WO2006015436A1 - Procede et dispositif pour l’isolation d’un emetteur-recepteur - Google Patents

Procede et dispositif pour l’isolation d’un emetteur-recepteur Download PDF

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Publication number
WO2006015436A1
WO2006015436A1 PCT/AU2005/001201 AU2005001201W WO2006015436A1 WO 2006015436 A1 WO2006015436 A1 WO 2006015436A1 AU 2005001201 W AU2005001201 W AU 2005001201W WO 2006015436 A1 WO2006015436 A1 WO 2006015436A1
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WO
WIPO (PCT)
Prior art keywords
switch
terminal
antenna
receiver
transmitter
Prior art date
Application number
PCT/AU2005/001201
Other languages
English (en)
Inventor
Pieter Willem Van Der Walt
Paulus Jocobus Van Der Merwe
Johannes Hendrik Cloete
Iain Mclaren Mason
Original Assignee
Geomole Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2004904543A external-priority patent/AU2004904543A0/en
Application filed by Geomole Pty Ltd filed Critical Geomole Pty Ltd
Priority to AU2005270744A priority Critical patent/AU2005270744B2/en
Priority to CA2576273A priority patent/CA2576273C/fr
Publication of WO2006015436A1 publication Critical patent/WO2006015436A1/fr

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Classifications

    • 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
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • 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
    • G01S7/03—Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
    • G01S7/034—Duplexers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
    • G01V3/30—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with electromagnetic waves
    • 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
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/885—Radar or analogous systems specially adapted for specific applications for ground probing
    • 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
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques

