dB Gain Improvement Research Articles

Gain Improvement of Enhancement-Mode AlGaN/GaN High-Electron-Mobility Transistors Using Dual-Gate Architecture

We demonstrate a dual-gate (DG) AlGaN/GaN high-electron-mobility transistor (HEMT) structure with enhancement-mode (E-mode) operation. The DG device consists of an E-mode gate and a depletion-mode (D-mode) gate instead of the dual D-mode gate electrodes used in previously reported works; thus no negative voltage supply is required when the DG device is used in amplifier circuits. The E-mode DG HEMTs exhibit similar DC characteristics to E-mode single-gate devices but show a 9 dB gain improvement at 2.1 GHz under the same bias conditions. The power gain improvement can be attributed to the higher output impedance and lower feedback capacitance in the DG structure.

Numerical analysis on the 4H-SiC MESFETs with a source field plate

A new structure of 4H-SiC MESFETs based on the source field plate technology is proposed in this paper. The source field plate has been applied not only to improve the breakdown voltage, but also to eliminate the drawback of low gain characteristics resulting from additional feedback capacitance associated with the field plate electrode. The off-state breakdown voltage was significantly improved by employing a source field plate electrode, and the highest value of 203 V was obtained with a source field plate length of 1.1 µm. As compared to the conventional structures, the MESFETs with a source field plate show an approximately 41% decrease in the gate-to-drain capacitance, which is responsible for the 2.2 dB gain improvement at 2 GHz. This is because the source field plate redistributes the electric fields in the gate-to-drain region and hence reduces the gate-to-drain capacitance in the intrinsic device. Therefore, the 4H-SiC MESFETs with the source field plate have superior dc and RF performances compared to similar devices based on the conventional structure.

