Digital Microwave Receivers

Abstract

AbstractReducing complexity in RF systems is a challenge. Research for new broadband and multistandard antennas, high‐frequency bus concepts, and software‐configurable hardware platforms in order to fulfill the needs caused by an increasing number of communication and navigation standards are ongoing tasks.The high‐speed building blocks of software‐configurable digital receivers are composed of lowpass or bandpass filters, sampling and analog‐to‐digital converter (ADC) circuits, and decimator functions that convert the high‐speed sampling rates into lower rates and higher resolution, respectively. The specific design of receiver hardware architecture is a compromise between the specifications of the services to be handled by the receiver and the availability of components.The concept of bandpass‐limited subsampling (i.e., where the sampling frequency is lower than the carrier frequency) has become a very appropriate architectural approach as increasing cutoff frequency and speed of semiconductor technologies can be traded against resolution in this concept.Direct sampling poses high requirements for the analog‐to‐digital converter (ADC). The requirements are reduced significantly if a six‐port digital receiver architecture is used. The functional principle of six‐port devices is based on the measurement of four independent output powers corresponding to the complex ratio between two superposed electromagnetic waves under different phase angles. The six‐port architecture can work under broadband conditions but may be disadvantageous compared to direct‐sampling receivers with respect to their dynamic properties.Antialiasing filters are necessary components in ADCs. Three‐dimensional micromachined filter structures can provide high quality factors and low insertion losses at microwave and millimeter‐wave frequencies. Transimpedance amplifiers for a bandpass‐limited subsampling approach and limiting amplifiers can be designed and realized in commercial SiGe technology. The sampling circuit itself may use high‐speed Schottky diodes. Using these technologies, digital receivers are now approaching the millimeter‐wave range.