Hadrian's Wall

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Hadrian's Wall,

ancient Roman wall, 73.5 mi (118.3 km) long, across the narrow part of the island of Great Britain from Wallsend on the Tyne River to Bowness at the head of Solway Firth. It was mainly built from c.A.D. 122 to 126 under Emperor Hadrian and was extended by Emperor Severus a century later. The wall demarcated the northern boundary and defense line of Roman Britain. Fragments of the wall, 6 ft (1.8 m) high and 8 ft (2.4 m) thick, and many of the "mile stations" (stone blockhouses along the wall constructed every Roman mile) remain. Hadrian's Wall, which has been preserved, is one of the largest and most significant remains of the Roman occupation.
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References in periodicals archive ?
In a cross sectional plane of the waveguide several unbalanced thin impedance vibrators (monopoles) are placed and a narrow slot is cut in the broad wall of the waveguide symmetrically relative to its longitudinal axis.
Here [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] are the tensor Green's functions components for a rectangular waveguide and half-space above the plane [3,4], [s.sub.1] = -[L.sub.1] and [s.sub.2] = -[L.sub.2] are coordinates of the vibrator mirror images, relative to the lower broad wall of the waveguide [4].
Here we present the results only for vibrators with inductive impedances ([[bar.X].sub.S1(2)] > 0), known to increase the vibrator electrical length, i.e., to increase [[lambda].sup.res.sub.1,2] as compared to case [[bar.Z].sub.Si(2)] = 0, without decreasing a distance between the vibrators ends and the upper broad wall of the waveguide.
For a small thickness (t) of section [s.sub.3] one can approximate the equivalent circuit for this type of loop feed with the one where grounding is obtained by directly connecting section [s.sub.2] to the broad wall [3].
The surface current density, induced by classical and the proposed end launcher, on the broad wall of the aluminium and CFRP waveguides and on section [s.sub.3] (Figure 1) is assessed (Figure 7).
In order to keep the waveguide losses to a minimum, a split body should have all waveguides split at the midpoint of the broad wall wherever possible, as symmetry of the TE10 mode ensures that no current crosses this boundary.
However, a slot shape that can be cut on the broad wall of a rectangular waveguide and be integrated into hat stiffener panels and provide full X-band coverage has not yet been reported in the literature.
In this paper, we show that a spiral slot cut into the broad wall of a WR-90 rectangular waveguide acts as a broad-band travelling wave radiator.
a is waveguide broad wall dimension, [b.sub.1] the narrow dimension of the waveguide ([C.sub.2]),[lambda] the free space wavelength, [[lambda].sub.g] the guide-wavelength of straight waveguide ([C.sub.2]) and ([E.sub.2]), and [r.sub.c] the tunnel radius.
Parameter Value (mm) waveguide broad wall dimension a 2.96 narrow dimension of the waveguide b 0.65 the length of the straight waveguide L 0.8 the length of the pitch of the RLFWG-SWS p 0.88 the radius of the beam tunnel [r.sub.c] 0.25 thickness of the ridge [b.sub.3] 0.2b height of the ridge 2[L.sub.3] L
A second example is the rectangular waveguide shown in Figure 8, where reducing the waveguide height and introducing slots at the midsection of both its broad walls suppresses spurious modes with minimal effect on the desired mode.
Compared with the rectangular waveguide, the T-shaped waveguide has a lower profile and the broadened top plates can support the resonant radiating slots without cutting into the adjacent broad walls. To suppress the surface wave, the metal fences are introduced between slots and the radiation performance is improved.