Vol. 41

A compact tunable dual-band bandpass filter (BPF) based on substrate integrated waveguide (SIW) and defected ground structure (DGS) is investigated in this paper. The second passband can be flexibly controlled by changing the dimensions of the up-down DGSs whereas the first passband is fixed. The proposed filter exhibits improved selectivity due to the introduction of four left-right DGSs generating transmission zeroes. To verify the design method, a compact dual-band filter with the second center frequency switched among 5.4 GHz, 5.8 GHz, 6.4 GHz and 6.8 GHz and the first center frequency fixed at 4.78 GHz, is designed and fabricated. The simulated and measured results are in good agreement with each other.

A novel defected ground structure unit is presented in this paper. This structure is composed of a traditional dumbbell DGS and a pair of coupling stubs in the aperture. In contrast to a single finite attenuation pole characteristic offered by the conventional dumbbell DGS, the proposed DGS unit provides dual finite attenuation poles that can be independently controlled. By adjusting the position of the two attenuation poles, a much sharper skirt and wider stopband could be achieved. A 3.2 GHz lowpass filter utilizing four cascaded novel DGS units is designed, fabricated and measured. This lowpass filter achieves a wide stopband with over 30-dB attenuation up-to 30 GHz. The results obtained from simulation and measurement have good agreement.

A new design of broadband circularly polarized antenna is proposed. The antenna is composed of a square patch and a horizontal L-shaped stripline that feeds the patch at two orthogonal directions by two probes. The L-shaped feeding structure provides excitements of approximately equal amplitude and 90° phase difference and then good circularly polarized characteristics are obtained. Measured results show that the proposed antenna has 10-dB impedance bandwidth of 14.3% (2.27-2.62 GHz) and 3-dB axial-ratio bandwidth of 13.1% (2.3-2.62 GHz). Moreover, the measured gain is over 7 dBic within the effective band.

This letter presents a dual-band bandpass filter (BPF) using interdigital coupling lines with a new defected ground structure (DGS) pattern. Traditional DGS structures are mainly used to realize wide bandstop characteristics. In this letter, by introducing a pair of coupling stubs in the aperture of the DGS, a narrow passband can be achieved within a wide stopband, so a dual-band bandpass filter can be implemented. An equivalent circuit model is derived to describe the filter. And the circuit simulation result agrees well with the EM simulation one. The position and bandwidth of the two passbands can be designed and adjusted independently. In order to verify the theory, a dual-band bandpass filter is designed, fabricated and measured. The simulated and measured results are in good agreement.

In this paper, we propose a novel frequency selective surface (FSS) with stable performance under large incident angles. The FSS is composed of hexagon metallic lines and hexagon patches. Using such a hexagon arrangement, the periodicity size could be miniaturized and thus the FSS unit cell is compact. The composite FSS has an excellent stability under large incident angles. In the passband 10.58-11.06 GHz, the insertion loss is still less than -1 dB for both TE and TM polarizations, even under incident angle up to 85 degree. Both the design procedure and experimental results of the novel FSS are presented and discussed.

In this paper, a novel pattern reconfigurable microstrip parasitic array is proposed, which is similar to the microstrip Yagi antenna. The antenna is printed on a dielectric substrate and has a probe feeding center strip with two parasitic strips on both sides of a higher plane. The driven patch is equipped with four RF PIN diodes by which we can change the antenna's state and vary its frequency at 2.1 GHz, 2.4 GHz and 2.6 GHz respectively. Each of the parasitic patches is equipped with six switched connections symmetrically which is utilized as a director or a reflector for pattern reconfiguration. Compared with conventional antenna, the proposed antenna combines both radiation pattern reconfiguration and frequency reconfiguration together, and by raising the plane of the dielectric substrate of the parasitic patch, the tilt angel of this antenna's maximum radiation direction is lager and the gain is higher.

