Claims:1. A synthesizer (100) comprising:
a radiofrequency module (106) comprising:
one or more phase-locked loop (PLLs) (202-1, 202-2) that comprises a first PLL (202-1) adapted to generate a first local oscillator signal and a second PLL (202-2) adapted to generate a second local oscillator signal;
an upconverter (300) having a first mixer and a second mixer and an upconverted coupled signal for further system level testing, the first mixer and the second mixer are driven by the generated local oscillator signals to generate output signals;
a power supply regulation and distribution card (102) adapted to supply power to the radiofrequency module; and
a reference signal module (104) adapted to distribute generated reference signals to the one or more PLLs, wherein stabilisation of phase noise of the output signals over vibration is obtained through control of phase noise of the reference signals.
2. The synthesizer as claimed in claim 1, wherein the first local oscillator signal is amplified with a first amplifier (204-1), so that the level is sufficient for driving the first mixer (302-1) of the upconverter (300).
3. The synthesizer as claimed in claim 1, wherein the second local oscillator signal is amplified with a second amplifier (204-2), so that the level is sufficient for driving the second mixer (302-2) of the upconverter (300).
4. The synthesizer as claimed in claim 1, wherein the first local oscillator signal is a fixed signal and the second local oscillator signal is a variable signal, wherein the fixed signal is L frequency band and variable signal is X frequency band.
5. The synthesizer as claimed in claim 1, wherein the power supply regulation and distribution card (102) adapted to receive main power supply and distribute supplies for amplifiers and switches configured in the radiofrequency module (106).
6. The synthesizer as claimed in claim 1, wherein the reference signal module (104) adapted for generation of internal reference signals for local oscillator signals generation and the generated reference signals are distributed to the one or more PLLs (204-1, 204-2).
7. The synthesizer as claimed in claim 1, wherein the reference signal module (104) comprises crystal unit (402) that is used to generate internal reference signals that is amplified and power divided into first reference signal and second reference signal.
8. The synthesizer as claimed in claim 1, wherein the one or more PLLs (202-1, 202-2) and digital signal circuitry combined in single printed circuit board (PCB), wherein appropriate channelization isolates RF circuit from digital signal circuitry.
9. The synthesizer as claimed in claim 1, wherein the appropriate channelization of each PLLs is obtained by providing individual power supply sections, wherein reference signals lines of the one or more PLLs is routed away from each other along with coplanar waveguide (CPWG) technique.
10. The synthesizer as claimed in claim 1, wherein the reference signals is isolated from mechanical vibration of the synthesizer using any or a combination of rubber suspension, separate regulators, twisting of supply wires and twisted pair of reference signal wires.

, Description:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to RADAR systems, and more specifically, relates to a low leakage synthesizer.

BACKGROUND
[0002] The radar systems need to detect and process very weak echoes from the target. If the phase noise of the local oscillator (LO) is not good, these weak echo signals get masked. Phase-locked loop synthesizers generate LO signals with low phase noise and low spurious. In systems like avionics, missiles, vehicles mount systems and industrial applications synthesizers experience a lot of vibrations and shocks. The performance of the systems should not degrade in such applications. The system can be made less acceleration sensitive with appropriate system design. Many avionics and space systems employ frequency hopping for multiple access communications, protection against jamming and interference and various C3 applications which in turn requires fast switching between frequencies.
[0003] A few existing technologies include a multiple frequency band synthesizer using a single voltage control oscillator that discloses a reference signal generation circuit for generating a reference signal of which frequency is controlled, a phase comparator for generating a phase difference signal, a low pass filter circuit for low-pass filtering the phase difference signal with one of a plurality of cut-off frequencies selected. a VCO for generating and outputting a LO signal according to an output of the low-pass filter, a frequency dividing circuit having an integer frequency dividing mode and a fraction frequency dividing mode to Supply the frequency divided signal to the phase comparator; and a control circuit for Supplying the reference frequency control Signal to the reference signal generation circuit, a filter control signal to the low-pass filter circuit, and frequency dividing control Signal (data) to the frequency dividing circuit in accordance with a frequency command Signal. Another existing PLL frequency synthesizer includes a phase-locked loop circuit using a multi-curve voltage-controlled oscillator (VCO) having a set of operating curves, each operating curve corresponding to a different frequency range over a control voltage range. The phase locked loop circuit includes a digital control circuit configured to generate a curve select signal using a closed loop curve search operation to select one of the operating curves in the multi-curve VCO, the selected operating curve being used by the VCO to generate an output signal with an output frequency being equal or close to a target frequency of the phase-locked loop.
