THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“A METHOD TO REALIZE DUAL CHANNEL MATCHED LINEAR DIGITAL RECEIVER FOR IDENTIFICATION FRIEND OR FOE RADAR”
By
BHARAT ELECTRONICS LIMITED
Nationality: Indian
Address: 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.
Field of the Invention
The present invention relates generally to Radar systems and more particularly to method of realizing Dual Channel Digital Receiver by Direct sampling of L-band Identification Friend or Foe (IFF) signals and generates Dual Channel Digital Video output with phase content.
Prior Arts
US20070140382A1 titled “Band pass Sampling Receiver and the Sampling Method" describes the method for band pass sampling in Radio Receiver. The method of band pass sampling receiver is proposed for receiving single channel Radio Frequency signals, comprising of two Analog to Digital Convertor, for converting Radio Frequency signals into digital signals under control of separate orthogonal sampling clocks. The patent describes that wideband Analog to Digital Convertor is required to move bits towards antenna as near as it can, where Analog to Digital Convertor converts the Radio Frequency signal directly .Various processing on the received signal should be implemented by programmable Digital Signal Processing devices as much as possible.
US 20100105349A1 titled" RF Signal Sampling Apparatus and Method" describes a method to sample Radio Frequency directly. The method comprises of transconductor circuit for converting received Radio Frequency voltage signals into current signals, a Infinite Impulse Response filter, for down-sampling and filtering the current signals, and an Finite Impulse Response filter, for further filtering, down sampling and outputting the signals.
WO 1996024193A1 titled "Wide dynamic range analog to digital conversion" provides an approach wherein high dynamic range is achieved without using Automatic Gain Controller Monolithic Microwave Integrated Circuit. An analog-to-digital converter circuit in which an extracted envelope of an input signal is used as a reference signal on an analog-to-digital converter, providing a wide dynamic range while avoiding the need for an automatic gain control.
The paper titled "Direct RF Under-Sampling Reception Method with Lower Sampling Frequency”. The paper describes a under sampling frequency selection technique that approximately halves the required under sampling frequency by aliasing out of band noise whilst preserving Signal to Noise Ratio. To reduce power consumption and still realize Radio Frequency direct sampling receivers, under sampling is employed. In conventional Radio Frequency under sampling receivers, the sampling frequency is selected to be larger than the anti-aliasing filter bandwidth. Simulation results shows approximately half the sampling frequency is enough to preserved the Signal to Noise Ratio.
The paper titled "A New 3-GSPS 65-GOPS UHF Digital Radar Receiver and Its Performance Characteristics" describes the method to samples the input directly at Radio frequencies in single channel Ultra High Frequency receiver. 8-bit Analog to Digital Convertor samples at 3 billion samples per second and perform the down-conversion in the digital domain. Minimizing the analog content of the receiver is the benefit of this approach at Ultra High Frequency band.
The paper titled "Design Considerations of the RF Front-End for High Dynamic Range Digital Radar Receivers" describes the dynamic range limitation due to noise figure degradation of Analog to Digital Convertor and linearity margin of every non-linear component in the receiver chain. The paper describes that from sensitivity point of view, the overall gain of the receiver should be high enough in order to decrease the noise figure degradation caused by the Analog to Digital Convertor. However, from dynamic range point of view, the overall gain of the receiver should not be too high. The third-order intercept point (IP3) and 1-dB compression point (P1dB) are two important parameters of non-linear components for high linear dynamic range applications.
The paper titled "Direct RF Sampling GNSS Receiver Design and Jitter Analysis" describes the design of a flexible Direct Radio Frequency Sampling based GNSS receiver as well as its use for the verification of jitter effects on various performance metrics. The proposed architecture allows the sampling and the real-time digital signal processing of real GNSS signals. The analysis of the measurements obtained from this system validates theoretical formulations from which the sampling jitter limit is established in order not to impact the GNSS signals.
The paper titled “The theory behind band-pass sampling” describes that the information bandwidth is replicated (through the aliasing principle) at integer multiples of the clock fundamental frequency (fs), thereby theoretically creating an infinite number of replicas of the information band in the frequency domain. A proper choice of the sampling frequency, one of these replica falls within a band- width below the sampling clock frequency divided by 2 (fs/2), and therefore is effectively being down-converted to an intermediate frequency (IF) below fs/2. The paper describes that effect of jitter on a sampled signal is the addition of noise to the sampled signal, thus reducing its Signal to Noise Ratio. This is more important for direct sampling receivers since the high sampled frequencies (in the L-band portion of the electro-magnetic spectrum) render the Signal to Noise Ratio more susceptible to this jitter effect.
The paper titled "Experience with Sampling of 500 MHz RF Signal for Digital Receiver Applications" describes the requirements, critical parameters, and measurements for direct Radio Frequency sampling. Radio Frequency front-end design is to minimize the Radio Frequency front-end complexity and to digitalize the signals as close as possible to the antenna. The Radio Frequency front-end mainly determines signal to noise ratio and linearity. As a result, down-conversion can be omitted and the Radio Frequency signal can be directly sampled using under-sampling technique. The results show that direct Radio Frequency sampling offers good performance from the signal to noise and from the SFDR (Spurious Free Dynamic Range) point of view.
Therefore there is a need in the proposed art for a method of realizing Dual Channel Digital Receiver by Direct sampling L-band Identification Friend or Foe (IFF) signals. It generates Dual Channel Digital Video output with phase content having advanced features compared to above mentioned Prior arts and it overcomes present limitations of Analog Receivers.

