This dissertation presents new concepts in front end design for receivers with large, multiband tuning ranges. Such receivers are required to support large bandwidths (up to 10's of MHz) over very large tuning ranges (30:1 and beyond) with antennas that are usually narrowband, or which at best support multiple narrow bandwidths. Traditional techniques to integrate a single antenna with such receivers are limited in their ability to handle simultaneous channels distributed over very large tuning ranges, which is important for frequency-agile cognitive radio, surveillance, and other applications requiring wideband or multiband monitoring. Direct conversion architecture is gaining popularity due to the recent advancements in CMOS--based RFIC technology. The possibility of multiple parallel transceivers in RF CMOS suggests an approach to antenna--receiver integration using multiplexers. This dissertation describes an improved use of multiplexers to integrate antennas to receivers. First, the notion of sensitivity--constrained design is considered. In this approach, the goal is first to achieve sensitivity which is nominally dominated by external (environmental) noise, and then secondly to improve bandwidth to the maximum possible consistent with this goal. Next, a procedure is developed for designing antenna-multiplexer-preamplifier assemblies using this philosophy. It is shown that the approach can significantly increase the usable bandwidth and number of bands that can be supported by a single, traditional antenna. This performance is verified through field experiments. A prototype multiband multimode radio for public safety applications using these concepts is designed and demonstrated. / Ph. D.