We report a MEMS (micro-electro-mechanical systems) compatible distributed loss type sever design for the 220 GHz double vane half period staggered traveling-wave tube amplifier (TWTA) [1]. The cold test simulations for a full TWT model including input/output couplers and broadband tapered vane transitions incorporating the sever, predicted a return loss (S₁₁) of < -10 dB in the pass band (205 GHz-275 GHz) while an insertion loss/isolation (S₂₁) of < ~-27 dB. The return loss of the TWT circuit did not degrade by the inclusion of the sever (< -10 dB) while still maintaining a good isolation (S₂₁) for the RF signal. Particle-In-Cell (PIC) simulation analysis for the full 220 GHz TWT circuit (a) without sever and (b) with sever was conducted. With the inclusion of the sever, the TWTA showed generally a stabilized output response for all cases. The maximum power from the long sever case was ~25 W for P_in ~50 mW and the gain was ~27 dB. The reverse power was decreased to ~30 mW. For the short sever, the PIC results were even better with a maximum output power of ~62 W and a gain of ~30.92 dB with a reduced reverse power of ~5 mW for an input power of 50 mW at 220 GHz. The FFT spectrum of the RF signal at the output port also showed a spectrally pure waveform at 220 GHz.

Based on the theory of microstrip-to-slotline transition, a series of power dividers using CPW-to-microstrip transition is developed. These power dividers can be made to be coplanar or non-coplanar structure, and the phase difference between the two output ports can be flexibly achieved in phase or out of phase. Two microstrip feed lines couple the energy from the two slots of the CPW with equal magnitude, thus realizing CPW-to-microstrip transition. An in-phase power divider and an out-of-phase one are designed, fabricated and measured. The measured results show that the power dividers provide good return loss, low insertion loss, and stable phase between the two output ports over the operating frequency band.

In this paper, an ultra-wideband (UWB) monopole printed antenna with wing-shaped coplanar waveguides (CPW) feeder is proposed, in which the wing-shaped CPW feeder is used to increase the impedance bandwidth. A CPW-fed antenna is used in this design for its simple structure, compact size and ease of integration with microwave circuits. The proposed antenna is fabricated on Durion Roger R4003c, 22×41 mm² substrate and measured. The simulated and measured results show that the antenna operates between 2.04 to 11.67 GHz. The unique wing-shaped CPW feeding structure causes a significant increase on the bandwidth of the proposed antenna compared to the present patch antennas. Also it removes unwanted ripples from the return loss and improves antenna's pattern.

A compact quad-band microstrip band-pass filter (BPF) based on novel step-impedance ring resonator (SIRR) is investigated in this paper. The proposed BPF is composed of one ring resonator and input/output coupled structure. The novel resonator is studied and employed to generate four desired independent passbands. A compact quad-band BPF centered at 1.57, 2.45, 3.5 and 5.2 GHz is designed and fabricated. The predicted results are compared with measured data, and good agreement is reported.

In this paper, a novel monolayer multi-octave bandwidth log-periodic microstrip antenna (LPMA) is presented. This antenna consists of a 50 Ω microstrip feed-line and fourteen rectangular patch elements. Twelve rectangular patch elements are fed by edge-coupling from the microstrip feed-line and two other patch elements are directly connected with the microstrip feed-line. A mixed microstrip line feed is applied to expand the bandwidth. Our measured results closely agree with the simulated results. These results show that the proposed antenna lends itself well to operation in the impedance bandwidth from 2 GHz to 8 GHz with a voltage standing-wave ratio (VSWR) less than 2.

A new design methodology for multi-band rectangular microstrip antenna using a metamaterial-inspired technique is proposed. The methodology uses the metal disk with SRR-shaped slot placed horizontally between the patch and the ground plane. With the introduction of the split ring, sub-wavelength resonance can be achieved while the dominant mode of patch cavity remains the same, so the antenna can operate at multi resonant frequencies. Construction of the multi-band antenna requires only the sandwiching of two etched circuit boards. The antenna has the properties of low profile, easy fabrication and low cost. Dual-band and tri-band antennas are fabricated and measured, which validate the design methodology.

A coplanar waveguide-fed slot antenna with wideband circular polarization characteristic is presented. The proposed antenna consists of an irregular slot with a stair-shaped edge and an L-shaped feed line. The stair-shaped edge can improve the circular polarization of the antenna. The simulated and measured results show that the antenna has an impedance bandwidth (VSWR < 2) about 1040 MHz (42%@2.47 GHz) and an axial ratio (AR) bandwidth (AR < 3 dB) about 640 MHz (25.8%@2.48 GHz) for 2.45 GHz RFID applications. The RHCP gain in the main radiation direction varies between 2.3 dBi and 3.8 dBi.

