Antenna Transfer Function Research Articles

Uniplanar Log-Periodic Slot Antenna Fed by a CPW for UWB Applications

A coplanar waveguide-fed uniplanar log-periodic slot antenna suitable for use in the ultra-wideband radio systems is presented. The in-band impedances and radiation performances are quite stable and satisfactory. A rejected narrow frequency band is further obtained within the wide bandwidth by inserting a pair of metallic stubs into two vertical slots of the proposed antenna. Experimental results reveal that the stub pair provides significant attenuation in the desired notched band but has little effect on the antenna operation outside of the notch. By means of a normalized antenna transfer function, the time-domain characteristics of the proposed antennas are also investigated. The transient responses show that the designs with and without the notched band are both acceptable for the pulsed systems

Characterization of small planar antennas for UWB mobile terminals

AbstractThis paper presents an extensive investigations to characterize antennas for small UWB mobile terminals. Two small planar UWB antennas (slot antenna and printed monopole antenna) were designed, using a full‐wave electromagnetic finite difference time domain (FDTD) method. The UWB slot antenna has a size of 32 × 29 mm, the monopole antenna size is 20 × 36.75 mm. Both antennas were characterized using true UWB parameters, such as antenna transfer functions, fidelity, and pulse energy spread. We have investigated angular‐dependence of antenna characteristics over the entire radiation sphere. Spatially averaged transfer functions were introduced to disclose antenna characteristics for different solid angles in the radiation sphere. We have also shown the difference in transient characteristics of antenna in transmitting (Tx) and receiving (Rx) mode. Finally, we have investigated the Tx/Rx antenna system, where any relative orientation between Tx and Rx antenna was assumed to be equally probable. Copyright © 2005 John Wiley & Sons, Ltd.

On the Electromagnetic Radiation of Printed-Circuit-Board Interconnections

Large ground and supply layers on interconnected boards represent a radiating antenna structure which may be efficiently excited at its resonances by small high-frequency potential differences. Such potential differences between the boards mainly originate from the inevitable inductive impedance of the signal-current return path in the connector, usually provided by ground pins. The presented modeling approach is based on an antenna transfer function for the global interconnecting structure and a partial-inductance equivalent circuit for the connector. As shown by the example of a motherboard-daughterboard structure, the model enables a systematic study of the radiation mechanism, depending on signal/ground-pin configuration, as well as geometrical and electrical parameters. In conjunction with SPICE simulations of the connector equivalent circuit, the signal driver and receiver dynamic characteristic can also be properly included. Validation is provided by full-wave simulation and measurement results.

Planar miniature tapered-slot-fed annular slot antennas for ultrawide-band radios

A novel planar tapered-slot-fed annular slot antenna is proposed in this paper. The antenna utilizes a unique tapered-slot feeding structure and simultaneously possesses ultrawide bandwidth, almost uniform radiation patterns, and low profile. It is, hence, adequate for ultrawide-band (UWB) applications. By means of a normalized antenna transfer function, both frequency domain and time domain characteristics of the antenna are carefully investigated. Two measures, the uniformity related to the radiation patterns and the fidelity associated with the transient behaviors, are used to quantitatively describe the performance of an antenna over such an ultrawide bandwidth. Effects of varying the antenna's geometric parameters on the performance are then investigated. Finally, the influence of minimizing the antenna dimension is discussed at the end of the paper.

Frequency notched printed slot antenna with parasitic open-circuit stub

A new frequency notched ultra-wideband microstrip slot antenna with a parasitic tuning stub is proposed. The antenna is similar in configuration to a conventional microstrip slot antenna; by introducing a parasitic open-circuit tuning stub, flexible frequency notched function is achieved. Several properties of the antenna, such as frequency notched function, antenna transfer function and gain, have been investigated. As is reported, the operation bandwidth of the antenna is 2.91–11.16 GHz, in which a frequency notched band of 5.10–5.85 GHz has been achieved. Furthermore, good ultra-wideband linear transmission performance over the entire operation frequency range has also been achieved.

