Apparatus and method for generating a monocycle

An apparatus for generating a monocycle comprises an input signal source (76) for providing an input signal, and a step recovery diode (SRD) (80) for receiving the input signal and producing an impulse. A shunt inductor (102) is provided to act as a first differentiator and a capacitor (92) connected in series to the output of the step recovery diode acts as a second differentiator. The first and second differentiators are arranged to double differentiate the impulse to produce a monocycle.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for generating a monocycle, for use, for example, in Ultra Wideband (UWB) systems.

BACKGROUND OF THE INVENTION

Ultra Wideband (UWB) technology, which is useful for both communication and sensing applications, is based on very short pulses and time domain signal processing. A very commonly used pulse in UWB systems is the monocycle and as the monocycle's width determines the bandwidth, a narrow pulse width is necessary for producing an ultra wideband signal.

There are several methods of generating pulses and devices used for pulse generation include, for example, tunnel diodes, avalanche transistors, and step recovery diodes (SRDs). In Ultra Wideband (UWB) applications, each pulse may represent a symbol. In a typical UWB application, the pulses are followed by a silence period (a space). The characteristics of the pulse are changed to represent the data.

FIG. 1shows conventional pulse position modulation where the position of the pulse is either advanced or delayed from its mean position to represent a symbol.FIG. 2shows conventional bi-phase modulation of the pulse to represent the symbol. InFIGS. 1 and 2, the distance between the peaks of the waveforms represents the pulse repetition period.

For high data rate applications, it is imperative that the pulse width is low to permit more pulses to be transmitted in a given period. If only one cycle of a pulse is generated, the energy may be spread over a wide frequency band. Also, the data rate may be improved as the silence period is larger and so more pulses may be transmitted, for a given duty cycle, by multiplexing other channels.

One conventional way of generating very narrow pulses is to use Step Recovery Diodes (SRDs).

Although there are many fast square wave pulse generators commercially available, there are few high speed monocycle generators.

Monocycles may be generated by twice differentiating the rising edge and falling edge of square pulses using differentiators or Impulse Forming Networks. This is described in the Impulse Forming Networks Data Sheet of Picosecond Pulse Labs. This document describes the use of the differentiation of fast rise time signals to generate pulses. Differentiation of the leading edge produces a positive impulse and differentiation of a trailing edge produces a negative impulse. One more differentiation produces a monocycle. Whilst passive resistor and capacitor elements may be used for the differentiation, the amplitude and the pulse width of the resultant monocycle depends, to a large extent, on the rise time and the fall time of the signal.

There are a number of further problems with this approach. Firstly, circuits for generating signals with fast rising edges with rise times of the order of tens of picoseconds are needed and such circuits or commercial instruments are generally expensive and not economical for low cost applications. Secondly, for every monocycle generated by the rising edge, a 180 degrees phase shifted monocycle would be generated by the falling edge. This reduces the flexibility of this approach. Thus the generation of sub-nanosecond monocycle pulses with pulse repetition rates of up to 1 GHz using low cost circuitry is very desirable. Most conventional monocycle generators use lumped elements instead of distributed elements and thus are more expensive and less repeatable due to component tolerances.

A number of alternative conventional monocycle generators use several active devices in the circuit. For example, in the system described in the document by Jeong Soo Lee, Cam Nguyen and Tom Scullion entitled “New Uniplanar Subnanosecond Monocycle Pulse Generator and Transformer for Time-Domain Microwave Applications”, June 2001 IEEE Transactions On Microwave Theory And Techniques, Vol. 49, No. 6, pp 1126-1129, Step Recovery Diodes (SRDs) are used together with Schottky diodes for generating very narrow pulses. The Schottky diode is included to overcome the ringing effect which tends otherwise to be exhibited as narrower monocycles and higher pulse repetition rates are attempted in systems using SRD circuits for generating sub-nanosecond monocycles.

The method described in the document by Jeong Soo Lee, Cam Nguyen and Tom Scullion in the document entitled “New Uniplanar Subnanosecond Monocycle Pulse Generator and Transformer for Time-Domain Microwave Applications”, June 2001 IEEE Transactions On Microwave Theory And Techniques, Vol. 49, No. 6, pp 1126-1129, combines two Gaussian pulses to produce a monocycle. The two Gaussian pulses are 180 degrees out of phase and have a time delay between them.

