The radio frequency connector is connected with a coaxial cable, a microstrip line or other radio frequency transmission line to realize the electrical connection and separation of the transmission line or the original part of the transfer of different types of transmission lines. It belongs to a mechatronics product and acts as a bridge.

The model of RF coaxial connector consists of two parts: the main name code and the structure code, separated by a dash “-” in the middle. The main designation code The main designation code of the radio frequency connector adopts the main designation code commonly used in the world, and the naming of different structures of specific products shall be specified by the detailed specifications. Structure code of the structure of the radio frequency connector.

According to the structure of the connection interface:

  • bayonet type (internal bayonet, external bayonet): BNC
  • Thread type (right-hand thread, left-hand thread): L29 (7/16), N, F, TNC, SMA, SMC, SSMA, SSMB, FME, L9 (1.6/5.6), 7mm, 3.5mm, 2.4mm, K (2.92mm), 1.85mm, 1mm;
  • Push type (in-line, self-locking): SMB, SSMB, MCX, MMCX, SMP, SMI, BMA, SAA;
  • Flange connection type

Classified by size:

  • Standard type: UHF, N, 7/16, 7mm;
  • Small size: BNC, TNC;
  • Subminiature: SMA, SMB, SMC, MCX, BMA, SAA, 3.5mm;
  • Micro: SSMA, SSMB, MMCX, 2.4mm, K (2.92mm), 1.85mm, 1mm;

Third, the main specifications of the RF connector

  1. Impedance: Almost all RF connectors and cables are standardized to 50Ω impedance. The only exception is that 75Ω systems are commonly used in cable TV installations. It is also important that the RF coaxial cable connector has the characteristic impedance of the matching cable. If this is not the case, a discontinuity is introduced and loss may result.
  2. VSWR (Voltage Standing Wave Ratio): Ideally, it should be unity, and good design and implementation can keep VSWR below 1.2 within the range of interest.
  3. Frequency range: Now most of the radio frequency work is in the range of 1 to 10GHz, therefore, the connector must have low loss in this area. For the case above 10GHz-there is a lot of work, now things in the 10 to 40GHz range-there are newer connectors among them to choose. They are expensive because of the cable itself.
  4. Insertion loss: This is the connector loss in the frequency range of interest. The loss is usually between 0.1 and 0.3 decibels. Determine how critical per watt (or fractional watt) is in most designs. Even such a small loss must be minimized and included in the link loss budget. It is in the low-noise front end, especially when the signal strength and signal-to-noise ratio are low.
  5. Operation cycle: How many connection/disconnection cycles can be connected and endured and still meet its specifications? This is usually in 500 or 1000 cycles. For threaded connectors, the tightening torque specified by the supplier is an important factor in maintaining performance and reliability.
  6. Power: Power handling is determined by two resistance losses (heating) and insulation breakdown. Although even decades of design are mainly pre-processing tens of watts, today’s design community focuses on low-power devices such as mobile phones, picocells and femtocell base stations, video interfaces, RF and gadgets. These are in the sub 1W range, so the connector can be much smaller and its power rating is a smaller constraint.

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The radio frequency connector is defined as a separable component that is usually installed on a cable or device for electrical connection of a transmission line system. It can be seen from this definition that it has the common feature of the “detachable element” connector. “Transmission line system” refers to the microwave transmission system. The common structure of transmission line is shown in the figure below:

Signal transmission principle

Take the commonly used coaxial line as an example, the main mode of the coaxial line is TEM wave, and the field distribution is shown in the figure below:

The electromagnetic wave transmitted is an oscillating particle wave derived from the same phase and perpendicular electric field and magnetic field in space. It is an electromagnetic field propagating in the form of wave and has wave-particle duality.

Electromagnetic waves move in the form of waves by electric and magnetic fields that oscillate in phase and are perpendicular to each other. The electric field direction, magnetic field direction, and propagation direction of electromagnetic waves are perpendicular to each other. Electromagnetic waves have no longitudinal components and are transverse electromagnetic waves.

Classification and main technical parameters

RF connectors are mainly divided into three categories: RF coaxial connectors, RF triaxial connectors and dual-core symmetrical RF connectors. The main uses are as follows:

  • RF coaxial connector: mainly used to transmit transverse electromagnetic waves (TEM waves);
  • Radio frequency triaxial connector: mainly used in occasions with higher requirements for shielding efficiency, to transmit transverse electromagnetic waves (TEM waves) or transmit pulse waves;
  • Dual-core symmetrical radio frequency connector: mainly used to transmit digital signals with a low speed.

The main performance parameters of radio frequency coaxial connectors

Including characteristic impedance, operating frequency, return loss, insertion loss, isolation, radio frequency leakage, phase consistency, third-order intermodulation, etc.

Commonly used materials and coatings for RF coaxial connectors

The radio frequency connector is mainly composed of outer conductor, inner conductor and insulating support medium and other parts. The commonly used materials are as follows:

  • Outer conductor: stainless steel passivation, copper alloy gold plating, copper alloy nickel plating, copper alloy plating ternary alloy, etc.;
  • Inner conductor: copper alloy plated with gold, copper alloy plated with silver, etc.;
  • Insulation support medium: PTFE, PEI, LCP, etc.

Dosin Hardware Electronics Co., Lrd. produces more than 30 series of RF connector products, such as SMA, SSMA, BMA, SBMA, SMP, SMPM, N, TNC, 2.92, 2.4, 1.85 and other products.

The maximum operating frequency of the product reaches 65GHz. The first sample of the 1.0 series millimeter wave connector with a working frequency of 110 GHz has been successfully developed. It is the first to introduce the L7 series radio frequency coaxial connector with a characteristic impedance of 75Ω and an operating frequency of 6GHz to meet the new needs of the military and civilian products. Products are widely used in weapons and equipment, communications, rail transit and medical fields.