An RF network analyzer normally uses a reference port to excite
a device under test. The return from the device is compared in amplitude and phase to the reference to characterize the S-Parameters (reflection and transmission) of the device under test (DUT). In this case, the DUT was 30 meteres of limestone above a mine in Northwest Pennsylvania, which was being tested for dielectric constant and attenuation at 3-33 MHz as part of a ground penetrating radar development effort. This paper describes the test configuration using a wideband fiber optic link for the reference signal, and provides plots of the experimental results.
Future space-based platforms can and will benefit from the implementation of photonics in both analog and digital subsystems. This paper will discuss potential applications and advantages to the platforms through the use of photonics.
When asked to demonstrate the performance of fiber optics engineers often resort to hundreds of thousand dollars worth of test equipment including plotters and displays to show a screen view and to prove the viability of the photonic system. This paper will present a relatively inexpensive and unusual method of allowing visitors to see and hear operation of a microwave link versus that of a coaxial coupled RF link.
This paper describes the development of compact, polarization insensitive mode-locked erbium-doped fiber lasers producing picosecond pulses for use as optical sampling sources in photonic analog to digital converters (ADCs). High-sampling rate and high resolution ADCs are required to convert the `naturally occurring' received analog signals to digital signals suitable for on-board data processing. The laser was constructed in a linear cavity, Fabry-Perot configuration with the saturable absorber at one end of the cavity and a chirped fiber Bragg grating at the other end. Theoretical modeling of the pulse formation within the laser cavity is presented and is in close agreement with the experimental data. The influence of radiation effects on erbium-doped fiber and fiber Bragg gratings is also investigated.
Existing manned airborne platforms are becoming increasingly loaded with additional mission performance
requirements. These requirements severely stress weight, mission performance, size and electromagnetic
interference (EM!) constraints. In addition, as platforms are reduced in size - such as space-based platforms - these
limitations become extremely critical.
Optical fiber-based systems can be used to provide both data and RF signal distribution for sensors and
avionics. These photonic-based systems are lighter weight, smaller in size, lower in loss, and reduce or
eliminate signal interference as compared to existing metallic-based signal distribution systems. These fiber
based systems apply to both RF and data transmission in manned and unmanned space-based and airborne
platforms as well as ground based applications.
Photonics also provides non-frequency dependent true time delay RF signal distribution. This results in the
additional benefit of improved interferometric direction finding and beam nulling through software applications in
sensor and avionics systems.
This paper will discuss research which is underway at Rome Laboratory to develop actively reconfigurable
photonic-based signal distribution systems, using either all optical techniques - including optical switching - or
through a combination of optics and electronics, to meet the future requirements for avionics and sensors in
airborne and space-based platforms.
A multistage optically implemented microwave frequency synthesizer has been designed and fabricated. The concept and implementation are described with emphasis on operational characteristics of a prototype 3-stage unit. The synthesizer is designed as an optical analogue of the mix-and-divide approach to frequency synthesis taking advantage of the single-sideband, supressed-carrier modulation produced by the Bragg acousto-optic interaction and the sum- only or difference-only mixing of optical heterodyne detection without the need for any in- stage passband filtering. The synthesizer exhibits a 500 MHz bandwidth and completely switches and settles stably upon a new frequency within 250 nanoseconds. Phase noise was measured to be less than -130 dBc/Hz at 10 KHz offset from the carrier.
The first microwave-phased array antenna steered by optical delay lines is described. The optical ''time shifters'' utilize the propagation of light waves through a finite length of fiber to generate the time delays that control the beam pointing angle. Delay times specified by the antenna steering angle were implemented by switching bias currents of high speed lasers pigtailed to fiber optic delay lines.
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