A new study of right-handed and composite right/left-handed metamaterial transmission lines (TL) using their equivalent circuits and a new approach of the wave concept iterative process method is presented. This approach has the advantage of simulating all the periodic structures by only simulating one basic cell thanks to the surrounding periodic walls. A suitable choice of the cell length is necessary to work with the current as well as voltage and to approach the real behavior of the TL. The simulation results of these circuits, such as the calculation of current, voltage and the parameters S, helped to validate all the theoretical study.

A novel multiport system, allowing for measurements of scattering parameters in over-two-octave frequency range is proposed. It is composed of two directional couplers and a standard 4 × 4 Butler matrix, and does not require any isolators. The presented system features a uniform power distribution providing the high precision of measurements, which can be further enhanced by a simple adjustment of the system's parameters. A comprehensive analysis of the proposed system configurations, a fully analytical calibration for transmission coefficient measurement, and the estimation of maximum measurement error are given. The proposed measuring system has been experimentally verified in a wide frequency range 1–5 GHz, by measurements of S-parameters of exemplary components. The measurement results are very close to the values obtained with the use of a commercial vector network analyser within the 50 dB range of measured values’ magnitude.

In order to counter active jamming, an adaptive polarization cancellation method based on dual-polarization radar is proposed in the paper. First, respectively being obtained by vertical and horizontal polarization channels of dual-polarization radar, the signals from the real target and active jamming are analyzed in composition and characteristic. Then, the weight coefficient is timely derived in practical scene to adjust difference of amplitude and phase of active jamming signals respectively acquired by the two orthogonal polarization channels, so the method can completely eliminate active jamming, but just a little power change for the real target signal. Furthermore, a compensating method for the target signal is developed to improve the angle measuring accuracy of monopulse radars. And the influence factors of adaptive polarization cancellation are analyzed in detail by simulation. Finally, the experimental results prove that it is very effective on both active blanket jamming and active deception jamming.

This paper describes a new configuration of frequency-selective structure (FSS) structures to reduce mutual coupling between the radiating elements. Also, the antenna performance before and after the implementation of FSS have been investigated. The proposed configuration provides an improvement in mutual coupling by 14 dB (measured value) with a reduced edge-to-edge spacing of 23 mm. The reduction of mutual coupling between antenna elements is interesting in the electromagnetic and antenna community. The use of electromagnetic band-gap structures constructed by microstrip technology is a way to appease the mutual coupling problem. Periodic structures such as FSS can help in the reduction of mutual coupling using their ability of suppressing surface waves propagation in a given frequency range. The goal of this present study is to use it in patch antenna arrays, keeping both the element separation smaller than λ0 for grating lobes evasion and the patch antenna size large enough to have good antenna directivity. The results showed that the proposed configuration eliminates disadvantages of similar structures presented in the previous works.

A new single-feed aperture-coupled, X-band microstrip patch antenna array with circular polarization (CP) is designed. CP is achieved using indented microstrip patches fed through the slots on a substrate integrated waveguide. The antenna has the high radiation efficiency more than 90% over the operating frequency. Impedance bandwidth (VSWR < 2) and axial ratio bandwidth (AR < 3 dB) of 11.8, and 10.9% is attained, respectively. Good agreement is achieved between simulated and measured results.

In this paper, a tri-band bandpass filter (BPF) using asymmetric stub-loaded stepped-impedance resonator (SL-SIR) is presented. The asymmetric characteristic of SL-SIR broadens degrees of freedom for three controllable modes design. Also, the coupling coefficients (Mij) and the external quality factors (Qei) at each passband of the filter can be independently adjusted by the proposed mixed-type feedline structure. Besides, multi-transmission zeros are produced to improve the isolation and selectivity of the passbands. Finally, a tri-band BPF is operated at 1.9 GHz (time division long term evolution – TD-LTE band), 3.2 GHz (worldwide interoperability for microwave access – WiMAX band), and 5.8 GHz (wireless local area networks – WLAN band) and their insertion loss are 1.03, 0.94, and 1.27 dB, respectively. The measured results of the fabricated tri-band BPF exhibit good agreement with simulated results.