고이득 특성을 갖는 성형 빔 안테나에 대한 연구

본 논문은 단위 방사 소자의 이득을 증가시키기 위한 성형 빔 안테나에 관한 것이다. 제안하는 안테나 구조는 크게 여기 소자와 다층 원형 도체 배열 구조로 구성된다. 광대역에 걸쳐 전자파 전력이 다층 원형 도체 배열로 방사하기 위한 여기 소자로 스택 마이크로스트립 패치 소자가 사용되었으며, 고이득 빔 성형을 위한 지향 소자의 역할을 담당하는 다층 원형 도체 배열 소자들은 여기 소자 위에 주기적으로 유한하게 적층되었다. 제안하는 안테나가 고이득 특성을 얻기 위해서는 여기 소자와 다층 원형 도체 배열 소자들 간의 효율적인 전력 결합이 이루어져야 하며, 이를 위해 주어진 설계 규격에 따라 여기 소자 및 다층 원형 도체 배열 소자들의 설계 변수들은 함께 최적화되어야 한다. 본 연구에서는 고이득 성형 빔 안테나는 <TEX>$9.6{\sim}10.4\;GHz$</TEX> 주파수 대역 및 선형 편파 조건하에서 최적화 설계되었으며, 또한 안테나의 다층 원형 도체 배열 소자들을 구현하는 2가지 방법 즉, 얇은 유전체 필름을 이용하는 방법과 유전체 폼을 이용하는 방법들도 제안되었다. 특히, 유전체 필름을 이용하는 안테나에 대해서는 컴퓨터 시뮬레이션 과정을 통해, 원형 도체 배열 소자들의 적층 수에 따른 안테나의 전기적인 성능 변화들을 보여주었다. 유전체 필름(Type 1)과 유전체 폼(Type 2)을 이용한 2종류의 안테나 시제품들을 제작하였으며, 얇은 유전체 필름을 이용한 안테나 시제품에 대해선 시뮬레이션 된 전기적 성능 결과와 비교를 위해 원형 도체 배열 적층 수에 따른 안테나의 전기적인 성능 변화들을 실험하였다. 측정된 이득 성능은 시뮬레이션 이득 성능과 거의 유사한 결과를 보여주었으며, 원형 도체 적층 수에 따라 안테나 이득 변화는 주기성을 보였다. 10 GHz 중심 주파수에서 측정된 Type 1 안테나의 전기적 성능은 원형 도체 배열을 10개 적층(disk10)하였을 때, 15.65 dBi의 최대 안테나 이득과 11.4 dB 이상의 입력 반사 손실 성능을 보여 주었으며, 다층 원형 도체 배열 구조에 의해 약 5 dB의 이득 향상 효과를 얻을 수 있었다. 또한, 원형 도체를 12개 적층하였을 때, 외곽 유전체 링 효과에 의해 Type 1 안테나는 Type 2 안테나보다 상대적으로 약 1.35 dB 만큼 이득이 더 높았으며, 각 안테나의 3 dB 빔 폭은 각각 약 <TEX>$28^{\circ}$</TEX>와 <TEX>$36^{\circ}$</TEX>로 측정되었다. This paper describes a shaped-beam antenna for increasing the antenna gain of a radiating element. The proposed antenna structure is composed of an exciting element and a multi-layered disk array structure(MDAS). The stack micro-strip patch elements were used as the exciter for effectively radiating the electromagnetic power to the MDAS over the broadband, and finite metallic disk array elements - which give the role of a director for shaping the antenna beam with the high gain - were finitely and periodically layered onto it. The efficient power coupling between the exciter and the MDAS should be carried out in such a way that the proposed antenna has a high gain characteristic. The design parameters of the exciter and the MDAS should be optimized together to meet the required specifications to meet the required specifications. In this study, a shaped-beam antenna with high gain was optimally designed under the operating conditions with a linear polarization and the frequency band of <TEX>$9.6{\sim}10.4\;GHz$</TEX>. Two methods constructed using thin dielectric film and dielectric foam materials respectively were also proposed in order to implement the MBAS of the antenna. In particular, through the computer simulation process, the electrical performance variations of the antenna with the MDAS realized by the thin dielectric film materials were shown according to the number of disk array elements in the stack layer. Two kinds of antenna breadboard with the MDAS realized with the thin dielectric film and dielectric foam materials were fabricated, but experimentation was conducted only on the antenna breadboard(Type 1) with the MDAS realized with the thin dielectric film materials according to the number of disk array elements in the stack layer in order to compare it with the electrical performance variations obtained during the simulation. The measured antenna gain performance was found to be in good agreement with the simulated one, and showed the periodicity of the antenna gain variations according to the stack layer number of the disk array elements. The electrical performance of the Type 1 antenna was measured at the center frequency of 10 GHz. As the disk away elements became the ten stacks, a maximum antenna gain of 15.65 dBi was obtained, and the measured return loss was not less than 11.4 dB within the operating band. Therefore, a 5 dB gain improvement of the Type 1 antenna can be obtained by the MDAS that is excited by the stack microstrip patch elements. As the disk array elements became the twelve stacks, the antenna gain of the Type 1 was measured to be 1.35 dB more than the antenna gain of the Type 2 by the outer dielectric ring effect, and the 3 dB beam widths measured from the two antenna breadboards were about <TEX>$28^{\circ}$</TEX> and <TEX>$36^{\circ}$</TEX> respectively.

A study on iterative video coding rate–distortion optimization and its rate control

AbstractEncoding a video clip with as large a compression ratio as possible within a framework of established standards is a key technology for digital TV broadcasting, content creation, distribution, and storage. Optimization, encoding a video clip at the highest possible quality within a given bit rate, is expected to become increasingly important in the future. As this process repeats encoding many times, rate control should converge quickly. This paper proposes an iterative encoding (N‐pass) optimization strategy based on the Lagrange multiplier method. It focuses on local coding units and knowledge about optimal multipliers within an MPEG‐2 framework. We also propose and demonstrate an affiliated accurate rate control algorithm. Simulation results show the PSNR gain for this optimization method is 1.0 to 1.9 dB higher than that offered by the TM5 method, and is significantly higher than the 0.03 to 0.7 dB gain improvement over TM5 we achieved with quantization‐parameter‐based optimization. The rate control framework is highly accurate; the error is less than 1% within one or two rate control iterations. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(10): 1–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10455

A differential active patch antenna element for array applications

This letter describes the implementation of an active receiving antenna at 5-6 GHz. An aperture-coupled patch antenna is designed to provide a differential interface toward monolithically integrated circuits. The integration with a low-noise amplifier is shown. The proposed structure offers new advantages for the construction of compact and robust adaptive antenna arrays. Measurements show around 5.5 dBi antenna gain with a cross-polarization below -27 dB. The differential low-noise amplifier provides more than 10 dB gain improvement.