[0004] Another existing apparatus and method for synthesizing low-noise, high stability, multi-frequency microwave signals are disclosed. The output frequencies of a lower frequency, low-noise, synthesizers are upconverted to higher microwave frequencies by mixing these frequencies with the output frequency of an ultra-low noise microwave oscillator, determined by a very high Q resonator. Another existing device includes a crystal oscillator having a plurality of quartz crystals that are manufactured so that the directional orientation of the acceleration sensitivity vector is essentially the same for each crystal. This enables convenient mounting of the crystals to a circuit assembly with consistent alignment of the acceleration vectors. The crystals are aligned with the acceleration vectors in an essentially anti-parallel relationship and can be coupled to the oscillator circuit in either a series or parallel arrangement.
[0005] Although multiple system exists today, these systems suffer from significant drawbacks. Therefore, it is desired to develop a simple and cost-effective means that generates signals with low phase noise and minimal spurs with frequency stability maintained in vibration.

OBJECTS OF THE PRESENT DISCLOSURE
[0006] An object of the present disclosure relates, in general, to RADAR systems, and more specifically, relates to a low leakage synthesizer.
[0007] Another object of the present disclosure is to provide a synthesizer that generates LO signals using a multi-curve VCO integrated PLL.
[0008] Another object of the present disclosure is to provide a synthesizer that switches fast between multiple frequencies, which is suitable for frequency hopping.
[0009] Another object of the present disclosure is to provide a synthesizer that generates signals with minimal degradation of phase noise over the vibration.
[0010] Another object of the present disclosure is to provide a synthesizer that generates two LO signal with spurious below -70dBc.
[0011] Another object of the present disclosure is to provide a synthesizer that provides an X band up-converted signal with minimal spurious and lower phase noise.
[0012] Another object of the present disclosure is to provide a synthesizer that provides low leakage of signal from coupled path during off condition of the path.
[0013] Another object of the present disclosure is to provide a synthesizer, where the number of components can be reduced to less than 30% by using VCO integrated PLL.
[0014] Another object of the present disclosure is to provide a synthesizer that isolates RF circuits from the digital circuit and coplanar waveguide (CPWG) techniques that control the crosstalk of signals.
[0015] Yet another object of the present disclosure is to provide a synthesizer that is simple by integration of digital control signal and RF signal on a single PCB.

SUMMARY
[0016] The present disclosure relates, in general, to RADAR systems, and more specifically, relates to a low leakage synthesizer.
[0017] In an aspect, the present disclosure relates to a synthesizer that includes a radio frequency module comprising one or more PLLs that comprises a first PLL adapted to generate a first local oscillator signal and a second PLL adapted to generate a second local oscillator signal, an upconverter having a first mixer and a second mixer, and an upconverted coupled signal for further system level testing, the first mixer and the second mixer are driven by the generated local oscillator signals to generate output signals, a power supply regulation and distribution card adapted to supply power to the radio frequency module; and a reference signal module adapted to distribute generated reference signals to the one or more PLLs, wherein stabilisation of phase noise of the output signals over vibration is obtained through control of phase noise of the reference signals.
[0018] According to the embodiment, the first local oscillator signal is amplified with a first amplifier, so that the level is sufficient for driving the first mixer of the upconverter.
[0019] According to the embodiment, the second local oscillator signal is amplified with a second amplifier, so that the level is sufficient for driving a second mixer of the upconverter.
[0020] According to the embodiment, the first local oscillator signal is a fixed signal and the second local oscillator signal is a variable signal, wherein the fixed signal is L frequency band and variable signal is X frequency band.
[0021] According to the embodiment, the power supply regulation and distribution card adapted to receive main power supply and distribute supplies for amplifiers and switches configured in the radio frequency module.
[0022] According to the embodiment, the reference signal module adapted for generation of internal reference signals for local oscillator signals generation and the generated reference signals are distributed to the one or more PLLs.
[0023] According to the embodiment, the reference signal module comprises crystal unit that is used to generate internal reference signals that is amplified and power divided into first reference signal and second reference signal.
[0024] According to the embodiment, the one or more PLLs and digital signal circuitry combined in single PCB, wherein appropriate channelization isolates RF circuit from digital signal circuitry.
[0025] According to the embodiment, the appropriate channelization of each PLLs is obtained by providing individual power supply sections, wherein reference signals lines of the one or more PLLs is routed away from each other along with coplanar waveguide (CPWG) technique.
