DESC:FORM – 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(SEE SECTION 10, RULE 13)

SYNTHESIZER AND COHERENT WAVEFORM GENERATOR FOR RADIO WAVE COMMUNICATION

BHARAT ELECTRONICS LIMITED
OUTER RING ROAD, NAGAVARA, BANGALORE 560045, KARNATAKA, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

TECHNICAL FIELD
[0001] The present invention relates to radio wave communication. The invention, more particularly, relates to multi-functional Direct Digital Synthesizer (DDS) with Phase Locked Loop (PLL) based synthesizer and coherent waveform generator for radio wave communication.
BACKGROUND
[0002] In modern radio wave communication systems, a beam of radio waves can be electronically steered to point in different directions without mechanically steering the antenna. Such systems typically include various devices/modules such as radiating structure, transmit-receive modules, up-down converters, frequency synthesizer, waveform generator, digital beam former and signal processing unit.
[0003] A synthesizer is capable of generating a range of frequencies from a single stable reference frequency source. The synthesizer can be realized using indirect and direct digital synthesis (DDS) techniques. In direct synthesis a reference signal is modified by summing and multiplying with mixers, dividers and multipliers. In indirect synthesis voltage controlled oscillator output is phase locked to a reference frequency. In DDS a signal is digitally constructed and then converted to analog signal. The main application of synthesizer in radio wave communication is to generate local oscillator (LO) signals for up and down conversion.
[0004] A signal is said to be phase coherent if a constant phase relationship is maintained between each of the transmitted pulses. In radio wave communication, phase coherency aids in better signal-to-noise ratio and detection of small phase shifts on echo signals. Further, doppler frequency processing can reduce the influence of fixed clutter.
[0005] There is therefore felt a need of an invention which provides multi-functional Direct Digital Synthesizer (DDS) with Phase Locked Loop (PLL) based synthesizer and coherent waveform generator for radio wave communication.
SUMMARY
[0006] This summary is provided to introduce concepts of the invention related to a synthesizer and coherent waveform generator for radio wave communication, as disclosed herein. This summary is neither intended to identify essential features of the invention as per the present invention nor is it intended for use in determining or limiting the scope of the invention as per the present invention.
[0007] In accordance with an exemplary implementation of the present invention there is provided, a synthesizer and coherent waveform generation system for radio wave communication. The system comprises: a plurality of synthesizer units configured to generate at least three synthesized frequencies; a plurality of mixers configured to mix at least two frequencies from the at least three synthesized frequencies to generate at least two S-band frequencies; a calibration unit configured to generate an X-band frequency from at least one of the S-band frequencies; and a control unit configured to control the synthesizer units for each transmit and receive operation to achieve the phase coherence between the S-band frequencies and the X-band frequency for the radio wave communication.
[0008] In an embodiment, the synthesizer units include: a first synthesizer unit, having a first direct digital synthesizer in combination with a phase locked loop, configured to generate a first synthesized frequency from a reference frequency; a second synthesizer unit, having a second direct digital synthesizer in combination with an up-converter, configured to generate a second synthesized frequency from the reference frequency; and a third synthesizer unit, having a third direct digital synthesizer in combination with an up-converter, configured to generate a third synthesized frequency from the reference frequency;
the mixers include: a first mixer configured to mix the first and second synthesized frequencies to generate a S-band local oscillator frequency; and a second mixer configured to mix the first and third synthesized frequencies to generate a S-band calibration frequency; and
the calibration unit includes a frequency multiplier configured to multiply the S-band CAL frequency by a predetermined factor to generate the X-band frequency (CAL).
[0009] In an embodiment, the calibration unit includes a third mixer and at least two SPDT switches, wherein each of a first SPDT switch and a second SPDT switch are configured to transmit a linear frequency modulated X-band CAL frequency in the event of receive calibration of the system, and
in the event of transmit calibration of the system, the first SPDT switch is configured to provide the X-band CAL frequency to the third mixer and the second SPDT switch is configured to provide the received external X-band frequency to said third mixer to generate an intermediate frequency.
