Prafulla Deo

Thickness Reduction and Performance Enhancement of Steerable Square Loop Antenna Using Hybrid High Impedance Surface

In order to reduce the thickness of a steerable beam square loop antenna, the effects of combining it with various periodic high impedance surfaces (HISs) are investigated. When a via-less HIS is used, the radiation pattern has high side lobes, which are shown to be due to surface waves propagating in the HIS lattice. Using a HIS with vias between the plates and ground removes the surface waves, but the beam is distorted due to strong coupling between the HISs vias and the antenna element. Consequently a hybrid HIS is designed. This uses a via-less lattice beneath the loop, with vias at the edge of the HIS to suppress surface wave propagation. Consequently, a square loop antenna with four feeds on a hybrid HIS substrate is proposed for beam steering applications. This antenna has a low-profile with a total thickness of 4.69 mm for a test frequency band of 4.3 GHz to 5.0 GHz. It exhibits a gain of 8.65 dB at the test frequency (4.7 GHz). Compared to the earlier reported steerable square loop antenna, the new antenna achieves a 61% reduction in substrate thickness, a bandwidth enhancement by 150 MHz and an increase in gain by 1.95 dB.

An HIS-Based Spiral Antenna for Pattern Reconfigurable Applications

Single arm rectangular spiral antenna with four open circuit switches over a high-impedance surface (HIS) is proposed for pattern reconfigurable applications. The HIS plane without vias is utilized to achieve a low-profile antenna design with a net thickness of 5.08 mm. This is equivalent to ~ lambdao/17 for the intended operating frequency of 3.3 GHz. By using the possible sixteen switching combinations a near 360deg beam steering is achieved, and the switched beams do not have a polarization variation from one pattern to another. The realized pattern reconfigurable antenna has both the tilted (thetasmax ges 25deg) and axial (5deg < thetasmax < 10deg) beams, which have an average directivity of 6.9 dBi.

Dual-Band Low-Profile Capacitively Coupled Beam-Steerable Square-Loop Antenna

In this paper, a dual-band low-profile switched beam square-loop antenna (SLA) fed by capacitively coupled feeding mechanism is presented. Two square loops are excited by four rectangular feeding patches which are fed with vertical probes. The capacitively coupled feeding arrangement introduces capacitance into the antenna input impedance and cancels the high inductance due to close proximity of ground plane and feeding probes. This feeding technique enables the antenna to be matched to 50 Ω feedline and helps in the realization of low-profile SLA. The antenna has a height of 3.04 mm; i.e., λ0 /26 for the operating frequency of 3.8 GHz. The dual-band capacitively coupled square-loop antenna (DBCCSLA) is developed for covering 3.8- and 4.7-GHz frequency bands, and each band possesses an impedance bandwidth of 120 MHz. In both frequency bands, when any of the four ports is excited, keeping other ports open circuited, the antenna generates a tilted beam directed away from the excited port, having a maximum directivity of 9.3 dBi. By exciting ports one at a time, the antenna can steer its tilted beam in four different quadrants to scan the entire space in front of the antenna.

Circularly polarized square patch antenna with square slots for RFID reader applications

A circularly polarized antenna with square patches and slots has been proposed for radio frequency identification reader applications. The design of reader antenna is optimized to reduce the overall size of an antenna. A ground plane with an arrow type slot has been utilized for efficient coupling of RF power from the feed line to the antennas square patches. On the square patches, square slots have been inserted to enable the antenna-reader to radiate a circular polarized wave. The test frequency of this antenna is 880 MHz at which it exhibits circularly polarized radiation patterns.

Microstrip Device for Broadband (15–65 GHz) Measurement of Dielectric Properties of Nematic Liquid Crystals

The essential dielectric properties, the basic alignment techniques, and the common measurement methods of the nematic liquid crystal (LC) at RF are briefly reviewed. A new device for the broadband measurement of the dielectric constants and loss tangents of nematic LCs at microwave and millimeter-wave frequencies is presented. This device whose specification and fabrication are outlined is essentially a two dielectric layer microstrip structure with coplanar-waveguide terminals, which is easy to fabricate. Compared to previous structures, the proposed device is extremely broadband with 15-65-GHz bandwidth, benefits from a solid exposed ground plane for easy temperature test, and operates under bias voltage. The technique for the extraction of the dielectric parameters of the nematic LC analyzed by this device is explained and the sources imposing the frequency limits on the device performance are identified. Two different nematic LCs, MDA-00-3506 and GT3-23001, are characterized and the results are shown to compare well with those available in the literature. In the comparisons, the maximum difference found for the dielectric constants for MDA-00-3506 is 5% and for GT3-23001 is 5.3%.

