Optical delay lines based on optical filters

Optical delay lines have some important applications, notably in optical communication systems and in phased arrays. These devices are based on the concept of optical group delay, which, in turn, can be understood as the property of an optical filter. Optical filters are well-understood devices and, in particular, their dispersive properties determine the group delay response. We review these dispersive properties and point out some of the inherent tradeoffs involved in generating large group delay. Fiber Bragg gratings and recent results on optical all-pass filters are used as examples     

Adaptive median filters: new algorithms and results

Based on two types of image models corrupted by impulse noise, we propose two new algorithms for adaptive median filters. They have variable window size for removal of impulses while preserving sharpness. The first one, called the ranked-order based adaptive median filter (RAMF), is based on a test for the presence of impulses in the center pixel itself followed by a test for the presence of residual impulses in the median filter output. The second one, called the impulse size based adaptive median filter (SAMF), is based on the detection of the size of the impulse noise. It is shown that the RAMF is superior to the nonlinear mean L(p) filter in removing positive and negative impulses while simultaneously preserving sharpness; the SAMF is superior to Lin's (1988) adaptive scheme because it is simpler with better performance in removing the high density impulsive noise as well as nonimpulsive noise and in preserving the fine details. Simulations on standard images confirm that these algorithms are superior to standard median filters.     

Wavelet transform based adaptive filters: analysis and new results

In this paper the wavelet transform is used in an adaptive filtering structure. The coefficients of the adaptive filter are updated by the help of the least mean square (LMS) algorithm. First, the wavelet transform based adaptive filter (WTAF) is described and it is analyzed for its Wiener optimal solution. Then the performance of the WTAF is studied by the help of learning curves for three different convergence factors: (1) constant convergence factor, (2) time-varying convergence factor, and (3) exponentially weighted convergence factor. The exponentially weighted convergence factor is proposed to introduce scale-based variation to the weight update equation. It is shown for two different sets of data that the rate of convergence increases significantly for all three WTAF structures as compared to that of time-domain LMS. The high convergence rates of the WTAF give us reason to expect that it will perform well in tracking rapid changes in a signal     

Further results on maximally flat nonrecursive digital filters

Starting with the Krawtchouk series representation of maximally flat FIR lowpass filters, a class of monotone bandpass filters is derived and exact design formulas are given.     

New experimental results of millimetre-wave whispering gallery modedielectric resonators excited by microstrip lines

Presents an experimental investigation of planar millimetre-wave dielectric resonators acting on whispering gallery modes and excited by microstrip lines. Experimental results including measured resonant frequencies and loaded quality factors obtained in both Ka bands (26.5-40 GHz and 90-100 GHz) are presented     

Design and experimental study of compensation fitting on the angle-tuned filters

For a 100 GHz DWDM angle-tuned filter with low polarization dependent loss, the insertion loss and the Gaussian- transformation tendency of the transmission spectrum will become more serious as the incident angle is increased. It is because of that the optical path and the transmission modes of the thin film filter will change when the incident angle is varied. According to the thin film matrix theory, the analysis model is established, the displacement change of the transmis- sion field is simulated, and a dynamic compensation fitting is also designed and fabricated in the paper. The experimental results show that it can effectively reduce the insertion loss and the phenomenon of Gaussian process. Using the compen- sation fitting, the tunable range of the filter is at about 20 nm which coincides with the theoretical design.     

Dual-band bandpass filters using equal-length coupled-serial-shunted lines and Z-transform technique

A synthesizing method is presented to design and implement digital dual-band filters in the microwave frequency range. A dual-band filter consists of a bandstop filter and a wide-band bandpass filter in a cascade connection, wherein the transfer functions of both the bandpass filter and bandstop filter are expressed in the Z domain. The bandstop filter is implemented by using a coupled-serial-shunted line structure, while the wide-band bandpass filter is constructed by using a serial-shunted line configuration. In particular, the bandwidth of each passband of the dual-band filter is controllable by adjusting the characteristics of both the bandpass filter and bandstop filter. By neglecting the dispersion effect between microstrip lines of different widths over a wide bandwidth, a dual-band filter is realized in the form of microstrip lines and its frequency responses are measured to validate this method.     

