Comments on “Wideband Radiation Reconfigurable Microstrip Patch Antenna Loaded With Two Inverted U-Slots”

This comment investigates some missing fundamental simulation and measurement results affecting the practical performance of the antenna presented in [1] . In order to properly demonstrate the practical consequences of these omissions, we provide simulation results as well as experimental validation using a prototype with the exact dimensions as in [1] , fed with an ultrawideband coupler [2] , as shown in Fig. 1 . Radavaram and Pour [1] have claimed 68% fractional bandwidth for a multiport antenna based only on a single-port input reflection coefficient ( S ₁₁ ). Unfortunately, the mutual coupling between the antenna ports ( S ₂₁ ) is not shown in their article. We have performed corresponding simulations using Ansys HFSS and found that the missing coupling coefficient between the elements within the band of interest has a magnitude close to 0 dB, which is validated by the experimental results, as illustrated in Fig. 2(a) . This suggests that the proposed design is operating as a wideband bandpass filter in lieu of a radiating element. The clear misunderstanding in the scattering performance arises from the fact that for dual-port antennas fed by in-phase and out-of-phase inputs, the active scattering parameters are of fundamental importance. Active scattering parameters for dual-port devices are defined as the combinations of S ₁₁ and S ₂₁ (some references, such as [4] and [5] , use differential and common mode scattering parameters or S_dd and S_cc ). They determine the overall scattering performance when a feeding network is connected to a multiport antenna. For instance, [3] (see [1, Ref. 20] ), [4] , and [5] are aimed at reducing S _dd11 to below −10 dB for the differential S-parameter. They use the correct definition of S _dd11 , as given in the following [3, eq. (8)] :