Patent Publication Number: US-2020295770-A1

Title: Frequency-converted self-injection-locked radar

Description:
FIELD OF THE INVENTION 
     This invention generally relates to a self-injection-locked (SIL) radar, and more particularly to a frequency-converted SIL radar. 
     BACKGROUND OF THE INVENTION 
     Conventional SIL radar includes a self-injection-locked oscillator (SILO) and an antenna. An oscillation signal generated from the SILO is transmitted from the antenna to an object as a transmitted signal and reflected from the object to the SILO as a reflected signal. The reflected signal received as an injection signal by the antenna is injected into the SILO such that the SILO is locked at a self-injection-locked state to generate a self-injection-locked signal. If the object has a motion relative to the antenna, the transmitted signal generates the Doppler Effect to lead the reflected signal and the injection signal contain phase shifts caused by the relative motion. After the injection signal injects into the SILO, the self-injection-locked signal outputted from the SILO also contains the motion information. Accordingly, the vibration frequency of the relative motion can be detected by demodulating the self-injection-locked signal. Because of non-contact detection of the object movement with high sensitivity, the conventional SILO has been widely used in vital sign measurement. 
     The sensitivity of the SIL radar is positively related to the center frequency level of the SILO, that is to say, the higher the center frequency of the SILO, the higher sensitivity the SIL radar has. However when increasing the center frequency of the SILO, the propagation loss of the transmitted signal from the antenna and the reflected signal from the object are raised and the available detection area is narrowed. Consequently, the conventional SIL radar having high sensitivity and penetration is difficult to realize. 
     SUMMARY 
     The object of the present invention is to convert center frequencies of oscillation signal outputted from SILO and injection signal by using frequency converter. The converted oscillation signal has a center frequency different to that of a transmitted signal, and the converted injection signal has a center frequency same as that of the SILO so that the SILO is injection-locked by the injection signal. For this reason, a SIL radar of the present invention has both high sensitivity and penetration. 
     A frequency-converted SIL radar of the present invention includes a self-injection-locked oscillator (SILO), a frequency converter, a transceiver antenna element and a demodulator. The frequency converter is electrically connected to the SILO, the transceiver antenna element is electrically connected to the frequency converter, and the demodulator is electrically connected to the SILO. The SILO generates an oscillation signal. The frequency converter receives the oscillation signal and converts a center frequency of the oscillation signal. The transceiver antenna element receives the converted oscillation signal, transmits the converted oscillation signal as a transmitted signal to an object and receives a reflected signal as an injection signal from the object. The frequency converter receives the injection signal and converts a center frequency of the injection signal. The converted injection signal injects into the SILO to lock the SILO in a self-injection-locked state. The demodulator receives and demodulates the oscillation signal. 
     The center frequencies of the oscillation signal and the injection signal are changed by the frequency converter such that the SILO has an oscillation frequency different to that of the transmitted signal and is injection-locked by the injection signal. Consequently, the frequency-converted SIL radar of the present invention has both high sensitivity and penetration, or has both high sensitivity and low cost. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a frequency-converted SIL radar in accordance with one embodiment of the present invention. 
         FIG. 2  is a circuit diagram illustrating a frequency-converted SIL radar in accordance with a first embodiment of the present invention. 
         FIG. 3  is a circuit diagram illustrating a transceiver antenna element in accordance with one embodiment of the present invention. 
         FIG. 4  is a circuit diagram illustrating a frequency-converted SIL radar in accordance with a second embodiment of the present invention. 
         FIG. 5  is a circuit diagram illustrating a frequency-converted SIL radar in accordance with a third embodiment of the present invention. 
         FIG. 6  is a circuit diagram illustrating a frequency-converted SIL radar in accordance with a fourth embodiment of the present invention. 
         FIG. 7  shows experimental results by using the frequency-converted SIL radar of the first embodiment of the present invention and a conventional SIL radar. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a frequency-converted SIL radar  100  of one embodiment of the present invention includes a self-injection-locked oscillator (SILO)  110 , a frequency converter  120 , a transceiver antenna element  130  and a demodulator  140 . The frequency converter  120  and the demodulator  140  are electrically connected to the SILO  110 , and the transceiver antenna element  130  is electrically connected to the frequency converter  120 . 
