Performance Enhancement of Multiband Ground Radiation Antenna Using Multi-Resonant Loops

Abstract

사물 인터넷의 시대가 도래하면서 수없이 많은 전자 기기들이 무선 통신 기능을 내장하게 되었다. 이에 따라 단말기에 내장된 안테나의 소형화, 광대역화, 다중대역화, 고성능 특성에 대한 요구 또한 급증하였다. 또한 최근의 휴대 단말기들은 휴대성과 패션 액세서리로서의 기능을 수행하기 위해 안테나를 위해 제공할 수 있는 공간의 매우 제한적이며, 단말기 자체도 매우 작은 경향이 있다. 소형 안테나의 성능은 그 크기와 밀접한 관련이 있어 안테나의 크기가 작아질수록 안테나의 성능은 나빠진다. 이러한 물리적 한계를 극복하기 위해 제시된 휴대 단말기 안테나 설계 기술이 바로 그라운드 방사 안테나이다. 그라운드 방사 안테나는 단말기의 그라운드를 방사체로 활용함으로써 크기의 제약을 극복하는 기술이다. 본 논문은 그라운드 특성 모드를 활용하여 성능이 향상된 소형 다중대역 그라운드 방사 안테나를 제시한다.

먼저 안테나의 크기에 따른 안테나 성능의 이론적 한계를 분석하고 도체 특성 모드 이론의 기초에 대해 논의함으로써 그라운드 방사 안테나 설계 기술이 개발된 배경에 대해 살펴본다. 이후 그라운드 방사 안테나의 기본 동작 원리를 알아보고 그라운드를 어떻게 급전 시켜야 좋은 방사체로 활용할 수 있는 지에 대해 논의한다.

논의된 그라운드 급전 방법을 토대로 설계된 소형화된 4중대역 그라운드 방사 안테나를 제시한다. 2개의 급전 루프와 4개의 방사 루프를 겹치게 설계하여 4개의 주파수 대역에서 독립적으로 제어가능한 소형 4중대역 안테나의 동작 원리와 성능을 분석한다.

다음으로, 병렬공진 급전구조를 활용하여 이중대역 그라운드 방사 안테나의 대역폭을 향상시키기 위한 방법을 연구한다. 기존의 급전구조는 단일 공진으로 이루어져 있어 두 주파수 대역에서 동시에 대역폭을 향상시키는 것이 불가능하였다. 본 논문에서는 급전구조를 2개의 병렬 공진의 조합으로 만듦으로써 각각의 대역에서 모두 대역폭 향상이 가능한 급전 구조를 설계한다. 제안된 안테나의 성능을 이전에 발표된 기존 이중대역 그라운드 방사 안테나들과 비교함으로써 해당 기술의 우수성을 확인하고자 한다.

그라운드 방사 기술을 활용하여 방사성능을 향상시키더라도 그라운드 자체의 크기가 매우 작아 방사에 열악할 경우 그라운드 방사 안테나의 성능도 좋지 않다. 이를 해결하기 위해 제시된 것이 그라운드 모드 튜닝 기법이다. 이 기술은 그라운드의 끝단에 공진 구조체를 추가적으로 형성하여 그라운드의 특성 모드 공진 주파수를 안테나의 동작 주파수 근처로 가져옴으로써 안테나의 방사 성능을 획기적으로 향상시키는 기술이다. 현재까지 이 기술은 그라운드의 수직 혹은 수평 방향 중 한쪽 방향의 주 모드만을 제어할 수 있기 때문에, 다중대역에 적용하는 것이 힘들었다. 본 논문에서는 이중대역 안테나의 이중대역 공진의 각 공진이 수평 혹은 수직 방향의 그라운드 특성 모드 중 하나와 각각 결합하도록 설계한다. 설계된 안테나는 두 동작 대역에서 모두 그라운드 특성모드와 결합하여 안테나 성능의 비약적인 향상이 가능하게 된다.

| With the advent of the Internet of Things, numerous electronic devices have built in wireless communications. Accordingly, the demand for miniaturization, wideband, multiband, and high performance of the mobile antenna has also increased rapidly. In addition, the recent portable terminals are very limited in the space that can be provided for the antenna to perform the function as portability and fashion accessories, and the device itself tends to be very small. The performance of a small antenna is closely related to its size. As the size of the antenna becomes smaller, the performance of the antenna becomes worse. The ground radiation antenna is a mobile antenna design technique proposed to overcome these physical limitations. In this dissertation, we present a small multiband ground radiation antenna with improved performance using ground characteristic mode.

