What are Microminiature and Ultraminiature RF connectors?

By AJ Born | September 12, 2023

Meet the Connector: Microminiature and Ultraminiature RF Connectors

RF (radio frequency) connectors work with radio frequencies in the multi-megahertz range. Technology advanced significantly in the 2000s to meet the demand for inexpensive, high-data-rate wireless transceivers. Wire-to-wire, wire-to-board, and board-to-board micro-miniature RF connectors and ultraminiature RF connectors were developed to work in smaller and smaller devices.

“Ever since radio was invented, there has been some sort of RF connector. Early radios and televisions relied on one huge transmitter and a bunch of other receivers that didn’t need as much power,” said Travis Amrine, global industry marketing manager with I-PEX. “The connectors started out really big and bulky. As we’ve progressed through frequencies and applications, they’ve been shrinking.”

I-PEX MHF I LK Micro RF coaxial connector with patented mechanical locking feature. (MHF is an I-PEX registered trademark that stands for “micro high frequency.”)

I-PEX MHF 4 LK Micro RF coaxial connector with patented mechanical locking feature.

“As the devices get smaller, the connectors get smaller too,” said Amrine. “If you have a laptop, there’s a pretty good chance that it has an MHF 4 receptacle and an MHF 4 plug for your Wi-Fi connection.”

RF connectors are made with CNC (computer numerical control) machining or, for extremely high-volume production, with stamping and molding. This is the case with MHF-style connectors, which are produced in the billions every year.

The variety of connector types in this category address application concerns about frequency, transmission speed, market, ruggedness, size and weight, performance, and durability. David Shaff, in his analysis of RF connectors for Bishop & Associates, World RF Coax Connector Market 2023, details the various microminiature and ultraminiature RF interfaces now available as follows:

MICROMINIATURE CONNECTORS

MCX (for Micro Coaxial) connectors were developed in the 1980s and are available in both 50- and 75-ohm versions. MCX has the same inner contact and insulator dimensions as SMB connectors but are almost one-third smaller and covered by EU standard CECC 22000. They are easy and quick to mate with snap-lock that allows full rotation.

MMCX (for Micro-Miniature Coaxial) connectors are smaller versions of the MCX, also per EU CECC 22000 specification. Both MCX and MMCX operate DC to 6 GHz.

Packaging includes single connector, trays, and tape-and-reel. Panel and PCB-mount jacks/female are available. Both straight and 90° plugs/male are available for both semi-rigid and flexible cable.

TLMP Connectors

TLMP stands for Times Locking Miniature Push-on, a new series released by Times Microwave Systems (an Amphenol Company). They are intended for DC to 60 GHz, mil/aero, and space applications, to overcome potential problems with SMP/SMPM connectors, which reportedly include environmental sealing, EMI capabilities, and power handling, plus high vibration, and high shock capabilities.

IDC Terminated Coax Connectors

KYOCERA AVX offers unique IDC (Insulation displacement connector) termination for coax cable, for 50-ohm DC to 6 GHz applications. IDC has been used for many years for cable-to-board and cable-to-cable for signal/power applications to provide quick and reliable termination. By adapting IDC for coax to board assemblies, microwave termination can be simplified plus the SMT housing can be placed by automated pick-and-place and lead-free reflow board assembly. Small package size and mechanical strength allows usage in automotive and industrial antenna applications.

QSL Connectors

This is another low profile (under 0.4 inches) series for low cost, rugged applications including PCIe and WNIC cards where SMA, mini-BNC, and other connectors are too large. Offered by TE Connectivity, for DC to 6 GHz. With positive 500-cycle mating, QSL is suitable for EIA/ECA-364-1000.01A (controlled environment) applications. Available in single and multi-position board-mount assemblies with cables for RG-174 and RG-316 cables.

