Zero-IF detection active antenna

A zero-IF receiver is implemented based on the active antenna design. The active devices, Schottky diodes, are compactly integrated with two patch antenna elements to act as the mixers. The active antenna can perform both direct-conversion demodulation and direction finding     

Polarisation-agile active patch antenna

A polarisation-agile active antenna has been constructed and tested. The radiation can be selected to be circularly polarised in either sense, or linearly polarised in the vertical, horizontal or either diagonal plane. The antenna consists of two varactor diode loaded active patches using npn bipolar transistors in the common base configuration as sources, and with the patch axes at right angles to each other. The two oscillators are locked to an external source, and the phase from each patch element is controlled by varying the diode bias voltage. By appropriate combination of the phase relationships, the various polarisations are produced.<>     

Planar active Yagi-like antenna

The authors introduce the Yagi concept into a simple active antenna. Antennas with director elements demonstrate an increased directivity and 30° beam-tilting compared with an active antenna     

A new quasi-Yagi antenna for planar active antenna arrays

In this paper, a novel broadband planar antenna based on the classic Yagi-Uda dipole antenna is presented, and its usefulness as an array antenna is explored. This “quasi-Yagi” antenna is realized on a high dielectric-constant substrate, and is completely compatible with microstrip circuitry and solid-state devices. This antenna achieves a measured 48% frequency bandwidth for voltage standing-wave ratio <2, better than a 12-dB front-to-back ratio, smaller than -15 dB cross polarization, and 3-5-dBi absolute gain. Mutual coupling of the antenna in an array environment is investigated. Finally, three simple arrays are presented, demonstrating the usefulness of the antenna as an array element. This novel antenna should find wide application in wireless communication systems, power combining, phased arrays, and active arrays, as well as millimeter-wave imaging arrays     

A harmonic suppression antenna for an active integrated antenna

An inset-fed antenna with a shorting pin and slots is presented for harmonic suppression of an active integrated antenna. Its fundamental resonant frequency is 5.8 GHz. At fundamental and harmonic frequencies, return loss and radiation characteristics are measured and compared with those of the conventional microstrip patch antenna. The second and third harmonic return losses of the proposed antenna are suppressed to 6.7 dB and 17.7 dB with respect to the conventional patch antenna, respectively.     

Two-port active coupled microstrip antenna

A multilayer structure, based on a patch antenna coupled through a nonresonant slot to a pair of feeding microstrips is a versatile module which can be used as a radiating and resonating element in a number of different configurations. Direct connection to a low cost transistor in a feedback loop results in a very simple active antenna, as reported. Different termination conditions at the four microstrip ports give rise to a number of alternative configurations for active generation/detection and multipatch arrays.<>     

Dual feeding active integrated antenna

A dual feeding active integrated antenna with high isolation between the Tx and Rx ports of a single triangular patch antenna is presented. The proposed antenna suppresses the third harmonics and isolates the Tx signal at the Rx ports to a high degree. The measured results of the return loss, isolation, and radiation patterns are provided     

Ring-coupled-oscillator sequentially rotated active antenna

In this paper, an active four-element patch antenna, backed by four GaAs monolithic-microwave integrated-circuit (MMIC) 4.4-GHz oscillators, self-locked by mutual coupling through a lumped capacitive ring MMIC network, has been designed, fabricated, and tested. The sequentially rotated arrangement given here when augmented with a lumped capacitive coupling network suggests that in-phase oscillator entrainment is guaranteed so that spatial power combination by the antenna array occurs with circular polarization characteristics     

Novel FET active patch antenna

A novel dual-FET active patch antenna element for quasi-optical power combining arrays is described. The circuit uses two FETs which symmetrically load a split patch antenna. The push-pull operation of the devices decreases H-plane crosspolarisation dramatically. A power output of 47 mW was achieved at 8.1 GHz.<>     

Short antenna with active inductance

It has been found that integration of an active inductance with a short antenna gives higher antenna gains over a relatively wide frequency range. The gain of this system can be further improved by integrating a suitable wideband amplifier with it.     

Rapid near-field antenna testing via arrays of modulated scatteringprobes

Key results are summarized of efforts to significantly reduce the near-field measurement time by utilizing one- or two-dimensional arrays of modulated scattering probes in lieu of the single probe ordinarily used in conventional near-field measurement techniques. Results of analytical, numerical, and experimental investigations show that the modulated-scattering technique (MST) using arrays of hundreds or even thousands of modulated scattering probes can be used to map the complex near-field of antennas or scatterers in a few seconds or minutes. The results also strongly indicate that classical (nonmodulated) receiving/transmitting arrays can be adapted for rapid near-field data collection. Major factors affecting the accuracy and speed of probe arrays for near-field measurement are delineated and discussed. Experimental results obtained using laboratory prototype MST systems are also presented and discussed     

Periodically modulated dielectrically filled waveguide as a microwave antenna

Complex solutions to a determinantal equation have been found numerically and employed to predict the properties of a frequency-scanning forward-radiating antenna obtained through a superposition of two waves propagating in oblique angles on an infinite periodic structure. The range of parameters of a usable antenna has been examined.     

Phase weighting for linear antenna arrays

A novel method for introducing an amplitude taper onto a linear array is described, using equal amplitude elements with randomised phase reversals to create an effective taper.     

Integrated active antenna with simultaneous transmit-receiveoperation

The authors present results for a novel two element active transmit-receive array using dual linear polarisation and sequential rotation. Each element includes an integrated oscillator and amplifier mounted on orthogonal edges of a square patch, such that transmit and receive paths are isolated and polarisation duplexed. The array gives in excess of 55 dB transmit-receive isolation at 3.77 GHz     

24 GHz active retrodirective antenna array

A 24 GHz active Van Atta planar antenna array proposed for increasing the vehicle radar echo in a vehicle collision avoidance system is designed and demonstrated. The antenna array contains two parallel linear sub-arrays. Each sub-array is composed of four receiving microstrip antennas, four transmitting microstrip antennas and four transistor amplifiers. At the angles of -40°<&thetas;<40°, except those very close to the specular direction (&thetas;=0°), the measured backscattering field levels of the fabricated array have variations <3 dB and are at least 10 dB higher than those of a metal plate of the same size     

FDTD simulation of active integrated antenna

The full wave design of an active integrated antenna using the extended FDTD method is presented. An active circulator using three gain blocks and a short circuited quarter wavelength patch are combined to form a transceiver. The effects of parasitic coupling are identified, and the isolation between transmit-receive is predicted     

Compact microstrip-T coupled patch antenna for dual polarisation and active antenna applications

A novel way of feeding single-layer microstrip patch antennas using electromagnetically coupled microstrip-T junctions is proposed. The measured isolation and 10 dB bandwidth of an X-band dual polarised antenna are /spl sim/32 dB and 2.1%, respectively, on an /spl epsiv//sub r/ 3.0 substrate. Since both ports of the antenna are electromagnetically coupled, the proposed antenna eliminates the need for capacitors in the RF path for active antenna applications.     

Phase center calculations of reflector antenna feeds

A method of determing the optimum phase center location of antenna feeds employed in reflector systems is described. The phase center of the wide-band scalar horn used in prime-focus and dual-reflector antennas has been calculated numerically and the results are discussed.     

Phase mode processing for spherical antenna arrays

It is shown how the concept of phase mode excitation of circular antenna arrays may be extended to spherical arrays, and in particular that a spherical phase mode of the excitation function of a spherical array results in a far field radiation pattern with the same spherical phase mode form. A number of applications and issues concerned with the practical implementation are discussed.