[0026] According to the embodiment, the reference signal is isolated from mechanical vibration of the synthesizer using any or a combination of rubber suspension, separate regulators, twisting of supply wires and twisted pair of reference signal wires.
[0027] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0029] FIG. 1 illustrates an exemplary representation of low leakage X band synthesizer, in accordance with the embodiment of the present disclosure.
[0030] FIGs. 2A and 2B illustrates exemplary local oscillator signals generation paths of radio frequency module, in accordance with the embodiment of the present disclosure.
[0031] FIG. 3 illustrates exemplary up-conversion path of radio frequency module, in accordance with the embodiment of the present disclosure.
[0032] FIG. 4 illustrates exemplary reference signal path of reference signal module, in accordance with the embodiment of the present disclosure.

DETAILED DESCRIPTION
[0033] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0034] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0035] The present disclosure relates, in general, to RADAR systems, and more specifically, relates to a low leakage synthesizer. The synthesizer of the present disclosure enables to overcome the limitations of the prior art by generating signals with low phase noise and minimal spurs. The phase noise of the synthesizer is stabilized over vibration and temperature. Therefore, the synthesizer finds its application in airborne systems and other radar systems.
[0036] The device of the present disclosure enables to overcome the limitations of the prior art by reducing the number of components to less than 30% by using VCO integrated PLL instead of traditional PLL method. The proposed RF section is realized in single PCB with proper PCB design and fabrication technologies. With proper transmission line topology, spurs and leakages are controlled. The two-stages of upconverter can be realized on the same PCB leading to simplification of the synthesizer without compromising the spurious. The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure. The description of terms and features related to the present disclosure shall be clear from the embodiments that are illustrated and described; however, the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents of the embodiments are possible within the scope of the present disclosure. Additionally, the invention can include other embodiments that are within the scope of the claims but are not described in detail with respect to the following description.
[0037] FIG. 1 illustrates an exemplary representation of low leakage X band synthesizer, in accordance with the embodiment of the present disclosure.
[0038] Referring to FIG. 1, the low leakage X-band synthesizer 100 of a radar system configured to enable frequency stability maintained in vibration. The synthesizer 100 can include power supply regulation and distribution card 102, reference signal module 104 and radiofrequency module 106. The radiofrequency module 106 can include one or more PLLs (202-1, 202-2) and an upconverter 300 shown in FIG. 2A, FIG. 2B and FIG. 3 respectively. The phase noise of the synthesizer 100 is stabilized over vibration and temperature. The synthesizer 100 can be employed in airborne systems and other radar systems.
[0039] The one or more PLLs (202-1, 202-2) are adapted to generate at least two local oscillator signals, where a first local oscillator signal generated is a fixed frequency, while a second local oscillator signal is multi-spot frequency. The upconverter 300 can include dual stages of the mixer, which are driven by the first local oscillator signal and the second local oscillator signal. The synthesizer 100 generates signals with low phase noise and minimal spurs. The two local oscillator signals are used to convert the baseband signal to X band with two stages of mixers.
[0040] In the embodiment, power supply regulation and distribution card 102 can receive the main power supply. The required voltages for amplifiers and switches are derived from the main supply and the power supply regulation and distribution card 102 has a protection circuit for conducted emission and susceptibility and reverse polarity connection. The power supply distribution is part of this card.
[0041] The reference signal module 104 is adapted for the generation of internal reference signals for local oscillator signals generation and the reference signals are distributed to one or more PLLs (202-1, 202-2) shown in FIG. 2A and FIG. 2B respectively. The generated internal reference signals are amplified and power divided into a first reference signal and a second reference signal. The stabilisation of phase noise of output signals over vibration is obtained through control of phase noise of reference signals.
[0042] In the embodiment, radiofrequency module 106 can include one or more PLLs (202-1, 202-2). In an exemplary embodiment, PLLs (202-1, 202-2) can be at least two voltage-controlled oscillators (VCO) integrated PLLs, where at least two VCO integrated PLLs are used to generate two local oscillator signals. One or more PLLs can include a first PLL 202-1 adapted to generate the first local oscillator signal and a second PLL 202-2 adapted to generate the second local oscillator signal. The first local oscillator signal is a fixed signal and the second local oscillator signal is a variable signal, where the fixed signal is L frequency band and variable signal is in X frequency band.
