Analytical Evaluation of the MoM Matrix Elements

Cataloged from PDF version of article.Derivation of the closed-form Green’s functions has eliminated the computationally expensive evaluation of the Sommerfeld integrals to obtain the Green’s functions in the spatial domain. Therefore, using the closed-form Green’s functions in conjunction with the method of moments (MOM) has improved the computational efficiency of the technique significantly. Further improvement can he achieved on the calculation of the matrix elements involved in the MOM, usually double integrals for planar geometries, by eliminating the numerical integration. The contribution of this paper is to present the analytical evaluation of the matrix elements when the closed-form Green’s functions are used, and to demonstrate the amount of improvement in computation time

ADAPTİF ANTEN DİZİLERİ

TÜBİTAK EEEAG Proje01.08.2002COST 260 projesi kapsamında uydu iletişimine yönelik 11.49 GHz_11.678 GHz frekans aralığında çalışan, faz taramalı adaptif bir almaç anten sistemi tasarlanmış üretilmiş ve test edilmiştir. Geliştirilen sistem aynı anda, farklı ya da aynı frekansta iki hüzme oluşturmaktadır. Antan dizisi sekiz adet dörtlü mikroşerit anten dizisinden oluşmaktadır ve her bir dörtlü dizi için ayrı ayrı almaç kanalları tasarlanmıştır. Sinyaller 490 MHz-678 MHz frekans aralığına indirilerek genlik ve fazları kompleks vektör modülatör yardımı ile elektronik olarak değiştirilip toplanmak suretiyle hüzme elde edilmektedir. Tüm kontroller bilgisayar ortamında gerçekleştirilmektedir. Sistem yüzey monteli (SMD- Surface Mount Device) konektörsüz mikrodalga ve elektronik komponentler ile MIC (Microwave Integrated Circuit) teknolojisineuygun olarak gerçekleştirilmiştir.In COST260 project, adaptive phased array receiving antenna system for satellite communication, which operates at 11.49-11.678GHz, has been designed, produced and tested. In the developed system, there are two simultaneous beams. These beams can be formed in the same frequency or two beams may have different frequencies. Array antenna consists of eight microstrip linear arrays of four patches. For each four element linear array, separate receiving channels have been designed. Received signals from each linear array are downconverted to 490-678 MHz band and then amplitudes and phases of these signals are adjusted by vector modulator electronically to produce the required pattern. The total signal is divided into two, one is used to control the pattern and the other one is for monitoring satellite signal. In broadcast channel, signal is upconverted to 1.2-1.7GHz frequency band. Then it is sent to DVB (Digital Video Broadcasting) demodulator/decoder card. System is fully computer controlled. In the production of the system Surface Mount Devices (SMD) and Microwave Integrated Circuit (MIC) technology has been used. This smart antenna system has the abilities of beam steering, tracking, and direction finding providing the necessary computer codes. There are two beam forming and broadcasting channels in the system. The functions of the produced prototype have been tested

