Navid Rezazadeh

A planar controlled reception pattern array with dual-mode TM11-TM21 microstrip antenna elements for increased angular coverage

A planar controlled reception pattern array (CRPA) with increased upper hemisphere angular coverage is designed and studied. The array consists of three dual-mode TM11-TM21 circular microstrip elements. The TM11 patch is circularly polarized (CP) while the TM21 patch is dual polarized to exploit more degrees of freedom. The nulling performance of the array is studied using a Monte Carlo approach and is benchmarked against a uniform circular array (UCA) of TM11 elements and a spherical array. It is shown that for low elevation angle RFIs, the proposed array provides more angular space available for reception, compared to the planar UCA.

A dual-polarized dual-mode annular ring microstrip antenna for GPS interference suppression

A dual-mode antenna consisting of an outer annular ring excited in TM21 mode and an inner annular ring excited in TM11 mode is proposed for GPS interference suppression. Two independent linear polarizations are excited at each mode through capacitive coupling by two arc-shaped mirostrip feed lines. The nulling performance of this four-channel antenna is studied through a Monte Carlo analysis and compared to that of a polarimetric array of two TM11 elements with half a wavelength separation. It is shown that the proposed antenna, with only 0.26 λ diameter, can cancel a maximum of three randomly polarized or two circularly polarized interferers near horizon while retaining better angular coverage than the single-mode array. The results are provided for the narrowband case, but can be generalized to the wideband case with space-time adaptive processing.

Resonance effects in antennas coated with material and metamaterials

Conducting antennas and sensors are often coated with insulating materials to protect them from the environment. Such coatings can cause resonances that will alter the input impedance and radiation characteristics. For dipole type antennas the problem is investigated analytically to determine the exact resonances, and their influence on the radiation power. The use of such resonance for shaping the radiation patterns of the antenna is also discussed.

Study of finite ground plane effects in circularly-polarized circular microstrip antennas

Finite ground plane effects of circularly-polarized circular microstrip antenna (CMA), working in dominant TM11 mode, are studied. The results of an analytic solution, based on the induced currents on the ground plane, show that the beamwidth where the axial ratio is below 3 dB, has its maximum value when the ground diameter is around 0.6 λ. This result is verified by full-wave simulation and through experiment. Based on the results, we conclude that for a single circularly polarized CMA, a ground diameter around 0.68 λ, ensures an axial ratio which remains below 3 dB in the upper hemisphere. This is particularly useful for the global positioning system.

GPS anti-jamming performance of multimode microstrip antennas

A multimode configuration of concentric TMn1 mode circular microstrip antennas is proposed for anti-jamming in GPS receivers. By calculating the performance of a five-element configuration in terms of availability of service in the presence of jammers, it is shown that theoretically, it provides improvement when compared to a planar and a spherical arrays with the same number of elements.

A novel ultra-wideband pattern diversity antenna for high-gain applications

An ultra-wideband (UWB) pattern diversity antenna design is proposed for high-gain applications and simulation and measurement results are presented. The proposed antenna is compact in size (50×41×21 mm3) and easy to fabricate. Its structure consists of two parallel disk radiating elements, each fed at two points by two microstrip lines. Ground plane is shaped like a cavity with two edges at an angle 70°. The disks are also slightly modified in geometry to suppress unwanted radiation and increase port isolation. The radiation pattern of the antenna is either directional or squinted for out-of-phase and in-phase excitations, respectively, which resembles the sum and difference patterns in monopulse feeds. Simulation results show -10 dB impedance bandwidths extending from 5 to more than 15 GHz. The radiation patterns maintain less than -15 dB sidelobe, backlobe and cross-polarization levels from 5 GHz up to 9 GHz. The pattern measurements are carried out on a prototype antenna for 6.5-8.5 GHz and show good agreement with the simulation data. The measured gain of the sum pattern in this band, varies from 8.6 dBi to 11.2 dBi, with less than -15 dB sidelobe, and cross-polarization levels. The peak gain of difference mode varies between 3 dBi to 5.5 dBi. This antenna can be used as a standalone directive wideband antenna, as a reflector feed, or for monopulse tracking applications.

Cross-polarization reduction in a directive ultra-wideband antenna using electromagnetic polarization filter

An electromagnetic polarization filter (EMPF) is designed to reduce the cross-polarization of a directive ultra-wideband (UWB) antenna. The filter is a rectangular cap with solid metal sheets on two sides and printed metal strips on the top and other sides. This cap increases the height of the whole structure by 5 mm while reducing the maximum cross-polarization level by 7 dB over the frequency band 8 GHz to 11 GHz. The resulting antenna has a maximum cross-polarization level of -20 dB over the frequency band.

Ultra-wideband pattern diversity antenna with cavity

A new ultra-wideband (UWB) pattern diversity antenna design is proposed and simulation results are presented. With a size 40×42×21 mm3, the proposed antenna structure consists of a disk radiating element, fed at two points at 90° angle by two coaxial lines. The excitation of feed lines determines the radiation pattern of the antenna, which is either directional or squinted. The disk and its feed lines are supported by a ground plane which is shaped like a cavity. The disks are also slightly modified in geometry to suppress unwanted radiation and increase ports isolation. The antenna shows an impedance bandwidth from 6.8 GHz to more than 15 GHz.