Time-coded aperture tomography: experimental results

In this paper, we discuss the applicability of a time-coded aperture system especially designed for thyroid tomography on the basis of phantom experiments. Our studies show that 1) the quality of the reconstructions is high (e.g., a cold spot of 6 mm diameter in a thyroid phantom can easily be detected), and 2) the reconstruction can be carried out in less than 11 min on a standard 16 bit minicomputer (HP1000). It is therefore concluded that the clinical potentiality of the device is good.     

Improvements in W-CDMA: principles and experimental results

This article first reviews the channel structure and spreading code assignment for the physical layer and transport channel multiplexing along with a sophisticated rate-matching scheme that accommodates composite transport channels with various levels of quality of service (QoS) on one physical channel. Then, the key technologies of wideband ds-cdma (w-cdma) wireless access are presented and the results of experiments pertaining to these technologies are evaluated. Flexible system deployment is possible by employing inter-cell asynchronous operation with a three-step fast cell search method. The signal-to-interference power ratio (sir) measurement based fast transmit power control (tpc) guarantees the minimum transmit power according to the channel load and the changes in the link conditions due to fading. Furthermore, various diversity technologies are described such as pilot symbol-assisted (psa) coherent Rake combining, antenna diversity, site diversity (soft/softer handover), and transmit diversity in the forward link that are effective in decreasing the required transmit power, which results in increases system capacity. This article also presents link-capacity enhancing techniques such as using an interference canceller (IC) and adaptive antenna array diversity (AMD) receiver/transmitter. Experimental results are presented for an actual multipath fading channel that indicate the potential of the IC and aaad transceiver to decrease the mobile transmit power in the reverse link and interference from high rate users with high transmit power in the forward link.     

Millimeter wave inductive post filters,theory and results

This paper briefly details the work carried out on the modelling of inductive post filters. This type of filter approach is particularly attractive at millimeter wave frequencies due to its ease of manufacture, however for modelling no true wide band equivalent circuit would seem to be available. In order to overcome this limitation we have developed a rigorous wide band model. The accuracy of the model has been confirmed by numerous experimental measurements and the resulting computer program quickly enables both analysis and synthesis to be carried out. The speed and efficiency of this approach has allowed the effect of mechanical tolerances to be taken into account, thus reducing cost, complexity and assembly times.     

Optical fiber Fabry-Perot cavities and recirculating delay lines astunable microwave filters

The radio frequency or microwave responses of single-mode fiber Fabry-Perot cavities and recirculating delay lines are studied. It is shown that fiber Fabry-Perot cavities may be used as bandpass filters and the recirculating delay lines as bandstop filters at radio or microwave frequencies. These electric filters are tunable by electrooptic effects since the bandpass or bandstop characteristic changes when the cavity or the delay line length is varied by a few tenths of an optical wavelength. The ultimate limit on speed of tuning is set by the coherence time of the light source. The dependence of the filter responses on the spectral purity of light is studied. Examples are given to illustrate the tunability of these electric filters. The availability of various components required to build the tunable RF or microwave filters is reviewed     

Further results on MAP optimality and strong consistency of certainclasses of morphological filters

Morphological openings and closings can be viewed as consistent MAP estimators of smooth random binary image signals immersed in i.i.d. clutter, or suffering from i.i.d. random dropouts. We revisit this viewpoint under much more general assumptions and show that, quite surprisingly, the above interpretation is still valid.     