Bilgi toplumu teknolojileri için anten sistemleri ve algılayıcılar

TÜBİTAK EEEAG01.10.2010Bu proje kapsamında, özellikle milimetre-dalga frekanslarında çalışan yeniden şekillendirilebilir anten, elektronik taramalı dizi anten ve yansıtıcı dizi anten tasarımı, üretimi ve ölçümleri yapılmıştır. Yeniden şekillendirilebilirlik özelliği için farklı teknolojiler kullanılmıştır. Huzmesi yönlendirilebilen sur biçimli mikroşerit yürüyen dalga anten dizisi X-bant uygulamalarında kullanılmak üzere tasarlamış, üretilmiş ve ölçülmüştür. Antenin ana huzmesinin istenilen yöne elektronik olarak döndürülebilmesini sağlayabilmek için mikroşerit hat üzerinde gerekli faz değişimini sağlayacak varaktör diyotlar kullanılmıştır. Yapılan EM benzetim ve ölçümler sonucu sur biçimli anten dizisinde, ana huzmenin diyot kontrolü ile tasarlandığı gibi 10 lik bir açı taraması yapabildiği gösterilmiştir. Bu kavram kanıtlaması şeklinde bir çalışmadır; huzmenin daha büyük açı aralığında tarama yapması için tasarımda yapılması gereken değişiklikler belirtilmiştir. MM-Dalga sabit genişlikli ve doğrusal sönümlenen yarık antenler tasarlanıp, üretilmiş ve antenin şeklinin, optik uyarımla bu iki yapı arasında değiştirilmesinin sağlanması durumunda ışıma örüntüsünün değiştirilebileceği gösterilmiştir. Proje kapsamında gerçekleştirilen bir diğer çalışmada da K ve Ka bantlarında bağımsız çalışabilen, RF MEMS anahtarlarla huzmesi elektronik olarak döndürülebilen dairesel polarizasyonlu yansıtıcı dizi anten tasarlanmış, üretilmiş ve ölçülmüştür. Çift frekanslı (24.4 GHz ve 35.5 GHz) dizi iç içe geçmiş farklı boyutlarda iki ayrık-halka dizisi şeklinde tasarlanmıştır. Huzme döndürme amacıyla her bir ayrık halkanın açısal konumunu RF MEMS anahtarlarla ayarlayarak, dairesel polarizasyonlu dalgaların fazları kontrol edilmektedir. Anten ODTÜ MEMS merkezinde geliştirilen yüzey mikro-işleme süreciyle üretilmiştir. Işıma örüntüleri ölçülmüş ve benzetim sonuçlarıyla karşılaştırılmıştır. Ölçümlerle, ana huzmenin, tasarlandığı gibi, Ka bandında 35°‟ye, K bandında 24°‟ye döndürülebildiği gösterilmiştir. Proje çalışmalarından sur biçimli mikroşerit anten dizisiyle ilgili hazırlanan makale Microwave and Optical Technology Letters adlı dergide yayınlanmak üzere kabul edilmiştir. Yansıtıcı dizi antenle ilgili makale de hazırlık sürecindedir. Saygın konferanslarda yedi bildiri sunulmuştur. Ayrıca, proje kapsamında üç yüksek lisans tez çalışması tamamlanmıştır.In this project, reconfigurable antenna, beam steering array and reflectarray have been designed, produced and measured, especially in mm-wave frequencies. To provide reconfigurability, different technologies have been considered. X-band electronically scanning meanderline microstrip traveling wave antenna array has been designed, produced and measured. To rotate the antenna beam to the desired direction, microstrip meander line has been loaded by varactor diodes that provide required phase shift values. EM simulations and rdiation pattern measurements of the meanderline antenna have demonstrated that the antenna has the capability to scan 10 with the control of varactors as designed. This is a proof-of-concept type study; alternative configurations to increase the scan range have also been discussed. MM-wave tapered slot antennas with a constant width and linear taper have been designed, produced and measured. It has been demonstrated that if the shape of the tapered slot antenna can be changed between constant width and linear taper structures by means of optical excitation, radiation pattern reconfigurability can be obtained. In another study accomplished in this project, electronically scanning circularly polarized reflectarray working independently in K and Ka bands has been designed, produced and measured. Dual band (24.4 GHz and 35.5 GHz) reflectarray has been designed as an interlaced array of split rings of two different sizes. In order to steer the beam, the phase of the incident circularly polarized wave is controlled by RF MEMS switches that modify the angular orientation of split-rings individually. The antenna has fabricated by using surface micromachining process developed in METU MEMS Center. Radiation patterns of the antenna are measured and compared with the simulations. It has been shown that the reflectarray is capable of beam switching to 35° in Ka band, 24° in K band as required. One journal paper on meanderline antenna has been accepted to be published in Microwave and Optical Technology Letters. Preparation of manuscript on reflectarray is under progress. Seven conference papers have been presented in well known Conferences. Furthermore, three Master Thesis studies have been accomplished during the project