Electromagnetic fields associated with the electric current flowing along a horizontal conductor located over perfectly conducting ground are estimated using electromagnetic fields pertinent to acceleration of electric charges. It is shown that the electric and magnetic fields that exist below a long overhead horizontal conductor are nothing but the radiation fields generated by the acceleration of charge at the point of injection of current into the horizontal conductor.

In order to realize bandpass filter with Chebyshev and elliptic function responses using a single resonator only, a dual-mode square resonant structure is proposed. Four small square loops are added into a large loop. One of small loops is defined a perturbation element, other small ones are references. By changing the thickness of the perturbation element with respect to that of a reference element, the resonator can produce a capacitive or inductive coupling between two degenerate modes. The capacitive coupling can acquire an elliptic function characteristic since it can create the transmission zeros on both the lower and upper sides of the passband, while the inductive coupling cancels them which exhibits a Chebyshev characteristic. Therefore, both Chebyshev and elliptic function responses can be obtained in a filter. The proposed bandpass filter is with a wider stopband and more compact in size. Experiment results have been verified this design.

This work presents a novel broadband monopole antenna for digital video broadcasting-terrestrial (DVB-T) application. The proposed antenna consists of a grating zigzag patch and a concave rectangular ground plane. The zigzag patch is used to enable the antenna height reduction for fixed ranges of operating frequency. The proposed antenna can operate from 420 MHz to 1050 MHz frequency range corresponding to 85% of impedance bandwidth for |S₁₁| better than -10 dB. This covers the working frequency band (470-862 MHz ) of DVB-T system. The radiation pattern of the proposed antenna is omnidirectional across the desired operating frequency band. Details of the proposed antenna design and experimental results of the constructed prototypes are presented and discussed. Furthermore than the bandwidth enhancement, we have also arranged the structure for network antennas application.

In this paper, a novel tunable antenna using graphene-based artificial magnetic conductor (AMC) is proposed and investigated. The resonance frequency of the AMC ground plane can be electrically tuned by applying a gate voltage. A bowtie-shaped antenna is mounted above the 15×15 AMC units. It is observed that the operating frequency of the antenna system shifts in a large range when varying the external electric field. The bandwidth of the antenna system can reach as high as 47% with a gain higher than 9 dB.

An investigation of dual-band balanced-to-unbalanced (blaun) bandpass filters (BPFs) is presented in this letter. Two types of balun BPFs named Type-A and Type-B filters based on coupled ring resonators are discussed and fabricated. Both the simulated and measured results show that these balun-BPFs have not only good amplitude performances but also excellent phase difference performances. The center frequencies of these balun BPFs are set at 2.4 GHz/5.6 GHz for Type-A and 1.57/4.65 GHz for Type-B balun filters. The differences are 180° ± 5° in phase and within 0.6 dB in magnitude of type A and 0.73 dB of type B, respectively. Thus, these balun BPFs can be used in many wireless communication systems.

A rectangular dielectric resonator antenna (DRA) with a square spiral microstrip feedline is investigated in this paper. The design utilizes a feeding structure to excite two resonant modes (TE_δ11 and TE_1δ1 modes) of the rectangular DRA that are spatially orthogonal in polarization and in phase. The antenna with the proposed feeding structure has provided a measured circular polarization(CP) over a bandwidth of ~15.5% in conjunction with an impedance-matching bandwidth of ~31.25% at the same frequency range. The gain of the dielectric resonator antenna varies between 6.8 and 7.2 dBi across the bandwidth (7.5~8.75 GHz). Reasonable agreement between the simulated and measured results is obtained.

This paper presents a stable grounding technique for the inner conductor of a coaxial resonator in vacuum and high-power condition applications, where the inner and outer conductors of the coaxial resonator are connected by a flange plate. When this novel technique is applied, the stable and unified microwave grounding ability is increased by making the stress on the contact surface uniform, the reliability of space products is improved by reducing the deformation of the rod-end at a transverse vibration load of 10 g by 75%, and the unstable tiny cracks of the high-power component are fully eliminated.