Transmission Characteristics of Helix Waveguide
A simple frequency transformation method to obtain propagation constant and mode coupling coefficients of a helix waveguide is introduced. Theoretical TE/sub 01/ mode losses agree well with measured results. Also the transmission characteristics of 5,700 of helix waveguide recently manufactured are described. The inner diameters of them are 51 mm and 60 mm and their unit length is 5 meters.
Normal modes and mode conversion in helix waveguide
Helix waveguide, composed of closely wound insulated copper wire covered with an absorptive or reactive jacket, transmits circular electric waves with low loss. Mechanical imperfections, such as curvature and deformation, cause coupling between the circular electric waves and unwanted modes and degrade the transmission. In designing a helix waveguide for a particular application, a jacket must be found that minimizes the transmission degradation. Unwanted mode characteristics and their coupling coefficients must be known; these quantities are given by the roots of a transcendental equation involving complex Bessel functions. A program has been set up for automatically finding the complex roots by iterative approximation. Starting from the known roots at infinite jacket conductivity, the characteristic equation is solved for all practical values of wall impedance of the jacket and all modes of interest. The representation of the mode characteristics as a function of wall impedance leads to a definite designation of modes in heterogeneous waveguide. The TE pn modes of helix waveguide with n ≠ 1 can have only a limited attenuation. These limits determine the design of mode filters. Manufacturing imperfections increase the average TE 01 loss independently of the wall impedance. Random curvature with large correlation distance is produced by laying tolerances, but its contribution to the average loss is minimized in a helix waveguide with very large wall impedance.
The Gospel and the land;: Early Christianity and Jewish territorial doctrine,
Ostensibly Davies' patient study of the concepton of the "land" (Israel, Jerusalem) in early Christianity is an essay in Biblical theology, but he also wishes to raise serious questions about Christian understanding (or misunderstanding) of Judaism. "Christians have usually understood Judaism in too theological, and therefore, too intellectual terms. And they have also looked at their own foundation document, the New Testament, in the same way. In their proper concern to unravel theological developments and subtleties in primitive Christianity, they have neglfected to search for evidences of an encounter between it and the realia of Judaism and for any possible resolutions of such an tencounter. In particular, they have failed to inquire after the place of the land in the thought and lives of early Christians" (p. 161). Davies observes, for example, that bible dictionaries often have no references whatsoever to "land" and those that do allot it but a few pages. Even in Old Testament scholarship, where the land is of central significance in the documents themselves, it has been neglected. His work is an attempt to provide a context of Jewish thinking from early Israelite writings up to the Talmud in which to place the Christian materials. The bulk of the book is an account of the historical and theological process by which early Christianity gave a "spiritual" interpretation of traditional Jewish views of the land. Read against the Jewish background, the radical spiritualizing of the tradition is striking. Yet Davies also shows that Jewish attitudes were not monolithic in the first century, that notions of a preexistent, heavenly or eschatological Jerusalem were present, and that some Jews considered the viability of Judaism apart from the land. At some point however what could be entertained as an abstraction in Judaism, when it was made concrete in the life of the Christian movement, could not be tolerated. The conflict was heightened, of course, by the destruction of Jerusalem and the continued existence of Christianity as a movement increasingly receptive to non-Jews. Christianity, however, while rejecting the link between the land and religion, did create a new sense of "holy space" by hallowing the places where Christ had been, a development which would find fullest expression some several centuries later. As a result of the Holocaust and the establishment of the modern state of Israel Christians are faced with a whole new series of issues which have lain dormant since the destruction of Jerusalem in A.D. 70. Davies' work must be read against this backdrop to appreciate its significance. It is as much a book about modern Christian thinking as it is about the past, as many of his citations and his several appendices of speeches at Jewish-Christian conferences show. To some it may appear that he has sided too closely with certain strands of Judaism and allowed this to color his way of handling the pre-Christian and pre-Rabbinic material, but such criticism is carping. Much of the material here is gathered together in this fashion for the first time, and he has successfully shown that a major preoccupation of ancient Judaism is missing in contemporary biblical scholarship. Further, he has given us a moving yet scholarly statement of the pathos of the modern Christian who cares about Christ and Israel and who tries to understand Israel while loving Christ.