An RF circuit is a special type of analog circuit operating at the very high frequencies suitable for wireless transmission. One salient feature of an RF circuit is the use of inductive elements to tune the resonant circuit operation around a specific radio carrier frequency. The primary difference between RF design and low-frequency analog design is the type of analysis performed on the circuit.
In RF design, steady-state operation is of primary concern. The behavior of the circuit is often modeled in frequency domain with attention focused on the signal fidelity, noise, distortion, and interference. When modeling a modulated signal on an RF carrier, a hybrid time-frequency domain analysis is most efficient, where time domain focuses on the dynamic signal changes and frequency domain focuses on the RF carrier and its harmonics and intermodulation products. RF circuit variability, both manufacturing and design induced, must be modeled, and compensated for.
To put RF circuits, analog circuits, and digital circuits together in a radio system, an analog-to-digital converter (ADC) acts as a bridge between analog circuits and digital circuits. A mixer acts as a bridge between analog circuits and RF circuits. An antenna acts as an interface between an RF circuit and air space.
Digital systems designers are likely familiar with some RF components and routing styles, but there is much more that goes into RF circuit design. An RF circuit can include integrated circuits, discrete semiconductors, and printed RF elements that work together to produce required functionality. RF circuit design involves combining all of these elements to build an entire system and create a PCB layout.
RF circuits are designed to mimic the standard circuit elements and some simple integrated circuits by constructing structures using printed elements on a circuit board design. RF circuits can appear a bit foreign as they do not always use off-the-shelf components. Instead, RF circuits can use printed traces on a PCB and some additional components to provide desired functionality in a circuit board.
Printed sections of an RF circuit board design will use copper traces to build circuit elements. The arrangements of traces, capacitor or inductor elements, and semiconductors in an RF circuit may appear un-intuitive, but they take advantage of propagation behavior in the electromagnetic field to produce the desired electrical behavior. There are some important conceptual points to remember about RF circuit design, as well as how RF circuits on a PCB will behave electrically:
Active RF circuits can include anything from an oscillator to driven amplifiers, ADCs, and transceivers. These components can be used in addition to printed traces to provide additional functionality. Many radar modules, wireless systems, amplifiers, and telecom components will use active components alongside passive circuits to route RF signals and provide required signal propagation behavior. Signal sampling, manipulation, and processing is performed with active components, which can also provide an interface back to digital systems.
Just like a high-speed digital PCB, successful RF circuit design relies on building a PCB stackup that can support your RF circuits. The stackup should be designed so that RF elements have the desired characteristic impedance, although the impedance of your system will be a much more complex function of your RF circuit layout and routing. In addition, the relevant frequency at which your board operates will determine how the stackup should be built, what types of printed circuit designs you might need, and what RF components you can use. RFIC design follows many of the same ideas as in RF PCB design, and a mastery of these concepts will help you succeed in any area of RF design.
FR4 materials are acceptable for RF transmission lines and interconnects operating up to WiFi frequencies (6 GHz). Beyond these frequencies, RF engineers recommend using alternative materials to support RF signal propagation and printed RF circuit designs. Standard FR4 laminates use resin-filled fiberglass weaves to hold components, but these fiber weave effects in certain materials could create signal and power integrity problems if fabrication procedures are not specified properly.
Printed RF circuits are designed by calculating transmission line sections for use in specific structures on a PCB. Your transmission line designs will guide propagating waves to components while also providing behavior like attenuation, amplification, filtering, resonance, and emission (e.g., as an antenna). Impedance transformation at stubs, interfaces with components, and antennas is often needed to overcome impedance mismatch seen by an RF signal as it propagates. The various printed structures that produce these functions are well-known in many textbooks.
If you also have digital components that must interface with your RF circuit designs, they need to be placed in a PCB layout using the same set of tools. Careful placement and proper stackup design will help prevent interference that corrupts high frequency circuits and RF signal collection. Native 3D design tools can be helpful here as well because some RF systems are multiboard systems, and the overall assembly needs to be inspected before preparing for manufacturing.
When you need to build advanced RF systems that also maintain signal integrity, you need a complete set of circuit design simulation tools, PCB routing and layout tools, and a layer stack design tool to help you reach impedance targets. Whether you need to layout a low noise amplifier for signal collection, RF power amplifier for broadcasting signals, or complex interconnects with unique trace and via structures, the best PCB layout tools will help you stay flexible as you create your RF PCB layout.
