With the development of micro-electronics and bandwidth device technology pushing digitalization forward, RF integration will climb to a higher level with wider bandwidth and gradual reduction in terms of volume, weight and cost. Moreover, revolutionized changes will take place on system hardware configuration and integrated structure and hardware generalization will be an inevitable trend. Through airborne mission system integration and miniaturization design, antennas from all systems can be summarized or reconstructed into antenna with a low number according to frequency band and functions. In addition, comprehensive processing is done on antenna, analog circuit, control circuit, digital circuit and connection network so that an RF transceiver system can be created with wide frequency spectrum, multiple channels and self adaptiveness. The purpose of integrated RF lies in reduction of cost, weight and volume so that users will regard the cost acceptable with both practicability and reliability going up as well. Based on experiments, it proves that MTBCF (Mean Time Between Critical Failures) of integrated systems can be increased by two times through means of community, modules, resource sharing, testability and reconstruction to realize objects discussed above.
Design Analysis of Integrated RF
Due to a series of limitations of real estate on port, weight, space and power supply, integration design is applied by airborne mission systems to integrate and share resources with similar functions. As a result, when ensuring the implementations of system functional indexes, goals will be realized including light weight, miniaturization and low power consumption so as to be compatible with requirement of airplane assembly.
a. From the point of system limitation, antennas on all sensors and transceiver system account for the majority of the whole system in terms of light, real estate and power consumption, responsible for signal emission and signal perception. To meet all the demands discussed above, it's necessary to carry out integrated RF system design:
b. From the point of system capability, fast feedback in accordance to military demands calls for such high functional flexibility that new functions can be added with a low cost during a short time to achieve rapid system upgrading and function expansion.
c. From the point of equipment configuration improvement, it is effective to implement integrated design, digital collection and information sharing.
d. From the point of platform flexibility, application of integrated RF design leads aerial carrier to meet requirement concerning assembly adaptability through weight reduction and energization. Furthermore, a series of issues can be successfully solved such as blocking, electromagnetic interference and reflection area increasing as a result of increasing of antenna account.
Attributes of Integrated RF
To be compatible with limited resources on platform and meet the demand of military operation, an open configuration is applied in airborne mission system with basic module contributing to the whole system. Integrated RF design combines radar detection, passive detection, communication/data chain and IFF (Identification Friend or Foe) so that an integrated electronic device can be generated featuring multiple spectrums, multiple means and self adaptability.
Attributes of integrated RF include:
a. Open RF construction;
b. Full embodiment of digitalization, modularization, generalization and standardization;
c. Capable of being robust and fault tolerant;
d. Ability of secondary development;
e. High reliability, access to support, expandability, light weight and low cost etc.
Elements in Integrated RF Design
• Design Elements of Radio Reception Integration
Radio reception integration refers to the process that different mission systems commonly share a RF input channel and achieve their own signal reception function. Functions of reception channel demand that RF signals received by reception antennas be amplified, filtered, frequency converted, digitalized and signal preprocessed and they be output to integrated core processor for signal processing and data processing. One of the signals possibly requires multiple reception channels that have to be operated together with performance demands including sharing network handover, low noise amplification, channel gains, AGC, dynamic range, channel bandwidth and channel balance.
The following elements should be taken into consideration concerning radio reception integration:
a. Operating frequency;
b. Transient bandwidth of reception channel;
c. Transient dynamic of reception signals;
d. Sensitivity of reception signals;
e. Output bandwidth larger than the overall bandwidth when all missions are holding the same channel.
• Design Elements of RF Emission Integration
RF emission integration drives different mission systems to commonly share RF output channel to complete their own signal emission functions. Emission channels provide corresponding signal waveform, modulation, frequency conversion, drive amplification and power output that'll be sent to antennas. Its leading performance lies in signal waveform, signal stability, channel gains, dynamic range, output power and output spectrum purity.
The following elements should be taken into consideration concerning RF emission integration:
a. Operating frequency;
b. Transient bandwidth of emission channel;
c. SFDR (Spurious Free Dynamic Range) of emitted signals;
d. Frequency of emitted signals;
e. Output signal waveform.
Elements mentioned above should be ensured by integrated RF emission. Different from radio reception integration that is capable of receiving signals at the same time, some issues are still available on same-time emission, which especially occurs to bandwidth waveform. The key issue lies in the fact that multi-source common emission leaves high demands on linearity of power amplifier.
