Leonard T. Hall

A Frequency- and Polarization-Reconfigurable Stub-Loaded Microstrip Patch Antenna

A stub-loaded microstrip patch antenna with reconfigurability in both frequency and polarization is presented. Using 12 varactors with two independent voltages, reconfigurability is achieved in a fractional bandwidth of around 40% while allowing selection between circular polarization (CP) with both rotating senses and linear polarization (LP). The design is optimized based on an analytical model, which significantly speeds up the process while yielding reasonably accurate predictions. For illustration of the concept, an antenna is designed, optimized, and manufactured for reconfigurable operation in the 2.4-3.6 GHz frequency range. A good agreement between simulations and measurements is obtained which validates the proposed method. A full reconfigurability is demonstrated in the operation band with the ability to both tune the antenna to a given frequency and select a polarization state among left-hand or right-hand CP or various states of LP.

Wireless RF communication in biomedical applications

This paper focuses on wireless transcutaneous RF communication in biomedical applications. It discusses current technology, restrictions and applications and also illustrates possible future developments. It focuses on the application in biotelemetry where the system consists of a transmitter and a receiver with a transmission link in between. The transmitted information can either be a biopotential or a nonelectric value like arterial pressure, respiration, body temperature or pH value. In this paper the use of radio-frequency (RF) communication and identification for those applications is described. Basically, radio-frequency identification or RFID is a technology that is analogous to the working principle of magnetic barcode systems. Unlike magnetic barcodes, passive RFID can be used in extreme climatic conditions—also the tags do not need to be within close proximity of the reader. Our proposed solution is to exploit an exciting new development in making circuits on polymers without the need for battery power. This solution exploits the principle of a surface acoustic wave (SAW) device on a polymer substrate. The SAW device is a set of interdigitated conducting fingers on the polymer substrate. If an appropriate RF signal is sent to the device, the fingers act as microantennas that pick up the signal, and this energy is then converted into acoustic waves that travel across the surface of the polymer substrate. Being a flexible polymer, the acoustic waves cause stresses that can either contract or stretch the material. In our case we mainly focus on an RF controllable microvalve that could ultimately be used for fertility control.

Analysis and Design of a Reconfigurable Antenna Based on Half-Mode Substrate-Integrated Cavity

The detailed analysis, design, and optimization of a reconfigurable antenna based on a periodically stub-loaded half-mode substrate-integrated waveguide (HMSIW) cavity is presented in this paper. The analysis demonstrates an excellent prediction of the resonance frequency for the cavity with an error of less than 2% compared to numerical simulations performed over a wide range of parameters. The fast computation of the resonance frequency based on the analytical model gives deep insight into the antenna operation and allows an efficient optimization process. The reconfigurable antenna has been designed and optimized to cover the whole S-band (WR-284 waveguide band), i.e., 2.60-3.95 GHz, using three varactors with measured capacitance varying from 0.149 to 1.304 pF. Experimental results validate the concept across the whole tuning range, with a return loss and antenna gain greater than 15 and 2.1 dB, respectively at resonance.

60GHz Radios: Enabling Next-Generation Wireless Applications

Up to 7 GHz of continuous bandwidth centred around 60 GHz has been allocated worldwide for license free wireless communications. Highly attenuated due to oxygen absorption and small in wavelength, this band is ideal for extremely high data rate wireless data applications. These include numerous WPAN/WLAN applications such as home multimedia streaming. Traditional RF circuits used in this band are based on expensive compound semiconductor technologies. However for viable consumer applications, alternatives must be found. SiGe and CMOS based circuits are showing promise for enabling this technology at a price within reach of the consumer. This paper summarises a joint project aimed at developing high rate consumer level mm-wave wireless data systems. In particular, results to date in our RF design efforts are summarised.