[0010] In an embodiment, the first direct digital synthesizer is configured to generate a first frequency from the reference frequency, and the phase locked loop is driven by the first frequency to generate the first synthesized frequency;
the second direct digital synthesizer is configured to generate a second frequency from the reference frequency, and the up-converter thereof is configured to combine the second frequency with the reference frequency to generate the second synthesized frequency; and
the third direct digital synthesizer is configured to generate a third frequency from the reference frequency, and the up-converter thereof is configured to combine the third frequency with the reference frequency to generate the third synthesized frequency.
[0011] In accordance with an exemplary implementation of the present invention there is provided, a method for synthesizing and generating coherent waveform for radio wave communication. The method comprises: generating, by a plurality of synthesizer units, at least three synthesized frequencies; generating, by a plurality of mixers, at least two S-band frequencies by mixing at least two frequencies from the at least three synthesized frequencies; generating, by a calibration unit, X-band frequencies from at least one of the S-band frequencies; and controlling, by a control unit, the synthesizer units for each transmit and receive operation to achieve the phase coherence between the S-band and X-band frequencies for radio wave communication.
[0012] In an embodiment, the method further includes: generating, by a first direct digital synthesizer in combination with a phase locked loop in a first synthesizer unit, a first synthesized frequency from a reference frequency, the first synthesized frequency being a spot frequency; generating, by a second direct digital synthesizer in combination with an up-converter in a second synthesizer unit, a second synthesized frequency from the reference frequency; generating, by a third direct digital synthesizer in combination with an up-converter in a third synthesizer unit, a third synthesized frequency from the reference frequency; generating, by a first mixer, an S-band local oscillator frequency by mixing the first and second synthesized frequencies; generating, by a second mixer, an S-band calibration frequency by mixing the first and third synthesized frequencies; and generating, by a frequency multiplier in the calibration unit, the X-band frequency (CAL) by multiplying the S-band CAL frequency by a predetermined factor.
[0013] In an embodiment, the method further includes: transmitting, by each of a first SPDT switch and a second SPDT switch, a linear frequency modulated X-band CAL frequency for receive calibration; and
for transmit calibration, providing, by the first SPDT switch, the X-band CAL frequency to a third mixer, and providing, by the second SPDT switch, the received external X-band frequency to the third mixer; and
generating, by the third mixer, an intermediate frequency by mixing the X-band CAL frequency with the received external X-band frequency.
[0014] In an embodiment, the step of generating the first synthesized frequency includes generating, by the first direct digital synthesizer, a first frequency from the reference frequency, and driving the phase locked loop by the first frequency;
the step of generating the second synthesized frequency includes generating, by the second direct digital synthesizer, a second frequency from the reference frequency, and combining, by the up-converter thereof, the second frequency with the reference frequency;
the step of generating the third synthesized frequency includes generating, by the third direct digital synthesizer, a third frequency from the reference frequency, and combining, by the up-converter thereof, the third frequency with the reference frequency.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0015] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and modules.
[0016] Figure 1 illustrates a block diagram depicting a multi-functional Direct Digital Synthesizer (DDS) with Phase Locked Loop (PLL) based synthesizer and coherent waveform generation system, according to an exemplary implementation of the present invention.
[0017] Figure 2 illustrates a block diagram depicting a control circuit of the synthesizer and coherent waveform generation system illustrated in Figure 1.
[0018] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present invention. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION
[0019] The various embodiments of the present invention describe about a multi-functional Direct Digital Synthesizer with Phase Locked Loop (DDS-PLL) based synthesizer and coherent waveform generation (S-CWG) system to generate phase coherent S-Band and X-Band frequencies for radio wave communication.
[0020] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.
[0021] However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present invention and are meant to avoid obscuring of the present invention.
[0022] It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0023] Referring to figure 1, the block diagram of a multi-functional DDS-PLL based S-CWG system (100) for radio wave communication, according to an exemplary implementation of the present invention, is illustrated. The S-CWG system (100) comprises, a plurality of synthesizer units, a plurality of mixers, a calibration unit and a control unit. The synthesizer units are configured to generate at least three synthesized frequencies, the mixers are configured to mix at least two frequencies from the at least three synthesized frequencies to generate at least two S-band frequencies, the calibration unit is configured to generate an X-band frequency from at least one of the S-band frequencies, and the control unit is configured to control the synthesizer units for each transmit and receive operation to achieve the phase coherence between the S-band frequencies and the X-band frequency for the radio wave communication.
