Hand Circular Polarization Research Articles

Reconfigurable Scan-Beam Single-Arm Spiral Antenna Integrated With RF-MEMS Switches

A fully integrated solution providing scan-beam capability with a single antenna is presented in this paper for the first time. The proposed system includes a reconfigurable rectangular spiral antenna with a set of micro electro mechanical system (MEMS) switches, which are monolithically integrated and packaged onto the same substrate. The system is based on a single-arm rectangular spiral antenna, capable of changing its radiation pattern using radio frequency-MEMS (RF-MEMS) switches. The rectangular spiral and RF-MEMS switches are monolithically integrated on a conventional microwave substrate printed circuit board (/spl epsiv//sub r/=3.27 and tan/spl delta/=0.004) and quartz substrate (/spl epsiv//sub r/=3.78 and tan/spl delta/=0.0002). The spiral is made out of multiple lines, which are interconnected by RF-MEMS switches strategically located along the spiral. On activating these switches, the spiral overall arm length is changed and consequently its radiation beam direction is changed. The two proposed antennas radiate right hand circular polarization (RHCP) and left hand circular polarization (LHCP) for printed circuit board and quartz substrate respectively. The gain of the two antennas varies between 3/spl sim/6 dBi. They both satisfy the 3-dB axial ratio criterion at their operating frequency band, i.e., at 10 GHz and 6 GHz for the printed circuit board and the quartz substrate respectively. To the best of our knowledge, this is the first truly reconfigurable printed antenna design using MEMS devices as active elements integrated in the same low loss substrate. The excellent performance of the proposed system emphasizes the importance of being able to integrate MEMS switches into the same low loss substrate for antenna applications. This technology pioneers the design of arbitrarily shaped reconfigurable antennas including the design of reconfigurable antenna arrays.

A Reconfigurable Microstrip Antenna with Switchable Polarization

A novel reconfigurable small microstrip antenna with switchable slots is proposed to achieve circular polarization diversity. Slots are cutting in the square patch and, by using the diodes to adjust the lengths of the slots, this antenna can radiate with either right hand circular polarization (RHCP) or left hand circular polarization (LHCP) using the same feeding probe. Simulation and experimental results are presented and it is demonstrated that this design is valid. The proposed antenna demonstrates useful features for wireless communication applications.

Null-Steering LMS Dual-Polarised Adaptive Antenna Arrays for GPS

The implementation of a null-steering antenna array using dual polarised patch antennas is considered. Several optimality criterion for adjusting the array weights are discussed. The most effective criteria minimises the output power of the array subject to maintaining a right hand circular polarisation (RHCP) response on the reference antenna. An unconstrained form of this criteria is derived, in which the reference channel is the RHCP output of the reference antenna and the LHCP output of the reference antenna is included as one of the auxiliary channels. An FPGA implementation of the LMS algorithm is then described. To prevent weight vector drift a variant of the circular leakage LMS algorithm was used. The implementation details of a simplified circular leakage algorithm more suited to an FPGA implementation are presented. This simplified leakage algorithm was shown to have a similar steady state weight vector as the full algorithm.

Low-cost monopulse radial line slot antenna

The authors propose the design of one radial line slot antenna with two simultaneous beams, one broadside beam and one conical beam. The antenna is a radial line slot antenna (RLSA), with the slots placed on the upper plate in concentric rings. The radiating element is a slot pair, designed for getting left hand circular polarization. The antenna has been designed to work in the range of 13.4 GHz and 14 GHz. Both beams are obtained independently through very simple excitation circuits, realized with microstrip technology. These feeding networks include a Butler Matrix Network. Comparing both radiation patterns, amplitude and phase, theta and phi angles of arrival direction can be obtained. This monopulse performance can be used to orientate the pencil beam for satellite communication antennas. Measurements for a first prototype are presented to validate the design.

Circular polarization of radio emission from relativistic jets

In inhomogeneous optically thick synchrotron sources a substantial part of the electron population at low energies can be hidden by self-absorption and overpowered by high energy electrons in optically thin emission. These invisible electrons produce Faraday rotation and conversion, leaving their footprints in the linear and circular polarized radiation of the source. An important factor is also the magnetic field structure, which can be characterized in most cases by a global magnetic field and a turbulent component. We present the basic radiative transfer coefficients for polarized synchrotron radiation and apply them to the standard jet model for relativistic radio jets. The model can successfully explain the unusual circular and linear polarization of the Galactic Centre radio source Sgr A* and its sibling M81*. It also can account for the circular polarization found in jets of more luminous quasars and X-ray binaries. The high ratio of circular to linear polarization requires the presence of a significant fraction of hidden matter and low-energy electrons in these jets. The stable handedness of circular polarization requires stable global magnetic field components with non-vanishing magnetic flux along the jet, while the low degree of total polarization implies also a significant turbulent field. The most favoured magnetic field configuration is that of a helix, while a purely toroidal field is unable to produce significant circular polarization. If connected to the magnetosphere of the black hole, the circular polarization and the jet direction determine the magnetic poles of the system which is stable over long periods of time. This may also have implications for possible magnetic field configurations in accretion flows.

