time, replacing the voltage-controlled oscillator and the mixer with a BJT or FET (for example: P-Hemt) can significantly improve both the volume and the power consumption rate. Therefore, the parking space detector of the present invention is easily integrated with the circuit of the existing outdoor solar lighting device. As a parking space detector for outdoor parking lots and road parking spaces, it can achieve intelligent management and application of urban parking. In addition, the modulation module of the present invention outputs a modulation signal generated by a sine wave. The modulated signal is generated by using the frequency of the sine wave as the modulated frequency, and the Bessel function of the modulated signal contains distributions of odd-order and even-order terms. The saturated high-order harmonics of the first demodulated signal generated after demodulation at the modulation frequency can demodulate the second demodulated signal. Because the present invention uses the second demodulated signal as the basis for target detection, it is different from the traditional FM continuous wave short-distance detection method. Since the parking space detector is not disturbed by weather or environmental factors no matter it is located indoors or outdoors, and at the same time, the parking space detector can provide accurate sensing methods for the public to conveniently and accurately know the vacancy of the parking lot.

In summary, although the present invention has been disclosed above with a preferred embodiment, the preferred embodiment is not intended to limit the present invention, and those of ordinary skill in the art may, without departing from the spirit and scope of the present invention, Various changes and modifications are made, so the protection scope of the present invention shall be determined by the scope defined in the claims.

Claims (10)

1. A parking space detector used to detect whether a parking space is occupied, characterized in that: the parking space detector comprises: a modulation module, used to provide a sine wave with a modulation frequency; An active antenna module, electrically connected to the modulation module, used to transmit a first FM continuous wave signal according to the modulation frequency, and receive a reflected second FM continuous wave signal; A first intermediate frequency filter, electrically connected to the active antenna module, for extracting a first demodulated signal from the second frequency-modulated continuous wave signal, the first demodulated signal having the modulated frequency; A second intermediate frequency filter, electrically connected to the first intermediate frequency filter, used to extract a second demodulated signal from the first demodulated signal, the second demodulated signal has a trigger frequency, the trigger frequency is the A predetermined multiple of the modulation frequency; an integrator, electrically connected to the second intermediate frequency filter, for integrating the second demodulated signal to output an integrated voltage; A trigger circuit, electrically connected to the integrator, is used to output a trigger signal when the integrated voltage of the second demodulated signal is greater than a reference voltage; and A controller, electrically connected to the trigger circuit, is used to perform the operation that the parking space is occupied when receiving the trigger signal. 2. The parking space detector according to claim 1, wherein the active antenna module comprises: A loop antenna, which includes a transmitting end and a receiving end, the transmitting end is used to transmit the first FM continuous wave signal, and the receiving end is used to transmit the second FM continuous wave signal; and A radio frequency transistor has a control port, a first port and a second port, the second port is coupled to the transmitting end, the control port is coupled to the receiving end, and the control port and the second port are inverse . 3. The parking space detector according to claim 2, wherein the RF transistor is a bipolar junction transistor, the control port is a base, the first port is an emitter, and the first port is an emitter. Two ports are one collector. 4. The parking space detector according to claim 2, characterized in that: the radio frequency transistor is a field effect transistor, and the field effect transistor includes a pseudo-type high-speed electron mobility transistor (P-Hemt), the control The port is a gate, the first port is a source, and the second port is a drain. 5. The parking space detector according to claim 2, characterized in that: the parking space detector further comprises a first capacitor, the two ends of the first capacitor are connected across the first port of the RF transistor and The second port, wherein the loop antenna contains: a first inductor coupled to the second port of the RF transistor; a second inductance; a third inductor coupled to the control port of the radio frequency transistor; a second capacitor coupled between the first inductor and the second inductor; and A third capacitor is coupled between the second inductor and the third inductor. 6. The parking space detector according to claim 2, wherein the active antenna module comprises A substrate, including a first surface and a second surface opposite to each other; a first microstrip antenna metal disposed on the first surface of the substrate; a second microstrip antenna metal disposed on the first surface of the substrate; a third microstrip antenna metal disposed on the first surface of the substrate; a first coupling metal sheet disposed on the second surface of the substrate; a second coupling metal sheet disposed on the second surface; and a third coupling metal sheet, disposed on the second surface; The radio frequency transistor is arranged on the first surface, the control port of the radio frequency transistor is connected to the third microstrip metal, and the first port and the second port are respectively connected to the first coupling metal sheet and the first microstrip with metal; Wherein, a first part of the first microstrip antenna metal and the first coupling metal sheet form a first capacitance, a second part of the first microstrip antenna metal, and the first coupling metal piece of the first microstrip antenna A first part of the second microstrip antenna metal adjacent to a part and the second coupling metal sheet form a third capacitor, a second part of the second microstrip antenna metal, and a second part of the second microstrip antenna metal The third microstrip antenna metal and the third coupling metal sheet adjacent to the second portion form a third capacitor. 7. The parking space detector according to claim 1, wherein the trigger frequency is 8-10 times of the modulation frequency. 8. The parking space detector according to claim 1, characterized in that: the parking space detector is located on the plane of the parking space, or above the parking space, and maintains a predetermined distance with the plane of the parking space. Set distance. 9. The parking space detector according to claim 1, characterized in that: the parking space detector further comprises a switch electrically connected to the modulation module and the controller, the controller is used for receiving When the trigger signal is output, a switching signal is output, and when the switching switch receives the switching signal, it controls the modulating module to suspend outputting the sine wave. 10. The parking space detector according to claim 9, wherein the switching switch controls the modulating module to output a DC voltage when receiving the switching signal.