CN112379361B - Planar microwave sensor - Google Patents
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- CN112379361B CN112379361B CN202110043799.2A CN202110043799A CN112379361B CN 112379361 B CN112379361 B CN 112379361B CN 202110043799 A CN202110043799 A CN 202110043799A CN 112379361 B CN112379361 B CN 112379361B
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- 150000003071 polychlorinated biphenyls Chemical class 0.000 abstract description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/04—Systems determining presence of a target
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
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Abstract
The invention discloses a planar microwave sensor, which comprises a transceiving circuit and a transceiving antenna, wherein the transceiving circuit and the transceiving antenna are pasted and mounted back to back through bonding pads on the back of respective PCBs; the receiving and transmitting circuit comprises a voltage stabilizing module, an oscillating circuit, a mixing circuit, an intermediate frequency amplifying circuit and an intermediate frequency processing module which are electrically connected in sequence. The circuit modules are integrated on the PCB, so that the size is saved, the cost is reduced, and the noise floor of the intermediate frequency signal is in the optimal level; the whole size is small, the manufacturing process is simple, the processing period is short, the cost is low, and the signal coverage is good.
Description
Technical Field
The invention belongs to the technical field of sensors, and particularly relates to a planar microwave sensor.
Background
Microwave sensors are devices that use microwave characteristics to detect some physical quantities, including sensing the presence of objects, speed of movement, distance, angle, etc. The microwave sensor is widely used by people in the household fields of automatic doors, security products, illumination and the like at present, is used for detecting the movement induction signals of human bodies, and is characterized by high detection sensitivity and strong interference resistance, and the principle of the microwave sensor is generally based on the Doppler radar principle. The current microwave sensor is generally composed of three parts, namely an oscillator, an antenna and a detector. The oscillator is a device for generating microwave signals, the traditional oscillator is mostly based on a speed regulating tube, a magnetron or some solid-state devices, and the small oscillator can also be based on a body effect tube. The antenna is used for transmitting and receiving microwave signals, such as a horn antenna, a microstrip antenna, a parabolic antenna, a slot antenna and the like. The working principle of the microwave sensor is that the oscillation circuit generates a single-tone continuous wave signal which is radiated by an antenna; the radiated electromagnetic waves encounter a moving object and are reflected back, and the frequency of the reflected electromagnetic waves changes along with the speed of the moving object; the reflected signal is received by the antenna of the radar, and is mixed with the signal generated by the oscillating circuit to obtain a low-frequency signal, and the low-frequency signal is sent to the intermediate-frequency detection module.
The traditional microwave sensor is mainly made of high-frequency plates, and a power divider or a circulator is needed to realize the functions of receiving and transmitting at the same time, so that the cost is high; in some microwave induction sensors, a microwave receiving and transmitting part and an intermediate frequency processing part are divided into two plates, and power supply and intermediate frequency signals are connected through a contact pin, so that the noise floor of the intermediate frequency signals can be raised, the overall sensitivity of the radar is reduced, the size is large, and the cost is higher; the antenna also generally has the problem of covering unevenly, having the detection blind area etc.. In addition, the oscillator, the detector and the antenna are composed of a plurality of PCBs, so that the manufacturing cost of materials is high, and the whole size is large.
Accordingly, there is a need for improvements to conventional microwave sensors.
Disclosure of Invention
The invention aims to solve the problems of large volume, high cost, uneven antenna coverage, blind areas and the like of the conventional microwave sensor and provides a planar microwave sensor.
In order to achieve the purpose, the invention adopts the following technical scheme: the PCB board back-to-back mounting device comprises a transceiving circuit and a transceiving antenna, wherein the transceiving circuit and the transceiving antenna are back-to-back mounted through bonding pads on the back of respective PCB boards; the transceiver circuit comprises a voltage stabilizing module, an oscillating circuit, a mixing circuit, an intermediate frequency amplifying circuit and an intermediate frequency processing module which are electrically connected in sequence,
the voltage stabilizing module is used for supplying power and converting external voltage into power supply voltage required by a circuit on the double-layer board;
the oscillation circuit is used for generating microwave signals, and the microwave signals are transmitted outwards through the transmitting-receiving antenna;
the frequency mixing circuit is used for frequency conversion, when the microwave signal meets a moving object, the frequency changes and is reflected to the receiving and transmitting antenna, and the frequency mixing circuit carries out frequency conversion on the microwave signal received and reflected by the receiving and transmitting antenna and converts the frequency to a low-frequency signal;
the intermediate frequency amplifying circuit is used for amplifying and filtering the low-frequency signal;
and the intermediate frequency processing module is used for processing and judging the amplified and filtered low-frequency signals and outputting high and low levels to indicate whether a moving object exists or not.
