No abstract

Abstract-The maximum obtainable resolution of a stripmap synthetic aperture radar (SAR) system can be retained by simply avoiding weighting, or tapering, data samples in the along-track compression process. However, this will lead to hazardous artifacts caused by strong sidelobes of the corresponding adjacent scatterers whose interference might severely weaken the desired targets or even introduce false targets. On the other hand, some residual artifacts, even after tapering process, may still deteriorate the quality (contrast) of the SAR image. These issues can be remedied by applying the so-called CLEAN technique, which can mitigate these ill-effects in strip-map SAR imagery while maintaining the maximum resolution. This, indeed, is carried out as a post processing step, i.e., after the azimuth compression is accomplished, in the SAR system. The objective of this paper is to extend the CLEAN technique to strip-map SAR system to produce high-quality images with a very good along-track resolution. The algorithm is then applied to data from a ground-based circular SAR (CSAR) system to verify its implementation as well as this new application of the CLEAN technique.

To investigate the excitation technique of high pressure gas lasers by high power microwave discharges, a WR-650 waveguide circuit was assembled. The pulsed microwave source was a magnetron transmitter with a frequency of 1355 MHz, a nominal pulsed power of 2.5 MW and a pulse length of 4 js. The pulse repetition frequency was 10 Hz. A double ridge waveguide coupling structure was designed. The results from these experiments have shown the need for a high power broadband modulateable microwave source to achieve further knowledge important for the design of compact, high power microwave excited lasers. For these purposes, a former radar transmitter, based on an amplifier chain terminated by a klystron, was modified. The transmitter has a center frequency of 1400 MHz with an instantaneous bandwidth of 100 MHz, a pulsed power of 10 MW, a maximum pulse length of 6 js and a maximum repetition frequency of 450 Hz. The amplifier chain is driven by a dielectric resonance oscillator which is pulse modulated by very fast pin diodes. This design allows the generation of multiple pulses within the 6 .is time window with microwave pulse rise times of the order of ten's of nanoseconds. The results obtained with this equipment will be presented.

This paper provides a synopsis of the accuracy calculation for the engineering calibration of a weather radar system. The underlying meteorological radar equation is optimized in order to reduce the total uncertainty of the calibration. Special emphasis is given to the determination of the different uncertainties of the various measurements which are required for a system calibration. A spreadsheet for the calculation of the total uncertainty of the calibration is presented.

During the last decade, the microwave discharge was investigated as an alternative technique avoiding some of the disadvantages associated with the transversely excited atmosphere (TEA-) discharge such as preionization, instabilities and pulse length limitations due to the metallic electrodes. However, up to now one drawback of the pulsed high power microwave discharge was the lack of commercially available high power microwave tubes with pulsed output powers in the region of 100 MW to 1 GW. There are two methods for achieving output powers comparable to relativistic sources. One way is the combining of several conventional tubes, which is rather complicated especially for magnetrons. The other method is the compression of the microwave pulse of a conventional tube by means of a microwave cavity or a network of delay lines and hybrids. This paper describes the application of microwave pulse compression using Q-switching for discharging the storage cavity.Under optimum conditions, up to 80 % of the microwave pulse energy can be stored in a cavity and delivered to a matched load via triggering a suited switching element. The design discussed in this paper uses the laser discharge as switch. The plasma tube is integrated in the storage cavity and the discharge is triggered when the electric field strength exceeds the holdoff field strength of the gas mixture. The microwave source was operated at power levels of 4.5 -5 MW and at repetition rates of 10 -20 Hz. With a stored energy of 1.4 J a XeCl laser featuring a pulse energy of 4 mJ and a pulse length of 16 ns could be realized without any preionization. The discharge structure was in no way optimized. Principal limitations in laser pulse energy and repetition frequency are arising from the fact that the discharge acts both as a switch and as laser amplifier. Considerable improvements in the performance of the complete system can be expected, if the cavity is discharged by an optimized switch while the laser discharge acts only as a load. Some theoretical aspects of the pulse compression circuit will be presented together with experimental results.The results show the potential of realizing microwave discharge pumped excimer lasers with output powers ranging from 10 to 100 d. A laser head powered by a S-band (3 GHz) magnetron would be rather compact, because it comprises only a storage cavity and a discharge structure without any high voltage component. The feeding could be done via a flexible waveguide. In this way using microwave pulse compression techniques, the microwave discharge is an interesting alternative to TEA-discharges.Alvarez obtained a power "gain" of 18 dB utilizing a klystron transmitter [5]. The second technique (SLED or LIPS) was proposed by Farkas et al.[2] at the Stanford Linear Accelerator Center. The third method, BPM, was also evaluated by Farkas [3]. The pulse compression is initiated by fast phase switching of the master oscillator signal. Therefore the compressed pulse is phase-correlated to the master oscillator. This feature is absolutel...