[0043] In the embodiment, the first LO frequency generated is the fixed frequency, while the second LO is a multi-spot frequency. The radiofrequency module 106 can include two stages of upconverter 300. For each stage of frequency conversion, local oscillator signals are also generated. An additional coupled path provides a signal for testing the further stages of the system. The upconverter 300 has dual stages of the mixer, which are driven by the first and second local oscillator signals. A high-speed microcontroller with high-speed serial peripheral interface (SPI) communications can be used for programming one or more PLLs (202-2, 202-2). Fast switching speed achieved with a suitable programming method and pre-calibration of VCOs.
[0044] The phase noise and spuriousness of these two local oscillator signals are critical and influence the phase noise and spuriousness of the upconverter signal. The phase noise of these local oscillator signals mainly dependent on the reference signal phase noise. Reference signal phase noise stabilization and spur removal are important even over the temperature. The implementation of stabilization of reference signal phase noise and the spur is presented in this disclosure.
[0045] The synthesizer 100 can achieve low phase noise and the low level of spurious better than 70dBc at the outputs of PLLs (202-2, 202-2). The upconverter 300 converts baseband signal to X band signal with dual-frequency conversion. The additional coupled path of upconverted signal presents low leakage of signal in OFF condition. The synthesizer 100 with a simplified and complete RF circuit is realised on a single PCB, the synthesizer 100 is stable over vibration and low phase noise degradation is achieved over vibration.
[0046] FIGs. 2A and 2B illustrates exemplary local oscillator signals generation path of radiofrequency module, in accordance with the embodiment of the present disclosure.
[0047] Referring to FIG. 2A, the first VCO integrated PLL 202-1 generates first signal, where the first signal is in L band, the first signal is then amplified with a first amplifier 204-1 coupled to the first VCO integrated PLL 202-1 so that the level is sufficient for driving the first mixer 302-1, where the first signal is used as local oscillator signal for the first stage of upconverter 300. The amplified signal is power divided using a power divider 206-1.
[0048] The second VCO integrated PLL 202-2 is shown in FIG. 2B is used for generating the second signal, where the second signal is X band multiple frequencies. The VCO integrated PLL with multi-curve VCO is used to generate multiple local oscillator frequencies for the second mixer. The second signal is amplified with a second amplifier 204-2 that is fed to the second mixer 302-2 of the second stage upconverter 300. The amplified signal is power divided using a power divider 206-2. The phase noise of both PLL signals is very critical to have better phase noise of the upconverted signal. These two local oscillator signals are used to convert the baseband signal to X band with two stages of mixers. Low phase noise and low level of spurious better than 70dBc is achieved at the outputs of PLLs.
[0049] The number of components is reduced to less than 30% by using VCO integrated PLL instead of the traditional PLL method. The two VCO integrated PLLs (202-1, 202-2) and digital signal circuitry combined in the single PCB, where the digital signal circuitry can include a microcontroller and RF circuit include two VCO integrated PLLs. When digital circuitries like microcontrollers are combined with RF circuitry leads to leakage of spurious in the main signal. The PLL frequency is selected based on the received frequency command word. Proper channelization isolates RF circuits from digital circuits and coplanar waveguide (CPWG) techniques control the crosstalk of signals.
[0050] In the embodiment, appropriate channelization of each PLLs is obtained by providing individual power supply sections. For example, when two PLLs (202-1, 202-2) are combined on one PCB, one signal may leak to others as spurious so channelization of each PLL section is required and both PLLs need to be isolated by having individual power supply sections. The reference signals lines of PLLs also to be routed away from each other along with the CPWG technique.
[0051] FIG. 3 illustrates exemplary up-conversion path of radiofrequency module, in accordance with the embodiment of the present disclosure.
[0052] Referring to FIG. 3, the two stages of upconverter 300 can be realized on the same PCB leading to simplification of the synthesizer 100 without compromising the spurious. The two stages of frequency conversions help in rejecting the nearest signal easily and a realistic filter can be designed and fabricated. The up-conversion path of the radio frequency module 106 can include the first stage of mixer 302-1 in the upconverter path and the second stage of mixer 302-2 in the upconverter path. The upconverted coupled signal adapted for further system level testing.
[0053] The mixer 302-1 is coupled to an amplifier 304 adapted for amplifying the signal, a bandpass filter 306, which rejects unwanted signals. A voltage variable attenuator 308 allows up to 20dB attenuation of the first output signal. The first output signal level is controlled with the attenuator 308, so that the travelling wave tube which follows the synthesizer 100 may not get damaged. Then the signal is fed to the second mixer 302-2, where the intermediate frequency mixes with the second LO signal in the X band and generates the final first output signal. A bandpass filter 310 which is critical, where the bandpass filter 310 should pass the first output signal and reject the nearest LO which is critical since both signals are closer to each other. The signal is amplified using amplifiers 312.
