N.C. Karmakar

A dual polarized aperture coupled circular patch antenna using a C-shaped coupling slot

The design and development of a dual linearly polarized aperture coupled circular microstrip patch antenna at C-band are presented. The antenna uses a novel configuration of symmetric and asymmetric coupling slots. Variations in isolation between orthogonal feedlines and antenna axial ratio with the position of coupling slots are studied and broadband isolation and axial ratio are achieved. The prototype antenna yields 7.6 dBi peak gain, 70/spl deg/ 3-dB beam width, 25 dB cross-polarization levels and an isolation better than 28 dB between the two ports. With an external quadrature hybrid coupler connected to the two orthogonal feedlines, the antenna yields 3-dB axial ratio bandwidth of more than 30% at 5.8 GHz.

Investigations into nonuniform photonic-bandgap microstripline low-pass filters

With the advent of planar photonic bandgap (PBG) materials, different PBG topologies have been proposed to improve bandgap performances of microwave signals. Conventional circular-patterned PBGs have constraints in the wide stopband performance due to high passband ripples. In this paper, we suggest two novel configurations with nonuniform dimensions of circular-patterned PBGs to improve the stop bandwidth and passband ripples. The dimensions of PBG units are varied proportionally to the coefficients of binomial and Chebyshev polynomials. The simulated and measured responses of the proposed PBG units are presented. It is seen that Chebyshev distribution produces excellent performance by suppressing passband ripples and producing distinct stopband. These performances of passband ripples and stop bandwidth are further improved with Chebyshev distributed annular-ring PBG units with their unique feature of aspect ratio control.

Investigations into a cavity-backed circular-patch antenna

An empirical formula for resonant frequency of a circular cavity-enclosed circular-patch antenna is tested with measured results. The patch miniaturization in the presence of the cavity is proved. Different design curves in terms of resonant frequencies and bandwidth are derived to facilitate antenna design without a priori knowledge of complex numerical techniques. A simple gain formula for a circular-patch antenna is derived and tested against the measured gain data. The results agree very well. The beamwidth, axial ratio, and mutual coupling in the presence of the cavity are investigated.

Circularly polarized aperture-coupled circular microstrip patch antennas for L-band applications

Circularly polarized aperture-coupled circular microstrip patch antennas are investigated with the goal of obtaining an 8% impedance and ellipticity bandwidth in the L-band. Three varieties-a single-feed patch with perturbation segments, a single-feed stacked patch with perturbation segments, and a dual-feed patch with a 3-dB branch line coupler as an external polarizer are considered to obtain the required performance. All the three investigated patch configurations meet the impedance bandwidth requirement, but only two varieties: the single-feed stacked patch and the dual-feed patch meet the required ellipticity bandwidth. These antennas feature more than 9-dBi gain. They use low-cost substrates and foam for bandwidth enhancement and, hence, they are attractive for applications where the production cost is of importance.

Shorting strap tunable stacked patch PIFA

An oppositely shorted dual-band stacked patch planar inverted-F antenna (PIFA) is developed. RF switches are integrated to the shorting straps of the stacked patches to make a tunable PIFA. The L band switch yields 0.45-dB insertion loss and 10-dB isolation bandwidth (BW) of 108% at 1.8 GHz. The tunable PIFA yields 10% frequency tunability BW at 745 MHz when the number of upper radiating patchs shorting straps changes and 20% BW at 1137 MHz when the number of lower radiating patchs shorting straps changes. Independent lower and upper frequency tunings are achieved through this technique.

Dual polarized reader antenna array for RFID application

This paper presents the design and development of a compact dual linearly polarized aperture coupled microstrip patch antenna array at S-band for RFID reader applications. The 2/spl times/2 array uses two symmetric dog-bone shaped coupling aperture. The prototype array yields 14.6 dBi peak gain, 36/spl deg/ half-power beam width (HPBW) in both E and H-planes, 28 dB cross-polarization levels and an isolation better than 35 dB between the two polarization at the designed frequency bandwidth. These performances make the antenna very much suitable for RFID reader applications.

Shorting strap tunable single feed dual-band PIFA

RF switches are integrated to the shorting straps of a single feed dual-band planar inverted-F antenna (PIFA) to make a tunable PIFA. The L-band switch yields 0.45-dB insertion loss (IL) and 10-dB isolation bandwidth (BW) of 40% at 1.5 GHz. The tunable PIFA yields 39% impedance BW at 900-MHz band and 7.8% BW at 2000-MHz band. The measured radiation patterns are nearly omni-directional and yield a gain of -7.8 dBi at 652 MHz and 4.3 dBi at 2104 MHz.

Shorting strap tunable single feed dual-band stacked patch PIFA

A single feed dual-band stacked patch planar inverted-F antenna (PIFA) is integrated with an RF switch array at one side of its shorting straps to make a tunable PIFA. The L-band switch yields 0.45 dB insertion loss (IL) and 10 dB isolation bandwidth (BW) of >100% at 1.2 GHz. The tunable PIFA yields >100% frequency tunability BW at the 800 MHz band and /spl sim/5% BW at the 1.9 GHz band. The measured radiation patterns are nearly omni-directional and yield a gain of 2.2 dBi at 800 MHz and 4.5 dBi at 1.9 GHz.

A two-ring circular phased-array antenna for mobile satellite communications

This paper presents the design and development of an L-band planar, multi-layer circular array for possible use with the Australian geostationary mobile-satellite-communications system, Mobilesat/sup TM/. Twelve single-feed, stacked aperture-coupled microstrip patches, interleaved with low-cost dielectric foam and arranged in two rings, form the array. The beam-forming network is comprised of three-bit phase shifters, which are located under the antenna elements. Low-cost UHF-band switching diodes were used to minimize the developmental cost of these phase shifters. In order to make the diodes operational at L-band, an LC compensation technique was applied to the diodes to tune out parasitic reactance. Experimental results for individual antenna elements and phase shifters, followed by the results for the entire array, are presented. The indoor testing results for the manufactured antenna showed that the array satisfies the specifications of Mobilesat/sup TM/. This was also confirmed by outdoor field trials with a NEC S1 transceiver terminal.

Combining beamforming with Alamouti scheme for multiuser MIMO communications

We combine optimum receive beamforming with the Alamouti space-time block code (STBC) transmission and modify the decoding process. In a multiuser multiple-input multiple-output (MIMO) communications scenario, the beamformer suppresses cochannel interference (CCI) by maximizing the uplink signal-to-noise-plus-interference ratio (SINR). It is shown that the beamforming process increases the bit-error-rate (BER) performance and maximizes the available uplink channel capacity for each user in the presence of CCI. The ergodic capacity of a conventional 2-by-1 Alamouti scheme is also increased from 3.2 to 4 bits/s/Hz by adding one receive antenna.