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Electronic Warfare and Radar Systems Engineering Handbook
- Microwave Coaxial Connectors -

[Go to TOC]

MICROWAVE COAXIAL CONNECTORS



For high-frequency operation, the average circumference of a coaxial cable must be limited to about one wavelength in order to reduce multimodal propagation and eliminate erratic reflection coefficients, power losses, and signal distortion. Except for the sexless APC-7 connector, all other connectors are identified as either male (plugs) which have a center conductor that is a probe or female (jacks) which have a center conductor that is a receptacle. Sometimes it is hard to distinguish them as some female jacks may have a hollow center "pin" which appears to be male, yet accepts a smaller male contact. An adapter is an . zero loss interface between two connectors and is called a barrel when both connectors are identical. Twelve types of coaxial connectors are described below, however other special purpose connectors exist, including blind mate connectors where spring fingers are used in place of threads to obtain shielding (desired connector shielding should be at least 90 dB). Figure 1 shows the frequency range of several connectors and Figure 2 shows most of these connectors pictorially (~ actual size).

1.  APC-2.4 (2.4mm) - The 50 S APC-2.4 (Amphenol Precision Connector-2.4 mm) is also known as an
     OS-50 connector. It was designed to operate at extremely high microwave frequencies (up to
     50 GHz).
2.  APC-3.5 (3.5mm) - The APC-3.5 was originally developed by Hewlett-Packard (HP), but is now
     manufactured by Amphenol. The connector provides repeatable connections and has a very low
     VSWR. Either the male or female end of this 50 Ω connector can mate with the opposite type of
     SMA connector. The APC-3.5 connector can work at frequencies up to 34 GHz.
3.  APC-7 (7mm) - The APC-7 was also developed by HP, but has been improved and is now
     manufactured by Amphenol. The connector provides a coupling mechanism without male or female
     distinction and is the most repeatable connecting device used for very accurate 50 Ω measurement
     applications. Its VSWR is extremely low up to 18 GHz. Other companies have 7mm series available.
4.  BNC (OSB) - The BNC (Bayonet Navy Connector) was originally designed for military system
     applications during World War II. The connector operates best at frequencies up to about 4 GHz;
     beyond that it tends to radiate electromagnetic energy. The BNC can accept flexible cables with
     diameters of up to 6.35 mm (0.25 in.) and characteristic impedance of 50 to 75 Ω. It is now the
     most commonly used connector for frequencies under 1 GHz.
5.  SC (OSSC) - The SC coaxial connector is a medium size, older type constant 50 Ω impedance. It is
     larger than the BNC, but about the same as Type N. It has a frequency range of 0-11 GHz.
6.  C - The C is a bayonet (twist and lock) version of the SC connector.
7.  SMA (OSM/3mm) - The SMA (Sub-Miniature A) connector was originally designed by Bendix Scintilla
     Corporation, but it has been manufactured by the Omni-Spectra division of M/ACOM (as the OSM
     connector) and many other electronic companies. It is a 50 Ω threaded connector. The main
     application of SMA connectors is on components for microwave systems. The connector normally
     has a frequency range to 18 GHz, but high performance varieties can be used to 26.5 GHz.
8.  SSMA (OSSM) - The SSMA is a microminiature version of the SMA. It is also 50 Ω and operates to
     26.5 GHz with flexible cable or 40 GHz with semi-rigid cable.
9.  SMC (OSMC) - The SMC (Sub-Miniature C) is a 50 Ω or 75 Ω connector that is smaller than the SMA.
     The connector can accept flexible cables with diameters of up to 3.17 mm (0.125 in.) for a frequency range
     of up to 7-10 GHz.
10.  SMB (OSMB) - The SMB is like the SMC except it uses quick disconnect instead of threaded fittings.
       It is a 50 / 75 Ω connector which operates to 4 GHz with a low reflection coefficient and is useable to 10 GHz.
11.  TNC (OST) - The TNC (Threaded Navy Connector) is merely a threaded BNC. The function of the thread is
       to stop radiation at higher frequencies, so that the connector can work at frequencies up to
      12 GHz (to 18 GHz when using semi-rigid cable). It can be 50 or 75 Ω.
12.  Type N (OSN) - The 50 or 75 S Type N (Navy) connector was originally designed for military systems during
       World War II and is the most popular measurement connector for the frequency range of 1 to 11 GHz. The
       precision 50 S APC-N and other manufacturers high frequency versions operate to 18 GHz.

