Altunkan Hizal

Frequency Diverse Array Antenna with Periodic Time Modulated Pattern in Range and Angle

A general analysis of a frequency diverse transmit array antenna with a periodic modulated pattern in range, angle and time is presented. This antenna array system makes a continuous scanning in range and angle without using any phase shifters. The scanning is achieved using the frequency diversity by inserting a small amount of progressive frequency shift to each antenna element. The theory shows that there is the same modulation pattern in time, range and angle by taking the remaining two parameters fixed. The simulation results for radiation patterns of a binomial distribution array are presented. The expressions for determining the position and the angular bearing of a target for this type of antenna array system are given.

A Dual-Polarized Wide-Band Patch Antenna for Indoor Mobile Communication Applications

This paper proposes the conflguration of a dual- polarized wide-band patch antenna system suitable for indoor mobile communication applications. This conflguration consists of two patch antennas, which have difierent feed structures from classical patch antenna conflguration. These antennas, which are separated by a thin absorber to have a good isolation, are fed independently to obtain dual polarization. The antenna structure is designed, simulated, manufactured and measured. The operation bandwidth spans 1900{ 2700MHz covering Bluetooth, Wireless Local Area Networks (WLAN) and Universal Mobile Telecommunications System (UMTS) bands. The simulations show good agreement with the measurement results that the antennas have return losses higher than 15dB, and the coupling between two antennas is below i20dB within the operation band.

Exploitation of Linear Frequency Modulated Continuous Waveform (LFMCW) for Frequency Diverse Arrays

Frequency diverse arrays (FDA) are recently introduced. Not only the phased array and frequency scanning arrays, but also FDA provides electronic beam scanning ability. Moreover, electronic beam scanning is provided without the use of phase shifters or vector modulators. Nevertheless, reported studies on this concept do not provide practically implementable results. In this paper, fundamental expressions of the FDA operation and its typical implementation schemes are reviewed, and an ultimately useful scheme for implementing and FDA is introduced based on linear frequency modulated continuous waveform (LFMCW). The mathematical foundations of LFMCW FDA are developed and used to design a basic proof of concept structure. This structure is also implemented and the measurements related to the implementation are presented with discussions on the results.

A compact corporate probe fed antenna array

This paper presents a linear antenna array system with a compact corporate feed network. The antenna elements are probe fed circularly polarized microstrip patch antennas. By using probe feed topology, it is possible to combine all the antenna elements on the backside of the array. Besides, the overall size of the feed network is reduced with the proposed special corporate feed topology. An 8 times 1 linear array is designed and produced as the building block of a larger 2D array. The antenna arrays return loss, radiation pattern and polarization characteristics give good agreement with the numerical calculations.

Effects of anisotropy of ferrite coating on the radiation characteristics of a cylindrical conductor excited by elementary sources

In this paper, radiation characteristics of an arbitrarily oriented source in an anisotropic multilayered cylindrical structure are investigated by using the state transition matrix approach. Full wave transversal field equations in spectral domain are derived for anisotropic medium in cylindrical coordinates. These expressions are formed into a set of linear first order differential equations. The solution at each layer is expressed in terms of the state transition matrices which are evaluated numerically. Fields are matched at the interfaces. Far fields are evaluated asymptotically by using the steepest descents method. Numerical results are presented for a conducting cylinder coated with an anisotropic ferrite excited by Hertzian dipole. The effects of changing the bias magnetic field of the ferrite and the other medium parameters on the radiation characteristics are examined. Beam scanning, beam splitting, pattern shaping, beamwidth adjustment and control on cross polarized component can be obtained by varying the medium parameters.

Microstrip patch antenna on magnetized cylindrical ferrite substrate

Resonant frequencies of a microstrip patch antenna on a cylindrical magnetized ferrite substrate are evaluated by using the cavity approach for thin substrates. Effects of anisotropy of the ferrite on resonant frequencies are examined. Resonant frequencies of this antenna can be tuned by an externally applied magnetic field.

Design of an active microstrip array using a microwave circuit simulator

An active antenna array design and simulation of this design with a microwave circuit simulator are presented. This active antenna array is a TV receive only (TVRO) antenna operating at 10 GHz. It is a 8/spl times/4 array of rectangular microstrip patch antennas. Eight low noise pHEMTs are placed in the antenna. Passive antenna characteristics are usually obtained by analytical techniques or using special softwares for this purpose. The numerical representation as well as the nonreciprocal nature of the active device necessitates the use of a circuit simulator. In this work, both the antenna and the active circuit characteristics are obtained in the same medium, using microwave circuit simulator LIBRA. The array structure is simulated with LIBRA for gain, noise temperature, radiation pattern, directivity and bandwidth.

Simultaneous Frequency and Direction Finding Technique using Frequency Scanning Antenna

A frequency and phase scannring antenna array svstem having the capability of finding simultaneously the frequency and the direction of arrival of the incident wave by using simple amplitude measurements is described. Microstrip wide slot is used as the antenna array element due to its broad bandwidth. The incident RF wave received by the antenna array is fed to a detector logarithmic video amplifier(DLVA) to determine its amplitude. Finally, the maximum likelihood estimation procedure is applied to the observation vector formed by the DLVA outputs to estimate the frequency and the angle of incidence of the incoming wave.

CA-CFAR detection in spatially correlated K-distributed sea clutter

Radar detection of targets in sea clutter modelled by compound K-distribution is examined from a statistical detection viewpoint by Monte Carlo simulations. The detection performance of Cell Averaging Constant False Alarm Rate (CA-CFAR) is compared with the performance of fixed threshold detection. The performance evaluations are quantified by CFAR loss. Curves for CFAR loss to the spatial correlation and spikiness of sea clutter, number of cells of CA-CFAR processor and the number of non-coherently integrated pulses are presented.

Comparison of the Detection Performance of an FMCW Coastal Surveillance Radar for V and H Polarizations

The present work supports the use of V-polarization instead of H-polarization under CFAR detection in FMCW coastal surveillance radars due to its statistical advantage. The sea clutter reflectivity, sigma0 , is about 3-5 dB less for H-polarization than for V-polarization. However, the sea clutter echoes are spikier for H-polarization than V-polarization for a high resolution radar. It has been suggested that for a high resolution radar V-polarization is to be preferred over H-polarization for a fixed threshold detection below a critical radar height (Watts, 1996). The new numerical results for the detection performance of an FMCW radar with CFAR detection supporting the above argument will be given in the following sections.