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A generalised stubs-integrated-microstrip (SIM) antenna with wide coverage circularly polarised (CP) radiation is proposed for radio-frequency energy harvesting applications. The antenna consists of a microstrip patch radiator with four integrated asymmetric/symmetric-stubs and a coaxial feed. Four stubs are integrated at the corners of a square microstrip radiator. The stub lengths or stub gaps from the microstrip radiator are optimised for wide-beam CP radiation. Four different combinations of asymmetric/symmetric based SIM antennas are designed, fabricated, and tested. The proposed antennas are able to cover upper-half area with CP radiation across the 3-dB axial ratio bandwidth.

The reflection coefficient phase is studied for four different artificial magnetic conductors (AMCs) having canonical frequency selective surface (FSS)-type two-dimensional periodic structures to be used as back reflectors for an aperture antenna. The bidirectional circularly polarised (CP) radiation of the octagonal-shaped aperture (OSA) antenna is made unidirectional using these AMC surfaces as ground planes. The antenna height measured from the upper surface of AMC reflector to the OSA radiator is chosen to be small to realise low-profile antenna: 0.0825λ o at the lowest analysis frequency of 4.5 GHz. Different antenna parameters like voltage standing wave ratio (VSWR) of 2, 3-dB axial ratio (AR) bandwidth, gain, and front-to-back ratio are studied and compared for these four AMCs and the conventionally used perfect electric conductor (PEC) ground plane as back reflectors. Four different aperture shapes with fixed aperture perimeter are designed to integrate with the square-loop AMC as back reflector to realise a low-profile unidirectional wideband CP aperture antenna. Hexagonal-shaped aperture antenna over the square-loop AMC shows the largest measured 3-dB AR bandwidth of 23.33% (5.65-7.05 GHz), VSWR of 2 bandwidth of 36.67% (5.16-7.36 GHz), and the gain of around 7 dBic over the band for overall antenna volume of 0.72λ o × 0.60λ o × 0.19λ o at 6.0 GHz.

A broadband microstrip antenna with low–high–low (sandwich) dielectric constant substrate combination using a microstrip line-via feed is presented for ultra-wideband applications. The proposed antenna consists of three dielectric substrates; low dielectric constant substrates that contain the microstrip feed line as well as parasitic patches and a high dielectric constant substrate that contains the driven patch. To achieve a large impedance bandwidth, parasitic patches and microstrip line-via combination feed to the driven patch in the multilayered microstrip antenna are used. The proposed antenna designed, fabricated and measured on the sandwich substrate. The antenna has measured 10 dB return loss bandwidth of 46.9% and directive gain >5.2 dBi at boresight across the impedance bandwidth. The total height of antenna is 5.77 mm or 0.077λo at 4 GHz.

A new sectorised antenna array (SAA) and measurement methodology are proposed for indoor ultra-wideband (UWB) applications. The proposed SAA comprises of one centre element and six side elements. The one centre element and six side elements are arranged in a semi-spherical antenna array configuration. The measurement system and methodology for the coverage of the SAA are developed. The measured bandwidth of the SAA for voltage standing wave ratio (VSWR) les2 is 37.5%, ranging from 3.06 to 4.47 GHz. The boresight gain is more than 5.2 dBi across the impedance bandwidth. The proposed SAA is able to provide omni-directional pattern with an average gain of 5.2 dBi over the angles (0-360deg). The discone reference antenna is used to measure the coverage of the proposed SAA. The proposed measurement study shows that the proposed SAA offers omni-directional coverage desirable in UWB indoor location and short-range communication systems.

Coplanar waveguide (CPW)-loop fed wideband multilayered microstrip antennas with and without via combinations are presented. The antenna consists of two dielectric substrates, CPW-loop on the ground plane layer, main patch on the middle layer and four asymmetric parasitic patches on the upper layer. The feed consists of a CPW, a loop on a ground plane and a via between main patch and feeding strip on the ground plane layer. Using via, the gain flatness over the impedance bandwidth and return loss are improved. The proposed antenna with four feeding structures is also studied. The 10 dB return loss bandwidths of the antenna with and without via are 34% (3.12 4.41 GHz) and 33.7% (3.18 4.47 GHz), respectively. The measured gain is >5.0 dBi over the impedance bandwidth.