Definitions

  • the present invention relates to a transmit/receive switch (T/R switch). More particularly, the invention relates to a T/R switch for a transceiver comprising a transmitter and a receiver, for providing high isolation between the transmitter and receiver, particularly in broadband applications where the delay between a transmitted signal and detection of a target echo is comparable to the duration of the transmission process.
  • T/R switch for a transceiver comprising a transmitter and a receiver, for providing high isolation between the transmitter and receiver, particularly in broadband applications where the delay between a transmitted signal and detection of a target echo is comparable to the duration of the transmission process.
  • a typical environment in which a transceiver may be used is borehole radar, and in particular a monostatic borehole radar using a single-feed point antenna.
  • a borehole radar comprises a relatively powerful transmitter (T x ), a wide-band antenna, and a sensitive receiver (R x ).
  • the transmitter (T x ) is positioned in a borehole and excites the antenna to radiate electromagnetic pulses which propagate into the surrounding rock or earth.
  • the transmitted electromagnetic pulses are characterized by short rise/fall times to obtain sufficient resolution in the eventual radar data, and by sufficiently high energy levels to overcome attenuation and spreading losses in the surrounding rock medium.
  • Transmitted electromagnetic pulses propagate through the rock and reflect off geological features such as interfaces between rock media having differing electromagnetic properties.
  • reflected signals may have a short two way propagation time.
  • a receiver (R x ) is used to detect such reflected signals.
  • the receiver is usually located in the same borehole as the transmitter, and must be sufficiently sensitive to detect signals which have suffered attenuation and reflection losses.
  • the receiver detects and amplifies the received signal, and records the arrival time relative to the time that the transmitted pulse was radiated.
  • the sensitive receiver may saturate or even be damaged if exposed to excessive input signals, for example if a substantially unattenuated signal is received directly from the transmitter. Any degradation of the signal to noise ratio in the receiver reduces the range of the system.
  • the bandwidth of the receiver should at least equal the bandwidth of the radiated pulse to preserve resolution and integrity of the data.
  • Borehole radar systems often employ a bi-static configuration, with the transmitter and receiver deployed as two completely separate units (probes) in the same borehole. The physical distance between the two probes is increased until adequate isolation between the receiver and the transmitted pulse is achieved. Signal synchronization is often achieved by use of an optic fibre between the two probes. The closest discernible target is determined by the duration of saturation (if present) in the receiver, and whether the resultant oblique signal path is within the radiation pattern of the transmitter- and receiver antennas. Bi-static systems perform well but are awkward to deploy in constrained spaces, for example mining stope faces. The optic fibre link is also susceptible to damage in mining and other industrial environments.
  • T/R-switches are typically 3-port (6-terminal) devices used in conjunction with a parallel connection of the transmitter, receiver and antenna, with the transmitter, receiver and antenna connected to separate ports, such that the T/R-switch may in the transmit state disconnect the terminals of the receiver, or in the receive state may disconnect the terminals of the transmitter from the parallel connection.
  • the present invention provides a transmit/receive
  • TfR switch comprising: a first switch terminal for connection to a first terminal of an antenna; a second switch terminal for connection to a first terminal of a transmitter; and switch receiver terminals for connection to a receiver; wherein the T/R switch is operable to implement a transmit state by connecting transmit signals from the second switch terminal to the first switch terminal, and by isolating the switch receiver terminals; wherein the T/R switch is operable to implement a receive state by causing short circuiting of a transmitter connected to the second switch terminal such that signals from a second terminal of an antenna may be received at the second switch terminal via the short circuited transmitter; and wherein in the receive state the T/R switch is operable to pass signals received at the first switch terminal and the second switch terminal to the receiver terminals
  • the present invention provides a transceiver comprising: an antenna for transmitting and receiving signals, having a first antenna terminal and a second antenna terminal; a transmitter for producing transmit signals in a transmit state and operable to be short circuited in a receive state, the transmitter having a first transmitter terminal and a second transmitter terminal; a receiver for receiving signals from the antenna; and a transmit/receive (T/R) switch having a first switch terminal, a second switch terminal, and switch receiver terminals, wherein the first switch terminal is connected to the first antenna terminal, the second switch terminal is connected to the first transmitter terminal, the second transmitter terminal is connected to the second antenna terminal, and the switch receiver terminals are connected to the receiver; wherein the T/R switch is operable in the transmit state to connect transmit signals from the second switch terminal to the first switch terminal, and to isolate the receiver terminals; wherein the T/R switch is operable in the receive state to receive signals from the second antenna terminal at the second switch terminal via the short circuited transmitter; and wherein the T/R
  • the present invention provides a method of operating a T/R switch, comprising: in a transmit state connecting transmit signals received at a second switch terminal to a first switch terminal, and isolating switch receiver terminals; and in a receive state causing short circuiting of a transmitter connected to the second switch terminal, and passing received signals from the first switch terminal and the second switch terminal to the receiver terminals.
  • the present invention provides a method of operating a transceiver, comprising: in a transmit state, connecting transmit signals of a transmitter from a second switch terminal to a first switch terminal, and isolating switch receiver terminals; and in a receive state, short circuiting the transmitter, passing a received signal from the antenna to the first switch terminal and via the short circuited transmitter to the second switch terminal, and passing the received signal from the first and second switch terminals to the receiver terminals.
  • the present invention provides a computer program for operating a TVR switch; comprising: code for connecting transmit signals received at a second switch terminal to a first switch terminal in a transmit state; code for isolating switch receiver terminals in the transmit state; code for causing short circuiting of a transmitter connected to the second switch terminal in a receive state; and code for passing received signals from the first switch terminal and the second switch terminal to the receiver terminals in the receive state.
