Gregory L. Tangonan

Two-dimensional beam steering using an electrically tunable impedance surface

By covering a metal ground plane with a periodic surface texture, we can alter its electromagnetic properties. The impedance of this metasurface can be modeled as a parallel resonant circuit, with sheet inductance L, and sheet capacitance C. The reflection phase varies with frequency from +/spl pi/ to -/spl pi/, and crosses through 0 at the LC resonance frequency, where the surface behaves as an artificial magnetic conductor. By incorporating varactor diodes into the texture, we have built a tunable impedance surface, in which an applied bias voltage controls the resonance frequency, and the reflection phase. We can program the surface to create a tunable phase gradient, which can electronically steer a reflected beam over +/- 40/spl deg/ in two dimensions, for both polarizations. We have also found that this type of resonant surface texture can provide greater bandwidth than conventional reflectarray structures. This new electronically steerable reflector offers a low-cost alternative to a conventional phased array.

A tunable impedance surface performing as a reconfigurable beam steering reflector

We describe a reconfigurable microwave surface that performs as a new kind of beam steering reflector. The surface is textured with an array of tiny resonators, which provide a frequency-dependent surface impedance. By tuning the individual resonators, the surface impedance, and thus the reflection coefficient phase, can be varied as a function of position across the reflector. Using a reflection phase gradient, the surface can steer a reflected beam. As an example, we have built a simple mechanically tuned surface in which physical motion of only 1/100 wavelength generates a sufficient phase gradient to steer a reflected beam by /spl plusmn/16 degrees. To steer to greater angles, the surface can be configured as an artificial microwave grating, capable of /spl plusmn/38 degrees of beam steering. The concept of the tunable impedance surface demonstrated here can be extended to electrically controlled structures, which would permit more elaborate reflection phase patterns, and provide more capabilities, such as the ability to focus or steer multiple beams.

Reconfigurable aperture antennas using RF MEMS switches for multi-octave tunability and beam steering

The requirements for increased functionality within a confined volume will place greater burdens on electromagnetic platforms for air, space, and sea over the next few decades. An important piece of the any solution to these new requirements are transmitting and receiving apertures that can handle multi-octave bandwidths with beam steering capability. The ability of an aperture to be reconfigured for a particular mission will become essential. New types of devices are being developed which will enable the realization of these reconfigurable apertures. This paper presents a discussion of how one of these new devices, the RF MEMS switch, can be utilized to change the phase and frequency characteristics of conventional antenna elements to perform beam steering over a wide range of microwave frequencies.

Planar Rowland spectrometer for fiber-optic wavelength demultiplexing

A planar Rowland spectrometer was fabricated and characterized as a wavelength demultiplexer for multimode fiber-optic applications. The spectrometer consisted of a planar multimode glass waveguide with two curved end faces and a cylindrical concave grating attached to one of the end faces. Semiconductor lasers with wavelengths between 0.825 and 0.845 microm were used for the measurements. Cross-talk isolation between two adjacent fibers with center-to-center separation of 175 microm (100 A in wavelength difference) was measured to be 18 dB. The devices performance was limited by grating diffraction efficiency, optical aberration , waveguide dispersion, and waveguide losses.

Electronic beam steering using a varactor-tuned impedance surface

Limited electronic steering can be accomplished using a focusing reflective surface by changing the feed location or direction of incidence. In this paper we describe a method of electronic beam steering by using a tunable impedance surface. Since there are no moving parts or complicated feed networks, this method of reflective beam steering can have great utility for low-cost and lightweight scanning antennas.

Spur-free dynamic range measurements of a fiber optic link with traveling wave linearized directional coupler modulators

Two-tone testing was performed on a laboratory fiber optic link with LiNbO/sub 3/ traveling wave linearized directional coupler modulators. The third-order distortion was measured at 500 MHz and 1000 MHz, and the spur-free dynamic range was determined. Two modulator configurations, with either one or two passive bias sections, were tested and the results were compared with measurements of simple directional coupler modulators. A 9.5-11 dB improvement in the dynamic range was found in the links employing the linearized modulators.<<ETX>>

Electrooptic diffraction modulation in Ti-diffused LiTaO 3

The design and fabriction of electrooptic Bragg diffraction modulators in Ti-diffused LiTaO(3) waveguides are reported. The modulators developed have demonstrated 98% deflection efficiency for visible and near-ir operation with extinction ratios of at least 250:1 for both deflected (m = 1) and nondeflected (m = 0) beams.

A novel optical modulator system with enhanced linearization properties

The authors propose a novel optical modulator system that has the properties of having a null third-order intermodulation distortion (IMD); a spurious signal free dynamic range in excess of 100 dB as determined by the second-, fourth-, and fifth-order IMD; and a linear dynamic range of 2.46 radians. It is shown that a combination of a tandem of two directional couplers has the property of eliminating completely third-order IMD term, gives a large spurious signal free dynamic range, and provides a simple and practical solution to the problem of linearization of optical modulators.<<ETX>>

Very-high-bandwidth In/sub 0.53/Ga/sub 0.47/As p-i-n detector arrays

The authors fabricated and packaged 1*4 arrays of In/sub 0.53/Ga/sub 0.47/As p-i-n photodetectors connected in a GaAs FET bias-switched, common cathode circuit. The bandwidth of the discrete (packaged) photodiodes in the arrays exceeds 11 GHz, and is 5 GHz for the packaged arrays. The on/off isolation ratio for fully packaged arrays using GaAs FET bias switches was measured at both low and high frequencies. It was found that the on/off isolation of the detectors in the array was 70 dB, and the bias switching times were less than 5 ns. The performance characteristics suggest that the p-i-n detector arrays used in a common cathode, current summing configuration have applications for high-freqeuncy digital and analog optical switching applications.<<ETX>>

Proton‐implanted GaP optical waveguide

Waveguiding in the visible spectrum has been observed in proton‐implanted n‐type GaP. The results obtained indicate that waveguide formation results from free carrier index change of the substrate refractive index with respect to that of the implanted layer.