同轴线的基本结构
具有多层结构，中心导体外包裹有绝缘层，外层导体和外被的电缆被称为同轴线。同轴电缆的外导体起着电磁屏蔽的作用，通过中心导体传输的电信号不易受到外界电磁波(电磁噪声)的影响。
    极细同轴线连接器
极细同轴线连接器主要用于连接通过极细同轴线的差分传输方式的模块板之间的数字信号。为了进行适当的信号传输，传输信号的中心导体需要通过连接器的端子连接到PCB板上的信号电路。电缆的外层导体需要通过连接器的金属部件-外壳而电气性连接到PCB板上。外层导体通过连接器外壳与PCB板的电气连接称为“接地”。

以下是对JAE FI-J40系列极细同轴线的分析
Thin wire coaxial connector for small portable devices
 
特征：                               

1. The smallest board mounting space in the industry (compared with other 0.4mm pitch product) with 2.5mm depth, 21.7mm pitch direction (for 40 pins), and 1.58mm height.                     
2. Ensures 0.4mm effective contact length and stable connection.
3. Highly reliable structure by supporting the contact points with contacts
4. Ensures low contact resistance with Gold plated ground contact points between plug and receptacle with stable connection.
5. Mis-mating prevention structure
6. Compatible with AWG #44 and #42 cables
7. Receptacle 

          Available on embossed tape for automatic mounting and ensures high mounting performance with adsorption cap.

1. Plug

           Small hinge can be passed through after harness processing.

 一般规格：
 

Number of Positions	40
Rated Current	AC, DC each 0.3 A/ contact
Rated Voltage	AC, DC each 50 V/ contact
Dielectric Withstanding Voltage	250 VACr.m.s. (1 minute)
Insulation Resistance	100 megohm min.
Contact Resistance	40 milliohm max.
Operating Temperature Range	-40 deg. C to +85 deg. C
Applicable Cable	#44, #42 AWG (fine-wire coaxial)
Durability Mating Cycles	30 times

本系列的产品列表明细：
 

Part Number	Pincount	connectorType	Features
FI-J40C2-SH-D-10000	30	Plug side shell	Thin wire coaxial connector for small portable devices, Plug side shell, 40 pos., Plug side shell
FI-J40C5-T3000	30	Plug side insulatorr	Thin wire coaxial connector for small portable devices, Thin wire coaxial connector for small portable devices, 40 pos., Plug side insulator
FI-J40S-VF15N	30	Receptacle	Thin wire coaxial connector for small portable devices, Thin wire coaxial connector for small portable devices, 40 pos., Receptacle
FI-J40S-VF15N-R3000	30	Receptacle	Thin wire coaxial connector for small portable devices, Thin wire coaxial connector for small portable devices, 40 pos., Receptacle