Omid Sotoudeh

Calculated and measured absorption cross sections of lossy objects in reverberation chamber

Reverberation chambers can be used to measure radiation efficiency of small antennas when these are located close to lossy objects. The lossy objects represent a heavy loading of the chamber. This loading is characterized by the mean absorption cross section of the lossy objects. This paper describes how this mean absorption cross section can be calculated from the scattered far field of an object by using the forward scattering theorem, or from a more laborious near-field evaluation. Results for lossy spheres and cylinders are calculated by using three different codes, based on spherical mode expansion, finite difference time domain techniques, and moment methods, respectively. The results for the cylinder are compared with measured levels in a reverberation chamber.

Single- and dual-band multimode hard horn antennas with partly corrugated walls

We introduce a partly corrugated hard horn, consisting of a smooth-walled horn with an attached longitudinally corrugated outer section. This alleviates the problems with the manufacturing when the longitudinal corrugations extend into the throat of the horn. The transition between the inner smooth walled part and the outer corrugated part is abrupt. This is used and controlled to design better and shorter single-band horns than otherwise possible. Furthermore, it enables the design of dual-band horns with low cross-polarization and high gain, for multifunction use at Ka-band with transmit and receive frequencies in the same antenna. Measurements on a model of such a dual-band horn are presented and discussed.

Dual band hard horn for use in cluster-fed multi-beam antennas in Ka-band

A hard hom for dual band operation is designed. Emphasis has been put on low cross-polar performance over both the Rx and Tx bands in the Ka-band multimedia application. The horn has also been designed with manufacturability in mind, with direct transition from the metal section to the corrugated section, and, with a corrugated section which is slightly conical with constant number of corrugations. The horn operates with high efficiency at the lower band (17.7-20.2 GHz) and medium efficiency at the higher band (27.5-30.0 GHz), and it has a maximum cross-polar level within the main beam which is low over both bands. The return-loss is below -35 dB over both bands.

Study of diversity gain obtained with two PIFA antennas on a small ground plane for a UMTS terminal

In this work, diversity performance of two PIFA antennas on a small ground plane is studied. In this case, when the second antenna is located on the left edge, better diversity gain can be obtained. Matching network can be used to reduce the correlation coefficient and consequently increase the diversity gain.

Theoretical study of the corrugated hard horn used as feed in multi-beam antennas for dual band operation at 20/30 GHz

We have demonstrated that in a cluster-fed reflector, a normal single-tuned hard horn can satisfy the usual -25 dB system requirements for the cross polarization over a large frequency band, but it cannot completely satisfy the requirements for the copolar level in the neighboring beam We have also tried larger reflector diameters than those presented here. In those cases, the beam isolation becomes better, but the 30 GHz footprint gets a dip in the center The reason for the dip is that the sidelobe of the feed is illuminating the reflector at 30 GHz. This may be improved for finite lengths of the horn, for which phase of the aperture field at the horn causes a beam broadening mainly at 30 GHz.

Characterization of lossy cylinder in reverberation chamber by computed and measured absorption cross sections

Recently it has been shown that reverberation chambers can be used to measure radiation efficiency and input impedance of small antennas. In particular, the it can be used to measure these characteristics for small antennas located close to lossy objects, such as a mobile phone antenna located in different positions relative to a head phantom filled with a brain tissue equivalent liquid. The present paper presents calculated and measured results for a lossy cylinder. The cylinder is filled with a brain tissue equivalent liquid of the type used in head phantoms when measuring specific absorption rate (SAR). We get the mean absorption cross section of the cylinder from measured average power levels in the reverberation chamber by using Hills formulas, and these are compared with the computed results.

Design of hard horn antenna using both single dominant quasi-TEM mode model and mode-matching

We have presented a simple design of the hard horn antenna, electrically designed to be used as feed in the Ka-band cluster-fed multibeam antenna systems, and which can cover both bands of the system with medium efficiency >75 % and maximum cross-polar level below -25 dB. We have also shown some comparisons between a classical quasi-TEM mode model and an accurate mode matching program, and defined an apex length of the hard horn which may be used for its design. These comparisons indicate that the classical model is, due to the fast computational time and rather good agreement, suitable for initial design and study of the hard horn.