Elham Ebrahimi

Integrated Wide-Narrowband Antenna for Multi-Standard Radio

An integration concept for multi-standard antennas is described. This technique is based on utilizing a relatively large antenna that is printed on the top side of a substrate, acting as a ground for a smaller antenna. The smaller antenna is printed onto the bottom side of the substrate. To validate this concept, an integrated wide-narrowband demonstrator antenna is presented. This antenna is composed of a shorted microstrip patch integrated with a coplanar waveguide (CPW) fed ultrawideband (UWB) antenna. A prototype of the integrated antenna was fabricated and its performance was verified. This arrangement is a promising candidate for applications where some level of reconfigurability is required. For this reason, a set of external tuning circuits were designed to demonstrate the potential of the proposed configuration for such applications. In order to improve the isolation between the wideband and narrowband ports several modified arrangements were presented and investigated.

A reconfigurable narrowband antenna integrated with wideband monopole for cognitive radio applications

A reconfigurable narrowband antenna integrated with a wideband monopole, suitable for cognitive radio applications, is proposed in this study. A set of matching circuits are designed to demonstrate that the structure can be tuned to wide range of frequencies in the narrowband mode of operation. The integrated structures have been manufactured and measured. The measured results agree well with the simulation results. Investigations show that the simulated total efficiency and realized gain is lower for lower frequency matching circuits, which agrees with the Chu-Harrington curve for electrically small antennas.

Feed network for antenna decoupling

A decoupling network for improving the isolation between two highly coupled antennas is proposed. In this method the input signals are combined linearly so that the mutual coupling between the ports becomes zero. The scattering matrix of the network is found using a mathematical procedure and has been demonstrated in this paper for a previously developed integrated wide/narrow band antenna. For this antenna the network can be realised using a rat race coupler and phase shift elements. Measurement results show that the mutual coupling has improved by 30 dB.

Integration of planar UWB antennas in real-life systems

A planar UWB monopole antenna shows very good radiation characteristics in an isolated scenario. However, in practice it must eventually be placed on or integrated into a printed circuit board (PCB). It is well known that this will degrade the antenna performance due to the field coupling between the antenna and the ground. In this paper, the integration of a CPW fed monopole antenna with a relatively large PCB is studied. To avoid the direct current flow between the antenna and the PCB, the antenna structure and the PCB ground are printed on different layers. To feed the antenna a microstrip to CPW transition is utilized. In order to maintain the radiation characteristic of the antenna when integrated in to the PCB, two pairs of quarter wavelength stubs are placed on the ground plane side.