Vol. 64

An active reconfigurable Radar absorbing structure (RAS) with the pin diode was proposed to reduce the radar cross section (RCS) of antenna. The operating states of the RAS reflector can be switched by using the pin diode. For ON-state and OFF-state diodes, the reflection coefficients of the RAS reflector were less than -25 dB and more than -0.8 dB around 8.3 GHz, respectively. The RAS reflector with ON-state diodes can be used as a dipole antenna reflector and has the same radiation performance as a dipole with a metal reflector, while the RAS reflector with OFF-state diodes can be used as a radar absorber for RCS reduction. Meanwhile, chessboard-like geometry RAS reflector was proposed to achieve wideband RCS reduction. The RCS reduction band covers the working band and is extended to 5-18 GHz. The results show that the reconfigurable RAS reflector can contribute to the antenna RCS reduction at working frequency without loss of radiation performance of dipole antenna.

Miniaturization and metal-housing environment are the two most critical problems in the design of antennas, because they can highly deteriorate the performances of antenna, which not only affects the antenna efficiency, but also influences the bandwidth. In this paper, a compact size antenna with full metal housing for GPS/WLAN applications is studied. The proposed antenna can excite triple-band operation that covers the GPS (1.575 GHz), WLAN 2.45 GHz and WLAN 5.2/5.8 GHz bands, and its corresponding measured average efficiencies over these three desired bands were 40%, 41%, and 70%, respectively. The proposed antenna has a volume of 20.5×5×4 mm³, which is probably the smallest antenna in the industry for full metal housing applications.

In this paper, a compact asymmetric coplanar strip (ACS)-fed mirrored L-shaped monopole antenna is presented. The proposed design consists of three mirrored L-shaped branches and a split ring resonator (SRR) loaded beneath the substrate, which are responsible for achieving multiband characteristics, compactness and good impedance matching. The proposed antenna with a compact dimension of 22 × 16.08 × 1.6 mm³ fabricated and tested. The experiment result indicates that the proposed design, having -10 dB impedance bandwidth of 200, 670 and 530 MHz for 2.44, 5.3 and 8.2 GHz, respectively, covers 2.4/5.2/5.8 GHz WLAN, 5.5 GHz WiMAX and 8.2 GHz ITU band. It has good radiation characteristics for both E-plane and H-plane in all the desired frequency bands, very compact and produces good performances compared to the existing literature. The loaded SRR structure performance is validated through various parametric studies.

Fractal array antenna design methodology is an artistic type of design methodology. Hence fractal array antennas are also called as artistic array antennas. This article proposed a concentric elliptical ring sub array generator geometric design methodology for a methodical expansion of multi-beam fractal array antennas. Using this new geometric design methodology any polygon shape can be constructed. This geometric design methodology provides a systematic approach for multiple beams of fractal array antennas, with unit amplitude constriction, using multi-beam sub arrays and without any increase in hardware complication. In this paper, a four element rhombus fractal array antenna examined using a proposed design methodology up to four concurrent iterations and for different eccentric values. Due to the recursive nature of the proposed methodology, the rhombus fractal array antenna shows multi-beam performance with abatement of beam width and better side lobe level. In the third and fourth iterations of rhombus fractal array for expansion factor two, beam width reached to single digit values of 7.2˚, 3.6˚ with side lobe level angles of 15.5˚ and 8.1˚ respectively. The behavior of the proposed array shows better performance than four element fractal array antenna generated by concentric circular sub array generator. Proposed fractal array antennas are analyzed and simulated by MATLAB programming.

A single stage 900 MHz power amplifier (PA) with linearization bias circuit is designed with HHNEC 0.5 μm BIS500G power SiGe BiCMOS process. It is implemented by single-ended common emitter structure as a class AB power amplifier. The adopted active bias circuit is originally explained by using two virtue current sources, so that the mechanism of the improvement of linearity can be described more clearly. Then the mechanism is applied to guide the design of a power amplifier with an active bias circuit, which shows better linearity than resistor biased power amplifier by simulation. Through further design and measurement, the fabricated single stage power amplifier exhibits output power 1 dB compression point (OP1 dB) of 18.9 dBm, with power added efficiency (PAE) of 26.75% and power gain of 20.9 dB under 3.3 V voltage supply.