  • the present invention provides a computer program for operating a transceiver, comprising: code for connecting transmit signals of a transmitter from a second switch terminal to a first switch terminal in a transmit state; code for isolating switch receiver terminals in the transmit state; code for short circuiting the transmitter in a receive state, such that a received signal from the antenna is passed to the first switch terminal and via the short circuited transmitter to the second switch terminal; and code for connecting the first and second switch terminals to the receiver terminals such that the received signal is passed from the first and second switch terminals to the receiver terminals.
  • the switch receiver terminals comprise a first switch receiver terminal and a second switch receiver terminal.
  • switching between the transmit state and the receive state is preferably balanced switching, such that switching transients appearing at the first switch receiver terminal are substantially equal to switching transients appearing at the second switch receiver terminal.
  • Such embodiments enable common mode rejection of such switching transients in the receiver, thus providing for sensing of received signals to be achieved immediately after settling of major switching transients, and thus enabling short two way propagation time signals, such as reflections from close targets, to be sensed.
  • a bypass circuit is incorporated between the first and second switch terminals on the one hand and the first and second receiver terminals on the other hand.
  • the bypass circuit is configured to minimise transmission of undesired low-frequency/long time constant signals caused by residual antenna transients to the receiver terminals, while allowing transmission of desired high-frequency signals such as target echoes to the receiver terminals.
  • the bypass circuit minimises transmission of differential transient signals by damping residual currents caused by antenna relaxation.
  • the bypass circuit may comprise a diplexer, and may be tuneable. Additionally or alternatively, the bypass circuit may provide for imposing a delay before the first and second switch terminals are connected to the receiver terminals, the delay being sufficient to allow post-transmission differential transients to decay below a receiver saturation level.
  • a controllable connection between the first switch terminal and the second switch terminal is provided by a first switch element and a second switch element in series and having a ground connection between the first switch element and the second switch element. Where the first switch terminal and second switch terminal are matched, such embodiments provide for balanced switching of the controllable connection between the first switch terminal and the second switch terminal.
  • a controllable connection between the first switch terminal and the first switch receiver terminal is preferably provided by a third switch element
  • a controllable connection between the second switch terminal and the second switch receiver terminal is preferably provided by a fourth switch element, wherein the third switch element and the fourth switch element are matched.
  • common mode switching transients may be substantially removed by use of a transformer, or by use of a differential amplifier.
  • the present invention recognises that, in designing a transceiver operable to both transmit and receive signals, it is desirable to use a T/R switch in order to enable a transmitter of the transceiver and a receiver of the transceiver to share a single antenna, thus realizing a monostatic system.
  • Use of a single antenna ensures identical transmitting and receiving beam shape, and further avoids the cost and increased physical size associated with providing two antennas.
  • size restrictions on the maximum dimensions of the radar device exist, and in such applications use of a single antenna can assist in meeting such restrictions.
  • the mining environment also promotes the use of the shortest possible system.
  • a T/R switch in accordance with the present invention is used to facilitate implementation of a monostatic system, where the receiver and the transmitter use the same antenna.
  • the time associated with switching from the transmit state to the receive state is typically significantly longer than the duration of the transmitted signal. This allows for frequency domain filtering to separate the switching signal, created by the T/R-switch, from the RF-signal to be detected.
  • Embodiments of the present invention may be used in implementing borehole radar, and in particular monostatic borehole radar using a single feedpoint antenna.
  • the antenna configuration may comprise a damped antenna, an undamped antenna, a symmetric antenna, an asymmetric antenna, a single feedpoint antenna and/or a double feedpoint antenna.
  • a monostatic antenna as disclosed in International Application No PCT/AU02/001382, the content of which is incorporated herein by reference, may be used.
  • an antenna in conjunction with which the transmit/receive switch is used is preferably matched to an expected medium of propagation. For example, where it is anticipated that the borehole radar is to be used in an air-filled borehole, the antenna is preferably matched to air.
  • the expected medium may additionally or alternatively comprise one or more of water, drilling fluid, or oil.
  • the expected medium may additionally or alternatively comprise one or more of water, drilling fluid, or oil.
  • the transmitter comprises an N-channel metal oxide semiconductor (NMOS) transistor, operable to produce transmit signals in the transmit state, and presenting a low impedance when the drain-source voltage is small, in the receive state.
  • NMOS N-channel metal oxide semiconductor
  • a borehole radar embodying the present invention may be deployed in accordance with the teachings of Australian Provisional Application No. 2004906114, the content of which is incorporated herein by reference.
  • a borehole radar embodying the present invention may be deployed in accordance with the teachings of Australian Provisional Application No. 2005900071, the content of which is incorporated herein by reference.
  • FIGS. Ia and Ib are schematics of a borehole radar transceiver in accordance with a first embodiment of the invention
  • Figure 2 is a schematic of a borehole radar transceiver in accordance with a second embodiment of the invention
  • Figure 3 is a circuit diagram of the borehole radar transceiver of Figure 2;
  • Figures 4a and 4b are schematics of a borehole radar transceiver in accordance with a third embodiment of the invention.
  • Figure 5 is a schematic of a borehole radar transceiver in accordance with a fourth embodiment of the invention
  • Figure 6 is a circuit diagrams of the borehole radar transceiver of Figure 5;
  • Figure 7 is a circuit diagram of a borehole radar transceiver in accordance with a fifth embodiment of the invention.
  • Transceiver 100 comprises an antenna 105, transmitter 110, transmit/receive (T/R) switch 120, and a receiver 130.
  • a first antenna terminal 106 is connected to a first switch terminal 121, and a second antenna terminal 107 is connected to a second transmitter terminal 111.
  • a first transmitter terminal 112 is connected to a second switch terminal 122.
  • First switch receiver terminal 123 and second switch receiver terminal 124 are connected to receiver 130.
  • Figure Ia illustrates transceiver 100 in a transmit state, in which second switch terminal 122 is connected to first switch terminal 121 due to switching means 125 being closed. Switches 126 and 127 are open thus isolating switch receiver terminals 123 and 124, and thus isolating receiver 130 in the transmit state. As receiver 130 would typically comprise high gain amplifiers, isolation is important during the production of high power signals by transmitter 110. The closing of switching means
  • FIG. 125 during the transmit state allows signals produced by transmitter 1 10 to be transmitted by antenna 105.
