Neville W. Harris

Quasi-optical ferrite reflection circulator

A quasi-optical Faraday rotation ferrite circulator for microwave or millimeter radiation is analyzed by a matrix formalism. Both reflection and transmission configurations at oblique incidence are examined. Numerical results are presented for the band centered at 35 GHz. Theory and experiment are compared over a 10%-20% band. Notwithstanding the complexities of oblique incidence, the reflection-type device promises favorable bandwidth, low loss, and isolation comparable to those of the transmission version now in system deployment, and offers the potential for much higher heat-dissipation capability. >

The quasi-optical ferrite reflection circulator: microwave performance and applications

We present experimental measurements of insertion loss and isolation on a reflection type quasi-optical circulator. We will also compare the results of the analysis of the microwave and thermal characteristics to experiment. Computed estimates of power capabilities show that megawatt average power levels at millimeter wavelengths are feasible.<<ETX>>

Quasi-optical reflection circulator: progress in theory and millimeter wave experiments

Development of a reflection circulator designed for use in quasi-optical beam systems is reported. Requirements of a millimeter-wave radar motivated the project, but the attractive performance features of the device, including broad bandwidth and high power capability, make it suitable for other applications as well. The discussion includes the underlying principle of nonreciprocity, problems of Faraday rotation, refraction, and polarization- insensitive anti-reflection matching at oblique angles of propagation. Comparisons of experimental measurements with a computational model show excellent agreement.

Quasi-optical reflection circulator

A quasi-optical Faraday rotation ferrite circulator for microwave or millimeter radiation is analyzed by a matrix formalism. Both reflection and transmission configurations at oblique incidence are examined. Numerical results are presented at 35 degrees and 45 degrees incidence across a band centered at 35 GHz. Calculations are also compared with transmission experiments over a 10% bandwidth. Notwithstanding the complexities of oblique incidence, the reflection-type device promises favorable bandwidth, low loss, and isolation comparable to those of the transmission version now in system deployment, and offers the potential for much higher heat-dissipation capability.<<ETX>>

Characteristics of the quasi-optical reflection circulator

Experimental measurements were made in Ku band on a reflection variant of the transmission quasi-optical Faraday rotation ferrite circulator. Measured isolation (load to transmitter) and insertion losses were 16 and 0.1 dB respectively. Theoretical predictions assuming double instead of single matching plates improve these figures to 21 and 0.03 dB respectively. The isolation (transmitter to receiver) is extremely high. The configuration planes a heat sink close to the area of RF loss and allows megawatt average power handling at millimeter wavelengths. >

Thermal lensing and frequency chirp in a heated CdTe modulator crystal and its effects on laser radar performance

The effects of optical and microwave heatings and thermally-induced birefringence in a CdTe modulator crystal on the performance of a linear FM CO2 laser radar are examined. This is conducted in terms of reductions in beam Strehl ratio and dynamic ranges of the Doppler shift and range for given optical and microwave powers. An analysis of the thermal lenses generated by these heatings is presented.

Tunable electro-optic modulators for laser radar applications - Experimental results

A tunable electro-optic single sideband modulator having a configuration consisting of a CdTe crystal surrounded by a ferrite placed inside a microwave waveguide can be used as a laser local oscillator to track the target translational Doppler frequency in a CO2 laser radar return. Results on measurements to determine the phase velocity matched bandwidth for the above composite modulator configuration are reported.

Design and construction of a wideband efficient electro-optic modulator

Modulators with a large instantaneous microwave bandwidth and high efficiency were developed for imposing frequency chirped waveforms on a high power CO2 laser output. These modulators may be cascaded to increase bandwidth and to increase efficiency. Details of the construction, together with the results, are presented.

Inhomogeneous quarter-wave transformers for a waveguide electro-optic modulator

Electro-optic frequency shifters, or modulators, have been built with almost 100 percent efficiency. Conversions over 50 percent require the interaction of a circularly polarized high power microwave beam traveling synchronously with a circularly polarized laser beam in an electro-optic crystal. We describe the inhomogeneous quarter-wave transformer structures made for a CO2 laser beam modulator with a conversion efficiency in excess of 80 percent. Conventional impedance matching synthesis was adapted to include the requirements for maintaining circular polarization and handling high power. Measured results are presented.

Theory of single and double sideband modulators

The concept of two magnetically tunable electro-optic (EO) modulators is described. A single-sideband in which the E-O crystal is surrounded by a hollow square tube of ferrite is axially magnetized in a square waveguide. The other is a double sideband device in a rectangular waveguide with the E-O crystal sandwiched between two ferrite slabs oppositely magnetized transverse to the waveguide. Each is tuned by a variable magnetic field in order to match the phase velocities of the varying microwave frequency and the optical velocity of the laser beam. Perturbation theory yields tuning curves of frequency versus magnetic field over a relatively broadband.