Design of a high–performance lowpass–bandpass diplexer using a novel microstrip structure for GSM and WiMAX applications

Abstract

In this work, a lowpass-bandpass diplexer is proposed based on a novel microstrip structure. This diplexer includes two lowpass and bandpass filters integrated by a simple transmission line. The lowpass channel has a cutoff frequency at 1.88 GHz, which makes it suitable for GSM applications. The resonance frequency of the bandpass channel is 3.56 GHz for IEEE 802.16 WiMAX applications. In comparison with the previously reported lowpass-bandpass diplexers, the proposed design has the lowest insertion and return losses at both channels while it occupies the most compact implementation area of 0.03 λg 2. The designed diplexer can suppress the harmonics up to 4.45F C with a maximum harmonic level of −20 dB, where F C is the cutoff frequency of the lowpass channel. The lowpass channel has a very sharp roll-off of ξ = 220, while the bandpass channel has a high selectivity with a high fractional bandwidth of 23.8%. To verify the design method and simulation results, the designed diplexer is fabricated and measured. The simulated and measured results are in a good agreement.

Design of a Compact Lowpass-Bandpass Diplexer With High Isolation

“…On the other hand, the diplexers in [2] and [3] have lower performance in terms of circuit size and isolation level. Although the diplexers in [7,8,13,14] have more compact circuit size, isolation levels are not as good as the proposed work.…”

“…In addition, novel lowpass filter sections have been introduced in [6-8, 13, 14] for lowpassbandpass diplexer design. However, single transmission pole is observed in the bandpass channel in [6], and isolation levels are not good enough in [7,8,13,14]. Besides, lowpass-bandpass triplexers [9,10] and a quintuplexer [9] have also been reported based on distributed coupling technique [9] and defected ground structures [10].…”

Design of diplexer with direct synthesis method for ground penetrating radar

“…A common way to design a diplexer is to use two filters, such as a lowpass filter and a bandpass filter, [3][4][5][6] or two bandpass filters, [7][8][9][10][11][12] or a lowpass filter and a highpass filter. 13 Several approaches are used in designing filters for diplexers.…”

Design and Performance of Microstrip Diplexers: A Review

“…Nevertheless, many designers did not give attention to attenuate the harmonics . Other types of diplexers are lowpass-bandpass diplexers (LBDs), which have been formed by a lowpass filter (LPF), BPF, and junction circuit Deng and Tsai, 2013;Rayatzadeh and Moloudian, 2019;Heshmati and Roshani, 2018;Capstick, 1999;Hayati, et al, 2019). An important factor related to the diplexer performance is the high selectivity.…”