Search

Phase shifters are a key component of nulling interferometry, one of the potential routes to enabling the measurement of faint exoplanet spectra. Here, three different achromatic phase shifters are evaluated experimentally in the mid-infrared, where such nulling interferometers may someday operate. The methods evaluated include the use of dispersive glasses, a through-focus field inversion, and field reversals on reflection from antisymmetric flat-mirror periscopes. All three approaches yielded deep, broadband, mid-infrared nulls, but the deepest broadband nulls were obtained with the periscope architecture. In the periscope system, average null depths of 4 x [10.sup.-5] were obtained with a 25% bandwidth, and 2 x [10.sup.-5] with a 20% bandwidth, at a central wavelength of 9.5 [micro]m. The best short term nulls at 20% bandwidth were approximately 9 x [10.sup.-6], in line with error budget predictions and the limits of the current generation of hardware. OCIS codes: 120.3180, 120.4570, 350.1260.

This paper presents new tunable phase shifters using perturbed dielectric image lines (DIL's). The propagation constant in the DIL was perturbed by a movable metal reflector plate installed in parallel with the ground plane of the DIL. The phase shift was thus controlled and adjusted by varying the perturbation spacing between the DIL and movable reflector plate at a given operating frequency. A rigorous hybrid-mode analysis was used for calculating the dispersion of propagation constants in the perturbed DIL, and then for designing tunable phase shifters. Ka-band tunable phase shifters have been designed, fabricated, and tested. Measurement results agree well with theoretical predictions. The device is especially useful for millimeter-wave applications where traditional phase shifters are lossy. Index Terms - Dielectric image lines, millimeter waves, tunable phase shifters.

We demonstrate a new type of broad-band microwave phase shifter with superior performance at frequencies up to 20 GHz. This is implemented by simply adding an offset voltage prior to the loop filter (LF) in a laser-diode-based digital optoelectronic phase-locked loop (OEPLL). Accurate control of the phase of microwave signals with a continuously tunable range exceeding 640 [degrees] ([approximately]3.6[Pi]) is achieved. The phase fluctuation and long-term drift of any desired phase shift are as small as 5 [+ or -] 0.4 [degrees] and 0.08 [degrees], respectively, at 20 GHz. The relative phase instability can be maintained within 0.09 [degrees] while operating in a phase-shift-keying (PSK) scheme. We also demonstrate accurate control of relative phase difference between dual phase-locked microwave sources using the phase shifter. Our results indicate potential application of this broad-band optoelectronic phase shifter in a phased-array antenna system. Index Terms - Microwave, optoelectronic, phase shifter.

An efficient computer synthesis technique for waveguide components, based on rigorous field-theoretical models, has been developed. A computer code has been specifically set up for the automatic design of fixed phase shifters in rectangular waveguide technology. Only the electrical specifications are required to generate, normally in 15 to 20 minutes on a 386/16 MHz IBM PC, the geometrical structure of the components. The agreement with the experiments is shown to be so accurate as to avoid any tuning of the circuits realized. The efficiency and accuracy of the code is based on i) a suitable segmentation technique of the microwave structure to obtain a very simple but rigorous network model; ii) the efficient representation of the modal series for the electromagnetic fields; iii) a synthesis procedure based on a simplified model to obtain a good initial guess for the final full-wave optimization routine.