First, the theoretical limits of the antenna performance according to the size of the antenna is analyzed and the basics of the conductor characteristic mode theory are discussed. After that, the basic operation principle of the ground radiation antenna is discussed and how to feed the ground can be used as a good radiator. In the following, the basic operating principle of the ground radiation antenna will be investigated, and the coupling method to feed the ground as a good radiator based on antenna current distributions.

A miniaturized quad band ground radiation antenna designed based on the ground radiation technique is presented. a small quad band antenna composing two feeding loops and four radiation loops designed to be independently controlled in four frequency bands is analyzed for the operation mechanisms and far-field radiation performance.

Next, a method for improving the bandwidth of a dual band ground radiation antenna using a parallel resonance feeding structure is studied. The feed structures of previous ground radiation antennas consist of a single resonance, which makes it impossible to simultaneously improve the bandwidth in two frequency bands. In this dissertation, a feed structure that can improve bandwidth in each band by making the feed structure consisting of two parallel resonances is proposed. The performance of the proposed antenna is compared with that of the reference dual band ground radiation antennas.

Even if the ground radiation technique is used to improve the far-field radiation performance of the mobile antenna, the performance of the ground radiation antenna is poor if the ground itself is too small to radiate. To solve this problem, the ground mode tuning technique is proposed. This technique adds a resonant structure at the end of the ground to bring the characteristic mode resonant frequency of the ground to near the operating frequency of the antenna, thereby dramatically improving the radiation performance of the antenna. To date, this technique has been difficult to apply to multiple bands because it can only control the dominant mode in either the vertical or horizontal direction of ground. In this dissertation, each radiation resonance of the dual band resonance is designed to be coupled with one of the horizontal or vertical ground characteristic modes. The proposed antenna couples with the ground characteristic modes in both operating bands, enabling a dramatic improvement in antenna performance.; With the advent of the Internet of Things, numerous electronic devices have built in wireless communications. Accordingly, the demand for miniaturization, wideband, multiband, and high performance of the mobile antenna has also increased rapidly. In addition, the recent portable terminals are very limited in the space that can be provided for the antenna to perform the function as portability and fashion accessories, and the device itself tends to be very small. The performance of a small antenna is closely related to its size. As the size of the antenna becomes smaller, the performance of the antenna becomes worse. The ground radiation antenna is a mobile antenna design technique proposed to overcome these physical limitations. In this dissertation, we present a small multiband ground radiation antenna with improved performance using ground characteristic mode.

First, the theoretical limits of the antenna performance according to the size of the antenna is analyzed and the basics of the conductor characteristic mode theory are discussed. After that, the basic operation principle of the ground radiation antenna is discussed and how to feed the ground can be used as a good radiator. In the following, the basic operating principle of the ground radiation antenna will be investigated, and the coupling method to feed the ground as a good radiator based on antenna current distributions.

A miniaturized quad band ground radiation antenna designed based on the ground radiation technique is presented. a small quad band antenna composing two feeding loops and four radiation loops designed to be independently controlled in four frequency bands is analyzed for the operation mechanisms and far-field radiation performance.

Next, a method for improving the bandwidth of a dual band ground radiation antenna using a parallel resonance feeding structure is studied. The feed structures of previous ground radiation antennas consist of a single resonance, which makes it impossible to simultaneously improve the bandwidth in two frequency bands. In this dissertation, a feed structure that can improve bandwidth in each band by making the feed structure consisting of two parallel resonances is proposed. The performance of the proposed antenna is compared with that of the reference dual band ground radiation antennas.

Even if the ground radiation technique is used to improve the far-field radiation performance of the mobile antenna, the performance of the ground radiation antenna is poor if the ground itself is too small to radiate. To solve this problem, the ground mode tuning technique is proposed. This technique adds a resonant structure at the end of the ground to bring the characteristic mode resonant frequency of the ground to near the operating frequency of the antenna, thereby dramatically improving the radiation performance of the antenna. To date, this technique has been difficult to apply to multiple bands because it can only control the dominant mode in either the vertical or horizontal direction of ground. In this dissertation, each radiation resonance of the dual band resonance is designed to be coupled with one of the horizontal or vertical ground characteristic modes. The proposed antenna couples with the ground characteristic modes in both operating bands, enabling a dramatic improvement in antenna performance.