Detail and experimental results of ferromagnetic levitation system of Japan air lines HSST-01/-02 vehicles

HSST is an acronym for high-speed surface transport and is the trade name of the vehicle levitated by the attractive electromagnets and propelled by the linear induction motor (LIM) developed by Japan Air Lines. Two test vehicles have been designed, manufactured, and flight-tested. The first test vehicle, HSST-01, marked a maximum speed of 307.8 km/h on a 1300-m long test track in February, 1978, whereas the second test vehicle, HSST-02, has demonstrated boarding test flights successfully to an aggregated total of abut 1500 passengers since April, 1978, onward. The HSST-01 weighs one ton, is 4 m long, designed for high-speed testing, and incorporates eight electromagnets and a LIM with a maximum thrust of 300 kg. The levitating power supply is taken from the batteries carried on board the vehicle, and the three-phase VVVF power for the LIM propulsion is supplied from the wayside power lines through the power collector. The nine-seated HSST-02 has a loaded weight of 2.3 tons. Major items of additional functions realized in the HSST-02 include: 1) the electromagnets are fitted to the flexible chassis for better riding comfort by incorporating mechanical suspension between the chassis and the body, and 2) with the continuous levitation, the power for the LIM is rectified and supplied to the electromagnets jointly serving with the batteries carried on board. In light of the test results obtained so far, it is shown that the predicted performances of the levitation magnets, LIM, and the power collector system have been satisfactorily established, and that there would be no major technical problems in the course of our future development for implementation of the HSST system toward commercial services. The design of a preoperational test vehicle is now underway, and its test flight is scheduled to he initiated in 1980. This 80-seated preoperational test vehicle will have test flights on a 15-km test tract at a target crusing speed of 300 km/h.     

Optimum feed for large radio-telescopes: experimental results

Corrugated waveguide structures can be used to design highly efficient aperture-type feeds for both spherical and paraboloidal reflector antennas. The letter presents a brief account of experimental results obtained with a 2-hybrid-mode horn. It is shown that theoretical and experimental results agree closely.     

T-BLAST for wireless communications: first experimental results

In earlier papers , we described a novel multitransmit, multireceive (MTMR) antenna system for wireless communications. This new system, turbo Bell-Labs layered space-time (T-BLAST) architecture, combines the benefits of layered space-time coding concepts and turbo principles in the multitransmit, multireceive antenna system design. In particular, the random layered space-time codes designed by using a set of block convolutional codes and random space-time interleavers and the space-time turbo-like decoding operation allow T-BLAST to realize the benefits of MTMR systems in a computationally feasible manner. The goal of this paper is to present experimental results of T-BLAST based on real-life data collected using the Bell-Labs experimental multiple antenna system with eight transmit and five and six receive antennas. The experimental results show the practical virtues of T-BLAST.     

A broad-band resistively loaded V-antenna: experimental results

A broadband receiving antenna was realized using a resistively loaded thin-film V-monopole and a 500-Ω oscilloscope probe. The pulse-receiving performance of the antenna was evaluated in a time-domain antenna range, for various directions of the incident pulse. The antenna is capable of receiving a 520 ps electromagnetic pulse, incident within 45° from the boresite direction, with good fidelity. The antenna was also tested in a transverse electromagnetic cell in the time and frequency domains. The frequency-domain receiving transfer function of the antenna was found to be within -57±3 dB in the 22 MHZ to 1.1 GHz frequency range     

Microstrip bandpass filters using coupled feed lines for third and fourth generation communications

In this paper, two compact tuneable bandpass filters (BPFs) based on the coupled feed lines are introduced. To approach a compact size, the coupled feed lines are bended. To design a high performance single-band bandpass filter (BPF), coupled feed lines are loaded by T-shaped stubs (as main resonators) and rectangular stubs (as suppressor stubs). Also, the mechanism of coupled feed lines combining with T-shaped open stubs is analyzed to show a tunable passband. The dual-band BPF includes two big radial-stubs, two small radial-stubs, two T-shaped structures and spiral coupled feed lines. The LC model of big radial-stubs is analyzed to compute the equation of transmission zero using its transfer function. The passband frequency of single-band BPF resonates at 2.12 GHz (3G) with corresponded insertion loss of 0.83 dB. Also, for dual-band BPF, the measured insertion-losses of first and second passbands are close to 0.8 and 1.1 dB, respectively. The frequency responses of BPFs are easily adjusted by altering the physical dimensions, demonstrating a adjustable performance. To verify the correct operation of circuits, the proffered filters are implemented and tested.