To: File

From: Jon Hagen

Date: 11-3-99

Subject: 430 MHZ Feed Room Waveguide

If the turnstile is mounted squarely on the top of the horn, its side arms will interfere with the door of an equipment cabinet and with the adjacent feeds. The turnstile must therefore be rotated slightly by an angle , which will be approximately 20 degrees counterclockwise, as viewed from above. Without this rotation, the transmitter waveguide across the ceiling would run parallel to the room's front (window) wall. But, as a result of the rotation, the last section of waveguide will angle across the ceiling. It will end at a point above the focal area . At this point, a 90-degree bend will be fitted to the end of the waveguide to connect to the removable vertical waveguide. We need to establish the position and orientation of this vertical waveguide in the plan view of the feed room before the ceiling waveguide run can be designed.

We will use a coordinate system whose origin is at the intersection of the horn axis with the top surface of the floor. The x and y axes are parallel to the floor. The positive x axis runs to the left, parallel to the window. The positive y axis runs back through the axis of the rotary floor. Positive z is toward the ceiling. The transmitter port on the turnstile will be fitted with a 90- degree bend, making the turnstile input guide parallel to the turnstile's circular waveguide. Before the rotation, the ith edge of the input waveguide can be represented parametrically by equations of the form

xi = const. 1)

yi = bi i 2)

zi = ci i 3)

where the parameter, zeta, is the length along the guide, measured from the aperture plane of the horn (the plane perpendicular to the horn axis and containing the origin). The rotation by the angle will change the equations to the form

xii = aii i 4)

yii = bii i 5)

zii = cii i 6).

We will select the height z for the horizontal plane containing the bottom flange of the removable waveguide and use Equation 6 to find the value of i . Equations 4 and 5 then give the xii and yii, the x and y values where the ith edge passes through the selected horizontal plane.