Return Loss Level Research Articles

Development of low loss waveguide filters for radio-astronomy applications

In this paper the modeling, fabrication and experimental characterization of a wideband band-pass filter operating in W-band (75–110GHz) is presented. This new high-performance waveguide filter can have several potential applications and will particularly be relevant in radio-astronomy receivers. The classical direct coupled cavity-based synthesis is first used. Then, an efficient full-wave analysis based on the mode matching technique is carried out, leading to a tenth order all-pole filter design. Two different prototypes were fabricated using an accurate electroforming machining technique. A good agreement between simulation and measurements is obtained with negligible frequency shift and 15dB return loss level. One should note the low level of insertion loss reported of about 0.4dB within the band-pass, which is a critical parameter for low-noise receivers.

Wideband Dual-Polarization Microstrip Patch Antenna Array for Airborne Ice Sounder

We present the design and realization of an antenna array based on cavity-backed microstrip patch antenna elements, with a relative operating bandwidth exceeding 20% at a return-loss level better than 15 dB. The antenna array of four elements did not show any compromise in bandwidth. It exhibited sidelobe levels better than 15 dB, with a gain of around 12 dBi. Excellent agreement was achieved between measurements and predictions for the designs of both the single element and the array. This antenna is part of the European Space Agency's airborne polarimetric P-band terrestrial ice sounder.

Metallic cone–sphere-inserted profiled Ku -band conical horn

A compact and low-cost, high-performance polynomial-profiled conical Ku-band horn with metallic cone–sphere insert is presented in this study. The horn has been designed to offer an aperture efficiency of higher than 90%, an acceptable return loss and low cross-polarisation level. Furthermore, in comparison with other high-performance horns, the proposed horn is shorter and lighter.

Design of multiple-passband filters using coupling matrix optimisation

This study presents the design of microwave filters based on the coupling matrix approach; determination of the matrix is based on a hybrid optimisation algorithm which may be applied to cross-coupled filters having diverse topologies. Various filter responses from dual-band to quad-band are given as examples of the approach. The optimisation is performed on the coupling matrix and a genetic algorithm (GA) is employed to generate initial values for the control variables for a subsequent local optimisation (sequential quadratic programming search). The novel cost function in this study measures the difference of the frequency locations of reflection and transmission zeros between the response produced by the coupling matrix and the ideal response. The ideal response in the form of characteristic polynomials is determined from the filter specifications and generated by a recently developed iterative technique which is capable of realising multi-band filters with different return loss levels. Convergence of the coupling matrix optimisation is fast, and no initial values for the control parameters are required by the GA. An eighth-order X-band dual-band waveguide filter with all-capacitive-coupling irises has been fabricated and measured to verify the design technique. Excellent agreement between simulation and experimental result has been achieved.

Use of partial Koch boundaries for improved return loss, gain and sidelobe levels of triangular patch antenna

The Koch fractals beyond the third iteration take on complex geometrical shapes and thus are difficult to implement. The possible solution to achieving high performance in antennas and to alleviate implementation issues is the use of partial Koch fractals. The introduction of partial boundaries to triangular patches results in antenna designs with high gain (9.44 dBi), low sidelobe levels (≤ - 20 dB), and improved return loss (- 59dB). The design antenna can be used in applications such as indoor LANs, GSM booster units etc.

Return loss and crosstalk mitigation in coupled vias for modern high-speed packaging

A method for mitigating the return loss and crosstalk corresponding to coupled vias is presented in this article. The method is based on selecting the proper dimensions for the antipad holes related to vias as well as the most adequate distribution of the ground vias, which allows to simultaneously reducing impedance mismatch and undesirable via coupling. The usefulness of the method is demonstrated by improving the performance of a 2 × 3 array of six signal vias. As a result, return loss levels below −45 dB and crosstalk levels below −40 dB are obtained in the 0–50 GHz frequency range. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012. © 2012 Wiley Periodicals, Inc.

Miniaturized patch antenna for RFID tags on metallic surfaces

AbstractThe majority of commercial ultra high frequency radio frequency identification tags are based on the dipole antenna, whose performance degrades significantly when the tag is placed near a conducting surface. In this article, we present a radio frequency identification patch tag to operate on conducting surfaces. The antenna provides good bandwidth and return loss level at 915 MHz. It has a very small size on low dielectric material, without the need for shorting pins or walls, which significantly lowers the fabrication cost in mass production using monolithic microwave integrated circuits. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26177

Monopole antenna based on wrench-shaped slot on circular disc patch for UWB application

A monopole antenna with circular-shaped patch has been proposed for ultra wideband (UWB) applications.With lack of current at the center of circular-shaped patch, a wrench-shaped design has been used for modifying blind spot center of patch and reinforcement of currents. In ground plane, a square and circular shape linked notch has been placed for proper impedance matching. Proposed antenna has a small size, and operates in 3.1 to 11.91 GHz frequency band. Laboratory and simulated antenna results show that proposed antenna has an acceptable return loss level and radiation pattern characteristics for the UWB frequency band range. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26125

