for dBm ,dB,dBi, The following description is correct (). (Select 3 Answers)

In WLAN RF terminology, dBm is an absolute unit expressing power level relative to 1 milliwatt (1 mW = 0 dBm). The units dBi and dBd characterize relative gain; dBi compares antenna gain against an isotropic antenna, while dBd references a half-wave dipole antenna. Decibel (dB) is a dimensionless relative unit used to quantify power ratios or signal gains and losses. Therefore, descriptions A, B, and C accurately define these fundamentals. Statement D is incorrect because the numerical difference between two gain measurements in dBi (14 dBi - 12 dBi) is expressed in relative decibels (2 dB), not 2 dBi, as the isotropic reference cancels out.

D. If the antenna of A is 12dBi, The second antenna is 14dBi, It can be said that A is smaller than B 2dBi is incorrect because subtracting gain values in dBi results in a relative ratio in dB (2 dB), not dBi.

1. Huawei Technologies Co., Ltd., HCIA-WLAN V3.0 Courseware, Module 1: WLAN Basics, "Radio Frequency Fundamentals: dB, dBm, dBi, and dBd."

2. NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B.8: Logarithmic quantities and units.