13,515 research outputs found
Stored Electromagnetic Energy and Antenna Q
Decomposition of the electromagnetic energy into its stored and radiated
parts is instrumental in the evaluation of antenna Q and the corresponding
fundamental limitations on antennas. This decomposition is not unique and there
are several proposals in the literature. Here, it is shown that stored energy
defined from the difference between the energy density and the far field energy
equals the new energy expressions proposed by Vandenbosch for many cases. This
also explains the observed cases with negative stored energy and suggests a
possible remedy to them. The results are compared with the classical explicit
expressions for spherical regions where the results only differ by ka that is
interpreted as the far-field energy in the interior of the sphere. Numerical
results of the Q-factors for dipole, loop, and inverted L-antennas are also
compared with estimates from circuit models and differentiation of the
impedance. The results indicate that the stored energy in the field agrees with
the stored energy in the Brune synthesized circuit models whereas the
differentiated impedance gives a lower value for some cases. The corresponding
results for the bandwidth suggest that the inverse proportionality between
bandwidth and Q depends on the relative bandwidth or equivalent the threshold
of the reflection coefficient. The Q from the differentiated impedance and
stored energy are most useful for relative narrow and wide bandwidths,
respectively
Exact Solution for the Protected TEM edge mode in a PTD-Symmetric Parallel-Plate Waveguide
A Parity Time-reversal Dual (PTD) symmetric structure constituted by a
Perfectly-Electric-Perfectly magnetic (PEC-PMC) parallel plate waveguide (PPW)
is analyzed. This waveguide supports unimodal transverse electromagnetic (TEM)
edge mode propagation protected against back-scattering from a certain class of
deformations and defects. The TEM solution is found in analytical form by using
three different methods, namely conformal mapping, mode-matching, and
Fourier-transform methods. It is shown through numerical simulations that the
mode propagation is robust with respect to deformations such as 90{\deg} bends
and discontinuity such as transition to free-space. Implementation of the PMC
boundary conditions via both a bed of nails and a mushroom structure is also
successfully investigated
Pembangunan dan penganalisisan aplikasi permohonan peruntukkan penyelenggaraan bangunan sekolah berasaskan proses pengurusan dalam kejuruteraan awam
Penyelenggaraan adalah aktiviti yang dilakukan secara berterusan bagi memastikan
fungsi bangunan dapat dilaksanakan sebagaimana fungsinya secara normal.
Penyelenggaraan bangunan sekolah adalah aktiviti rutin yang harus dijalankan
memandangkan sekolah adalah lokasi pertama dalam pengembangan minda kanak�kanak. Namun begitu, kajian literatur menunjukkan terdapat beberapa masalah
dalam pengurusan penyelenggaraan yang lazimnya diselia oleh ahli jawatankuasa
penyelenggaraan sekolah. Antaranya ialah kegagalan mereka mematuhi Pekeliling
Am Bil.2 Tahun 1995 dalam proses permohonan penyelenggaraan. Disebabkan
permasalahan tersebut, tesis ini diwujudkan bagi membantu mereka dalam
menyelesaikan sebahagian masalah yang dihadapi dengan cara membangunkan satu
aplikasi permohonan penyelenggaraan sekolah berkomputer. Pembangunan aplikasi
adalah menggunakan Microsoft Access. Aplikasi pertama yang dibangunkan adalah
CoRTMaS di mana ia hanya tertumpu kepada penyelenggaraan bumbung dan tandas
berdasarkan kepada kajian literatur yang mengatakan 2 komponen ini paling kerap
mengalami kerosakan. Hasil soal selidik diuji menggunakan SPSS dan mendapati
kadar ketepatan hasil kajian adalah α = 0.893. Walaupun hasil kajian CoRTMaS
amat memuaskan, aplikasi SiPBaS dibangunkan bagi menambah baik fungsi aplikasi
dalam CoRTMaS. Kesimpulannya, pembangunan aplikasi dapat menyumbang
kepada kelancaran proses permohonan penyelenggaraan sekolah namun terdapat
beberapa cadangan lanjutan yang dicadangkan bagi memantapkan aplikasi SiPBaS
iaitu menjadikan aplikasi ini berfungsi secara atas talian, mewujudkan ruangan bagi
memuat turun gambar kerosakan serta mewujudkan kod keselamatan untuk
kontraktor terlibat
Hubungan di antara status Sosio Ekonomi (SSE) keluarga dengan pencapaian akademk : satu kajian ke at as pelajar aliran teknikal di Sekolah Menengah Teknik Negeri Sembilan
Kajian ini bertujuan untuk melihat hubungan di antara status sosio ekonomi (SSE) keluarga dengan pencapaian akademik di kalangan pelajar aliran teknikal. Kajian ini dijalankan ke atas pelajar tingkatan empat aliran teknikal di lima buah Sekolah Menengah Teknik di Negeri Sembilan iaitu Sekolah Menengah Teknik Tuanku Jaafar, Sekolah Menengah Teknik Juasseh, Sekolah Menengah Teknik Pertanian Rembau, Sekolah Menengah Teknik Ampangan dan Sekolah Menengah Teknik Port Dicksoa Seramai 350 orang pelajar terlibat dalam kajian ini dan dipilih secara rawak mudah. Analisis regresi mudah dan regresi berbilang digunakan untuk melihat hubungan di antara pembolehubah yang dikaji. Keseluruhan data kajian telah dianahsis menggunakan perisian Statistical Packages for the Social Sciences (SPSS) versi 11.5 dengan membuat pengiraan peratusan dan regresi. Dapatan kajian menunjukkan secara majoritinya, SSE mempunyai hubungan yang signifikan dengan tahap pencapaian akademik pelajar. Dengan itu dapat dirumuskan bahawa SSE mempengaruhi tahap pencapaian akademik pelajar aliran teknikal. Beberapa cadangan dikemukakan untuk panduan kajian selanjutnya
Novel Approach to Design Ultra Wideband Microwave Amplifiers: Normalized Gain Function Method
In this work, we propose a novel approach called as “Normalized Gain Function (NGF) method” to design low/medium power single stage ultra wide band microwave amplifiers based on linear S parameters of the active device. Normalized Gain Function TNGF is defined as the ratio of T and |S21|^2, desired shape or frequency response of the gain function of the amplifier to be designed and the shape of the transistor forward gain function, respectively. Synthesis of input/output matching networks (IMN/OMN) of the amplifier requires mathematically generated target gain functions to be tracked in two different nonlinear optimization processes. In this manner, NGF not only facilitates a mathematical base to share the amplifier gain function into such two distinct target gain functions, but also allows their precise computation in terms of TNGF=T/|S21|^2 at the very beginning of the design. The particular amplifier presented as the design example operates over 800-5200 MHz to target GSM, UMTS, Wi-Fi and WiMAX applications. An SRFT (Simplified Real Frequency Technique) based design example supported by simulations in MWO (MicroWave Office from AWR Corporation) is given using a 1400mW pHEMT transistor, TGF2021-01 from TriQuint Semiconductor
Reflection Coefficient Transformations for Phase-Shift Circuits
It is shown how switchable one-port circuits having two impedance states may be transformed so as to exhibit reflection coefficients which have a prescribed phase angle difference and equal magnitude in the two states. In reflection-type phase shifters, arbitrary phase shift may be obtained without change of signal amplitude. The reflection properties are achieved by the use of an impedance-transforming two-port network. Design equations and an example are given
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