Furthermore, the voltage regulation module comprises a low dropout regulator LDO, a capacitor C1 and a capacitor C2, and an input end and an output end of the low dropout regulator LDO are respectively connected with the capacitor C1 and the capacitor C2 and then grounded.
Furthermore, the oscillation circuit comprises an oscillator, a microstrip line MLIN1, a microstrip line MLIN2, a microstrip line MLIN3, a microstrip line MLIN4, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a resistor R1, a resistor R2 and a bjt Q1, wherein one end of the resistor R1 is connected with one end of the capacitor C3 and then connected to the output end of the voltage stabilizing module, the other end of the resistor R1 is connected to one end of the resistor R2, the collector of the bjt Q1 and one end of the capacitor C6, the other end of the resistor R2 is connected to one end of the capacitor C4, one end of the capacitor C5 and the base of the bjt Q1, the other end of the capacitor C5, the microstrip line MLIN1, the oscillator and one end of the microstrip line MLIN2 are sequentially connected, and the other end of the microstrip line MLIN2 is connected to the other end of the capacitor C6 and then connected to the transceiving antenna and the mixer circuit; the microstrip line MLIN2 is further connected to a microstrip line MLIN3 and a microstrip line MLIN4, respectively, and the other end of the capacitor C3, the other end of the capacitor C4, and the emitter of the bipolar junction transistor Q1 are grounded.
Furthermore, by changing the length of the microstrip line MLIN3 or MLIN4, the operating frequency of the oscillator is changed accordingly.
Furthermore, the frequency mixing circuit comprises a Schottky diode single-balanced mixer, two high-frequency chokes RFC for bypassing radio-frequency signals, a capacitor C10 and a microstrip line MLIN5, wherein two input ends of the Schottky diode single-balanced mixer are respectively connected with one high-frequency choke RFC, the output end of the Schottky diode single-balanced mixer is respectively connected with one end of the capacitor C10 and one end of the microstrip line MLIN5, and one end of the high-frequency choke RFC and the other end of the capacitor C10 are grounded; the other end of the microstrip line MLIN5 is connected with the intermediate frequency amplifying circuit.
Further, the oscillation circuit comprises an oscillator, a microstrip line MLIN1, a microstrip line MLIN2, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8, a resistor R4, a resistor R2 and a bjt Q1, wherein one end of the resistor R4 is connected with one end of the capacitor C3 and then connected to the output end of the voltage stabilizing module, the other end of the resistor R4 is connected to one end of the resistor R2, the collector of the bjt Q1 and one end of the capacitor C6, the other end of the resistor R2 is connected to one end of the capacitor C4, one end of the capacitor C5 and the base of the bjt Q1, the other end of the capacitor C5, the microstrip line MLIN1, the oscillator and one end of the microstrip line MLIN2 are sequentially connected, and the other end of the microstrip line MLIN2 is connected to the other end of the capacitor C6 and then connected to the transceiving antenna and the mixer circuit; the microstrip line MLIN2 is further connected to a capacitor C7 and a capacitor C8, respectively, and the other end of the capacitor C3, the other end of the capacitor C4, and the emitter of the bjt Q1 are grounded.
Furthermore, by adjusting the capacitance values of the capacitor C7 and the capacitor C8, the operating frequency of the oscillator is changed.
Compared with the prior art, the invention has the beneficial effects that: the planar antenna type microwave sensor integrates a plurality of circuit modules on one PCB, thereby saving the volume, reducing the cost and ensuring the noise floor of intermediate frequency signals to be at the optimal level; the whole size is small, the manufacturing process is simple, the processing period is short, the cost is low, and the signal coverage is good.
