Vijay K. Nair

A Low-Profile Branched Monopole Laptop Reconfigurable Multiband Antenna for Wireless Applications

A reconfigurable low-profile branched monopole antenna has been developed. It can operate at six different frequency bands that are 800 MHz, 900 MHz, 1.7 GHz, 1.9 GHz, 2.4 GHz, and 5.2 GHz. The developed antenna is compact and has a low-profile structure with dimensions of 96 mm times 9 mm times 3 mm, which makes it optimum for the laptop implementation. The antenna comprises two branches that are reconfigurable and is printed on a 0.05 -mm-thick Kapton substrate. Each branch is a multiband structure. Embedded switches are used for reconfiguration and are strategically positioned next to the ground plane to simplify the implementation of direct current (dc) biasing.

Antenna miniaturization using magneto-dielectric substrates

Effective antenna miniaturization is a challenging problem due to the inevitable trade-off between the size and the performance of the antenna due to the fact that antenna performance is bound with the fundamental limits based on the size of the antenna. Antenna miniaturization is also a critical issue since the key component determining the size of a mobile device is usually the antenna. Recent studies on novel materials called magneto-dielectrics have raised hope to miniaturize the antenna effectively. Magneto-dielectrics are materials with both the relative permittivity (∊r) and the relative permeability (µr) of the substrate greater than unity. In this paper, several issues regarding the magneto-dielectrics and their application to the antenna miniaturization are investigated. The theoretical reason why the magneto-dielectrics are better substrates for planar antennas than the dielectric materials is investigated along with a material synthesis technique to explain how to realize these materials. Additionally, a characterization methodology to extract the frequency dependent properties (∊′, ∊″ µ′, and µ″) of these materials is presented in this paper. Finally, the advantages and the limitations of these substrates for antenna applications are discussed in the paper.

Low current GaAs integrated down converter for portable communication applications

A low current GaAs MMIC amplifier/mixer was designed and characterized for portable communication applications in the 900 MHz band. This single chip integrated front-end IC (90 mil /spl times/ 110 mil) achieved - 118 dBM sensitivity at the cellular band. The extremely low power dissipation, high level of integration, and very good RF performance of this monolithic IC make it an ideal candidate for portable communication applications.<<ETX>>

Ultralow DC power VCO based on InP-HEMT and heterojunction interband tunnel diode for wireless applications

The monolithic integration of tunneling diodes (TDs) with other semiconductor devices such as high electron-mobility transistors (HEMTs) or HBTs, creates novel quantum functional nonlinear devices and circuits with unique properties: the negative differential resistance and the extremely low dc power consumption. In this paper, we present a family of InP-HEMT-TD-based voltage-controlled oscillators operating in the 4-6-GHz band suitable for wireless applications, along with an effective analytical treatment of the stability issues. Prototypes having different circuit topologies of HEMT-TD devices have been designed and fabricated. The circuits generated an output power in the range of -11 to -18 dBm when operated at a bias current of 1.75 mA at 500 mV. Phase noise characteristics and tuning capability of the circuit configuration have been experimentally determined. The maximum tuning range of 150 MHz and the maximum single sideband-to-carrier ratio of -97 dBc/Hz at 200 kHz have been achieved.

MMIC applications of heterostructure interband tunnel devices

This paper deals with recent achievements in the field of an emerging technology termed the quantum monolithic microwave integrated circuit (QMMIC). QMMIC consists of a heterojunction interband tunneling diode and a high electron-mobility transistor monolithically integrated to obtain a new functional device. This technology enables the realization of low-voltage, high-density, and high-functionality circuits. A detailed description of the design and analysis techniques for several circuits such as an amplifier, an oscillator, and a mixer, along with the analytical treatment of the principle of operation are given in this paper. A number of prototypes implemented in InP technology constitute the proof-of-concept of the unique features of QMMIC circuit blocks for low-power wireless systems.

Increasing channel capacity on MIMO system employing adaptive pattern/polarization reconfigurable antenna

This paper presents a pattern/polarization reconfigurable single turn square spiral microstrip antenna that is designed to operate in the 5 GHz indoor band and tested with Intel-developed CMOS MIMO transceivers. Experimental results show that different environments between transmitter and receiver antenna MIMO system require different antenna configurations to achieve lower correlation between paths and increase the throughput.

Magneto-Dielectric Nanocomposite for Antenna Miniaturization and SAR Reduction

A 900-MHz meander planar inverted-F antenna (PIFA) on a magneto-dielectric nanocomposite (MDNC) substrate for mobile communication is presented. Cobalt nanoparticles were synthesized with polymer matrix, and its properties were measured up to 4 GHz. Bandwidth, gain, and radiation efficiency of antenna on different substrates (MDNC, High K material, and FR4) were compared, and it is demonstrated that MDNC is beneficial for antenna miniaturization with acceptable antenna performance. Head effects due to the antenna were studied, and specific absorption rate (SAR) was calculated. The simulation results demonstrate that the MDNC reduces the head effects and the magnetic loss of MDNC helps to decrease SAR due to the antenna.

X-band heterostructure interband tunneling FET (HITFET) VCOs

This paper reports on the DC and microwave performance of novel X-band voltage controlled oscillators fabricated by integrating heterostructure interband tunneling diode (HITD) with a heterostructure FET. The measured RF performance of VCOs incorporating single and double HITDs is discussed. The power output of the single HITD VCO was 2.0 dBm and that of the dual HITD was 4.3 dBm at a center frequency of 8.2 GHz. The dual HITD VCO also exhibited a wider tuning range than the single HITD VCO. The phase noise of these VCOs was approximately -128 dBc, 3 MHz away from the center frequency.

A novel reconfigurable maze antenna for multi-service wireless universal receivers

A novel design of multi-band multi-service reconfigurable antenna has been developed, and is comprised of multi-segment printed loop structure. The developed antenna looks like a maze and can be easily configured by altering its multi-segment interconnectivity using multitude of switches. Modeled and measured results including the effects of the switching elements will be presented here in details.

Reconfigurable Single-Armed Square Spiral Microstrip Antenna Design

In the past decade, wireless technologies have advanced dramatically [1-2]. Software Defined Radio (SDR) and Multiple-Input and Multiple-Output (MIMO) are two emerging technologies to deliver the desired functionality over a wide range of frequencies and provide dramatic increases in throughput. To support and enable the cutting edge wireless technologies, antenna designs need to meet the dynamic requirements for different frequency operating bands, radiation patterns and polarizations. Reconfigurable antennas are good candidates to meet those requirements. Several researchers have developed multiple reconfigurable antenna designs in various structures to deliver antenna frequency tunability, pattern reformability, and polarization selection with PIN diodes, MESFETs and RF MEMs [3-8]. In this paper, a frequency and pattern reconfigurable single-armed square spiral microstrip antenna is presented. Simulations indicate an average 3-7dBi gain can be achieved with this small single-armed square spiral antenna.