[0024] The system (100) typically comprises three synthesizer units with three direct digital synthesizers (DDSs) synchronized using a single clock. An input frequency (F0) is multiplied M times to generate a reference frequency (Fref) which is then distributed through a power divider (PD) to the synthesizer units. This reference frequency (Fref) generated after several multiplication and filtering stages from the input frequency (F0) is also given to up-converters for up-converting the DDS outputs. Each DDS internally generates time varying digital signal which is then converted to generate analog waveforms. Since internal operations within the DDS are in digital domain the parameters of the analog waveform can be easily modified by use of internal registers. Each DDS includes integrated random access memory (RAM) which can be used to store various combinations of the analog signal parameters and can be applied with fast update rates.
[0025] A first synthesizer unit (101) includes a first direct digital synthesizer (DDS-1) configured in single tone mode. DDS-1 is configured to generate a first frequency (FDDS1) from the reference frequency (Fref). DDS-1 drives a discrete Phase Locked Loop (PLL) by the first frequency (FDDS1) whereby the PLL generates fixed N times frequency multiplied signal with low spurious content and fine frequency steps to cover the bandwidth of operation with high frequency resolution. The discrete PLL comprises phase frequency detector (PFD), loop filter, voltage controlled oscillator (VCO) and fixed N divider, to have a high phase comparison frequency which will reduce the locking times. In an exemplary non-limiting embodiment, the divider is configured to divide the VCO output by a factor of 16. Thus the first synthesizer unit (101), having the DDS-1 in combination with the PLL, generates a first synthesized frequency (F1) from the reference frequency (Fref). The first synthesized frequency (F1) which is a spot frequency (Fspot) generated from this section goes to both the mixers.
[0026] A second synthesizer unit (102) includes a second direct digital synthesizer (DDS-2) and an up-converter (102a). DDS-2 is configured to generate a second frequency (FDDS2) from the reference frequency (Fref), and the up-converter (102a) is configured to combine the second frequency (FDDS2) with the reference frequency (Fref) to generate a second synthesized frequency (F2 = Fref + FDDS2) used for generation of an S-Band frequency. Thus the second synthesizer unit (102), having the DDS-2 in combination with the up-converter (102a), generates the second synthesized frequency (F2) from the reference frequency (Fref).
[0027] A third synthesizer unit (103) includes a third direct digital synthesizer (DDS-3) and an up-converter (103a). DDS-3 is configured to generate a third frequency (FDDS3) from the reference frequency (Fref), and the up-converter (103a) is configured to combine the third frequency (FDDS3) with the reference frequency (Fref) to generate a third synthesized frequency (F3 = Fref + FDDS3) used for generation of another S-band frequency. Thus the third synthesizer unit (103), having the DDS-3 in combination with the up-converter (103a), generates the third synthesized frequency (F3) from the reference frequency (Fref).
[0028] DDS-1, DDS-2 and DDS-3 are synchronized by a single clock. DDS-2 and DDS-3 are used in master-slave configuration. They are configured to access their internal high speed RAM’s to enable Linear Frequency Modulation (LFM) and spot frequency generation based on mode of operation. For LFM, waveforms of multiple frequencies are stored in the RAM of each of DDS-2 and DDS-3. In an exemplary non-limiting embodiment, waveforms of four types of frequencies are stored in the RAM of each of DDS-2 and DDS-3.
[0029] Referring to figure 2, the block diagram of the control circuit of the synthesizer and coherent waveform generation (S-CWG) system, is illustrated. As shown in the circuit of figure 2, DDS-2 and DDS-3 are synchronized (SYNC) using the control unit (104) which, in a non-limiting exemplary embodiment, can be a Field Programmable Gate Array (FPGA) based control unit. The control unit (104) is fed with a reference clock (SYN_CLK) generated by dividing the single clock used for synchronizing DDS-1, DDS-2 and DDS-3. The control unit (104) configures DDS-1 in the single-tone mode, and periodically updates a frequency tuning word register of DDS-1 for changing the first synthesized / spot frequency (F1 /Fspot). The control unit (104) generates control signals for synthesizing one or more of the multiple (four) types of frequencies to generate linear frequency modulated (LFM) second and third synthesized frequencies (F2, F3). The control unit (104) further configures DDS-2 and DDS-3 as master-slave respectively, and resets the phase accumulators of DDS-2 and DDS-3 at start of each transmit and receive operation by the to achieve phase coherence between the generated S-band frequencies and the X-band frequency for the radio wave communication. The control unit (104) communicates with DDS-1, DDS-2 and DDS-3 through the DATA / CONTROL buses. In another non-limiting exemplary embodiment, the control unit (104) can be a Microprocessor/Microcontroller based control unit.
