Alireza Pourghorban Saghati

Tunable SIW Structures: Antennas, VCOs, and Filters

Due to their high quality factor (hundreds), high power handling, and good isolation, SIW structures are excellent candidates for a variety of microwave devices, including filters, antennas, VCOs, and isolators. However, their use has been hindered due to their narrow BW and high sensitivity to the fabrication process. Tuning the SIW-based microwave structures has the advantages of covering more bands, the possibility of post-fabrication fine-tuning, and less crosstalk sensitivity. However, the conventional tuning methods applicable to regular microwave structures are not effective for SIWs. Finding a way to tune these structures over a wide tuning range while maintaining their high Q seems to be very appealing and, at the same time, very challenging. To address all these points in more detail, the main focus of this article was on frequency-tunable/ reconfigurable SIW structures. The reported tuning methods applied to SIW structures so far are studied, and their pros and cons are discussed in detail. Also, separate libraries for SIW-based tunable filters, antennas, and VCOs are provided.

A Miniaturized Microfluidically Reconfigurable Coplanar Waveguide Bandpass Filter With Maximum Power Handling of 10 Watts

In this paper, a microfluidically reconfigurable coplanar waveguide (CPW) filter is presented with a tuning range of ~ 1.6:1 and four different states. The passband frequency of the filter is changed based on employing the capacitive loading effect of a liquid metal placed on top of each CPW resonator using three parallel micro-channels. In addition, because of the loading effect of the metal bridges, miniaturization by a factor of 40% is achieved. The filter is digitally tuned from 3.4 to 5.5 GHz with an insertion loss of less than 5.0 dB and a relative bandwidth of 5 ± 0.35%. The RF power-handling capability of the filter is characterized using a customized measurement setup. It is observed that the filter can be used for input RF powers of up to ~ 20 W for short-duration excitation conditions and 10 W for high-average-power excitation conditions. The filter is realized using common printed circuit board technology and a polydimethylsiloxane structure. Design methodology, simulation, and measurement results of the filter prototype are presented.

Fluidics in Microwave Components

Thanks to the efforts of various research groups over the past decade in the area of tunable microwave passive components, the idea of tunability has become very well established within the RF/microwave community [1]-[5]. Many different designs have shown that tunable microwave components can improve the performance of a radio system in many ways. The tunability of microwave components has been realized using semiconductor devices (such as varactors or p-i-n diodes) and microelectromechanical systems (MEMS) devices. While these offer many advantages, such as high-quality factor and high-bandwidth operation (mainly for MEMS devices) and fast switching speeds (mainly for varactors and p-i-n diodes), they come with two major drawbacks.

Miniature and Reconfigurable CPW Folded Slot Antennas Employing Liquid-Metal Capacitive Loading

Microfluidic channels filled with liquid metal are used to realize miniature and reconfigurable CPW folded slot antennas. The method is based on employing the reactive loading effect of fluid metal bridges on top of the CPW slot antenna. As a result of this reactive loading, the frequency of the antenna reduces and the antenna is miniaturized by a factor of 85%. Also, by changing the configuration of filled and empty channels, each channel can be used as a switch. By using two pairs of microfluidic channels, three different frequency bands of 2.4, 3.5, and 5.8 GHz can be achieved. This translates to a switching ratio (fTR = f2/f1) of more than 2.5. The antenna is realized using common PCB techniques for the antenna circuit board and three-dimensional (3-D) printing technology for PDMS-based microfluidics structure. The antenna circuit board and the PDMS structure are bonded to each other using a very thin spin-coated PDMS layer. Design methodology, simulation, and measurement results of both antenna prototypes are presented. Both the miniature and reconfigurable antennas have similar radiation patterns to a normal CPW folded slot antenna and show low cross-polarization levels at all operating frequencies.