  • Figure Ib illustrates transceiver 100 in a receive state, wherein electromagnetic signals detected by antenna 105 are passed to receiver 130.
  • Transmitter 110 has been short circuited such that signals from second antenna terminal 107 are passed to second switch terminal 122. Opening of switching means 125, and closing of switching means
  • transceiver 100 passes received signals to receiver 130.
  • FIG. 2 is a schematic of a monostatic borehole radar transceiver 200 in accordance with a second embodiment of the invention.
  • the antenna 210 has a first terminal Al and a second terminal A2
  • transmitter 220 has a first terminal TXl and a second terminal TX2
  • T/R-switch has two input terminals TRl and TR2.
  • Al is connected to TRl
  • TR2 is connected to TX2
  • TXl is connected to A2.
  • the T/R- switch is also connected to the input terminals RXl and RX2 of the receiver 240.
  • the T/R-switch has a pair of identical shunt switches Pl and P2 and a pair of identical series switches Sl and S2.
  • Pl is connected between TRl and ground, while P2 is connected between TR2 and ground.
  • Sl is connected between TRl and RXl, while S2 is connected between TR2 and RX2.
  • the shunt switches Pl and P2 are on and thus in a low impedance state, and the series switches Sl and S2 are off, in a high impedance state. This effectively connects TX2 to Al and disconnects RXl and RX2 from Al and TX2 respectively.
  • the transmitter 220 consequently drives the antenna 210 directly and the receiver 240 is isolated in two stages.
  • shunt switches Pl and P2 are off, in a high impedance state, and the series switches S 1 and S2 are on, in a low impedance state.
  • the transmitter 220 is in a low RF impedance state so that A2 appears to be connected to TR2.
  • RXl is effectively connected to Al and RX2 is effectively connected to A2.
  • the antenna 210 consequently drives the receiver 240 directly with minimum loss in the transmitter 240 and T/R-switch.
  • Switching the switches Pl, P2, Sl and S2 between low and high impedance states introduces switching transients into the signal path. Such switching transients have sufficient amplitude to cause prolonged saturation of the input amplifiers of receiver 240 if applied directly to the receiver's input.
  • the T/R-switch is able to switch the transceiver 200 from the transmit state to the receive state in a time comparable to the duration of the signal transmitted and received on the antenna 210, in order for the receiver 240 to discern close-in targets.
  • This causes the frequency spectrum of the switching transients to overlap that of the signal received on the antenna 210. Consequently the signal received on the antenna 210 cannot be separated from the switching transient by frequency domain filtering.
  • shunt switch Pl is operated so that the transient it creates on TRl relative to ground is substantially identical to the transient created by shunt switch P2 on TR2 relative to ground.
  • FIG. 3 is a circuit diagram of the monostatic borehole radar transceiver of
  • the transmitter 220 comprises an N-channel metal oxide semiconductor (NMOS) transistor QTX connected to a DC power supply VCCl through resistor RTX.
  • NMOS metal oxide semiconductor
  • a control voltage TX-CTRL is applied between the gate and source of QTX.
  • the drain of QTX is at a voltage level close to that of VCCl in the steady state condition, where the transmitter's control voltage TX-CTRL is zero.
  • the gate voltage of QTX rises rapidly relative to the source voltage during transmit mode. This causes QTX to create a sharp falling voltage transient between terminals TXl and TX2 (QTX drain-source voltage). The equivalent drain-source impedance of QTX is then very low and remains in this state during the receive mode, which commences after the sharp falling transient has been generated. The transmitter 220 is allowed to recover to its steady state condition upon completion of the receive state.
  • the second terminal TR2 of T/R switch 230 is connected to TX2 of the transmitter, and the first input terminal TRl of T/R switch 230 is connected to an antenna terminal Al.
  • Transformer TFl allows the T/R-switch 230 and transmitter 220 to have a common ground, even though the signal monitored by the T/R-switch 230 is superimposed on the drain voltage of transistor QTX.
  • the two shunt switches Pl and P2 of Figure 2 are realized by two identical NMOS transistors Ql and Q2, with their drains connected to nodes TRlA and TR2A, respectively, and to a second, common DC power supply VCC2 through two identical resistors Rl and R2, respectively.
  • the sources of Ql and Q2 are connected to the ground of the T/R-switch 230.
  • the single control voltage TR-CTRL of the T/R-switch 230 is applied to the gates of both Ql and Q2.
  • Two identical Schottky diodes Dl and D2 and two identical resistors R3 and R4 are used to implement the series switches Sl and S2 of Figure 2.
  • the anodes of Dl and D2 are connected to nodes TRlA and TR2A, respectively.
  • the cathodes of Dl and D2 are in turn connected to a third, common DC power supply VCC3 through R3 and R4, respectively.
  • the node at the cathode of Dl is TRlB and the node at the cathode of D2 is TR2B.
  • the voltage level of VCC3 is slightly higher than the anticipated voltage levels associated with leakage from the transmitted pulse through to TRlA and TRlB, and is significantly lower than the voltage of VCC2.
  • a positive voltage higher than the gate-source threshold voltage of the NMOS transistors Ql and Q2 is applied to the control voltage input TR-CTRL of the T/R- switch 230 during the transmit state.
  • This combination of the low impedance between TRlA and TR2A, the high impedance between TRlA and TRlB and the high impedance between TR2A and TR2B isolates the receiver 240 from the transmitted pulse.
  • the impedance seen between TRl and TR2 is close to zero so that TX2 is in effect directly connected to Al.
  • TXl is already hard wired to A2.
  • the transient generated by the transmitter 220 between TXl and TX2 will therefore be applied to and radiated by the antenna 210.
  • the control voltage TR-CTRL of the T/R-switch 230 is reduced to zero soon after the transmitter 220 radiates the voltage transient on the antenna 210, to initiate the receive state.
  • This causes the drain-source impedance of Ql and Q2 to rise and the voltages on TRlA and TR2A to recover concurrently to a value slightly higher than VCC3.
  • Dl and D2 become conducting substantially simultaneously and enter a low impedance state.
  • This causes the quiescent voltage at TRlA to rise further to a bias point determined by VCC2, VCC3, Rl, R3 and the forward voltage of Dl.
  • the quiescent voltage at TR2A rises to substantially the same bias point, determined by
  • the low output impedance of the NMOS transistor QTX of the transmitter 220 during the receive state effectively connects TR2 to A2.
  • TRl is already hard wired to the Al.
  • the signal received on the antenna Al, A2 is therefore passed through to the receiver terminals RXl, RX2 with minimum loss.
  • the synchronous switching action of Ql and Q2 causes substantially identical switching transient waveforms on TRlA and TR2A relative to ground.
  • Dl is consequently activated in a substantially identical manner as D2 and similar waveforms are generated between TRlA and TRlB and between TR2A and TR2B.
  • the waveform observed on TRlB relative to ground is therefore substantially identical to that observed on TR2B relative to ground, and thus switching transients are controlled to be a common mode signal.
