Composite right/left-handed (CRLH) substrate integrated waveguide (SIW) and half mode substrate integrated waveguide (HMSIW) leaky-wave structures for antenna applications are proposed and investigated. Their propagation properties and radiation characteristics are studied extensively. Their backfire-to-endfire beam-steering capabilities through frequency scanning are demonstrated and discussed. These metamaterial radiating structures are realized by etching interdigital slots on the waveguide surface and the ground. The slot behaves as a series capacitor as well as a radiator leading to a CRLH leaky-wave application. Four antennas are fabricated, measured, and analyzed, including two balanced CRLH SIW designs characterized by single-side or double-side radiation, and two unbalanced HMSIW designs characterized by different boundary conditions. Antenna parameters such as return loss, radiation patterns, gain, and efficiency are all provided. Measured results are consistent with the simulation. All these proposed antennas possess the advantages of low profile, low cost, and low weight, while they are also showing their own unique features, like high directivity, quasi-omnidirectional radiation, miniaturized size, continuous beam-steering capabilities covering both the backward and forward quadrants, etc., providing much design flexibility for the real applications.

Composite Right/Left-Handed Substrate Integrated Waveguide and Half Mode Substrate Integrated Waveguide Leaky-Wave Structures

This paper presents design equations for the microstrip-to-Substrate Integrated Waveguide (SIW) transition. The transition is decomposed in two distinct parts: the microstrip taper and the microstrip-to-SIW step. Analytical equations are used for the microstrip taper. As for the step, the microstrip is modeled by an equivalent transverse electromagnetic (TEM) waveguide. An equation relating the optimum microstrip width to the SIW width is derived using a curve fitting technique. It is shown that when the step is properly sized, it provides a return loss superior to 20 dB. Three design examples are presented using different substrate permittivity and frequency bands between 18 GHz and 75 GHz. An experimental verification is also presented. The presented technique allows to design transitions covering the complete single-mode SIW bandwidth.

Design equations for tapered microstrip-to-Substrate Integrated Waveguide transitions

In this paper, synthesis and design techniques of dual- and triple-passband filters with Chebyshev and quasi-elliptic symmetric frequency responses are proposed and demonstrated for the first time on the basis of substrate integrated waveguide technology. The inverter coupled resonator section is first investigated, and then a dual-passband Chebyshev filter, a triple-passband Chebyshev filter, and a dual-passband quasi-elliptic filter, which consist of the inverter coupled resonator sections, are synthesized from the generalized low-pass prototypes having Chebyshev or quasi-elliptic responses, respectively. Subsequently, theses filters with a symmetric response are designed and implemented using the substrate integrated waveguide scheme over the -band frequency range. The inverter coupled resonator sections composed of side-by-side horizontally oriented substrate integrated waveguide cavities are coupled, in turn, by post-wall irises. 50-Omega microstrip lines are used to directly excite the filters. Measured results are presented and compared to those simulated by Ansoft's High Frequency Structure Simulator (HFSS) software package. A good agreement between the simulated and measured results is observed, which has also validated the proposed concept of design and synthesis with the substrate integration technology.

Dual-Band and Triple-Band Substrate Integrated Waveguide Filters With Chebyshev and Quasi-Elliptic Responses

A novel high-performance millimeter-wave planar diplexer is developed based on the complementary characters of substrate integrated waveguide (SIW) dual-mode filters with circular and elliptic cavities by making the tradeoff between the isolation, insertion loss, and selectivity. The responses of the dual-mode SIW circular and elliptic cavities are first investigated. It can be found that the upper side response of the circular cavity and the lower side response of the elliptic cavity are very steep. The diplexers with high isolation performance are then designed based on the complementary response characters of circular and elliptic cavities. A diplexer with two dual-mode SIW circular and elliptic cavities is designed and fabricated with a normal printed circuit board process. The measured insertion losses are 1.95 and 2.09 dB in the upper and lower passbands centered at 26 and 25 GHz with the fractional bandwidths of 5.2% and 5.4%. The isolation is lower than - 50dB

Development of Millimeter-Wave Planar Diplexers Based on Complementary Characters of Dual-Mode Substrate Integrated Waveguide Filters With Circular and Elliptic Cavities

This letter presents a second-order tri-band bandpass filter (BPF) designed using tri-section stepped-impedance resonators (TSSIRs). The impedance ratios of the TSSIRs were computed using the formulas expressed as functions of the passband center frequencies, which are located at 1.57, 2.45, and 3.5 GHz. A cross-coupled configuration was arranged to sharpen the passband skirts. The newly designed tri-band BPF was verified by circuit implementation and very good agreement between the simulated and measured results was observed.

