Mutual coupling effect in closely coupled microstrip antennas.

摘要

The main objective of this dissertation is to study the effect of mutual coupling on wireless communication systems. A typical wireless communication system consists of transmitter and receiver. There are several blocks that construct the transmitter and receiver. Antennas are considered one of the main blocks in the entire system. Operators and network equipment companies are always working diligently to improve the network performance by accommodate the latest technologies. Today, telecommunication technology evolves more rapidly than 20 years ago. This allows operators and OEMs to enable higher capacity, better reliability and a large number of supported users. One example to this motivation is the introduction of MIMO (Multiple Input Multiple Output) technique in wireless networks. MIMO technique brings more challenges and complicity in the antenna design on both transmitter and receiver side. This is due to the number of antennas that are installed close to each other which creates multi-antenna crosstalk. The crosstalk or mutual coupling affects the propagating signals and gain of the antennas. Therefore, reducing the mutual coupling effect on closely coupled antenna elements is considered one of the most important and attractive fields in antenna design.;This dissertation proposes a new optimization technique to reduce the mutual coupling between two coupled microstrip elements. The solution uses Microstrip patch antennas which are placed closely to each other to simulate the coupling. The feed striplines are connected in such a way to cancel the coupling. By choosing the proper values of the thickness, height and length of the connection line between two ports, a significant reduction of mutual coupling is realized. The proposed solution achieved -22 dB of coupling reduction from intensive coupling of -5 dB between two antenna elements. The results showed good agreement between simulation and experiments. The proposed scheme is relatively easy to fabricate and implement in practical applications. This technique can be referred to as mutual coupling reduction.;The second major mutual coupling effect that impacts wireless systems are noticed on wireless power transfer (WPT) systems. WPT was introduced to solve the challenges on wireline charging on mobile devices. In addition, the WPT technique offers a universal charging system. This solves the issue with having multiple of power charging interface between each mobile devices manufacturing. Here wireless power transfer system also uses transmitter and receiver antennas to transfer the energy from one side to the other. The coupling is the mechanism that allows the power to transfer. In this case, increasing the mutual coupling improves power efficiency and therefore the output product is used as a wireless charging device which can be used for charging batteries on mobile devices. This technique can be referred to as mutual coupling enhancement.;This dissertation proposes a novel study in mutual coupling near-field wireless charging system operating at 4.5 GHz for mobile devices to enhance the coupling on WPT system. The proposed wireless charging system consists of a transmitter and receiver microstrip patch antennas to demonstrate the size-compact, easy fabrication and efficient characteristics. To enhance the coupling of wireless power transmission (WPT) system, the microstrip patch antennas are stacked facing each other to establish power transfer. The dissertation showed that power efficiency can be maximized if the receiver antenna design is optimized. The proposed system had good agreement between simulation and experiments. It was observed and demonstrated the validity and versatility of the proposed solution. The presented WPT system exhibits high power transfer efficiency up to 80%.;Both proposed solutions utilized microstrip antenna to prove the concept. Microstrip patch antennas are increasing in popularity for use in wireless applications due to their low-profile structure. Therefore they are extremely compatible for embedded antennas in handheld wireless devices such as cellular phones, radar system and telemetry equipment. There are many advantages of using Microstrip antenna such as its light weight and low volume, low profile planar configuration which can be easily made conformal to host surface, low fabrication cost, hence can be manufactured in large quantities, capable of dual and triple frequency operations and mechanically robust when mounted on rigid surfaces.