Drawings
Fig. 1 is a schematic structural view of a planar microwave sensor;
FIG. 2 is a PCB layout of a transceiver circuit;
FIG. 3 is a corresponding transceiver circuit diagram of FIG. 2;
FIG. 4 is another PCB layout of a transceiver circuit;
FIG. 5 is a diagram of a corresponding transceiver circuit of FIG. 4;
FIG. 6 is a PCB layout of a transceiver antenna;
fig. 7 is a pattern diagram of a transmitting and receiving antenna.
In the figure: 1 transceiver circuit, 2 transceiver antenna, 3 bonding pad, 4 transceiver circuit back, 5 transceiver antenna back.
Detailed Description
The technical scheme of the invention is further described and illustrated by specific embodiments below, so that the technical scheme is clearer and more obvious. Other advantages and effects of the present invention will be readily apparent to those skilled in the art from the disclosure herein.
Example 1
As shown in fig. 1, the embodiment discloses a planar microwave sensor, which includes two key components, namely, a transceiver circuit 1 and a transceiver antenna 2, wherein the transceiver antenna and the transceiver circuit are two ordinary FR4 double-layer boards, the transceiver circuit 1 and the transceiver antenna 2 are mounted back to back and are respectively connected through a pad 3 on the back of a PCB board, that is, the transceiver circuit back 4 and the pad 3 on the transceiver antenna back 5 are connected, and the mounting can also be directly performed by using a chip mounter, so that the welding process is simplified. The transmitting signal generated by the transmitting-receiving circuit is fed into the transmitting-receiving antenna through the connecting welding spot, the transmitting-receiving antenna radiates electromagnetic waves to the environment, and when the moving object is met, part of the electromagnetic waves are reflected to the microwave induction radar and are received by the transmitting-receiving antenna. The received signal is input to the transceiver circuit through the connecting welding spot. The metal shielding cover is welded on the receiving and generating circuit to shield external signal interference and prevent foreign matters from falling into the receiving and generating circuit to influence the performance of the receiving and generating circuit.
As shown in fig. 2-3, the PCB layout and circuit schematic diagram of the transceiver circuit 1 of the present embodiment are shown, the transceiver circuit includes a voltage stabilizing module, an oscillating circuit, a mixing circuit, an intermediate frequency amplifying circuit and an intermediate frequency processing module which are electrically connected in sequence,
the voltage stabilizing module is used for supplying power and converting external voltage into power supply voltage required by a circuit on the double-layer board;
the oscillation circuit is used for generating microwave signals, and the microwave signals are transmitted (radiated) outwards through the transceiving antenna;
the frequency mixing circuit is used for frequency conversion, when the microwave signal meets a moving object, the frequency changes, the frequency shifts and is reflected to the transceiving antenna, and the frequency mixing circuit carries out frequency conversion on the microwave signal received and reflected by the transceiving antenna and converts the frequency to a low-frequency signal;
the intermediate frequency amplifying circuit is used for amplifying and filtering the low-frequency signal;
and the intermediate frequency processing module is used for processing and judging the amplified and filtered low-frequency signals and outputting high and low levels to indicate whether a moving object exists or not.
The voltage stabilizing module of the embodiment includes a low dropout regulator LDO, a capacitor C1, and a capacitor C2, where an input end and an output end of the low dropout regulator LDO are connected to the capacitor C1 and the capacitor C2, respectively, and then grounded.
