Akhilesh Mohan

A Compact Koch Fractal UWB MIMO Antenna With WLAN Band-Rejection

In this letter, a compact octagonal shaped fractal ultrawideband multiple-input-multiple-output antenna is presented, and its characteristics are investigated. In order to achieve the desired miniaturization and wideband phenomena, self-similar and space filling properties of Koch fractal geometry are used in the antenna design. These fractal monopoles are placed orthogonal to each other for good isolation. Moreover, grounded stubs are used in the geometry to provide further improvement in the isolation. The band rejection phenomenon in wireless local area network band is achieved by etching a C-shaped slot from the monopole of the antenna. The proposed antenna has compact dimensions of 45 mm × 45 mm and exhibits quasi-omnidirectional radiation pattern. In addition, it shows an impedance bandwidth (S11 <; -10 dB ) from 2 to 10.6 GHz with isolation better than 17 dB over the entire ultra-wideband range. Diversity performance is also evaluated in terms of envelope correlation coefficient and capacity loss. The measured results show good agreement with the simulated ones.

Compact MIMO Slot Antenna for UWB Applications

A compact four-element multiple-input-multiple-output (MIMO) antenna for portable wireless ultrawideband (UWB) applications is presented in this letter. The proposed UWB MIMO antenna has the compact size of 42 ×25 mm2. The microstrip-fed stepped-slot antenna acts as a single UWB antenna element. The UWB antenna covers the wide frequency band from 3.1 to 12 GHz. High isolation ( ≥ 22 dB) is achieved between the UWB antenna elements without any decoupling network. It is due to inherent directional radiation properties of slot antennas (SAs) and their asymmetrical placements. The measured impedance bandwidth of UWB MIMO antenna is from 3.2 to 12 GHz with the isolation better than 22 dB over the entire UWB spectrum. The envelope correlation coefficient (ECC) as well as channel capacity loss (CCL) are investigated, and they are within their acceptable limits.

GENERALIZED SYNTHESIS AND DESIGN OF SYMMETRICAL MULTIPLE PASSBAND FILTERS

In this paper, we present a new synthesis method for a generalized symmetric multiple band bandpass fllter. By using frequency transformations on the low pass prototype, the poles and zeros of the single/dual band flltering function are obtained. These poles and zeros are combined and re-arranged to get the multiband flltering function. The coupling matrix is obtained from this multiband flltering function. A variety of fllters are synthesized in order to validate the proposed theory. A triple band and quadruple band fllters have been designed, fabricated and measured. The measured results have good agreement with the simulated results.

Single-Layer Wideband Microwave Absorber Using Array of Crossed Dipoles

In this letter, a single-layer wideband absorber with compact thickness is proposed, and its ability to reduce the radar cross section (RCS) is investigated. The absorber consists of two-dimensional array of conductive crossed dipoles with lumped resistor elements on the top of a single-layer FR4 substrate, backed by continuous metallic layer. Simple methodologies for design and analysis of the absorber are presented. The thickness of the fabricated sample is less than 0.077λL. (wavelength at the lowest cutoff frequency). It offers the 10-dB reflection reduction bandwidth of 70.7% (5.3-11.2 GHz) and full width at half-maximum (FWHM) absorption bandwidth of 104.76% (3.75-12 GHz). The experimentally demonstrated performance of the absorber shows good agreement with the numerical simulations.

Compact Reconfigurable UWB Slot Antenna for Cognitive Radio Applications

A very compact reconfigurable ultrawideband (UWB) stepped-slot antenna for cognitive radio (CR) applications is presented in this letter. The proposed antenna operates in two modes: UWB mode for sensing application and communicating mode for different narrow/wideband communication applications. The UWB mode of antenna is obtained by the creation of three resonances that lie in UWB spectrum. The narrow/wide communicating bands are obtained by different switching states of five p-i-n diodes. The impedance bandwidth of the proposed antenna in UWB mode is 2.8−10.7 GHz. The communicating bands (3.2−4.5, 4.3−7.8, and 7.9−11.2 GHz) cover the entire UWB spectrum. The proposed antenna has the compact size of 21 × 9 mm2. A prototype of the designed antenna is fabricated and measured. The measured results are in good agreement with the simulated results that validate the proposed approach of reconfigurable UWB antenna design for CR applications.

