Fri - 01 Dec 2023                            



RF and Microwave Connectors Part-3

High Frequency Precision Connectors


  1. APC-7 Connector

  2. APC-3.5 Connector

  3. 2.4 mm Connector

  4. 1.85 mm Connector

  5. K and 2.92 mm Connectors

  6. V Connector

  7. 1.0 mm Connector

  8. W Connector


1. APC-7 (7 mm)Connector

The APC-7 or Amphenol Precision Connector-7 mm, contrary to its name, was developed by Agilent in early 1960s, improved upon and manufactured by Amphenol. Agilent designed it for their test and measurement equipment such as the HP 8510 network analyzer. It is a precision 7 millimetres (0.28 in) coaxial connector used mainly in Microwave Testing labs. The connectors are expensive and seldom used outside the laboratory.

APC-7 Connector

Recessed Threads

The connector provides a coupling mechanism without male or female orientation. Please refer to the section “Connectors which are neither male nor female “ in this website, which discusses this unique mating connection. This connector offers the lowest reflection coefficient amongst all the 18 GHz connectors, and hence low VSWR (close to unity), for making 50-ohm measurements with frequency of operation upto 18 GHz. It can undergo repeatable connect/disconnect operations (1000s of interconnect cycles) and well suited for laboratory environment. Care should be taken to keep the mating surfaces clean. As mentioned earlier, these connectors are found on the front panel of some of the network analysers. Adapters are available to SMA, N, Waveguide and other precision connections.

How to properly connect two APC-7 mm connectors.

As the APC connectors are genderless, and hence the mating of connectors is a little tricky. In the example shown (Figure b), we are trying to connect an APC attenuator to the bulkhead APC connector of the instrument. Here, it is convenient to connect, if the connector attached to the instrument has the protruding threads and the device being connected has recessed thread. Of course, it could be otherwise also depending on which procedure is convenient.

  1. To prepare both connectors, spin the knurled nuts such that the thread is recessed in one connector, and the thread is protruding in the other.

  1. Insert left connector into right connector until seated.

  2. Thread left connector nut onto the protruding threads of the right connector until it is closely attached to the right connector. Do not turn the right nut, it should be able to spin freely (completely unthreaded).

  3. Finger tighten the protruding nut (about 12 in-lb of torque).

2. 3.5 mm or APC-3.5 Connector

APC-3.5 or Amphenol Precision Connector-3.5 mm is a connector jointly developed by Amphenol and Hewlett-Packard engineers. The Precision family is comprised of APC-2.4, APC-3.5, APC-7, and APC-N. The APC series of connector is an instrument-grade coaxial connector that achieves repeatable TE11 mode resonance-free signal transmission from DC - 50 GHz with a minimum return loss of 26 dB ( These 50-ohm connectors are designed primarily for use in test and measurement equipment where reliable performance is critical for repeated connect/disconnect cycles.

APC-7 to 3.5 Adapter

3.5mm Connectors(Male and Female)

Photo Courtesy: NPL, UK

The APC connector has the following advantages:        

  • Interface dimensions minimize distortion and deterioration of the mating surfaces
  • Fixed bead-contact assembly prevents transmission of mating torques to circuit elements
  • M7xO.75 thread for coupling durability and small overall connector size
  • Mating sequence touches outer contacts before center contacts, eliminating female center contact damage during mating
  • Plug coupling nut extends beyond the male center contact, protecting the contact while not mated

The APC connectors are used in applications such as Cable Assemblies, Instrumentation, Military, Radio Astronomy, Satcom.

Difference between a 3.5 mm and the SMA connector is that the 3.5 mm connector uses an air dielectric throughout the connector. The term 3.5 mm represents the inner diameter of the outer conductor inside the connector. The outside diameter of the outer conductor is 4.55 mm so that it is compatible with the mating surface of other compatible series. When mated with SMA and other precision SMA type connectors, the performance is limited by the connector with lesser performance. There are some male versions of this connector with a large knurled shell for hand tightening, especially on instrumentation cables. This allows quick connection without a wrench.

Either the male or female end of this 50-ohm connector can mate with the opposite type of SMA connector.

3. 2.4 mm Connector

HP, Amphenol and M/A-COM developed the 2.4 mm 50 ohm connector for frequency of operation up to 50 GHz. M/A-Com refers to it as OS-2.4 (OS-50). This design eliminates the fragility of the SMA and 2.92-mm connectors by increasing the outer wall thickness and strengthening the female receptacle fingers.


2.4mm Female Connector


2.4mm Male Connector

The inside of the outer conductor is 2.4 mm in diameter, and the outside is 4.7 mm. Because they are not mechanically compatible with SMA, 3.5-mm and 2.92-mm, precision adapters are required in order to mate to those types. This family is not directly mate-able with the SMA family. This is so because of its different geometry. The design goal for this connector was to overcome the SMA interface drawback and by utilizing a different geometry extract maximum performance at the highest frequency of operation. The male hex head is the same outer size as that of a SMA connector, 0.312 in, tightened with a 5/16 inch wrench, but the threads, are metric, at M7 x .76-6G. It is difficult to visually distinguish a 2.4 mm and a SMA connector.

The 2.4-mm product is offered in three quality grades; general purpose, instrument, and metrology. General-purpose grade is intended for economy use on components, cables and microstrip, where limited connections and low repeatability is acceptable. The higher grades are appropriate for their respective applications.