[0030] Referring again to figure 1, a first mixer (MX1) is configured to mix the first synthesized / spot frequency (F1/Fspot) generated by DDS1-PLL combination in the first synthesizer unit (101) with the up-converted second synthesized frequency (F2) generated by the second synthesizer unit (102) to generate a variable and switched S-Band local oscillator (LO) frequency (LO = Fspot + F1). For this signal LFM is carried during transmit operation and spot frequencies are generated during receive operation with fixed frequency offset from transmit frequency by DDS-2. This S-Band LO frequency is further converted in an up-stream system (not particularly shown) to generate an X-Band LO frequency. Typically, the second synthesized frequency (F2) is filtered by a band pass filter (BPF) before mixing with the first synthesized / spot frequency (F1/Fspot), and the S-band LO frequency is also filtered by a BPF before conversion in the up-stream system.
[0031] A second mixer (MX2) is configured to mix the first synthesized / spot frequency (F1/Fspot) generated by DDS1-PLL combination in the first synthesizer unit (101) with the up-converted third synthesized frequency (F3) generated by the third synthesizer unit (103) to generate a variable and switched S-Band calibration (CAL) frequency (CAL = Fspot + F3). Typically, the third synthesized frequency (F3) is filtered by a band pass filter (BPF) before mixing with the first synthesized / spot frequency (F1/Fspot), and the S-band CAL frequency is also filtered by a BPF.
[0032] The S-band CAL frequency signal which is phase coherent with the S-Band LO frequency signal is multiplied to obtain an X-Band calibration (CAL) frequency signal. The calibration unit (105) comprises a single up-down converter or frequency multiplier (X4) configured to multiply the S-band CAL frequency by a predetermined factor to generate the X-band CAL frequency. LFM is carried out during receive calibration (RX_CAL) and spot frequencies are generated for transmit calibration (TX_CAL) maintaining frequency offset by DDS-3.
[0033] During receive calibration (RX_CAL) of the S-CWG system (100), the linear frequency modulated (LFM) X-band CAL frequency signal is transmitted to the CAL port of the calibration unit (105) for radiating the LFM X-band CAL frequency signal to external systems (not particularly shown). This is received by transmit-receive modules (not particularly shown) of external systems and further down converted therein to IF for further processing by signal processing unit of the external systems. During transmit calibration (TX_CAL) of the S-CWG system (100), an external X-band frequency signal radiated by the transmit-receive modules (not particularly shown) of external systems is received at the CAL port of the calibration unit (105). The received external X-Band frequency signal during transmit calibration is down converted by mixing with the internally generated spot frequencies to obtain the intermediate frequency (IF) which is fed to a down-stream system (not particularly shown) for further processing.
[0034] The calibration unit (105) further comprises two single-pole-double-throw (SPDT) switches. Each of a first SPDT switch (SPDT1) and a second SPDT switch (SPDT2) is configured to transmit the LFM X-band CAL frequency during receive calibration (RX_CAL) of the S-CWG system. Further, during transmit calibration (TX_CAL) of the S-CWG system (100), the first SPDT switch (SPDT1) is configured to provide the X-band CAL frequency to a third mixer (MX3) and the second SPDT switch is configured to provide the received external X-band frequency to the third mixer (MX3) to generate the intermediate frequency (IF).
[0035] In an exemplary advantageous aspect, the S-Band and X-Band frequencies generated in the S-CWG system (100) are phase coherent and are switched between transmit and receive operation with a switching time of less than 350ns.
[0036] The operational aspects of the multi-functional Direct Digital Synthesizer with Phase Locked Loop (DDS-PLL) based synthesizer and coherent waveform generation (S-CWG) system gives rise to a corresponding method for synthesizing and generating coherent waveform for radio wave communication. The method comprises steps of: generating, by a plurality of synthesizer units, at least three synthesized frequencies (F1, F2, F3); generating, by a plurality of mixers, at least two S-band frequencies (LO, CAL) by mixing at least two frequencies from the at least three synthesized frequencies; generating, by a calibration unit (105), X-band frequencies from at least one of the S-band frequencies; and controlling, by a control unit (104), the synthesizer units for each transmit and receive operation to achieve the phase coherence between the S-band and X-band frequencies for radio wave communication.
