Coherent Antenna Modulation

Ian M. Broadbooks

doi:10.1109/tap.2026.3687470

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Coherent Antenna Modulation

2026-04-30

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Ian M. Broadbooks

Daniel F. Sievenpiper

DOI：10.1109/tap.2026.3687470

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Abstract

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In this article, the authors propose and explore a new concept for a receive-configuration direct antenna modulation (DAM) system, called coherent antenna modulation (CAM). Antennas that can be tuned rapidly and synchronously in frequency have been demonstrated in previous work, allowing an electrically small antenna (ESA) to surpass the traditional LTI bandwidth efficiency product limit asserted by Wheeler and Chu. This approach is easily applied in transmitting frequency-modulated (FM) applications where the instantaneous frequency is known a priori. However, applying the same approach in a receiver is more difficult because the instantaneous frequency carries the information and therefore cannot be known in advance. Coherent antenna modulation takes a frequency-tunable electrically small antenna as its foundation. Then, the received RF signal is fed into a phase-locked loop to detect the incoming frequency. That information is then used to create a corresponding bias signal to tune the antenna to the detected frequency, all in real time. The result is that an ESA that is instantaneously narrowband can self-tune to a wideband FM signal without a priori knowledge of the incoming signal. Thus, the limit imposed by Wheeler and Chu can be practically surpassed in the receive configuration. The authors explore and show agreement between theoretical foundations, simulated performance, and measurement data from a prototype to demonstrate the functionality of the CAM concept.

Keywords:

Antenna Q

direct antenna modulation (DAM)

efficiency-bandwidth product (EBP)

electrically small antennas (ESAs)

time-modulated systems

time-varying systems