Modeling of ground-penetrating Radar for accurate characterization of subsurface electric properties

The possibility to estimate accurately the subsurface electric properties from ground-penetrating radar (GPR) signals using inverse modeling is obstructed by the appropriateness of the forward model describing the GPR subsurface system. In this paper, we improved the recently developed approach of Lambot et al. whose success relies on a stepped-frequency continuous-wave (SFCW) radar combined with an off-ground monostatic transverse electromagnetic horn antenna. This radar configuration enables realistic and efficient forward modeling. We included in the initial model: 1) the multiple reflections occurring between the antenna and the soil surface using a positive feedback loop in the antenna block diagram and 2) the frequency dependence of the electric properties using a local linear approximation of the Debye model. The model was validated in laboratory conditions on a tank filled with a two-layered sand subject to different water contents. Results showed remarkable agreement between the measured and modeled Green's functions. Model inversion for the dielectric permittivity further demonstrated the accuracy of the method. Inversion for the electric conductivity led to less satisfactory results. However, a sensitivity analysis demonstrated the good stability properties of the inverse solution and put forward the necessity to reduce the remaining clutter by a factor 10. This may partly be achieved through a better characterization of the antenna transfer functions and by performing measurements in an environment without close extraneous scatterers.

Singular value decomposition methods for wave propagation analysis

We describe several newly developed methods for propagation analysis of electromagnetic plasma waves. We make use of singular value decomposition (SVD) technique and we determine the wave vector direction, ellipticity and directions of axes of the polarization ellipse, wave refractive index, transfer function of electric antennas, estimators of the planarity of polarization, and electromagnetic planarity. Simulations of Z‐mode waves, which simultaneously propagate with different wave vectors, indicate that the SVD methods give reasonable results even if the assumption on the presence of a single plane wave is invalid. Simulations of whistler mode waves show that these methods can be used to recognize cases when the waves simultaneously propagate with wave vectors in two opposite hemispheres. Finally, we show an example of analysis of natural whistler mode and Z‐mode emissions measured in the high‐altitude auroral region by the MEMO experiment onboard the INTERBALL spacecraft.

Antenna compensation method using direct coupling wave in polarimetric borehole radar measurement

Crosshole borehole radar measurement is needed to compensate the antenna transfer functions in polarimetric single-hole radar measurement with combinations of a dipole antenna and a cylindrical conducting slot antenna. This paper presents a method to estimate the antenna transfer functions from the single-hole measurement alone. A small dipole model in a homogeneous medium is used to approximate the relationship between the direct coupling wave in the single-hole measurement and the direct wave in crosshole measurement (antenna transfer function). We show that the far field crosshole signal approximately has the same frequency dependency as the time derivative of the direct coupling signal measured via single-hole measurement. We experimentally demonstrate that the measured far field waveforms have good agreement with the time derivative of the measured direct coupling waveform for dipole–dipole and slot–slot arrangements with an antenna separation of 1.6 m. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(11): 11–21, 2000

Antenna compensation method using direct coupling wave in polarimetric borehole radar measurement

Crosshole borehole radar measurement is needed to compensate the antenna transfer functions in polarimetric single-hole radar measurement with combinations of a dipole antenna and a cylindrical conducting slot antenna. This paper presents a method to estimate the antenna transfer functions from the single-hole measurement alone. A small dipole model in a homogeneous medium is used to approximate the relationship between the direct coupling wave in the single-hole measurement and the direct wave in crosshole measurement (antenna transfer function). We show that the far field crosshole signal approximately has the same frequency dependency as the time derivative of the direct coupling signal measured via single-hole measurement. We experimentally demonstrate that the measured far field waveforms have good agreement with the time derivative of the measured direct coupling waveform for dipole–dipole and slot–slot arrangements with an antenna separation of 1.6 m. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(11): 11–21, 2000

Enhancement of reflected waves in single-hole polarimetric borehole radar measurement

A polarimetric approach is presented to extract information of reflected waves that is masked by the transmitter-receiver directly coupled wave in a single-hole borehole radar measurement. Radar polarimetry theory is expanded to an omnidirectional radar system with electric and magnetic dipoles arranged on the same axis. First, we formulate the transfer functions directly coupled between the antennas for cross-hole and single-hole arrangements in copolarized channels. We found that the theoretical scattering matrices of the direct-wave coupling is identical to the scattering matrix from a dihedral corner reflector. Second, we also consider signals in polarimetric channel of a wave reflected from a plane scatter in single-hole arrangements. As advanced reflection borehole radar measurement, we demonstrate a technique for both reduction of the directly coupled wave and enhancement of the reflected waves from a plane fracture with measured data in dipole-dipole and slot-slot antenna combinations. For quantitative determination of the scattering matrix, we use a technique to compensate the antenna transfer functions by the time derivative of the directly coupled signals in single-hole measurement. Also, we propose a technique to reduce the directly coupled component by adding vertical (VV) and horizontal (HH) signals and we showed that the directly coupled wave is effectively reduced and reflected waves are enhanced with experimental data. Finally, we show that this technique is more useful for near-range reflector detection than a conventional subtraction technique with moving average of the measured waveforms.