An Electron Density Model above the Sunspot from a Mapping of NOAA 7260 at 17 GHz

The brightness temperature distribution of microwave emission in a solar active region generally shows a ring structure, with a dip at the centre. However, no dip was found in the Nobeyama Radioheliograph left handed circular polarization (LCP) image on 1992 August 18; instead, there was a peak. This is a completely LCP source with zero right-handed circular polarization (RCP). We examine this structure in terms of the joint effect of gyroresonance and bremsstrahlung mechanism with a raised electron density above the central part of the sunspot, and the commonly assumed temperature and vertical dipole magnetic field models. The raised electron density is found to be 1.4 x 10(11) cm(-3) at the chromosphere base.

A reconfigurable patch antenna using switchable slots for circular polarization diversity

A novel design of a microstrip patch antenna with switchable slots (PASS) is proposed to achieve circular polarization diversity. Two orthogonal slots are incorporated into the patch and two pin diodes are utilized to switch the slots on and off. By turning the diodes on or off, this antenna can radiate with either right hand circular polarization (RHCP) or left hand circular polarization (LHCP) using the same feeding probe. Experimental results validate this concept. This design demonstrates useful features for wireless communication applications and future planetary missions.

Observation of beam-induced changes in the polarization of Balmer- alpha radiation emitted following beam-tilted-foil transmission.

Measurements of the circular polarization of Balmer-\ensuremath{\alpha} radiation emitted by excited hydrogen atoms, following the transmission of (20--50)-keV protons through thin, tilted amorphous carbon foils, exhibit markedly unexpected behavior as a function of exposure of the foil to the proton beam. Specifically, the circular polarization changes from an initially well understood tilt-angle dependence to a behavior which, for low tilt angles, gives the opposite handedness of circular polarization from that predicted. In addition, the degree of alignment, indicated by the linear Stokes parameter M/I, is enhanced also as a function of dose. These changes in the tilt-angle dependence of the Stokes parameters have been systematically correlated with beam-induced graphitization of the foil, which is observed to occur from Raman measurements.

Varactor-diode loaded passive polarisation-agile patch antenna

A passive polarisation-agile microstrip patch antenna has been developed. Using independently biased varactor diodes on the patch axes to tune or detune orthogonal modes, it can produce linear polarisation, or left or right hand circular polarisation according to the bias voltages. Crosspolar levels when operated in the linear state, and axial ratios in the circular state can be optimised by fine adjustment of the diode bias.

New coplanar waveguide/stripline feed network for seven patch hexagonal CP subarray

A novel CPW-to-stripline post coupler is demonstrated. This device couples the output power from a coax-to-CPW inphase seven-way radial power divider to a balanced stripline line stretcher and together forms a multilayer probe-type feed network. The feed network excites a seven-patch hexagonal circularly polarized (CP) subarray. The measured return loss and insertion loss of the coupler are better than 17 dB and 0.25 dB at the design frequency of 2.875 GHz. The measured on-axis axial ratio for the left hand circular polarization (LHCP) is 1.5 dB and the 3 dB beam widths are 36 deg in the principal planes of the subarray. The gain of the subarray is 13 dB. The input return loss of the subarray is better than 10 dB.

On the origin of continuum polarization in white dwarfs.

We propose a model in which classical cyclotron emission from a hot corona can account for much of the continuum linear and circular polarization which has been observed at optical frequencies for several white dwarfs. Important features of our model are: (1) The degree of linear polarization (p) approx. = degree of circular polarization (q) for a variety of magnetic field configurations; (2) continuum polarization occurs in the optical only for surface magnetic field strengths B> or =10/sup 8/ gauss; (3) changes with wavelength in the handedness of circular polarization and in the position angle of the linear polarization occur naturally; and (4) the strong fields required imply severe shifting and smearing of sectral lines, for which there is evidence in some white dwarfs. Possible energy sources for and structures of such coronae are discussed. Observational tests of the model are suggested. (AIP)