FIG. 3shows the circuit for generating a monocycle according to the above mentioned publication by Jeong Soo Lee, Cam Nguyen and Tom Scullion. The circuit is driven by a local oscillator1which supplies 10 MHz square wave signal to the anode of an SRD diode2. The cathode of the SRD diode is connected to a 50 Ohm short circuited transmission line3and to the anode of a Schottky diode4. The cathode of the Schottky diode4is connected to a capacitor6and to a resistor8. The resistor8is earthed. The capacitor6is connected to two further transmission lines10,12, one of which is terminated12and the other of which is short circuited10.

This method has the disadvantage of wider pulse width, as the width of the monocycle is twice the impulse width. Furthermore, the use of Schottky diodes to limit the ringing effect adds to the cost of the pulse generator.

The document by Jeong Soo Lee, Cam Nguyen and Tom Scullion in the document entitled “New Uniplanar Subnanosecond Monocycle Pulse Generator and Transformer for Time-Domain Microwave Applications”, June 2001 IEEE Transactions On Microwave Theory And Techniques, Vol. 49, No. 6, pp 1126-1129, also describes a pulse-to-monocycle converter. This differs from the circuit described above in that the SRD2is omitted, together with the short circuited transmission line3. However, the converter requires a narrow pulse to drive it instead of a square wave and it is not itself a pulse generator.

In another prior art document, entitled “A New Ultra-Wideband, Ultra-Short Monocycle Pulse Generator With Reduced Ringing”, Jeongwoo Han and Cam Nguyen, June 2002, IEEE Microwave And Wireless Components Letters, Vol. 12, No. 6, pp 206-208, a system is described and which is illustrated inFIG. 4. The circuit includes a square wave generator14which is connected to the anode of an SRD16. The cathode of the SRD is connected to a short circuited transmission line18and also to the anode of a Schottky diode20. The cathode of the Schottky diode is connected to a terminated transmission line22and to a capacitor24. The output of the capacitor24is connected to the cathode of a further Schottky diode26, the anode of which is earthed. The output of the capacitor24is also connected to a resistor28and to a further capacitor30, the output of which is earthed by a further resistor32. The output of the resistor28is connected, via a further capacitor34, to ground. A voltage source36is connected across the capacitor34. The SRD16produces a Gaussian pulse and the resistor32and capacitor30form a high pass filter which acts as a differentiator to convert the Gaussian pulse into a monocycle. The width of the monocycle formed after differentiation of the Gaussian pulse is almost the same as that of the pulse itself. The two Schottky diodes20and26act to reduce the ringing effect. The main disadvantage associated with this system is the use of the Schottky diodes, which adds to the cost of the system.

In Jeong Soo Lee and Cam Nguyen, “Novel Low-cost Ultra-Wideband, Ultra-Short-Pulse Transmitter with MESFET Impulse-Shaping Circuitry for Reduced Distortion and Improved Pulse Repetition Rate”, May 2001, IEEE Microwave And Wireless Components Letters, Vol. 11, No. 5, pp 208-210, a system is described which includes, as shown inFIG. 5, a generator37connected to the cathode of an SRD38, the anode of which is connected to a short circuited transmission line40. The anode of the SRD38is also connected to an earthed resistor42and to the gate of a MESFET44. The source of the MESFET44is earthed. The drain of the MESFET44is connected to the anode of a Schottky diode46. The cathode of the Schottky diode46is connected to an earthed resistor48and also to a capacitor50. The output of the capacitor50is connected to a short circuited transmission line52and to the input of an MMIC amplifier54. The output of the MMIC amplifier54is terminated in a resistor56which is connected to ground. The MESFET44is used as an impulse-shaping network and it enables the circuit to achieve higher pulse repetition frequencies of up to several hundreds of mega Hertz. However, the use of the MESFET44, and the Schottky diode46add to the cost of the system.

U.S. Pat. No. 4,442,362 describes a short pulse generator using an SRD. A plurality of capacitors are charged in parallel and then connected in series by a plurality of avalanche transistors to obtain a voltage which is substantially equal to the sum of the capacitor voltages when charged. The series coupled capacitors are then coupled, via an output avalanche transistor, to a differentiator which produces a monocycle pulse. This method can generate high peak amplitude pulses. However, the use of the avalanche transistors adds to the cost of the system making it too expensive for low cost systems. Also, the use of avalanche transistors limits the pulse repetition rate.