The oscillation circuit of the embodiment comprises an oscillator, a microstrip line MLIN1, a microstrip line MLIN2, a microstrip line MLIN3, a microstrip line MLIN4, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a resistor R1, a resistor R2 and a bipolar junction transistor Q1, wherein one end of the resistor R1 is connected with one end of the capacitor C3 and then connected with the output end of the voltage stabilizing module, the other end of the resistor R1 is respectively connected with one end of the resistor R2, the collector of the bipolar junction transistor Q1 and one end of the capacitor C6, the other end of the resistor R2 is respectively connected with one end of the capacitor C4, one end of the capacitor C5 and the base of the bipolar junction transistor Q1, the other end of the capacitor C5, the microstrip line MLIN1, the oscillator and one end of the microstrip line MLIN2 are sequentially connected, and the other end of the microstrip line MLIN2 is connected with the other end of the capacitor C6 and then respectively connected with the transceiving antenna and the mixer circuit; the microstrip line MLIN2 is further connected to a microstrip line MLIN3 and a microstrip line MLIN4, respectively, and the other end of the capacitor C3, the other end of the capacitor C4, and the emitter of the bipolar junction transistor Q1 are grounded. The input end and the output end of the amplifying circuit are respectively and electrically connected with the input end and the output end of the band-pass filter to form a feedback loop. By adjusting the length of the microstrip line between the amplifying circuit and the band-pass filter, the phase shift of the loop is 0 degree or N x 360 degrees (N is an integer) at the oscillation frequency, and the loop gain is greater than 1. In the embodiment, the operating frequency of the oscillator can be adjusted by changing the lengths of the microstrip line MLIN3 and the microstrip line MLIN 4.
The embodiment provides a mixer circuit, which is a 5.8GHz mixer circuit, and specifically comprises a Schottky diode single-balanced mixer, two high-frequency chokes RFC, a capacitor C10 and a microstrip line MLIN5, wherein two input ends of the Schottky diode single-balanced mixer are respectively connected with one high-frequency choke RFC, an output end of the Schottky diode single-balanced mixer is respectively connected with one end of the capacitor C10 and one end of the microstrip line MLIN5, and one end of the high-frequency choke RFC and the other end of the capacitor C10 are grounded; the other end of the microstrip line MLIN5 is connected with the intermediate frequency amplifying circuit. The 5.8GHz mixing circuit is a Schottky diode single-balanced mixer and has the functions of power distribution and mixing. The oscillating signal is divided into two parts by the mixer, one is a local oscillator signal, and the other is output from the RF end of the mixer to generate a transmitting signal which is radiated from the antenna. The 5.8GHz signal reflected by the moving object is mixed with the local oscillation signal to generate a low-frequency intermediate frequency signal, and the low-frequency intermediate frequency signal is input to the intermediate frequency amplifying circuit. A Schottky diode single balanced mixer is used. Design timing is different from the size calculation of the traditional single balanced mixer, and corresponding optimization adjustment is carried out, so that the single balanced mixer has the functions of power distribution and frequency mixing. The oscillating signal is divided into two parts by a mixer. One is local oscillator signal, and the other is output from the RF end of the mixer, which generates a transmission signal radiated from the antenna. The 5.8GHz signal reflected by the moving object is mixed with the local oscillation signal to generate a low-frequency intermediate frequency signal, and the low-frequency intermediate frequency signal is input to the intermediate frequency amplifying circuit.
Such as the PCB layout of the transceiver antenna shown in fig. 6. The antenna is a rectangular antenna with microstrip feed, and feed signals are fed in through a receiving and transmitting circuit and welding points of the receiving and transmitting antenna. The transceiver circuit PCB is characterized in that: the double-layer board is an FR4 board, and is low in cost, the size of the double-layer board is 45mm x 21.2mm, and the thickness of the double-layer board is 0.6-0.8 mm. The transmitting and receiving antenna is made of FR4 plates, the size is 30mm 16.2mm, and the thickness is 1.8 mm-2.0 mm. The antenna is matched with a transmitting-receiving circuit PCB for use, and the signal coverage is uniform.
The antenna pattern is shown in figure 7. The two curves in the diagram represent the longitudinal cutting diagram of the directional diagram when the azimuth angle is 0 degree and 90 degrees respectively. It can be seen that the upper half of the two curves are more consistent, showing more uniform coverage.
Example 2
Unlike embodiment 1, the planar microwave sensor of the present embodiment uses a transceiver circuit having another structure, specifically, an oscillator circuit having a different element structure, as shown in fig. 4 to 5.
