Radiation from an Antenna Entering the Martian Atmosphere

• Main Author: Norgard, John Dennis
• Format: Others
• Language: en
• Published: 1969
• Online Access: https://thesis.library.caltech.edu/10105/1/Norgard_JD_1969.pdf; Norgard, John Dennis (1969) Radiation from an Antenna Entering the Martian Atmosphere. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/pd64-rx94. https://resolver.caltech.edu/CaltechTHESIS:03242017-095341798 <https://resolver.caltech.edu/CaltechTHESIS:03242017-095341798>

<p>The interaction between the ionized wake of a capsule entering the Martian atmosphere and the circularly polarized radiation emitted by an antenna located on the aft part of the capsule is theoretically investigated in this study. A simplified mathematical model of the atmosphere of Mars, the entry-trajectory of the capsule, and the flow field surrounding the capsule are used in the analysis. The near wake of the capsule is approximated by a cylindrically stratified plasma shell consisting of n plasma regions. The plasma in each region is assumed to be homogeneous, anisotropic, and conducting, and moving at a uniform velocity relative to the antenna. The antenna is represented by a turnstile antenna located off-axis λ_o/4 above an infinite ground plane and operates at the signal frequencies of 400 MHz and 2.295 GHz.</p> <p>Integral expressions for the cylindrical components of the field vectors are obtained by a rigorous relativistic formulation of the problem, and are evaluated using the techniques of asymptotic expansions to yield the radiation patterns of the antenna. Radiation patterns for the special case of an on-axis antenna radiating through a uniform, lossless, and isotropic plasma shell are presented and are compared with the free space patterns.</p> <p>The analysis shows that blackout occurs during the entry of a capsule into the Martian atmosphere, Before and after blackout, the radiation patterns of the antenna exhibit an on-axis null region whose angular extent is proportional to the electron concentration of the plasma. Also, sharp peaks which are attributed to leaky wave radiation, are present in the null region of the patterns. For the non-null region of the patterns, the values of the gain function of the antenna oscillate about the free space values. As the electron concentration of the plasma increases, the peaks in the radiation patterns become more numerous and more sharply defined. The effects of the motion of the plasma on the radiation emitted by the antenna are to shift the peaks of the radiation patterns to smaller cone angles and to introduce more peaks into the patterns.</p> <p>For the low velocity case corresponding to an entry into the Martian atmosphere, no serious motional or depolarization effects occur, and communications with the capsule can be satisfactorily carried out when the condition of blackout does not exist.</p>