Microwave/RF module technology has advanced to traditionally planar formats to three-dimensional, multilayer assemblies with subsystem functionality in component packages.
Modules mean many things to many people. At the military systems level, they are generally ruggedized subsystems that can be as complex as a complete receiver or digital frequency discriminator (DFD). In the world of commercial high-frequency electronics, the term module suggests a small, packaged combination of components meant to group related functions together for ease of installation in a larger design. In spite of differences in technology, the ultimate goal of a module design is to combine parts of functions into a trouble- free single unit that can be treated as a more-or-less “plug-and-play” component.
High-frequency modules have become smaller and denser over time, with help from advances in materials. Several decades ago, multifunction modules were also known as “supercomponents,” fabricated in stripline and microstrip and combining related components such as local-oscillator (LO) buffer amplifiers, RF preamplifiers, and mixers. Modern multifunction modules are often close to systems in a single package, including complete receivers, transmitters, and transceivers. The proprietary Epsilon Packaging™ approach developed by Endwave Corp. (www.endwave.com), for example, was used to create a full 24-GHz transceiver in a component-sized package. The transceiver achieves +27 dBm transmit output power with receiver noise figure of 5 dB. The firm’s packaging concept combines different technologies, including monolithic-microwave integrated circuits (MMICs), discrete semiconductors and devices, chip-on-board (COB) devices, and surface-mount-technology (SMT) components, into a single compact module.
Component integration at the module level usually starts with the capability to embed circuits elements, such as capacitors, resistors, and inductors, within a laminated substrate, or to form these elements directly on the substrate as part of the metallization process. Late last year, for example, Dielectric Laboratories (www.dilabs.com) unveiled their latest ceramic circuit technology using semiconductor photolithography techniques to pattern fine-lined structures on their temperature-stable ceramic substrates. Given the capability of forming basic circuit elements with wide ranges of values on their ceramic materials, the firm has succeeded in producing high-quality-factor (high-Q) resonators as well as high-rejection filters through millimeter-wave frequencies in extremely compact footprints. The technology is also suitable for placement of active components in designing more complex multifunction modules. In the area of ceramic materials, American Technical Ceramics (www.atceramics.com) offers a wide range of thin-film fabrication processes and services suitable for producing integrated passive modules or modules on which active devices can be mounted with supporting circuitry.
Similarly, Merrimac Industries (www.merrimacind.com) has developed and refined a multilayer circuit technology called Multi-Mix® which supports the fabrication of multilayer microwave active and passive assemblies with discrete and integrated devices. In contrast to the ceramic materials of the Dielectric Laboratories’ process, Multi-Mix is based on fluoropolymer composite substrates, which are bonded together into a multilayer structure using a fusion bonding process. The fusion process provides a homogeneous dielectric medium for superior electrical performance at microwave frequencies. The bonded multilayers, with embedded semiconductor devices, MMICs, etched resistors, circuit patterns, and plated-through viaholes, form a surface-mount module, which requires no further packaging. The technology, which is compatible with microstrip and coplanar waveguide (CPW) circuitry, is particularly well suited to the efficient dissipation of heat in highpower designs. The company also offers a version of the technology called Multi-Mix PICO® is the next big leap for Multi-Mix technology. Multi-Mix PICO®, which is designed to reduce the size of single-function microwave components.
Another company basing module development on “soft” substrates is Jacket Micro Devices, Inc. (www.jacketmicro.com). Started as an outgrowth of the Georgia Institute of Technology (Atlanta, GA), the firm has developed an innovative patented process to embed high-Q RF passive components into organic laminate materials. One example is the S100000 series of antenna switch module substrates, available in dual-band and quad-band GSM 850 GSM 900, DCS 1800 and PCS 1900 configurations. With typical insertion loss of 0.5 to 0.6 dB, these compact antenna switches measure only 3.2 × 3.2 × 0.7 mm or less.
Perhaps the largest number of microwave modules are devoted to different types of amplifiers, given an amplifier’s need associated circuitry such as biasing, temperature compensation, and gain control. The modular approach allows amplifier designers to pack several optimized amplifier circuits into a common housing for different wireless standards, for example. One such amplifier module is the RF3133 from RF Micro Devices (www.rfmd.com). This quad-band power amplifier module covers GSM850, EGSM900, DCS, and PCS battery-powered, handset applications with frequency bands of 824 to 849 MHz, 880 to 915 MHz, 1710 to 1785 MHz, and 1850 to 1910 MHz, respectively. The lead-free, RoHS-compliant module incorporates GaAs heterojunction- bipolar (HBT) and silicon CMOS technologies in a housing with bias and power control circuitry measuring just 7 × 10 × 0.45 mm.