     The SILO  110  is configured to generate a first oscillation signal S O1  which has a center frequency controlled by a voltage (not shown) received by the SILO  110 . The frequency converter  120  receives the first oscillation signal S O1  from the SILO  110  and converts its center frequency to output a second oscillation signal S O2 . The frequency converter  120  can either up or down convert the center frequency of the first oscillation signal S O1  to the second oscillation signal S O2 . 
     The transceiver antenna element  130  receives the second oscillation signal S O2  from the frequency converter  120 , transmits the second oscillation signal S O2  as a transmitted signal S T  toward an object O and receives a reflected signal S R  as a first injection signal S IN1  from the object O. The first injection signal S IN1  is delivered to the frequency converter  120 . The Doppler Effect may be observed in the transmitted signal S T  when there is a motion of the object O relative to the transceiver antenna element  130 , consequently, the reflected signal S R  and the first injection signal S IN1  contain the Doppler shift components caused by the relative movement. 
     The frequency converter  120  receives the first injection signal S IN1  and changes a center frequency of the first injection signal S IN1  to output a second injection signal S IN2  which also contains the Doppler shift components caused by the relative movement. The center frequency of the first injection signal S IN1  may be up or down converted to the second injection signal S IN2  by the frequency converter  120 . The frequency converter  120  is configured to convert the first oscillation signal S O1  and the first injection signal S IN1  reversely so that the center frequency of the second injection signal S IN2  is similar to the oscillating frequency of the SILO  110 . The center frequency of the first injection signal S IN1  is down when that of the first oscillation signal S O1  is up. On the contrary, the center frequency of the first injection signal S IN1  is up when that of the first oscillation signal S O1  is down. If the second injection signal S IN2  converted by the frequency converter  120  injects into the SILO  110 , the SILO  110  is locked in a self-injection-locked state and a frequency variation of the first oscillation signal S O1  from the locked SILO  110  is observed due to the second injection signal S IN2  contains the Doppler shift components. The demodulator  140  receives and demodulates the first oscillation signal S O1  so as to measure the vibration frequency of the moving object O relative to the transceiver antenna element  130 . 
       FIG. 2  is a circuit diagram showing a first embodiment of the present invention, and the frequency converter  120  of the first embodiment is provided to down the center frequency of the first oscillation signal S O1  and up the center frequency of the first injection signal S IN1 . In the first embodiment, the SILO  110  is a voltage-controlled oscillator adapted to output the first oscillation signal S O1  having a center frequency of 5.8 GHz. The first oscillation signal S O1  is divided into two signals by a coupler C, the two signals are delivered to the frequency converter  120  and the demodulator  140 , respectively. The frequency converter  120  of the first embodiment includes a local oscillator  121 , a power splitter  122 , a down mixer  123  and an up mixer  124 . The local oscillator  121  is configured to generate a local oscillation signal S LO  having a frequency of 4.885 GHz. The power splitter  122  is electrically connected to the local oscillator  121  and configured to receive and divide the local oscillation signal S LO  into two signals. The down mixer  123  is electrically connected to the local oscillator  121  via the power splitter  122  and electrically connected to the SILO  110  via the coupler C. The down mixer  123  receives the local oscillation signal S LO  from the power splitter  122  and receive the first oscillation signal S O1  from the coupler C, and further, the down mixer  123  mixes the local oscillation signal S LO  and the first oscillation signal S O1  to down-convert the center frequency of the first oscillation signal S O1 . The second oscillation signal S O2  converted from the first oscillation signal S O1  has a center frequency of 0.915 GHz. 
     The second oscillation signal S O2  from the frequency converter  120  is received and transmitted as the transmitted signal S T  by a transmitting antenna  131  of the transceiver antenna element  130 , and the reflected signal S R  from the object O is received as the first injection signal S IN1  by a receiving antenna  132  of the transceiver antenna element  130 . The transmitted signal S T , the reflected signal S R  and the first injection signal S IN1  are all centered in 0.915 GHz with lower wireless propagation loss and better penetration because of the second oscillation signal S O2  having a center frequency of 0.915 GHz. The up mixer  124  is electrically connected to the local oscillator  121  via the power splitter  122  and electrically connected to the receiving antenna  132  via a low-noise amplifier LNA such that the up mixer  124  can receive the local oscillation signal S LO  from the power splitter  122  and receive the first injection signal S IN1  from the low-noise amplifier LNA which is provided to amplify the first injection signal S IN1 . The first injection signal S IN1  is mixed with the local oscillation signal S LO  by the up mixer  124  to increase center frequency so that the second injection signal S IN2  has a center frequency of 5.8 GHz, similar to the oscillating frequency of the SILO  110 , and is able to injection-lock the SILO  110 . 