Integrated Dual-Band Radiating Bandpass Filter Using Dual-Mode Circular Cavities

A new technique for the design of integrated dual-band multilayer substrate integrated waveguide (SIW) bandpass filter and microstrip antenna is presented. The design is based on a dual-mode TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> circular cavity structure, where two orthogonal modes co-exist in a single layer. The first layer has the first resonator for each band, and the second layer has the second radiating resonator. The two layers are coupled via capacitive rectangular irises at the common ground plane. The complete integrated device behaves as two second ordered bandpass filters each of which simultaneously filters and radiates. Simulation and measured results exhibit excellent agreement with the return loss level of 8 dB and gain of 5 dBi at 1.96-1.988 GHz and 2.06-2.09 GHz. This technique has the advantage of miniaturizing the overall structure and eliminates the need of external matching circuits.

Design of Microstrip-to-Microstrip Via Transition in Multilayered LTCC for Frequencies up to 67 GHz

A wide-band microstrip-to-microstrip via transition proposed for connecting an integrated circuit chip and an antenna array on the opposite sides of a multilayered low-temperature co-fired ceramic substrate is investigated in this paper. To facilitate the design, it is decomposed into external and internal segments, which consist of two microstrip-to-via transitions and a multilayered through-hole via with four ground vias, respectively. The equivalent impedance of the internal segment is carefully calculated from the lump-circuit model extracted by Ansoft Q3D, and verified by high-frequency structure simulation (HFSS). The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameters of external segments are simulated by HFSS for impedance matching, thereby obtaining the appropriate physical parameters. The physical mechanisms that result in the insertion loss are explored in detail, and the effects of via diameter are also investigated for the reduction of insertion loss. By combining the designs of the external and internal segments, the simulated <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameters demonstrated that the overall return loss level was above 20 dB within 57-67 GHz spectrum and insertion loss was better than 0.48 dB from d.c. up to 67 GHz. Coherent results between simulation and measurement were also obtained with a back-to-back transition structure.

Efficient DRW antenna for quasi‐optics feed in W‐band imaging radiometer system

AbstractModification in tapered dielectric rod waveguide antenna is achieved by the implementation of step change in width in metallic waveguide transition. The proposed antenna has circular symmetric radiation pattern and gain about 15.3 dB with improved return loss and side lobes level at W‐band. It has 10 dB beamwidth 53.2° and 48.6° in the E‐ and H‐plane. Proposed antenna can be used for a millimeter wave quasi‐optics feed array design in W‐band imaging radiometer design. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1221–1223, 2010; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/mop.25107

Multi-notch slot loaded wide band planar plate monopole antenna

A tuneable notch through the use of a small modified U-slot (MU-slot) in a wideband, 3–16 GHz, planar monopole plate antenna is presented. The MU-slot shape with its low width and long effective perimeter length (long current length) can result in a notch even at the lower frequency limit of the antenna. By optimising the MU-slot parameters and their relative positions, the centre frequency, the return loss level and bandwidth of the notch can be controlled. Based on slot current length, a formula for the notch centre frequency is derived. Also, because of the low width of the proposed slot, several MU-slots can be placed on top of each other along the axis of the monopole antenna to produce multiband notch behaviour. Based on the height of the given monopole antenna, up to four tuneable notch bands with good characteristics are shown. Simulation and measurement results are presented and discussed.

Advanced Coupling Matrix and Admittance Function Synthesis Techniques for Dissipative Microwave Filters

In this paper, novel approaches to synthesize admittance function polynomials and canonical <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> +2 coupling matrices for narrowband lossy filters are presented. The methods are simpler and more general than the ones found in the literature. The polynomial synthesis approach is fully analytical and also very useful for lossless polynomial synthesis with simpler derivations. The coupling matrix synthesis method is based on a lossy transversal network model, which can also accommodate direct source to load coupling. Unlike the lossless transversal coupling matrix, the lossy coupling matrix model requires the assumption of complex <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> -inverters and additional resistive elements in the network. The complex <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> -inverter circuit model is defined and explained in detail in this paper. The lossy transversal <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> +2 matrix can be systematically rotated to obtain a number of practical realizations. Parallel-coupled pairs and folded lossy configurations are shown as examples. Moreover, the synthesis of novel networks with different return-loss levels at source and load is presented. A performance comparison with a predistorted filter is also included in this paper.

Microwave attenuation with composite of copper microwires

It is shown that copper microwires composite media attenuates microwave reflection of metallic surfaces. We show how the distance to the metallic surface, as well as the length and volume fraction of microwires, determine the frequency of maximum absorption and the return loss level. Furthermore, we were able to fit the experimental results with a theoretical model based on Maxwell-Garnett mixing formula.

