A new compact balanced ultra-wideband (UWB) bandpass filter using half mode dumbbell defected ground structure (DGS) is presented. To realise the UWB response, the 'T' shape multiple-mode resonator with short-ended stub is employed. To achieve wideband common mode (CM) suppression and compact design simultaneously, the concept of half-mode DGS is introduced in the two stacked microstrip layers. Afterwards, a balanced UWB filter is designed and measured for verifying the feasibility of the presented design method. The measured results match well with the expected results which indicate the proposed filter exhibits better than −30 dB CM suppression within the DM passband covering from 3.1 to 10.6 GHz.
A method of designing two‐element compact multiple‐input and multiple‐output (MIMO) antennas with good isolation based on slow‐wave corrugated strips (CSs) is presented in this paper. Using the slow‐wave characteristic, a pair of CSs is applied as arms of each dipole antenna element to realise the compact design. A metal plane is placed between the two dielectric boards serving as the reflector so that the antenna can achieve good forward radiation. There are two coupling paths between the closely placed antennas: the coupling between the adjacent antenna arms and the coupling with the reflector. By adjusting the phase constants of the two coupling paths, good isolation is achieved in the operating frequency band without any additional de‐coupling structures. A sample of a two‐element MIMO antenna is fabricated at the centre frequency of 5.1 GHz with a bandwidth of 330 MHz. Measured results show good performance to support the design method. As each arm is about 1/8λ0 (λ0 is wavelength in free space), the edge‐to‐edge distance is 0.04λ0, and the isolation in the operating frequency is 15 dB.
A design method of compact wideband balun bandpass filter (BPF) with high selectivity based on corrugated slot is proposed here. To realize wideband balun response in compact size, metal strips are deployed parallel to the half-mode corrugated slot (HMCS). Besides, the coupling of corrugated slot to the metal stripline provides the conversion of slot to microstrip structure at the balanced ports. By placing a pair of resonators at the balanced ports, a wideband balun BPF response with high selectivity can be realized. In addition, a U-shaped resonator is also loaded at the end of the corrugated slot to suppress harmonics. Afterwards, a compact wideband balun BPF centred at 2.42 GHz with 3-dB FBW of 45% is designed, fabricated, and measured. The effective size is 0.13λ g × 0.39λ g (λ g is the guided wavelength of the centre frequency) and the measured results indicate that the magnitude imbalance is less than 0.45 dB and the phase imbalance is less than 4.8°within the operation frequency band.
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