U.S. Pat. No. 3,622,808 describes a pulse shaping circuit for producing high frequency pulses using two step recovery diodes and other lumped components. The circuit is shown inFIG. 6. A signal source58, for example, a sine wave, is connected to an inductance60, the other end of which is connected via a resistor62to a voltage source (not shown). The signal source58is also connected to the cathode of an SRD64. The anode of the SRD64is connected via a further inductor66to ground. The anode of the SRD64is also connected to the cathode of a further SRD68and to the output70of the system. The anode of the further SRD68is connected via a capacitor72to ground and via a resistor74to a further power supply (not shown). This system produces narrow pulses at high frequency but does not itself produce a monocycle. The main disadvantage of this system is the high cost of the system.

Thus, there is a need for a low cost monocycle generator preferably capable of generating sub-nanosecond monocycles with pulse repetition frequencies in excess of 1 GHz.

SUMMARY OF THE INVENTION

In general terms, the present invention proposes an apparatus and method for generating a monocycle comprising an SRD together with elements for pulse generation, the impulse generated being double differentiated to generate the monocycle. This is particularly advantageous as it makes the apparatus simple and cheap to use and easily reproduceable.

Furthermore, the methods of the present invention are easily performed and the apparatus embodying the present invention is easily created.

According to a first aspect of the present invention there is provided an apparatus for generating a monocycle comprising:an input signal source for providing an input signal;a step recovery diode (SRD) to receive said input signal and produce an impulse, said step recovery diode having an input and an output; andone or more differentiators arranged to double differentiate said impulse to produce a monocycle.

According to a second aspect of the present invention there is provided an Ultra Wideband system comprising the apparatus defined above.

According to a third aspect of the present invention there is provided a system for producing multi-band signals comprising the apparatus defined above, the apparatus having an output, the system further comprising one or more band pass filters having associated inputs and outputs, wherein the output of the apparatus is connected to the inputs of said one or more band pass filters, said system further comprising one or more modulators, each modulator having an associated output, said one or more modulators being arranged to modulate the outputs of the band pass filters, and said one or more modulators being arranged such that said outputs of said one or more modulators are combined to produce a multi-band ultra-wide band signal.

According to a fourth aspect of the present invention there is provided a method for generating a monocycle comprising:providing an input signal from an input signal source to a step recovery diode;producing an impulse using said step recovery diode;differentiating said impulse twice to produce a monocycle.

According to a fifth aspect of the present invention there is provided a method for producing multi-band signals comprising:(a) generating a monocycle by:(i) providing an input signal from an input signal source to a step recovery diode;(ii) producing an impulse using said step recovery diode; and(iii) differentiating said impulse twice to produce a monocycle;(b) applying said monocycle as an input to one or more band pass filters, said one or more band pass filters having one or more outputs;(c) modulating said one or more outputs of said one or more band pass filters using one or more modulators to produce one or more modulated output signals; and(d) combining said one or more modulated output signals to produce a multi-band ultra-wide band signal.

Preferred embodiments of the invention provide a very low cost solution for generating sub-nanosecond monocycles with pulse repetition frequencies in excess of around 1 GHz.

Preferred embodiments of the invention do not require expensive circuitry for generating fast rise/fall time pulses. Furthermore, as the component count in preferred embodiments of the invention is lower than in conventional monocycle generators, and preferably only a single active element (an SRD) is required, the apparatus embodying the invention is economical to use and produce.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 6show conventional circuits for producing monocycles and/or pulses and associated waveforms. These circuits have been described above in the Background of The Invention section.

The methods and devices which illustrate preferred embodiments of the invention will be explained with reference toFIGS. 7 to 23.

Preferred embodiments of the invention relate to the generation of narrow monocycles using step recovery diodes (SRDs). These monocycles are suitable for Ultra Wideband applications. Preferably, the embodiments of the invention make use of the reverse recovery phenomenon of the SRD to generate fast transitions, and preferably use distributed microstrip elements to generate very narrow monocycle pulses from these transitions.

The SRD has the ability to store charge and to change impedance levels very rapidly. During the forward biased condition, the SRD conducts and stores the charge. When the biasing changes from the forward biased condition to the reverse biased condition, the SRD conducts for a very short duration until the stored charge is removed, after which the diode no longer conducts. This transition from the conducting to the non-conducting state is extremely fast, in the range of a few tens of picoseconds.