Summary of the Invention
An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.
Accordingly, in one aspect of the present invention relates to a method of receiving Radar signals, the method comprising: a dual path receiver for receiving a first and a second IFF signals simultaneously, the dual path receiver generates first and second video signals from the simultaneously received first and second IFF signals and additional phase information between the channels is provided, conditioning the received first and second IFF signals by the radio frequency conditioning chain, wherein the RF conditioning chain consists of gain stage followed by filter stage by maintaining the linearity in the analog chain, sampling the conditioned frequencies by using Analog-to-Digital converter for down conversion & digitization and processing the sampled frequencies for both channels which are captured by high end by Field Programmable Gate Array.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

Brief description of the drawings
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1 illustrates the developed module to realize L-band Dual channel high dynamic range linear digital receiver with Radio Frequency sub sampling for radars according to one embodiment of the present invention.
Figure 2 illustrates the block diagram describing sampling scheme to realize L-band Dual channel high dynamic range linear digital receiver according to one embodiment of the present invention.
Figure 3 illustrates the Block diagram of RF signal conditioning chain according to one embodiment of the present invention.
Figure 4 illustrates the flowchart describing the implementation of algorithms required to realize to L-band Dual channel high dynamic range linear digital receiver with Radio frequency sub sampling for radars according to one embodiment of the present invention.
Figure 5 illustrates the input to module for both channels. The input is pulse modulated with pulse width of 0.45us and PRF of 1.45us. The CW frequency is 1090MHz according to one embodiment of the present invention.
Figure 6 illustrates the outputs of module after phase calibration.
Figure 7 illustrates the two channel video outputs and one bit sign output of digital receiver according to one embodiment of the present invention.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
Detailed description of the invention
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.
By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic is intended to provide.
Figs. 1 through 7, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged Radar system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions, in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.
The brief objective of the present invention is to realize a dual channel programmable Identification Friend or Foe Radar receiver with good linearity, gain and phase matching. Direct Radio Frequency sampling receiver module for Identification Friend or Foe radar application which can give pulse video output as well as phase information.
The present invention is realized with two channel gain and phase matched digital receiver. Receiver efficiency is improved by band pass sampling of L-band Identification Friend or Foe signals. All critical RF blocks are implemented in digital and their functions are programmable. High spurious free dynamic range is achieved by splitting dynamic range as analog and digital dynamic range. The feature unique to present invention is adaptive calibration among the two channels in terms of phase and amplitude. The module does not require any Monolithic Microwave Integrated Circuit for phase and amplitude matching, it is done using Digital Signal Processing algorithm digitally. Another unique feature in digitally implemented RF blocks, nonlinearities and DC offsets are minimized which improves receiver performance.
Figure 1 illustrates the developed module to realize L-band Dual channel high dynamic range linear digital receiver with Radio Frequency sub sampling for radars.
Figure 2 illustrates the block diagram describing sampling scheme to realize L-band Dual channel high dynamic range linear digital receiver with radio frequency sub sampling for radars wherein the module consists of two radio frequency channels. One channel receives from SUM Antennae port and other channel receives from DELTA Antennae port. The module consists of radio frequency signal conditioning and digital signal processing blocks. Radio Frequency signal conditioning is designed to maintain the required Radio frequency power levels at the analog to digital convertor with low noise. Digital signal processing consists of high speed Field programmable gate array where algorithms are implemented to achieve desired performance from receiver. The receiver outputs are Sum and Delta digital video signals and one bit sign data.
Figure 3 illustrates the Block diagram of RF signal conditioning chain.
Figure 4 illustrates the flowchart describing the implementation of algorithms required to realize to L-band Dual channel high dynamic range linear digital receiver with Radio frequency sub sampling for radars. After getting the control signal for calibration, the two channels are calibrated for phase as well as gain matching among the channels. After calibration, Receiver takes SUM & DELTA signals and demodulates the L-band signals. Dual channel log Video and phase difference among the two channels RF signals are the digital outputs of the Digital Receiver.
In one embodiment, the present invention relates to a method of receiving Radar signals, the method comprising: a dual path receiver for receiving a first and a second IFF signals simultaneously, the dual path receiver generates first and second video signals from the simultaneously received first and second IFF signals and additional phase information between the channels is provided, conditioning the received first and second IFF signals by the radio frequency conditioning chain, wherein the RF conditioning chain consists of gain stage followed by filter stage by maintaining the linearity in the analog chain, sampling the conditioned frequencies by using Analog-to-Digital converter for down conversion & digitization and processing the sampled frequencies for both channels which are captured by high end by Field Programmable Gate Array.
The sampling for dual channel with RF sub sampling is with minimum hardware. The programmable critical radio frequency functional blocks are implemented in digital.
The sub sampling consists of programmable processing bandwidth, wherein the conditioned signal captured is passed through band pass filter whose 3dB bandwidth is programmable which is directly effects the sensitivity of the receiver. The sub sampling has adaptive calibration between the channels for gain and phase matching, wherein phase and gain difference between channel caused by signal condition chains and external cable mismatches are minimized adaptively in digital domain with digitally implemented blocks. The sub sampling split spurious free dynamic range in analog and digital domain. The analog-to-digital converter spurious free dynamic range in digital domain which is used as lower side dynamic range of receiver for low power signals and analog variable gain are used for higher side of dynamic range for high power signals.
Figure 5 illustrates the input to module for both channels. The input is pulse modulated with pulse width of 0.45us and PRT of 1.45us. The CW frequency is 1090MHz.
Figure 6 illustrates the outputs of module after phase calibration. The plot is taken in real time from Signal-tap software which is a part of Altera Quartus. Adjusted phase and magnitude among the channels of digital receiver is shown.
Figure 7 illustrates the two channel video outputs and one bit sign output of digital receiver. When RF signals in both the channels phase varying from 0 to89°, sign output shows high. Otherwise if phase difference greater than or equal to 90° and pulse off condition, it maintains low value. This feature is mainly used for mono pulse Radars.
In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.
It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.

