Asim Ghalib

TCM Analysis of Defected Ground Structures for MIMO Antenna Designs in Mobile Terminals

In this paper, the theory of characteristic modes (TCMs) is used for the first time to analyze the behavior of defected ground structures (DGS), when added to antenna designs. A properly designed DGS introduces currents opposite in direction to the original characteristic modes (CM) currents thus reducing mutual coupling. TCM is also applied to multiple-input-multiple-output (MIMO) antenna systems to develop a systematic approach that can predict whether the isolation can be enhanced further or not. For this purpose two 4-element and one 2-element MIMO designs, i.e. monopole and planar inverted-F antennas are studied. The addition of different antenna elements affects the CM significantly as well as differently. Some of the CM excited on the antenna surface contributes to the coupling between the antenna ports that is why they can be classified as coupling modes. To improve the isolation, the DGS should be introduced at certain locations that blocks the coupling modes but at the same time does not affect the non-coupling modes. If there is no such location or the current on the surface of the chassis for coupling and non-coupling modes is approximately same, the isolation cannot be enhanced further. Using this approach, isolation was improved on an average by 11 dB in all the designs considered, giving the most isolation enhancement following a systematic way compared to other works.

Compact 4-element MIMO antenna with isolation enhancement for 4G LTE terminals

In this work, a wide-band, planar, printed inverted-F antenna (PIFA) is proposed with multiple-input-multiple-output (MIMO) antenna configuration. The MIMO antenna system consists of 4-elements operating at 2.1 GHz frequency band for 4G LTE applications. The proposed design is compact, low profile and suitable for wireless handheld devices. The MIMO antenna is fabricated on commercially available FR4 substrate with εr equal to 4.4. The dimensions of single element are 26×6 mm2 with board volume equal to 100×60×0.8 mm3. Isolation is improved by 5 dB in the proposed design using ground slots. Characteristics mode analysis (CMA) is used to analyze the behaviour of the antenna system.

Analyzing DGS behavior for a MIMO antenna system using theory of characteristic modes

In this paper, the Theory of characteristic modes (TCM) is used for analyzing the behavior of a defected ground structure (DGS) as an Isolation enhancement method for Multi-Input-Multi-Output (MIMO) antenna systems. For analysis purposes a MIMO antenna system consisting of PIFA elements is used. Modes of the antennas were analyzed and the modes contributing to coupling were blocked by the DGS. The other modes are not significantly affected by the addition of the DGS. Using this approach we were able to get 5 dB extra isolation in the Bandwidth of interest.

A comparison between the antenna current green function and theory of characteristic modes

In this paper, we compare the procedures and practicality/complexity of the antenna current green function (ACGF) and theory of characteristic modes (TCM) when applied to antenna design problems. Some recent works on both methods are summarized. The ACGF is an analytical method that relies on the antenna current equation, that is why its application is limited. In TCM the main focus, thus far has been on the chassis behavior and excitation of the modes on the chassis. In real scenarios, the chassis can not be used as the main radiating element because it acts as a base to many electronic components and this will obviously effect the natural modes of the antenna.

Excitation shape and placement effects on natural radiating modes

Theory of characteristic modes (TCM) is becoming used more often for the analysis of chassis based radiators. Normally the chassis is modified for different reasons such as excitation of chassis modes or for the antenna placement. In this work, we investigate five shapes at various location on the chassis and study their effect on radiating modes. It was observed that for same size of slots, it is the shape of slot that determines how much the chassis modes will be affected. For slots irrespective of their shape having small size as compared to chassis, no new modes are generated.

Characteristic modes of circular slot antennas etched on a finite ground plane

The theory of characteristic modes (TCM) is gaining momentum in the analysis of slot antennas, whose size is comperable to the metallic plane or chassis. In this paper, we will analyze the behavior of a circular slot on a fixed ground plane (GND). Circular slots having small dimensions compared to the GND do not alter the characteristic mode (CM) current distribution and the Modal Significance (MS) plots significantly but when the size of such slots increases, new slot modes are created. Some of the chassis modes are modified due to the presence of a slot at their current maxima. The generation of the slot mode depends on the size and the location of circular slot on the chassis.

A slotted waveguide based MIMO antenna system for wireless access points

In this work, a slotted rectangular waveguide (SRWG) with multiple input multiple output (MIMO) antenna configuration for wireless access points is presented. The MIMO antenna system consists of 4 elements and operates from 5 to 6 GHz. A Genetic Algorithm (GA) was applied to find the optimized position of the slots. A gain of 13.2 dB was obtained over the whole band. The dimensions of the waveguide (WG) were considered according to a standard WG WR159. The Size of a single element WG was 40.38 × 20.1 × 308.06 mm3. The beam of the antenna was tilted by 15°, while the side lobe level (SLL) on average over the whole band was 14.25 dB. The envelope correlation coefficient (ECC) of the MIMO design was 0.002 which represents highly uncorrelated beams.