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A back-to- back microstrip patch antenna with a switchable pattern is proposed for WLAN applications. The patch elements, printed on FR-4 substrates with a common ground plane, are switched with a single-pole double-throw PIN diode circuit. Switching the feed selects either of two identical radiation patterns in the opposing hemispheres for spatial diversity that would benefit a distributed network.

An omnidirectional microstrip patch antenna, capable of reconfiguring both polarisation and radiation pattern is proposed. It operates with two orthogonal ±45° slanted linear polarisations and can produce two dipole-like radiation patterns, providing 360° coverage in either the horizontal or elevation plane. With appropriate steering, this enables a single antenna to provide full spherical coverage for any polarisation. The reconfiguration is realised by phase shifting, thus does not require switching elements, such as microelectromechanical system or pin diodes embedded into antenna. The basic principles of operation are discussed and validated by numerical and measured data.

An omnidirectional circularly polarized antenna with a rotatable dipole-shaped radiation pattern is proposed. The antenna is realized using a back-to-back coupled microstrip patch arrangement. The pattern is rotated by means of a phase shift, enabling reception (or transmission) of signals from all angles around a sphere. The method enables continuous pattern steering without the need for semiconductor or MEMS components integrated into the antenna. It also allows the use of more than one radiation pattern simultaneously, potentially providing coverage for any spherical angle. The theory is supported by simulation and measurement of four typical antenna configurations. The maximum gains are between 1.9 and 4 dBic and average axial-ratio varies between 2.5 and 3.65 dB at 2.47 GHz. The impedance bandwidth is from 2.4 to 2.51 GHz and the reconfigurable circular polarization is achieved from 2.464 to 2.484 GHz.

This communication proposes a new patch antenna with dual circularly polarized capability at 2.575 GHz. The design exploits the even and odd modes in a coplanar waveguide transmission line and enables simultaneous right- and left-handed circular polarization, with two individual excitation ports. A patch antenna is fed by multimode transmission line and the advantages and disadvantages are discussed. A prototyped antenna realized up to 20 dB isolation between ports with S21

A differentially-fed omnidirectional circularly-polarized antenna is investigated for application in RF energy harvesting. The antenna is composed of a two-layer substrate and back-to-back printed square patches which have two diagonal stubs and one truncation. The patches share a common ground plane. Both patches generate circular polarization (CP) and omnidirectional CP is provided. The antenna provides an axial-ratio bandwidth of 20 MHz from 2.43 GHz to 2.45 GHz. In order to measure the proposed differentially-fed antenna, a feed network connected between the SMA port and differential port is designed. Furthermore, the combined configurations with the proposed antenna, bandpass filter and rectifier can be built and convert the electromagnetic field to DC. The measured output voltage is 255mV at 2.40GHz.

A novel probe-fed single-layer annular-ring patch antenna for dual-frequency circular polarization is evaluated numerically and experimentally verified. The proposed antenna consists of a small circular patch surrounded by two concentric annular-rings, which is loaded by an unequal lateral cross-slot ground plane. The circularly-polarized frequency ratio of the two resonant modes is tunable to a small value, suitable for wireless communications systems. The patch size of the proposed antenna is reduced by about 53% compared to the conventional circular patch at a given frequency. The radiation characteristics of the novel antenna are also presented.

A novel low-cost low-profile dual-frequency circularly polarized patch antenna for GPS applications is presented. By stacking two square patches with truncated corners on a two-layer fractal electromagnetic bandgap structure substrate, the coverage of the entire GPS bandwidth is achieved. Two bandgaps exist for the proposed fractal EBG structure, from 1.16 to 1.32 GHz and from 1.45 to 2.10 GHz, which include the lower and upper frequency GPS band. The antenna is low-profile and has improved gain and axial ratio bandwidth, as well as broader impedance bandwidths compared to the same antenna without EBG. Good circularly polarized radiation patterns are realized. Measurements on prototypes are in good agreement with simulation. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2630–2634, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22815

A back-to-back linearly polarized patch antenna with a single microstrip line feed is proposed for WLAN applications. The antenna consists of two identical rectangular patch elements on the front and rear sides of a common ground plane. One patch antenna can be switched on at a time using a single-pole double-throw PIN diode switching circuit, offering a switched pattern angle of 180° in the Z-axis.