  • transformer TF2 can only couple a differential signal from its primary winding to its secondary winding, the common mode switching transients are rejected whereas the differential signal applied between TRlC and TR2C passes through TF2 to terminals RXl and RX2.
  • the parasitic reactance of the devices used in this embodiment limits the bandwidth and phase response of the differential path of the T/R switch 230 in receive mode.
  • the main contributors of parasitic reactance are the drain-source capacitance of the NMOS transistors Ql and Q2 and the leakage inductance of the transformers TFl and TF2.
  • Ll, Cl and C2 compensates for the parasitic reactance of Ql, Q2 and TF2 in a second order, flat phase, band pass filter, to ensure a controlled frequency response.
  • the T/R-switch 230 then combines with the receiver to create a path with fixed characteristic impedance, in the pass band.
  • Rl and R2 and the value of R3 and R4 are compromises between minimum loss in the differential path of the T/R-switch 230, quick recovery time of the respective drain voltages of Ql and Q2 as well as sufficient bias current for Dl and D2. While the embodiment of the invention set out in Figure 3 and described in the preceding operates in a desired manner, particularly when the antenna Al, A2 is in an air environment, it has been recognised that immersion of antenna Al, A2 in a high- susceptibility electrically polarizable medium, such as water, drilling fluid or oil, can cause performance degradation. It has further been recognised that this degradation arises for the following reasons.
  • the antenna Al, A2 Prior to closing of switch QTX, the antenna Al, A2 is charged to a high energy state in preparation for electromagnetic (EM) pulse radiation.
  • EM electromagnetic
  • the desired EM pulse is promptly radiated by the antenna Al, A2.
  • the antenna Al, A2 discharges or relaxes electroquasistatically by means of a residual current flowing through the primary winding of TFl, between arms Al and A2.
  • This residual current induces a secondary current in the low resistance loop created by the secondary winding of transformer TFl and the two switches Ql and Q2 in their low impedance state. No signal is produced at the output of the TR switch, while switches Dl and D2 are open with the TR switch in transmit mode or isolate mode.
  • the differential transient is generated by the antenna. It is fundamentally dependent on antenna capacitance. Notably, antenna capacitance, and thus potential energy stored on the antenna, is significantly increased when the antenna is immersed in a high-susceptibility electrically polarizable medium, and the associated significant increase in electroquasistatic (EQS) charge relaxation time.
  • EQS electroquasistatic
  • the amplitude of the differential transient may be substantially reduced by incorporating a low-frequency bypass circuit in the T/R switch, as exemplified by the embodiments of Figures 4 to 7.
  • FIGS 4a and 4b are schematics of a monostatic borehole radar transceiver 400 in accordance with a first embodiment of the invention.
  • Transceiver 400 comprises an antenna 405, transmitter 410, transmit/receive (T/R) switch 420, and a receiver 430.
  • a first antenna terminal 406 is connected to a first switch terminal 421, and a second antenna terminal 407 is connected to a second transmitter terminal 411.
  • a first transmitter terminal 412 is connected to a second switch terminal 422.
  • First switch receiver terminal 423 and second switch receiver terminal 424 are connected to receiver 430.
  • FIG 4a illustrates transceiver 400 in a transmit state, in which second switch terminal 422 is connected to first switch terminal 421 via bypass circuit 428 due to switching means 425 being closed.
  • Switches 426 and 427 are open thus isolating switch receiver terminals 423 and 424, and thus isolating receiver 430 in the transmit state.
  • receiver 430 would typically comprise high gain amplifiers, isolation is important during the production of high power signals by transmitter 410.
  • the closing of switching means 425 during the transmit state allows signals produced by transmitter 410 to be transmitted by antenna 405. Following such transmission, bypass circuit 428 acts to damp residual currents caused by relaxation of antenna 405.
  • FIG. 4b illustrates transceiver 400 in a receive state, wherein electromagnetic signals detected by antenna 405 are passed to receiver 430.
  • Transmitter 410 has been short circuited such that signals from second antenna terminal 407 are passed to second switch terminal 422. Opening of switching means 425, and closing of switching means 426 and switching means 427, permits received signals to pass from first switch terminal 421 to first receiver terminal 423, and from second switch terminal 422 to second receiver terminal 424, via bypass circuit 428.
  • transceiver 400 passes received signals to receiver 430.
  • Figure 5 is a schematic of a monostatic borehole radar transceiver 500 in accordance with a second embodiment of the invention.
  • the antenna 510 has a first terminal A51 and a second terminal A52
  • transmitter 520 has a first terminal TX51 and a second terminal TX52
  • T/R-switch has two input terminals TR51 and TR52.
  • A51 is connected to TR51
  • TR52 is connected to TX52
  • TX51 is connected to A52.
  • the T/R-switch is also connected to the input terminals RX51 and RX52 of the receiver 540.
  • the T/R-switch has a pair of identical shunt switches P51 and P52 and a pair of identical series switches S51 and S52.
  • P51 is connected between TR51 and ground via bypass circuit 550
  • P52 is connected between TR52 and ground via bypass circuit 550.
  • S51 is connected between TR51 and RX51 via bypass circuit 550, while S52 is connected between TR52 and RX52 via bypass circuit 550.
  • bypass circuit 428 acts to damp residual currents caused by relaxation of antenna 405, prior to switching the circuit 500 to a receive state.
  • the bypass circuit 428 imposes resistive damping to dissipate the residual transient, while having a minimal effect on insertion loss to the receiver.
  • shunt switches P51 and P52 are off, in a high impedance state, and the series switches S51 and S52 are on, in a low impedance state.
  • the transmitter 520 is in a low RF impedance state so that A52 appears to be connected to TR52.
  • RX51 is effectively connected to A51 and RX52 is effectively connected to A52.
  • the antenna 510 consequently drives the receiver 540 directly with minimum loss in the transmitter 540 and T/R-switch. Switching the switches P51, P52, S51 and S52 between low and high impedance states introduces switching transients into the signal path. Such switching transients have sufficient amplitude to cause prolonged saturation of the input amplifiers of receiver 540 if applied directly to the receiver's input.
  • the T/R-switch it is desirable for the T/R-switch to be able to switch the transceiver 500 from the transmit state to the receive state in a time comparable to the duration of the signal transmitted and received on the antenna 510, in order for the receiver 540 to discern close-in targets. This causes the frequency spectrum of the switching transients to overlap that of the signal received on the antenna 510. Consequently the signal received on the antenna 510 cannot be separated from the switching transient by frequency domain filtering.
  • shunt switch P51 is operated so that the transient it creates on TR51 relative to ground is substantially identical to the transient created by shunt switch P52 on TR52 relative to ground.
  • series switch S51 is operated so that the transient it creates between TR51 and RX51 is substantially identical to the transient created by series switch S52 between TR52 and RX52.
  • Such switching causes the transient observed on RX51 relative to ground to be substantially identical to that observed on RX52 relative to ground.
