This paper presents a compact slotted MIMO cube antenna operating at 5.8 GHz, consisting of three orthogonal slots, each with a distinct main direction of radiation. Each slot produces linear polarization enabling the structure to radiate three orthogonal polarizations. This provides spatial diversity which helps mitigating the effects of multipath propagation and enhances the diversity gain. The cube is filled with a dielectric with a relative permittivity, ε r thus reducing the minimum dimension of the cube by a factor of 1/ √ ε r. The antenna has a return loss of 20 dB and a coupling of less than −26 dB between the ports. This paper describes the principle operation as well as the design and manufacturing process of the proposed antenna.

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Printed, circularly polarised, microstrip line fed antenna having asymmetric slotted structure is presented. Two antennas, antenna 1 (A1) and antenna 2 (A2), having the same design but radiating with opposite senses of circular polarisation are fabricated. The geometrical structure consists of uneven combination of elements fixed through parametric variations. The measurements yielded significant impedance bandwidth (IBW) and axial ratio bandwidth (ARBW) for axial ratio (AR) ≤ 3 dB. A1 offered IBW of 9.67 GHz (2.46-12.13 GHz, 132.6%), ARBW of 7 GHz (4-11 GHz, 93.33%) and a peak realised gain of 4.05 dBi. A2 offered IBW of 10.05 GHz (2.55-12.6 GHz, 132.7%), ARBW of 7.3 GHz (3.9-11.2 GHz, 96.7%) and a peak realised gain of 4.1 dBi. This constitutes a wide coverage of over 88% of the ultra-wideband (UWB) spectrum (3.1-10.6 GHz). Omnidirectional radiation patterns and marginal group delays are the other features of these antennas. The proposed design is validated through simulations and experimental investigations.

2287from that part of the trajectory due to the occlusion from the buildings. Instead, signals from BS3 propagate via the identified reflector to this part of the trajectory. These parts of the trajectory are also marked with corresponding NLOS range, via the identified reflector in Fig. 4. Clearly, these markings coincide with the impulse response and explain the NLOS component. Note that the interruption and the NLOS component in Fig. 4 is due to that the van leaves the street with the occlusion for a detour, and when the van returns to the street with the occlusion, the NLOS component is back. Beyond doubt, it is the identified reflector that is active in the NLOS propagation during these segments. VI. CONCLUSIONS AND FUTURE WORKIn this communication we devise a method for estimating a map of NLOS reflectors for a mobile radio network based on multistatic SAR imaging. We apply the back-projection principle for the image creation which is a well known method from computerized tomography and also conventional SAR imaging. The obtained images give promising results where the reflectors are well-correlated with the large buildings detectable in the aerial map of the environment. Also, the possibility to extract which part of the trajectory contributed to different reflectors and from which base station is added. In this way a map where dominating reflectors are present can be built up.The applicability of the estimated reflectors is still unexploited. One possible application area is to consider the estimated reflectors and occlusions in position estimation, [15]. ACKNOWLEDGMENTThe evaluation data from the radio channel measurements has been kindly provided by J. Medbo, Ericsson. REFERENCES[1] M. A. Jensen and J. W. Wallace, "A review of antennas and propagation of channel and radio propagation models for wireless MIMO systems," EURASIP J. Wireless Commun. [3] 3GPP, "Spatial channel model for multiple input multiple output (MIMO) simulations," (TS 25.996). [4] J. Medbo, M. Riback, and J.-E. Berg, "Validation of 3GPP spatial channel model including WINNER wideband extension using measurements," presented at the IEEE Vehicular Technology Conf., 2006. [5] T. Fügen, J. Maurer, T. Kayser, and W. Wiesbeck, "Capability of 3-D ray tracing for defining parameter sets for the specification of future mobile communications systems," IEEE Trans.

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