Design Methods of Integrated RF
• Design Method of Antenna Aperture Integration
Integrated antenna or antenna array is a key physical component contributing to airborne mission system and implements conversion between space electrical RF energy and high-frequency electrical RF energy by subsystems. According to the requirement in terms of air domain, frequency domain, time domain and modulation domain, along with its properties on functions, operating mode, operating frequency range, covering air domain, operating period, modulation mode, polarization and airborne adaptability, all kinds of antennas should be integrated and advanced technologies of current antenna design should be applied as much as possible such as super bandwidth, conformal, miniaturization, common aperture and reconstruction. Optimal design target should be hit around index, volume, weight and cost and all kinds of antennas should receive integrated design with their functions and frequencies optimized released in order to finally integrate antenna aperture.
a. Integrated type design. With requirement such as operating frequency, covering air domain and polarization considered, antenna with high bandwidth, high efficiency and high gains should be applied and antenna or antenna array should receive uniform design with antenna classification simplified.
b. Integrated aperture design. With demand on antenna performance met, common aperture design should be carried out on antenna or antenna array as much as possible with an optimized design target on cost, volume and weight. Based on considerations on antenna operating frequency, assembly position, space size & covering range and fundamental discussion result, common aperture design is implemented on antennas with similar assembly positions so that multiple antennas or antenna array is arranged at the same aperture to reduce antenna assembly space and improve aperture usage efficiency.
c. Antenna sharing design. When it comes to antennas with similar index requirement in terms of operating frequency, polarization type, gains and covering space, antenna sharing design is carried out through switch changeover, signal combiner or splitter and time-sharing application in order to minimize the account of antennas.
• RF front end integration design
Based on high-power bandwidth device technology, Microsystem Technology, MEMS (micro electro mechanical system) and distributed technology, an integrated RF standard system is established through generalization, digitalization and modularization design. Moreover, general RF transceiver channel and hardware platform are set up so that RF system channel can be compatible with all spectrum, reconstructable, digitalized and microsystematized.
According to general development requirement of airborne mission system and its structural definition, along with integrated design principles, RF front end integration design methods contain the following aspects:
a. RF channelization. Discreteness and dedication of each functional subsystem should be broken and all RF systems receive channelization design so as to lead RF transceiver channel to be all spectrum compatible and generally integrated.
b. Resource modularization. All hardware resources are designed through plane frame, back plane and modules compatible with standard in order to achieve uniform assembly power supply and thermal dissipation of hardware resource modules.
c. Module generalization. RF front end public resource modules go through generalization design, including power supply module, reception module, and switch module and generalization design is gradually implemented on multi-function preprocessing module. On one hand, generalization design of modules helps reducing resource classification. On the other hand, basis is established for function backup and reconstruction.
d. Interface standardization. Standard bus is applied in RF front end and sensor network is accessed through a uniform-designed general interface module. Standardization of interfaces is able to effectively reduce system bus type and number, beneficial for interconnection between systems.
e. Resource management unification. General interface module at RF front end uniformly receives and analyzes resource administration demands from core processor and sends them to corresponding preprocessing modules and other modules with uniform administration on RF front end completed.
Design Methods of Modularization
Sensor section belonging to airborne mission system, including analog circuit at RF front end and digital circuit at RF rear end, applies an open system structure and uses standard hardware modules with different functions and few types that contain RF front end module, general reception module, preprocessing module, signal processing module, multi-frequency emission module, multi-function modulator module, antenna interface unit and matrix switch array. Those modules can be combined dynamically based on demands on RF functions of sensors to realize functions of different sensors. They can be designed and manufactured based on a stringent and uniform structural standard dimensions and be installed and used on a standard installation frame.
Antenna interface unit completes functions of RF change-over switches, responsible for sending RF signals received by antennas to RF front end module. Connected with multi-frequency emitter module, antenna interface unit transmits RF signals that are ready to be emitted to corresponding antennas. Antenna interface unit is capable of resolving conflicts that will possibly take place when transceiver signals are sharing antenna.
RF front end reception module converts RF signals into standard medium frequency and medium frequency switch transmits medium-frequency signals output by RF front end reception module to general reception module, medium-frequency modulation signals generated by multi-functional modulator to corresponding emitter module. Medium frequency switches are responsible for resolving conflicts that may be created when transceiver medium-frequency signals are sharing general reception module and multi-functional modulator module.
Medium-frequency signals are transmitted to signal preprocessor after they are processed by general reception module including band-pass filtering, A/D conversion, and DDC (Digital Down Conversion). Signal preprocessor carries out matched filtering on signals after general reception module digitalization with baseband signal's phase transformation, pulse capturing and digital dispreading completed. Moreover, it also shares part of processing work of signal processors and digital signals after preprocessing are transmitted to signal processing module. In the process of emission, signal preprocessor sends baseband signals to multi-function modulator after implementing digital spread spectrum and pulse shaping.
Signal processing module is in charge of signal processing of all sensors' functions, including demodulation, channel self-adaptive balance, error correcting encoding and decoding and encryption and decryption.