A compact high-performance circularly-polarized microstrip antenna for the global positioning system application is proposed. It comprises a fractal hi-impedance surface electromagnetic bandgap (EBG) structure printed on a high permittivity substrate. Measurements and simulation of return loss and axial ratio are in good agreement. It is shown that the proposed Global Positioning System antenna has good axial ratio performance in the upper half-plane, an improvement in gain and a significantly wider axial ratio bandwidth when compared to the same antenna without EBG

Several novel compact circularly-polarized probe-fed annular-ring microstrip patch antennas are examined experimentally and numerically. In order to reduce the antenna size and provide a suitable input impedance match, two techniques are employed; the insertion of strips into the annular ring and placing a cross-slot into the ground plane. The proposed annular-ring patch with a cross-slotted ground plane yields a much smaller size for a given frequency. This novel patch antenna can effectively be reduced by about 55 percent in size compared to conventional annular-ring patch antennas. The antenna displays wide bandwidth and good circular polarization characteristics. The results of a parametric study for three novel strip-loaded annular-ring patch antennas and for the compact circular patch antenna augmented by a narrow annular ring with a cross-slotted ground plane are discussed in this paper.

A triple-band circularly polarised microstrip patch antenna operating in the 2.4, 3.5 and 5.7 GHz bands is presented. The antenna consists of two substrate layers with an electromagnetically coupled low-band patch in the middle layer and a probe-fed dual-band patch on the top layer. The impedance bandwidths (voltage standing wave ratio (VSWR) < 2.5) for the three frequency bands are 112, 118 and 427 MHz with 3 dB axial-ratio bandwidths of 15, 44 and 36 MHz, respectively. The peak gains across the operating bands are 4.2, 5.5 and 4 dBic, respectively.

A printed circularly polarized monopole antenna operating at 2.45 GHz is presented. It consists of a half-cross shape radiating component fed by a microstrip line and matched to a 50 Ω microstrip feed. It is fabricated on a FR-4 substrate with dielectric constant of 4.6. Simulated and measured results are reported and effect of key parameters is described.

A novel omni-directional circularly-polarised GPS antenna suitable for differential feed is presented. The antenna covers the GPS L1 frequency band. The antenna provides an input impedance of 300 Ω and an axial-ratio bandwidth of 10 MHz from 1.570 GHz to 1.580 GHz. The cross polarization is better than 20 dB.

We propose an omnidirectional circularly polarised planar microstrip patch antenna, in which both impedance bandwidth and circular polarization properties can be adjusted after antenna manufacture. This is done by appropriately tuning four adjustable capacitors, incorporated into the patches. To demonstrate the properties, the proposed antenna is tuned to the GPS L1 band and then re-tuned for Beidou/Galileo E2 band by only changing capacitors values. Design guidelines for such retuning are provided.

A dual-band omnidirectional circularly polarized antenna is proposed. The antenna comprises back-to-back microstrip patches fed by a coplanar waveguide. A very low frequency ratio of 1.182 has been achieved, which can be easily tuned by adjusting four lumped capacitors incorporated into the antenna. An analysis of the omnidirectional circular polarization mechanism as well the dual band operation is provided and confirmed by numerical and experimental data. Key parameters to tune the resonant frequencies and the axial ratio have been identified. The prototype antenna provides omnidirectional circular polarization in one plane with cross polar isolation better than 12 dB for both frequency bands.

A bidirectional circularly polarised (CP) antenna for 1.575 GHz GPS L1 band is presented. The antenna consists of two back-to-back coupled patches and is fed directly by 50Ω Coplanar Waveguide (CPW). It is compact and relatively easy to manufacture compared to other antennas with similar properties. The bidirectional CP pattern is achieved by proper adjustment of patch dimensions as well as feed parameters. A study of the key parameter is provided.

A small microstrip patch/slot antenna, which achieves a very large bandwidth on a relatively thin substrate (about 0.01lambda0), is presented. The performance is achieved by employing a combination of annular-ring loading on the patch radiator and the use of a crossed-slot for miniaturisation. An additional ring-slot in the ground plane is used to produce the wideband characteristics of the antenna. Simulated and measured results indicate that a 53% fractional impedance bandwidth is achieved with respect to the centre frequency of 1.409 GHz and the size of the antenna is reduced by 50% compared to the conventional circular patch antenna with respect to a given frequency

The proliferation of wireless communication systems has promoted the development of miniaturized antenna designs. Annular ring patch antennas are reported to reduce antenna size. In this paper, several novel compact probe-fed annular-ring microstrip patch antennas are presented. In order to reduce the antenna size and provide a suitable input impedance match, two techniques are employed; the insertion of strips into the annular ring and placing a cross-slot into the ground plane. The proposed annular-ring patch antennas with a cross-slotted ground plane yield a much smaller size for a given frequency and are easily matched to 50 Ohms. These novel patch antennas can effectively be reduced by about 55 percent in size compared to conventional annular-ring patch antennas. The antenna can be designed for single band circular-polarization, dual-band circular polarization, triple band, or wideband operation, depending on parameter selection. Some significant advantages are evident for these structures, such as the centre-frequency exhibiting weak dependence on the position of the feedpoint as well as compact size. Good circularly polarized properties and wide CP bandwidths are obtained for these compact antennas. The multiband versions can provide small frequency ratios. The optimized dimensions for four different type antennas are displayed.