FIG. 7is a schematic circuit diagram of a system according to a first preferred embodiment for generating narrow monocycles. The circuit makes use of resistive matching between an SRD and a pulse forming network comprising distributed Microstrip elements to reduce the ringing. An input signal source76, which may be any form of bi-polar signal, for example a sine wave, a square wave or a pulse, is connected to a first transmission line78, the output of which is connected to the anode of an SRD80. The cathode of the SRD80is connected to a resistor88which is connected to ground. The cathode of the SRD80is also connected to a distributed capacitor92, the output of which is connected to a short circuited transmission line96in the form of a distributed inductor and to a resistor100. The distributed inductor96is also connected to ground.

In the circuit ofFIG. 7, the SRD80generates a fast transition when the input signal changes the biasing of the SRD80from forward to reverse. The resistor88is used to provide resistive matching and helps to reduce ringing.

The resistor88also provides a DC path for the SRD80. The short circuited transmission line96is used as an inductor and this transmission line and the distributed capacitor92act as differentiators. The resistor100represents the load resistance.

The output of the SRD80is fed to the pulse-forming network comprising the transmission line96and the capacitor92which each act as a differentiator to generate impulses and monocycles.

The output voltage of a differentiator is given by:
Vout=TdVin/dt
where
Vout=the output of a differentiator
Vin=the input voltage, and
T=the time derivative coefficient

Thus, the differentiators convert the fast transition of the SRD output into a pulse. The rest of the SRD output after differentiation becomes negligible.

The system illustrated inFIG. 7may generate highly symmetrical monocycles of widths less than around 300 ps with negligible ringing.

The waveform at the output of the SRD80in the circuit ofFIG. 7is shown inFIG. 8a, the impulse being formed at a point A as shown inFIG. 8a.

The circuit shown inFIG. 7has been simulated using Agilent Technologies' Advanced Design Systems (ADS) and the pulse obtained after simulation is shown inFIG. 8b. The circuit was also fabricated and tested and the measured pulse is shown inFIG. 9. The monocycle pulse generator ofFIG. 7was fabricated on 32 mil Duroid substrate with a dielectric constant of 3.38. The SRD80used was MP4023 from M/s Mpulse Microwave. The measurement was made using a 50 GHz Digital Sampling Oscilloscope. It will be seen that the measured pulse obtained from the system ofFIG. 7has good symmetry on the positive and negative parts and has a width of 260 ps. The amount of ringing is very low and is acceptable for most practical systems. The pulse repetition rate of the monocycle shown inFIG. 9is 250 MHz. It was found that the pulse generator is capable of generating monocycles at a repetition frequency in the range of around 10 MHz to around 1 GHz.

FIG. 10is a schematic circuit diagram of a system according to a second preferred embodiment for generating narrow monocycles. The circuit ofFIG. 10differs from the circuit shown inFIG. 7in that it omits the lumped passive resistor88and has a single SRD and distributed Microstrip elements.

The elements of the circuit illustrated inFIG. 10which correspond exactly to elements in the circuit shown inFIG. 7are allotted the same reference numerals.

The circuit ofFIG. 10comprises a signal source76connected to a first transmission line78. The output of the first transmission line78is connected to the anode of an SRD80and the cathode of the SRD80is connected to a first terminal of a second transmission line102comprising a distributed inductor which is short circuited. The second terminal of the second transmission line102is connected to ground and acts as a DC return for the SRD80. The cathode of the SRD80is also connected to a distributed capacitor92and the output of the capacitor92is terminated in a resistor100. The other terminal of the resistor100is connected to ground.

In the circuit ofFIG. 10, the monocycle generation begins with an impulse that is first formed by the SRD80. This impulse is differentiated once by the second transmission line102which acts as a shunt inductor and the resultant pulse is differentiated again by the distributed capacitor92. The waveform seen by the load (resistor100) is thus a monocycle.

The circuit ofFIG. 10was simulated using Agilent Technologies' ADS. The simulated result is shown inFIG. 11. The simulated pulse width was about 250 ps and the pulse repetition frequency was 250 MHz. However, the pulse repetition frequency may be increased to higher frequencies without affecting the performance. By changing the length of the second transmission line102which is acting as a shunt inductor, the inductance may be varied to adjust the shape of the monocycle. Thus, in the circuits ofFIGS. 7 and 10, at least one transmission line is used as an inductor rather than a delay line, which is in contrast to prior art systems.

