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This article presents an experimental demonstration of antenna blockage reduction based on the concept of radio-frequency (RF) cloaking. The proposed cloaking configuration is validated by studying the antenna characteristics in the presence of obstacles that are covered with and without the cloaking surface. The known concept of thin cloaks used for reducing the scattering width is extended in this article to mitigate the blockage in antennas. An attempt is made to improve the degraded radiation characteristics of the antenna due to the presence of metal obstacles loaded in front of the aperture. This is accomplished by covering the obstacles with a cloaking surface made up of a periodic arrangement of interconnected patches and microstrip lines. The optimizations are carried out for various scenarios by varying the thickness of the substrate and the length of the interconnecting microstrip line to achieve an optimum cloaking performance. It is demonstrated through measurements that the RF cloaking could be achieved between the frequencies 3 and 3.3 GHz. At 3.2 GHz, the gain of the horn antenna in free space is measured to be 17.2 dBi, and the gain of the horn antenna with uncloaked obstacles at the aperture is 3.73 dBi. The same configuration with cloaked obstacles exhibits a gain of 12.13 dBi.

A compact, shared-aperture antenna (SAA) configuration consisting of various planar antennas embedded into a single footprint is presented in this article. An L-probefed, suspended-plate, horizontally polarized antenna operating in an 900-MHz band; an aperture-coupled, vertically polarized, microstrip antenna operating at 4.2-GHz; a 2 × 2 microstrip patch array operating at the X band; a low-side-lobe level (SLL), corporate-fed, 8 × 4 microstrip planar array for synthetic aperture radar (SAR) in the X band; and a printed, single-arm, circularly polarized, tilted-beam spiral antenna operating at the C band are integrated into a single aperture for simultaneous operation. This antenna system could find potential application in many airborne and unmanned aircraft vehicle (UAV) technologies. While the design of these antennas is not that critical, their optimal placement in a compact configuration for simultaneous operation with minimal interference poses a significant challenge to the designer. The placement optimization was arrived at based on extensive numerical fullwave optimizations.

A novel technique for obtaining low sidelobes pattern in a planar microstrip array antenna is proposed. This technique involves the addition of two external complementary split ring resonators (CSRRs) at both the ends of each row of the antenna in the ground plane. These two CSRRs together produce an interferometer pattern for the reduction of sidelobes. An $8\times4$ planar array at 9.9 GHz is designed and fabricated to demonstrate the concept and a sidelobe reduction of 4.3 dB achieved.

Series-fed array of square patches designed at 10 GHz, with three different configurations has been analyzed for sidelobe level and cross-polarization characteristics. A series-fed 8×2 planar array is analyzed to provide a sidelobe level of − 24.2dB and cross-polarization level of −21.8dB. The second configuration; a 2-line series array of 8 elements oriented back to back and fed with 180° out of phase exhibits a sidelobe level of − 25dB and low cross-polarization better than −51.6dB over all the angles. In the third configuration, a single line series array of 8 elements displaced on both the sides of the feed line is analyzed. The sidelobe level has been increased to −13.3dB with maximum cross-polarization level −27.7dB. The impedance bandwidth of 220MHz, 270MHz and 350MHz for a VSWR of 2, is observed for the three antenna types respectively.

An analytical method is proposed for the estimation of gain enhancement in superstrate-loaded microstrip patch antenna, when its dielectric substrate and superstrate are replaced by air. The validity of the proposed analytical model is verified over different physical dimensions of the antenna. Analysis is carried on a rectangular microstrip patch antenna and a hexagonal microstrip patch with various combinations of air and dielectric materials as substrate and superstrates. Rectangular microstrip patch antenna etched on dielectric substrate and loaded with superstrate resonates at 1.67GHz and the same antenna resonates at 2.97GHz when both the dielectrics are replaced with air. Similarly the rectangular microstrip patch resonates at 2.41 GHz when only the substrate is replaced with air and resonates at 1.8 GHz when the superstrate is replaced with air. The hexagonal microstrip patch antenna resonates at 3.9GHz when it is etched on dielectric substrate and loaded with dielectric superstrate. By replacing both dielectric substrate and superstrate with air the hexagonal microstrip patch antenna resonates at 8.3GHz. Similarly, when the substrate is alone replaced with air the hexagonal microstrip patch antenna resonates at 6.7GHz. The hexagonal microstrip patch antenna resonates at 4.3GHz when the superstrate is alone replaced with air. The antenna's performance evaluation is done at their respective resonant frequencies. Alternatively Finite element method based 3D simulator is utilized to calculate the gain enhancement. Both the theoretical and simulation results are comparable with the proposed analytical model.