Broadband meanderline slot spiral antenna

A new broadband, cavity-backed slot spiral antenna is proposed. It combines variable growth rates at the centre region for improved high band radiation, with meandering in the outer turns for more efficient low band operation. A detailed characterisation of all antenna components and parameters is provided along with guidelines and recommendations for miniaturisation and realisation. The performance degradation due to cavity resonances is discussed and their suppression is also demonstrated. The developed design has broadband UHF to S-band operation with up to 20 dB gain improvement at 250 MHz using a 15 cm aperture. Using the same design concept, 45 cm apertures are realised and their operation from VHF to S-band is demonstrated.

Gain enhancement in cascaded fiber parametric amplifier with quasi-phase matching: theory and experiment

We report a novel gain enhancement scheme for fiber-optic parametric amplifiers utilizing cascaded amplification and quasi-phase matching (QPM). The theory and method of QPM for four-wave mixing (FWM) are developed for the first time to our knowledge. In experimental implementations of the theory, we achieve >12 dB gain improvement in a three-stage dispersion-shifted (DS) fiber parametric amplifier. A 16-dB overall gain is obtained with 11 nm separation between zero-dispersion wavelength and pump wavelength. The experimental results show good agreement with theory and simulations. The influence of QPM on spectral characteristics of parametric gain is investigated with numerical simulations.

Metallic photonic band-gap materials (MPBG) as angular selective reflector or radome: Application to antenna grating lobe reduction

This paper presents numerical and experimental results on metallic photonic band-gap materials (mpbg), composed of metallic wires and used as antenna reflector or radome. Attention is focused on mpbg angular response. In fact, with specified angular characteristics, MPBG materials can be interesting in order to reduce antenna grating lobes. One possible grating lobe reduction solution is based on the use of mpbg as angular filter. The radiation characteristics obtained with this solution are then improved by using a mpbg reflector to enhance the gain. Regarded to a classical metallic reflector, 20 dB and 12 dB gain improvement in the theoretical and in the experimental cases are respectively obtained, when the reflector is composed of more than two layers. The scanning performances are also presented. We show that angular filtering characteristics can be improved either by changing the array interface or by changing the mpbg lattice. In order to select the structure with the best angular behavior, an experimental and numerical characterization method is also presented.

Broadband active microstrip antenna design with the simplified real frequency technique

This paper deals with the design of broadband active microstrip antennas where the amplifier is integrated with the radiator. Theoretically sound definitions for gain and noise figure of the active antenna are introduced, and their relationships with the definitions for the composing circuit and radiator parts are explained. A sequential design procedure is presented that allows the straightforward and optimal design of transmitting and receiving antennas with multiple active stages, taking into account input and output matching, the gain-versus-frequency curve as well as the noise performance. The theoretical concepts are illustrated with two examples: one of a transmitting active antenna and one of a receiving antenna. The former one is a two-stage design that achieves nearly 25% of bandwidth with regard to gain and matching and 24 dB gain improvement as compared to the matched passive antenna. The second one is a receiving antenna (one stage) with a measured noise figure of 1.2 dB in a bandwidth of over 17% and a gain improvement of 11.9 dB over the corresponding passive antenna. Finally co- and cross-polar radiation patterns in E- and H-plane prove that the antennas also have favorable radiation characteristics in a wide bandwidth (at least 18%). >

Superconducting antennas

Two high-temperature superconducting antenna systems are tested. The first is a small closed helical antenna which shows nearly 6 dB gain improvement over a similar copper antenna. The second is a simple two-element end-fire superdirective array for which initial results of the gain improvement are given. This antenna with its matching network shows a significant increase in gain.

9 dB gain improvement of 1300 nm optical amplifier by amplified spontaneous emission suppressing fibre design

A new design of an Nd-doped fluoride fibre for 1300 nm small-signal amplification is presented. By placing the active material so that the 1050 nm amplified spontaneous emission is discriminated, a gain improvement of up to 6.6 dB is predicted. By including higher order pump modes an extra 2.1 dB gain improvement is achieved.