Wideband omnidirectional and sector coverage antenna arrays for base stations

By using parallel strip line fed printed dipole antennas as array elements, an omnidirectional antenna array and a wide angle sector coverage array operating in octave band are designed. A maximum deviation of ±1.25 dB from the omnidirectional pattern is achieved for the omnidirectional array, and the average gain of the antenna was measured as being 5 dB in the 1.35–2.7GHz band. For the sector coverage array, a special reflector design is utilized to maintain a half power beam width of around 115◦ with a standard deviation of 14◦ in the aforementioned frequency band. The average gain of the sector coverage array was measured as 10 dB, thereby being almost three fold larger than the average gain of the omnidirectional array. © 2018, Electromagnetics Academy. All rights reserved

Use of computationally efficient MoM in the analysis and design of printed structures

Ph.D. - Doctoral Progra

Singularity Cancellation for Accurate MoM Analysis of Periodic Planar Structures in Layered Media

One of the singularity cancellation schemes proposed in the literature is applied to calculate singular integrals arising in the method of moments (MoM) analysis of 2-D periodic planar structures in multilayered media. Discrete complex image method is utilized for the accurate approximation of Green's function which also makes possible the application of the Ewald transformation for the efficient computation of the series associated with the periodic structure. This approximation and transformation modifies the kernel of the integral appearing in the computation of the MoM matrix entries. Formulation of the problem for this new kernel is presented together with numerical results demonstrating the achieved accuracy

The effect of antenna in the forward model of near field microwave imaging systems

A fast and accurate forward problem solver for near-field microwave imaging systems is developed by considering the electric field intensity as the measured quantity. Since the antenna port voltage values will be the real measured quantity in practical applications, the effects of transmitting/receiving antennas in the forward problem model is investigated

An application of singularity cancellation for periodic structures in free space

A singularity problem arises in the computation of MoM matrix entries. Several singularity cancellation schemes are proposed in literature. One of these singularity cancellation methods is applied to handle the singularity problem associated with the MoM analysis of 2D periodic structures. For the efficient computation of the 2D periodic Green's function, Ewald transformation is used, resulting in a change in the kernel of the integral associated with the MoM matrix entries. Formulation of the problem for this new kernel is presented together with numerical results for a sample problem

Use of Asymptotic Waveform Evaluation Technique in the Analysis of Multilayer Structures With Doubly Periodic Dielectric Gratings

The reflection and dispersion characteristics of multilayer structures that involve periodically implanted material blocks are obtained by using the MoM solution of the volume integral equation. The asymptotic waveform evaluation (AWE) technique is utilized to obtain a Pade approximation of the solution in terms of a parameter such as frequency or incident angle. The use of AWE technique enables a fast sweep with respect to the approximation parameter. Moreover, a robust method for extracting the dispersion characteristics of periodic structures via Pade approximation is proposed. The AWE procedure requires the calculation of high order derivatives of the complicated kernel function that consists of Green's functions for stratified medium. These derivatives are calculated by employing the Automatic Differentiation Theory. The reflection coefficient, propagation constant and band diagram of the structure are obtained both via point-by-point simulations and through the use of AWE technique. It is observed that AWE technique increases the computational efficiency without losing accuracy

A Non-Galerkin Spatial-Domain Approach for Efficient Calculation of the Dispersion Characteristics of Microstrip Lines

In the analysis of dispersion characteristics of microstrip lines, spectral domain approaches has been preferred as opposed to the spatial domain calculations since the spatial domain Green's functions corresponding to the microstrip structure require the numerical evaluation of inverse Fourier transform integrals which are computationally expensive. However as demonstrated in Bernal, J. et al, (2000), the discrete complex image representation of the spatial domain Greenpsilas functions eliminates the need for the evaluation of numerical integrals and renders the spatial domain method to be more efficient compared to the spectral domain approach. When the discrete complex image method (DCIM) is used, the matrix entries of the eigenvalue problem involve double integrations in the spatial domain. One of them is the convolution integral with the basis function, the other one is the inner product integral with the testing function to impose the boundary conditions. In case a Galerkin approach with basis functions satisfying the edge conditions on the conducting strips is preferred as in Bernal, J. et al, (2000), these integrals need to be evaluated numerically. However, if a non-Galerkin approach with pulse type testing functions is adopted, one of the integrals could be evaluated analytically and a single numerical integration is required. In this paper, the non-Galerkin method is utilized and the accuracy of the method is demonstrated by comparing the results of dispersion characteristics to the ones found in the literature