Design of 50–70 GHz Planar Wideband Bandpass Filter on Liquid Crystal Polymer Substrate

In this paper, the authors propose a novel and compact 50-70 GHz planar microstrip bandpass filter, possessing sharp-rejection, low insertion-loss and wide-band characteristics, based on Liquid Crystal Polymer (LCP) substrates. The filter is fabricated on LCP substrates by using standard processing technologies. The proposed filter exhibits a return loss level better than 10 dB, an insertion loss of 5 dB and a 3-dB bandwidth of 30%.The measured and simulated results show good agreement, proving that LCPs are potential and very promising materials for flexible millimeter-wave substrate applications.

Compact 90$^{\circ}$ Twist Formed by a Double-Corner-Cut Square Waveguide Section

Simple and compact rectangular waveguide 90deg twist is proposed. The twist transformer region is a square waveguide section with two square corner cuts. The twist full-wave model is based on the mode-matching and generalized <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -matrix techniques. It is found that the optimized twists can provide the bandwidths of no less than 30% at the 30-dB return-loss level or 16% at the 40-dB level over a lower, middle, or higher part of the rectangular waveguide operating band. The twist lengths are five times less than the rectangular waveguide wavelength at the central frequency of the chosen operating band. Role of evanescent modes in the interaction of two small-distanced twist transitions is discussed. The design results are confirmed by the results of real device measurements.

Design procedure for active microwave filters using the high quality active negative capacitance circuit for RF low‐noise bandpass applications

AbstractThis article presents a new methodology based on active band pass filter. In the proposed design, a resonator consists of an active negative capacitor together with a conventional inductor represented. The active negative capacitor is made of a field‐effect transistor that exhibits negative capacitance and negative resistance. It can, therefore, compensate the loss of an inductor. Two pole active bandpass filter centered 1.3 GHz, with 3 dB bandwidth of 640 MHz, high gain 1.5 dB, including a very low‐noise active filter which exhibits a noise figure of 2.5 dB are realized in the fist part. Compared with the conventional BPF, the proposed design shows better gain, noise figure, and the return loss level. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1086–1093, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23296

MEANDERED SLOT AND SLIT LOADED COMPACT MICROSTRIP ANTENNA WITH INTEGRATED IMPEDANCE TUNING NETWORK

In this paper, novel compact broadband dual frequency microstrip antennas are presented and broad-band impedance matching is proposed as a method for improve the matching level of antennas. The first proposed design consists of a rectangular microstrip antenna with a pair of parallel slots loaded close to the radiating edge of the patch and three meandering narrow slots embedded in the antenna surface. The second proposed design consists of a rectangular microstrip antenna with a meandering slits. With the first proposed design a size reduction of 34% and 45% for the two resonant frequencies is obtained respectively. The two frequencies have an operation frequency ratio of 1.30 and 1.25. The theoretical design implementation of compensated compact rectangular microstrip antennas with new configuration Pi-matching networks was presented. A new compensation network consisting of RC Mutator circuit and discrete capacitors are employed at the input of the microstrip antenna operating at 1.5 GHz and 2.5 GHz. The performance parameters of the designed microstrip antenna with and without compensation network were compared. The results show that compensation network can improve the return loss level and the resonant frequency can be controlled in a wide RF band.

A discussion on the performance of impedance matched antenna system and considerations for a better performance

AbstractImpedance matching networks are used extensively in radio communications. In this study, π‐matching circuit has been used as a matching network. The return loss level of several impedance matched microstrip antennas are compared as a function of matching techniques. The π‐matching device is used to construct the antenna tuning units, which is only used to match the front module and the antenna. This circuit impedance region has been investigated analytically under the variable load condition. When the mismatch is occurred, the result is an increase in the energy consumption or transmission quality deterioration. In addition, the input module in antenna system could be damaged if reflection of the signal levels is excessively high. This is interesting application because antennas cannot be considered alone as component with changing electromagnetic properties. The rectangular microstrip antenna was designed at 2.5 GHz frequency by using microstrip feed line. Better return loss level which is −16.86 dB has been obtained for this antenna using π‐matching circuit. It is shown that theoretical, simulation, and laboratory results are good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 410–415, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23101

Wide‐band compact microwave transistor amplifier methodology and the analysis of its input‐matching mechanism using negative impedance converter

AbstractThe design of broadband active‐compensated amplifier system is an important problem in microwave systems. In this letter, a wide‐band high‐gain microwave transistor amplifier (MTA) design is presented with −10 dB input reflection coefficient. To achieve its characteristics, a novel input‐matching mechanism is proposed. The recognition and comprehensive interpretation of this new input‐matching mechanism is important for future development of wide‐band MTA. In this article, broad‐band impedance matching is proposed as a method for improving the matching level of amplifier. A new compensation network consisting of negative impedance converter (NIC) circuit is employed at the input of the amplifier operating at 4.2 GHz. The results show that the compensation network can improve the return loss level from −5.9 dB to −13.01 dB, and the resonant frequency can be controlled in a wide RF band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 192–197, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23046