Radio frequency Fundamentals


Radio frequency (RF) basic terms, the principle of operations, practical design, and testings are discussed.

Basic RF Terms

Radio Frequency (RF)

Carrier Signal

Baseband Signal

Quadrature: Orthogonal relationship (i.e. 90 degrees) between two vectors.

Quadrature I/Q Components: two components I (in-phase signal) and Q (out-of-phase signal) are 90 degrees out of phase. IQ signals are the building block of modern digital modulation and demodulation schemes.


Modulation means encoding a message. In the context of RF, one can think of it in two ways:

Analog Modulation

Digital Modulation.

Analog/Digital Demodulation

Basic Principles of Operations

RF system is responsible for the transmission and reception of wireless signals.

Basic RF System Building Blocks

Simplified Wireless Communication Block Diagram

Simple RF System

In conclusion, the main RF system design criteria is to minimize path loss and maximize power transfer using lumped matching network.

Block Descriptions

RF Performance Characterization

Smith Chart: it's an impedance visualization tool that is used to characterize impedance of a lumped passive circuit.



System Level

Link Budget: it is used to estimate line of sight range of wireless communication link by calculate received power at receiver.

Link Margin: it is used to calculate much margin is needed for a communication system accounting signal attenuation due to multi-path fading during the transmission channel.

Adjacent Channels Power Ratio (ACPR): It is a measurement of the amount of interference in the adjacent frequency channel usually as the ratio of average power adjacent outband channel to the average power in the in-band channel,

Phase Noise: Random frequency fluctuations of the main RF carrier frequency cause by imperfect clock generator source such as the local oscillator used for generating RF carrier frequency.

Noise Figure: A measure of degradation of signal SNR caused by RF hardware placed in the transmission and reception path. 

Component Level


Common Wireless System Level Test items

Practical Design Overview

Summary & Conclusion.

Wireless communication system involves understanding principles of operation, practical design trade-offs, and performance measurements. As an electronics system design engineer, understanding the basics of wireless connectivity shortens design, testing, and debug time.

Reference and Further Reading

"Back to Basics Impedance Matching Part 3", 

"Lumped Matching Network", 


"What is QAM?", 

"Carrier to Noise Ratio", 

"Analysis and Design-RF and Digital Systems Using PathWave System Design (SystemVue) ",