th iteration). For the 1 st and 2 rd iteration, each side is replaced with new scaled generator (A1=A/3; B1=0.5*A1, A2=A1/3, B2=0.5*A2), where A1, A2 and B1, B2 are segment and indentation lengths, respectively (Fig.1). The period of the proposed EBG structure is 32.5mm, and A=27mm. A fractal patch connected to the continuous ground plane through a shorting pin constitutes a unit of the lattice. The radius of the shorting pin is 0.5mm. The dispersion characteristics of the fractal Hi-Impedance Surface EBG structure is calculated using the Finite Element Method (FEM). The results illustrated in Fig.2 show a wide bandgap from 1.27GHz to 2.05GHz. A square patch antenna with truncated opposite corners is designed as Fig.3, which excites both the TM01 and TM10 orthogonal modes, can produce circularly polarized fields. The square patch antenna size is 56.0×56.0m

An annular-ring loaded circular patch antenna with slot-ring array of EBG cells on the ground plane is presented. A comparison is made between the annular ring loaded patch on a conventional PEC groundplane and the same patch on a groundplane with a 2times2, a 4times4 and a 6times6 slot-ring EBG array. It was found that the annular-ring patch antenna with a 4 times 4 slot-ring array in the ground plane is superior in the overall performance (gain, impedance and axial-ratio bandwidth). The array of EBG was found to improve gain by 3.5dB and increase the bandwidth of input impedance by about 60% (from 56 MHz to 85 MHz) and the bandwidth of axial ratio increased by about 70% (from 14 MHz to 24 MHz).

A dual-frequency dual-circularly polarised patch antenna with wide beamwidth is proposed. The two-layer structure comprises circular patches with offset circular slots connected to rectangular slots. They provide orthogonal perturbations realising RHCP and LHCP for the lower and upper bands, respectively. The wide beamwidth is realised by extending the substrate beyond the groundplane. Measurements show a maximum beamwidth of 180deg and gains of 3.9 and 0.5 dBic for zenith and 10deg elevation, respectively, for the upper band. The measured beamwidth for the low band is 130deg with a maximum gain of 3.9 and -0.7 dBic for zenith and 10deg elevation, respectively. The axial-ratio is less than 3 dB in the hemisphere for elevations greater than 10deg for both bands.

An omnidirectional circularly-polarised patch antenna is proposed. The antenna radiates right-handed circular-polarisation with an average axial ratio of 2.3 dB over a full 360° . A shallow diagonal CPW inset-feed was used to achieve good matching to the back-to-back coupled patches, providing a measured S11 < -15 dB at the centre frequency. The measured cross-polar performance is better than 13 dB and the realised gain variation is ~3 dB in the plane normal to the substrate.

A novel radial layout for mushroom-like electromagnetic-bandgap (EBG) cells surrounding a printed circularly-polarised patch antenna is proposed. Two radial EBG configurations surrounding a circular patch are compared to a reference patch on a conventional ground plane of the same dimension. The radial shape and displacement of the EBG cells around the patch offers improvements in terms of gain and axial-ratio compared to the reference antenna and is more suitable for circular geometries compared to conventional Cartesian layouts. In particular, the distance between the patch and the surrounding EBG cells is independent of the cell period, which can be arbitrarily chosen, and the overall layout offers footprint reduction.

A dual-frequency dual-circularly polarised patch antenna with wide beamwidth is proposed. The two-layer structure comprises circular patches with offset circular slots connected to rectangular slots. They provide orthogonal perturbations realising RHCP and LHCP for the lower and upper bands, respectively. The wide beamwidth is realised by extending the substrate beyond the groundplane. Measurements show a maximum beamwidth of 180deg and gains of 3.9 and 0.5 dBic for zenith and 10deg elevation, respectively, for the upper band. The measured beamwidth for the low band is 130deg with a maximum gain of 3.9 and -0.7 dBic for zenith and 10deg elevation, respectively. The axial-ratio is less than 3 dB in the hemisphere for elevations greater than 10deg for both bands.

A novel single-layer, single-feed concentric annular-ring microstrip patch antenna providing triple-frequency operation is proposed and experimentally studied. This is achieved by embedding a small circular patch into a dual stub-loaded concentric annular-ring structure and by employing a cross-slot in the ground plane. The proposed technique can provide triple-band operation and reduce the antenna size by over 50% compared to the conventional annular-ring patch antenna for a given frequency. Experimental results show the proposed antenna to have impedance bandwidths of 6.38, 6.30 and 35% for the three bands, at 1.17, 1.428 and 1.9 GHz, respectively. The proposed structure is capable of realising a dramatically small frequency ratio. The measured radiation patterns for each band are presented