A microstrip power splitter with band-pass responses is presented in this paper. The design is based on square open loop resonator topology. This filtered power splitter does not require quarter wavelength transformers and will result in a smaller size than a conventional Wilkinson power divider with integrated band-pass filter. It is a two-way equal power splitter with fifth order band-pass filter characteristics. The power splitter is designed to have Chebyshev band-pass response function. A theoretical analytical circuit model will be presented. From the theoretical model, a microstrip filtered power splitter will be designed and simulated. The proposed filtered power splitter is small in size and reduces circuit complexity. The power splitter is simulated and measured, and the results are presented.

A new compact 30:1 bandwidth ratio balun and its application to balanced antennas are presented in this paper. To realize the balun-type function, two different types of wideband transition structures are adopted for unbalanced and balanced outputs of the balun. Further, a Vivaldi antenna integrated with the proposed balun is designed and fabricated to validate the feasibility of the new approach. Results indicated that the proposed balun can operate from 0.2 GHz to 6 GHz (a bandwidth ratio of 30:1). And it exhibits a good balanced performance within 0.5 dB magnitude imbalance and less than 6 degree phase imbalance between the two balanced outputs. In addition, the antenna can operate from 0.9 GHz to 6 GHz with good unidirectional radiation patterns.

In this work we report an ultra-thin all-dielectric antenna that was designed, built, tested, and compared with simulated data. The objective of this research was to develop an antenna that is easily manufactured by common 3-D printers available today. 3-D printing is quickly revolutionizing manufacturing and the need to incorporate electrical elements like antennas is rising. Multi-material 3-D printing that can build parts with conductors and dielectrics is the future, but at present it is very immature and largely inaccessible. The antenna presented here represents our first steps in developing all-dielectric antennas that can be manufactured today with commonly available 3-D printers and materials. A monolithic antenna would have additional mechanical benefits when subjected to bending or thermal cycling. With this goal in mind, an ultra-thin all-dielectric antenna was developed. The antenna operates by taking advantage of total internal reflection and exciting a leaky whispering gallery mode. The antenna reported here operates at 2.4 GHz and was able to be as thin as 1.5 mm.

A compact Phi-shaped monopole antenna for super wideband applications is proposed. It consists of a Phi-shaped radiator derived from a conventional elliptical monopole and quarter elliptical CPW ground plane. An impedance bandwidth from 3.5 to 37.2 GHz is achieved with a ratio bandwidth of 10:1. It provides an average peak realized gain of 3.5 dB with a group delay of less than 0.5 ns. The proposed antenna structure provides large bandwidth with the advantage of miniaturized dimensions compared to other SWB antenna structures.

A thin phase-correcting element that consists of four identical metallic and three identical dielectric layers is presented for the design of microwave and millimeter-wave transmitarrays. The metallic layers consist of the octagon conducting strip, which are tuned to obtain the desired phase compensation on an incident wave, while maintaining a high amplitude of transmission coefficient. A transmitarray is designed at K band using the element. Fed by a standard horn and three planar slot-fed patch antennas with different beamwidths alternately, the wave-focusing performance of the transmitarray was demonstrated by simulations and experiments.

This paper presents a third-order digital tunable bandpass filter based on digitally tunable capacitor loaded microstrip open ring resonator. Magnetic dominated mixed coupling is utilized to make the coupling coefficient meet the requirement of stable bandwidth response. Electric source-load coupling is designed to generate a transmission zero for improving the frequency selectivity. This filter is designed, fabricated and measured. The measurement shows that the filter can be digitally tuned by 5-bits pure digital command. The fractional bandwidth is 9±1%, and the tuning range is from 410 MHz to 820 MHz.

Novel types of dual circular polarizer are developed to convert TE₁₀ mode into two different polarizated TE₁₁ modes in a circular waveguide. These designs have MHz bandwidth and high power transmission capability. They can be used for broadcasting and receiving circular polarized signals.

In this work, we present a new systematic technique for the design of a flat lens using modified commercial off-the-shelf (COTS) materials, as opposed to metamaterials (MTMs) that are often required in lens designs based on the Transformation Optics (TO) approach. While lens designs based on Ray Optics (RO) do not suffer from the drawback of having to use metamaterials, they still require dielectric materials that may not be commercially available off-the-shelf. This paper describes a systematic procedure for realizing the desired materials by modifying the COTS types, and illustrates its application with some practical examples.

A compact dual-band dual-polarized antenna is proposed in this paper. The two pair dipoles with strong end coupling are used for the lower frequency band, and cross-placed patch dipoles are used for the upper frequency band. Breaches are introduced at the ends of the dipoles of the upper band, which can benefit the compactness and bandwidth of the antenna. The ends of the dipoles for upper frequency band are cut off a corner, which also benefit the compactness and matching of the antenna. An antenna prototype was fabricated and measured. The measured results show that the antenna can cover from 790 MHz to 960 MHz (19.4%) for lower band and from 1710 MHz to 2170 MHz (23.7%) for upper band with VSWR<1.5. It is expected to be a good candidate design for base station antennas.