CRLH Unit Cell Loaded Triband Compact MIMO Antenna for WLAN/WiMAX Applications

A compact triple-band two-element multiple-input–multiple-output (MIMO) antenna is designed in this letter. The triple-band characteristic is achieved by loading a modified square-loop antenna with composite right/left-handed (CRLH) unit cell. Open-ended slot is etched from ground plane of the MIMO antenna to improve the isolation. The two-element antenna is well suited for WLAN/WiMAX applications as it covers 2.37–2.64, 3.39–3.58, and 4.86–6.98 GHz. Both envelope correlation coefficient and channel capacity loss are within their acceptable limits. Moreover, the antenna exhibits quasi-omnidirectional radiation pattern in xz -plane, which is useful for portable wireless communication devices.

Reduction of cross-polarized reflection to enhance dual-band absorption

In this paper, cross-polarized reflection from a periodic array of metal-dielectric-metal resonator units is reduced to improve its absorbing performance. Through this simple and typical example, it is shown that some reported absorbers are actually poor absorbers but efficient polarization converters, when the cross-polarized reflection is considered. Using a frequency selective surface, sandwiched between the top layer and the ground plane, the cross-polarized reflection is reduced by 7.2 dB at 5.672 GHz and 8.5 dB at 9.56 GHz, while negligibly affecting the co-polarized reflection reduction performance. The polarization conversion ratio is reduced from 90. 74% to 34.12% and 98.51% to 27.2% and total absorption is improved up to 80% from 26% and 21% around the two resonant frequencies. The reflection characteristics of the proposed absorber are quantitatively analyzed using interference theory, where the near field coupling of the resonant geometries and ground is taken into account. Measurement results...

A miniaturized dual mode CRLH unit cell loaded SIW antenna

A dual-mode substrate integrated waveguide (SIW) antenna, based on composite right/left handed (CRLH) unit cell, is proposed in this paper. The CRLH unit cell is a designed by etching an interdigital capacitor (IDC) slot on the top plane along with a circular complimentary split ring resonator (CSRR) on the ground plane. Due to application of CRLH unit cell, zeroth order resonance (ZOR) is obtained at 1.95 GHz along with the conventional first order resonance mode. Analytical and parametric studies show that the electrical size of the antenna can be effectively reduced by increasing the width of the complimentary split rings. Compared to other SIW-IDC antenna, the present design has a smaller cavity size of 0.13λ0×0.13λ0 at lowest resonant frequency. For n=1 mode resonant frequency, a significantly high gain of 5.97 dBi is obtained at 5.65 GHz.

Bandpass Filter Realization Using Degenerate Dual-Modes of a New Type of Patch Resonator for Significant Size Reduction

A new type of dual mode patch resonator is proposed and dual-mode bandpass filters are designed by perturbing its degenerate modes using two slots which are orthogonal to each other. It has been shown that resonant frequencies of the degenerate modes can be varied independently by adjusting one slot length at a time. Geometrical size as well as radiation loss has been reduced further by using inductively loaded cross-slotted patch resonator. A bandpass filter operating at 2.98GHz with a fractional bandwidth of 4.69% is designed after miniaturization. A size reduction of approximately 30% is observed when compared with miniaturized triangular patch resonators, for the same center frequency.

A differential wideband bandpass filter

A wideband differential bandpass filter with enhanced common mode suppression and better out of band performance is presented in this paper. This filter consists of two back to back connected stepped impedance resonators (SIRs) coupled to each other through two dumbbell shaped slotline resonators. The size of the filter is 22 mm × 43 mm. The proposed filter has the differential passband bandwidth of 65 % centered around 4.85 GHz, with the common mode (CM) suppression better than 22 dB over the entire differential passband of the proposed filter. The insertion loss varies from 1.27 dB to 2.5 dB in the passband of the filter.