Tayfun Nesimoglu

Wide tuning-range planar filters using lumped-distributed coupled resonators

This paper describes a discretely tunable filter topology based on lumped-distributed coupled transmission lines, particularly suitable for microelectromechanical systems switching devices. This topology is capable of simultaneous wide-band center frequency and bandwidth tuning, limited only by the electrical size of the transmission lines and the placement density of the switching devices. Low fractional bandwidths can be achieved without the need for large coupled-line spacings due to the antiphase relationship of the lumped capacitive and distributed electromagnetic coupling coefficients. The positions of the additional poles of attenuation due to the lumped capacitive coupling can be selected either above or below band leading to the choice of a narrow bandwidth design having good high-side performance or a design with compromised upper stopband performance, but with no bandwidth tuning limitations. The interaction between a pair of lumped-distributed coupled transmission lines is analyzed and the resulting model is used to develop a filter synthesis procedure. The synthesis procedure and filter performance are validated through theoretical and experimental comparisons using a filter with low-side attenuation poles

Enabling technologies for software defined radio transceivers

This paper discusses the design considerations related to the transceiver hardware elements within a software defined radio (SDR). Receiver architectures are reviewed and the viability of manufacturing these in the short to medium term is considered. The filtering functions required for a conventional receiver are examined, and the problems associated with implementation of these filters within a SDR receiver discussed, including that of image filtering. Receiver linearity requirements are evaluated in terms of typical user applications and it is shown that these will be onerous in the case of a SDR receiver. A novel technique for mixer linearisation is presented as a potentially enabling element within a re-configurable transceiver and some initial performance results are reported. The possibility of constructing an electronically tunable preselection filter using micro-electromechanical systems (MEMS) technology is examined. Some simulation and prototype measurement results are presented.

A Tunable Metamaterial Resonator Using Varactor Diodes to Facilitate the Design of Reconfigurable Microwave Circuits

In this brief, we designed, constructed, and analyzed a frequency-tunable metamaterial resonator. The proposed design consists of an S-shaped resonator, a ground frame, and a feeding transmission line. First, the structure is designed as a nontunable resonator and then tunability is achieved by employing varactor diodes. In order to verify and demonstrate its tunable metamaterial properties, reflection and transmission parameters, group delay, electric and magnetic field distributions, and permittivity and permeability at each tuned frequency were analyzed. Simulation and measured results agree well and show that a high transmission and reflection peak occurs at each resonance frequency that may be tuned with the applied control voltage. Therefore, the proposed tunable metamaterial resonator may be used to realize reconfigurable microwave circuits such as reflection/transmission filters, antennas, and sensors, and for achieving flexibility in many other microwave circuits.

Software defined radio receiver test-bed

This paper identifies the issues that are important in the design of a SDR receiver. Receiver architectures are first discussed, and the conclusion drawn that the conventional superheterodyne structure is most appropriate for a SDR receiver. Issues associated with image rejection, and receiver linearity are discussed. The design of a sweepable preselect filter is discussed in detail. Design considerations for a practical SDR test-bed are presented.

Design and Analysis of Frequency-Tunable Amplifiers using Varactor Diode Topologies

AbstractThe design of frequency-tunable amplifiers is investigated and the trade-off between linearity, efficiency and tunability is revealed. Several tunable amplifiers using various varactor diode topologies as tunable devices are designed by using load-pull techniques and their performances are compared. The amplifier using anti-series distortion-free varactor stack topology achieves 38% power added efficiency and it may be tuned from 1.74 to 2.36 GHz (about 35% tunable range). The amplifier using anti-series/anti-parallel topology is tunable from 1.74 to 2.14 GHz (about 23% tunable range) and provides 42% power added efficiency. It is demonstrated that tunable amplifiers using distortion-free varactor stack topologies provide better power added efficiency than the tunable amplifiers using reverse biased varactor diodes and their linearity is similar to that of a conventional amplifier. These amplifiers may facilitate the realization of frequency agile radio frequency transceiver front-ends and may replace several parallel connected amplifiers used in conventional multimode radios.