This paper presents a Complementary Split Ring Loaded Resonator (CLSRR) based compact, wideband, waveguide bandpass filter. Three identical CLSRRs were fabricated and placed on the transverse plane of a standard WR-90 waveguide at a quarter wavelength distance to form the filter. The proposed filter was initially simulated using Ansoft HFSS (version 14) and then fabricated and measured. The measured result shows a fractional bandwidth of 18.80% at 10.05 GHz. Total length of the filter is only 20.33 mm which is compact enough. Detailed design procedure has been presented along with the equivalent circuit of the filter. A table has been provided to compare the performance of the proposed filter with those already available in the literatures. The table shows that the proposed filter is compact and has higher bandwidth, lower insertion loss and higher return loss.

A conformal patch array antenna with omnidirectional pattern in the azimuth plane at S-band is presented. A theoretical study of the generated ripple in the omnidirectional radiation pattern according to the number of faces that conform the array has been computed. A six-faced regular prism 3D structure has been chosen following a maximum 3 dB ripple criteria in the omnidirectional radiation pattern. A rectangular microstrip patch fed by a microstrip line has been designed as single radiating element. An equal power divider has been designed as feeding network in microstrip technology to feed each radiating element. Several prototypes have been manufactured and measured to validate the theoretical and simulated results. The entire conformal array has been assembled on a hexagonal regular prism manufactured in PolyLactic Acid (PLA) material using a 3D printer. In spite of the complexity of the proposed antenna structure, the used manufacturing processes, such as microstrip and 3D printing, allows to perform a low cost, low weight and compact final antenna. A higher radiated field ripple than the expected one is generated due to small deviations between experimental and theoretical critical parameters such as the feeding network performance or the 3 dB beam-width of the single element radiation pattern. A maximum ripple value of 4 dB has been experimentally obtained in the omnidirectional radiating pattern.

A symmetrical open-circuited λ/4 trans-directional (TRD) coupled line is proposed to replace the 3λ/4 reference line of an existing 90° Schiffman phase shifter for miniaturization. The coupling factor of the TRD coupled line can be used to control input matching and phase ripple, which adds an additional optimization variable to the design of a Schiffman phase shifter. There are two transmission zeros near the operational frequency band, which can be used to suppress adjacent frequency interferences and accompanies two phase leaps so that the realizable bandwidth is about 28~42%. Simulated and measured results are given to verify the proposed method.

This paper presents a high-gain cavity resonant antenna (CRA), consisting of an FSS layer placed above an aperture coupled microstrip patch antenna (ACMPA). Geometry of the proposed FSS superstrate is highly reflective with |Γ>0.9|. Ray-tracing method has been employed for determining the resonant condition of the antenna. ACMPA operating at S-band is serving as a feeding source. The coupling aperture of the antenna is of novel design, and several figures of merit have been presented for the proposed coupling aperture. Analysis of CRA has been carried out with the design parameters of the CRA. HFSS-13 has been utilized as simulation tool. Measured results are in good agreement with the simulated ones.

Magnetodielectric substrate gives a new dimension for reducing the size of the planar antennas. In this article, the patch size is reduced by taking a substrate with nano-sized nickel ferrite inclusions in LDPE polymer matrix. The antenna is made to operate in X- and Ku-bands by engraving T slots along the resonant length of the patch. Structural modification of the substrate geometry as a step profile is incorporated along the slotted patch edges to enhance performance. The T-slots, on both the radiating edges with the magnetodielectric stepped substrate show four resonant frequencies in both the X- and Ku-bands with S₁₁ < -15 dB and a maximum -10 dB bandwidth of 22.4%. A miniaturization factor of 2.97 is obtained.

The bandwidth of artificial magnetic conductor structures based on the square patch geometry has been significantly increased by using composite ferrite particles. These magnetic composites are non-conducting materials which achieve extraordinarily high values of magnetic permeability in the VHF and UHF range. Two AMC designs are presented for two different bands: the lower VHF and the VHF/UHF bands. To realize the ultra-high bandwidth for those ranges two particular materials were considered; nickel zinc and bismuth strontium titanate based ferrites. The AMCs were designed and modeled via numerical simulations using real material parameters as reported in literature. A cross-dipole radiator was integrated with the AMC to create a wideband directive antenna for SATCOM applications.