The second chapter examines the communication, matching, and filtering schemes used in the external RF interface in various versions of its implementation: strip, planar, or consisting of discrete components. The optimal way to organize such a structure is a combination of filtering and matching properties. At the same time, the mode of impedance matching (power matching) becomes especially relevant for SHF receivers due to the low signal level caused by increasing losses in the radio channel with increasing frequency. This requires the development of receivers with high sensitivity, but at the same time, it allows the use of a tuned antenna and a nontunable input circuit. The block diagram of the RF front-end of the receiver primarily includes INc, the function of which is to allocate the operating frequency band in direct conversion receivers or also to provide suppression of the mirror channel in superheterodyne-type receivers. It is a tunable or nontunable filter and can be structurally implemented on discrete, distributed, or components with piezoelectric properties. The transition to operation in the microwave range, when signal losses in the radio channel increase and the bandwidth of the RF front-end increases, requires ensuring low losses in the input circuit and a low level of the receiver’s own noise. This is especially true for broadband radio receivers, when it is necessary to choose a mode with minimal noise figure instead of the INc power matching mode with the antenna. Section 2.1 describes the methods of intercascade communication using passive four terminals and the possibility of combining the functions of filtering, supplying the offset voltage to the AE, and the mode of mutual coordination in one circuit. The most difficult task is the problem of matching the complex load with the complex resistance of the signal source, which, however, in many cases can be solved by connecting the simplest three-terminal networks of the type R-L or R-C between them. An increase in the operating frequency makes it possible to implement them in the form of segments of strip circuits or planar structures. Descriptions of various types and designs of filters depending on their purpose and method of implementation are given in Sect. 2.2. Low-pass filters (LPF) with discrete implementation or on segments of strip lines are considered. Bandpass filters (BPF) can also be implemented both on discrete components (quartz filters implemented using SAW technology) and on striplines using quarter-wave transformers or their segments, including those based on Hilbert fractals. Then, we describe the bandpass filters, including the electric-acoustic filters, quartz resonators, and SAW filters. Active filters implemented entirely using integral technology have been successfully used: transduction amplifiers, continuous-time filters, switched capacitor filters, polyphase complex filters, tunable active bandpass filters, and multichannel multiplexing filters. The appendix to Chap. 2 provides an example of calculating a bandpass filter with SAW technology and performed computer simulations in the MicroCap environment.