A microwave radiometer relies on the power linearity of its microwave receivers to accurately measure the temperature of remote microwave noise sources. This paper considers linearity issues in the design and characterization of such receivers. Analysis is presented relating the radiometer temperature interpolation error to a second order power nonlinearity coefficient for the receiver. Formulas are also developed specifying the temperature error in terms of individual receiver component parameters. It is shown that the key parameter for the RF detector in the receiver is A 4 , a fourth order RF distortion coefficient, and the key parameter for the RF amplifiers in the receiver is IP 3 , the third order intercept. This paper also discusses experimental methods for measuring the power linearity of RF detectors to the levels required for radiometric applications. Three methods are discussed: the two-tone method, the amplitude modulation method, and the constant ratio method. The theory of determining the coefficients that characterize the nonlinearity of the detector from experimental data is presented. Experimental results are presented showing that the two-tone method and the constant ratio method agree to within experimental error. The sensitivity for measuring nonlinearities and the difficulties encountered in implementing each of these methods are also discussed.

This paper discusses and presents experimental results on methods for measuring the power linearity of microwave power detectors to the levels required for radiometric applications. Three methods for measuring detector power linearity are discussed: the two-tone method, the amplitude modulation method, and the constant ratio method. The theory of determining coefficients which characterize the nonlinearity of the detector from experimental data is presented. Experimental results are presented showing that the twotone method and the constant ratio method agree within experimental error. The difficulties encountered in implementing each of these methods are also discussed.

Currently, Chlamydia is a major cause of pelvic inflammatory disease (PID), which can be complicated by perihepatitis. Our patient presented with ascites secondary to Chlamydia infection and responded well to treatment with tetracycline. Since Chlamydia infection is becoming more prevalent in the United States, it should be considered in the differential diagnosis of ascites in all young sexually active females.

No abstract

A new type of large liquid crystal modulator, the ZScreen(R), has been developed for use in a stereoscopic display system and has been put into production by StereoGraphics Corporation.The fabrication of large area surface mode liquid crystal cells requiring extreme uniformity of thickness has been achieved in a two year development program.Two of these cells are placed in optical series, with their alignment axes orthogonal. Laminated to the liquid crystal cells is a linear polarizer whose absorption axis besects the alignment axes of the liquid crystal cells. When placed in intimate juxtaposition with a CRT display with the linear polarizer facing the CRT screen, and when the cells are driven electrically out of phase, the light output of the CRT is alternately left and right handed circularly polarized.When this so-called push -pull modulator is viewed through passive circularly pollarized spectacles worn by an observer, a shutter is formed having a high dynamic range. Each eye of the observer is sequentially occluded.By properly choosing the parameters of construction, such a liquid crystal modulator can have a broad cone of view, high dynamic range, and good transmission. This type of modulator is superior to a single liquid crystal cell modulator since it has fast and symmetrical rise and decay times and identical dynamic range for both eyes.These features are of particular importance in a field -sequential stereoscopic system, because the rise and decay time of such a shutter should take place substantially within the vertical blanking interval, which is generally on the order of a millisecond.The 9 -inch diagonal versions of the modulator have been in production since the last quarter of 1986 and now are being supplied in up to 19 -inch diagonal sizes for computer graphics and video displays.