Effects of the Presence of a Cable and of Feed Displacements on Beam Shape (CHIME-like Feed)

Introduction

Presented here are the effects on the beam of adding a 0.4" diameter PEC cable going from the feed can to the mounting point on the dish, and for displacements of the cloverleaf feed in the 3m dish (with no cable).

The following picture serves as a reference for the (x,y,z) coordinates (z is the boresight axis).

clover_in_3m.png

The simulations were ran in CST Microwave Studio 2018, using the Feed_B.cst file found in the HIRAX github CST repository, with the choke removed.

For the cable effect results, they are presented from 400 MHz to 800 MHz inclusively, in 100 MHz increments. For the displacement results, they are presented in 200 MHz increments.

The results are presented in a 2D projection of the phi-theta plane, with a resolution of 1 degree in both phi and theta.

The displacements were simulated with magnitude 0.1 mm, 1 mm and 10 mm, along the positive and negative z axis, the positive x axis, and the x=y axis (positive quadrant).

The "no cable", "with cable" and "no displacement" simulations are presented as a linearized directivity on an arbitrary linear scale (). The "with cable" and "with displacement" cases are presented as a difference in linearized directivity.

Metric R

The metric for reproducibility is called R, and is defined as the sum (over phi and theta) of the absolute value of the difference in linearized directivity ΔD, normalized by the sum of the "no cable" or "no displacement" cases. That is,

It is presented in all difference plots, although it is mostly relevant for reproducibility in the case of small displacements.

Results (Effect of Cable on Beam)

Effect of Cable on Beam, 400 MHz

2D_cable_400_MHz.png

Effect of Cable on Beam, 500 MHz

2D_cable_500_MHz.png

Effect of Cable on Beam, 600 MHz

2D_cable_600_MHz.png

Effect of Cable on Beam, 700 MHz

2D_cable_700_MHz.png

Effect of Cable on Beam, 800 MHz


2D_cable_800_MHz.png

Results (Clover Feed Displacements)

400 MHz:

Negative z axis displacements, 400 MHz

2D_400_MHz_zm.png

Positive z axis displacements, 400 MHz

2D_400_MHz_z.png

Positive x axis displacements, 400 MHz

2D_400_MHz_x.png

Positive x=y axis displacements, 400 MHz

2D_400_MHz_xy.png

600 MHz:

Negative z axis displacements, 600 MHz

2D_600_MHz_zm.png

Positive z axis displacements, 600 MHz

2D_600_MHz_z.png

Positive x axis displacements, 600 MHz

2D_600_MHz_x.png

Positive x=y axis displacements, 600 MHz

2D_600_MHz_xy.png

800 MHz:

Negative z axis displacements, 800 MHz

2D_800_MHz_zm.png

Positive z axis displacements, 800 MHz

2D_800_MHz_z.png

Positive x axis displacements, 800 MHz

2D_800_MHz_x.png

Positive x=y axis displacements, 800 MHz

2D_800_MHz_xy.png