[0037] The method further includes: generating, by a first direct digital synthesizer (DDS-1) in combination with a phase locked loop (PLL) in a first synthesizer unit (101), a first synthesized frequency (F1) from a reference frequency (Fref), the first synthesized frequency being a spot frequency (Fspot); generating, by a second direct digital synthesizer (DDS-2) in combination with an up-converter (102a) in a second synthesizer unit (102), a second synthesized frequency (F2) from the reference frequency (Fref); generating, by a third direct digital synthesizer (DDS-3) in combination with an up-converter (103a) in a third synthesizer unit (103), a third synthesized frequency (F3) from the reference frequency (Fref); generating, by a first mixer (MX1), an S-band local oscillator (LO) frequency by mixing the first and second synthesized frequencies (F1, F2); generating, by a second mixer (MX2), an S-band calibration (CAL) frequency by mixing the first and third synthesized frequencies (F1, F3); and generating, by a frequency multiplier (X4) in the calibration unit (105), the X-band frequency (CAL) by multiplying the S-band CAL frequency by a predetermined factor.
[0038] In accordance with the method, the step of generating the first synthesized frequency (F1/Fspot) includes generating, by the first direct digital synthesizer (DDS-1), a first frequency (FDDS1) from the reference frequency (Fref), and driving the phase locked loop (PLL) by the first frequency (FDDS1); the step of generating the second synthesized frequency (F2) includes generating, by the second direct digital synthesizer (DDS-2), a second frequency (FDDS2) from the reference frequency (Fref), and combining, by the up-converter (102a) thereof, the second frequency (FDDS2) with the reference frequency (Fref); the step of generating the third synthesized frequency (F3) includes generating, by the third direct digital synthesizer (DDS-3), a third frequency (FDDS3) from the reference frequency (Fref), and combining, by the up-converter (103a) thereof, the third frequency (FDDS3) with the reference frequency (Fref).
[0039] The method further includes: transmitting, by each of a first SPDT switch (SPDT1) and a second SPDT switch (SPDT2), a linear frequency modulated X-band CAL frequency for receive calibration (RX_CAL); and for transmit calibration (TX_CAL), providing, by the first SPDT switch (SPDT1), the X-band CAL frequency to a third mixer (MX3), and providing, by the second SPDT switch, the received external X-band frequency to the third mixer (MX3), and generating, by the third mixer (MX3), an intermediate frequency (IF) by mixing the X-band CAL frequency with the received external X-band frequency.
[0040] Advantageously, the S-Band and X-Band frequencies generated through implementation of the method are phase coherent and are switched between transmit and receive operation with a switching time of less than 350ns.
[0041] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:We Claim:
1. A synthesizer and coherent waveform generation system (100) for radio wave communication, said system comprising:
a plurality of synthesizer units configured to generate at least three synthesized frequencies (F1, F2, F3);
a plurality of mixers configured to mix at least two frequencies from the at least three synthesized frequencies to generate at least two S-band frequencies (LO, CAL);
a calibration unit (105) configured to generate an X-band frequency from at least one of the S-band frequencies; and
a control unit (104) configured to control said synthesizer units for each transmit and receive operation to achieve the phase coherence between the S-band frequencies and the X-band frequency for the radio wave communication.
2. The synthesizer and coherent waveform generation system (100) as claimed in claim 1, wherein,
said synthesizer units include:
a first synthesizer unit (101), having a first direct digital synthesizer (DDS-1) in combination with a phase locked loop (PLL), configured to generate a first synthesized frequency (F1) from a reference frequency (Fref);
a second synthesizer unit (102), having a second direct digital synthesizer (DDS-2) in combination with an up-converter (102a), configured to generate a second synthesized frequency (F2) from the reference frequency (Fref); and
a third synthesizer unit (103), having a third direct digital synthesizer (DDS-3) in combination with an up-converter (103a), configured to generate a third synthesized frequency (F3) from the reference frequency (Fref);
wherein said mixers include:
a first mixer (MX1) configured to mix the first and second synthesized frequencies (F1, F2) to generate an S-band local oscillator (LO) frequency; and
a second mixer (MX2) configured to mix the first and third synthesized frequencies (F1, F3) to generate an S-band calibration (CAL) frequency; and
wherein said calibration unit (105) includes a frequency multiplier (X4) configured to multiply the S-band CAL frequency by a predetermined factor to generate the X-band frequency (CAL).
