Sidelobe Suppression Ratio Research Articles

An integrated two-stage cascaded Mach-Zehnder device in GaAs

An integrated, cascaded, asymmetric GaAs-AlGaAs Mach-Zehnder (MZ) interferometer, for use in wavelength filtering and time-domain multiplexing, has been designed, fabricated, and tested, This device employs several new passive components, including height-tapered Y-branches, for uniform splitting and recombining, and index-tailored waveguide bends, for low-loss operation. The waveguide bend is designed with a predistorted index profile for minimizing both transition loss and radiation loss. The circuit is fabricated with a resistless, light-induced local etching technique, which enables rapid iterative fabrication of the device geometry to achieve the desired operating path delays. Acting as a wavelength filter, the fabricated device has a -24.3 dB minimum-to-maximum extinction ratio and a -10.5 dB side-lobe suppression ratio. Acting as a pulse-rate multiplexer, the device generates a four-pulse train with a 10-ps pulse-to-pulse separation and an amplitude uniformity of 80% for each input pulse.

Demonstration of InP-InGaAsP vertical grating-assisted codirectional coupler filters and receivers with tapered coupling coefficient distributions

In this letter, we demonstrate the first vertical grating-assisted codirectional coupler filter and receiver with a tapered coupling coefficient distribution. The tapering is achieved by modulating the grating duty ratio. By doing so, filter responses with sidelobe suppression ratios (SSR) better than conventional devices are observed. Using this design in an integrated receiver, a record SSR of 16 dB is reported. With perfect input coupling, it is found that the receiver sidelobe levels using this approach can be lower than /spl sim/40 dB.

Horizontal directional coupler filter suitable forintegration in a 1.3 + /1.3 - µm duplexer

The authors report the design and first realisation of a grating-assisted horizontal directional coupler filter exibiting a highly reduced polarisation sensitivity (below 1 dB on the filtered channel) and a high sidelobe suppression ratio (>25 dB for both polarisations). This filter is particulary suitable for integration in a 1.3+/1.3-µm duplexer.

Dispersion measurements of one-element short backfire (SBF) antennas

Three one-element short backfire (SBF) antennas at 40 MHz, 140 MHz, and 350 MHz were built in the institute for the use with the ATS-6 radio beacon experiment (RBE). Ehrenspeck's data experimentally measured in the GHz range were transformed into the VHF range. Since there were no relevant data available concerning the dipoles and feeder systems, various types were tested in combination with differently shaped SBF reflectors. The antennas were optimized with respect to gain, sidelobe suppression (ss), and forward-backward ratio (fbr). For all antennas ss was better than 20 dB and fbr better than 30 dB. The data, measured with the two identical antenna methods, are presented and compared with Ehrenspeck's data obtained with the pattern integration method. Ehrenspeck's gain seems to be about 0.8 dB higher than that measured at the antenna test range at Lindau, very likely due to the different measuring methods. In all other aspects the agreement of the data seems to be fairly good. The ATS-6 RBE yields the opportunity to measure the differential group delay of the RF signals. For this purpose the relative dispersion-phase shift \Delta_{D} -between the 40-MHz, 140-MHz, and 360-MHz carriers and their \pm1 -MHz sidebands has to be known fairly accurately. The following data were obtained: |\Delta_{D40/41}| \leq 4\deg /MHz; |\Delta_{140/141}| \leq 1.03\deg /MHz; |\Delta_{D360/361}| \leq 0.4\deg /MHz. Furthermore the total delay with respect to vacuum of the 360-MHz, 140-MHz, and 40-MHz SBF antennas was coarsely measured by using the two identical antennas method. We got the following figures 52.5 \times 10^{-9} s at 40 MHz, 15 \times 10^{-9} s at 140 MHz, and 5.8 \times 10^{-9} s at 360 MHz. These data are practically independent from azimuth and elevation angles of the antennas and from the conductivity of the ground as long as the elevation angle is larger than 15\deg . Similar measurements with Yagi antennas showed a strong variation of the aforementioned parameters when installing them at different locations. Thus the SBF antennas seem to be the best possible compromise of any antenna type for the specific purpose of the differential group delay measurements.