SUMMARY / RELATED TOPICS

Cassegrain antenna

In telecommunications and radar, a Cassegrain antenna is a parabolic antenna in which the feed antenna is mounted at or behind the surface of the concave main parabolic reflector dish and is aimed at a smaller convex secondary reflector suspended in front of the primary reflector. The beam of radio waves from the feed illuminates the secondary reflector, which reflects it back to the main reflector dish, which reflects it forward again to form the desired beam; the Cassegrain design is used in parabolic antennas in large antennas such as those in satellite ground stations, radio telescopes, communication satellites. The primary reflector is a paraboloid, while the shape of the convex secondary reflector is a hyperboloid; the geometrical condition for radiating a collimated, plane wave beam is that the feed antenna is located at the far focus of the hyperboloid, while the focus of the primary reflector coincides with the near focus of the hyperboloid. The secondary reflector and the feed antenna are located on the central axis of the dish.

However, in offset Cassegrain configurations, the primary dish reflector is asymmetric, its focus, the secondary reflector, are located to one side of the dish, so that the secondary reflector does not obstruct the beam. This design is an alternative to the most common parabolic antenna design, called "front feed" or "prime focus", in which the feed antenna itself is mounted suspended in front of the dish at the focus, pointed back toward the dish; the Cassegrain is a more complex design, but in certain applications it has advantages over front feed that can justify its increased complexity: The feed antennas and associated waveguides and "front end" electronics can be located on or behind the dish, rather than suspended in front where they block part of the outgoing beam. Therefore, this design is used for antennas with bulky or complicated feeds, such as satellite communication ground antennas, radio telescopes, the antennas on some communication satellites. Another advantage, important in satellite ground antennas, is that because the feed antenna is directed forward, rather than backward toward the dish as in a front-fed antenna, the spillover sidelobes caused by portions of the beam that miss the secondary reflector are directed upwards toward the cold sky rather than downwards towards the warm earth.

In receiving antennas this reduces reception of ground noise, resulting in a lower antenna noise temperature. Dual reflector shaping: The presence of a second reflecting surface in the signal path allows additional opportunities for tailoring the radiation pattern for maximum performance. For example, the gain of ordinary parabolic antennas is reduced because the radiation of the feed antenna falls off toward the outer parts of the dish, resulting in lower "illumination" of those parts. In "dual reflector shaping" the shape of the secondary reflector is altered to direct more signal power to outer areas of the dish, resulting in more uniform illumination of the primary, to maximize the gain. However, this results in a secondary, no longer hyperbolic, so the constant phase property is lost; this phase error, can be compensated for by tweaking the shape of the primary mirror. The result is a higher gain, or gain/spillover ratio, at the cost of surfaces that are trickier to fabricate and test. Other dish illumination patterns can be synthesized, such as patterns with high taper at the dish edge for ultra-low spillover sidelobes, patterns with a central "hole" to reduce feed shadowing.

Another reason for using the Cassegrain design is to increase the focal length of the antenna, to reduce sidelobes, among other advantages. Parabolic reflectors used in dish antennas have short focal length; the focal ratio of typical parabolic antennas is 0.25 - 0.8, compared to 3 - 8 for parabolic mirrors used in optical systems such as telescopes. In a front-fed antenna, a "flatter" parabolic dish with a long focal length would require an impractically elaborate support structure to hold the feed rigid with respect to the dish. However, the drawback of this small focal ratio is that the antenna is sensitive to small deviations from the focal point: the angular width that it can focus is small. Modern parabolic antennas in radio telescopes and communications satellites use arrays of feedhorns clustered around the focal point, to create a particular beam pattern; these require the good off-axis focusing characteristics of a large focal ratio, because the convex secondary reflector of the Cassegrain antenna increases it these antennas use a Cassegrain design.

The longer focal length improves crosspolarization discrimination of off-axis feeds, important in satellite antennas that use the two orthogonal polarization modes to transmit separate channels of information. A disadvantage of the Cassegrain is that the feed horn must have a narrower beamwidth to focus its radiation on the smaller secondary reflector, instead of the wider primary reflector as in front-fed dishes; the angular width the secondary reflector subtends at the feed horn is 10° - 15°, as opposed to 120° - 180° the main reflector subtends in a front-fed dish. Therefore, the feed horn must be longer for a given wavelength. A beam waveguide antenna is a type of complicated Cassegrain antenna with a long radio wave path to allow the feed electronics to be located at ground level, it is used in large steerable radio telescopes and satellite ground

Code of Ur-Nammu

The Code of Ur-Nammu is the oldest known law code surviving today. It is written on tablets, in the Sumerian language c. 2100–2050 BC. The first copy of the code, in two fragments found at Nippur, was translated by Samuel Kramer in 1952; these fragments are held at the Istanbul Archaeological Museums. Owing to its partial preservation, only the prologue and 5 of the laws were discernible. Kramer noted that luck was involved in the discovery: In all probability I would have missed the Ur-Nammu tablet altogether had it not been for an opportune letter from F. R. Kraus, now Professor of Cuneiform Studies at the University of Leiden in Holland... His letter said that some years ago, in the course of his duties as curator in the Istanbul Museum, he had come upon two fragments of a tablet inscribed with Sumerian laws, had made a "join" of the two pieces, had catalogued the resulting tablet as No. 3191 of the Nippur collection of the Museum... Since Sumerian law tablets are rare, I had No. 3191 brought to my working table at once.