Tunable liquid-crystal millimeter-wave bandpass filter using periodical structure

For the first time, a tunable liquid crystal (LC) bandpass filter using a microstrip periodical structure for applications at millimeter-waves is presented. In the LC default state, it operates at 49 GHz with about 20% fractional bandwidth (9 GHz). The filter tunability range is 3.2 GHz over bias voltages 0 to 10 V and its insertion loss is about 4.7 dB. Dimensions of the filter can be scaled to increase its operating frequency to 77 GHz and hence, is a promising component for 60 GHz systems.

Slotted microstrip patch antenna with embedded feed

A 60 GHz band slotted microstrip patch antenna with embedded microstrip line feed is presented. The slotted patch effectively provides two degrees of freedom for achieving the same operating frequency. These are the patch and the slot lengths. An equation is reached to determine the operating frequency of the antenna, verified to be accurate to within 1% for various patch and slot dimensions. Also, the effect of the feed-line end position with reference to the slotted patch is studied and results are reported. This antenna is suitable for operation in 60 GHz band in single or in array arrangement.

Beam switched loop antennas - square to circular

Systematic investigations for three beam switched antenna configurations, namely, the square loop with middle feeding, the square loop with corner feeding and the circular loop antenna are undertaken and the results focusing on their radiation patterns are presented. All these configurations exhibit two zones of impedance bandwidth in the UWB region (3.1 GHz - 10.6 GHz), however, only one of them generates a distortion free tilted beam pattern. This titled beam can be switched in the different space quadrants by using different feeding points on the antenna. Comparison of the radiation patterns of these configurations reveals that the middle fed square loop antenna exhibits the lowest level of co-polarized side-lobes (≪ 9.0 dB), leading to a conclusion that for beam switched applications the middle fed square loop is the most suitable choice amongst the three loop antennas.

Next generation sub-millimeter wave focal plane array coupling concepts: An ESA TRP project to develop multichroic focal plane pixels for future CMB polarization experiments

The main objective of this activity is to develop new focal plane coupling array concepts and technologies that optimise the coupling from reflector optics to the large number of detectors for next generation sub millimetre wave telescopes particularly targeting measurement of the polarization of the cosmic microwave background (CMB). In this 18 month TRP programme the consortium are tasked with developing, manufacturing and experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays which will be demanded to reach the required sensitivity of future CMB polarization missions. One major development was to have multichroic operation to potentially reduce the required focal plane size of a CMB mission. After research in the optimum telescope design and definition of requirements based on a stringent science case review, a number of compact focal plane architecture concepts were investigated before a pixel demonstrator consisting of a planar mesh lens feeding a backend Resonant Cold Electron Bolometer RCEB for filtering and detection of the dual frequency signal was planned for manufacture and test. In this demonstrator the frequencies of the channels was chosen to be 75 and 105 GHz in the w band close to the peak CMB signal. In the next year the prototype breadboards will be developed to test the beams produced by the manufactured flat lenses fed by a variety of antenna configurations and the spectral response of the RCEBs will also be verified.

Accurate Modelling of Liquid Crystal-Based Microwave Devices

Liquid crystal substrates have been shown to provide the means to develop low-cost, reconfigurable, adaptive and tuneable microwave devices for mobile and wireless communication systems. In order to take maximum advantage of the possibilities that these materials offer and to design LC-based devices appropriately, techniques for the characterisation of the liquid crystal dielectric properties are needed. Similarly, appropriate modelling methods are required to simulate accurately the switching behaviour of the liquid crystal and the characteristics of the wave propagation through the devices, taking full consideration of the point-by-point variation of the material tensor permittivity.