The circuit ofFIG. 10was also fabricated on 32 mil Duroid substrate with a dielectric constant of 3.38. The measurement result is shown inFIG. 12.

The pulse repetition frequency was 250 MHz and the measured pulse width was about 290 ps. It was found that the pulse generator76ofFIG. 10is capable of generating monocycles at a repetition frequency in excess of 1 GHz.

A comparison of the measured results shown inFIGS. 12 and 9(which relate to the circuits ofFIGS. 10 and 7respectively), shows that there is a little additional ringing in the circuit ofFIG. 10due to the lack of a matching resistive element which is present in the circuit ofFIG. 7. This leads to some degradation in performance. However, the circuit ofFIG. 10is a lower cost alternative to the circuit ofFIG. 7due to the use of purely distributed elements and may be used when the system requirements allow for a reduction in cost to be traded-off for a small amount of additional ringing. Despite the lack of resistive matching, the generated monocycle from the circuit ofFIG. 10is comparable to that of the circuit ofFIG. 7.

Thus, the circuits ofFIGS. 7 and 10provide two low cost, high performance circuits for monocycle generation. The circuit ofFIG. 7provides very good performance whilst using two lumped elements in the circuit, namely an SRD and a shunt resistor. The circuit ofFIG. 10allows for an even lower cost implementation by using only one lumped element, an SRD, in return for a very small sacrifice in performance.

The circuits ofFIGS. 7 and 10may be used to achieve pulse repetition frequencies in excess of 1 GHz. The circuit ofFIG. 7may enable the generation of highly symmetrical monocycles of widths less than around 300 ps with negligible ringing. The circuit ofFIG. 10sacrifices a very small amount of performance in return for a cut in the cost of fabrication. The use of purely distributed components in the circuit ofFIG. 10also increases the repeatability in the performance of the circuit. This will be a major advantage in mass production.

Sub-nanosecond pulse width monocycle generators with the kind of high pulse repetition frequencies demonstrated by preferred embodiments of the invention are currently not available commercially. Furthermore, preferred embodiments of the invention may be fabricated using very low cost components. Also, preferred embodiments of the invention preferably do not make use of any other active device to reduce the ringing, unlike conventional systems.

FIG. 13is a schematic circuit diagram of a system according to a further preferred embodiment of the present invention. The circuit ofFIG. 13differs from the circuit ofFIG. 7in that the distributed capacitor92and distributed inductor96of the circuit ofFIG. 7are replaced with lumped passive elements in the form of a lumped capacitor110and a lumped inductor112. The elements of the circuit illustrated inFIG. 13which correspond exactly to elements in the circuit shown inFIG. 7are allotted the same reference numerals.

The circuit ofFIG. 13comprises a signal source76connected to the anode of an SRD80and the cathode of the SRD80is connected to a first terminal of a resistor88which provides a DC path for the SRD80. The other terminal of the resistor88is connected to ground. The cathode of the SRD80is also connected to the input of a lumped capacitor110and the output of the capacitor110is connected to a first terminal of a lumped inductor112and to a first terminal of a load resistor100. The other terminal of the inductor112is connected to ground, as is the other terminal of the load resistor100.

In the circuit ofFIG. 13, the monocycle generation begins with an impulse that is first formed by the SRD80. This impulse is differentiated by a second order inductor capacitor differentiator comprising the capacitor110and the shunt inductor112to produce the monocycle. The waveform seen by the load resistor100is thus a monocycle. The waveform produced by the SRD80is shown inFIG. 14.

The circuit ofFIG. 13was simulated using Agilent Technologies' ADS. The simulated result is shown inFIG. 15. The simulated pulse width was about 250 ps and the pulse repetition frequency was 250 MHz.

The circuit ofFIG. 13was also fabricated on 32 mil Duroid substrate with a dielectric constant of 3.38. The measurement result is shown inFIG. 16. The pulse repetition frequency was 250 MHz and the measured pulse width was about 290 ps.

FIG. 17is a schematic circuit diagram of a system according to a further preferred embodiment and is similar to the circuit ofFIG. 10. However, in the circuit ofFIG. 17, the distributed capacitor92of the circuit ofFIG. 10is replaced by a lumped capacitor114and a lumped shunt inductor116replaces the distributed inductor102. The lumped shunt inductor116provides a DC return path for the SRD80.