  • the large switching transient is thus made to be a substantially common mode event and consequently the receiver 540 which detects the differential mode signal between RX51 and RX52, is substantially protected from saturation.
  • FIG. 6 is a circuit diagram of the monostatic borehole radar transceiver of Figure 5.
  • the transmitter 620 comprises an N-channel metal oxide semiconductor (NMOS) transistor QTX6 connected to a DC power supply VCC61 through resistor RTX6 A control voltage TX-CTRL6 is applied between the gate and source of QTX6.
  • the drain of QTX6 is at a voltage level close to that of VCC61 in the steady state condition, where the transmitter's control voltage TX-CTRL6 is zero.
  • NMOS N-channel metal oxide semiconductor
  • the gate voltage of QTX6 rises rapidly relative to the source voltage during transmit mode. This causes QTX6 to create a sharp falling voltage transient between terminals TX61 and TX62 (QTX6 drain-source voltage). The equivalent drain-source impedance of QTX6 is then very low and remains in this state during the receive mode, which commences after the sharp falling transient has been generated. The transmitter 620 is allowed to recover to its steady state condition upon completion of the receive state.
  • the second terminal TR62 of T/R switch 630 is connected to TX62 of the transmitter 620, and the first input terminal TR61 of T/R switch 630 is connected to an antenna terminal A61.
  • Transformer TF61 allows the T/R-switch 630 and transmitter
  • the two shunt switches S51, S52 of Figure 5 are realized by two identical NMOS transistors Q61 and Q62, with their drains connected to nodes TR61A and TR62A, respectively, and to a second, common DC power supply VCC62 through two identical resistors R61 and R62, respectively.
  • the sources of Q61 and Q62 are connected to the ground of the T/R-switch 630.
  • the single control voltage TR-CTRL6 of the T/R-switch 630 is applied to the gates of both Q61 and Q62.
  • Two identical PIN diodes D61 and D62 and two identical resistors R63 and R64 are used to implement the series switches S61 and S62 of Figure 5.
  • the anodes of D61 and D62 are connected to nodes TR61A and TR62A, respectively.
  • the cathodes of D61 and D62 are in turn connected to a third, common DC power supply VCC63 through R63 and R64, respectively.
  • the node at the cathode of D61 is TR61B and the node at the cathode of D62 is TR62B.
  • the voltage level of VCC63 is slightly higher than the anticipated voltage levels associated with leakage from the transmitted pulse through to TR61 A and TR61B, and is significantly lower than the voltage of VCC62.
  • a positive voltage higher than the gate-source threshold voltage of the NMOS transistors Q61 and Q62 is applied to the control voltage input TR-CTRL6 of the T/R- switch 630 during the transmit state.
  • the impedance seen between TR61 and TR62 is close to zero so that TX62 is in effect directly connected to A61.
  • TX61 is already hard wired to A62.
  • the transient generated by the transmitter 620 between TX61 and TX62 will therefore be applied to and radiated by the antenna 610.
  • the control voltage TR-CTRL6 of the T/R-switch 630 is reduced to zero soon after the transmitter 620 radiates the voltage transient on the antenna 610, to initiate the receive state.
  • the resultant high impedance between TR61A and TR62A, the low impedance between TR61A and TR61B and the low impedance between TR62A and TR62B allows a differential signal to pass through with minimum loss from the input TR61, TR62 to the output RX61, RX62 of the T/R-switch 630.
  • the low output impedance of the NMOS transistor QTX6 of the transmitter 620 during the receive state effectively connects TR62 to A62.
  • TR61 is already hard wired to A61.
  • the signal received on the antenna A61, A62 is therefore passed through to the receiver terminals RX61 and RX62 with minimum loss.
  • the synchronous switching action of Q61 and Q62 causes substantially identical switching transient waveforms on TR61A and TR62A relative to ground.
  • D61 is consequently activated in a substantially identical manner as D62 and similar waveforms are generated between TR61A and TR61B and between TR62A and TR62B.
  • the waveform observed on TR61B relative to ground is therefore substantially identical to that observed on TR62B relative to ground, and thus switching transients are controlled to be a common mode signal.
  • transformer TF62 can only couple a differential signal from its primary winding to its secondary winding, the common mode switching transients are rejected whereas the differential signal applied between TR61 C and TR62C passes through TF62 to terminals RX61 and RX62.
  • the parasitic reactance of the devices used in this embodiment limits the bandwidth and phase response of the differential path of the T/R switch 630 in receive mode.
  • the main contributors of parasitic reactance are the drain-source capacitance of the NMOS transistors Q61 and Q62 and the leakage inductance of the transformers TF61 and TF62.
  • the inclusion of L61, C61 and C62 compensates for the parasitic reactance of Q61, Q62 and TF62 in a second order, flat phase, band pass filter, to ensure a controlled frequency response.
  • the T/R-switch 630 then combines with the receiver to create a path with fixed characteristic impedance, in the pass band.
  • R61 and R62 and the value of R63 and R64 are compromises between minimum loss in the differential path of the T/R-switch 630, quick recovery time of the respective drain voltages of Q61 and Q62 as well as sufficient bias current for D ⁇ l and D62.
  • T/R switch 630 further includes a bypass circuit comprising resistors RD62, RD61, and capacitors CD61, CD62, CD63. Following transmission by antenna A61, A62, the bypass circuit damps residual currents caused by relaxation of antenna A61, A62.
  • FIG. 7 is a circuit diagram of a further embodiment of the present invention.
  • the transmitter 720 comprises an N-channel metal oxide semiconductor (NMOS) transistor QTX7 connected to a DC power supply VCC71 through resistor RTX7 A control voltage TX-CTRL7 is applied between the gate and source of QTX7.
  • the drain of QTX7 is at a voltage level close to that of VCC71 in the steady state condition, where the transmitter's control voltage TX-CTRL7 is zero.
  • NMOS N-channel metal oxide semiconductor
  • the gate voltage of QTX7 rises rapidly relative to the source voltage during transmit mode. This causes QTX7 to create a sharp falling voltage transient between terminals TX71 and TX72 (QTX7 drain-source voltage). The equivalent drain-source impedance of QTX7 is then very low and remains in this state during the receive mode, which commences after the sharp falling transient has been generated.
  • the transmitter 720 is allowed to recover to its steady state condition upon completion of the receive state.
  • the second terminal TR72 of T/R switch 730 is connected to TX72 of the transmitter 720, and the first input terminal TR71 of T/R switch 730 is connected to an antenna terminal A71.
  • Transformer TF71 allows the T/R-s witch 730 and transmitter 720 to have a common ground, even though the signal monitored by the T/R-switch 730 is superimposed on the drain voltage of transistor QTX7.
  • Two shunt switches are realized by two identical NMOS transistors Q71 and
  • Two identical Schottky or PIN diodes D73 and D74 and two identical inductors L73 and L74 are used to implement series switches.
  • the anodes of D73 and D74 are connected to nodes TR71A and TR72A, respectively.
  • the cathodes of D73 and D74 are in turn connected to a third, common DC power supply VCC74 through L73 and L74, respectively.
  • the node at the cathode of D73 is TR71B and the node at the cathode of D74 is TR72B.