The oscillation circuit of the embodiment comprises an oscillator, a microstrip line MLIN1, a microstrip line MLIN2, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8, a resistor R4, a resistor R2 and a bipolar junction transistor Q1, wherein one end of the resistor R4 is connected with one end of the capacitor C3 and then connected with the output end of the voltage stabilizing module, the other end of the resistor R4 is connected with one end of the resistor R2, the collector of the bipolar junction transistor Q1 and one end of the capacitor C6, the other end of the resistor R2 is connected with one end of the capacitor C4, one end of the capacitor C5 and the base of the bipolar junction transistor Q1, the other end of the capacitor C5, one end of the microstrip line MLIN1, the oscillator and one end of the microstrip line MLIN2 are connected in sequence, and the other end of the microstrip line MLIN2 is connected with the other end of the capacitor C6 and then connected with the transceiving antenna and the mixer circuit respectively; the microstrip line MLIN2 is further connected to a capacitor C7 and a capacitor C8, respectively, and the other end of the capacitor C3, the other end of the capacitor C4, and the emitter of the bjt Q1 are grounded.
The frequency adjustment method of the oscillator in this embodiment is as follows: the oscillator operates at the target frequency by selecting a capacitor with a proper capacitance value for the capacitor C7 and the capacitor C8. In a preferred embodiment, the capacitors C7 and C8 affect the operating frequency of the oscillator, and the operating frequency of the oscillator is changed by selecting capacitors with other capacitance values.
Related circuits or modules and the like used in the embodiments of the present invention are designed by techniques commonly used in the art, if not specifically stated.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (8)
1. A planar microwave sensor is characterized by comprising a transceiving circuit and a transceiving antenna, wherein the transceiving circuit and the transceiving antenna are attached back to back through bonding pads on the back of a PCB respectively; the transceiver circuit comprises a voltage stabilizing module, an oscillating circuit, a mixing circuit, an intermediate frequency amplifying circuit and an intermediate frequency processing module which are electrically connected in sequence,
the voltage stabilizing module is used for supplying power and converting external voltage into power supply voltage required by a circuit on the double-layer board;
the oscillation circuit is used for generating microwave signals, and the microwave signals are transmitted outwards through the transmitting-receiving antenna;
the frequency mixing circuit is used for frequency conversion, when the microwave signal meets a moving object, the frequency changes and is reflected to the receiving and transmitting antenna, and the frequency mixing circuit carries out frequency conversion on the microwave signal received and reflected by the receiving and transmitting antenna and converts the frequency to a low-frequency signal;
the intermediate frequency amplifying circuit is used for amplifying and filtering the low-frequency signal;
the intermediate frequency processing module is used for processing and judging the amplified and filtered low-frequency signal and outputting a high level and a low level to indicate whether a moving object exists or not;
the oscillating circuit comprises an oscillator, a microstrip line MLIN1, a microstrip line MLIN2, a microstrip line MLIN3, a microstrip line MLIN4, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a resistor R1, a resistor R2 and a bipolar junction transistor Q1, wherein one end of the resistor R1 is connected with one end of the capacitor C3 and then connected with the output end of the voltage stabilizing module, the other end of the resistor R1 is respectively connected with one end of the resistor R2, the collector of the bipolar junction transistor Q1 and one end of the capacitor C6, the other end of the resistor R2 is respectively connected with one end of the capacitor C4, one end of the capacitor C5 and the base of the bipolar junction transistor Q1, the other end of the capacitor C5, the microstrip line MLIN1, the oscillator and one end of the microstrip line MLIN2 are sequentially connected, and the other end of the microstrip line MLIN2 is connected with the other end of the capacitor C6 and then respectively connected with the transceiving antenna and the mixing circuit; the microstrip line MLIN2 is further connected to a microstrip line MLIN3 and a microstrip line MLIN4, respectively, and the other end of the capacitor C3, the other end of the capacitor C4, and the emitter of the bipolar junction transistor Q1 are grounded.
2. The planar microwave sensor of claim 1, wherein the voltage regulator module comprises a low dropout regulator (LDO), a capacitor C1 and a capacitor C2, and an input end and an output end of the LDO are respectively connected to the capacitor C1 and the capacitor C2 and then grounded.