4. 1.85 mm Connector

The 1.85 mm connector pushes the limit of frequency of operation to 65 GHz as compared to 2.4 mm connector. HP developed the 1.85 mm connector in the mid-1980s. It exhibits single mode performance up to 65 GHz. It is often used with UT-085 and UT-047 coaxial cables with performance through 60 GHz.

1.85mm Connector

However, the smaller UT-047 coax will be lossier compared to UT-085. The inside of the outer conductor is 1.85 mm in diameter, while the outside dimension of the outer conductor is 4.7mm allowing compatibility in mating with 2.4 mm connector. This family is not mate-able to the SMA family. Since the design came into public domain, other manufacturers have come out with their 1.85 mm connector design. One such case is, the V connector designed by another equipment manufacturer, Wiltron.

5. "K" and 2.92 mm Connectors

The K connector or the 2.92 mm connector is a precision miniature, air dielectric connector that operates in single mode up to a frequency of operation of 40 GHz. The connector was first introduced by Maury Microwave ( in 1974 and then improvised upon by the test and measurement equipment manufacturer, Wiltron Corporation. Maury had named it as MPC3 connector, which was subsequently given another name, that of K connector, by Wiltron in 1984.

The K connector is trademark of the Wiltron Corporation (now part of the Anritsu Corporation), and it complies with IEEE 287 (GPC 2.92) standard.

K or 2.92 mm Connector




K or 2.92 mm connector

The K connector is mate-able with the SMA, WSMA (the Wiltron SMA series) and 3.5 mm series of connectors. Although its performance is rated at 40 GHz, it is usable up to 46 GHz. The K connector is also referred as SMK connector.

The K and 2.92 mm equivalent connector use an air dielectric. The diameter of the inside of the outer conductor (in the connector) is 2.92 mm. The outside of the outer conductor is kept at 4.55 mm, so that it is compatible with the mating surface of the other compatible connector series. In some cases, as in the instrumentation cables, the K connector ( similar to 3.5 mm connector), has a male version with a knurled outer shell for the convenience of manual tightening while making a connection. This facilitates quick manual connect/disconnect cycles without the use of a wrench tool.

The K connector can be assembled with a coaxial cable such as the UT-141 for a performance up to 34 GHz and with UT-085 up to 61 GHz. Useful performance can be obtained from a mated K connector up to 46 GHz. The K connector exhibits a flat performance over 10,000 interconnects cycles. To improve upon the mechanical support to the center pin of an air-dielectric K connector, dielectric material with holes have been used with satisfactory insertion loss performance.

6. V Connector

The V connector is another Wiltron/Anritsu Corporation connector, developed in 1989. This connector uses 1.85 mm geometry and construction dimension. It was designed to meet the standardization effort carried out in the 1980s (in 1988, HP released their 1.85 mm connector design to the public domain). It is also mechanically compatible with the 2.4 mm connector. It will not thread onto an SMA, 3.5 or 2.92 mm connector ensuring that inserting into a wrong mating connector does not accidentally damage the connector. At these frequencies, connectors become very expensive, and more susceptible to any impurities.  

V-Connector Socket and Plug

Photo Courtesy: NPL, UK.

V- Connector Socket and Plug

The V connector is used in a cable assembly featuring "V085" 50 Ohm type of coaxial cable. This cable assembly performs through 65 GHz of frequency operation. Other coaxial cable, such as UT085 coax, performs up to 61 GHz of frequency of operation, when assembled with a V connector, by limiting its performance. Both the 2.4 and V/1.85 mm connector require a 5/16 inch wrench.

7. 1.0 mm Connector

The 1.0 mm connector was designed by Hewlett Packard (now Agilent Technologies) and in is described in IEEE 287 Standard. The1.0 mm air dielectric connector, addresses the interconnect system needs of millimetre wave engineering and test and measurement instrumentation requirements. It replaces traditional waveguide used for measurement in the W band of frequencies from 70 GHz to 110 GHz.

Anritsu 1 mm Connector Plug and Socket

1mm Jack

 The 1.0 mm connector is based on the 1.0 mm geometry, wherein the inner diameter of the outer conductor is 1.0 mm. The 1.0 mm connector performs through the W band range from DC to 110 GHz with repeatable and reliable interconnections. The 1.0 mm connector is useful in laboratory environment such millimetre-wave measurement and analysis. This connector is also in a semiconductor chip-testing environment such as semiconductor probe stations for evaluating the millimetre-wave RF MMICs. The coaxial design of the 1.0 mm connector minimizes the use of waveguide in waveguide-based measurements to a single step. The connector is one of the costlier ones in the market.

8. W Connector

The W connector was designed and developed by Wiltron/Anritsu Corporation in 1996. The W connector performs in the W band or millimetre-wave covering a frequency range from 70 GHz to 110 GHz. The performance characteristics of this connector are similar to that of a HP 1.0 mm connector. Designed to be as simple as a SMA connector, it facilitates easy installation and operation during its usage. The W connector is assembled with UT-47 coaxial cable in probe station applications.

Key Words : APC-7 Connector ,  APC-3.5 Connector ,  2.4mm Connector ,  1.85mm Connector ,  K Connector ,  V Connector ,  1.0mm Connector ,  W Connector

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