The performance and efficiency of envelope elimination and restoration transmitters for future multiple-input multiple-output wireless local area networks

The inefficiency of contemporary power amplifiers (PAs), when operating in their linear region, is a major obstacle to mobile operation of wireless local area networks (WLANs) based on IEEE 802.11n. Therefore the use of more efficient envelope elimination and restoration (EER) transmitter architectures is considered. In addition to high efficiency it is also necessary to satisfy the spectral mask and achieve satisfactory link-level performance. Link-level simulations of a contemporary WLAN PA show that, at the power back-offs necessary to achieve sufficient linearity, the power added efficiency (PAE) is only ~1% for a system with four transmit antennas. In contrast, simulations of a phase feedback EER PA architecture show that it is possible to achieve an average PAE of 70%, while satisfying the spectral mask, with only a small degradation in link-level performance.

A review of Software Defined Radio enabling technologies

This paper reviews the state-of-the-art in microwave technology by investigating the most important elements of transceivers. It identifies the enabling technologies and research areas in radio frequency engineering that may facilitate the development of Software Defined Radios. Receiver architectures are also discussed and their viability for a reconfigurable radio application is investigated. The design of tunable radio frequency components, linear and power efficient amplifiers as well as linear mixers, and interference rejection techniques are the identified long term research areas.

Second harmonic injecting technique for low intermodulation RF-microwave amplifiers

An amplifier where the third order IM distortion has been reduced is proposed. If two signals at different carrier frequencies are incident at the input of an amplifier, due to the nonlinearity, these signals will interact with each other and the output will contain additional signals at all combinations of sum and difference of these frequencies, which are IM products. The injection of the second harmonics of the two input in the amplifier together with the fundamental signals will produce additional IM products at the output. By proper selection of phase and amplitude of the injected second harmonics, it is possible to make the third order IM products produced by the second harmonics and the original third order IM products out of phase and equal in amplitude. As a result third order IM products will be eliminated, in principle. Theory and simulation results obtained at 2.5 GHz are presented which supports the suggestion.

Improved EER transmitters for WLAN

The envelope elimination and restoration (EER) transmitter architecture is capable of providing high power efficiency without compromising linearity. This paper shows that for a wireless local area network (WLAN) application, the envelope reconstruction process modulates the supply voltage of the switching amplifier over a large dynamic range. This introduces sufficient nonlinearity to violate emission specifications. Fortunately, the EER architecture can be improved by applying envelope and phase feedback. The phase feedback architecture satisfies the emission specifications of IEEE 802.11a, while envelope feedback provides modest adjacent channel power ratio (ACPR) improvement. The impact of clipping on the ACPR and error vector magnitude (EVM) is also investigated. It is shown that for a WLAN application, a clipping of only 1 dB can be tolerated before the output signal is degraded significantly.

Design and characterization of a resonator-based metamaterial and its sensor application using microstrip technology

Abstract. Design of a metamaterial based on an S-shaped resonator surrounded by a ground frame and excited by using a feeding transmission line on microstrip technology is presented. Since the resonator, ground frame, and its excitation mechanism are all realized on a microstrip, its characterization can be carried out using common laboratory equipment without needing any waveguide components or plane-wave-illumination techniques. The structure presented here may be realized on any microstrip and does not require special materials. The resonator and ground frame are both on the same side of the microstrip, thus the proposed topology may also be populated with active and passive microwave components, and hybrid active, passive, or reconfigurable microwave circuits may be realized. In metamaterial designs that require plane wave illumination, usually many numbers of periodic unit cells are needed; however, in our design, only one cell is capable of achieving metamaterial properties. The constitutive parameters of the metamaterial are retrieved and compared to demonstrate the agreement between simulations and measurements. The proposed topology is also demonstrated in a sensor application, where simulated and measured results agree well. Thus, it can be realized using standard microwave technology and used for numerous applications where metamaterial properties are needed.