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Frequency Modulation Fundamentals

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)

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

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.

MMIC Package Customization – Footprint-Compatible Solutions for Your System

MMIC Package Customization – Footprint-Compatible Solutions for Your System Obsolescence Management and EOL Part Replacement LTB (Last Time Buy) and EOL (End of Life) are among the most unwelcome acronyms in the ranks of Procurement and Engineering. Component obsolescence saddles customers with the burden of tying cash up in inventory on their balance sheet, or […]

MIMO Systems

MIMO Systems

In modern radio communications (particularly commercial cellular and Wi-Fi), Multiple-Input, Multiple-Output (MIMO) is a common method of utilizing multiple transmitting and receiving antennas to increase the capacity of the radio link, reduce errors, and maximize speed. As user demand for bandwidth and data speed have grown, MIMO systems have been integral in the evolution of modern communication systems including cellular communications, Wi-Fi networks and many more.

This article will explore the origins of MIMO technology and explain how concepts of polarization diversity and spatial diversity enable these systems to scale capacity for higher data rates and multiple simultaneous connections to user equipment. Use of MIMO in LTE-Advanced (LTE-A) communications and Wi-Fi 6/6E are then described by way of example.

A Brief Overview of Phased Array 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.

Channelizing High-Power SMT Couplers to Optimize Coupling, Directivity & Isolation

Figure 1: Bidirectional coupler schematic diagram with port nomenclature and port numbers.

An ideal directional coupler has 0 dB of insertion loss, a constant coupling value vs. frequency, and infinite isolation and directivity. However, the physical, internal construction of directional couplers introduces frequency-dependent losses and finite isolation and directivity. Compounding these internal effects, PCB-mounted couplers face additional challenges. Stray coupling from port to port on a PCB-mounted directional coupler can have significant, adverse effects on the coupler isolation, directivity and even coupling value.

Fortunately, many packaging and shielding methods are available to the designer to mitigate stray coupling. This application note examines form-in-place gasketing for two distinct bidirectional coupler styles: the core & wire and the stripline SMT. Modern day form-in-place gasket machinery is capable of depositing very tiny beads with good adhesion over intricate patterns. The use of conductive silicone elastomers is common, and generally results in high-performance RF/microwave shielding. This technique is

While this application note emphasizes directional coupler external packaging, form-in-place gasket shielding is used broadly to optimize a myriad of components as well as for entire receive and transmit subsystems. This technique is cost effective, repeatable practical to implement in most industry manufacturing environments.

In another application note we will explore some of the more traditional methods of shielding couplers including sheet metal fencing with a lid (commonly referred to as a “doghouse”) and surface-mountable conductive silicone elastomers.

A Primer on Quadrature Amplitude Modulation (QAM)

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.

RF/Microwave Bias Tees from Theory to Practice

RF/Microwave Bias Tees from Theory to Practice

The bias tee is an essential component for applying DC voltage to any component that must also pass RF/microwave signals, most commonly an RF amplifier that requires a DC supply. For narrowband applications, bias tee design and construction are relatively straightforward, provided attention is paid to component self-resonant frequencies (SRFs). For broadband applications, however, bias tee design and construction are nontrivial, and attention to component characteristics is paramount to a successful, high-performance design. In this article, we examine narrowband bias tee design, component SRFs, and how they impact the design, then extend those ideas to broadband bias tees.  We will also compare the electrical and physical performance attributes of different types of broadband bias tee designs including discrete circuits with conical inductors as well as MMICs. 

Fully Non-Blocking (Full Fan-Out) RF Switch Matrices

Figure 1: 8×8 fully non-blocking / full fan-out matrix configuration.

The first two articles in this series established that blocking switch matrices use switches to allow one-to-one connections between input and output ports, while non-blocking switch matrices use splitter/combiners on either the input our output ports to allow one-to-many or many-to-one connections. In this article, we’ll examine the fully non-blocking or “full fan-out” configuration in which all inputs are connected simultaneously to all outputs via splitter/combiners, sometimes with programmable attenuation on every path. Features, advantages, applications and examples will be reviewed.

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Aharon

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