The objective of this chapter is to provide a high-level perspective on the growing conflict over use of the radio-frequency (RF) spectrum, a precious and highly sought resource extending from below 1 MHz to above 100 GHz, caused by the accelerating demand for consumer use via 4G and soon-to-be 5G wireless communications. The world at large now faces serious spectrum-compatibility problems that require new and innovative solutions-increased spectral congestion and crowding are especially challenging. However, anticipated improvements in electromagnetic (EM) systems up to 300 GHz are beginning to be realized. Less restrictive constraints on communication systems, inherent in one-way propagation paths and much less expensive components, have allowed that community to design and develop more diverse waveforms and systems. Consequently, commercial cellular systems are proliferating at incredible rates, resulting in extremely spectrally dense environments and fierce competition for spectrum that traditionally has been the almost exclusive province of radars as primary legal users. For radar applications, however, the promise is being realized much more slowly, and the inundation of communication devices from the commercial sector has caused significant radar-communication interference problems. In addition, radar and communication systems are important components of military operations, and advances in waveform-diversity signal and data-processing techniques that are likewise relevant to spectrum sharing offer the promise of significantly improved performance.

Chapter Contents:

• 5.1 Introduction
• 5.2 Impacts of EM spectral interactions between communication and radar systems
• 5.2.1 Impacts of radars on communication systems
• 5.2.2 Impacts of communication systems on radars
• 5.3 Radar spectrum-mitigation efforts
• 5.3.1 Selected efforts since 1998
• 5.3.2 Current efforts
• 5.4 Suggested research areas for radar–communications spectral harmony
• 5.4.1 Adjacent-band interference mitigation for radar emissions
• 5.4.1.1 Adaptive RF filter technology
• 5.4.1.2 Transmitter topology
• 5.4.1.3 Linearizing radar transmitters
• 5.4.2 Radar waveforms
• 5.4.3 Innovative antenna elements and arrays
• 5.4.4 Innovative radar receivers
• 5.4.4.1 Radar receiver design using digital beamforming
• 5.4.4.2 Receiver interference rejection
• 5.4.5 Propagation
• 5.4.6 Adaptive and cognitive emission control
• 5.4.7 Radar–communications co-design
• 5.4.7.1 Code-transmitted signal at RF
• 5.5 Some essential EM theory for communications and radar
• 5.5.1 Physically realizable waveforms
• 5.5.2 Notions of far field and antenna pattern for communication cell sizes
• 5.5.3 Maxwellian-based use of capacity
• 5.5.4 Antenna pattern and placement for communications
• 5.5.5 Essential antenna properties for system design
• 5.6 Closing observations
• 5.6.1 Radar–communications spectral harmony
• References

Inspec keywords: cellular radio; radiowave propagation; radar; radio spectrum management; diversity reception; 4G mobile communication; 5G mobile communication; radiofrequency interference

Other keywords: spectrum sharing; 5G wireless communications; commercial cellular systems; radio-frequencies; radar applications; spectrally dense environments; one-way propagation paths; RF spectrum; spectral crowding; radar-communication interference; spectrum-compatibility problems; military operations; 4G wireless communications; waveform-diversity signal; spectral congestion; EM systems; electromagnetic systems; data-processing techniques; spectrum congestion; spectrum use

Subjects: Electromagnetic compatibility and interference; Mobile radio systems; Radar equipment, systems and applications; Radiowave propagation; Legislation, frequency allocation and spectrum pollution