  • the voltage level of VCC74 is slightly higher than the anticipated voltage levels associated with leakage from the transmitted pulse through to TR71 A and TR71B, and is significantly lower than the voltage of VCC72.
  • a positive voltage higher than the gate-source threshold voltage of the NMOS transistors Q71 and Q72 is applied to the control voltage input TR-CTRL7 of the T/R- switch 730 during the transmit state.
  • the control voltage TR-CTRL7 of the T/R-switch 730 is reduced to zero soon after the transmitter 720 radiates the voltage transient on the antenna 710, to initiate the receive state. This causes the drain-source impedance of Q71 and Q72 to rise and the voltages on TR71A and TR72A to recover concurrently to a value slightly higher than VCC74. At this point D73 and D74 become conducting substantially simultaneously and enter a low impedance state. This causes the quiescent voltage at TR71A to rise further to a bias point determined by VCC72, VCC74, R75, L73 and the forward voltage of D73.
  • the quiescent voltage at TR72A rises to substantially the same bias point, determined by VCC72, VCC74, R76, L74 and the forward voltage of D74.
  • the resultant high impedance between TR71A and TR72A, the low impedance between TR71A and TR71B and the low impedance between TR72A and TR72B allows a differential signal to pass through with minimum loss from the input TR71, TR72 to the output RX71, RX72 of the T/R-switch 730.
  • the low output impedance of the NMOS transistor QTX7 of the transmitter 720 during the receive state effectively connects TR72 to A72.
  • TR71 is already hard wired to A71.
  • the signal received on the antenna A71, A72 is therefore passed through to the receiver terminals RX71 and RX72 with minimum loss.
  • the synchronous switching action of Q71 and Q72 causes substantially identical switching transient waveforms on TR71A and TR72A relative to ground.
  • D73 is consequently activated in a substantially identical manner as D74 and similar waveforms are generated between TR71A and TR71B and between TR72A and TR72B.
  • the waveform observed on TR71B relative to ground is therefore substantially identical to that observed on TR72B relative to ground, and thus switching transients are controlled to be a common mode signal.
  • transformer TF72 can only couple a differential signal between its primary winding and its secondary winding, the common mode switching transients are rejected whereas the differential signal applied between TR71C and TR72C passes through TF72 to terminals RX71 and RX72.
  • the parasitic reactance of the devices used in this embodiment limits the bandwidth and phase response of the differential path of the T/R switch 730 in receive mode.
  • the main contributors of parasitic reactance are the drain-source capacitance of the NMOS transistors Q71 and Q72 and the leakage inductance of the transformers TF71 and TF72.
  • in switch 700 inductor L75 is positioned on a downstream side of capacitors C73, C74. This location of L75 is precautionary should there be energy transmitted through switch 700. Further, inductors L73 and L74 are used in place of resistors. The inclusion of L73, L74, L75, C73 and C74 implements a fourth order filter, as opposed to the second order filter provided by L61, C61 and C62 in the embodiment of Figure 6, and compensates for the parasitic reactance of Q71, Q72 and TF72 to ensure a controlled frequency response. The fourth order filter further reduces the amplitude of low frequency differential transients.
  • the T/R-switch 730 then combines with the receiver to create a path with fixed characteristic impedance, in the pass band.
  • R75 and R75 and the value of L73 and L74 are compromises between minimum loss in the differential path of the T/R-switch 730, quick recovery time of the respective drain voltages of Q71 and Q72 as well as sufficient bias current for D73 and D73.
  • T/R switch 730 further includes a bypass circuit comprising resistors RD72, RD71, and capacitors CD71, CD72, CD73. Following transmission by antenna A71, A72, the bypass circuit damps residual currents caused by relaxation of antenna A71, A72.
  • the exemplary embodiments relate to a duplexer or transmit/receive switch (T/R-switch) that enables a transmitter and a receiver to use the same antenna.
  • the T/R-switch of these embodiments has sufficient instantaneous bandwidth and linearity in its phase response to function in a pulse system without compromising the pulse shape, range or resolution of the system.
  • the T/R-switch in accordance with such embodiments of the invention provides adequate isolation between the transmitted pulse and the receiver during transmit-mode to prevent the receiver from saturating for prolonged periods. Further, the loss introduced by the T/R-switch between the antenna and the receiver in receive-mode is small enough to avoid substantial reduction in the signal to noise ratio, which would otherwise reduce the range of the system.
  • the T/R-switch possesses the ability to switch from maximum isolation in the transmit state to minimum attenuation in the receive state in a time comparable to the transmission process, in order to enable the receiver to record reflections from close-in targets.
  • the T/R-switch and transmitter are inserted in front of the receiver, in the receiver path.
  • the T/R-switch In a transmit state, the T/R-switch is responsible for isolating the receiver from the transmitted signal such that the energy from the transmitted pulse is substantially radiated by the antenna.
  • the transmitter In the receive state, the transmitter itself presents a radio frequency (RF) short circuit, thus substantially preventing echoed or reflected signals collected by the antenna from dissipating in the transmitter circuitry.
  • RF radio frequency
  • the T/R switch of the preferred embodiments relates to transceivers in which a transmit/receive switch connects an antenna to the transmitter while transmitting a signal and connects the same antenna to the receiver while receiving the reflected signal.
  • the described embodiments of the invention specifically relate to a T/R-switch with wide instantaneous bandwidth, such as a pulsed system where the delay between the radiation of the transmitted signal and the detecting of the reflected signal is comparable to the duration of the transmission process.
  • the bypass circuit enables the T/R switch to be relatively unaffected by changes in the antenna impedance due to changing conditions in the surrounding medium.
  • the receiver used in conjunction with the transmit receive switch of any of the previously described embodiments may comprise an analogue to digital converter (ADC) to allow digital sampling of a received signal.
  • ADC analogue to digital converter
  • a sensitivity time control (STC) and/or automatic gain control (AGC) is provided upstream of the STC and/or AGC to match the received analogue signal to the dynamic range of the ADC.
  • STC sensitivity time control
  • AGC automatic gain control
  • a first order high pass filter may be implemented by use of an inductor across the input of the STC or AGC, in order to speed recovery of the receiver electronics during decay of differential transients caused by antenna relaxation.
  • differential transients can have substantial low frequency components outside a frequency band of interest, and thus a high pass filter at the input to the STC or AGC assists in removing such low frequency components.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Remote Sensing (AREA)
  • Radar, Positioning & Navigation (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geophysics (AREA)
  • Transceivers (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Electronic Switches (AREA)