0.9 mm SuperMini

This is a miniaturized threaded coupling connector for MIL/aerospace applications. The 0.9 mm interface provides theoretical cutoff above 120 GHz, but production (for performance at max. frequency) is tested based upon customer needs for 65 GHz or 110 GHz applications. It has a Teflon insulator and resembles an ultra-miniature SSMA. Cable plugs accept 0.047 flex cable such as Molex/Temp-Flex 047SC cable. Primary supplier is Southwest Microwave. For space, UAV/UAS, and other applications that need to minimize payload, consider that a mated pair of SMA connectors weighs approximately 5.0 grams versus a mated pair of 0.9 mm at 0.56 grams (both cable plugs weighed unterminated).

MOEBIUS MC-CARD and Switching Connectors

MOEBIUS connectors are a family of microminiature, 50-ohm, 8 GHz interconnects, developed for high-cycle-mating mobile applications. Termed “CN,” they were initially provided by Radiall who chose the name “Moebius” in reference to the “Möbius strip,” which is considered the basis for the infinity symbol, to illustrate high durability performance for snap-on coax connectors for applications where size, weight, performance, and durability are important. First applications were for snap-on antennas, but usage can include wearables, radio, mezzanine cards with end-on termination requirements, and wherever a manual, single-line RF interconnection is desired.

CN is an alternative to MMCX connectors for numerous wireless and telecom applications. Moebius was designed in 2005 to replace MMCX and MC-Card for wireless LAN remote antenna connection due to its extremely high durability which exceeds 25,000 mating cycles.

Nano Coax

Most coax contacts provided by Omnetics are used in Micro-D and Nano-D connectors and are sold pre-terminated with RF-178/U, which limits operation to about 1 GHz. Realizing application requirements, Omnetics Corp. optimized its coax designs for use with flexible .047 coax cable, which enabled its 50-ohm Nano Coax for applications to 20 GHz. The male/plug’s center pin contact has twist-pin construction.

PCIe M2

These are the next-generation small form factor connectors in accordance with the PCIe M.2 Specification Rev. 1.x, (released February 26, 2020). The M.2 form factor is intended for mobile adapters and is a transition from the PCIe Mini 3 Card and Half-Mini Card (refer to the PCI Express Mini CEM Specification) to a smaller form factor in both size and volume. The M.2 family of form factors enables expansion, contraction, and higher integration of functions onto a single module solution.

To enable implementation of cabled PCI Express, the companion specification for cabling, “PCIe External Cabling Specification, Rev. 3.0,” was released September 26, 2019.

Applications include almost all newer thin mobile equipment, per IEEE 802.11 a/b/g/n, WiMAX, ZigBee, Bluetooth, MIMO, etc., for tablets, gaming sets, smartphones, and almost everything focusing on lowest silhouette and miniaturization.

MHF I LK Locking Connectors

One of the customer-identified issues associated with these connectors is their potential to disengage under high-vibration and shock conditions. Epoxy and adhesives often are used to assure that connectors remain mated. I-PEX has released its MHF I LK and MHF 4L LK plug connector assemblies to address these mechanical retention issues. The patented locking mechanism keeps them mated using a simple slide-on mechanism. The connectors have the same mating interface as the company’s standard MHF 1 and MHF 4L. The locking plug mates with all MHF 1 and 4/4Lreceptacles, respectively, and is offered with a variety of miniature coax cables from 0.81 to 1.80 mm OD. (A video showing the locking mechanism up close is available here.) Mating involves vertical snap-down and then manually sliding the lock into position, which has a tactile “click” to confirm locking. Removal involves a simple cover push-back and lift.

ULTRAMINIATURE CONNECTORS

U.FL are ultra-low silhouette snap-together connectors for miniature cable-to-board applications to 6 GHz. Originally developed by the Hirose Electric Group, there now are multiple similar series: AMC, MHF, UMCC, and others. Packaging usually is tape and reel. Although the connectors may be snapped together manually, special tools are used for unmating/extraction. Mating heights are 2.0 mm and 2.5 mm max., plus a slightly larger series E.FL with 3.2 mm height.

Applications include cellular phones, miniature instrumentation, GPS, Bluetooth devices, and almost any other assemblies involving relatively high frequency using small coaxial cable/connectors.