A broadband fractal slot coupled stacked microstrip antenna is presented. Third order fractal slots are used, to improve the antenna bandwidth. The antenna resonates at the center frequency of 1.5GHz and offers 30% bandwidth for a return loss criterion of 10dB. The introduction of fractal slot also leads to antenna miniaturization. The proposed configuration is fabricated and characterized for gain, return loss and radiation patterns. While the measured peak gain of the fractal slot coupled antenna configuration is 8 dB at the center frequency, an average gain of 7dB is measured over the band.

A simple and compact planar printed monopole antenna for ultra wideband application is presented. The proposed antenna comprising of bevel slots in the lower parts of the antenna with annular ring slot. Partial ground plane has been used to enhance the impedance bandwidth. The simulated results show that the proposed antenna exhibits UWB for 2.7 GHz to 11.22 GHz with -10dB return loss and VSWR

In this paper, a new configuration of UWB planar printed compact monopole antenna has been presented. The proposed antenna comprising of U-shaped notch loaded with tuning stubs and annular ring slot. It has a partial ground plane to achieve an excellent impedance matching to increase the impedance bandwidth. The simulated results show that the proposed antenna exhibits UWB for 4.32 GHz to 12.92 GHz with -10dB return loss and VSWR

In this paper, a new configuration of UWB planar printed compact monopole antenna comprising of symmetrical slots and PI notched with parasitic patches. It has a partial ground plane to achieve an excellent impedance matching to increase the impedance bandwidth. The proposed antenna rejects the 5GHz WLAN band in the frequency range of 5.42-5.74 GHz by introducing PI shaped notch. The simulated results show that the proposed antenna exhibits UWB for 3.52 GHz to 11.06 GHz with -10dB return loss and VSWR

This paper presents an UWB planar printed compact monopole antenna comprising of U-shaped notch loaded with L-slot and tuning stubs. It has a partial ground plane to achieve an excellent impedance matching to increase the impedance bandwidth. The simulated results show that the proposed antenna exhibit UWB for 3.84 GHz to 11.61 GHz with –10dB return loss and VSWR < 2. Antenna gain and radiation pattern plots for different frequencies are also investigated. The performance characteristics of the proposed antenna are simulated using Ansoft HFSS software. Index Terms planar antenna, ultra wideband, partial ground plane.

Design of two element printed crank-line array is presented as an inverted microstrip line structure. High gain circularly polarized (CP) tilted beam is achieved from this configuration. The antenna consists of crank-line element as a travelling wave radiator and fed with a printed Z-feed with a printed vertical stub termination. A microstrip power divider is employed to feed array elements with equal amplitude and quadrature phase difference to tilt the main beam direction to 410. Power divider and radiating elements both share the common ground. The antenna exhibits an impedance bandwidth of 43% (3.58-5.3 GHz) for a VSWR

A circularly polarized (CP) printed slot antenna configuration on a shared aperture is proposed. Antenna is designed to operate at two distinct frequency bands of 4GHz and 8GHz. Dual slot CP elements at two frequencies are created on a common shared aperture and the antenna is fed by a single microstrip feed line. To achieve unidirectional beam, the slot antenna is backed by a stepped reflector. The stepped reflector is optimized to provide proper phase for pattern combining and axial ratio improvement at both the frequency bands. Antenna operates over a frequency range of 3.5 to 4.5GHz and 7.5 to 8.5GHz for a VSWR

A microstrip antenna couplet on a periodic patterned ground plane is proposed to provide circularly polarized tilted beam. Circular polarization is achieved by employing two wide microstrip antenna elements designed to operate in C-band. The elements are fed at the corners with 900 phase difference along a travelling wave microstrip feed line. A novel concept of patterned slotted ground plane is utilized in tilting the main beam from the broadside. The slot patterns on the ground plane and the dimensions of microstrip patches and their angle with respect to the feed line are optimized to achieve wideband axial ratio. The designed antenna exhibits a maximum gain of 3.2dB with beam pointing angle at 300 and operates over a bandwidth of around 8% for a VSWR