A new Ku-band reflectarray with an artificial anisotropic slab that consists of periodic holes, backed by a planar artificial magnetic conductor (AMC) is proposed. The unit-cell of the reflectarray is a two-layered structure that consists of a dielectric with a hole on a grounded patch. The phase diagram of the proposed unit-cell is calculated by a full-wave computational technique, which uses the dyadic Green's function evaluated by an equivalent transmission line modeling in the spectral domain. The obtained dyadic Green's function is used in an integral equation formulated for the surface current densities on the metallic grating. The resultant integral equation is then solved using the method of moments. The required phase shift at Ku-band is obtained by changing the radius of holes in the artificial slab. The introduced unit cell has linear phase range between 13.95 and 14.95 GHz. It is shown that this frequency band is the usable bandwidth of AMC structure. Finally, the designed reflectarray is analyzed using a full-wave electromagnetic solver. The numerical results show a maximum gain of 27.4 dBi, and 48.09% efficiency, at 14.45 GHz with 4.15% 1-dB gain bandwidth for the designed 21 × 21 cm2 reflectarray.

Bitstreams, square wave digital signals, enable flexible radar implementations in modern digital technology. By using bitstreams in place of analog sinusoidal waveforms, we can realize continuous-wave (CW), stepped-frequency CW, frequency-modulated CW, or even pseudo random noise-sequence and pulsed radars, all with a single bit of amplitude resolution. The building blocks are a programable waveform generator, a sweep threshold quantizer, digital delay, and a digital XOR gate as a mixer. This gives us a novel, almost fully digital (requiring only a comparator) system, as previously proposed and which is extended here. The flexibility of the transmitter allows for easy switching between waveforms and the bitstream signal can be processed with single-bit digital gates. Single-bit signals allows for exploration of novel continuous time non-clocked digital implementations to maximize speed and energy efficiency. Mixing frequencies with a digital XOR gate creates harmonics, which are explored for multiple solutions utilizing digital delay. Analytical as well as simulation results are presented. Initial measurements from a 90 nm CMOS chip is provided for the transmitter and the full system, proving the feasibility of a digital future in radar.

A compact quad band slot antenna with high isolation suitable for multiple-input–multiple-output (MIMO) applications is developed. The quad bands are achieved by introducing slots in a modified, size reduced circular patch antenna. The single-antenna element consists of a substrate sandwiched between a modified circular patch with F shape slot, a feeder line and a via running between the radiating patch and the feeder line. The proposed design resonates at the frequencies of 1.8 GHz (1.7–1.88 GHz), 3.6 GHz (3.50–3.76 GHz), 5.4 GHz (5.25–5.38 GHz), and 7.2 GHz (7.15–7.35 GHz) covering the GSM II, WIMAX, wireless local area network (WLAN), and C-band applications, respectively. The independent tuning of frequency bands is achieved by varying the length of the slots. Orthogonally placed two- and four-element MIMO antenna system are fabricated, tested, and the measurement results are presented. The separation between each element is reduced to 0.085λ while introducing slotted and pulsed stubs to improve isolation between elements. A detailed analysis, including mutual coupling, low correlation, diversity gain, and total array reflection coefficient had been reported. The two- and four-element MIMO antennas achieved correlation as low as 0.005, mutual coupling ≤−15 dB, and diversity gain nearly 10 dB.

A novel compact directional antenna with improved gain is proposed for microwave breast imaging (MBI) applications. The radiating fins are modified by etching several slots to make the antenna compact and enhance antenna performance in terms of bandwidth, gain, efficiency, and directivity. Several parameters are studied and optimized to frequency from 3.1 to 6.5 GHz, which is typically used in the breast imaging system. The electrical length of the antenna is 0.39λ × 0.46λ × 0.01λ at the lower frequency band. The result shows that the antenna exhibits −10 dB impedance bandwidth of 4.3 GHz (2.7–7 GHz) with directional radiation pattern. The peak gain of the proposed prototype is 7.8 dBi and fractional bandwidth is 92%. The time domain results show that the fidelity factor for face to face is 0.92 and for side by side is 0.62, which prove the directivity and lower distortion of the signal. The proposed prototype is successfully simulated, fabricated, and measured.

The design and integration of penta-band planar antenna with a low noise amplifier (LNA) for vehicular wireless applications is discussed in this research. By integrating antenna with a LNA, the return loss can be kept low with the increased bandwidth compared with a passive antenna with the same design. The performance of the passive antenna, LNA, and integrated active antenna (IAA) are individually validated with the aid of vector network analyzer. The designed IAA covers navigational frequencies 1.2 and 1.5 GHz, wireless communication frequencies 2.4, 3.3 GHz and dedicated short range communication frequency 5.8 GHz, with LNA gain (>10 dB) and noise figure (<2 dB). The proposed design gives room for simultaneous reception of all the desired frequency bands with better performance for vehicular communications.

