How do you choose the right RF connector?

Match the connector to the system requirements: (1) Frequency: BNC for DC-4 GHz, SMA for DC-18 GHz (26.5 GHz for precision SMA), N-type for DC-18 GHz with higher power, 2.92mm (K) for DC-40 GHz, 1.85mm for DC-65 GHz, 1.0mm for DC-110 GHz. (2) Power: larger connectors handle more power. N-type handles 300W at 1 GHz, SMA handles 100W at 1 GHz. (3) Mating cycles: SMA rated for 500 cycles, precision connectors for 1000+. (4) Environment: IP67-rated connectors for outdoor use, hermetically sealed for space. (5) Cost: BNC and SMA are commodity connectors. Precision 1.0mm connectors cost $200+ each.

What determines connector frequency range?

The maximum frequency is set by the cutoff frequency of the first higher-order mode in the connector's air-dielectric coaxial cross-section. The interface diameter determines this cutoff: larger connectors have lower cutoff frequencies. The standardized interface dimensions are: Type N: 7mm interface, cutoff approximately 18 GHz. SMA: 3.5mm compatible interface, cutoff approximately 26.5 GHz. 2.92mm (K): cutoff approximately 40 GHz. 2.4mm: cutoff approximately 50 GHz. 1.85mm (V): cutoff approximately 65 GHz. 1.0mm (W1): cutoff approximately 110 GHz. Within a connector family, precision versions have tighter tolerances and better return loss than commercial versions.

What is the difference between SMA and 3.5mm connectors?

SMA and 3.5mm connectors share the same interface dimensions and can mate with each other. The difference is precision: SMA uses a PTFE-filled dielectric bead in the interface, limiting it to approximately 18-24 GHz. The 3.5mm connector uses an air dielectric interface with precision center conductor dimensions, extending the useful range to 26.5-34 GHz. SMA connectors are cheaper and adequate for most applications below 18 GHz. 3.5mm connectors are used for calibration standards and precision measurements up to 26.5 GHz. Never use a standard SMA where a 3.5mm is required for calibration, as the PTFE bead degrades the calibration accuracy above 18 GHz.

Interconnects

RF Connector

/kuh-nek-ter/

An RF Connector is a demountable, impedance-controlled interface for coaxial systems. The interface diameter determines the maximum frequency: N-type (18 GHz), SMA (18-26.5 GHz), 2.92mm/K (40 GHz), 1.85mm/V (65 GHz), 1.0mm/W (110 GHz). Connector quality directly affects return loss, insertion loss, and measurement repeatability across the entire RF system.

Category: Interconnects

Z₀: 50Ω or 75Ω

Key Spec: Return loss, freq range

Understanding RF Connectors

The connector is often the weakest link in an RF system. A perfect amplifier connected with a poor connector will show poor return loss, amplitude ripple, and phase instability. Every connector introduces a small impedance discontinuity that creates reflections. The smaller the discontinuity, the better the connector. Precision connectors are manufactured to micrometer tolerances to minimize these discontinuities, and the interface diameter determines the highest frequency at which the connector can maintain its impedance.

Connector Interface Dimensions

Connector VSWR:
VSWR = (1+|Γ|)/(1−|Γ|)

Insertion loss per mated pair:
IL = −10log(1−|Γ|²) + α_conductor

Repeatability:
ΔIL ≤ 0.03 dB (precision)
ΔIL ≤ 0.15 dB (general)

RF Connector Comparison

Connector	Freq Range	Power (1 GHz)	Mating Cycles	Typical RL	Application
BNC	DC-4 GHz	80W	500	>20 dB	Lab, video, test
N-type	DC-18 GHz	300W	500	>25 dB	Base stations, power
SMA	DC-18 GHz	100W	500	>20 dB	General RF, PCB
2.92mm (K)	DC-40 GHz	50W	500	>22 dB	mmWave, 5G
1.85mm (V)	DC-65 GHz	10W	500	>20 dB	V-band, E-band
1.0mm (W1)	DC-110 GHz	1W	500	>18 dB	W-band, test

Key Equations

Decibel conversion:
Power: dB = 10log(P₂/P₁)
Voltage: dB = 20log(V₂/V₁)

dBm to watts:
P(W) = 10^{(dBm−30)/10}
0 dBm = 1 mW, +30 dBm = 1 W

Wavelength:
λ = c/f = 300/f(MHz) meters

Comparison

Type	Max freq	IL @max	VSWR	Application
SMA	18 GHz	0.15 dB	1.15:1	General RF
N	11 GHz	0.10 dB	1.10:1	Base station
2.92mm (K)	40 GHz	0.25 dB	1.25:1	mmW test
1.85mm (V)	67 GHz	0.35 dB	1.35:1	E/V-band
1.0mm	110 GHz	0.40 dB	1.50:1	W-band test

Common Questions

Frequently Asked Questions

How to choose?

Match to frequency (BNC DC-4G, SMA DC-18G, 2.92mm DC-40G, 1.85mm DC-65G, 1.0mm DC-110G), power (N-type 300W, SMA 100W), environment (IP67 outdoor), and budget (1.0mm = $200+ each).

What sets frequency range?

Interface diameter determines TE11 cutoff. Larger = lower frequency limit. Standard interface dimensions: 7mm, 3.5mm, 2.92mm, 2.4mm, 1.85mm, 1.0mm. Precision versions have tighter tolerances and better RL.

SMA vs. 3.5mm?

Same interface, mate together. SMA: PTFE bead, good to 18-24 GHz, cheaper. 3.5mm: air dielectric, precision, good to 26.5-34 GHz. Never use SMA for calibration requiring 3.5mm accuracy.

Related Terms

← Compression Point Conversion Loss →