Charles Free

A Frequency Tuning Method for a Planar Inverted-F Antenna

A novel method is presented for electrically tuning the frequency of a planar inverted-F antenna (PIFA). A tuning circuit, comprising an RF switch and discrete passive components, has been completely integrated into the antenna element, which is thus free of dc wires. The proposed tuning method has been demonstrated with a dual-band PIFA capable of operating in four frequency bands. The antenna covers the GSM850, GSM900, GSM1800, PCS1900 and UMTS frequency ranges with over 40% total efficiency. The impact of the tuning circuit on the antennas efficiency and radiation pattern have been experimentally studied through comparison with the performance of a reference antenna not incorporating the tuning circuit. The proposed frequency tuning concept can be extended to more complex PIFA structures as well as other types of antennas to give enhanced electrical performance.

Enhanced electrical conductivity of silver nanoparticles for high frequency electronic applications.

An enhancement in the electrical performance of low temperature screen-printed silver nanoparticles (nAg) has been measured at frequencies up to 220 GHz. We show that for frequencies above 80 GHz the electrical losses in coplanar waveguide structures fabricated using nAg at 350 °C are lower than those found in conventional thick film Ag conductors consisting of micrometer-sized grains and fabricated at 850 °C. The improved electrical performance is attributed to the better packing of the silver nanoparticles resulting in lower surface roughness by a factor of 3. We discuss how the use of silver nanoparticles offers new routes to high frequency applications on temperature sensitive conformal substrates and in sub-THz metamaterials.

A novel traveling-wave feed technique for circularly polarized planar antennas

A novel, circularly polarized (CP) microstrip antenna array is described, in which the radiating patches are fed via a slot in the ground plane. Design and simulation data are provided for a prototype antenna working at 5 GHz. The antenna provides a high quality CP wave, and the structure is partially suitable for incorporating in multilayer microwave circuits.

A novel traveling-wave feed technique for circularly polarized planar microstrip antennas

Many current communication and sensor systems require high-density packing for transceivers. In particular, many such systems require the antenna to be closely integrated with the other transceiver circuitry. In this paper, we propose a new technique, which is capable of yielding high quality circular polarization, with a feeding system that is particularly suitable for incorporating in multi-layer microwave circuits. This type of circuit can be fabricated either in thick-film or LTCC, which are attractive because they can provide a combination of high-performance and low-cost fabrication. The proposed traveling-wave feed system offers a number of advantages over the rear-fed patch techniques. It does not require a probe through the dielectric layer beneath the patch. The current work is an extension of the concept of using a circular slotline channel beneath the dielectric layer to excite four rectangular patch antennas to provide circular polarization. In order to establish the validity of the proposed technique, a prototype 5 GHz antenna with a progressive incremental offset of 500 /spl mu/m was designed and tested.

Design and measurement data for a microwave CP antenna using a new travelling-wave feed concept

In this paper, we propose a new technique, which is capable of yielding high quality circular polarization, with a feeding system that is particularly suitable for incorporating in multilayer microwave circuits. This type of circuit can be fabricated either in thick-film or LTCC, which are attractive because they can provide a combination of high-performance and low-cost fabrication.

Electrical performance of carbon nanotube-polymer composites at frequencies up to 220 GHz

We have measured the sub-THz electrical response of screen printed carbon nanotube-poly(methyl methacrylate) polymer composites up to 220 GHz. The measured electrical losses using mm long coplanar waveguide geometries averaged as low as 0.15 dB/mm in the frequency range 40 GHz–110 GHz and showed a reduction in signal loss with increasing frequency; a behaviour opposite to that found in conventional metallic conductors. Between 140 and 220 GHz, the electrical losses averaged 0.28 dB/mm. We show that the low electrical losses are associated with the capacitive coupling between the nanotubes and discuss potential high frequency applications.

A simple method for accurate loss tangent measurement of dielectrics using a microwave resonant cavity

A simple yet rigorous method has been developed to enable the loss tangent of dielectrics, having a known relative permittivity, to be accurately measured using a waveguide resonant cavity. The novel method eliminates the need for any physical measurement, either on the cavity or dielectric sample under test. The only electrical parameters that need to be measured are resonant frequencies and Q-factors of a reference cavity and those of the same cavity loaded with the dielectric sample. One of the advantages of the new technique is that dielectrics, of arbitrary shape, can be characterized at very high microwave frequencies. The new method has been verified through measurement over X-band.

Electrical Characterization of LTCC Coplanar Lines up to 110 GHz

The losses in typical LTCC interconnections at millimeter wave frequencies up to 110 GHz have been measured using FGCPW meander line test structures. The percentage contributions of conductor loss, dielectric loss and surface roughness loss have been analyzed and the significance of the conductor geometry, surface roughness and fabrication errors are evaluated. The relative permittivity and loss tangent for several LTCC samples are also presented over a range of millimeter wave frequencies

Design and measurement data for a microwave dual-CP antenna using a new traveling-wave feed concept

Design and measurement data are presented that show how the novel concept of a traveling-wave-fed circular-polarization (CP) microstrip antenna can be extended to provide an antenna with dual CP. A new refinement to the basic antenna structure is also introduced that shows that the efficiency of radiation can be enhanced by using a dual dielectric to improve the fringing fields at the edges of the radiating patches by around 40%. Furthermore, new theoretical and simulated data are introduced to support the original traveling-wave feed concept

Dual-Ring Circularly-Polarized Microstrip Patch Array Using Hybrid Feed

We describe the design of a new form of traveling-wave-fed, circularly polarized microstrip patch array at X -band. The antenna employs a dual-ring array structure in which the radiating elements are fed by non-radiating slots with sequential phase excitations to generate circular polarization. The antenna incorporates two novel features: firstly, two concentric ring sub-arrays of linearly polarized elements are used to improve the axial ratio and, secondly, development of a new model for power distribution to ensure that all the elements radiate the same power, thus ensuring pattern symmetry and high-quality circular polarization. The proposed design was validated through practical measurements, which showed a well-matched antenna with good axial ratio and well-defined radiation patterns.