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All-Dielectric, Non-Electronic Radio-Receiver Front Ends

Receivers would be made much less vulnerable to electromagnetic weapons.

All-dielectric, non-electronic, photonicassisted front ends are being developed as alternatives to traditional metal antennas and the associated metal connections and input electronic circuitry of radio receivers — especially microwave receivers. The main motivation for this development is the need to make radio receivers much less vulnerable to electromagnetic weapons.

An electromagnetic weapon produces an electric power surge capable of destroying or damaging sensitive electronic circuitry. The trend toward reduced feature size and reduced voltage renders modern electronic circuitry increasingly susceptible to such damage. Radio communication systems are particularly vulnerable because antennas and other traditional front-end parts serve as direct ports of entry for undesired radio-frequency (RF) electromagnetic radiation. In equipping a receiver with a non-electronic, alldielectric front end, one would eliminate the traditional metal antenna and the associated metal interconnections and input electronic circuitry, thereby eliminating the main traditional points of electromagnetic vulnerability.

An Incident Radio Wave excites a desired resonance in a dielectric resonator antenna. The resonance-enhanced field acts via the electro-optical effect to modulate an optical carrier signal. The RF modulation in the photodetector output is a replica of the incident radio signal.
From one perspective, a front end of the type now being developed can be characterized as a combination of a dielectric antenna that incorporates an electro-optical RF-field sensor (see figure). The dielectric antenna is a leaky RF resonator. Most of the RF resonator is made of a material that exhibits low RF loss and high relative permittivity. A small part of the RF resonator consists of a microdisk optical resonator made of an electro-optical material. A desired incident radio signal in the form of a free-space electromagnetic field excites a resonance mode of the antenna, resulting in a desired buildup of the electric field inside the antenna. The design of the antenna provides for placement of the electro-optical microdisk at the location of maximum enhancement of the resonant- frequency electric field.

An optical carrier signal is generated by a laser. A single-mode optical fiber couples the optical carrier signal from the laser to the electro-optical microdisk; another single-mode optical fiber couples the optical signal from the microdisk into a photodiode. By virtue of the electro-optical effect in the microdisk, the optical signal becomes modulated by the resonant RF signal. The modulation is present in the photodiode output and is subsequently processed by conventional receiver electronic circuitry. The laser, the photodiode, and all of the conventional receiver electronic circuitry can be enclosed in electromagnetic shielding to further reduce susceptibility to undesired electromagnetic radiation.

In addition to the absence of metal and delicate electronic components that could be damaged by the intense RF field from an electromagnetic weapon, the all-dielectric front end offers the advantage of electrical isolation of the RF electronic circuitry. Yet another advantage is that because of the high permittivity of the dielectric antenna material, the antenna can be smaller than a metallic antenna that resonates at the same frequency.

A front end of this type for an operating frequency of 7.38 GHz was built and tested in a proof-of-concept experiment. The main part of the resonator consisted of a BaTiO3 (relative permittivity = 38) cylinder 9 mm in axial length and 11.25 cm in diameter. The electro-optical microdisk was made of LiNbO3. The dimensions of the cylinder were chosen to obtain 7.38-GHz resonance in a mode in which the maximum enhancement of the electric field occurred at the center of an end face, where the electro-optical microdisk was located. The front end was found to be capable of detecting a 7.38-GHz signal with a sensitivity of 4.3 x 10-3 V/mHz1/2.

This work was done by Bahram Jalali of the University of California for the Air Force Research Laboratory.

Topics:
Antennas Communication systems Electric power Electronic equipment Fiber optics Off-board energy sources Optics Physical Sciences Radio equipment Sensors and actuators Telecommunications
This Brief includes a Technical Support Package (TSP).
Document cover
All-Dielectric, Non-Electronic Radio-Receiver Front Ends

(reference AFRL-0042) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

    This article first appeared in the October, 2007 issue of Defense Tech Briefs Magazine (Vol. 1 No. 5).

    Read more articles from the archives here.

    Overview

    The document is the Final Technical Report on the Non-Electronic Radio Front-End (NERF) project, conducted by researchers at the University of California and sponsored by the Defense Advanced Research Projects Agency (DARPA). The report, dated April 2007, outlines the development and experimental demonstration of a novel radio front-end technology that aims to enhance the performance of radio frequency (RF) communication systems.

    The report begins with a summary highlighting the increasing vulnerability of modern electronics to high power electromagnetic weapons, particularly in the post-September 11 context. These weapons can produce power surges that damage sensitive circuitry, making RF communication systems especially at risk due to their direct exposure through antennas.

    The introduction section provides background on the need for improved RF front-end technologies, emphasizing the limitations of current electronic systems in terms of resilience and performance. The NERF project aims to address these challenges by exploring non-electronic methods for RF signal processing, which could potentially offer greater robustness against electromagnetic interference.

    The methods, assumptions, and procedures section details the experimental setup used to demonstrate the new device. This includes the design and implementation of a photonic-assisted all-dielectric RF front-end technology, which leverages optical components to enhance signal detection and processing capabilities.

    Results and discussion are presented, showcasing the performance of the prototype receiver developed during the project. The report includes various figures illustrating the optical resonance spectrum, electro-optic modulation, and the measured transfer characteristics of the prototype. These results indicate promising advancements in receiver sensitivity and the ability to detect free space RF signals.

    The conclusion summarizes the findings and implications of the research, suggesting that the NERF technology could significantly improve the resilience and efficiency of RF communication systems. The report emphasizes the importance of continued research in this area to further develop non-electronic solutions that can withstand the threats posed by electromagnetic weapons.

    Overall, the document serves as a comprehensive overview of the NERF project, detailing its objectives, methodologies, experimental results, and potential impact on the field of RF communication technology. It underscores the critical need for innovative approaches to enhance the security and reliability of electronic systems in an increasingly complex threat landscape.

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