Abstract

La présente invention concerne un interrupteur (120) de transmission/réception (T/R) pour émetteur-récepteur (100). L’interrupteur T/R (120) possède une première borne d’interrupteur (121) pour connexion à une première borne (106) d’une antenne (105) et une deuxième borne d’interrupteur (122) pour connexion à une première borne (112) d’un émetteur (110). L’interrupteur T/R (120) possède également des bornes récepteur d’interrupteur (123, 124) pour connexion à un récepteur (130). En mode transmission, l’interrupteur T/R (120) se connecte et transmet des signaux à partir de l’émetteur (110) à la deuxième borne d’interrupteur (122) vers la première borne d’interrupteur (121), pour transmission par une antenne (105). Les terminaux récepteurs (123, 124) sont isolés pendant le mode transmission. En mode réception, l’émetteur (110) est court-circuité de telle sorte que les signaux d’une deuxième borne (107) de l’antenne (105) sont reçus à la deuxième borne d’interrupteur (122) à travers l’émetteur court-circuité (110). Pendant le mode réception, l’interrupteur T/R (120) passe des signaux reçus à la première borne d’interrupteur (121) et la deuxième borne d’interrupteur (122) vers les terminaux récepteurs (123, 124). Les transitoires résiduels d’antenne sont amortis.
PCT/AU2005/001201 2004-08-10 2005-08-10 Procede et dispositif pour l’isolation d’un emetteur-recepteur WO2006015436A1 (fr)

Priority Applications (2)

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AU2005270744A AU2005270744B2 (en) 2004-08-10 2005-08-10 Method and device for transceiver isolation
CA2576273A CA2576273C (fr) 2004-08-10 2005-08-10 Procede et dispositif pour l'isolation d'un emetteur-recepteur

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AU2004904543 2004-08-10
AU2004904543A AU2004904543A0 (en) 2004-08-10 Method and device for transceiver isolation

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PCT/AU2004/001382 WO2006015402A1 (fr) 2004-08-10 2004-10-11 Méthode et appareil pour radar de forage monostatique
PCT/AU2005/001201 WO2006015436A1 (fr) 2004-08-10 2005-08-10 Procede et dispositif pour l’isolation d’un emetteur-recepteur

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PE (1) PE20060708A1 (fr)
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CA2868602A1 (fr) * 2012-04-05 2013-10-10 Geosonde Pty Ltd Radar a courte portee pour trou de forage
US9244190B2 (en) * 2012-07-13 2016-01-26 Osaka Electro-Communication University Transmitting electric power using electromagnetic waves
CN104656154B (zh) * 2015-03-13 2018-05-04 厦门大学 共发射源探地雷达多偏移距数据自动快速测量系统
CN105911526B (zh) * 2016-04-13 2018-07-27 电子科技大学 一种井中雷达时域接收机前端
GB2563872B (en) 2017-06-28 2022-06-15 Kirintec Ltd Communications system

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EP0667684B1 (fr) * 1994-02-09 2000-06-07 Lk-Products Oy Dispositif de séparation des signaux de transmission et réception dans un émmetteur-récepteur
US5697069A (en) * 1995-10-05 1997-12-09 Daimler-Benz Aktiengesellschaft Transmit-receiver switch
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PE20060708A1 (es) 2006-08-12
CA2576273A1 (fr) 2006-02-16
ZA200701196B (en) 2009-12-30
ZA200701195B (en) 2009-12-30
CA2576169A1 (fr) 2006-02-16
CA2576273C (fr) 2016-07-19
WO2006015402A1 (fr) 2006-02-16
CA2576169C (fr) 2014-07-15

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