Rotman lens for mm-wavelengths

The 77 GHz band has been reserved for intelligent cruise control in luxury cars and some public transport services in America and the United Kingdom. The Rotman lens offers a cheap and compact means to extend the single beam systems generally used, to fully functional beam staring arrangements. Rotman lenses have been built for microwave frequencies with limited success. The flexibility of microstrip transmission lines and the advent of fast accurate simulation packages allow practical Rotman lenses to be designed at mm-wavelengths. This paper discusses the limitations of the conventional design approach and predicts the performance of a new Rotman lens designed at 77 GHz.

A Frequency- and Pattern-Reconfigurable Center-Shorted Microstrip Antenna

A frequency- and pattern-reconfigurable antenna based on a center-shorted microstrip patch is presented. The novel design utilizes two resonance modes of a microstrip antenna with shorting vias at the patch center. To set up the antenna tuning mechanism, two groups of varactors with a measured tuning range of [0.149, 1.304] pF are placed at two opposite sides of the antenna, followed by open-circuited loading stubs. For a particular bias voltage configuration, the structure operates as a dual-band antenna with broadside radiation at the upper resonance frequency and monopole-like radiation at the lower band. By varying the dc bias voltage, both resonance frequencies can be changed simultaneously. Based on the proposed concept, a demonstration antenna has been designed so that the two types of aforementioned patterns can be reconfigured across a continuous fractional frequency range of more than 20%. Experimental results are provided, which validate the proposed concept and design procedure.

Variational Analysis of Folded Substrate-Integrated Waveguides

An accurate numerical solution describing the propagation behavior of two types of folded substrate-integrated waveguide (FSIW) is demonstrated in this letter. The computation is based on a variational method which can be carried out efficiently by solving the stationary equation corresponding to each type of FSIW. The approach can be extended to solve various folded structures, i.e., with different gap positions, where the layers are made of substrates with different thicknesses and material properties.

A Frequency- and Polarization-Reconfigurable Circular Cavity Antenna

The principle and experimental validation of a frequency- and polarization-reconfigurable antenna using switching PIN diodes is presented in this letter. The antenna is based on a center-fed circular cavity with switchable shorting vias along its outer edge. Turning a set of shorting vias on on one side and off on the other side creates a radiating slot with controllable length and location along the side wall of the cavity that results in different antenna resonance frequencies and polarizations. As a proof of concept, a particular realization of the antenna is designed that can change the linear polarization in six different angles and at five discrete frequencies (spanning more than one octave). Based on the proposed concept, quasi-continuous frequency- and polarization-reconfiguration is feasible using individual control of a large number of switching devices.

Transmission-Line Model of Nonuniform Leaky-Wave Antennas

Nonuniform leaky-wave antennas (LWAs) are analyzed and synthesized using a lossy transmission line model. The analysis is based on a general waveguide circuit theory. Compared to the classical approach, the model yields a higher accuracy in the computation of both aperture field distribution and radiation patterns. The proposed analysis is also able to provide scattering parameters of the whole structure in a fraction of a second, which is valuable for antenna optimization. Based on the analysis, a general method for far-field pattern synthesis utilizing global optimization is presented. As an application demonstration, the half-mode substrate-integrated waveguide (HMSIW), or half-width microstrip line, has been selected as basis structure for the LWA designs. Two antennas have been optimized targeting different specifications, i.e., a low-sidelobe level and a wide null in the radiation pattern. Experimental results are provided for these selected examples of nonuniform LWAs, which ultimately validate the proposed technique as an improvement over the classical approach.

A

A compact balanced frequency doubler with more than 35 dB odd-harmonic rejection and fractional bandwidth of 73% is presented in this letter. Wide bandwidth and high odd-harmonic suppression is achieved by adopting a new technique for the transformer balun design, resulting in a very low magnitude imbalance of 0.13 dB and a phase imbalance of 0.4° over 7-15 GHz. The balun performance is improved by offsetting the radius of the primary and secondary coils, which reduces the parasitic coupling capacitance. The input and output frequency ranges for the doubler are 7-15 GHz and 14-30 GHz respectively. The circuit was fabricated in 0.13-μm SiGe technology. The chip size is 0.6 mm × 0.4 mm.