Jussi Rahola

Quarter-wavelength wideband slot antenna for 3-5 GHz mobile applications

In this letter, a quarter-wavelength ultra-wideband (UWB) slot antenna for 3-5 GHz mobile applications is proposed. Numerical results indicate that the performance of the antenna is insensitive to the size of the ground plane and an optimal performance of the antenna can be easily obtained by varying the dimensions of the slot and tuning stubs. Furthermore, a prototype of the antenna is made and a good agreement between simulation and measurement is achieved.

Power Waves and Conjugate Matching

The concept of power waves gives more natural relations between incident and reflected power in a microwave network than the typically used traveling waves. The reflection coefficient for power waves directly describes the reflection of power whereas the reflection coefficient of traveling waves describes the reflection of the waves themselves. In this brief, new physical reasoning of power waves is given starting from the principle of conjugate matching. In addition, a new formula for the reference impedances for a two-port system is given such that the system is simultaneously conjugate matched for both ports.

Optimal antenna placement for mobile terminals using characteristic mode analysis

When an electrically small antenna element is placed on a small finite ground plane, as in mobile terminals, the ground plane resonances strongly affect the impedance and radiation characteristics of the antenna system. In this paper, we show how characteristic mode analysis can predict the optimal locations of antennas on finite ground planes. As patch-type antennas couple to the ground plane resonances mainly through the electric field, it is natural that the strongest coupling and thus the maximum impedance bandwidth is obtained when the antenna element is placed at the maximum of the electric field of a ground plane mode. This is verified by moving a small probe antenna at selected locations over a rectangular 100 mm by 40 mm ground plane and by computing the obtainable bandwidth at each point.

Electromagnetic Sensitivity Analysis and Shape Optimization Using Method of Moments and Automatic Differentiation

Sensitivity analysis is an important part of gradient-based optimization of electromagnetic devices. We demonstrate how sensitivity analysis can be incorporated into an existing in-house method of moments solver with a relatively small amount of labor by using a technique called automatic differentiation (AD). This approach enables us to obtain (geometrical) sensitivities of the discrete solution with accuracy up to numerical precision. We compare the assembly time and memory usage of the modified and original solvers. Moreover, we optimize the shape of a dipole antenna and the dimensions of a Yagi-Uda array using the presented AD technique, traditional response level finite difference sensitivities, and so-called feasible adjoint sensitivity technique.

Compact printed patch and bent-patch monopole Ultra-Wideband (UWB) antennas for mobile terminals

In this paper, in order to reduce the effective size of UWB antennas (in other words, to increase the effective size of the PWB), a printed patch monopole UWB antenna that is located at the top-left (or right) corner of the PWB is proposed. With such an arrangement, part of the ground plane located at the top-right (or left) corner of PWB can be retained, which, in turn, reduces the effective size of the antenna. To further decrease the effective size of the antenna, a bent-patch monopole UWB antenna is also proposed. Moreover, the wider bandwidth of the proposed monopole antennas is achieved by adjusting the gaps between the edge of the patch /monopole and the edge of the ground plane surrounding the patch.

Removing the effect of antenna matching in isolation analyses using the concept of electromagnetic isolation

Isolation between antennas in a multiantenna terminal plays an important role in the performance analysis of wireless systems. When comparing different methods for increasing isolation between the antennas, it is important to note that isolation depends strongly on antenna matching. The effect of matching on isolation can be removed by numerically matching two antennas simultaneously. The resulting isolation is called electromagnetic isolation and it gives the worst-case isolation between the antennas. An example of the application of this concept to the analysis of ground plane slots is presented. It is shown that the phase information in scattering and impedance matrices is essential to obtain reliable values of the electromagnetic isolation.

Numerical and experimental study of a quarter-wavelength wideband slot antenna for mobile applications

This paper describes a quarter-wavelength ultra-wideband (UWB) slot antenna, fed by an L-shaped tuning stub, for 3-5 GHz mobile applications. In particular, geometrical parameters that affect the performance of the antenna are investigated. Numerical results indicate that the performance of the antenna can be easily optimized by varying the location and dimension of the tuning stub. Furthermore, a prototype of the antenna is made and a good agreement between simulation and measurement is achieved.

Characteristic modes and antenna bandwidth

We examine the connection between the characteristic mode analysis of a radiating body and the impedance bandwidth of the body when used as an antenna. The impedance bandwidth depends on the characteristic modes of the body and how the various modes are excited. To estimate the obtainable bandwidth of non-resonant antennas, we use the bandwidth potential technique which gives more reliable and practical results for wideband antennas than the Q factor analysis.

Estimation of signal correlation of diversity antennas from complex radiation patterns

A new formula is derived for the estimation of signal correlation based on radiation patterns of multiantenna terminals and a power distribution model of the radio channel. The new formula takes into account the correlation between the vertical and horizontal components of the incoming signals in the radio channel. The formula can be used in situations where the properties of the radio channel are averaged over some tens of seconds and a distribution of correlation values over different radio environments is determined. An example of the effect of different radio channel parameters to the antenna correlation values is presented.

Simultaneous multiport matching optimization for antennas and amplifiers

In this paper we discuss the differences of simultaneous multiport matching for antennas and non-radiating RF components, such as amplifiers. In antenna matching, the goal is to get maximal efficiency for all antenna ports, and this is not necessarily achieved with the best possible impedance match. In contrast, for non-radiating multiport RF systems the goal is typically to get best transfer of power between the ports, which is related to but not equivalent to having an optimal impedance match for both ports.