MicroWave Technology (www.mwtinc.com) offers the MwT-0618S/ZH16P3 balanced amplifier module in a transistor-sized flange-mount package. It provides 6 dB gain from 6 to 18 GHz with +30 dBm typical output power at 1-dB compression. CAP Wireless (www.capwireless.com) is also a supplier of compact broadband power modules, including the model CPM0220- 6 with 30-dB gain and +25-dBm output power from 2 to 20 GHz. Among the most broadband of amplifier modules, an OC-768 modulator driver amplifier from Narda Microwave (www.nardamicrowave.com) is designed for telecommunications systems operating at 40 Gb/s and supports data rates to 44 Gb/s.
On a larger scale, Empower RF Systems (www.empowerrf.com) has developed the BBM2E3KKO RF power module with 100 W output power from 20 to 500 MHz. It operates from a +28 VDC supply and features 50-dB gain and 40 percent efficiency. It draws about 1 A idle current but can be put into a muted condition in which current consumption is only around 100 mA. In addition, L-3 Electron Devices (wwwedd.tw.l-3com.com), the former Litton Industries, offers a line of microwave power modules (MPMs), including a unit capable of 1 kW output power for narrowband applications. Designed for +28 VDC prime power, the M1221 series MPMs provide as much as 100 W output power over the range of 6 to 18 GHz. Another supplier of amplifier modules is the appropriately named Microwave Modules of Leeds, England (www.microwave-modules.com). Based on miniature traveling-wave tubes, the MPP series of MPMs from CPI (www.cpii.com) provide power output levels from 50 to 100 W CW (to 350 W pulsed) at frequency range of 2 to 6, 2 to 8, 4.5 to 11, and 6 to 18 GHz.
To assist companies designing amplifier modules, Microwave Power (www.microwavepower.com) has developed a proprietary monolithic ceramic circuit (MCC) technology optimized for power applications. Also suitable for GaAs-based MCMs, the process can form gold viaholes through the ceramic substrate material while maintaining good integrity of the circuit patterns in close proximity to the viaholes. The process also features air bridge interconnection of components, fine-line resolution through dry etching, and good step coverage of plasma-deposited silicon-nitride protective passivation. The process can form lines or gaps as fine as 5 µm with minimum viahole diameter of 100 µm. Resistors are available with values from 20 to 200 Ω/square and capacitors from 30 to 350 pF/mm2.
One of the more popular materials technologies in support of module development is low-temperature-cofiredceramic (LTCC) technology, which allows dramatic size reduction through integration of passive and active devices. Adopted, for example, by leading component supplier Mini-Circuits (www.minicircuits. com) as a means of shrinking various of the company’s passive component products, the technology has been used for years at Anaren (www.anaren.com) to fabricate highreliability circuits and modules for commercial, industrial, and military customers. Also supplying circuits based on traditional ceramic substrates, the firm employs a cost-effective process capable of fine features and tight line and gap tolerances. Plextek Ltd. (www.plextek.com) provides a variety of LTCC design services for fabricating multilayer ceramic circuits and modules.
For some companies, building a module amounts to matching the best fabrication process to a particular set of requirements. Custom-module specialist Maxtek (www.maxtek.com), for example, relies on a number of technologies when creating a design, including flip-chip, hybrid, LTCC, high-temperature- cofired-ceramic (HTCC), thick-film, thin-film, and chip-on-board (COB) technologies. Aeroflex (www.aeroflex.com) has employed a variety of technologies in their multichip- module (MCM) technology, including surface-mount-technology (SMT) components, plastic packaging, COB, LTCC, thin-film, and thick-film structures.
Boeing’s Microelectronics Phased Array Antenna Center (www.boeing.com) has employed a wide range of technologies for more than 35 years in producing MCMs suitable for satellites, submarines, commercial airliners, missiles, or tactical fighters. The center expanded to the design and manufacture of phased-array antenna modules in 1993 and has produced over 250,000 RF modules and 100 Flight worthy antennas. Similarly, Teledyne Microelectronic Technologies (www.teledynemicro.com) has employed sophisticated design, processing, manufacturing, and test processes to crate an impressive record of MCM development.
The list of microwave/RF module suppliers is too long for an article of this brief scope. But a working list can be found by visiting the online version of the Microwaves & RF Product Data Directory at www.m-rf.com, performing the “Search Manufacturers by Product Category,” clicking on the category“Integrated Circuits,” and then clicking on the subcategory “Components, Multifunction.”