Note: Always rotate the movable coupling nut of the plug, not the cable or fixed connector, when mating connectors. Since the center pin is stationary with respect to the jack, rotating the jack puts torque on the center pin. With TNC and smaller connectors, the center pin will eventually break off.
 

An approximate size comparison of these connectors is depicted below (not to scale).

RF Cafe - Coaxial connector sizes

Frequency Range of Microwave Connectors - RF Cafe

Figure 1. Frequency Range of Microwave Connectors


APC 2.4 Jack - APC 3.5 Jack - RF Cafe
APC 2.4 Jack - APC 3.5 Jack
SC Jack - Type N Jack - RF Cafe
SC Jack - Type N Jack
Type N Jack - TNC Jack - RF Cafe
Type N Jack - TNC Jack
SMA Plug - TNC Plug - RF Cafe
SMA Plug - TNC Plug
SSMA Jack - BNC Jack - RF Cafe
SSMA Jack - BNC Jack
Type N Plug - TNC Jack - RF Cafe
Type N Plug - TNC Jack

Figure 2.  Microwave Coaxial Connectors (Connector Orientation Corresponds to Name Below It)


Standard Waveguide - 7mm - RF Cafe
Standard
Waveguide - 7mm
SMC Plug - SMA Jack - RF Cafe
SMC Plug - SMA Jack
Double ridge Waveguide - SMA Jack - RF Cafe
Double ridge
Waveguide  - SMA Jack
7mm - 3.5mm Plug - RF Cafe
7mm - 3.5mm Plug

Figure 2. Microwave Coaxial connectors (Continued)


Table of Contents for Electronics Warfare and Radar Engineering Handbook
Introduction | Abbreviations | Decibel | Duty Cycle | Doppler Shift | Radar Horizon / Line of Sight | Propagation Time / Resolution | Modulation | Transforms / Wavelets | Antenna Introduction / Basics | Polarization | Radiation Patterns | Frequency / Phase Effects of Antennas | Antenna Near Field | Radiation Hazards | Power Density | One-Way Radar Equation / RF Propagation | Two-Way Radar Equation (Monostatic) | Alternate Two-Way Radar Equation | Two-Way Radar Equation (Bistatic) | Jamming to Signal (J/S) Ratio - Constant Power [Saturated] Jamming | Support Jamming | Radar Cross Section (RCS) | Emission Control (EMCON) | RF Atmospheric Absorption / Ducting | Receiver Sensitivity / Noise | Receiver Types and Characteristics | General Radar Display Types | IFF - Identification - Friend or Foe | Receiver Tests | Signal Sorting Methods and Direction Finding | Voltage Standing Wave Ratio (VSWR) / Reflection Coefficient / Return Loss / Mismatch Loss | Microwave Coaxial Connectors | Power Dividers/Combiner and Directional Couplers | Attenuators / Filters / DC Blocks | Terminations / Dummy Loads | Circulators and Diplexers | Mixers and Frequency Discriminators | Detectors | Microwave Measurements | Microwave Waveguides and Coaxial Cable | Electro-Optics | Laser Safety | Mach Number and Airspeed vs. Altitude Mach Number | EMP/  Aircraft Dimensions | Data Busses | RS-232 Interface | RS-422 Balanced Voltage Interface | RS-485 Interface | IEEE-488 Interface Bus (HP-IB/GP-IB) | MIL-STD-1553 & 1773 Data Bus |
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