[0054] A coupler 314 couples a part of the output signal to the coupled path. The amplifier 316 is used to provide a sufficient module output level. An additional filter 318 adapted for spur rejection, the low pass filter 320 adapted for rejecting harmonics of the signals. There are switches (322-1, 322-2) in the output path, which is used to switch OFF output signal if not required. A temperature compensator 324 coupled between the switches (322-1, 322-2). The switch 322-3 in the coupled path to switch OFF the path when in not use. Signal leakage in the OFF level should be very minimal so that it may not disturb the normal functioning of the main system.
[0055] The control of leakage of signal in the channel in OFF condition is difficult when high level(0dBm) signal present in the adjacent channel even with multiple switches in the path. To overcome the above limitation, the synthesizer 100 enable the isolation of two channels mechanically along with CPWG line for RF track, edge plating of PCBs and cap filling of holes of PCB helped in achieving a low leakage in OFF condition in the X band.
[0056] FIG. 4 illustrates exemplary reference signal path of reference signal module, in accordance with the embodiment of the present disclosure.
[0057] Referring to FIG. 4, the reference signal module 104 adapted for the generation of internal reference signals for LO signals generation and the signal are distributed to one or more PLLs. The reference signal module 104 can include crystal unit 402 that is used to generate the internal reference signal. The signal is amplified with an amplifier 404 and signal is divided into two parts i.e., first reference signal and second reference signal using a power divider 406. A dedicated PCB provides regulated supply to crystal so that no spurious from power supply leaks into crystal output.
[0058] The phase noise of the output signal is dependent on PLL output signals and the phase noise of PLL output signals is dependent on the reference signal. Therefore, stabilizing the phase noise of the reference signal is crucial. For example, when a module is subjected to vibration with high amplitude, mechanical vibration can be seen as electrical signals, which disturb the phase noise of the output signal. To overcome the above limitations, selection of less acceleration sensitive signal is required for reference frequency generation. Isolation of reference signal from mechanical vibration can be achieved by using proper isolation techniques like rubber suspension of the module. The next level of isolation of mechanical vibration signal is by having separate regulators for the reference signal, the converted electrical signals get eliminated. Twisting of supply wires may act as differential lines for vibration and controls noise addition and twisted pair of wires for reference signal routing from reference board to PLL board controls the addition of noise in the routed path.
[0059] The embodiments of the present disclosure described above provide several advantages. The present disclosure provides a synthesizer that generates LO signals using a multicurve-VCO integrated PLL. The synthesizer switches fast between multiple frequencies which is suitable for frequency hopping. The synthesizer generates signals with minimal degradation of phase noise over the vibration, generates two LO signal with spurious below -70dBc and provides an X Band upconverted signal with minimal spurious and lower phase noise. The synthesizer provides low leakage -110dBm of signal from coupled path during OFF condition of the path. The number of components can be reduced to less than 30% by using VCO integrated PLL. The RF circuit is isolated from the digital circuit and coplanar waveguide (CPWG) techniques control the crosstalk of signals. The synthesizer is simple by integration of digital control signal and RF signal on the single PCB.
[0060] It will be apparent to those skilled in the art that the synthesizer 100 of the disclosure may be provided using some or all of the mentioned features and components without departing from the scope of the present disclosure. While various embodiments of the present disclosure have been illustrated and described herein, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the disclosure, as described in the claims.

ADVANTAGES OF THE PRESENT DISCLOSURE
[0061] The present disclosure provides a synthesizer that generates LO signals using a multi-curve VCO integrated PLL.
[0062] The present disclosure provides a synthesizer that switches fast between multiple frequencies which is suitable for frequency hopping.
[0063] The present disclosure provides a synthesizer that generates signals with minimal degradation of phase noise over the vibration.
[0064] The present disclosure provides a synthesizer that generates two LO signals with spurious below -70dBc.
[0065] The present disclosure provides a synthesizer that provides an X band up-converted signal with minimal spurious and lower phase noise.
[0066] The present disclosure provides a synthesizer that provides low leakage of signal from coupled path during OFF condition of the path.
[0067] The present disclosure provides a synthesizer, where the number of components can be reduced to less than 30% by using VCO integrated PLL.
[0068] The present disclosure provides a synthesizer that isolates RF circuits from the digital circuit and coplanar waveguide (CPWG) techniques that control the crosstalk of signals.
[0069] The present disclosure provides a synthesizer that is simple by integration of digital control signal and RF signal on single PCB.