Design Methods of Channelization
As multiple channels are working together or independently at integrated RF front end and a certain signal waveform is being processed, all the hardware module resources can be combined together within digital conversion network to create a hardware thread supporting signal waveform processing. Integrated RF front end is capable of supporting multiple hardware threads that can uniformly or independently work in conformity with antenna scanning strategy or signal processing procedure. As a result, RF front end of the system is capable of processing multiple signals with multiple functions achieved based on system information processing demand. Redundant channels are still available in channels of RF, tuning and medium frequency so that all channels are maintained as backups with each other to increase reliability of the system. If there's something wrong with some signal channels that fail to completely support parallel processing of multiple signals, different parallel or time-sharing processing threads can be formed according to system working mode and signal processing priority.
As is indicated in Figure 1, numerous parallel channels of multiple signals are available in RF front end, which can be switched or work in a parallel way through system control. Tuning reception channel extracts all kinds of relatively pure signals which then fall into medium frequency through frequency conversion. All the signals can be reasonably divided into some public medium-frequency channels with frequency-sharing or time-sharing methods and are processed in multi-function digital receiver after selection and combination by switch array. The system applies integrated frequency integrator with properties of broad band, multi-point frequency, rapid agility and combination output.
Design Methods of Microsystemization
Microsystems integrates components such as sensors, reading circuits, digital signal processor, AD/DA, transceiver components and power supplies within micrometer range so that volume and power consumption can be drastically reduced of system and configuration. Configuration of RF transceiver channel microsystem, device and components with application of 3S (Sop, Sip, Soc) technology leads to key development of wide frequency band.
• Integrated Design Technologies of System
Integrated design technology of system plays a potential role in reaching mission system integration, making the best use of all kinds of electronic device efficiency and ensuring integrated military capabilities. Centering on the perspective of systems, integration has to be implemented on its composition, construction, functions and interconnection method so that integration design of mission system can be optimized. Conforming to military missions and mission requirement, mission system integration design is responsible for defining, analyzing, designing, testing and evaluating the whole system so as to drive mission system to be compatible with mission demand in terms of functions, performance, reliability, maintenance, supportability and life-cycle cost. System designers should participate in planning and research in accordance with industry conformal, long-standing and fundamental projects.
• Open System Construction Design Technology
Open system construction is beneficial for forming of distributed systems provides convenience for interconnection and interoperation between hardware from different manufacturers, computers with varied type numbers or others. It is convenient for hardware and software transplantation and enhancement and expansion of system functions. Also, it helps shrinking research and development period as it supports system's volatile scale.
The key to the implementation of open system construction lies in all kinds of standard interface manufacturing and conformability so that the same standard and regulations can be followed by different product development and manufacturing unit. Apart from hardware, software is also involved in open system construction, still playing a significant role in software open system, reusability and volatile scale. Furthermore, it is regarded as an important measure to reduce system life-cycle cost and development period. A new version of integrated mission system software should conform to uniform standard and regulations and some properties of software, including reusability, standardization, intellectualization, transplantation and reliability should be included among characteristic parameters of representational software technology.
• Antenna Aperture Integrity Design Technology
As an essential part of airborne mission system, antenna or antenna array is in charge of emitting and receiving numerous radio signals. Due to a large number of system compositions, demands rise towards antenna types and amount and different demands are available in terms of operating frequency range, polarization mode, gains and covering air space. Furthermore, due to the limitation of airborne platform space and install positions of antenna, system antenna layout becomes rough, leaving a stringent demand for antenna account reduction.
To lower difficulty of system antenna layout, antenna or antenna array integrity design should be carried out after demands are met on antenna in compatible with functions. All antennas should be integrated and shared to make them front end of sharing sensors so that antenna aperture can be applied in an integrating way. Moreover, to ensure the EMC (Electromagnetic Compatibility) between functions as the system is working, optimized design should be taken on antenna layout in the system to minimize the effect on antenna performance and mutual effect between antennas.
• CIP Technology
CIP with a high-level integration in the system combines multiple advanced technologies and lots of computing, processing, control and administration functions are completed within it. CIP is responsible for integrated processing, data fusion, mission computing, video information generation, navigation computing, store management, electronic backup and defense management, communication management, system control and failure monitoring, inspection and reconstruction of sensor input data. Lots of significant characteristics of a new version of mission system are involved in CIP that technically makes the best use of properties of common module, parallel processing system and distributed real-time operating system, processes resources with sharing core and improves performance and reliability to meet demands of airborne processing capability and fast development of computing capability.
• Broadband Configurable RF Channel Digitalization Technology
Airborne mission system covers a wide frequency range, numerous types of signal modulation methods and signal formats and signal levels with wide differences. Devices in traditional hardware density communication system feature a complicated interconnection relation, high cost, a high level of upgrading transferring difficulty and difficult interconnection between systems. Therefore, it's necessary to depend on software radio and RF sampling technology, to push digitalization forward and to reduce RF front end processing channel and to increase function re-usage of digital signal processing at rear end in order to solve some integration issues concerning multiple functions, wide range of frequency and multiple modulation methods of the system. Plus, application of modular hardware and software brings convenience to system design and the introduction of new technologies so that performance will be improved, cost and time reduced.