# New Miniature Narrow Band Microstrip Diplexer for Recent Wireless Communications
## 2 Related Work  
[PERSON] and [PERSON] presented a new structure for a flat dual-channel microstrip diplexer. It was built at the height of 0.787 mm on a dielectric substrate and has a tiny surface area of 95.7 mm\({}^{2}\). The fractional bandwidth of the first channel is 34.3%, while the second is 38.6%. Modifying the suggested diplexer allows for the second channel to be used for broadband purposes. The value of \(\Omega=1.6\) GHz is where the L-resonance band's frequencies can be found. WiMAX uses a frequency of f2 = 3 GHz [5]. Patch and thin cells tailored for 0.78 GHz and 1.85 GHz for GSM requirements are the primary emphases of the structural design, as indicated in [6]. Given the symmetrical nature of the suggested resonator, it is possible to learn more about its behavior by doing investigations in both the odd and even modes. In addition to its small size, sound isolation, and return loss performance, this diplexer also offers low insertion and return loss. Compact substrate integrated waveguide (SIW) diplexers with square cavities for C-band applications are shown in a new design [7]. This diplexer functions at frequencies below the cut-off frequency of the concavity, taking advantage of the propagation of evanescent modes. The computed insertion losses for the lower and higher passbands, with their centers at 6.16 GHz and 7.72 GHz are 0.83 dB and 0.77 dB, respectively. For each high insulation passband greater than 22 dB, the suggested diplexer offers a fractional bandwidth of more than 5.1%. Due to these characteristics, the suggested diplexer is a viable option for the C-band requirement. In [8], two microstrip multiband diplexers are described. The diplexers have long feed lines and bandpass filters (BPFs) for each channel. One BPF controls all the individual channel parameters, allowing for greater freedom in the layout. Long, high-isolating microstrip feeding lines support the channel filters. A microwave diplexer was built by exchanging a dual-band BPF for two single-band BPFs [9]. In contrast to the traditional diplexer, which uses many junctions to split up the energy, this design reduces the requirement for external connectors. In [10], a high-efficiency and commercial Ku-band diplexer made up of fourth-order TX and RX Chebyshev filters is introduced  
Figure 1: TX/RX diplexer. along with a design and realization of a microwave diplexer using groove gap waveguide resonators. The interesting consistency between the simulation and measurement data validates the design process. In [11], the authors presented a microstrip diplexer that uses modernized H-shaped resonators to achieve small size and sound band isolation. This layout is compatible with the ISM (2.4 GHz) band and the GPS (1.575 GHz) frequencies. The diplexer was created by attaching two BPFs designed with the modified H-shaped resonator and tapped microstrip input/output lines. The paper introduces a new H-shaped BPF and provides an analytic theory for its H-shaped resonator and a model of its equivalent LC circuit. The electrical capabilities of the presented microstrip diplexer are enhanced by etching two cross-slots in the ground plane to create the passbands at low frequencies. Unfortunately, the circuit's poor grounding means it cannot function properly on the GPS L1 or L2 frequencies. An ADS simulator has been used to analyze the diplexer's performance, and CST microwave studio has been used to verify those results. In [12], the authors developed a microwave diplexer using substrate-integrated waveguide (SIW) technology. For simplicity and compactness, the diplexer was made using a common junction rather than the traditionally used external connection for energy distribution. The use of microstrip structures with a huge relative dielectric constant of 80 and no short-circuited elements [13] allows for the development of diplexers using two- and three-resonator microstrip structures.