The circuit ofFIG. 17comprises a signal source76connected to the anode of an SRD80, the cathode of which is connected to a first terminal of a lumped inductor116and the input of a lumped capacitor114. The second terminal of the inductor116is connected to ground and the output of the capacitor114is connected to a load resistor100, the other end of the resistor100being connected to ground.

In the circuit ofFIG. 17, the SRD80generates a sharp voltage transition which is differentiated by a second order inductor-capacitor (L-C) differentiator comprising the capacitor114and the inductor116, to produce a monocycle across the load resistor100.

The circuit ofFIG. 17was simulated using Agilent Technologies' ADS. The simulated result is shown inFIG. 18. Simulated pulse width was about 250 ps and the pulse repetition frequency was 250 MHz.

FIG. 19is a further alternative embodiment of the present invention for monocycle generation using two first order differentiators. The circuit ofFIG. 19comprises a signal source76connected to the anode of an SRD80. The cathode of the SRD80is connected to a resistor88which provides a DC return path to ground. The cathode of the SRD80is also connected to the input of a lumped capacitor118, the output of the lumped capacitor118being connected to a first terminal of a resistor120. The other terminal of the resistor120is connected to ground. The output of the capacitor118is connected to the input of a further capacitor122. The output of the further capacitor122is connected to a first terminal of a load resistor100, the other terminal of the load resistor100being connected to ground.

The circuit ofFIG. 19was simulated using Agilent Technologies' ADS. The simulated result is shown inFIG. 20. The SRD80generates a sharp voltage transition and this is differentiated by the first differentiator comprising the capacitor118and the resistor120to produce the impulse and by the second differentiator comprising the capacitor122and the resistor100to produce a monocycle.

A further preferred embodiment of the invention is shown inFIG. 21. In this embodiment, two first order differentiators are used but the lumped capacitors118and122of the circuit ofFIG. 19are replaced by distributed capacitors124and126.

The circuit ofFIG. 21comprises a signal source76connected to the anode of an SRD80, the cathode of the SRD80being connected to a resistor88which provides a DC return to ground. The cathode of the SRD80is further connected to the input of a distributed capacitor124, the output of the capacitor124being connected to a first terminal of a resistor120. The second terminal of the resistor120is connected to ground. The output of the capacitor124is connected to the input of a further distributed capacitor126. The output of the distributed capacitor126is connected to a first terminal of a load resistor100, the second terminal of the load resistor100being connected to ground.

The SRD80generates a sharp voltage transition which is doubly differentiated by the resistor-capacitor (R-C) networks formed by capacitor124and resistor120, and capacitor126and resistor100to produce a monocycle at the output.

The circuit ofFIG. 21was simulated using Agilent Technologies' ADS. The simulated result is shown inFIG. 22. The simulated pulse width was about 250 ps and the pulse repetition frequency was 250 MHz.

FIG. 23is a schematic of a system for multi-band operation which may include any of the pulse generator systems shown in the circuits ofFIGS. 7,10,13,17,19and21. In the embodiment ofFIG. 23, a pulse generator system128according to any of the embodiments shown in the circuits ofFIGS. 7,10,13,17,19and21is connected to a number (1 to n) of band pass filters130and the output of each band pass filter130is connected to the input of a respective modulator132. The outputs of the modulators132are combined to produce a multi-band ultra wideband signal134. The output of the pulse generator128is a monocycle which covers the frequency band defined by the band pass filters130. The output may therefore be de-multiplexed in the frequency domain using the band pass filters130. Each of the de-multiplexed signals may be modulated in a respective modulator132to produce a range of modulated signals in different wavebands which may be combined to produce the multi-band ultra wideband signal output134.

The input signal source76from which the monocycles are to be generated using the circuits ofFIGS. 7,10,13,17,19and21may be, for example, a sinusoidal waveform, a square wave, a pulse or any other bi-polar signal.

The systems and methods according to the present invention may be particularly useful in the production of devices for use, for example, in the fields of communications, radar, ranging, imaging, depth measurement, and position locating.

Various modifications to the embodiments of the present invention described above may be made. For example, other components, materials and method steps can be added or substituted for those described above. Thus, although the invention has been described using particular embodiments, many variations are possible within the scope of the claims, as will be clear to the skilled reader, without departing from the spirit and scope of the invention.