3. The synthesizer and coherent waveform generation system (100) as claimed in claim 2, wherein the first synthesized frequency (F1) is a spot frequency (Fspot).
4. The synthesizer and coherent waveform generation system (100) as claimed in claims 1-2, wherein said first, second and third direct digital synthesizers (DDS-1, DDS-2, DDS-3) are synchronized by a single clock, and
wherein said control unit (104) is fed with a reference clock generated by dividing said single clock.
5. The synthesizer and coherent waveform generation system (100) as claimed in claim 2, wherein,
said first direct digital synthesizer (DDS-1) is configured in a single-tone mode; and
said second and third direct digital synthesizers (DDS-2, DDS-3) are configured as master-slave respectively.
6. The synthesizer and coherent waveform generator system (100) as claimed in claims 1-4, wherein said control unit (104) is configured to:
periodically update a frequency tuning word register of said first direct digital synthesizer (DDS-1) for changing the first synthesized frequency (F1 /Fspot); and
reset a phase accumulator of each of said second and third direct digital synthesizers (DDS-2, DDS-3) at start of each transmit and receive operations to achieve the phase coherence.
7. The synthesizer and coherent waveform generation system (100) as claimed in claim 2, wherein a plurality of frequencies are stored in a memory of each of said second and third direct digital synthesizers (DDS-2, DDS-3) for linear frequency modulation, and
wherein said control unit (104) is configured to generate control signals for synthesizing one or more of the plurality of frequencies to generate linear frequency modulated second and third synthesized frequencies (F2, F3).
8. The synthesizer and coherent waveform generator system as claimed in claim 2, wherein said calibration unit (105) includes a third mixer (MX3) and at least two SPDT switches, and
wherein each of a first SPDT switch (SPDT1) and a second SPDT switch (SPDT2) are configured to transmit a linear frequency modulated X-band CAL frequency in the event of receive calibration (RX_CAL) of said system (100), and
in the event of transmit calibration (TX_CAL) of said system (100), said first SPDT switch (SPDT1) is configured to provide the X-band CAL frequency to said third mixer (MX3) and said second SPDT switch (SPDT2) is configured to provide the received external X-band frequency to said third mixer (MX3) to generate an intermediate frequency (IF).
9. The synthesizer and coherent waveform generator system as claimed in claim 2, wherein said reference frequency (Fref) is generated by multiplying an input frequency with a predetermined factor.
10. The synthesizer and coherent waveform generator system as claimed in claim 2, wherein,
said first direct digital synthesizer (DDS-1) is configured to generate a first frequency (FDDS1) from the reference frequency (Fref), and said phase locked loop (PLL) is driven by the first frequency (FDDS1) to generate the first synthesized frequency (F1 / Fspot);
said second direct digital synthesizer (DDS-2) is configured to generate a second frequency (FDDS2) from the reference frequency (Fref), and said up-converter (102a) thereof is configured to combine the second frequency (FDDS2) with the reference frequency (Fref) to generate the second synthesized frequency (F2); and
said third direct digital synthesizer (DDS-3) is configured to generate a third frequency (FDDS3) from the reference frequency (Fref), and said up-converter (103a) thereof is configured to combine the third frequency (FDDS3) with the reference frequency (Fref) to generate the third synthesized frequency (F3).
11. A method for synthesizing and generating coherent waveform for radio wave communication, the method comprising:
generating, by a plurality of synthesizer units, at least three synthesized frequencies (F1, F2, F3);
generating, by a plurality of mixers, at least two S-band frequencies(LO, CAL) by mixing at least two frequencies from the at least three synthesized frequencies;
generating, by a calibration unit (105), X-band frequencies from at least one of the S-band frequencies; and
controlling, by a control unit (104), the synthesizer units for each transmit and receive operation to achieve the phase coherence between the S-band and X-band frequencies for radio wave communication.