A reconfigurable quarter-mode substrate integrated waveguide cavity filter employing liquid-metal capacitive loading

A microfluidically-tunable substrate integrated cavity filter is presented for the first time. Quarter mode cylindrical substrate integrated waveguide (SIW) cavities are used to design an ultra-compact two-pole filter with a center frequency of ~1.12 GHz. A corner via is connected to a surface ring gap in order to capacitively load each SIW cavity resonator. Frequency tuning of the filter is achieved using the capacitive loading effect of a liquid metal channel placed on top of the surface gap capacitors. The Polydimethylsiloxane (PDMS) structure including the micro-channel is bonded to the SIW circuit board using a unique fabrication technique. Measured results verify a tuning ratio of 1.72;1 and an insertion loss of 2.5 and 3.45 dB at 1.12 and 0.65 GHz, respectively.

A 1.7–2.2 GHz Compact Low Phase-Noise VCO Using a Widely-Tuned SIW Resonator

A 1.7-2.2 GHz low phase-noise voltage controlled oscillator (VCO) based on a widely-tuned substrate integrated waveguide (SIW) cavity resonator is presented. The frequency of the SIW resonator is tuned based on loading the cavity with three via posts and thus changing the field distribution inside the cavity. The widely-tunable SIW resonator is employed inside a reflective-type VCO structure resulting in a tuning range of 1.7-2.2 GHz ( ~ 26%) and a phase noise better than -109 dBc/Hz at a 100 kHz offset over the entire tuning range.

A microfluidically-tuned dual-band slot antenna

A reconfigurable dual-band slot antenna with the capability of independently controlling each band is proposed. The tuning method is based on employing the reactive loading effect of a fluid metal placed on top of each slot antenna. Digital frequency tuning is achieved by using different configurations of four empty and filled channels. This way a 4-bit reconfigurable antenna is achieved in which each resonant frequency of the dual-band response can be controlled separately. Realization of the tunable antenna using common PCB technologies and PDMS structure is demonstrated. The implemented prototype antenna is measured and tuning ranges of 2.2-3.3 GHz and 4.15-5.4 GHz are achieved for the first and second bands, respectively.

A microfluidically-switched CPW folded slot antenna

A microfluidically-switched CPW folded slot antenna is proposed. The switching technique is based on employing the capacitive loading effect of two fluid metal channels placed on top of the CPW slot antenna. By filling the channels with Galinstan, the antenna is reactively loaded and as a result the resonant frequency of the antenna is reduced. Implementation of the microfluidically-switched antenna is realized using the common PCB techniques and PDMS structures. The PDMS structures including the micro-channels are bonded to the circuit board using a very thin layer of spin-coated PDMS employed as the bonding layer. A frequency switching ratio (fTR=f2/f1) of more than an octave (2.6-5.5 GHz) is obtained for the proposed antenna. The antenna shows similar radiation pattern with high purity (Co- to Cross polarization level > 15dB) for both frequency bands.

A miniaturized switchable SIW-CBS antenna using positive and negative order resonances

A switchable SIW-CBS antenna with two different operating bands using a new switching method is presented. The method uses the reactive loading effect of shortening posts inside the cavity to change the overall resonance order from negative to positive. In order to achieve the negative order resonance, a composite right/left-handed (CRLH) structure is used by inserting an interdigital slot on the top side of a SIW cavity instead of a conventional rectangular slot. Using a two-layer substrate structure the antenna is totally isolated from the biasing circuit. Thus, the operating resonance frequency can be easily tuned by switching the posts using p-i-n diodes. Using this technique and by switching between the negative and positive order resonances, a frequency tuning ratio (fTR=fup/flow) of 2.7 (1.83-4.93 GHz) is achieved. The antenna shows similar radiation patterns with high purity and front-to-back ratio for both operating bands.

An Ultra-Miniature SIW Cavity-Backed Slot Antenna

A metamaterial-inspired ultra-miniature substrate integrated waveguide (SIW) cavity-backed slot antenna (CBSA) is presented in this letter. A ramp-shaped slot is used in an SIW CBSA to force the structure to work in the first negative-order resonance. Other miniaturization elements such as ramp-shaped strips as the ground plane around the antenna and another loading patch underneath the slot antenna are used to achieve an 87% miniature antenna working at 2.1 GHz. Close agreement is observed for the proposed simulated and measured performance results and suggests maximum gain of 3.6 dBi with an 80% efficiency.