Reflections in coaxial connectors

Technics

Assembly and functional description

All connectors produce signal reflections at high frequencies. This is due to a minor variation of the connector impedance to that of the overall system. These irregularities have either inductive or capacitive behaviour depending on the operating frequency and the degradation of the performance at higher frequencies. The unmatched impedances can also be caused by a combination of internal dimension changes and tolerances, material and termination techniques. Different mating interfaces can also effect the overall system performance.
The reflection performance is commonly expressed as returnloss (a), S-Parameter (S-11), the Voltage Standing Wave Ratio VSWR (s) and the reflection coefficient (r) and all three correspond to each other mathematically:

Return loss [-dB]	VSWR s	Reflection coefficient r
1	17,3910	0,8913
2	8,27242	0,7943
3	5,8480	0,7079
4	4,4194	0,6310
5	3,5698	0,5623
6	3,0095	0,5012
7	2,6146	0,4467
8	2,3229	0,3981
9	2,0999	0,3548
10	1,9250	0,3162
11	1,7849	0,2818
12	1,6709	0,2512
13	1,5769	0,2239
14	1,4985	0,1995
15	1,4326	0,1778
16	1,3767	0,1585
17	1,3290	0,1413
18	1,2880	0,1259
19	1,2528	0,1122
20	1,2222	0,1000
21	1,1957	0,0891
22	1,1726	0,0794
23	1,1524	0,0708
24	1,1347	0,0631
25	1,1192	0,0562
26	1,1055	0,0501
27	1,0935	0,0447
28	1,0829	0,0398
29	1,0736	0,0355
30	1,0653	0,0316

Return loss [-dB]	VSWR s	Reflection coefficient r
31	1,0580	0,0282
32	1,0515	0,0251
33	1,0458	0,0224
34	1,0407	0,0200
35	1,0362	0,0178
36	1,0322	0,0158
37	1,0287	0,0141
38	1,0255	0,0126
39	1,0227	0,0112
40	1,0202	0,0100
41	1,0180	0,0089
42	1,0160	0,0079
43	1,0143	0,0071
44	1,0127	0,0063
45	1,0113	0,0056
46	1,0101	0,0050
47	1,0090	0,0045
48	1,0080	0,0040
49	1,0071	0,0035
50	1,0063	0,0032
51	1,0057	0,0028
52	1,0050	0,0025
53	1,0045	0,0022
54	1,0040	0,0020
55	1,0036	0,0018
56	1,0032	0,0016
57	1,0028	0,0014
58	1,0025	0,0013
59	1,0022	0,0011
60	1,0020	0,0010

Due to the increased accuracy of cutting and solder termination of semi rigid cables, smaller impedance irregularities are achieved when compared with flexible coaxial cables. Connector styles also effect the reflection i.e. straight connectors generally produce a better performance than right angle versions. Therefore the reflection performance can vary within the same connector series dependent on style and cable.

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