Sharif Digital Repository

A new equivalent paraboloid is presented for classical offset dual reflector antennas which do not satisfy the Mizugutchi condition. To derive the equivalent paraboloid structure, the GO is applied to obtain the main reflector aperture field in terms of the feed pattern and geometrical parameters of the antenna. Then a hypothetical angle is defined as a function of the subreflector eccentricity and the subreflector tilt angle. With the aid of this definition, the formula which relates the aperture field to the feed pattern is rearranged such that an equivalent paraboloid structure can be derived  

A miniaturized patch antenna is proposed and its radiation properties are experimentally investigated. A new metamaterial configuration based on circular spiral inclusion is used as the patch antenna substrate. The proposed antenna has not only a lighter profile but also a higher gain in comparison with its previously reported counterparts. It is shown that by using this new configuration a miniaturization factor of 3.1 can be realized. © 2017 Wiley Periodicals, Inc  

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

In this paper a closed-form expression is introduced to calculate slot shape of long slot leaky wave waveguide antennas at its fundamental mode of operation with minimum side lobe level (SLL). The derived equation is a function of geometrical parameters of the structure. This is an advantage because they show a clear relationship between geometrical parameters of the antenna and radiated field that allows intelligent modification of the pattern. The Gaussian slot is used to obtain the best radiation pattern with lowest SLL. The results obtained by introduced formula are compared with the full wave commercial simulator such as HFSS software which confirms the accuracy of the introduced... 

A new planar spiral antenna with integrated impedance transformer is presented which needs no external balun and can be fed by a coplanar waveguide.The proposed structure has a return loss of <-10 dB over a broad bandwidth of 0.5-5 GHz that is suitable for cognitive radio applications. The effects of different spiral and transformer parameters are investigated through various simulations. A case of the proposed antenna is fabricated, and measurement results are presented including return loss, gain, and radiation patterns  

It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite... 

We propose a wideband circularly polarized antenna that consists of a metallic patch and some parasitically coupled elements mounted on a grounded dielectric-ferrite substrate. The metallic patch is fed by a proximity-coupled feed line placed between the ferrite and the dielectric layers. The parasitically coupled elements are included to improve the impedance bandwidth of antenna and are excited through the metallic patch. The antenna utilizes the resonant modes of the structure, which rotate only in the clockwise or counter-clockwise direction. A semi-Analytical solution based on the magnetic wall approximation shows that the resonance frequencies of the clock-and counter-clockwise... 

In ground penetrating radar (GPR), back projection (BP) approach is a reliable method to image underground buried objects which unfortunately suffers from a high computational burden. In the BP algorithm, the refraction points have to be approximated to decrease the computational complexity. Another parameter that can improve both the accuracy and the speed of the algorithm is the antenna pattern. The 2-D algorithm is a convenient method which entails high artifacts. The proposed algorithm implemented in the 3-D domain is able to decrease the artifacts and is also a better discriminator. Meanwhile, it is possible to reconstruct a 2-D image with a better resolution in which artifacts have... 

This paper describes the design procedure and measurement results of a single-layer low-cost, and wideband frequency scanning antenna, which exhibits a nearly symmetrical beam-steering around broadside direction. The measured antenna bandwidth ranges from 27.5 to 40 GHz, which covers most of the Ka-band. In addition, the antenna main beam scans from − 52° to + 42° as the frequency sweeps from 27.5 to 36.5 GHz, showing 94° beam-steering range. At the center frequency of 32 GHz, the beam points to the broadside direction. The measured radiation patterns verify that the beam-pointing error is less than 2° over the scanning range. Furthermore, the measured gain for a 10-cell structure with 6-cm... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

In most applications of antenna arrays, side lobe levels (SLLs) are commonly unwanted. Especially, the first side lobe level which determines maximum SLL is the main source of electromagnetic interference (EMI), and hence, it should be lowered. A procedure of finding the optimum side lobe-minimizing weights for an arbitrary linear equally spaced array is derived, which holds for any scan direction, beam width, and type of antenna element used. In this science article, the use of convolution procedure and the time scaling property reduces the side lobe level for any type of linear equally spaced array. Results show that by this procedure, the side lobe level is reduced about two times or even... 