A wideband four element triangular dielectric resonator antenna (TDRA) has been designed and fabricated by using 50 Ω coaxial probe feed. The input and radiation characteristics of the proposed antenna have been extracted through Ansoft HFSS and CST Microwave Studio simulation software and compared with the experimental results. The simulated results have been in good agreement with the experimental results. The proposed antenna characteristics have also been compared with the same dimensions of the single element TDRA, and found enhancement in bandwidth with lower resonant frequency. Its performance has also been compared with same area (equal to proposed antenna) of single element TDRA. The proposed antenna provides nearly 37% bandwidth (|S11| < −10 dB) at a resonant frequency of 5.45 GHz with 4.76 dBi peak gain. The symmetry and uniformity in the radiation patterns is obtained consistently for the entire operating bandwidth. The proposed antenna shows consistently symmetric monopole type radiation pattern with low cross polarization for WLAN (IEEE 802.16) and WiMAX applications. The performance of the proposed antenna has been compared with some similar type of dielectric resonator antenna (DRA) shapes and it has been observed that TDRA is taking very less radiation area for giving better performance than other DRA shapes.

In this paper, an X-shaped fractal antenna with defected ground structure (DGS) is presented for multiband and wideband applications. The X shape is used due to its simple design and DGS is utilized to achieve size reduction with multiband and wideband features in the frequency range of 1–7 GHz. The proposed structure is fabricated on FR4 substrate with 1.6 mm thickness. We have proposed two different antennas both are having X-shaped fractal patch with a slotted ground plane to have more impedance bandwidth and better return loss. Various parameters like scale factor, width of ground plane, number of slots with their dimensions and feed line length are optimized to have size reduction and for enhancing the performance of antenna. Reflection coefficient shows the multiband and wideband features of proposed antenna. One of the proposed antennas covers various applications like IEEE802.11y at 3.65 and 4.9 GHz, IEEE 802.11a at 5.4 GHz, 802.11P at 5.9 GHz. Other antenna covers applications like IEEE802.16 at 3.5 GHz; 5 cm band for amateur radio and satellite and future 5 G communication systems over 6 GHz. The antenna designing was done using CST software and simulation results were compared with experimental results (using E5071C network analyzer).

Air target recognition is a critical step in the radar processing chain and reliable features are necessary to make a decision. The number and position of jet engines are useful features to perform a pre-classification and give a list of possible targets. To extract these features, a sparse decomposition framework for inverse synthetic aperture radar (ISAR) images is presented. With this framework different components of the target can be detected, if signal models for these parts are available. To use it for the detection of jet engines, a review of a signal model for air intakes, which was developed by Borden, is given. This model is based on the common assumption that the propagation of electromagnetic waves inside jet engines has the same dispersive behavior as inside waveguides. With this model a decomposition of a real ISAR image, measured with the tracking and imaging radar system of Fraunhofer FHR, into point-like scattering centers and jet engines is presented.

A simple and compact printed ultra-wideband antenna with dual-band-notched characteristics is presented. The proposed antenna is composed of a rectangular patch and a modified ground plane. The rectangular patch is etched onto a lossy FR4 substrate. A circular ring strip parasitizes the rectangular patch embedded by a U-shaped slot. Two inverted-L slits and a rectangular slit are embedded onto the ground plane. Some bandwidth enhancement and band-notched techniques are applied in the antenna structure for broadening the bandwidth and generating notches. The simulated and measured results show that the proposed antenna offers a very wider bandwidth ranging from 3.04 to 17.30 GHz, defined by the return loss less than −10 dB, with dual-notched bands of 3.30–4.20 and 5.10–5.85 GHz covering the 3.3/3.7 GHz WiMAX, 3.7/4.2 GHz C-band, and 5.2/5.8 GHz wireless local area network systems. Furthermore, the proposed antenna presents relatively high antenna gain and quasi-omnidirectional radiation patterns.