The authors present multipatches multilayered ultra-wideband (UWB) microstrip antennas. The antenna comprises a driven patch radiator with five parasitic patch radiators. Two antennas with different dielectric substrate combinations are studied. The antenna with low-high-low dielectric constant substrate combination (Antenna no. 1) has an improved performance in terms of impedance bandwidth, gain, overall antenna size and beam-squinting over the antenna with low-low-low dielectric constant substrate combination (Antenna no. 2). The low-high-low dielectric constant combination consisting of three dielectric substrates, namely low dielectric constant (ɛr=3.38) for both bottom and upper substrate but, high dielectric constant (ɛr=6.15) for middle substrate. Five parasitic patches and multi-dielectric layers are used for wide impedance bandwidth and less boresight gain variation with frequency. A measured 10 dB return loss bandwidth of 48% with boresight gain >5.0 dBi is achieved. Antenna no. 1 can have 8% wider impedance bandwidth, 40% overall area reduction and less beam-squinting compared with Antenna no. 2.

A novel aperture-coupled, asymmetrical C-shaped slot, square microstrip antenna is proposed for circular polarisation (CP). A narrow and asymmetrical C-shaped slot, microstrip antenna is fed at the centre using an aperture coupling to obtain a CP operation. The compactness of the antenna is easily obtained by inserting a C-shaped slot. Wide CP radiation is achieved simply by making the C-shaped slot asymmetrical. With this antenna, the measured 3 dB AR bandwidth is around 3.3% and the 10 dB return loss bandwidth achieved is 16.0%. The overall antenna size is 0.48lambda o times 0.48lambda o times 0.092lambda o at 2.4 GHz. The proposed slot microstrip patch technology is useful to design compact, broadband, circularly polarised antennas and arrays.

The gain of a standard rectangular dielectric resonator antenna (DRA) is enhanced by integrating it with a surface mounted short horn (SMSH). An enhancement of gain by 3.7 dB to 9.8 dBi at 5.95 GHz, and a 10 dB return bandwidth of 3.2% has been achieved from this configuration. Performances of antennas with different types of SMSHs are studied; SMSHs made out of thin metal strips or strips supported by foam are found to be best. Next, the bandwidth of the antennas is enhanced by replacing the DRA with a wideband hybrid antenna, consists of a rectangular DR on a patch resonator. A return loss bandwidth of 25%, and a gain better than 8.5 dBi over this bandwidth, has been achieved. The boresight cross-polarisation level is less than -27 dB and the sidelobe level is less than -15 dB over the entire bandwidth

A new feed system is presented for improving the quality and bandwidth of circularly polarised stacked microstrip antennas (CPSMAs). The feed system consists of a microstrip line and a via (or pin) from the microstrip line to a driven patch. A systematic design process to achieve near-optimal CP performance from these antennas is presented. An example design demonstrated a measured 3 dB axial-ratio (AR) bandwidth of 17% and a measured 10 dB return bandwidth of 35%. The measured gain is more than 8 dBic over the 3 dB AR bandwidth. The total height of the antenna is 8.536 mm or 0.156lo at 5.5 GHz. The new feed system is found to be very useful for the design of wideband, compact, low-cost, CP microstrip antennas and arrays.

The microstrip patch resonator in several configurations can be used for determination of the dielectric constant and the loss tangent of materials available in sheet, paste and liquid forms. A suspended patch resonator was developed to determine the dielectric constant and loss tangent of wax, kerosene, petrol and vaseline. The measured dielectric constant of the sample is within /spl plusmn/ 2% and the loss tangent has a variation /spl plusmn/0.001 for the sample with moderate loss.

An analytical single-layer reduction quasi-static formulation to accurately compute all the line parameters of metal insulator semiconductor (MIS) and Schottky contact multilayer slow-wave microstrip lines is presented. It is valid for a wide range of parameters and its validity is compared with the full-wave spectral domain analysis technique. We also obtain a circuit model, which is able to accurately explain the experimental results, including dispersion at the lower end of the frequency range, for both the MIS and Schottky contact microstrip lines. Useful data to design passive components based on these lines are also presented.

The input and radiation characteristics of a circular microstrip antenna on thick and lossy iso/anisotropic substrate are computed with the help of its equivalent rectangular microstrip antenna. The computed results show good agreement with the results of mode matching methods and experimental results. Results using three commercial software products are also compared against the same set of the experimental results. The performance of the present method (MWM) is better than the performance of commercial software.

A modified cavity model to compute the resonance frequency of a rectangular patch antenna on a thick polytetrafluoroethylene substrate (0.037/spl lambda//sub g/ 0.229/spl lambda//sub g/) with maximum deviation of 2% against experimental results is presented. This accuracy is achieved by accounting for the effect of anisotropy and total losses on the resonance frequency. All other models, including the method of moments (MOM)-based Ensemble, compute resonance frequency with error between 4 and 36%.