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Small omni-directional antenna development for Mars sample return mission

This work addresses the design, analysis and test of omni-directional antennas at 401.5 MH2 and 437.1 MHz frequencies, on Mars Orbital Sample (OS) return canisters, which are part of a Mars Sample Return (MSR) mission. The OS in Mars orbit will have a tumbling random orientation. The OS antennas are electrically small (order of 0.2 wavelength or less) and linearly polarized. Either a single antenna with two resonant frequencies and a diplexer to provide isolation, or a two-antenna system with a natural isolation of at least 10 dB between the antenna input ports are needed. In this paper results of theoretical and experimental studies on several different types of antennas appropriate to this application are presented. Many of these antennas are designed, fabricated, and tested, and their critical parameters are addressed and investigated. Acceptable near omnidirectional pattern coverage and minimum gain levels of better than -2 dB are obtained. These antennas include dual circular patch antennas with slots used to shorten the dimensions, very small square patch antennas with ultra high dielectric ceramic substrates, narrow width patch (ribbon) antennas wrapped around the spherical shell, top-loaded monopoles with different load configurations, and variant PIFA type antennas similar to those used in wireless systems. Many numerical and experimental results are presented and future efforts to further improve the performance are outlined.