Tri-Band Bandpass Filter With Sharp Passband Skirts Designed Using Tri-Section SIRs

A novel method for designing multiband bandpass filters has been proposed in this paper. Coupling structures with both Chebyshev and quasi-elliptic frequency responses are presented to achieve dual- and triple-band characteristics without a significant increase in circuit size. The design concept is to add some extra coupled resonator sections in a single-circuit filter to increase the degrees of freedom in extracting coupling coefficients of a multiband filter and, therefore, the filter is capable of realizing the specifications of coupling coefficients at all passbands. To verify the presented concept, four experimental examples of filters with a dual-band Chebyshev, triple-band Chebyshev, dual-band quasi-elliptic, and triple-band quasi-elliptic response have been designed and fabricated with microstrip technology. The measured results are in good agreement with the full-wave simulation results

Design of Dual- and Triple-Passband Filters Using Alternately Cascaded Multiband Resonators

High isolation and compact size microstrip diplexers designed with common resonator sections have been proposed. By exploiting the variable frequency response of the stepped-impedance resonator, resonators can be shared by the two filter channels of the desired diplexer if their fundamental and the first spurious resonant frequency are properly assigned. Size reduction are, therefore, achieved by introducing a few common resonator sections in the circuit. This concept has been verified by the experimental results of two diplexer circuits. One of the diplexers is composed of two three-pole parallel-coupled bandpass filters and the other is composed of two four-pole cross-coupled bandpass filters, which are formed by only five and six resonators, respectively. Both of them occupy extremely small areas while still keeping good isolations. Good agreements are also achieved between measurement and simulation.

Microstrip diplexers design with common resonator sections for compact size, but high isolation

This paper proposes a bandpass filter design method for suppressing spurious responses in the stopband by choosing the constitutive resonators with the same fundamental frequency, but staggered higher order resonant frequencies. The design concept is demonstrated by a four-pole parallel-coupled Chebyshev bandpass filter and a compact four-pole cross-coupled elliptic-type bandpass filter. Each filter is composed of four different stepped-impedance resonators (SIRs) for which a general design guideline has been provided in order to have the same fundamental frequency and different spurious frequencies by proper adjusting the impedance and length ratios of the SIR. Being based on knowledge of the coupling coefficients and following the traditional design procedure, the resultant filter structures are simple and easy to synthesize. The measured results are in good agreement with the simulated predictions, showing that better than -30-dB rejection levels in the stopband up to 5.4f/sub 0/ and 8.2f/sub 0/ are achieved by the Chebyshev and quasi-elliptic filters, respectively.

Design of microstrip bandpass filters with multiorder spurious-mode suppression

Miniaturized power dividers with high-selectivity bandpass behavior are presented and analyzed theoretically in this paper. Based on the coupled-resonator topology, the circuit area of the proposed power divider can be reduced as the size of the assembled resonators shrinks. Therefore, in order to effectively reduce the circuit area and improve the stopband performance, the net-type resonator is selected to design the filtering power dividers. For demonstration, power dividers with Chebyshev- and quasi-elliptic bandpass responses have been designed and fabricated with microstrip in printed circuit boards. The highly symmetric structure of each power divider provides a low in-band magnitude and phase imbalances. Consequently, the proposed filtering power dividers have advantages of small size, sharp skirt selectivity, high isolation, and superior out-of-band performance. All measured results are in good agreement with the full-wave simulation results.

Design of Miniaturized Filtering Power Dividers for System-in-a-Package

Compact and high isolation microstrip filtering power dividers (PDs) have been presented in this letter. In order to effectively reduce circuit area, the compact folded net-type resonator is selected to build up the resonator-based PDs with a filtering response. The highly symmetric structure of the divider provides not only a good in-band isolation performance, but also a low magnitude imbalance and phase imbalance. For the demonstration, two design examples of in-phase and out-of-phase PDs with second-order Chebyshev filtering response have been designed and fabricated with microstrip technology. As a result, both dividers have an extremely small size of 0.19 λg by 0.19 λg. The measured results are in good agreement with the simulated predictions, showing that better than 30 dB isolation within the whole passband is achieved with a tradeoff of the bandwidth.

Chi-Feng Chen

Papers

Design of Dual- and Triple-Passband Filters Using Alternately Cascaded Multiband Resonators

Microstrip diplexers design with common resonator sections for compact size, but high isolation

Design of microstrip bandpass filters with multiorder spurious-mode suppression

Design of Miniaturized Filtering Power Dividers for System-in-a-Package

Compact Microstrip Filtering Power Dividers With Good In-Band Isolation Performance