Measuring transmission between four antennas in microwave cavities, we investigate directly the channel cross-correlations C of the cross sections σ ab from antenna at ra to antenna r b . Specifically we look for the CΣ and CΛ, where the only difference is that CΛ has none of the four channels in common, whereas CΣ has exactly one channel in common. We find experimentally that these two channel cross-correlations are anti-phased as a function of the channel coupling strength, as predicted by theory. This anti-correlation is essential to give the correct values for the universal conductance fluctuations. To obtain a good agreement between experiment and predictions from random matrix theory the effect of absorption had to be included.PACS numbers: 03.65. Nk, 42.25.Bs Quantum transport in mesoscopic systems is at the center of interest in different fields for its relevance to quantum devices and information technology [1,2]. Quantum transport in mesoscopic systems occurs when the coherence length is larger than the system size [3]. From this point of view microwave experiments are an extraordinary laboratory for testing quantum transport in the mesoscopic regime, since the coherence length is basically infinite. Within this regime the transport is ballistic when the mean free path l is larger than the system size L and it is diffusive when l < L < ξ, where ξ is the localization length. One of the prominent examples of quantum phenomena in mesoscopic systems is given by the universal conductance fluctuations (UCF) [1,4,5]. In the UCF regime, the dimensionless variance of the conductance is independent of sample size or disorder strength and it attains the universal value of 1/8 in the ballistic regime and of 2/15 in the diffusive regime. These universal values are valid in the limit of large number of channels in the external leads and of perfect coupling between the leads and the disordered systems. On the other side, the transport properties in the mesoscopic regime are strongly affected by the coupling strength with the leads [6, 7] and by absorption or dephasing. The coupling strength with the channels can be tuned in several relevant systems, such as quantum dots or microwave cavities [1], and the number of channels can be small.At the core of UCF lies the strong correlations between the transmissions through different channels. These correlations are the signature of coherent transport, indeed for incoherent transport the correlations are zero. Channel correlations play an important role in mesoscopic transport [6], but their direct measurement is a difficult task. Here we present the results obtained from the analysis of transport through a chaotic microwave 0 0.2 0.4 0.6 0.8 1 κ -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006 C Σ,Λ FIG. 1. (color online) Correlation functions CΣ (blue dots) and CΛ (red squares) as a function of the mean coupling κ using a frequency average of 100 MHz and all measured samples. Symbols are experimental data. Numerical data (dashed curves) have been obtained from a GO...