**1. Introduction**

Design of wideband RF modules, filters, and antennas are presented in [1–12]. Wideband RF technologies such as MIC, MIMIC, and MEMS are presented in [1–7]. Wideband RF modules are crucial in the development of direction finding (DF) systems. A fully integrated 10–40 GHz superheterodyne receiver frontend using a 40–46 GHz IF is presented in [8]. Wideband RF technologies are used to develop wideband RF modules such as frontends, SFBs, and receiving and transmitting channels, as presented in [1–15]. A DF system measures the direction from which a received signal was transmitted. Radio DF is used in the navigation of ships, aircrafts, vehicles, and missiles to locate emergency transmitters for search and rescue, to locate illegal or interfering transmitters, and to track wildlife. The transmitted signal direction may be found by combining the direction information from two or more suitably spaced receivers by using triangulation. Triangulation is the process of determining the location of a point by forming triangles. Triangulation involves only angle measurements. A DF system provides the ability to locate the position of an enemy transmitter.

The demand for wide bandwidth makes the Ka band attractive for future commercial communication and the radar industry. Front-end modules, filter banks, and coupler modules are important units in radar, seekers, and communication systems. This chapter presents several wideband mm-wave RF modules. It also discusses the design and development of a compact wideband (18–40 GHz) frontend and a wideband (18–40 GHz) SBF. Advanced design system (ADS) full-wave electromagnetic software is used to develop wideband RF modules, as presented in [16].
