What is Antenna Reciprocity?
Antenna reciprocity is a fundamental electromagnetic principle stating that the transmit and receive properties of an antenna are identical in a given medium. This means that an antenna’s radiation pattern, gain, impedance, and polarization characteristics are the same whether it is transmitting or receiving. The principle is derived from the Lorentz reciprocity theorem and is foundational to antenna design, testing methodology, and link budget calculations in all wireless systems including 5G.
How Does Antenna Reciprocity Work?
The reciprocity theorem establishes that if an antenna produces a certain radiation pattern when excited as a transmitter, it will exhibit the same directional sensitivity pattern when used as a receiver. This holds true for all passive, linear antenna structures in isotropic media. In practice, this allows engineers to characterise an antenna in either transmit or receive mode and apply the results to both. However, reciprocity does not apply to active antenna systems with non-reciprocal components (e.g., amplifiers, circulators) unless the active elements are accounted for separately.
Use Cases
Antenna design and simulation validation, OTA testing methodology (where receive-mode measurements predict transmit performance), link budget calculations for 5G NR, MIMO channel modelling, and phased array antenna calibration.
3GPP / Standards Reference
IEEE Standard 145 (Definitions of Terms for Antennas), 3GPP TR 38.810 (Study on test methods for NR)
Related Terms
Beamforming | Phased array antenna | MIMO | OTA | EIRP
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