12. The method for synthesizing and generating coherent waveform as claimed in claim 11, wherein the method includes:
generating, by a first direct digital synthesizer (DDS-1) in combination with a phase locked loop (PLL) in a first synthesizer unit (101), a first synthesized frequency (F1) from a reference frequency (Fref), the first synthesized frequency being a spot frequency (Fspot);
generating, by a second direct digital synthesizer (DDS-2) in combination with an up-converter (102a) in a second synthesizer unit (102), a second synthesized frequency (F2) from the reference frequency (Fref);
generating, by a third direct digital synthesizer (DDS-3) in combination with an up-converter (103a) in a third synthesizer unit (103), a third synthesized frequency (F3) from the reference frequency (Fref);
generating, by a first mixer (MX1), an S-band local oscillator (LO) frequency by mixing the first and second synthesized frequencies (F1, F2);
generating, by a second mixer (MX2), an S-band calibration (CAL) frequency by mixing the first and third synthesized frequencies (F1, F3); and
generating, by a frequency multiplier (X4) in the calibration unit (105), the X-band frequency (CAL) by multiplying the S-band CAL frequency by a predetermined factor.
13. The method for synthesizing and generating coherent waveform as claimed in claims 11-12, wherein the method includes:
synchronizing the first, second and third direct digital synthesizers (DDS-1, DDS-2, DDS-3) by a single clock;
generating a reference clock for the control unit (104) by dividing the single clock;
configuring the first direct digital synthesizer (DDS-1) in a single-tone mode; and
configuring the second and third direct digital synthesizers (DDS-2, DDS-3) as master-slave respectively.
14. The method for synthesizing and generating coherent waveform as claimed in claims 11-13, wherein the method includes:
updating, by the control unit (104), a frequency tuning word register of the first direct digital synthesizer (DDS-1) for changing the first synthesized frequency (F1 / Fspot); and
resetting, by the control unit (104), a phase accumulator of each of the second and third direct digital synthesizers (DDS-2, DDS-3) at start of each transmit and receive operations to achieve the phase coherence.
15. The method for synthesizing and generating coherent waveform as claimed in claim 12, wherein the method includes:
storing, in a memory of each of the second and third direct digital synthesizers (DDS-2, DDS-3), a plurality of frequencies for linear frequency modulation, and
generating, by the control unit (104), control signals for synthesizing one or more of the plurality of frequencies to generate linear frequency modulated second and third synthesized frequencies (F2, F3).
16. The method for synthesizing and generating coherent waveform as claimed in claim 12, wherein the method includes:
transmitting, by each of a first SPDT switch (SPDT1) and a second SPDT switch (SPDT2), a linear frequency modulated X-band CAL frequency for receive calibration (RX_CAL);
for transmit calibration (TX_CAL), providing, by the first SPDT switch (SPDT1), the X-band CAL frequency to a third mixer (MX3), and
providing, by the second SPDT switch, the received external X-band frequency to the third mixer (MX3); and
generating, by the third mixer (MX3), an intermediate frequency (IF) by mixing the X-band CAL frequency with the received external X-band frequency.
17. The method for synthesizing and generating coherent waveform as claimed in claim 12, wherein the method includes generating the reference frequency (Fref) by multiplying an input frequency with a predetermined factor.
18. The method for synthesizing and generating coherent waveform as claimed in claim 12, wherein,
the step of generating the first synthesized frequency (F1/Fspot) includes:
generating, by the first direct digital synthesizer (DDS-1), a first frequency (FDDS1) from the reference frequency (Fref), and driving the phase locked loop (PLL) by the first frequency (FDDS1);
the step of generating the second synthesized frequency (F2) includes:
generating, by the second direct digital synthesizer (DDS-2), a second frequency (FDDS2) from the reference frequency (Fref), and combining, by the up-converter (102a) thereof, the second frequency (FDDS2) with the reference frequency (Fref);
the step of generating the third synthesized frequency (F3) includes:
generating, by the third direct digital synthesizer (DDS-3), a third frequency (FDDS3) from the reference frequency (Fref), and combining, by the up-converter (103a) thereof, the third frequency (FDDS3) with the reference frequency (Fref).
Dated this 29th day of March, 2019
FOR BHARAT ELECTRONICS LIMITED
By their Agent)

D. Manoj Kumar) (IN/PA 2110)
KRISHNA & SAURASTRI ASSOCIATES LLP