There it lay, light brown in color, 20 by 10 centimeters in size. More than half of the writing was destroyed, what was preserved seemed at first hopelessly unintelligible, but after several days of concentrated study, its contents began to become clear and take shape, I realized with no little excitement that what I held in my hand was a copy of the oldest law code as yet known to man. Further tablets were found in Ur and translated in 1965, allowing some 30 of the 57 laws to be reconstructed. Another copy found in Sippar contains slight variants; the preface directly credits the laws to king Ur-Nammu of Ur. The author who had the laws written onto cuneiform tablets is still somewhat under dispute; some scholars have attributed it to Ur-Nammu's son Shulgi. Although it is known that earlier law-codes existed, such as the Code of Urukagina, this represents the earliest extant legal text, it is three centuries older than the Code of Hammurabi. The laws are arranged in casuistic form of IF THEN —a pattern followed in nearly all codes.

For the oldest extant law-code known to history, it is considered remarkably advanced because it institutes fines of monetary compensation for bodily damage as opposed to the lex talionis principle of Babylonian law. However, robbery and rape were capital offenses; the code reveals a glimpse at societal structure during the "Sumerian Renaissance". Beneath the lugal, all members of society belonged to one of two basic strata: the "lu" or free person, or the slave; the son of a lu was called a dumu-nita until he married, becoming a "young man". A woman went from being a daughter to a wife if she outlived her husband, a widow, who could remarry; the prologue, typical of Mesopotamian law codes, invokes the deities for Ur-Nammu's kingship and Utu, decrees "equity in the land".... After An and Enlil had turned over the Kingship of Ur to Nanna, at that time did Ur-Nammu, son born of Ninsun, for his beloved mother who bore him, in accordance with his principles of equity and truth... Did Ur-Nammu the mighty warrior, king of Ur, king of Sumer and Akkad, by the might of Nanna, lord of the city, in accordance with the true word of Utu, establish equity in the land.

He fashioned the bronze sila-measure, standardized the one-mina weight, standardized the stone weight of a shekel of silver in relation to one mina... The orphan was not delivered up to the rich man. One mina was made equal to 60 shekels. Among the surviving laws are these: 1. If a man commits a murder, that man must be killed. 2. If a man commits a robbery, he will be killed. 3. If a man commits a kidnapping, he is to pay 15 shekels of silver. 4. If a slave marries a slave, that slave is set free, he does not leave the household.^ 5. If a slave marries a native person, he/she is to hand the firstborn son over to his owner. 6. If a man violates the right of another and deflowers the virgin wife of a young man, they shall kill that male. 7. If the wife of a man followed after another man and he slept with her, they shall slay that woman, but that male shall be set free. 8. If a man proceeded by force, deflowered the virgin female slave of another man, that man must pay five shekels of silver. 9. If a man divorces his first-time wife, he shall pay one mina of silver.

10. If it is a widow whom he divorces, he shall pay half a mina of silver. 11. If the man had slept with the widow without there having been any marriage contract, he need not pay any silver. 13. If a man is accused of, he must undergo ordeal by water. 14. If a man accused the wife of a man of adultery, the river ordeal proved her innocent the man who had accused her must pay one-third of a mina of silver. 15. If a prospective son-in-law enters the house of his prospective father-in-law, but his father-in-law gives his daughter to another man, the father-in-law shall return to the rejected son-in-law twofold the amount of bridal presents he had brought. 16. If, he shall weigh and deliver to him 2 shekels of silver. 17. If a slave escapes from the city limits, someone returns him, the ow

Hauge Synod

The Hauge Synod, was the name of a Norwegian Lutheran church body in the United States in the late 19th century and early 20th century. The Hauge Synod was named after Norwegian revivalist lay preacher Hans Nielsen Hauge; the synod was "low church" de-emphasizing formal worship and stressing personal faith in the Haugean tradition. The Hauge Synod was formed in 1876 following a split with The Evangelical Lutheran Church of North America; the Eielsen Synod was founded in 1846 by Rev. Elling Eielsen in Jefferson Prairie Settlement, Wisconsin. Eielsen was a lay preacher and evangelist from Norway, considered the chief transplanter of the Haugean movement from Norway to America. Red Wing Seminary was the Hauge Synod educational center located in Minnesota; the Hauge Synod opened the seminary in 1879, it continued in operation until 1917. The Hauge Synod merged in 1917 into the Norwegian Lutheran Church of America; that group was renamed the Evangelical Lutheran Church and merged into the American Lutheran Church in 1960.

The ALC merged into the Evangelical Lutheran Church in America. The Norwegian Lutheran Church in the United States Nelson, E. Clifford, Fevold, Eugene L; the Lutheran Church among Norwegian-Americans: a history of the Evangelical Lutheran Church Satre, Lowell J The Hauge's Synod: education for awakening Eielsen, Sigrid. A Haugean Woman in America: the Autobiography of Sigrid Eielsen, Arne Bugge The Haugean Heritage – a Symbol of National History, Hauge Synod Luther Seminary: Lutheran Family Trees Red Wing Seminary The Hauge Log Church