Determining Antenna Separation Requirements for Co-Located Transmitters
Minimum antenna separation depends on transmitter power, receiver blocking thresholds, intermodulation mixing products, and regulatory simultaneous exposure ratios.
Electromagnetic Bandgap
Meaning
Periodic dielectric or metallic structures can prevent the propagation of electromagnetic waves within a specific frequency band. An electromagnetic bandgap refers to this range of frequencies where surface currents and waves are blocked by the periodic lattice. Using these structures helps isolate sensitive radio frequency circuits from high-frequency board noise.
Structural Pattern
Arranging metal patches or vias in a repeating pattern on a circuit board creates a high impedance surface that acts as a filter. When a surface wave encounters this electromagnetic bandgap, the wave is reflected and attenuated instead of traveling along the substrate. Designers calculate the grid spacing and patch size to target the exact operating frequency of the noise sources.
Noise Mitigation
Power plane noise in high-speed digital designs often couples into sensitive analog receivers, degrading system performance. Implementing an electromagnetic bandgap between the digital and analog regions of the board prevents this coupling, ensuring clean signal paths. This isolation technique reduces jitter and improves the overall sensitivity of the onboard receiver module.
Design Limitation
Manufacturing these periodic structures requires tight tolerancing on the board drill and etch processes. If the vias are misaligned, the stopband frequency shifts. This shift ruins the filtering effect.