Let P be a set of points in the plane, each equipped with a directional antenna that can cover a sector of angle α and range r. In the symmetric model of communication, two antennas u and v can communicate to each other, if and only if v lies in u’s coverage area and vice versa. In this paper, we introduce the concept of fault-tolerant spanners for directional antennas, which enables us to construct communication networks that retain their connectivity and spanning ratio even if a subset of antennas are removed from the network. We show how to orient the antennas with angle α and range r to obtain a k-fault-tolerant spanner for any positive integer k. For α ≥ π, we show that the range 13 for... 

The bandwidth of the E-shaped microstrip antenna is optimized using the genetic algorithm (GA) based on fuzzy decision-making, The method of moments is employed for the analysis of the microstrip antenna at the frequency band of 1.8GHz to 2.6GHz by the optimization parameters of supply locations and slot dimensions. Fuzzy inference system is used for the control of the parameters of the genetic algorithm. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters such as crossover and mutation rates. Simulation results show the genetic algorithm to optimize the bandwidth of the E-shaped microstrip patch by 33.3%. The measured results of the optimized... 

A helical antenna is a helical shaped conductor winded around a cylinder. This antenna can radiate in different modes but the axial mode is one of the most commonly used ones since in this mode, it gives the maximum radiation power. This paper presents a novel, simple and inexpensive method to measure the radiated power density around base transceiver stations (BTS). We designed an optimized helical antenna for this application. Our simulation results show that it is possible to measure the power density with about 10% error, which is acceptable for this application. Furthermore, we implemented the designed antenna based on our analytical results and calibrate it. Experimental tests have... 

We propose a circularly polarized antenna with a wide axial ratio (AR) beamwidth that consists of a normally magnetized ferrite disk mounted on a ground plane. The device uses the resonant modes of the disk, which rotate only in the clockwise or counter-clockwise sense in the frequency range where the effective permeability of ferrite is negative. A semianalytical model is derived for the antenna fed by a single, conventional current probe and is validated numerically by finite element method. For a yttrium iron garnet disk with the radius and height of 5 and 1 mm, respectively, the results show a 3 dB AR beamwidth of 90° with an operation frequency, which can be tuned in the 4-4.5 GHz range... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

A novel approach for the design of wideband doubly curved shaped reflector antennas is introduced. By assuming a virtual aperture in front of the feed antenna and using a PObased near-field method, a fast and precise method for the design of doubly curved shaped reflector antennas is introduces. To prove the effectiveness of method, a 3-15 GHz prototype is fabricated and tested. © IEEE  

In this short paper, we study the deafness problem raised in the directional multi Gigabit transmission of IEEE 802.11ad standard which causes the devices to experience unequal chance of accessing the medium. We define three groups of Quasi-Omni (QO) antennas and propose two simple approaches to mitigate the deafness problem. Our simulation results show that the fairness increases up to 99% compared with current definition of IEEE 802.11ad which is less than 40%. © 2017 IEEE  

In this paper a novel form of the familiar E-shaped patch antenna is presented. In the presented approach, by using the genetic algorithm (GA) based on fuzzy decision-making, some modifications have been implemented to the incorporated slots which lead to even more enhancement in the antenna bandwidth. The MOM (Method of Moment) is employed for analysis at the frequency band of 1.8GHz-2.6GHz by the optimization parameters of supply locations and slot dimensions. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters like recombination to produce the next generation. Fuzzy inference system (FIS) is used for the control of GA parameters. The design... 

The Time Modulated Array (TMA) provides multiple radiation beams at different frequencies, by turning the radiating elements on and off. In this paper, we propose to add polarization diversity to a wireless communication link by leveraging the capabilities of the TMA. The proposed architecture switches between two orthogonal polarizations, instead of turning the antenna off, providing polarization diversity for the receivers. We show that the beams of each polarization at the sidebandsare exactly the same. However, the switching sequence should be optimized for the fundamental frequency to provide the same radiation level at each sideband. Two different switching sequences are proposed,...