Hirose Microminiature RF Connectors

In 1993, coaxial connectors for antennas were large and expensive. Anticipating a coming tide of miniaturization, Hirose developed a series which uses stamped and formed components to achieve a significant size and cost reduction starting with the H.FL. Continuing to develop this trend with the release of the U.FL connector in 1997, these compact coaxial connectors matched the needs of mobile phone antenna connectors, and have been widely used since the advent of the mobile phone. The U.FL(A) coaxial connector (above left) is suitable for applications that require high-frequency connectivity in a compact footprint. Measuring only 2 mm x 2 mm with a 2.1 mm mated height, it delivers high signal integrity and low insertion loss up to 18 GHz and features a self-alignment design that ensures stable and secure mating. Featuring gold-plated contacts for corrosion resistance and superior peeling strength using four ground contacts for shock and vibration resistance, the U.FL(K) Series coaxial connector (above right) offers a long operational life in harsh environment applications. Combining a low-profile of only 2.5 mm with excellent high-frequency performance up to 8 GHz, the U.FL(K) Series is commonly used in automotive applications, including antennas, AVN (audio, video, and navigation), camera modules, and telematics. Measuring only 3.0 mm x 3.1 mm, the ultra-miniature footprint enables automotive designers to miniaturize the design or add more functionality in the same space.

X.FL are a series of low-profile, ultraminiature, and extremely lightweight SMT coaxial connectors, for six and 12 GHz WiGig applications, produced by Hirose. Mating heights are 0.94 or 1.2 mm. Provided in embossed tape carrier reels, for automated assembly. Board receptacles are available with straight and right-angle center contacts. Cable versions use ultra-fine (fluorinated resin insulated) coaxial cables.

SW* Connectors

Subseries includes (from large to smallest in size) SWD, SWF, SWG, SWH, and SWJ connectors. These subminiature coax connectors by Murata Manufacturing Co., Ltd. include several versions with switching functions, used for the measurement of microwave circuits for cellular phone and small wireless equipment such as wearables. SWD and SWF are used in PCs, while SWG and SWH are for tablets and mobile phones, and the smaller SWH and SWJ are used in phones and wearable devices.

Device RF circuit and antenna characteristics can be measured by mounting the connector in an RF transmission line. The internally built-in mechanical switch separates the RF circuit and ANT circuit, so that the circuit can be measured without any mutual effect using a dedicated probe (also made by Murata). Specifications include 1.3 Voltage Standing Wave Ratio (VSWR) from DC to 6GHz and 50 cycles connector durability with a probe.

Design Notes

How to specify

The main electrical considerations are frequency of operation, VSWR (voltage standard standing wave ratio) and insertion loss metric. The primary mechanical considerations are PCB area and stack height when mated.

Applications

Cell phones, laptops, Bluetooth devices, miniature instrumentation, routers, automotive infotainment

Suppliers

COAX Connectors Ltd, Hirose Electric, I-PEX, Omnetics Connector Corporation

Connectors such as COAX Connectors’ Micro BNC have taken the proven BNC connector design and reduced its size and weight so that it offers a packing density in excess of four times that of the standard product.

COAX Connectors 0.4/2.5 & 0.4/2.8 are some of the smallest true 75- or 50-ohm connectors available. Originally designed for a miniature CCTV camera manufacturer, these connectors offer a board-to-board mating height of just 5.0 mm. This micro-miniature series is ideal for high-definition camera and CCTV applications or anywhere that a very small board-to-board or board-to-cable connection is required.

 

Related Products

  • Coaxial connectors
  • Microwave connectors
  • Subminiature RF Connectors (QMA, SMA, SSMA, SMB, SMC, SSMC, SMD, mini-FAKRA
  • Miniature RF Connectors (BNC, mini-BNC, HD-BNC, UHF, mini-UHF, SHV, F, G)

Like this article? Check out our other Meet the Connector and Miniaturization articles, and our 2023 Article Archive

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AJ Born
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