Zachariah Peterson has an extensive technical background in academia and industry. He currently provides research, design, and marketing services to companies in the electronics industry. Prior to working in the PCB industry, he taught at Portland State University and conducted research on random laser theory, materials, and stability. His background in scientific research spans topics in nanoparticle lasers, electronic and optoelectronic semiconductor devices, environmental sensors, and stochastics. His work has been published in over a dozen peer-reviewed journals and conference proceedings, and he has written 2000+ technical articles on PCB design for a number of companies. He is a member of IEEE Photonics Society, IEEE Electronics Packaging Society, American Physical Society, and the Printed Circuit Engineering Association (PCEA). He previously served as a voting member on the INCITS Quantum Computing Technical Advisory Committee working on technical standards for quantum electronics, and he currently serves on the IEEE P3186 Working Group focused on Port Interface Representing Photonic Signals Using SPICE-class Circuit Simulators.
Section 2: Power Have a complete understanding of power in Radio FrequencyLecture 3: Instantaneous and average powerLecture 4: Power Example 1Lecture 5: power and phasorLecture 6: Power Example 2Lecture 7: Complex powerLecture 8: Complex Power SummaryLecture 9: Power Example 3Lecture 10: Complex Power ADS simulationLecture 11: Maximum powerLecture 12: Max power ADS simulationLecture 13: Power and Matching(Preview enabled)Lecture 14: Max Power and Matching SummaryLecture 15: dB, dBm and power gainSection 3: Mos TransistorLecture 16: MOS Transistor structure and DC characteristicsLecture 17: Small signalLecture 18: Small signal modelLecture 19: Parasitic cap and fTLecture 20: ADS FTLecture 21: MOS Example 1Section 4: Non LinearityLecture 22: IntroLecture 23: Harmonic distortionLecture 24: Gain CompressionLecture 25: Gain Compression ADS exampleLecture 26: Harmonic Distortion and Gain Compression SummaryLecture 27: Desensitization(Preview enabled)Lecture 28: Desensitization ExampleLecture 29: IntermodulationLecture 30: Intermodulation IIP3Lecture 31: Intermodulation Example 1Lecture 32: Intermodulation Example 2Lecture 33: Intermodulation Example 3Lecture 34: Cascaded StagesSection 5 : NoiseLecture 35: IntroLecture 36: Device NoiseLecture 37: Input Referred NoiseLecture 38: Input Referred Noise ExampleLecture 39: Noise Figure (NF) First Part(Preview enabled)Lecture 40: Noise Figure (NF) Second PartLecture 41: Noise Figure (NF) Example 1Lecture 42: Noise Figure (NF) Example 2Lecture 43: Noise in Cascaded stagesLecture 44: Noise in Cascaded stages ExampleLecture 45: Noise in Passive Reciprocal CircuitsLecture 46: Noise in Passive Reciprocal Circuits ExampleSection 6 : Sensitivity and Dynamic RangeLecture 47: Sesitivity(Preview enabled)Lecture 48: Sensitivity ExampleLecture 49: Dynamic RangeLecture 50: Dynamic Range ExampleSection 7: RLC circuitLecture 51: RLC resonance CircuitsLecture 52: Bandwidth and Quality FactorLecture 53: RLC ADS simulationLecture 54: Two component networksLecture 55: Low Quality Factor ExampleLecture 56: Matching Circuit
The DreamCatcher(Keysight solution partner) ME1000 RF Circuit Design teaching solution offers a ready-to-teach package in the areas of RF and wireless communications. The provided CAE design files of the RF Transceiver Kit (based on ADS and Genesys Software from Keysight Technologies) allow students to learn RF circuit design principles, modeling, and simulation techniques.
Provides up-to-date coverage of the fundamentals of high-frequency microwave technology, written by two leading voices in the field RF and Microwave Circuit Design: Theory and Applications is an authoritative, highly practical introduction to basic RF and microwave circuits. With an emphasis on real-world examples, the text explains how distributed circuits using microstrip and other planar transmission lines can be designed and fabricated for use in modern high-frequency passive and active circuits and sub-systems. The authors pro