Fig. 4.10 Concept of levels in EMC

ably allocated, and the system performance can be optimized by continuously iterating during the entire system design phase.

The “system design method” emphasizes top-level design, process control, and continuous iteration, and therefore, it requires technical methods and physical environment, which includes analysis, prediction, design, evaluation, and other methods; models, databases, and other resources; testing, verification, and other test facilities. The system design method embodies the iterative and spiral-up optimization ideas. A large number of applications indicate that system design method plays an important role in effective solving of system-level EMC problems.

With the advancement of technology, the system design method is moving toward the direction of all digital design, digital physical collaborative design, and multi-site collaborative design.

4.2.3 System-Level EMC

Correct understanding of the system-level concept in EMC research is very important for quantitative system-level EMC design. The following section describes the system-level concept in the EMC field.

According to different functions, forms, and methods of problem solving, EMC problems can be classified into five levels: device level, circuit board level, equipment level, subsystem level, and system level, as shown in Fig. 4.10.

It should be pointed out that the form of system level has been changed significantly with advancement in technology, from single-entity systems (such as aircraft, ships, satellites, vehicles) to multi-entity systems (such as drone systems). Therefore, the concept of system-level EMC has also been broadened.

The concept of system-level EMC also includes intra-system EMC issues, intersystem EMC issues, and issues between the system and the environment.

(1)Intra-system EMC issues. The whole unit, which is used to accomplish the intended task and can achieve mutual EMC through design synchronization during the development phase, is called the “system,” e.g., single-entity systems such as aircraft and ships, multi-entity systems such as drone systems, and even aircraft carrier systems that contain aircraft carrier and carrier-based aircraft.

When the whole system is intended to accomplish one task, and in the development phase, mutual EMC can be realized through design synchronization (if any unit in the whole is not electromagnetically compatible with other units, the overall intended task cannot be completed), and the EMC problem that occurs within the entire system should be the intra-system EMC issue.

(2)Inter-system EMC issues. The unit that is used to accomplish the tasks but unable to achieve mutual EMC through design synchronization during the development phase is called “multi-system.” If aircraft fleets developed at different times are used, these aircraft cannot achieve mutual EMC through design synchronization at the development phase. Even though the development of aircraft in the later stage has fully considered the EMC with “old aircraft,” its design often needs to reconcile with the performance of the “old aircraft” which can hardly be changed.

Ship fleets developed at different times and new carrier-based aircraft used for existing aircraft carrier systems often have such problems.

(3)EMC issues between the system and the environment. The system needs to complete its task in a new environment (such as the unexpected natural or manmade electromagnetic environments), which has not been considered during the system development phase.

The reason that we make distinction among intra-system EMC issues, intersystem EMC issues, and EMC issues between the system and the environment is that there are different approaches to achieve system EMC for different types of issues. EMC of all three types can be achieved through system-level EMC design, control, and evaluation in the development phase. The latter two can also be achieved through comprehensive technical methods such as spectrum management.

4.2.4 Characteristics of System-Level EMC

EMC is usually concealed and is closely related to the inherent attributes of electronic information systems, so that EMC indicators, EMC models, EMC design, EMC detection, EMC evaluation, and EMC testing all have the following specialties:

(1)Different from other electrical indicators, the EMC indicators have probabilistic statistical characteristics. Since the EMC of the whole aircraft is the result of the comprehensive action of all the electronic information systems of the aircraft, both the electromagnetic emission characteristics and the electromagnetic susceptibility characteristics of the whole aircraft have probabilistic statistical characteristics. Therefore, the EMC data sample of the aircraft, the data acquisition method, and statistical method are crucial for the determination of the EMC indicators of the aircraft.

(2)Different from other electrical design, EMC design is a combination of functional design and non-functional design. Functional design, also known as nor-

mal signal design, is the complete electrical design based on functional specifications; e.g., radio stations are designed based on operating frequency, RF bandwidth, working mode, receiver sensitivity, demodulation mode, out-of- band spurious and harmonics suppression, transmit power, modulation method, and parameters. Non-functional design is to predict and minimize the effect of non-functional signals with the presence of both functional and non-functional signals.

The EMC design consists of functional design and non-functional design. The design process includes design for normal signal and the design with the combination input of normal signal and abnormal signal. Specifically, non-functional signals refer to the interference caused by the aircraft on the airborne radio and the sum of airborne electromagnetic environment signals of the airborne radio. The interference signal caused by the aircraft mainly refers to the interference due to unsatisfactory loading conditions of onboard power supply and impedance, and the interference of other onboard electronic information devices to radio stations. The electromagnetic environment signal mainly refers to the EMI to the aircraft during operation, such as the impact of civil communications on the aircraft.

The design using normal signal and non-functional signal together as a design input means that the normal design signal and the interference signal from the internal and external environment of the aircraft are used as the input of the radio station to evaluate its impact. Only when the airborne radio station has a corresponding protective design for the interference signal, can it have the capacity to be installed and be compatible with other equipment on the aircraft.

(3)Different from other tests, EMC tests are used for diagnosis through external inspection. The system-level EMC test is performed on the whole aircraft, and the data generated is comprehensive from the whole system in operation. Therefore, the identification of the aircraft’s EMC problem is similar to “diagnosis with traditional Chinese doctors,” which means detecting the internal problems through observing external appearance. One major task of the system-level EMC test is to detect new EMC problems due to interconnects and couplings in subsystems who has passed EMC tests, respectively. This diagnostic kind of test makes the entire EMC test complex and important.

(4)Different from equipmentand subsystem-level test, system-level EMC tests belong to large-scale system tests. According to the system scale, EMC problems can be categorized into different levels, including device level, circuit board level, equipment level, subsystem level, and system level. Since the aircraft assembles a large number of electronic information and control equipment which are distributed on a large scale, the test antenna can only cover parts of the aircraft and some equipment in electromagnetic emission test and electromagnetic susceptibility test. Therefore, the system-level EMC test is essentially different from the tests at device level, circuit board level, equipment level, and subsystem level both in terms of indicators and methods.