     With reference to  FIG. 3 , the transceiver antenna element  130  may be a single antenna system having a circulator  133  and a transceiver antenna  134 . The second oscillation signal S O2  can be delivered to a first port  133   a  of the circulator  133 , outputted to the transceiver antenna  134  from a second port  133   b  of the circulator  133 , and transmitted as the transmitted signal S T  from the transceiver antenna  134 . The reflected signal S R  is received as the first injection signal S IN1  by the transceiver antenna  134 , and the first injection signal S IN1  is delivered to the second port  133   b  of the circulator  133  and outputted from a third port  133   c  of the circulator  133  to the low-noise amplifier LNA. 
     With reference to  FIG. 2 , the center frequencies of the first oscillation signal S O1  and the second oscillation signal S O2  are, but not limited to, 5.8 GHz and 0.915 GHz, respectively. The SILO  110  operating at 5.8 GHz has a good sensitivity to the Doppler shift components caused by tiny movements, and the transmitted signal S T  and the reflected signal S R  centered in the 0.915 GHz by the frequency converter  120  have better penetration. Because of the frequency conversion of the frequency converter  120 , the frequency-converted SIL radar  100  of the first embodiment has both high sensitivity and penetration. 
     With reference to  FIG. 2 , the demodulator  140  of the first embodiment is a frequency demodulator including a power splitter  141 , a delay line  142 , a first mixer  143 , a second mixer  144  and a processor  145 . The power splitter  141  is electrically connected to the SILO  110  via the coupler C, the delay line  142  is electrically connected to the power splitter  141 , the first mixer  143  and the second mixer  144  are electrically connected to the power splitter  141  and the delay line  142 , and the processor  145  is electrically connected to the first mixer  143  and the second mixer  144 . The power splitter  141  receives the first oscillation signal S O1  from the coupler C and divide the first oscillation signal S O1  into two paths. The first oscillation signal S O1  in one path is delivered to the first mixer  143  and the second mixer  144  directly, and the first oscillation signal S O1  in the other path is delivered to the first mixer  143  and the second mixer  144  as a quadrature signal 90° and an in-phase signal 0°, respectively, via the delay line  142  and a quadrature power splitter (not shown). The first mixer  143  and the second mixer  144  mix the signals to output a first mixing signal S Q  and a second mixing signal S I , respectively. The processor  145  receives and processes the first mixing signal S O  and the second mixing signal S I  to output a demodulated signal S demod . 
       FIG. 4  represents the frequency converter  120  of a second embodiment of the present invention. The frequency converter  120  in the second embodiment utilizes a frequency divider  125  and a frequency multiplier  126  to down-convert the center frequency of the first oscillation signal S O1  and up-convert the center frequency of the first injection signal S IN1 . The frequency divider  125  is electrically connected to the SILO  110  for receiving the first oscillation signal S O1  and is provided to divide the center frequency of the first oscillation signal S O1  by a constant N to down-convert the first oscillation signal S O1  to the second oscillation signal S O2 . The frequency multiplier  126  is electrically connected to the transceiver antenna element  130  to receive the first injection signal S IN1  and provided to multiply the center frequency of the first injection signal S IN1  by the constant N to up-convert the first injection signal S IN1  into the second injection signal S IN2 . The frequency converter  120  of the second embodiment is utilized to change the center frequencies of the first oscillation signal S O1  and the first injection signal S IN1  such that the SILO  110  can operate at high frequency and the transmitted signal S T  can be transmitted at low frequency. As a result, the frequency-converted SIL radar  100  of the second embodiment is capable of achieving balance between sensitivity and penetration. 
