Frequency Modulation Fundamentals

In the 1920s, many brilliant scientists applied themselves to the study of frequency modulation (FM). One of these scientists was a communications systems theorist who worked for AT&T named John Renshaw Carson. Carson performed a comprehensive analysis of FM in his 1922 paper which yielded the Carson bandwidth rule.1 Carson was so convinced that FM was not a suitable solution to the static found in AM transmission systems that he once remarked, “Static, like the poor, will always be with us.”2

Beginning in 1923, in Columbia University’s Marcellus Hartley Research Laboratory, in the basement of Philosophy Hall, a driven genius in electronic circuitry named Edwin Howard Armstrong set out to reduce static through the use of FM. After approximately 8 years of toil, Armstrong had a brainstorm and decided to challenge the assumption that the FM transmission bandwidth had to be narrow to keep noise low. After painstakingly designing this new FM system, with as many as 100 tubes spread over several tables in the laboratory, “[Armstrong] was able to prove that wideband FM made possible a drastic reduction of noise and static.”3 Armstrong was issued patent number US1941069A, which specifically addresses noise suppression in wideband FM, on December 26, 1933, along with three additional patents for FM that same day.

The Basics of Orthogonal Frequency-Division Multiplexing (OFDM)

While traditional Frequency Division Multiplexing has been around for over 100 years, Orthogonal Frequency Division Multiplexing (OFDM) was first introduced by Robert W. Chang of Bell Laboratories in 1966.1,2,3,4 In OFDM, the stream of information is split between many closely-spaced, narrowband subcarriers instead of being relegated to a single wideband channel frequency.5 Single-channel modulation schemes tend to be sequential whereas, in OFDM, many bits can be sent in parallel, simultaneously, in the many subcarriers.5 So many bits can be packed onto the subcarriers simultaneously that the data rate of each subcarrier’s modulation can be much lower than that of a single-carrier architecture.

LTCC High Pass Filters for mmWave

Mini-Circuits has introduced new high pass filters that achieve breakthrough performance for Q-band and lower V-band applications up to 58 GHz. The HFCQ, HFCN, and HFCV LTCC filters offer a combination of low insertion loss, high return loss, excellent rejection, small size, cost-effectiveness, repeatability, ruggedness and reliability. These filters enable designers to cover filter blocks with traditional SMT technology versus more exotic solutions. Key benefits include smaller footprint compared to stripline filters, repeatable performance suited for volume production, and robustness. The filters simplify designs for applications like 5G FR2 and satellite communications. Mini-Circuits’ latest LTCC high pass filters set a new standard for electrical performance and ease of implementation in demanding mmWave systems.

A Brief Overview of Phased Array Systems

The concept of the phased array antenna system was first put into practice by German Physicist Ferdinand Braun and his assistants in the spring of 1905. In short, he and his assistants carefully controlled the excitation phase of each antenna in an array and determined that the combined effect exhibited significant directivity. In the nearly 12 decades since Braun first described the phased array antenna system, this technology has become commonplace in 4G/5G communications, electronic warfare, radar, nonlethal weaponry, and advanced imaging applications.1 

This article begins with an overview of the evolution of phased array systems through history. A functional description of their basic operation in both analog and digital domains is provided, and a brief survey of common and emerging applications is given by way of example.

BOOST YOUR KNOWLEDGE: A COMPREHENSIVE GUIDE TO RF FILTERS – TYPES AND APPLICATIONS EXPLAINED

RF filters, also known as radio frequency filters, are electronic devices that are used to selectively pass or block specific frequencies of an RF signal. These devices are used in a wide range of applications, including wireless communication systems, test and measurement equipment, and RF circuit design. RF filters can also be used to remove unwanted interference or noise from a signal, or to separate different signals in a system.
There are several different types of RF filters, each with their own unique characteristics and uses. In this blog post, we will discuss the different types of RF filters and their applications.

A Primer on Quadrature Amplitude Modulation (QAM)

While other modulation schemes discussed in this blog series (pulse, frequency, amplitude, phase) date back to the early chapters of RF engineering history, quadrature amplitude modulation (QAM) was first described by C. R. Cahn in 19602 and evolved steadily over the next few decades. In the last 25 to 30 years, no modulation scheme has seen such widespread development and application as QAM. The technology has played a pivotal role in the industry’s ability to scale data speed and capacity with user demand by packing more data onto the carrier waveform and pushing a fixed channel bandwidth closer to Shannon’s limit. QAM modulation is used widely in cellular networks and backhaul, CATV networks and fixed wireless access points (802.11), and satellite communications to name a few. See Table 3 in Reference [3] for a more detailed list of applications.

In this article, we describe QAM using basic mathematics and illustrate how a QAM modulator operates. We introduce the concept of a constellation diagram and how it relates to the time domain plots for QAM modulation. A representative set of components is then utilized to design a functional QAM modulator by way of illustration. We conclude by describing how the QAM signal is demodulated at the receiver.

LTCC Filter Innovations Enable Next Generation Aircraft Internet Links

For all the headlines and personal anecdotes lamenting how commercial air travel isn’t what it used to be, there are some clear benefits enabled by recent advances in technology we might be taking for granted. One of these is in-flight internet service. Whether domestic or international, most flights now offer internet service via satellite, allowing passengers to remain connected for personal and business use throughout the majority of their journey.

For most aircraft in service today, the satellite up/downlink connection is achieved with a mechanically steerable antenna mounted to the top of the fuselage. The antenna has a limited range of motion to maintain connection with the satellite while compensating for the movements of the aircraft during normal flight operation. These mechanical systems are now giving way to electronically steerable systems using phased array antennas to deliver more reliable connectivity with lower costs of operation and maintenance for the carriers.

Exploring the Fundamentals of Thin-Film Filter Technology in RF & Microwave Applications

Finding the right filter for frequency ranges above the 3 GHz range is a perennial challenge for RF system engineers. Designers are typically looking for repeatable performance at production volume and a small, surface-mount form factor robust enough to withstand reflow onto their existing printed wiring board (PWB). Lumped element filters utilizing discrete wire-wound inductors and chip capacitors meet these criteria handily for passbands below about 3 GHz, but frequency response becomes more sensitive to variations in the physical structure of the device and temperature at higher frequencies, rendering this approach impractical.

Every Block Covered: Cascaded P1dB and IP3 in a 26 GHz 5G Front-End

The goal of this article was to provide students and designers alike with a deeper understanding of the equations behind the cascading of P1dB and IP3 as the system expands to include multiple nonlinear components such as those utilized in the RF, frequency conversion and IF sections of a receiver chain. A 5G RF front end was presented for the 24.25 – 25.1 GHz portion of the 5G n258 frequency band comprised of all SMT parts. Calculated data for linearity parameters was presented for individual components in the signal chain as well as cascaded at each stage. The equations used to calculate those results were provided, and an examples were given showing how to calculate cascaded linearity parameters OP1dB and OIP3 from one stage to the next.

Understanding Suspended Substrate Stripline Filters

To manage signal purity in communications and test systems, no component is more important than RF filters. To meet the needs of these advanced systems, Mini-Circuits’ suspended substrate stripline filter products offer state-of-the-art performance featuring unique passband, stopband characteristics and outstanding reliability in harsh operating environments. The range of available filter types supports the needs of military, aerospace and commercial systems, including instrument systems, ultra-broadband receivers, laboratory testing, 5G and many other wideband communications systems.