In this paper, a compact dual-band bandpass filter (DB-BPF) using new dual-mode resonator-loaded resonators (DM-RLRs) is presented and investigated to simultaneously achieve controllable return loss (RL), bandwidth (BW) and transmission zeros (TZs), and the simple strategy for this type of filter design is proposed. The DB-BPF consists of two high-flexibility DM-RLRs with separated electric and magnetic coupling (SEMC). Specifically, the proposed DM-RLR provides the DB-BPF with center frequency control as well as RL control, and SEMC is utilized for the BW and TZ control. To facilitate the design, a simple optimization-based design strategy is proposed and employed, resulting in an example layout. Finally, the example filter, with center frequencies of 1.57 GHz (channel 1 for GPS) and 3.5 GHz (channel 2 for WiMAX), is fabricated and measured. The measurement insertion loss and RL are 0.9/0.9 and 17/20 dB. The fabricated DB-BPF also exhibits a compact size of 0.12λg × 0.08λg at 1.57 GHz.

A compact microstrip multi-stub loaded bandpass filter (BPF) with ultra-wide stopband is introduced and investigated. Lumped-equivalent circuit (LEC) method is adopted to analyze the characteristics of the in-band response based upon the low frequency LEC and even-odd mode analytical method. Besides, equivalent transmission line circuit method with even-odd mode analytical method are adopted to discuss the mechanism of the out-band rejection based upon the transmission poles and the transmission zeros analysis of the even-/odd-mode equivalent circuits. Accordingly, the design and the optimization procedures of this type of filters are summarized. To experimentally validate the proposed method, the filter is fabricated and measured. The measured results illustrate this BPF centered at f0 = 2.8 GHz, with −3 dB fractional bandwidth of 109.3%, the insert loss (IL) of less than 1 dB from 1.4 to 4 GHz, and the rejection level of 20 dB from 5.1 to 33.5 GHz(1.82f0 to 11.96f0).

The design and measurement of reconfigurable circularly polarized capacitive fed microstrip antenna are presented. Small isosceles right angle triangular sections are removed from diagonally opposite corners for the generation of circular polarization (CP) of axial ratio bandwidth of 11.1%. Horizontal slits of different lengths are inserted at the edges of the truncated patch to provide the dual-band CP and by switching PIN diodes across the slits ON and OFF, reconfigurable circularly polarized antenna is realized. The antenna shows dual-band behavior with reconfigurable CP. In order to enhance the operation bandwidth of the antenna, an inclined slot was embedded on the patch along with PIN diodes across the horizontal slits. This proposed antenna gave an impedance bandwidth of 66.61% (ON state) ranging from 4.42 to 8.80 GHz and 68.42% (OFF state) ranging from 4.12 to 8.91 GHz and exhibits dual-frequency CP with PIN diode in OFF state and single-frequency CP with PIN diode in ON state with good axial ratio bandwidth. The axial ratio bandwidth of 4.42, 2.35, and 2.72% is obtained from the antenna. The antenna has a similar radiation pattern in all the three different CP bands and almost constant gain within the bands of CP operation.

In this contribution, fractal antenna arrays are analyzed for their applicability in multiple-input multiple-output (MIMO) radars. Array geometries based on the Fudgeflake fractal and the Gosper island fractal are investigated. In addition, a concept for the combination of both fractals is shown in order to increase the flexibility concerning the number of transmitting and receiving antennas. The presented fractal MIMO concepts can be utilized in order to improve the angular resolution and to reduce the sidelobe level for a given number of transmitting and receiving antennas. It is shown that a fractal MIMO concept with 21 transmitting antennas and 21 receiving antennas improves the angular resolution to 4.6 degrees and reduces side lobe level by 3.1 dB compared to a MIMO configuration based on two linear arrays with the same number of antenna elements. In addition, the results are experimentally validated by broadband radar measurements.

In this paper, a wideband bandpass filter using multi-mode resonator and mixed electromagnetic (EM) coupling is presented. To increase the bandwidth while not enlarge the circuit size, multi-short-stub multi-mode resonator, which produces multiple resonances, is utilized. Furthermore, the capacitive gap between open ends of the stubs is utilized to realize electric coupling between the multi-mode resonator and quarter-wavelength stepped impedance resonator. Meanwhile, a high-impedance transmission line between them is used to implement magnetic coupling. This mixed EM coupling can produce transmission zero near the passband, consequently improving the frequency selectivity of proposed filter. Measured results of the filter prototype are in good agreement with the simulated ones. The filter is with an insertion loss at central frequency of 15.86 GHz about 2.5 dB, a 3 dB bandwidth about 5.72 GHz (the fractional bandwidth about 36%), and the variation of group delay over the whole passband <0.28 ns. Additionally, the effective circuit size of the filter is about 0.126 λg2, where λg is the wavelength of 15.86 GHz. All these results have shown that proposed filter is promising for future high-precision imaging system or high-speed communication application.