Subsurface fracture measurement with polarimetric borehole radar

A full-polarimetric borehole radar system is presented with combinations of dipole antennas and axial slot antennas and is applied to subsurface fracture measurement. First, to determine a scattering matrix from measurements with antennas having different antenna transfer functions between orthogonal polarizations, the authors present an antenna compensation algorithm that is achieved by an inverse filtering method with the antenna transfer functions experimentally determined by crosshole measurements. The results of crosshole and single-hole measurements carried out in granite at the Kamaishi Mine are shown to verify the proposed method. In the crosshole measurement, the authors find that the used dipole and slot antennas have almost the same radiation pattern and frequency dependency from 50 to 120 MHz. The transmission matrices through the host rock are the unit matrix for most paths, while depolarization is observed in some sections. Reflections from subsurface fractures show significant depolarization in the polarimetric single-hole reflection measurements. Using the scattering matrix, it is evaluated that subsurface fractures have a randomly isotropic rough surface for wavelengths between 1 and 2 m on the rotation of polarization basis.

Polarimetric calibration for wideband synthetic aperture radar imaging

Multi-channel techniques are introduced to calibrate for effects of antenna shading and crosstalk in wideband, wide-angle full polarisation radar imaging. The system is modelled as a two-dimensional integral operator which includes the transmit pulse function, receive and transmit antenna transfer functions, and response from scattering objects. Existing imaging algorithms provide an approximate inversion of this integral operator, without compensation for the effect of the multi-channel antenna transfer functions. Thus, standard processing yields poor image quality, due to the inherent variation of the antenna response (in magnitude, phase, and polarisation) across the large band of frequencies and wide range of aspect angles. Two techniques are proposed for regularised inversion of the system model. Both techniques require measurements of the antenna transfer function over the look angles and frequency band of interest. The first technique adopts a local approximation to process multi-channel range lines separately and is suitable for imaging small regions. The second technique achieves multi-channel deconvolution of the antenna response in the transform (Doppler) domain and is suitable for large data records. The result is imagery with improved polarisation purity and a more localised point spread function.

Angular and frequency response of LISA

The sensitivity of LISA at frequencies above about 10 mHz is determined by the shot noise of the light together with the decreasing antenna transfer function, finally being limited by mechanical resonances above 1 Hz. In this paper we will investigate the transfer function of laser-interferometric gravitational-wave antennas in the upper frequency range, where the physical arm length of the antenna becomes comparable to or even greater than the wavelength of the gravitational waves. This analysis reveals results which are also interesting for ground-based detectors. Furthermore, we calculate the dependence of the LISA transfer function on orbit azimuth, source azimuth, source declination and polarization, and finally we form the average over these angles in order to arrive at a mean LISA sensitivity curve. It turns out that the resulting response is even better than estimated previously.

Microwave delay characteristics of Cassegrainian antennas

An approach is presented in which the time an RF signal is delayed in propagating through a Cassegrainian antenna can be determined. The approach is based on the recognition that both the group delay (time) and the envelope delay (time) can be obtained from the antenna transfer function. Two antenna transfer functions are derived. The delay time under various antenna operating conditions is discussed.

Applications of Time-Domain Metrology to the Automation of Broad-Band Microwave Measurements

It is only recently that measurement of the transient response of microwave systems directly in the time domain has become practicable. It has led to growing interest in the concept of specifying broad-band performance solely by a transient-response measurement. Results of the use of time-domain techniques to obtain, within the range 0.1 to 10 GHz, such data as the S parameters of networks, the constitutive parameters of microwave materials, the driving-point impedance and transfer function of microwave antennas, and the frequency-domain scattering parameters of conducting surfaces in free space are described.

Application of Spatial Frequency Concepts to the Radar Ground-Mapping Problem

The mapping of extended, cultural ground targets by an airborne radar is examined, using communication theory techniques including the concepts of the antenna transfer function and the target spatial frequency spectrum. The targets are specified directly in terms of their spatial frequency spectra, and the transfer functions are those which correspond to the Taylor one-parameter line sources. The results indicate that resolution for a particular class of ground targets can be better than is predicted by the Rayleigh two-point resolution criterion and that the shape of the antenna images can be quite independent of the choice of radiation pattern.