We Claim:

1. A method of receiving Radar signals, the method comprising:
a dual path receiver for receiving a first and a second IFF signals simultaneously, the dual path receiver generates first and second video signals from the simultaneously received first and second IFF signals and additional phase information between the channels is provided;
conditioning the received first and second IFF signals by the radio frequency conditioning chain, wherein the RF conditioning chain consists of gain stage followed by filter stage by maintaining the linearity in the analog chain;
sampling the conditioned frequencies by using Analog-to-Digital converter for down conversion & digitization; and
processing the sampled frequencies for both channels which are captured by high end by Field Programmable Gate Array.

2. The method as claimed in claim 1, wherein the sampling for dual channel with RF sub sampling with minimum hardware.

3. The method as claimed in claim 1, wherein programmable critical radio frequency functional blocks are implemented in digital.

4. The method as claimed in claim 2, wherein sub sampling consists of programmable processing bandwidth, wherein the conditioned signal captured is passed through band pass filter whose 3dB bandwidth is programmable which is directly effects the sensitivity of the receiver.

5. The method as claimed in claim 2, wherein sub sampling has adaptive calibration between the channels for gain and phase matching, wherein phase and gain difference between channel caused by signal condition chains and external cable mismatches are minimized adaptively in digital domain with digitally implemented blocks.

6. The method as claimed in claim 2, wherein sub sampling split spurious free dynamic range in analog and digital domain.

7. The method as claimed in claim 6, wherein analog-to-digital converter spurious free dynamic range in digital domain which is used as lower side dynamic range of receiver for low power signals and analog variable gain are used for higher side of dynamic range for high power signals.

Abstract

The invention relates method to realize Programmable Dual channels matched linear Identification Friend or Foe Radar Digital Receiver. The Digital receiver has two channel Radio frequency front ends with minimum hardware for signal conditioning. Analog to digital convertors in both channels under-samples directly the Identification Friend or Foe signal after signal conditioning. Critical RF modules are implemented in digital and nonlinearity issues of Receiver are minimized. Adaptive calibration is implemented in digital to match gain and phase between the channels.
,CLAIMS:We Claim:

1. A method of receiving Radar signals, the method comprising:
a dual path receiver for receiving a first and a second IFF signals simultaneously, the dual path receiver generates first and second video signals from the simultaneously received first and second IFF signals and additional phase information between the channels is provided;
conditioning the received first and second IFF signals by the radio frequency conditioning chain, wherein the RF conditioning chain consists of gain stage followed by filter stage by maintaining the linearity in the analog chain;
sampling the conditioned frequencies by using Analog-to-Digital converter for down conversion & digitization; and
processing the sampled frequencies for both channels which are captured by high end by Field Programmable Gate Array.

2. The method as claimed in claim 1, wherein the sampling for dual channel with RF sub sampling with minimum hardware.

3. The method as claimed in claim 1, wherein programmable critical radio frequency functional blocks are implemented in digital.

4. The method as claimed in claim 2, wherein sub sampling consists of programmable processing bandwidth, wherein the conditioned signal captured is passed through band pass filter whose 3dB bandwidth is programmable which is directly effects the sensitivity of the receiver.

5. The method as claimed in claim 2, wherein sub sampling has adaptive calibration between the channels for gain and phase matching, wherein phase and gain difference between channel caused by signal condition chains and external cable mismatches are minimized adaptively in digital domain with digitally implemented blocks.

6. The method as claimed in claim 2, wherein sub sampling split spurious free dynamic range in analog and digital domain.

7. The method as claimed in claim 6, wherein analog-to-digital converter spurious free dynamic range in digital domain which is used as lower side dynamic range of receiver for low power signals and analog variable gain are used for higher side of dynamic range for high power signals.