     With reference to  FIG. 5 , different to the first embodiment, the frequency converter  120  of a third embodiment is provided to up-convert the center frequency of the first oscillation signal S O1  and down-convert the center frequency of the first injection signal S IN1 . In the third embodiment, the up mixer  124  of the frequency converter  120  is electrically connected to the local oscillator  121  and the SILO  110  in order to receive the local oscillation signal S LO  from the local oscillator  121  and receive the first oscillation signal S O1  from the SILO  110 . The first oscillation signal S O1  is mixed with the local oscillation signal S LO  by the up mixer  124  to increase center frequency so that the first oscillation signal S O1  is converted into the second oscillation signal S O2 . The second oscillation signal S O2  is delivered to the transceiver antenna element  130  and transmitted as the transmitted signal S T . The down mixer  123  of the frequency converter  120  is electrically connected to the local oscillator  121  and the transceiver antenna element  130  for receiving the local oscillation signal S LO  from the local oscillator  121  and receiving the first injection signal S IN1  from the transceiver antenna element  130 . And the down mixer  123  mixes the local oscillation signal S LO  and the first injection signal S IN1  to decrease the center frequency of the first injection signal S IN1 , as a result, the first injection signal S IN1  is converted to the second injection signal S IN2 . The center frequency of the transmitted signal S T  from the transceiver antenna element  130  is higher than the oscillating frequency of the SILO  110  so the frequency-converted SIL radar  100  of the third embodiment is highly sensitive to tiny movements and able to reduce size because of the transmitted signal S T  having high frequency. Besides, the SILO  110  operating at low frequency also can simplify the architecture. 
     With reference to  FIG. 6 , the frequency converter  120  of a fourth embodiment is designed to up-convert the center frequency of the first oscillation signal S O1  and down-convert the center frequency of the first injection signal S IN1 . Different to the third embodiment, the frequency converter  120  utilizes a frequency divider  125  and a frequency multiplier  126  to convert frequency in the fourth embodiment. The frequency multiplier  126  is electrically connected to the SILO  110  and configured to receive the first oscillation signal S O1  and multiply the center frequency of the first oscillation signal S O1  by a constant N such that the first oscillation signal S O1  is up-converted into the second oscillation signal S O2 . The frequency divider  125  is electrically connected to the transceiver antenna element  130  and configured to receive the first injection signal S IN1  and divide the center frequency of the first injection signal S IN1  by the constant N to down-convert the first injection signal S IN1  into the second injection signal S IN2 . Similarly, the center frequencies of the first oscillation signal S O1  and the first injection signal S IN1  are changed by the frequency converter  120  to allow the SILO  110  to operate at low frequency and allow the transmitted signal S T  to be transmitted at high frequency. Hence, the frequency-converted SIL radar  100  of the fourth embodiment has advantages of high sensitivity and low manufacturing cost. 
     With reference to  FIG. 7 , it shows experimental results by using the frequency-converted SIL radar  100  of the first embodiment and a conventional SIL radar. The present and conventional SIL radars are used to detect vital signs of a subject behind a 30 cm-thick concrete wall, and the distances from the radars to the wall and the subject are 0.5 m and 1.5 m. The conventional SIL radar has no frequency converter and its oscillation signal and transmitted signal both have a frequency of 5.8 GHz. As shown in  FIG. 7 , the frequency-converted SIL radar  100  of the present invention has better sensitivity to detect respiration and heartbeat of the subject. Compared to the present SIL radar, the conventional SIL radar can detect the respiration, but not the heartbeat. The results proves that the center frequency down conversion of the oscillation signal S O  by using the frequency converter  120  of the present invention actually can improve the penetration of the transmitted signal S T  and also maintain the high sensitivity to the tiny vibration. 
     The center frequencies of the oscillation signal S O  and the injection signal S IN  are changed by the frequency converter  120  such that the SILO  110  has an oscillation frequency different to that of the transmitted signal S T  and is injection-locked by the injection signal S IN . Consequently, the frequency-converted SIL radar  100  of the present invention has both high sensitivity and penetration, or has both high sensitivity and low cost. 
     The scope of the present invention is only limited by the following claims. Any alternation and modification without departing from the scope and spirit of the present invention will become apparent to those skilled in the art.