Using the branch-line directional coupler in the design of microwave bandpass filters

Grupo de Microondas y Radar, Univ. Politecnica de Madrid, Spain
IEEE Transactions on Microwave Theory and Techniques (Impact Factor: 2.24). 11/2005; 53(10):3221 - 3229. DOI: 10.1109/TMTT.2005.855140
Source: IEEE Xplore


This paper addresses the application of the branch-line directional coupler to the design of microwave bandpass filters. The basic idea consists of using the branch-line coupler as a transversal filtering section by loading the coupled ports of the coupler with suitable transmission-line segments ending in an open circuit and taking the isolated port as the output node. Thus, under the signal interference philosophy involved in classic transversal filter schemes, bandpass transfer functions with perceptible stopbands and sharp cutoff slopes are derived. Furthermore, the main characteristics of the synthesized filtering response, such as the bandwidth or the position of the out-of-band power transmission zeros, can be easily controlled by means of the design parameters of the transversal section. Hence, a large variety of bandpass filtering profiles different from those offered by classical filter schemes can be realized. Finally, the experimental usefulness of the transversal filtering section based on the branch-line coupler is proven with the design and construction in microstrip technology of two microwave bandpass filter prototypes at 5 GHz.

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    • "1-3. As the basic circuit mode in [13]-[16], two transmission paths are used to realize the signal transmission from Port 1 to Port 2; quarterwavelength open stubs , half-wavelength shorted stubs and open/shorted coupled lines are parallel connected to realize two different high-order wideband bandpass filters. Through a similar analysis as the filters in [13]-[16], the in-band/out-ofband transmission zeros and poles can be realized by the superposition of signals for the two transmission paths. "
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    ABSTRACT: Two high-order wideband bandpass filters with improved upper stopband based on transversal signal-interference techniques are analyzed and designed in this paper. By choosing different open stubs and open/shorted coupled lines, two wideband bandpass filters with several transmission zeros from 0 GHz to 2f0 (f0 is center frequency of the stopband) can be achieved respectively, due to the superposition of signals of the two transmission paths. The bandwidths of the two wideband bandpass filters can be easily adjusted by changing the characteristic impedance of the resonant structures of the two transmission paths. One wideband bandpass filter prototype with 3-dB fractional bandwidth of 80% (0.6-1.8 GHz) is designed and fabricated for demonstration. The theoretical and measured results are in good agreement and show good in-band filtering performance and high selectivity.
    The 6th International High Speed Intelligent Communication (HSIC2014); 12/2014
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    • "The transmission is between Ports 1 and 2. Fig. 4. Sub-networks connected to the coupled ports of 3-dB: (a) 90 and (b) 180 hybrid couplers. The transmission is between Ports 1 and 2. evident that the transversal BPFs utilizing branch-line couplers proposed in [7] are a special case of the Cul-De-Sac networks presented here. This is because branch-line couplers may also be utilized to design bandstop networks as proven above. "
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    ABSTRACT: A synthesis procedure is described for the design of Cul-De-Sac networks realizing either bandpass or bandstop filter characteristics. The prototypes comprise a pair of one-port ladder sub-networks each connected at one of the coupled ports of a 3-dB, 90deg or 180deg hybrid coupler. Numerical examples and simulated filter layouts are presented to illustrate the design methodology
    IEEE Microwave and Wireless Components Letters 06/2007; 17(5-17):334 - 336. DOI:10.1109/LMWC.2007.895696 · 1.70 Impact Factor
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    ABSTRACT: The objective of this thesis is to present the design and implementation of ultra-low power radio transceivers at microwave frequencies, which are applicable to wireless sensor network (WSN) and, in particular, to the requirement of the Speckled Computing Consortium (or SpeckNet). This was achieved through quasi-MMIC prototypes and monolithic microwave integrated circuit (MMIC) with dc power consumption of less than 1mW and radio communication ranges operating at least one metre. A wireless sensor network is made up of widely distributed autonomous devices incorporating sensors to cooperatively monitor physical environments. There are different kinds of sensor network applications in which sensors perform a wide range of activities. Among these, a certain set of applications require that sensor nodes collect information about the physical environment. Each sensor node operates autonomously without a central node of control. However, there are many implementation challenges associated with sensor nodes. These nodes must consume extremely low power and must communicate with their neighbours at bit-rates in the order of hundreds of kilobits per second and potentially need to operate at high volumetric densities. Since the power constraint is the most challenging requirement, the radio transceiver must consume ultra-low power in order to prolong the limited battery capacity of a node. The radio transceiver must also be compact, less than 5×5 mm2, to achieve a target size for sensor node and operate over a range of at least one metre to allow communication between widely deployed nodes. Different transceiver topologies are discussed to choose the radio transceiver architecture with specifications that are required in this project. The conventional heterodyne and homodyne topologies are discussed to be unsuitable methods to achieve low power transceiver due to power hungry circuits and their high complexity. The super-regenerative transceiver is also discussed to be unsuitable method because it has a drawback of inherent frequency instability and its characteristics strongly depend on the performance of the super-regenerative oscillator. Instead, a more efficient method of modulation and demodulation such as on-off keying (OOK) is presented. Furthermore, design considerations are shown which can be used to achieve relatively large output voltages for small input powers using an OOK modulation system. This is important because transceiver does not require the use of additional circuits to increase gain or sensitivity and consequently it achieves lower power consumption in a sensor node. This thesis details the circuit design with both a commercial and in-house device technology with ultra-low dc power consumption while retaining adequate RF performance. It details the design of radio building blocks including amplifiers, oscillators, switches and detectors. Furthermore, the circuit integration is presented to achieve a compact transceiver and different circuit topologies to minimize dc power consumption are described. To achieve the sensitivity requirements of receiver, a detector design method with large output voltage is presented. The receiver is measured to have output voltages of 1mVp-p for input powers of -60dBm over a 1 metre operating range while consuming as much as 420μW. The first prototype combines all required blocks using an in-house GaAs MMIC process with commercial pseudomorphic high electron mobility transistor (PHEMT). The OOK radio transceiver successfully operates at the centre frequency of 10GHz for compact antenna and with ultra-low power consumption and shows an output power of -10.4dBm for the transmitter, an output voltage of 1mVp-p at an operating range of 1 metre for the receiver and a total power consumption of 840μW. Based on this prototype, an MMIC radio transceiver at the 24GHz band is also designed to further improve the performance and reduce the physical size with an advanced 50nm gate-length GaAs metamorphic high electron mobility transistor (MHEMT) device technology.
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