3. The planar microwave sensor of claim 1, wherein changing the length of the microstrip line MLIN3 or MLIN4 changes the operating frequency of the oscillator.
4. The planar microwave sensor according to claim 1, wherein the mixer circuit comprises a Schottky diode single balanced mixer, two high frequency chokes RFC, a capacitor C10 and a microstrip line MLIN5, wherein two input terminals of the Schottky diode single balanced mixer are respectively connected to one high frequency choke RFC, an output terminal of the Schottky diode single balanced mixer is respectively connected to one end of the capacitor C10 and one end of the microstrip line MLIN5, and one end of the high frequency choke RFC and the other end of the capacitor C10 are grounded; the other end of the microstrip line MLIN5 is connected with the intermediate frequency amplifying circuit.
5. A planar microwave sensor is characterized by comprising a transceiving circuit and a transceiving antenna, wherein the transceiving circuit and the transceiving antenna are attached back to back through bonding pads on the back of a PCB respectively; the transceiver circuit comprises a voltage stabilizing module, an oscillating circuit, a mixing circuit, an intermediate frequency amplifying circuit and an intermediate frequency processing module which are electrically connected in sequence,
the voltage stabilizing module is used for supplying power and converting external voltage into power supply voltage required by a circuit on the double-layer board;
the oscillation circuit is used for generating microwave signals, and the microwave signals are transmitted outwards through the transmitting-receiving antenna;
the frequency mixing circuit is used for frequency conversion, when the microwave signal meets a moving object, the frequency changes and is reflected to the receiving and transmitting antenna, and the frequency mixing circuit carries out frequency conversion on the microwave signal received and reflected by the receiving and transmitting antenna and converts the frequency to a low-frequency signal;
the intermediate frequency amplifying circuit is used for amplifying and filtering the low-frequency signal;
the intermediate frequency processing module is used for processing and judging the amplified and filtered low-frequency signal and outputting a high level and a low level to indicate whether a moving object exists or not;
the oscillating circuit comprises an oscillator, a microstrip line MLIN1, a microstrip line MLIN2, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8, a resistor R4, a resistor R2 and a bipolar junction transistor Q1, wherein one end of the resistor R4 is connected with one end of the capacitor C3 and then connected with the output end of the voltage stabilizing module, the other end of the resistor R4 is respectively connected with one end of the resistor R2, the collector of the bipolar junction transistor Q1 and one end of the capacitor C6, the other end of the resistor R2 is respectively connected with one end of the capacitor C4, one end of the capacitor C5 and the base of the bipolar junction transistor Q1, the other end of the capacitor C5, one end of the microstrip line MLIN1, the oscillator and one end of the microstrip line MLIN2 are sequentially connected, and the other end of the microstrip line MLIN2 is connected with the other end of the capacitor C6 and then respectively connected with the transceiving antenna and the mixer circuit; the microstrip line MLIN2 is further connected to a capacitor C7 and a capacitor C8, respectively, and the other end of the capacitor C3, the other end of the capacitor C4, the other end of the capacitor C7, the other end of the capacitor C8, and the emitter of the bjt Q1 are grounded.
6. The planar microwave sensor of claim 5, wherein the voltage regulator module comprises a low dropout regulator (LDO), a capacitor C1 and a capacitor C2, and an input end and an output end of the LDO are respectively connected to the capacitor C1 and the capacitor C2 and then grounded.
7. The planar microwave sensor according to claim 5, wherein the mixer circuit comprises a Schottky diode single balanced mixer, two high frequency chokes RFC, a capacitor C10 and a microstrip line MLIN3, wherein two input terminals of the Schottky diode single balanced mixer are respectively connected to one high frequency choke RFC, an output terminal of the Schottky diode single balanced mixer is respectively connected to one end of the capacitor C10 and one end of the microstrip line MLIN3, and one end of the high frequency choke RFC and the other end of the capacitor C10 are grounded; the other end of the microstrip line MLIN3 is connected with the intermediate frequency amplifying circuit.
8. The planar microwave sensor of claim 5, wherein the operating frequency of the oscillator is changed by changing the capacitance values of the capacitor C7 and the capacitor C8.
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